{"paper_id":"117e69e9-c2d2-4b85-9e72-488c1db49b4c","body_text":"Facile synthesis and effective adsorption of magnetic alginate biogel composite for lanthanum ions from water | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Facile synthesis and effective adsorption of magnetic alginate biogel composite for lanthanum ions from water Nier Su, Beigang Li This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5218034/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract A novel eco-friendly magnetic alginate biogel composite (Ca-SA@Fe 3 O 4 ) was synthesized through droplet polymerization and characterized using multiple techniques. Furthermore, the impact of factors, such as dosage, pH, contact time, temperature and the presence of co-existing ions on the efficiency of the removal for La(III) ions by the composite were systematically investigated. The evaluation and exploration were conducted on the adsorption performance, reusability, and interaction mechanism of the magnetic composite towards La(III) ions. The results show that the magnetic composite gel beats have a particle scale of approximately 1.3 mm, a peculiar folded structure with numerous surface pores and sensitive magnetive responsiveness. La(III)-ion removal from water by Ca-SA@Fe 3 O 4 reached 90.2% at pH 7.0, contact time of 20 h and 298 K. The La(III) adsorption behaviour was in accordance with the Langmuir model, and the maximum adsorption capacity was up to 91.0 mg/g. The spontaneous adsorption process exhibited kinetics that were in accordance with the Pseudo-second-order model, suggesting a favorable agreement. Complexation and electrostatic adsorption between the composite and La(III) ions facilitate the strong adsorption of La(III) ions. The commonly coexisting ions and ionic strength hardly interfered with the La(III) adsorption, apart from a minor influence of Ca 2+ ions. The biogel composite following adsorption of La(III) ions can be completely recovered and reused at least four times. Ca-SA@Fe 3 O 4 composite would be a cost-effective macroparticle biosorbent. Alginate Lanthanum ions adsorption Magnetism Biogel composite Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Rare earth elements (REEs) are composed of 15 lanthanides along 2 pseudo lanthanides (scandium, Sc and yttrium, Y) [ 1 ]. REEs also known as the \"industrial vitamin\" have been used extensively in many technical devices such as superconductors, magnets, catalysts and batteries [ 2 ]. However, the widespread use of rare earths has the potential to give rise to environmental issues. Currently, with the increasing mining of rare earths, more and more rare earths have being released into aquatic environment, leading to bio-toxicity and resource wastage [ 3 ]. Rare-earth metal ion concentrations in natural waters should stay below 20 µg/L [ 4 , 5 ]. Therefore, the recovery of REEs from rare earth-containing wastewater and secondary rare earth waste materials is particularly critical for the recycling of limited natural rare earth resources and environmental and economic sustainability. Lanthanum is one of the elements with the highest percentage of rare earth abundance in the earth's crust and has garnered heightedened inrested owing to its robust chemical reactivity and abundant reserves, which in turn has been widely used in a variety of industries such as metallurgy, petroleum, glass, ceramics, etc. Consequently, the increased demand for this element in many important technologies, as well as the rapid exploitation of rare earth resources, has resulted in the migration of La(III) into the biosphere, subsequently altering the equilibrium of elements in the environment and potentially posing a risk to public health [ 6 , 7 ]. There are multiple approaches available for the segregation and retrieval of rare earth ions, which encompass adsorption methodologies, chemical precipitation techniques, and ion exchange [ 8 ]. To effectively capture and retain rare earth elements in aqueous solutions using adsorption methodologies that is easy to implement and highly efficient, the selection of adsorbent raw materials, the preparation of eco-friendly adsorbents with stronger adsorption properties and easy recycling are crucial [ 9 – 11 ]. At present, various types of adsorbents prepared from a variety of raw materials and reagents have been reported, including silicon-based, carbon/graphene-based composite adsorbents [ 12 – 14 ], metal-organic skeletons (MOFs)/nanoadsorbents [ 15 , 16 ] and agricultural-waste-based adsorbents [ 17 , 18 ]. However, high cost, low stability, adsorption capacity, difficult liquid/solid complete separation and low reuse rate of certain adsorbents limit their application. Therefore, the development of rapid-separating adsorbents has become crucial for the successful implementation of sorption technology, which is a key process in the efficient recovery and separation of ions [ 19 ]. Sodium alginate (SA), a naturally abundant polysaccharide derived from marine sources, possesses exceptional biocompatibility, non-toxic properties, and biodegradability. SA versatility has led to its widespread adoption in various industries, including food processing, pharmaceutical manufacturing, textiles, printing and dyeing, as well as paper production. Recently, SA has attracted remarkable attention as a cost-effectiveness biomass material, offering unique advantages in water treatment applications [ 20 ]. Currently, SA featuring robust hydrophilic properties, the tendency to gel, the capability for polymerization, and a heightened level of chemical reactivity can be prepared into a variety of gel composites with a large space for modification as bio-based adsorbents, and applied to the effective treatment of various industrial wastewater and efficient recovery of rare earths. SA can react with multivalent metals by cross-linking polymerization to form water-insoluble polymer gel spheres commonly referred to as “egg carton model” [ 21 , 22 ], which can be an optimal framework for subsequently crafting a diverse array of granular adsorbent materials that exhibit superior performance. In recent years, magnetic composites have been widely developed as promising adsorbents due to their rapid separability from the aqueous environment, chemical stability and biocompatibility [ 23 , 24 ]. Drawing upon the established groundwork from prior studies and the comprehensive analysis presented above, the research endeavor focused on harnessing the amplified polymerization capabilities of economical calcium ions with SA, aiming to reduce production expenses and optimize the performance of the gel spheres. Our objective was to develop an environmentally sustainable gel composite that could efficiently recover La(III) ions. Therefore, innovative and biosafe magnetic gel composite was subsequently crafted through the crosslinking polymerization of calcium ions with SA and Fe 3 O 4 in this paper. Optimized conditions of preparation and adsorption for macroparticle Ca-SA@Fe 3 O 4 gel composite was examined. The adsorption capacity, stability, magnetic responsiveness, and adsorption kinetics and thermodynamics of the gel composite were investigated. Recovery capacity, reusability and adsorption mechanisms of lanthanum ions by Ca-SA@Fe 3 O 4 examined and scrutinized. We aspire to create economical and environmentally benign, sorptive materials integrated with magnetic separation capabilities, crafted via a straightforward and accessible method using natural biological resources, With the aim of promoting the efficient utilization of natural resources, enhancing the purification processes for wastewater laden with rare earth elements, and fostering the responsible recycling of these valuable resources. Material and Methods Chemicals and Materials AR-grade CaCl 2 , La(NO 3 ) 3 ·6H 2 O, Fe 3 O 4 , HCl, and SA were obtained from Damao Chemical, Tianjin, China. Preparation of Ca-SA@FeO gel composite The Ca-SA@Fe 3 O 4 was prepared, detailed as follows: 0.06 g of Fe 3 O 4 was introduced into 25 mL of a 16 g/L sodium alginate (SA) solution and mixed thoroughly. The solution was then sonicated at 25°C for 0.5 hours. Next, it was methodically dripped into 20 mL of a 15 g/L Ca 2+ ion solution, ultimately yielding the production of brown gel beads. Following a 2-hour curing process, the larger gel beads underwent removal, washing, and drying. This resulted in the production of the final magnetic bio-based adsorbent, Ca-SA@Fe 3 O 4 , ready for subsequent studies. Characterization To analyze the microstructure and elemental composition, scanning electron microscopy with energy dispersive spectroscopy (SEM–EDS, SU8010, Hitachi, Japan) was used. The crystalline structure of the raw materials and gel composite was examined using X-ray diffraction (XRD, PW-1830, Philips, Netherlands) with Cu-Kα radiation (λ = 0.154056 nm). Fourier transform infrared spectroscopy (FTIR) was conducted with a Nicolet 6700 spectrometer (KBr method, Thermo Fisher Scientific, USA). Magnetic properties were assessed using a vibrating sample magnetometer (VSM, 7407, Lake Shore, USA), and X-ray photoelectron spectroscopy (XPS) analysis was performed with an Al Kα X-ray source on an Axis Ultra instrument (Shimadzu, Japan). Adsorption testing Adsorbent was introduced into multiple conical flasks, containing 25 mL of La(III) ion solutions at specific concentrations ( C 0 , mg/L). The flasks were agitated at 25°C for 20 h, after which the adsorbent was removed. The residual concentration of La(III) ions ( C e , mg/L) was then determined using colorimetric spectrophotometry at λ max = 650 nm.The adsorption capacity ( q e , mg/g) and removal rate ( η , %) of La(III) ions by the composite gel was calculated using the equations q e = ( C 0 - C e ) × V / m and η = ( C 0 - C e ) / C 0 × 100%, respectively, where m is the mass of the composite (g) and V is the volume of La(III) solution (L). The effects of adsorbent dosage, pH, adsorption time, adsorption temperature and coexisting ions on the La(III) removal efficiency by the composite were examined following the described adsorption experimental method. Regeneration experiment The reusability of the Ca-SA@Fe 3 O 4 gel composite was assessed through repeated adsorption/desorption cycle. 0.04 g of the gel,which had adsorbed La(III) ions was subjected to desorption using an appropriate regenerating agent at room temperature. The gel was then washed and dried before being used in the next cycle. The percentage of regeneration efficiency ( RE , %) for Ca-SA@Fe 3 O 4 was determined by appling the formula RE = q n / q 1 × 100%, where ( q 1 ) represents the amount of La(III) ions adsorbed during the first cycle and ( q n ) denotes the amount of La(III) ions adsorbed during the n th cycle [ 25 ]. Results and Discussion Optimizing the Synthesis Parameters for Ca-SA@Fe 3 O 4 Gel Composite Sodium alginate (SA) is known for its stability, biodegradability, and non-toxicity. When it interacts with divalent metal ions like Ca²⁺ and forms gel particles, facilitating ion separation and adsorption. In this study, different SA concentrations were tested for their ability to form polymers adsorbing La(III) ions at 30 g/L of fixed Ca²⁺ concentration. As demonstrated in Fig. 1 a, at a SA concentration of 16 g/L, the La(III) adsorption capacity and removal efficiency reached maximum values of 64.29 mg/g and 70.2%. Therefore, 16 g/L was chosen as the optimal SA concentration for preparing the Ca-SA gel composite. Calcium ions act as cross-linking agents and are crucial for forming stable gel particles. Various Ca²⁺ concentrations were evaluated, and it was found that a concentration of 15 g/L provided the highest adsorption capacity (76.25 mg/g) and removal efficiency (83.2%) for the prepared Ca-Sacomposite adsorbing La(III) ions as shown in Fig. 1 b. This indicates that Ca-SA polymer cross-linked at this concentration show significantly improved adsorption performance. As a result, a concentration of 15 g/L Ca²⁺ was was chosen for the preparation of the Ca-SA gel composite. To impart magnetic properties to the Ca-SA composite, Fe₃O₄ was added to the composite. It was observed that the Ca-SA@Fe₃O₄ composite prepared with 2.5 g/L Fe₃O₄ exhibited the best adsorption performance. Additionally, magnetic separation tests confirmed that this concentration provided effective separation while enhancing adsorption compared to the non-magnetic Ca-SA polymer. As shown in Fig. 1 c, Consequently, it was determined that 2.5 g/L of Fe₃O₄ was the most effective concentration for the fabrication of the Ca-SA@Fe₃O₄ magnetic composite. The impact of setting time on the durability and cohesion of the cross-linked gel composite was also studied (Fig. 1 d). The adsorption capacity ( q e ) and removal efficiency ( R %) of the forming Ca-SA@Fe₃O₄ for La(III) ions increased steadily as the curing time extended up to 2 hours, after which both values began to decline. Therefore, a curing time of 2 hours was chosen as the optimal duration. As demonstrated in Fig. 1 e, the adsorption potential for La(III) ions showed only minor fluctuations across a temperature range of 25°C to 55°C. Therefore, 25°C was determined to be the appropriate temperature, balancing performance, operational convenience, and energy conservation. (Inserting Fig. 1 here) Material characterisation As depicted in the SEM micrographs (Fig. 2 a-d), the black dried macrogel beads of Ca-SA@Fe₃O₄, initially crafted from a milky white SA powder, exhibit a distinctive undulating surface with grooves and clefts of varying depths and irregular geometries. This intricate surface topography serves as an advantage, enhancing the adsorption capabilities of the gel composite. Additionally, the white specks discernible on the surface of the gel beads are likely indicative of Fe₃O₄ particles, a finding that aligns with prior studies [ 26 , 27 ]. The observation is further corroborated by the elemental distribution results obtained from the Energy EDS analysis (Fig. 2 e). The concentrations of Ca and Fe in the gel composite increased to 15.26% and 5.64%, respectively, compared to their small amounts in the SA. This confirms the presence of Fe₃O₄ particles as indicated by the white spots in the SEM images. Additionally, the Na content decreased significantly from 10.87% in SA to 1.87% in Ca-SA@Fe₃O₄. The distribution of elements such as O, Fe, and Ca in the gel beads was also found to be homogeneous (Figs. 2 f-i). These results suggest that Ca²⁺ ions initially reacted with Na⁺ ions in the SA solution through ion exchange. Subsequently, the Ca-SA@Fe₃O₄ composite was successfully synthesized via cross-linking and polymerization of Ca²⁺ ions with SA molecular chains, resulting in the characteristic ‘egg carton’ structure [ 28 ]. In the XRD pattern of Fig. 2 j, the broad diffraction peak of SA observed at 2θ of 14°-50° [ 29 ] is nearly absent in the Ca-SA@Fe₃O₄ XRD pattern [ 30 ], but distinct diffraction peaks of Fe₃O₄ [ 31 ] are present, confirming that the Ca-SA@Fe₃O₄ composite was successfully synthesized. (Inserting Fig. 2 here) To further assess the stability of the Ca-SA@Fe₃O₄ gel composite, the composite was immersed in solutions with pH values from 3.0 to 11.0 for 10 hours, and the resulting morphological changes were observed. As illustrated in Fig. 3 a, the morphology and stability of the Ca-SA@Fe₃O₄ composite were largely unaffected by the solution's acidity. XRD analysis of the composites after immersion in various pH solutions further revealed no significant changes in the crystallographic structure of the magnetic gel beads (Fig. 3 b), showing the remarkable stability of the Ca-SA@Fe₃O₄ composite. UV-Vis absorption spectra of Fig. 3 c show that the absorption spectrum of Ca-SA@Fe₃O₄ differs significantly from that of SA, with all characteristic absorption peaks of SA disappearing. This indicates the successful preparation of the Ca-SA@Fe₃O₄ composite. FT-IR spectra of SA and the Ca-SA@Fe₃O₄ gel composite were recorded in Fig. 3 d. In the SA spectrum, a band at 3223 cm⁻¹ is attributed to the stretching vibration of the –OH group [ 32 ]. Absorption peaks for the asymmetric and symmetric stretching vibrations of -COO⁻ and C-O-C stretching vibration at 1615, 1417, and 1034 cm⁻¹, separately [ 32 ]. In the FT-IR spectrum of Ca-SA@Fe₃O₄, the -OH stretching vibration shifts to 3409 cm⁻¹, and the peak area decreases. Additionally, a new absorption peak appears at 562 cm⁻¹, attributed to the Fe-O vibration of Fe₃O₄, verifing the successful fabrication of the Ca-SA@Fe₃O₄ composite [ 33 ]. The obtained saturation magnetization of the Ca-SA@Fe₃O₄ composite is 6.84 emu/g in the magnetic hysteresis loop of Fig. 3 e. This indicates that the Ca-SA@Fe₃O₄ composite exhibits a sufficient magnetic response, Ca-SA@Fe₃O₄ gel beats from treated water using an external magnetic field, ensuring there is no secondary contamination or depletion of the adsorbent. The isotherms for adsorption and desorption, along with the pore size distribution of Ca-SA@Fe₃O₄ were assessed utilizing the N₂ adsorption-desorption method (Fig. 3 f). According to IUPAC classification, the isotherms exhibited Type IV behavior with Type H3 hysteresis. The BET analysis revealed that the Ca-SA@Fe₃O₄ possesses a specific surface area of 1.858 m²/g and a pore volume of 0.001505 cm³/g. Furthermore, the pore size distribution analysis reveals that the Ca-SA@Fe₃O₄ composite primarily consists of mesopores, with the presence of macropores as well. (Inserting Fig. 3 here) Impact of important adsorption conditions Influence of adsorbent dose The adsorbent dosage, ranging from 0.01 to 0.06 g, significantly impacts both the efficiency of La(III) ion removal and the overall cost of the process. This study explores the impact of different Ca-SA@Fe₃O₄ dosages on the adsorption of La(III) ions with an initial concentration of 110 mg/L (Fig. 4 a). As the adsorbent dosage increased from 0.01 to 0.06 g, the q e value of La(III) ions by Ca-SA@Fe₃O₄ decreased from 105.5 to 44.5mg/g. However, the removal rate ( R ) rose from 39.0–97.3%. At an adsorbent dosage of 0.01 g, the maximum adsorption capacity achieved 105.5 mg/g, yet the removal rate was limited to 39.0% owing to the scarcity of sites on the adsorbent surface, leading to swift loading with La(III) ions. Conversely, an adsorbent dosage of 0.04 g enhanced both the equilibrium adsorption capacity ( q e ) to 65.0 mg/g and the removal rate ( R ) to 94.5%. Consequently, 0.04 g of adsorbent was deemed a suitable choice for further adsorption studies. (Inserting Fig. 4 here) Effect of different adsorption time and temperatures The plot in Fig. 4 b demonstrates how the adsorption time and the temperature conditions affect the adsorption of La(III) ions by the Ca-SA@Fe₃O₄ composite. At 298 K, the q e value for La(III) ions on Ca-SA@Fe₃O₄ increased rapidly within the first 2.5 hours and then rose more slowly, reaching dynamic equilibrium within 20 hours. At this equilibrium, q e and R values were 73.0 mg/g and 90%, respectively. The initial surged in adsorption can be attributed to the plethora of accessible adsorption sites present on the surface of the adsorbent. As the adsorption sites become fewer over time, the rate of La(III) ion uptake slows until equilibrium is reached. As the temperature ranged from 298 to 328 K, the Ca-SA@Fe₃O₄ composite displayed increased adsorption rates for La(III) ions, signifying that the adsorption process is endothermic in nature. This can be explained by the intensification of interactions between the La(III) ions and the active sites present on the Ca-SA@Fe₃O₄ surface. Furthermore, the equilibrium time for La(III) adsorption by Ca-SA@Fe₃O₄ remained largely unaffected by temperature variations, suggesting that this adsorbent is highly efficient for treating lanthanide-containing wastewater even under ambient conditions. This characteristic offers a practical and energy-saving approach for wastewater treatment. Effect of pH Water pH significantly impacts the effectiveness of adsorbent treatment. Therefore, the effect of pH on the adsorption of La(III) ions onto Ca-SA@Fe₃O₄ was investigated. As revealed in Fig. 4 c, as the solution pH was raised from 2.0 to 7.0, the adsorption efficiency ( q e ) of La(III) ions was observed to increase from 11.3 mg/g to 73.2 mg/g. Correspondingly, the removal efficiency ( R %) increased sharply from 13.9–90.0%. The point of zero charge (pHpzc) for the Ca-SA@Fe₃O₄ composite was determined to be 8.1 (Fig. 4 d) [ 9 ]. This indicates that the composite maintains a positive surface charge at water pH equal to or less than 8.1, and as the pH decreases, Increase in the number of positive charges on the Ca-SA@Fe₃O₄ surface due to enhanced protonation, leading to an increased repulsion of La(III) ions by Ca-SA@Fe₃O₄. Consequently, the adsorption of La(III) ions is weakest at pH 2.0 [ 34 ]. The chosen pH range of 5.0 to 7.0 is optimal, as La(III) ions tend to precipitate when the solution pH exceeds 7.0. However, within this range, we aim to find the most suitable pH value for our experiments. Impact of co-existing ions and ionic strength The presence of other ions in water can potentially contend with La(III) ions for the available adsorption sites on the surface of the adsorbent, thereby affecting the overall efficiency of La(III) ion removal from the water [ 35 ]. The effect of common ions on La(III) adsorption was investigated at varying concentrations. As shown in Fig. 4 e, some familiar ions such as SO₄²⁻, CO₃²⁻, HCO₃⁻, Cl⁻, Mg²⁺, Ca²⁺, and NO₃⁻ had minimal impact on the adsorption of La(III) ions by Ca-SA@Fe₃O₄ except for the slight effect of Ca²⁺ions. These results demonstrate that the composite exhibits strong selectivity for La(III) ions in aqueous solutions, suggesting its prospect of treating real lanthanide-containing wastewater [ 36 ]. Additionally, the effect of solution ionic strength on the adsorption of La(III) ions by Ca-SA@Fe₃O₄ was examined. As illustrated in Fig. 4 f, variations in ionic strength had minimal impact on the q e and R values for La(III) ion adsorption, indicating that the Ca-SA@Fe₃O₄ composite remains effective in treating wastewater with varying ionic strengths. (Inserting Figure. 5 here) Study on adsorption kinetics To grasp the adsorption mechanism of La(III) ions by Ca-SA@Fe₃O₄, kinetic experimental data at 298, 313, and 328 K (Fig. 5 a-b) were fitted via the Pseudo-First-Order (PFO) and Pseudo-Second-Order (PSO) rate models [ 37 ]. The equations for these models are expressed as follows: q t = q e (1 − e −k 1 t ) (1) q t =(k 2 q e 2 t)/(1 + k 2 q e t) (2) where k 1 (min − 1 ) and k 2 [g/(mg•min)] represent the rate constants for the PFO and PSO models, respectively. q e and q t (mg/g) denote the amount of La(III) adsorbed at equilibrium and t (min). As depicted in Fig. 5 (a, b) and Table 1 , the kinetic data at 298 K, 313 K, and 328 K are more in line with the PSO model ( R ² ≥ 0.975) and provide a better fit than the PFO model ( R ² ≥ 0.945). The calculated equilibrium capacities ( q e , 2 ) from the PSO model align superior with the experimental values ( q e , exp ) [ 9 ], confirming its superior accuracy in describing the adsorption process [ 38 ]. Furthermore, the slight increase in both q e , 1 and q e , 2 values with temperature underscores the endothermic nature of the adsorption reaction. Table 1 Results from fitting different kinetic and isothermal adsorption models, as well as the thermodynamic parameters for La(III) ions adsorption by the Ca-SA@Fe 3 O 4 Adsorbate T(K) q e,exp (mg/g) Pseudo-first-order Pseudo-second-order k 1 (min − 1 ) q e,1 (mg/g) R 2 k 2 [g/(mg·min)] q e,2 (mg/g) R 2 208 73.0 0.55 67.0 0.968 0.0094 75.2 0.990 313 76.0 0.78 69.4 0.945 0.0131 76.2 0.975 328 76.6 0.77 71.3 0.972 0.0120 78.5 0.989 Adsorbate T/K q e,exp (mg/g) Langmuir Freundlich q e (mg/g) K L (L/mg) R 2 n K F R 2 Lanthanum 298 73.0 91.0 0.363 0.928 5.38 40.3 0.858 313 76.0 96.4 0.517 0.986 5.44 45.4 0.899 328 76.6 98.1 0.550 0.936 5.45 48.7 0.865 Adsorbate T/K Thermodynamic parameters ∆G (kJ/mol) ∆H (kJ/mol) ∆S [kJ/(mol·K)] Lanthanum 298 -4.32 36.2 0.136 313 -6.24 328 -8.40 Adsorption isotherms and adsorption thermodynamics Figure 5 c depicts how the initial concentration of lanthanide ions ( C 0 ) affects the adsorption capacity ( q e ) of the gel composite. As C 0 enhanced from 100 to 150mg/L, the q e (mg/g) correspondingly rose from 58 to 90mg/g, indicating enhanced adsorption performance. This behavior can be attributed to the rapid mass transfer of lanthanide ions at higher concentrations and the availability of sufficient active sites on the adsorbent surface [ 39 ].The adsorption isotherm describes the relationship between q e and C e at a given temperature. The q e value for La(III) ions increased as the temperature rose from 298 K to 328 K, consistent with the findings on temperature effects from the adsorption kinetics. To further understand the interaction of the composite with La(III) ions in terms of adsorption, equilibrium adsorption data were fitted using the Langmuir and Freundlich isothermal adsorption models, and their expressions are as follows: q e = ( q m K L C e )/(1 + K L C e ) (3) q e = K F C e 1/n (4) here, q m (mg/g) is the maximum adsorption capacity, K L (L/mg) is the Langmuir coefficient, and n and K F are the Freundlich constants. From the modeling outcomes presented in Fig. 5 (c and d) and Table 1 , it is evident that the equilibrium data for La(III) ion adsorption onto the Ca-SA@Fe₃O₄ composite better align with the Langmuir model ( R ² ≥ 0.928) compared to the Freundlich model ( R ² ≥0.858). This indicates that the Langmuir model provides a more accurate description for the adsorption behavior of La(III) ions on the Ca-SA@Fe₃O₄ composite. The calculated maximum adsorption capacities were 91.0, 96.4, and 98.1 mg/g at 298, 313, and 328 K, respectively. Furthermore, n values between 2 and 10 generally indicate beneficial adsorption. In this study, n was greater than 2, suggesting that the gel composite exhibits effective adsorption of La(III) ions [ 40 ]. The Langmuir constant ( K L ) and Freundlich constant ( K F ), indicative of adsorption efficacy and attraction, both showed an upward trend with temperature across the range of 298 to 328 K. This indicates an endothermic nature of the adsorption, consistent with the temperature effects observed within the adsorption kinetics. To compare the adsorption activity of different materials for lanthanide ions, the maximum adsorption capacities ( q m , mg/g) for La(III) ions by various reported adsorbents are summarized in Table 2 . The Ca-SA@Fe₃O₄ composite exhibits high adsorption capacity for La(III) ions and provides notable benefits, including cost-effectiveness, easy separation from water, safety, non-toxicity, ease of implementation, complete recoverability and reusability. Table 2 Comparison of maximum adsorption capacities ( q m ) of various adsorbents for La(III) ions. Adsorbents q m (mg/g) Ref. Functionalized magnetic multi-walled carbon nanotube bundles 23.23 [ 41 ] graphene oxide/poly (N-isopropyl acrylamide-maleic acid) cryogel 33.1 [ 15 ] durian rind biosorbent 71 [ 18 ] Pectin Extracted from Durian Rind 41.2 [ 17 ] commercial diatomite 22.8 [ 42 ] Penicillium simplicissimum INCQS 40,211 7.81 [ 43 ] Phosphonic-based La-IIP 62.8 [ 44 ] SBA-15-HESI-Fe 3 O 4 -NPs 2.81 [ 45 ] [GO/P(NIPAM-MA)] 33.1 [ 46 ] Ca-SA@Fe 3 O 4 91.0 This study The thermodynamic parameters, including the Gibbs free energy change (Δ G , kJ/mol), entropy change (Δ S , J/(mol⋅K)) and enthalpy change (Δ H , kJ/mol) for the adsorption of La(III) ions onto Ca-SA@Fe₃O₄ were calculated using the following expression: Δ G = - RTlnk (5) Δ G = Δ H - TΔ S (6) Using the adsorption equilibrium constant k ( k = q e / C e ) (L/g) and the constant R = 8.314 J/(mol⋅K) gives Δ G value, Δ H , and Δ S were derived from the linear relationship between Δ G and T. As shown in Table 1 , the Δ G < 0 and Δ H > 0 imply that the adsorption of La(III) ions onto Ca-SA@Fe 3 O 4 proceeds spontaneously and is endothermic. This indicates that the adsorption is favorable. Additionally, Δ S > 0 indicate that the adsorption increases the system’s entropy. Regeneration research To evaluate the potential for reuse of the Ca-SA@Fe₃O₄ composite, desorption experiments were conducted utilizing a solution-mediated regeneration method. Figure 5 e shows that the regeneration results obtained with 0.05 mol/L hydrochloric acid solution as an effective regenerator. After four cycles of La(III) ion adsorption and desorption, the regeneration efficiency ( RE , %) of the composite was 89.9%, 79.5%, 77.0%, and 73.8%, respectively. These finding suggest that the Ca-SA@Fe₃O₄ gel composite can be effectively recovered from water after adsorption and successfully regenerated for reuse. This capability is crucial for enhancing resource utilization, recovering lanthanum—a valuable rare earth element from wastewater, and supporting sustainable development. (Inserting Figure. 6 here) Adsorption mechanism To elucidate the interaction mechanism between the Ca-SA@Fe₃O₄ composite and La(III) ions, FTIR spectra of the composite before and after La(III) ion adsorption were analyzed (Fig. 6 a). Notable changes were observed in the locations and magnitudes of the distinctive peaks. Specifically, the peaks at 3409 cm⁻¹ (corresponding to -OH), 1604 cm⁻¹, and 1426 cm⁻¹ (representing the asymmetric and symmetric -COO⁻ stretches) shifted significantly after La(III) adsorption. Additionally, the peaks at 1031 cm⁻¹ (C-O-C) and 562 cm⁻¹ (Fe-O) shifted and changed, confirming the involvement of oxygen-containing groups and Fe₃O₄ in the interaction with La(III) ions [ 31 ]. XPS analysis of the Ca-SA@Fe₃O₄ composite before and after La(III) adsorption provided further insights. Full spectral scans (Fig. 6 b) showed that the main elements in the composite are C, O and Fe. After La(III) adsorption, significant changes were observed in the characteristic peaks for C 1s, O 1s, and Fe 2p, and new peaks corresponding to La 3d appeared, indicating chemisorption of La(III) ions. The high-resolution XPS spectra of La 3d (Fig. 6 c) revealed four prominent peaks after adsorption: La 3d₅ / ₂ at 834.7 and 838.0 eV, and La 3d₃ / ₂ at 851.7 and 854.8 eV, confirming La(III) ions were indeed adsorbed by undergoing complexation with the oxygen-containing active groups present on the composite. During the high-definition XPS spectra for C 1s (Fig. 6 d), two peaks corresponding to binding energies of 284.0 eV (C-C) and 286.3 eV (C-O, C-OH) [ 47 ] were shifted to 285.1 eV and 286.8 eV, respectively after La(III) adsorption. A new peak at 288.4 eV, attributable to the C atom in COO⁻, appeared. The respective peak area ratios shifted to 0.24:1 and 0.21:1, demonstrating complexation of La(III) ions with COO⁻ groups in Ca-SA@Fe₃O₄. In the O 1s XPS spectra (Fig. 6 e), the peak originally located at 529.4 eV, which corresponds to the C = O bond, disappeared completely from the spectrum. Additionally, the peak at 531.8 eV, associated with the C-O and COO⁻ bonds, underwent a shift and was observed at a new position of 532.2 eV in the spectrum after La(III) adsorption[ 48 ], with a peak area ratio of 0.70:1[ 49 ].This confirms the coordination reaction between La(III) and the oxygen-containing groups on the Ca-SA@Fe₃O₄ surface. High-resolution XPS spectra of Fe 2p (Fig. 6 f) showed that the peaks for Fe 2p₃ / ₂ and Fe 2p₁ / ₂ were shifted from 711.0 and 724.0 eV to 711.4 and 724.7 eV, respectively, with peak area ratios changing to 0.69:1 and 0.87:1 after La(III) adsorption, indicating the presence of Fe in the + 3 oxidation level and suggests that Fe-O groups in the magnetic gel composite are involved in La(III) ion adsorption [ 50 ]. Overall, the XPS results confirm the findings from FTIR analysis and demonstrate that the strong adsorption of La(III) ions by Ca-SA@Fe₃O₄ occurs primarily through complexation, in addition to electrostatic interactions. Conclusion The synthesized Ca-SA@Fe₃O₄ gel composite was characterized by its unique morphology and abundant pore structure, proves to be a cost-effective and reusable biosorbent for the efficient recovery of La(III) ions from wastewater. The Ca-SA@Fe₃O₄ composite exhibits remarkable performance in capturing La(III) ions, reaching a 90.2% removal rate with 0.04 g adsorbent dosage at pH 7.0 and 298 K. The adsorption process mechanism is both spontaneous and endothermic in nature, adhering to the pseudo-second-order kinetic model. The Langmuir adsorption isotherm fits the data well, with a maximum adsorption capacity of 91.0 mg/g at 298 K. The strong adsorption of La(III) ions is attributed to both complexation and electrostatic interactions. Furthermore, the Ca-SA@Fe₃O₄ composite can be completely recovered and regenerated after La(III) ion adsorption, maintaining effectiveness through at least four adsorption/desorption cycles. The gel composite stands out as an environmentally friendly biosorbent with excellent adsorption properties and significant potential for applications in magnetic separation. Declarations Acknowledgement This work was supported by the National Natural Science Foundation of China (No.21167011); the Natural Science Foundation of Inner Mongolia Autonomous Region, China (No. 2020LH02009); the Collaborative Innovation Center for Water Environment Security of Inner Mongolia Autonomous Region, China (XTCX003); and the Fundamental Research Funds for the Inner Mongolia Normal University, China (2022JBTD009). Declarations of interest The authors explicitly state that they have no conflicts of interest, either financial or personal, in relation to the content of this work. Data availability Upon receiving a request, the data will be made accessible. References European Commission. (n.d.). Report on the impact of rare earth elements. Retrieved from http:// doi.org/10.2873/876644 Moriwaki, H., R. Koide, R. Yoshikawa, et al. (2012) Adsorption of rare earth ions onto the cell walls of wild-type and lipoteichoic acid-defective strains of Bacillus subtilis . 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-5218034\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":true,\"archivedVersions\":[],\"articleType\":\"Research Article\",\"associatedPublications\":[],\"authors\":[{\"id\":375677034,\"identity\":\"07c9a78c-ce11-4165-91e1-3c295ec46e4e\",\"order_by\":0,\"name\":\"Nier Su\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Inner Mongolia Normal University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Nier\",\"middleName\":\"\",\"lastName\":\"Su\",\"suffix\":\"\"},{\"id\":375677035,\"identity\":\"61a0895a-6fcf-4341-95c2-175b982feb80\",\"order_by\":1,\"name\":\"Beigang Li\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBklEQVRIiWNgGAWjYBACPmYeBoYEMJOx8cEHHhsefvYG/FrYEFqYmw1nyKTJSPYcIKCFgQfGZG+T5rA5bGNww4GAFnbegw8e/LLLk3dgbJNmyDnPw3CDgfHDxxx8DuNLNkjsSy42PMDYbF1w5jYP4+wGZsmZ2/D6xUwisYc5cWMDY+PtmT23eZhlDrAx8+LXYv4jsacepKVBmvffOR42iQSCWswYEn4cTpzPwNgkzcNzgIeHsBa+ZInEhuOJGxgYgYHMk8wjwXOwGa9f+PnPHvz440914vwG9ofAqLSztz/efPDDRzxawICxjYHB4P4DOLeBgHoQ+MPAIE+MulEwCkbBKBiZAACz7E6fWDLihAAAAABJRU5ErkJggg==\",\"orcid\":\"\",\"institution\":\"Inner Mongolia Normal University\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Beigang\",\"middleName\":\"\",\"lastName\":\"Li\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2024-10-07 12:08:20\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-5218034/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-5218034/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":69917456,\"identity\":\"dca63b40-7fc1-4fd3-9869-df69d2e37f19\",\"added_by\":\"auto\",\"created_at\":\"2024-11-26 14:46:45\",\"extension\":\"png\",\"order_by\":1,\"title\":\"Figure 1\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":585354,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eEffect of SA concentration (a), Ca\\u003csup\\u003e2+\\u003c/sup\\u003e concentration (b), Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e concentration (c), curing time (d) and crosslinking reaction temperature (e) on the adsorption amounts and removal rates (C\\u003csub\\u003e0\\u003c/sub\\u003e：110 mg/L, 20 h adsorption time)\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-5218034/v1/f0e8a18141fd93a615d7652b.png\"},{\"id\":69917455,\"identity\":\"a0fbb1e2-b838-46e7-ad4b-10c71b812d09\",\"added_by\":\"auto\",\"created_at\":\"2024-11-26 14:46:45\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":2713268,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSEM pictures of SA (a), Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e (b-d); EDS element analysis results (e) and element distribution of composite (f-i);. XRD patterns of SA, Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e and Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e composite (j)\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-5218034/v1/b1967e631baf5b8100049066.png\"},{\"id\":69917458,\"identity\":\"0c38ffcb-8cad-4486-80f0-25ec32a346b3\",\"added_by\":\"auto\",\"created_at\":\"2024-11-26 14:46:45\",\"extension\":\"png\",\"order_by\":3,\"title\":\"Figure 3\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1708922,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eEffect of different pH on the stability of hybrid hydrogel (a, b); UV–Vis (c) and FT-IR (d) spectra of samples of SA and Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e; Magnetic hysteresis loop of Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e (e); N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption-desorption isotherms and pore size distribution of Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e (f)\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"3.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-5218034/v1/e192e30ed4edbe985b0942c3.png\"},{\"id\":69918929,\"identity\":\"8cbf9d88-50e6-46cb-9552-0b351372370a\",\"added_by\":\"auto\",\"created_at\":\"2024-11-26 15:02:45\",\"extension\":\"png\",\"order_by\":4,\"title\":\"Figure 4\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1051477,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eEffect of dosage (a: \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e = 110 mg/L, natural pH of solution at 298 K) and contact time and temperature (b: 298–328 K, 0.04 g adsorbent dosage, \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e = 130 mg/L, pH 7.0) on La(III) adsorption; Effect of pH (c) and determination of point of zero charge of Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e (d); Effect of coexisting ions and ionic strength (e and f: 0.04 g adsorbent dosage, \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e = 130 mg/L, pH = 7.0, 20 h contact time and 298K)\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"4.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-5218034/v1/98d8b39c3498bcf7d046fb77.png\"},{\"id\":69919896,\"identity\":\"2e623e86-bfaf-49a4-8bbc-7ad4b8014418\",\"added_by\":\"auto\",\"created_at\":\"2024-11-26 15:10:45\",\"extension\":\"png\",\"order_by\":5,\"title\":\"Figure 5\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":952902,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eFitting curves of the experimental data for La(III) adsorption gained by Pseudo-first-order and Pseudo-second-order dynamic models (a and b: 0.04 g adsorbent dosage, \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e = 130 mg/L, pH = 7.0, 298–328 K); The fitting curves of Langmuir and Freundlich isothermal models for La(III) adsorption by Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e (c and d: \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e = 50-260 mg/L, 0.04 g adsorbent dosage, pH = 7.0, 20 h contact time, 298–328 K); Effect of regeneration cycle times on regeneration rate (e)\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"5.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-5218034/v1/2eb4cdbba087ffcbd10d5f72.png\"},{\"id\":69918468,\"identity\":\"f60f399c-454f-4747-a807-dc0debbd4a5f\",\"added_by\":\"auto\",\"created_at\":\"2024-11-26 14:54:45\",\"extension\":\"png\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1156748,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eFTIR (b) and XPS (b-f) spectra of Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e before and after La(III)\\u003csup\\u003e \\u003c/sup\\u003eadsorption\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"6.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-5218034/v1/2a956813eb04c25966808760.png\"},{\"id\":71369075,\"identity\":\"f7a98ef0-12c5-4f29-b727-832dea840620\",\"added_by\":\"auto\",\"created_at\":\"2024-12-13 18:31:59\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":9888099,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-5218034/v1/dd307c93-b6c2-471a-b566-20c08a787737.pdf\"}],\"financialInterests\":\"No competing interests reported.\",\"formattedTitle\":\"Facile synthesis and effective adsorption of magnetic alginate biogel composite for lanthanum ions from water\",\"fulltext\":[{\"header\":\"Introduction\",\"content\":\"\\u003cp\\u003eRare earth elements (REEs) are composed of 15 lanthanides along 2 pseudo lanthanides (scandium, Sc and yttrium, Y) [\\u003cspan citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1\\u003c/span\\u003e]. REEs also known as the \\\"industrial vitamin\\\" have been used extensively in many technical devices such as superconductors, magnets, catalysts and batteries [\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e]. However, the widespread use of rare earths has the potential to give rise to environmental issues. Currently, with the increasing mining of rare earths, more and more rare earths have being released into aquatic environment, leading to bio-toxicity and resource wastage [\\u003cspan citationid=\\\"CR3\\\" class=\\\"CitationRef\\\"\\u003e3\\u003c/span\\u003e]. Rare-earth metal ion concentrations in natural waters should stay below 20 \\u0026micro;g/L [\\u003cspan citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e]. Therefore, the recovery of REEs from rare earth-containing wastewater and secondary rare earth waste materials is particularly critical for the recycling of limited natural rare earth resources and environmental and economic sustainability. Lanthanum is one of the elements with the highest percentage of rare earth abundance in the earth's crust and has garnered heightedened inrested owing to its robust chemical reactivity and abundant reserves, which in turn has been widely used in a variety of industries such as metallurgy, petroleum, glass, ceramics, etc. Consequently, the increased demand for this element in many important technologies, as well as the rapid exploitation of rare earth resources, has resulted in the migration of La(III) into the biosphere, subsequently altering the equilibrium of elements in the environment and potentially posing a risk to public health [\\u003cspan citationid=\\\"CR6\\\" class=\\\"CitationRef\\\"\\u003e6\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR7\\\" class=\\\"CitationRef\\\"\\u003e7\\u003c/span\\u003e]. There are multiple approaches available for the segregation and retrieval of rare earth ions, which encompass adsorption methodologies, chemical precipitation techniques, and ion exchange [\\u003cspan citationid=\\\"CR8\\\" class=\\\"CitationRef\\\"\\u003e8\\u003c/span\\u003e]. To effectively capture and retain rare earth elements in aqueous solutions using adsorption methodologies that is easy to implement and highly efficient, the selection of adsorbent raw materials, the preparation of eco-friendly adsorbents with stronger adsorption properties and easy recycling are crucial [\\u003cspan additionalcitationids=\\\"CR10\\\" citationid=\\\"CR9\\\" class=\\\"CitationRef\\\"\\u003e9\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR11\\\" class=\\\"CitationRef\\\"\\u003e11\\u003c/span\\u003e]. At present, various types of adsorbents prepared from a variety of raw materials and reagents have been reported, including silicon-based, carbon/graphene-based composite adsorbents [\\u003cspan additionalcitationids=\\\"CR13\\\" citationid=\\\"CR12\\\" class=\\\"CitationRef\\\"\\u003e12\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR14\\\" class=\\\"CitationRef\\\"\\u003e14\\u003c/span\\u003e], metal-organic skeletons (MOFs)/nanoadsorbents [\\u003cspan citationid=\\\"CR15\\\" class=\\\"CitationRef\\\"\\u003e15\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR16\\\" class=\\\"CitationRef\\\"\\u003e16\\u003c/span\\u003e] and agricultural-waste-based adsorbents [\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e]. However, high cost, low stability, adsorption capacity, difficult liquid/solid complete separation and low reuse rate of certain adsorbents limit their application. Therefore, the development of rapid-separating adsorbents has become crucial for the successful implementation of sorption technology, which is a key process in the efficient recovery and separation of ions [\\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e19\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eSodium alginate (SA), a naturally abundant polysaccharide derived from marine sources, possesses exceptional biocompatibility, non-toxic properties, and biodegradability. SA versatility has led to its widespread adoption in various industries, including food processing, pharmaceutical manufacturing, textiles, printing and dyeing, as well as paper production. Recently, SA has attracted remarkable attention as a cost-effectiveness biomass material, offering unique advantages in water treatment applications [\\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e20\\u003c/span\\u003e]. Currently, SA featuring robust hydrophilic properties, the tendency to gel, the capability for polymerization, and a heightened level of chemical reactivity can be prepared into a variety of gel composites with a large space for modification as bio-based adsorbents, and applied to the effective treatment of various industrial wastewater and efficient recovery of rare earths. SA can react with multivalent metals by cross-linking polymerization to form water-insoluble polymer gel spheres commonly referred to as \\u0026ldquo;egg carton model\\u0026rdquo; [\\u003cspan citationid=\\\"CR21\\\" class=\\\"CitationRef\\\"\\u003e21\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR22\\\" class=\\\"CitationRef\\\"\\u003e22\\u003c/span\\u003e], which can be an optimal framework for subsequently crafting a diverse array of granular adsorbent materials that exhibit superior performance. In recent years, magnetic composites have been widely developed as promising adsorbents due to their rapid separability from the aqueous environment, chemical stability and biocompatibility [\\u003cspan citationid=\\\"CR23\\\" class=\\\"CitationRef\\\"\\u003e23\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR24\\\" class=\\\"CitationRef\\\"\\u003e24\\u003c/span\\u003e].\\u003c/p\\u003e \\u003cp\\u003eDrawing upon the established groundwork from prior studies and the comprehensive analysis presented above, the research endeavor focused on harnessing the amplified polymerization capabilities of economical calcium ions with SA, aiming to reduce production expenses and optimize the performance of the gel spheres. Our objective was to develop an environmentally sustainable gel composite that could efficiently recover La(III) ions. Therefore, innovative and biosafe magnetic gel composite was subsequently crafted through the crosslinking polymerization of calcium ions with SA and Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e in this paper. Optimized conditions of preparation and adsorption for macroparticle Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e gel composite was examined. The adsorption capacity, stability, magnetic responsiveness, and adsorption kinetics and thermodynamics of the gel composite were investigated. Recovery capacity, reusability and adsorption mechanisms of lanthanum ions by Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e examined and scrutinized. We aspire to create economical and environmentally benign, sorptive materials integrated with magnetic separation capabilities, crafted via a straightforward and accessible method using natural biological resources, With the aim of promoting the efficient utilization of natural resources, enhancing the purification processes for wastewater laden with rare earth elements, and fostering the responsible recycling of these valuable resources.\\u003c/p\\u003e\"},{\"header\":\"Material and Methods\",\"content\":\"\\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eChemicals and Materials\\u003c/h2\\u003e \\u003cp\\u003eAR-grade CaCl\\u003csub\\u003e2\\u003c/sub\\u003e, La(NO\\u003csub\\u003e3\\u003c/sub\\u003e)\\u003csub\\u003e3\\u003c/sub\\u003e\\u0026middot;6H\\u003csub\\u003e2\\u003c/sub\\u003eO, Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e, HCl, and SA were obtained from Damao Chemical, Tianjin, China.\\u003c/p\\u003e \\u003c/div\\u003e\\n\\u003ch3\\u003ePreparation of Ca-SA@FeO gel composite\\u003c/h3\\u003e\\n\\u003cp\\u003eThe Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e was prepared, detailed as follows: 0.06 g of Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e was introduced into 25 mL of a 16 g/L sodium alginate (SA) solution and mixed thoroughly. The solution was then sonicated at 25\\u0026deg;C for 0.5 hours. Next, it was methodically dripped into 20 mL of a 15 g/L Ca\\u003csup\\u003e2+\\u003c/sup\\u003e ion solution, ultimately yielding the production of brown gel beads. Following a 2-hour curing process, the larger gel beads underwent removal, washing, and drying. This resulted in the production of the final magnetic bio-based adsorbent, Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e, ready for subsequent studies.\\u003c/p\\u003e\\n\\u003ch3\\u003eCharacterization\\u003c/h3\\u003e\\n\\u003cp\\u003eTo analyze the microstructure and elemental composition, scanning electron microscopy with energy dispersive spectroscopy (SEM\\u0026ndash;EDS, SU8010, Hitachi, Japan) was used. The crystalline structure of the raw materials and gel composite was examined using X-ray diffraction (XRD, PW-1830, Philips, Netherlands) with Cu-Kα radiation (λ\\u0026thinsp;=\\u0026thinsp;0.154056 nm). Fourier transform infrared spectroscopy (FTIR) was conducted with a Nicolet 6700 spectrometer (KBr method, Thermo Fisher Scientific, USA). Magnetic properties were assessed using a vibrating sample magnetometer (VSM, 7407, Lake Shore, USA), and X-ray photoelectron spectroscopy (XPS) analysis was performed with an Al Kα X-ray source on an Axis Ultra instrument (Shimadzu, Japan).\\u003c/p\\u003e\\n\\u003ch3\\u003eAdsorption testing\\u003c/h3\\u003e\\n\\u003cp\\u003eAdsorbent was introduced into multiple conical flasks, containing 25 mL of La(III) ion solutions at specific concentrations (\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e, mg/L). The flasks were agitated at 25\\u0026deg;C for 20 h, after which the adsorbent was removed. The residual concentration of La(III) ions (\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e, mg/L) was then determined using colorimetric spectrophotometry at \\u003cem\\u003eλ\\u003c/em\\u003e\\u003csub\\u003emax\\u003c/sub\\u003e\\u0026thinsp;=\\u0026thinsp;650 nm.The adsorption capacity (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e, mg/g) and removal rate (\\u003cem\\u003eη\\u003c/em\\u003e, %) of La(III) ions by the composite gel was calculated using the equations \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e = (\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e- \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e) \\u0026times; \\u003cem\\u003eV\\u003c/em\\u003e/\\u003cem\\u003em\\u003c/em\\u003e and \\u003cem\\u003eη\\u003c/em\\u003e = (\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e- \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e) /\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e \\u0026times; 100%, respectively, where \\u003cem\\u003em\\u003c/em\\u003e is the mass of the composite (g) and \\u003cem\\u003eV\\u003c/em\\u003e is the volume of La(III) solution (L). The effects of adsorbent dosage, pH, adsorption time, adsorption temperature and coexisting ions on the La(III) removal efficiency by the composite were examined following the described adsorption experimental method.\\u003c/p\\u003e\\n\\u003ch3\\u003eRegeneration experiment\\u003c/h3\\u003e\\n\\u003cp\\u003eThe reusability of the Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e gel composite was assessed through repeated adsorption/desorption cycle. 0.04 g of the gel,which had adsorbed La(III) ions was subjected to desorption using an appropriate regenerating agent at room temperature. The gel was then washed and dried before being used in the next cycle. The percentage of regeneration efficiency (\\u003cem\\u003eRE\\u003c/em\\u003e, %) for Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e was determined by appling the formula \\u003cem\\u003eRE\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003en\\u003c/sub\\u003e/\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003e1\\u003c/sub\\u003e \\u0026times; 100%, where (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003e1\\u003c/sub\\u003e) represents the amount of La(III) ions adsorbed during the first cycle and (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003en\\u003c/sub\\u003e) denotes the amount of La(III) ions adsorbed during the n\\u003csup\\u003eth\\u003c/sup\\u003e cycle [\\u003cspan citationid=\\\"CR25\\\" class=\\\"CitationRef\\\"\\u003e25\\u003c/span\\u003e].\\u003c/p\\u003e\"},{\"header\":\"Results and Discussion\",\"content\":\"\\u003cdiv id=\\\"Sec9\\\"\\u003e\\n \\u003ch2\\u003eOptimizing the Synthesis Parameters for Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e Gel Composite\\u003c/h2\\u003e\\n \\u003cp\\u003eSodium alginate (SA) is known for its stability, biodegradability, and non-toxicity. When it interacts with divalent metal ions like Ca\\u0026sup2;⁺ and forms gel particles, facilitating ion separation and adsorption. In this study, different SA concentrations were tested for their ability to form polymers adsorbing La(III) ions at 30 g/L of fixed Ca\\u0026sup2;⁺ concentration. As demonstrated in Fig.\\u0026nbsp;\\u003cspan\\u003e1\\u003c/span\\u003ea, at a SA concentration of 16 g/L, the La(III) adsorption capacity and removal efficiency reached maximum values of 64.29 mg/g and 70.2%. Therefore, 16 g/L was chosen as the optimal SA concentration for preparing the Ca-SA gel composite. Calcium ions act as cross-linking agents and are crucial for forming stable gel particles. Various Ca\\u0026sup2;⁺ concentrations were evaluated, and it was found that a concentration of 15 g/L provided the highest adsorption capacity (76.25 mg/g) and removal efficiency (83.2%) for the prepared Ca-Sacomposite adsorbing La(III) ions as shown in Fig.\\u0026nbsp;\\u003cspan\\u003e1\\u003c/span\\u003eb. This indicates that Ca-SA polymer cross-linked at this concentration show significantly improved adsorption performance. As a result, a concentration of 15 g/L Ca\\u0026sup2;⁺ was was chosen for the preparation of the Ca-SA gel composite. To impart magnetic properties to the Ca-SA composite, Fe₃O₄ was added to the composite. It was observed that the Ca-SA@Fe₃O₄ composite prepared with 2.5 g/L Fe₃O₄ exhibited the best adsorption performance. Additionally, magnetic separation tests confirmed that this concentration provided effective separation while enhancing adsorption compared to the non-magnetic Ca-SA polymer. As shown in Fig.\\u0026nbsp;\\u003cspan\\u003e1\\u003c/span\\u003ec, Consequently, it was determined that 2.5 g/L of Fe₃O₄ was the most effective concentration for the fabrication of the Ca-SA@Fe₃O₄ magnetic composite. The impact of setting time on the durability and cohesion of the cross-linked gel composite was also studied (Fig.\\u0026nbsp;\\u003cspan\\u003e1\\u003c/span\\u003ed). The adsorption capacity (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e) and removal efficiency (\\u003cem\\u003eR\\u003c/em\\u003e%) of the forming Ca-SA@Fe₃O₄ for La(III) ions increased steadily as the curing time extended up to 2 hours, after which both values began to decline. Therefore, a curing time of 2 hours was chosen as the optimal duration. As demonstrated in Fig.\\u0026nbsp;\\u003cspan\\u003e1\\u003c/span\\u003ee, the adsorption potential for La(III) ions showed only minor fluctuations across a temperature range of 25\\u0026deg;C to 55\\u0026deg;C. Therefore, 25\\u0026deg;C was determined to be the appropriate temperature, balancing performance, operational convenience, and energy conservation.\\u003c/p\\u003e\\n \\u003cp\\u003e(Inserting Fig.\\u0026nbsp;\\u003cspan\\u003e1\\u003c/span\\u003e here)\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003ch3\\u003eMaterial characterisation\\u003c/h3\\u003e\\n\\u003cp\\u003eAs depicted in the SEM micrographs (Fig.\\u0026nbsp;\\u003cspan\\u003e2\\u003c/span\\u003ea-d), the black dried macrogel beads of Ca-SA@Fe₃O₄, initially crafted from a milky white SA powder, exhibit a distinctive undulating surface with grooves and clefts of varying depths and irregular geometries. This intricate surface topography serves as an advantage, enhancing the adsorption capabilities of the gel composite. Additionally, the white specks discernible on the surface of the gel beads are likely indicative of Fe₃O₄ particles, a finding that aligns with prior studies [\\u003cspan\\u003e26\\u003c/span\\u003e, \\u003cspan\\u003e27\\u003c/span\\u003e].\\u003c/p\\u003e\\n\\u003cp\\u003eThe observation is further corroborated by the elemental distribution results obtained from the Energy EDS analysis (Fig.\\u0026nbsp;\\u003cspan\\u003e2\\u003c/span\\u003ee). The concentrations of Ca and Fe in the gel composite increased to 15.26% and 5.64%, respectively, compared to their small amounts in the SA. This confirms the presence of Fe₃O₄ particles as indicated by the white spots in the SEM images. Additionally, the Na content decreased significantly from 10.87% in SA to 1.87% in Ca-SA@Fe₃O₄. The distribution of elements such as O, Fe, and Ca in the gel beads was also found to be homogeneous (Figs.\\u0026nbsp;\\u003cspan\\u003e2\\u003c/span\\u003ef-i). These results suggest that Ca\\u0026sup2;⁺ ions initially reacted with Na⁺ ions in the SA solution through ion exchange. Subsequently, the Ca-SA@Fe₃O₄ composite was successfully synthesized via cross-linking and polymerization of Ca\\u0026sup2;⁺ ions with SA molecular chains, resulting in the characteristic \\u0026lsquo;egg carton\\u0026rsquo; structure [\\u003cspan\\u003e28\\u003c/span\\u003e]. In the XRD pattern of Fig.\\u0026nbsp;\\u003cspan\\u003e2\\u003c/span\\u003ej, the broad diffraction peak of SA observed at 2\\u0026theta; of 14\\u0026deg;-50\\u0026deg; [\\u003cspan\\u003e29\\u003c/span\\u003e] is nearly absent in the Ca-SA@Fe₃O₄ XRD pattern [\\u003cspan\\u003e30\\u003c/span\\u003e], but distinct diffraction peaks of Fe₃O₄ [\\u003cspan\\u003e31\\u003c/span\\u003e] are present, confirming that the Ca-SA@Fe₃O₄ composite was successfully synthesized.\\u003c/p\\u003e\\n\\u003cp\\u003e(Inserting Fig.\\u0026nbsp;\\u003cspan\\u003e2\\u003c/span\\u003e here)\\u003c/p\\u003e\\n\\u003cp\\u003eTo further assess the stability of the Ca-SA@Fe₃O₄ gel composite, the composite was immersed in solutions with pH values from 3.0 to 11.0 for 10 hours, and the resulting morphological changes were observed. As illustrated in Fig.\\u0026nbsp;\\u003cspan\\u003e3\\u003c/span\\u003ea, the morphology and stability of the Ca-SA@Fe₃O₄ composite were largely unaffected by the solution\\u0026apos;s acidity. XRD analysis of the composites after immersion in various pH solutions further revealed no significant changes in the crystallographic structure of the magnetic gel beads (Fig.\\u0026nbsp;\\u003cspan\\u003e3\\u003c/span\\u003eb), showing the remarkable stability of the Ca-SA@Fe₃O₄ composite. UV-Vis absorption spectra of Fig.\\u0026nbsp;\\u003cspan\\u003e3\\u003c/span\\u003ec show that the absorption spectrum of Ca-SA@Fe₃O₄ differs significantly from that of SA, with all characteristic absorption peaks of SA disappearing. This indicates the successful preparation of the Ca-SA@Fe₃O₄ composite. FT-IR spectra of SA and the Ca-SA@Fe₃O₄ gel composite were recorded in Fig.\\u0026nbsp;\\u003cspan\\u003e3\\u003c/span\\u003ed. In the SA spectrum, a band at 3223 cm⁻\\u0026sup1; is attributed to the stretching vibration of the \\u0026ndash;OH group [\\u003cspan\\u003e32\\u003c/span\\u003e]. Absorption peaks for the asymmetric and symmetric stretching vibrations of -COO⁻ and C-O-C stretching vibration at 1615, 1417, and 1034 cm⁻\\u0026sup1;, separately [\\u003cspan\\u003e32\\u003c/span\\u003e]. In the FT-IR spectrum of Ca-SA@Fe₃O₄, the -OH stretching vibration shifts to 3409 cm⁻\\u0026sup1;, and the peak area decreases. Additionally, a new absorption peak appears at 562 cm⁻\\u0026sup1;, attributed to the Fe-O vibration of Fe₃O₄, verifing the successful fabrication of the Ca-SA@Fe₃O₄ composite [\\u003cspan\\u003e33\\u003c/span\\u003e]. The obtained saturation magnetization of the Ca-SA@Fe₃O₄ composite is 6.84 emu/g in the magnetic hysteresis loop of Fig.\\u0026nbsp;\\u003cspan\\u003e3\\u003c/span\\u003ee. This indicates that the Ca-SA@Fe₃O₄ composite exhibits a sufficient magnetic response, Ca-SA@Fe₃O₄ gel beats from treated water using an external magnetic field, ensuring there is no secondary contamination or depletion of the adsorbent.\\u003c/p\\u003e\\n\\u003cp\\u003eThe isotherms for adsorption and desorption, along with the pore size distribution of Ca-SA@Fe₃O₄ were assessed utilizing the N₂ adsorption-desorption method (Fig.\\u0026nbsp;\\u003cspan\\u003e3\\u003c/span\\u003ef). According to IUPAC classification, the isotherms exhibited Type IV behavior with Type H3 hysteresis. The BET analysis revealed that the Ca-SA@Fe₃O₄ possesses a specific surface area of 1.858 m\\u0026sup2;/g and a pore volume of 0.001505 cm\\u0026sup3;/g. Furthermore, the pore size distribution analysis reveals that the Ca-SA@Fe₃O₄ composite primarily consists of mesopores, with the presence of macropores as well.\\u003c/p\\u003e\\n\\u003cp\\u003e(Inserting Fig.\\u0026nbsp;\\u003cspan\\u003e3\\u003c/span\\u003e here)\\u003c/p\\u003e\\n\\u003cdiv id=\\\"Sec11\\\"\\u003e\\n \\u003ch2\\u003eImpact of important adsorption conditions\\u003c/h2\\u003e\\n \\u003cdiv id=\\\"Sec12\\\"\\u003e\\n \\u003ch2\\u003eInfluence of adsorbent dose\\u003c/h2\\u003e\\n \\u003cp\\u003eThe adsorbent dosage, ranging from 0.01 to 0.06 g, significantly impacts both the efficiency of La(III) ion removal and the overall cost of the process. This study explores the impact of different Ca-SA@Fe₃O₄ dosages on the adsorption of La(III) ions with an initial concentration of 110 mg/L (Fig.\\u0026nbsp;\\u003cspan\\u003e4\\u003c/span\\u003ea). As the adsorbent dosage increased from 0.01 to 0.06 g, the \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003ee\\u003c/em\\u003e\\u003c/sub\\u003e value of La(III) ions by Ca-SA@Fe₃O₄ decreased from 105.5 to 44.5mg/g. However, the removal rate (\\u003cem\\u003eR\\u003c/em\\u003e) rose from 39.0\\u0026ndash;97.3%. At an adsorbent dosage of 0.01 g, the maximum adsorption capacity achieved 105.5 mg/g, yet the removal rate was limited to 39.0% owing to the scarcity of sites on the adsorbent surface, leading to swift loading with La(III) ions. Conversely, an adsorbent dosage of 0.04 g enhanced both the equilibrium adsorption capacity (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e) to 65.0 mg/g and the removal rate (\\u003cem\\u003eR\\u003c/em\\u003e) to 94.5%. Consequently, 0.04 g of adsorbent was deemed a suitable choice for further adsorption studies.\\u003c/p\\u003e\\n \\u003cp\\u003e(Inserting Fig.\\u0026nbsp;\\u003cspan\\u003e4\\u003c/span\\u003e here)\\u003c/p\\u003e\\n \\u003c/div\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec13\\\"\\u003e\\n \\u003ch2\\u003eEffect of different adsorption time and temperatures\\u003c/h2\\u003e\\n \\u003cp\\u003eThe plot in Fig.\\u0026nbsp;\\u003cspan\\u003e4\\u003c/span\\u003eb demonstrates how the adsorption time and the temperature conditions affect the adsorption of La(III) ions by the Ca-SA@Fe₃O₄ composite. At 298 K, the \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e value for La(III) ions on Ca-SA@Fe₃O₄ increased rapidly within the first 2.5 hours and then rose more slowly, reaching dynamic equilibrium within 20 hours. At this equilibrium, \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003ee\\u003c/em\\u003e\\u003c/sub\\u003e and \\u003cem\\u003eR\\u003c/em\\u003e values were 73.0 mg/g and 90%, respectively. The initial surged in adsorption can be attributed to the plethora of accessible adsorption sites present on the surface of the adsorbent. As the adsorption sites become fewer over time, the rate of La(III) ion uptake slows until equilibrium is reached. As the temperature ranged from 298 to 328 K, the Ca-SA@Fe₃O₄ composite displayed increased adsorption rates for La(III) ions, signifying that the adsorption process is endothermic in nature. This can be explained by the intensification of interactions between the La(III) ions and the active sites present on the Ca-SA@Fe₃O₄ surface. Furthermore, the equilibrium time for La(III) adsorption by Ca-SA@Fe₃O₄ remained largely unaffected by temperature variations, suggesting that this adsorbent is highly efficient for treating lanthanide-containing wastewater even under ambient conditions. This characteristic offers a practical and energy-saving approach for wastewater treatment.\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec14\\\"\\u003e\\n \\u003ch2\\u003eEffect of pH\\u003c/h2\\u003e\\n \\u003cp\\u003eWater pH significantly impacts the effectiveness of adsorbent treatment. Therefore, the effect of pH on the adsorption of La(III) ions onto Ca-SA@Fe₃O₄ was investigated. As revealed in Fig.\\u0026nbsp;\\u003cspan\\u003e4\\u003c/span\\u003ec, as the solution pH was raised from 2.0 to 7.0, the adsorption efficiency (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e) of La(III) ions was observed to increase from 11.3 mg/g to 73.2 mg/g. Correspondingly, the removal efficiency (\\u003cem\\u003eR\\u003c/em\\u003e %) increased sharply from 13.9\\u0026ndash;90.0%. The point of zero charge (pHpzc) for the Ca-SA@Fe₃O₄ composite was determined to be 8.1 (Fig.\\u0026nbsp;\\u003cspan\\u003e4\\u003c/span\\u003ed) [\\u003cspan\\u003e9\\u003c/span\\u003e]. This indicates that the composite maintains a positive surface charge at water pH equal to or less than 8.1, and as the pH decreases, Increase in the number of positive charges on the Ca-SA@Fe₃O₄ surface due to enhanced protonation, leading to an increased repulsion of La(III) ions by Ca-SA@Fe₃O₄. Consequently, the adsorption of La(III) ions is weakest at pH 2.0 [\\u003cspan\\u003e34\\u003c/span\\u003e]. The chosen pH range of 5.0 to 7.0 is optimal, as La(III) ions tend to precipitate when the solution pH exceeds 7.0. However, within this range, we aim to find the most suitable pH value for our experiments.\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec15\\\"\\u003e\\n \\u003ch2\\u003eImpact of co-existing ions and ionic strength\\u003c/h2\\u003e\\n \\u003cp\\u003eThe presence of other ions in water can potentially contend with La(III) ions for the available adsorption sites on the surface of the adsorbent, thereby affecting the overall efficiency of La(III) ion removal from the water [\\u003cspan\\u003e35\\u003c/span\\u003e]. The effect of common ions on La(III) adsorption was investigated at varying concentrations. As shown in Fig.\\u0026nbsp;\\u003cspan\\u003e4\\u003c/span\\u003ee, some familiar ions such as SO₄\\u0026sup2;⁻, CO₃\\u0026sup2;⁻, HCO₃⁻, Cl⁻, Mg\\u0026sup2;⁺, Ca\\u0026sup2;⁺, and NO₃⁻ had minimal impact on the adsorption of La(III) ions by Ca-SA@Fe₃O₄ except for the slight effect of Ca\\u0026sup2;⁺ions. These results demonstrate that the composite exhibits strong selectivity for La(III) ions in aqueous solutions, suggesting its prospect of treating real lanthanide-containing wastewater [\\u003cspan\\u003e36\\u003c/span\\u003e]. Additionally, the effect of solution ionic strength on the adsorption of La(III) ions by Ca-SA@Fe₃O₄ was examined. As illustrated in Fig.\\u0026nbsp;\\u003cspan\\u003e4\\u003c/span\\u003ef, variations in ionic strength had minimal impact on the \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003ee\\u003c/em\\u003e\\u003c/sub\\u003e and \\u003cem\\u003eR\\u003c/em\\u003e values for La(III) ion adsorption, indicating that the Ca-SA@Fe₃O₄ composite remains effective in treating wastewater with varying ionic strengths.\\u003c/p\\u003e\\n \\u003cp\\u003e(Inserting Figure. 5 here)\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec16\\\"\\u003e\\n \\u003ch2\\u003eStudy on adsorption kinetics\\u003c/h2\\u003e\\n \\u003cp\\u003eTo grasp the adsorption mechanism of La(III) ions by Ca-SA@Fe₃O₄, kinetic experimental data at 298, 313, and 328 K (Fig.\\u0026nbsp;\\u003cspan\\u003e5\\u003c/span\\u003ea-b) were fitted via the Pseudo-First-Order (PFO) and Pseudo-Second-Order (PSO) rate models [\\u003cspan\\u003e37\\u003c/span\\u003e]. The equations for these models are expressed as follows:\\u003c/p\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e \\u003csub\\u003et\\u003c/sub\\u003e = \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e(1\\u0026thinsp;\\u0026minus;\\u0026thinsp;e\\u003csup\\u003e\\u0026minus;k\\u003c/sup\\u003e\\u003csub\\u003e1\\u003c/sub\\u003e\\u003csup\\u003et\\u003c/sup\\u003e) (1)\\u003c/p\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e \\u003csub\\u003et\\u003c/sub\\u003e =(k\\u003csub\\u003e2\\u003c/sub\\u003e\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e\\u003csup\\u003e2\\u003c/sup\\u003et)/(1\\u0026thinsp;+\\u0026thinsp;k\\u003csub\\u003e2\\u003c/sub\\u003e\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003et) (2)\\u003c/p\\u003e\\n \\u003cp\\u003ewhere \\u003cem\\u003ek\\u003c/em\\u003e\\u003csub\\u003e1\\u003c/sub\\u003e (min\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e) and \\u003cem\\u003ek\\u003c/em\\u003e\\u003csub\\u003e2\\u003c/sub\\u003e [g/(mg\\u0026bull;min)] represent the rate constants for the PFO and PSO models, respectively. \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e and \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003et\\u003c/sub\\u003e (mg/g) denote the amount of La(III) adsorbed at equilibrium and \\u003cem\\u003et\\u003c/em\\u003e (min).\\u003c/p\\u003e\\n \\u003cp\\u003eAs depicted in Fig.\\u0026nbsp;\\u003cspan\\u003e5\\u003c/span\\u003e(a, b) and Table\\u0026nbsp;\\u003cspan\\u003e1\\u003c/span\\u003e, the kinetic data at 298 K, 313 K, and 328 K are more in line with the PSO model (\\u003cem\\u003eR\\u003c/em\\u003e\\u0026sup2; \\u0026ge; 0.975) and provide a better fit than the PFO model (\\u003cem\\u003eR\\u003c/em\\u003e\\u0026sup2; \\u0026ge; 0.945). The calculated equilibrium capacities (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e,\\u003csub\\u003e2\\u003c/sub\\u003e) from the PSO model align superior with the experimental values (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e,\\u003csub\\u003eexp\\u003c/sub\\u003e) [\\u003cspan\\u003e9\\u003c/span\\u003e], confirming its superior accuracy in describing the adsorption process [\\u003cspan\\u003e38\\u003c/span\\u003e]. Furthermore, the slight increase in both \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e,\\u003csub\\u003e1\\u003c/sub\\u003e and \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e,\\u003csub\\u003e2\\u003c/sub\\u003e values with temperature underscores the endothermic nature of the adsorption reaction.\\u003c/p\\u003e\\n \\u003cdiv\\u003e\\n \\u003ctable id=\\\"Tab1\\\" border=\\\"1\\\"\\u003e\\n \\u003ccaption language=\\\"En\\\"\\u003e\\n \\u003cdiv\\u003eTable 1\\u003c/div\\u003e\\n \\u003cdiv\\u003e\\n \\u003cp\\u003eResults from fitting different kinetic and isothermal adsorption models, as well as the thermodynamic parameters for La(III) ions adsorption by the Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003c/div\\u003e\\n \\u003c/caption\\u003e\\n \\u003ccolgroup cols=\\\"12\\\"\\u003e\\u003c/colgroup\\u003e\\n \\u003cthead\\u003e\\n \\u003ctr\\u003e\\n \\u003cth align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eAdsorbate\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eT(K)\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee,exp\\u003c/sub\\u003e (mg/g)\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\" colspan=\\\"4\\\"\\u003e\\n \\u003cp\\u003ePseudo-first-order\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\" colspan=\\\"5\\\"\\u003e\\n \\u003cp\\u003ePseudo-second-order\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003c/tr\\u003e\\n \\u003c/thead\\u003e\\n \\u003ctbody\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003ek\\u003c/em\\u003e\\u003csub\\u003e1\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003cp\\u003e(min\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee,1\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003cp\\u003e(mg/g)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eR\\u003csup\\u003e2\\u003c/sup\\u003e\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003ek\\u003c/em\\u003e\\u003csub\\u003e2\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003cp\\u003e[g/(mg\\u0026middot;min)]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee,2\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003cp\\u003e(mg/g)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003eR\\u003csup\\u003e2\\u003c/sup\\u003e\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" rowspan=\\\"3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e208\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e73.0\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.55\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e67.0\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.968\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.0094\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e75.2\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.990\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e313\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e76.0\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.78\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e69.4\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.945\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.0131\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e76.2\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.975\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e328\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e76.6\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.77\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e71.3\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.972\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.0120\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e78.5\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.989\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" rowspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003eAdsorbate\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" rowspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003eT/K\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" rowspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee,exp\\u003c/sub\\u003e (mg/g)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"4\\\"\\u003e\\n \\u003cp\\u003eLangmuir\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"5\\\"\\u003e\\n \\u003cp\\u003eFreundlich\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003ee\\u003c/em\\u003e\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003cp\\u003e(mg/g)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eK\\u003c/em\\u003e\\u003csub\\u003eL\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003cp\\u003e(L/mg)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eR\\u003csup\\u003e2\\u003c/sup\\u003e\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003en\\u003c/em\\u003e\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eK\\u003c/em\\u003e\\u003csub\\u003eF\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003eR\\u003csup\\u003e2\\u003c/sup\\u003e\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" rowspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003eLanthanum\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e298\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e73.0\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e91.0\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.363\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.928\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e5.38\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e40.3\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.858\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e313\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e76.0\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e96.4\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.517\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.986\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e5.44\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e45.4\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.899\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e328\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e76.6\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e98.1\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.550\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e0.936\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e5.45\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e48.7\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003e0.865\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" rowspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003eAdsorbate\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" rowspan=\\\"2\\\"\\u003e\\n \\u003cp\\u003eT/K\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"10\\\"\\u003e\\n \\u003cp\\u003eThermodynamic parameters\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003e∆G\\u003c/em\\u003e (kJ/mol)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003e∆H\\u003c/em\\u003e (kJ/mol)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003e∆S\\u003c/em\\u003e [kJ/(mol\\u0026middot;K)]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"1\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\" rowspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003eLanthanum\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e298\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003e-4.32\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"3\\\" rowspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003e36.2\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"3\\\" rowspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003e0.136\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"1\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e313\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003e-6.24\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"1\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e328\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"3\\\"\\u003e\\n \\u003cp\\u003e-8.40\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\" colspan=\\\"1\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003c/tbody\\u003e\\n \\u003c/table\\u003e\\n \\u003c/div\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec17\\\"\\u003e\\n \\u003ch2\\u003eAdsorption isotherms and adsorption thermodynamics\\u003c/h2\\u003e\\n \\u003cp\\u003eFigure\\u0026nbsp;\\u003cspan\\u003e5\\u003c/span\\u003ec depicts how the initial concentration of lanthanide ions (\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e) affects the adsorption capacity (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e) of the gel composite. As \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003e0\\u003c/sub\\u003e enhanced from 100 to 150mg/L, the \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e (mg/g) correspondingly rose from 58 to 90mg/g, indicating enhanced adsorption performance. This behavior can be attributed to the rapid mass transfer of lanthanide ions at higher concentrations and the availability of sufficient active sites on the adsorbent surface [\\u003cspan\\u003e39\\u003c/span\\u003e].The adsorption isotherm describes the relationship between \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e and \\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e at a given temperature. The \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e value for La(III) ions increased as the temperature rose from 298 K to 328 K, consistent with the findings on temperature effects from the adsorption kinetics. To further understand the interaction of the composite with La(III) ions in terms of adsorption, equilibrium adsorption data were fitted using the Langmuir and Freundlich isothermal adsorption models, and their expressions are as follows:\\u003c/p\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e \\u003csub\\u003ee\\u003c/sub\\u003e = (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003em\\u003c/sub\\u003eK\\u003csub\\u003eL\\u003c/sub\\u003e\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e)/(1\\u0026thinsp;+\\u0026thinsp;K\\u003csub\\u003eL\\u003c/sub\\u003e\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e) (3)\\u003c/p\\u003e\\n \\u003cp\\u003e\\u003cstrong\\u003eq\\u003c/strong\\u003e \\u003csub\\u003ee\\u003c/sub\\u003e = K\\u003csub\\u003eF\\u003c/sub\\u003e\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e\\u003csup\\u003e1/n\\u003c/sup\\u003e (4)\\u003c/p\\u003e\\n \\u003cp\\u003ehere, \\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003em\\u003c/sub\\u003e (mg/g) is the maximum adsorption capacity, \\u003cem\\u003eK\\u003c/em\\u003e\\u003csub\\u003eL\\u003c/sub\\u003e (L/mg) is the Langmuir coefficient, and \\u003cem\\u003en\\u003c/em\\u003e and \\u003cem\\u003eK\\u003c/em\\u003e\\u003csub\\u003eF\\u003c/sub\\u003e are the Freundlich constants.\\u003c/p\\u003e\\n \\u003cp\\u003eFrom the modeling outcomes presented in Fig.\\u0026nbsp;\\u003cspan\\u003e5\\u003c/span\\u003e(c and d) and Table\\u0026nbsp;\\u003cspan\\u003e1\\u003c/span\\u003e, it is evident that the equilibrium data for La(III) ion adsorption onto the Ca-SA@Fe₃O₄ composite better align with the Langmuir model (\\u003cem\\u003eR\\u003c/em\\u003e\\u0026sup2; \\u0026ge; 0.928) compared to the Freundlich model (\\u003cem\\u003eR\\u003c/em\\u003e\\u0026sup2; \\u0026ge;0.858). This indicates that the Langmuir model provides a more accurate description for the adsorption behavior of La(III) ions on the Ca-SA@Fe₃O₄ composite. The calculated maximum adsorption capacities were 91.0, 96.4, and 98.1 mg/g at 298, 313, and 328 K, respectively. Furthermore, \\u003cem\\u003en\\u003c/em\\u003e values between 2 and 10 generally indicate beneficial adsorption. In this study, \\u003cem\\u003en\\u003c/em\\u003e was greater than 2, suggesting that the gel composite exhibits effective adsorption of La(III) ions [\\u003cspan\\u003e40\\u003c/span\\u003e]. The Langmuir constant (\\u003cem\\u003eK\\u003c/em\\u003e\\u003csub\\u003eL\\u003c/sub\\u003e) and Freundlich constant (\\u003cem\\u003eK\\u003c/em\\u003e\\u003csub\\u003eF\\u003c/sub\\u003e), indicative of adsorption efficacy and attraction, both showed an upward trend with temperature across the range of 298 to 328 K. This indicates an endothermic nature of the adsorption, consistent with the temperature effects observed within the adsorption kinetics.\\u003c/p\\u003e\\n \\u003cp\\u003eTo compare the adsorption activity of different materials for lanthanide ions, the maximum adsorption capacities (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003em\\u003c/sub\\u003e, mg/g) for La(III) ions by various reported adsorbents are summarized in Table\\u0026nbsp;\\u003cspan\\u003e2\\u003c/span\\u003e. The Ca-SA@Fe₃O₄ composite exhibits high adsorption capacity for La(III) ions and provides notable benefits, including cost-effectiveness, easy separation from water, safety, non-toxicity, ease of implementation, complete recoverability and reusability.\\u003c/p\\u003e\\n \\u003cdiv\\u003e\\n \\u003ctable id=\\\"Tab2\\\" border=\\\"1\\\"\\u003e\\n \\u003ccaption language=\\\"En\\\"\\u003e\\n \\u003cdiv\\u003eTable 2\\u003c/div\\u003e\\n \\u003cdiv\\u003e\\n \\u003cp\\u003eComparison of maximum adsorption capacities (\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003em\\u003c/sub\\u003e) of various adsorbents for La(III) ions.\\u003c/p\\u003e\\n \\u003c/div\\u003e\\n \\u003c/caption\\u003e\\n \\u003ccolgroup cols=\\\"3\\\"\\u003e\\u003c/colgroup\\u003e\\n \\u003cthead\\u003e\\n \\u003ctr\\u003e\\n \\u003cth align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eAdsorbents\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003e\\u003cem\\u003em\\u003c/em\\u003e\\u003c/sub\\u003e (mg/g)\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003cth align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eRef.\\u003c/p\\u003e\\n \\u003c/th\\u003e\\n \\u003c/tr\\u003e\\n \\u003c/thead\\u003e\\n \\u003ctbody\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eFunctionalized magnetic multi-walled carbon nanotube bundles\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e23.23\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e41\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003egraphene oxide/poly (N-isopropyl acrylamide-maleic acid) cryogel\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e33.1\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e15\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003edurian rind biosorbent\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e71\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e18\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003ePectin Extracted from Durian Rind\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e41.2\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e17\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003ecommercial diatomite\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e22.8\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e42\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003ePenicillium simplicissimum INCQS 40,211\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e7.81\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e43\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003ePhosphonic-based La-IIP\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e62.8\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e44\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eSBA-15-HESI-Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e-NPs\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e2.81\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e45\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[GO/P(NIPAM-MA)]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e33.1\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e[\\u003cspan\\u003e46\\u003c/span\\u003e]\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eCa-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003e91.0\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd align=\\\"left\\\"\\u003e\\n \\u003cp\\u003eThis study\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003c/tbody\\u003e\\n \\u003c/table\\u003e\\n \\u003c/div\\u003e\\n \\u003cp\\u003eThe thermodynamic parameters, including the Gibbs free energy change (\\u0026Delta;\\u003cem\\u003eG\\u003c/em\\u003e, kJ/mol), entropy change (\\u0026Delta;\\u003cem\\u003eS\\u003c/em\\u003e, J/(mol\\u0026sdot;K)) and enthalpy change (\\u0026Delta;\\u003cem\\u003eH\\u003c/em\\u003e, kJ/mol) for the adsorption of La(III) ions onto Ca-SA@Fe₃O₄ were calculated using the following expression:\\u003c/p\\u003e\\n \\u003cp\\u003e\\u0026Delta;\\u003cem\\u003eG\\u003c/em\\u003e = - RTlnk \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; (5)\\u003c/p\\u003e\\n \\u003cp\\u003e\\u0026Delta;\\u003cem\\u003eG\\u003c/em\\u003e = \\u0026Delta;\\u003cem\\u003eH\\u003c/em\\u003e- T\\u0026Delta;\\u003cem\\u003eS\\u003c/em\\u003e\\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; (6)\\u003c/p\\u003e\\n \\u003cp\\u003eUsing the adsorption equilibrium constant \\u003cem\\u003ek\\u003c/em\\u003e (\\u003cem\\u003ek\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;\\u003cem\\u003eq\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e/\\u003cem\\u003eC\\u003c/em\\u003e\\u003csub\\u003ee\\u003c/sub\\u003e) (L/g) and the constant R\\u0026thinsp;=\\u0026thinsp;8.314 J/(mol\\u0026sdot;K) gives \\u0026Delta;\\u003cem\\u003eG\\u003c/em\\u003e value, \\u0026Delta;\\u003cem\\u003eH\\u003c/em\\u003e, and \\u0026Delta;\\u003cem\\u003eS\\u003c/em\\u003e were derived from the linear relationship between \\u0026Delta;\\u003cem\\u003eG\\u003c/em\\u003e and T. As shown in Table \\u003cspan\\u003e1\\u003c/span\\u003e, the \\u0026Delta;\\u003cem\\u003eG\\u003c/em\\u003e\\u0026thinsp;\\u0026lt;\\u0026thinsp;0 and \\u0026Delta;\\u003cem\\u003eH\\u003c/em\\u003e\\u0026thinsp;\\u0026gt;\\u0026thinsp;0 imply that the adsorption of La(III) ions onto Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e proceeds spontaneously and is endothermic. This indicates that the adsorption is favorable. Additionally, \\u0026Delta;\\u003cem\\u003eS\\u003c/em\\u003e\\u0026thinsp;\\u0026gt;\\u0026thinsp;0 indicate that the adsorption increases the system\\u0026rsquo;s entropy.\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec18\\\"\\u003e\\n \\u003ch2\\u003eRegeneration research\\u003c/h2\\u003e\\n \\u003cp\\u003eTo evaluate the potential for reuse of the Ca-SA@Fe₃O₄ composite, desorption experiments were conducted utilizing a solution-mediated regeneration method. Figure\\u0026nbsp;\\u003cspan\\u003e5\\u003c/span\\u003ee shows that the regeneration results obtained with 0.05 mol/L hydrochloric acid solution as an effective regenerator. After four cycles of La(III) ion adsorption and desorption, the regeneration efficiency (\\u003cem\\u003eRE\\u003c/em\\u003e, %) of the composite was 89.9%, 79.5%, 77.0%, and 73.8%, respectively. These finding suggest that the Ca-SA@Fe₃O₄ gel composite can be effectively recovered from water after adsorption and successfully regenerated for reuse. This capability is crucial for enhancing resource utilization, recovering lanthanum\\u0026mdash;a valuable rare earth element from wastewater, and supporting sustainable development.\\u003c/p\\u003e\\n \\u003cp\\u003e(Inserting Figure. 6 here)\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv id=\\\"Sec19\\\"\\u003e\\n \\u003ch2\\u003eAdsorption mechanism\\u003c/h2\\u003e\\n \\u003cp\\u003eTo elucidate the interaction mechanism between the Ca-SA@Fe₃O₄ composite and La(III) ions, FTIR spectra of the composite before and after La(III) ion adsorption were analyzed (Fig.\\u0026nbsp;\\u003cspan\\u003e6\\u003c/span\\u003ea). Notable changes were observed in the locations and magnitudes of the distinctive peaks. Specifically, the peaks at 3409 cm⁻\\u0026sup1; (corresponding to -OH), 1604 cm⁻\\u0026sup1;, and 1426 cm⁻\\u0026sup1; (representing the asymmetric and symmetric -COO⁻ stretches) shifted significantly after La(III) adsorption. Additionally, the peaks at 1031 cm⁻\\u0026sup1; (C-O-C) and 562 cm⁻\\u0026sup1; (Fe-O) shifted and changed, confirming the involvement of oxygen-containing groups and Fe₃O₄ in the interaction with La(III) ions [\\u003cspan\\u003e31\\u003c/span\\u003e]. XPS analysis of the Ca-SA@Fe₃O₄ composite before and after La(III) adsorption provided further insights. Full spectral scans (Fig.\\u0026nbsp;\\u003cspan\\u003e6\\u003c/span\\u003eb) showed that the main elements in the composite are C, O and Fe. After La(III) adsorption, significant changes were observed in the characteristic peaks for C 1s, O 1s, and Fe 2p, and new peaks corresponding to La 3d appeared, indicating chemisorption of La(III) ions. The high-resolution XPS spectra of La 3d (Fig.\\u0026nbsp;\\u003cspan\\u003e6\\u003c/span\\u003ec) revealed four prominent peaks after adsorption: La 3d₅\\u003csub\\u003e/\\u003c/sub\\u003e₂ at 834.7 and 838.0 eV, and La 3d₃\\u003csub\\u003e/\\u003c/sub\\u003e₂ at 851.7 and 854.8 eV, confirming La(III) ions were indeed adsorbed by undergoing complexation with the oxygen-containing active groups present on the composite. During the high-definition XPS spectra for C 1s (Fig.\\u0026nbsp;\\u003cspan\\u003e6\\u003c/span\\u003ed), two peaks corresponding to binding energies of 284.0 eV (C-C) and 286.3 eV (C-O, C-OH) [\\u003cspan\\u003e47\\u003c/span\\u003e] were shifted to 285.1 eV and 286.8 eV, respectively after La(III) adsorption. A new peak at 288.4 eV, attributable to the C atom in COO⁻, appeared. The respective peak area ratios shifted to 0.24:1 and 0.21:1, demonstrating complexation of La(III) ions with COO⁻ groups in Ca-SA@Fe₃O₄. In the O 1s XPS spectra (Fig.\\u0026nbsp;\\u003cspan\\u003e6\\u003c/span\\u003ee), the peak originally located at 529.4 eV, which corresponds to the C\\u0026thinsp;=\\u0026thinsp;O bond, disappeared completely from the spectrum. Additionally, the peak at 531.8 eV, associated with the C-O and COO⁻ bonds, underwent a shift and was observed at a new position of 532.2 eV in the spectrum after La(III) adsorption[\\u003cspan\\u003e48\\u003c/span\\u003e], with a peak area ratio of 0.70:1[\\u003cspan\\u003e49\\u003c/span\\u003e].This confirms the coordination reaction between La(III) and the oxygen-containing groups on the Ca-SA@Fe₃O₄ surface. High-resolution XPS spectra of Fe 2p (Fig.\\u0026nbsp;\\u003cspan\\u003e6\\u003c/span\\u003ef) showed that the peaks for Fe 2p₃\\u003csub\\u003e/\\u003c/sub\\u003e₂ and Fe 2p₁\\u003csub\\u003e/\\u003c/sub\\u003e₂ were shifted from 711.0 and 724.0 eV to 711.4 and 724.7 eV, respectively, with peak area ratios changing to 0.69:1 and 0.87:1 after La(III) adsorption, indicating the presence of Fe in the +\\u0026thinsp;3 oxidation level and suggests that Fe-O groups in the magnetic gel composite are involved in La(III) ion adsorption [\\u003cspan\\u003e50\\u003c/span\\u003e].\\u003c/p\\u003e\\n \\u003cp\\u003eOverall, the XPS results confirm the findings from FTIR analysis and demonstrate that the strong adsorption of La(III) ions by Ca-SA@Fe₃O₄ occurs primarily through complexation, in addition to electrostatic interactions.\\u003c/p\\u003e\\n\\u003c/div\\u003e\"},{\"header\":\"Conclusion\",\"content\":\"\\u003cp\\u003eThe synthesized Ca-SA@Fe₃O₄ gel composite was characterized by its unique morphology and abundant pore structure, proves to be a cost-effective and reusable biosorbent for the efficient recovery of La(III) ions from wastewater. The Ca-SA@Fe₃O₄ composite exhibits remarkable performance in capturing La(III) ions, reaching a 90.2% removal rate with 0.04 g adsorbent dosage at pH 7.0 and 298 K. The adsorption process mechanism is both spontaneous and endothermic in nature, adhering to the pseudo-second-order kinetic model. The Langmuir adsorption isotherm fits the data well, with a maximum adsorption capacity of 91.0 mg/g at 298 K. The strong adsorption of La(III) ions is attributed to both complexation and electrostatic interactions. Furthermore, the Ca-SA@Fe₃O₄ composite can be completely recovered and regenerated after La(III) ion adsorption, maintaining effectiveness through at least four adsorption/desorption cycles. The gel composite stands out as an environmentally friendly biosorbent with excellent adsorption properties and significant potential for applications in magnetic separation.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eAcknowledgement\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThis work was supported by the National Natural Science Foundation of China (No.21167011); the Natural Science Foundation of Inner Mongolia Autonomous Region, China (No. 2020LH02009); the Collaborative Innovation Center for Water Environment Security of Inner Mongolia Autonomous Region, China (XTCX003); and the Fundamental Research Funds for the Inner Mongolia Normal University, China (2022JBTD009).\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eDeclarations of interest\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe authors explicitly state that they have no conflicts of interest, either financial or personal, in relation to the content of this work.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eData availability\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eUpon receiving a request, the data will be made accessible.\\u0026nbsp;\\u003c/p\\u003e\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\n\\u003cli\\u003eEuropean Commission. 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Dakroury (2022) Recovery of Some Rare-Earth Elements by Sorption Technique onto Graphene Oxide\\u003cem\\u003e.\\u003c/em\\u003e Journal of Sustainable Metallurgy. 8(2): 715-731.http:// doi.org/10.1007/s40831-022-00520-0\\u003c/li\\u003e\\n\\u003cli\\u003eZhao, X., X. Jiang, D. Peng, et al. (2021) Behavior and mechanism of graphene oxide-tris(4-aminophenyl)amine composites in adsorption of rare earth elements\\u003cem\\u003e.\\u003c/em\\u003e Journal of Rare Earths. 39(1): 90-97.http:// doi.org/10.1016/j.jre.2020.02.006\\u003c/li\\u003e\\n\\u003cli\\u003eZhao, L., X. Duan, M.R. Azhar, et al. (2020) Selective adsorption of rare earth ions from aqueous solution on metal-organic framework HKUST-1\\u003cem\\u003e.\\u003c/em\\u003e Chemical Engineering Journal Advances. 1.http:// doi.org/10.1016/j.ceja.2020.100009\\u003c/li\\u003e\\n\\u003cli\\u003eMaranescu, B., L. LupaA. 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Sci. 254 (2008) 2441\\u0026ndash;2449]\\u003cem\\u003e.\\u003c/em\\u003e Applied Surface Science. 255(18): 8194.https://doi.org/10.1016/j.apsusc.2009.04.153\\u003c/li\\u003e\\n\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":true,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":false,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true},\"keywords\":\"Alginate, Lanthanum ions, adsorption, Magnetism, Biogel composite\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-5218034/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-5218034/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eA novel eco-friendly magnetic alginate biogel composite (Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e) was synthesized through droplet polymerization and characterized using multiple techniques. Furthermore, the impact of factors, such as dosage, pH, contact time, temperature and the presence of co-existing ions on the efficiency of the removal for La(III) ions by the composite were systematically investigated. The evaluation and exploration were conducted on the adsorption performance, reusability, and interaction mechanism of the magnetic composite towards La(III) ions. The results show that the magnetic composite gel beats have a particle scale of approximately 1.3 mm, a peculiar folded structure with numerous surface pores and sensitive magnetive responsiveness. La(III)-ion removal from water by Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e reached 90.2% at pH 7.0, contact time of 20 h and 298 K. The La(III) adsorption behaviour was in accordance with the Langmuir model, and the maximum adsorption capacity was up to 91.0 mg/g. The spontaneous adsorption process exhibited kinetics that were in accordance with the Pseudo-second-order model, suggesting a favorable agreement. Complexation and electrostatic adsorption between the composite and La(III) ions facilitate the strong adsorption of La(III) ions. The commonly coexisting ions and ionic strength hardly interfered with the La(III) adsorption, apart from a minor influence of Ca\\u003csup\\u003e2+\\u003c/sup\\u003e ions. The biogel composite following adsorption of La(III) ions can be completely recovered and reused at least four times. Ca-SA@Fe\\u003csub\\u003e3\\u003c/sub\\u003eO\\u003csub\\u003e4\\u003c/sub\\u003e composite would be a cost-effective macroparticle biosorbent.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Facile synthesis and effective adsorption of magnetic alginate biogel composite for lanthanum ions from water\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2024-11-26 14:46:40\",\"doi\":\"10.21203/rs.3.rs-5218034/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true}}],\"origin\":\"\",\"ownerIdentity\":\"e21ca135-ba3a-4c5f-a116-3f35a37b8cd2\",\"owner\":[],\"postedDate\":\"November 26th, 2024\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"posted\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2024-12-13T18:23:44+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2024-11-26 14:46:40\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-5218034\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-5218034\",\"identity\":\"rs-5218034\",\"version\":[\"v1\"]},\"buildId\":\"qtupq5eGEP_6zYnWcrvyt\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}