Performance Research of the natural sand grains for adsorption enrichment and removal of Cd(II) from aqueous solution

Performance Research of the natural sand grains for adsorption enrichment and removal of Cd(II) from aqueous solution | 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 Performance Research of the natural sand grains for adsorption enrichment and removal of Cd(II) from aqueous solution Jiaxiang Qi, Yixin Sui, SuaiBing Gao, LinLin Chai, shawket abliz This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8364648/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Apr, 2026 Read the published version in Environmental Science and Pollution Research → Version 1 posted 6 You are reading this latest preprint version Abstract This study investigates the performance of natural sand particles from the Taklamakan Desert as a low-cost adsorbent for removing Cd(II) from water. SEM, FTIR, and XRD characterization revealed a multi-porous silica structure with abundant Si–OH and Si–O–Si groups. Using a microcolumn coupled with FAAS under optimal conditions (pH 5.5–6.5, flow rate 3 mL·min − 1 , room temperature), the sand particles exhibited a dynamic saturation adsorption capacity of 10.2 mg·g − 1 for Cd(II) ions, achieving an adsorption rate of 90.2%. Equilibrium data conformed to the Freundlich model (R 2 = 0.938), indicating heterogeneous multilayer adsorption. Kinetic data followed pseudo-second-order kinetics (R 2 = 0.966), revealing a chemically controlled mechanism. Thermodynamic analysis confirmed the process as a spontaneous, endothermic reaction. After desorption using 0.01 mol·L − 1 hydrochloric acid, the desorption rate reached 98.4% with no significant loss of adsorption capacity. This demonstrates that natural sand particles represent a sustainable and highly efficient adsorbent for Cd(II) remediation. Natural sand grains Cadmium ions Flame atomic absorption spectroscopy Adsorption model Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Cadmium is introduced into the environment through both geochemical weathering and a wide range of industrial activities such as electroplating, base-metal smelting, Ni-Cd battery manufacture, pigment and plastic production, and the formulation of phosphate fertilisers and pesticides ( Wang 2024; Chi et al. 2018; Radha et al. 2021 ). Once released, Cd(II) accumulates in soils and aquatic systems, enters the food chain via irrigation water and crops, and persists in human soft tissues-particularly the kidneys and liver-for decades. Because cadmium is non-essential and classified as a human carcinogen, even trace concentrations represent a serious environmental and public-health risk ( Chen et al. 2020; Hong et al. 2020; Ma et al. 2024 ). Consequently, the efficient removal of Cd(II) from water and wastewater is imperative. Among the technologies available (chemical precipitation, solvent extraction, ion exchange, membrane separation and adsorption ( Ma et al. 2020; Jomova et al. 2024 )), adsorption is especially attractive for low-to-medium strength effluents because it can be implemented at ambient temperature and pressure, does not generate sludge volumes requiring further treatment, and is capable of reducing Cd(II) to sub-ppm levels ( Ayach et al. 2024 ). Although activated carbons, synthetic resins and engineered nanomaterials exhibit high capacities, their cost and/or complex synthesis limit large-scale application ( Qasem et al. 2021; Feng et al. 2021; Aziz et al. 2025 ). There is therefore growing interest in the use of raw or minimally processed natural solids-clays, zeolites, peat, rice husk, etc.-that already possess favourable surface area, porosity and surface functionality ( Awual et al. 2018 ). Here, we evaluated the potential of untreated sand from China's largest desert-the Taklamakan Desert-as a low-cost, abundant, and non-toxic Cd(II) adsorbent. Previous mineralogical investigations indicate that these sand grains contain over 90% silica (wt%) and exhibit a hierarchically rough microporous structure with terminal silanol (Si-OH) and siloxane (Si-O-Si) groups-features theoretically favorable for metal ion binding ( Amjlef et al. 2021; Lee et al. 2010; Medine et al. 2015; Nan H et al. 2015 ). This study employed a miniature packed-bed column filled with natural sand grains (NSGs) coupled online with flame atomic absorption spectroscopy (FAAS) for real-time monitoring of adsorption kinetics. By systematically varying pH, flow rate, and feed concentration, the saturation capacity and rate-limiting steps were successfully quantified.The schematic diagram of the serial connection is shown in Fig. 1 below. Structural changes in samples before and after Cd(II) adsorption were verified using SEM, FTIR, and XRD techniques. Equilibrium data successfully fit the Freundlich adsorption model and pseudo-second-order kinetic model, indicating a heterogeneous multilayer adsorption mechanism where the process is primarily chemically controlled. Adsorption thermodynamics analysis confirmed the process is endothermic and spontaneous. These findings demonstrate that Taklamakan natural sand grains serve as an efficient, renewable, and genuinely low-cost biosorbent for Cd(II) removal from aqueous media. 1 Experimental part 1.1 Instruments and Reagents Flame atomic absorption spectrometer (AA-6880, Shimadzu); Fourier transform infrared spectrometer (type EQUINOX55, BRUKER, Germany); Scanning electron microscope (LEO-1430VP, Zeiss AG, Germany); X-ray powder diffractometer (D8 Advance, AXS GmbH, Bruker, Germany); Electric constant temperature drying oven (DHG-9140A, Shanghai Jinghong Experimental Equipment Co, Ltd.); Vacuum drying oven (DZF-6020, Shanghai Anting Scientific Instrument Factory); Electronic balance (JY302, Shanghai METTLER TOLEDO Instrument Co, Ltd.); Peristaltic pump (BTOO-300M type; Beijing Baoding Town Lange Constant Flow Pump Co, Ltd.); cadmium hollow cathode lamp; grains of sand (grains of sand collected at different points in the Taklamakan Desert); Cadmium carbonate (Tianjin Beilian Fine Chemical Development Co, Ltd.); Ethanol, acetic acid (Tianjin Damao Chemical Reagent Factory); hydrochloric acid, sodium hydroxide (Urumqi Dicheng Chemical Co, Ltd.); Deionized water (deionized water supply room, School of Chemical Engineering, Xinjiang University). 1.2 Preparation of sand pretreatment and adsorption separation microcolumns An appropriate amount of sand grains were weighed, deionized water was washed repeatedly and repeatedly to remove dust and water-soluble components on the surface of the sand particles, and then dried at a constant temperature of 80℃ in an oven for 24 h. A certain mass of sand particles as a solid-phase adsorption material was added to a 4×50 mm glass microcolumn, and the separation microcolumn was used in conjunction with a peristaltic pump for dynamic adsorption and desorption experiments. 1.3 Verify the adsorption of Cd(II) ions by sand particles After the Cd(II) ion standard solution passed through the adsorption separation microcolumn at a certain flow rate, 0.010 mol· L − 1 hydrochloric acid was eluted, and the Cd(II) ion solution and desorption solution flowing from the microcolumn were quantitatively collected, respectively. The concentration of Cd(II) ions in the original solution, Cd(II) ion solution and desorption solution was determined by FAAS method. Compared with the original solution, the decrease of Cd(II) ion concentration in the column solution indicates that the sand particles have adsorption effect on the Cd(II) ion solution, and the larger the concentration decrease, the better the adsorption effect. The determination of Cd(II) ions in the desorption solution can further prove the adsorption performance of Cd(II) ions by sand particles. 1.4 Dynamic adsorption and desorption experiments At room temperature, a Cd(II) ionic solution or sample with pH = 6 was passed through the adsorption separation microcolumn at an appropriate flow rate, and then 0.010 mol·L − 1 hydrochloric acid was eluted through the microcolumn at a natural flow rate, and the concentration of Cd(II) ions in solution was determined by FAAS method. The relevant adsorption parameters are calculated according to equations (1), (2) and (3) ( Huang et al. 2025 ). $$\:\begin{array}{c}\text{Q}\text{=}\frac{\text{(}{\text{C}}_{\text{0}}\text{−}{\text{C}}_{\text{e}}\text{)}\text{V}}{\text{W}}\#\text{(}\text{1}\text{)}\end{array}$$ $$\:\begin{array}{c}\text{E}\text{(}\text{%}\text{)}\text{=}\frac{\text{(}{\text{C}}_{\text{0}}\text{-}{\text{C}}_{\text{e}}\text{)}}{{\text{C}}_{\text{0}}}\text{×}\text{100}\text{%}\text{}\text{}\#\text{(}\text{2}\text{)}\end{array}$$ $$\:\begin{array}{c}\text{B}\text{(}\text{%}\text{)}\text{=}\frac{{\text{C}}_{\text{d}}{\text{V}}_{\text{d}}}{\text{(}{\text{C}}_{\text{0}}\text{-}{\text{C}}_{\text{e}}\text{)}\text{V}}\text{×}\text{100}\text{%}\text{}\#\text{(}\text{3}\text{)}\end{array}$$ C 0 is the concentration of Cd(II) ions in the original solution before adsorption, C e is the concentration of Cd(II) ions in the column solution, C d is the concentration of Cd(II) ions in the desorption solution (mg/L), V is the volume of the solution passing through the microcolumn, V d is the volume of the desorption solution (ml), and W is the dry weight (g) of the adsorbent added. 2 Results and Discussion 2.1 SEM characterization Surface morphology of natural sand particles before and after adsorption was analyzed using SEM. As shown in Fig. 2 (a,b), the pre-adsorption images reveal that sand particles, as granular natural products, exhibit diverse and irregular shapes with a dense, porous, and rough surface morphology. This characteristic enhances the specific surface area of the sand particles, thereby increasing the number of adsorption sites available on their surfaces during the adsorption process. Comparing with Figs. 2 (c,d), it is evident that the overall particle contours remain largely unchanged after cadmium ion loading. However, high-magnification images reveal partial blockage of numerous surface pores and smoothing of localized protrusions. These subtle yet discernible morphological changes provide direct qualitative evidence for the successful immobilization of cadmium ions on the surface of natural sand particles. 2.2 FTIR Analysis The composition and functional groups of the sand particles were characterized by Fourier transform infrared (FTIR) spectroscopy. Analysis of the peak assignments in Fig. 3 indicates that the natural sand particles are primarily composed of silica, with silanol (Si-OH) and siloxane (Si-O-Si) groups being the predominant functional groups. The broad absorption peaks at 3618 cm -1 and 3424.8 cm -1 are attributed to the O-H stretching vibrations of water molecules (H-O-H) adsorbed on the sand particle surface. The absorption peaks observed at 2982.8 cm -1 and 2876.2 cm -1 correspond to the C-H stretching vibrations from trace organic matter present in the natural sand. The peak at 1796.9 cm -1 is assigned to a combination band of the Si-O bond. The strong absorption at 1006.3 cm -1 is attributed to the asymmetric stretching vibration of the siloxane (Si-O-Si) covalent bond. The peak at 875.3 cm -1 is associated with the symmetric stretching vibration of the Si-O-Si bond, while the absorption at 710.9 cm -1 corresponds to the bending vibration of the silanol (Si-OH) group. All these characteristic peaks are indicative of the quartz phase of SiO 2 in the natural sand.The coordinating atoms present in the functional groups of sand particles contribute to their adsorption capacity through coordination interactions. 2.3 XRD Analysis The composition and functional groups of the natural sand particles were further characterized using X-ray diffraction (XRD), and the results are presented in Fig. 4 . The strong diffraction peaks observed at 2θ = 20.76°,26.60°,36.51°,50.09°,59.92° are attributed to SiO 2 . The diffraction peaks appearing at 2θ = 19.84°,20.79°,21.95°,26.68°,27.96°,36.50°,39.49°,59.98°,67.64° correspond to CaAl 2 Si 2 O 8 ·4H 2 O. Additionally, the peaks at 2θ = 19.84°,20.79°,21.95°,26.68°,27.96°,36.50°,39.49°,59.98°,67.64° are identified as CaCO 3 . The results indicate that the main components of the natural sand particles include SiO 2 , Si(OH) n , Mn(SiO 4 ) 2 , among others. Combined characterization by XRD and FTIR demonstrates that the sand particles, serving as a carrier abundant in silanol and siloxane functional groups, possess certain adsorption capabilities. 2.4 Isothermal adsorption curves The pore structure characteristics of natural sand particles were characterized by nitrogen adsorption-desorption measurements. The specific surface area was determined to be 3.1731 m²/g, with an average pore width of 8.3451 nm. Mesopores close to the average pore size were found to dominate the porosity contribution (0.00589 cm 3 /g). As shown in Fig. 5 , the adsorption-desorption isotherm can be classified as Type IV according to the IUPAC classification. At low relative pressures (p/p 0 < 0.8), the adsorption quantity increased gradually, corresponding to monolayer-to-multilayer physical adsorption of nitrogen on the particle surfaces and within the pore channels. As the relative pressure approached 1.0, a sharp increase in adsorption quantity was observed, which is characteristic of capillary condensation occurring in mesopores (2–50 nm). The adsorption and desorption branches form an H 3 -type hysteresis loop in the medium-to-high relative pressure range (p/p 0 ≈ 0.8-1.0). This type of hysteresis is associated with slit-shaped pores, which is consistent with the physical nature of natural sand particles—primarily composed of dense mineral grains such as quartz, where the porosity originates not from intrinsic intraparticle pores but from interparticle voids formed during accumulation, thus exhibiting typical slit-like pore features of a packed structure. 2.5 Isothermal adsorption curves A 0.01 g portion of acid-washed natural sand grains was packed into a 4 mm i.d. micro-column and challenged with Cd(II) standard solutions (20–200 mg·L -1 ) at 25 ℃ and a constant loading flow rate of 3 mg·min -1 . Effluent fractions were collected and analysed by on-line FAAS to construct the equilibrium isotherm shown in Fig. 6 (a). Uptake increases monotonically with inlet Cd(II) concentration as the enhanced concentration gradient drives mass transfer. A plateau is reached at ≥ 120 mg·L -1 , signalling saturation of the surface binding sites; the corresponding maximum capacity is 10.2 mg·g -1 , in good agreement with the value predicted by the Freundlich model. 2.6 Effect of solution acidity on adsorption The influence of pH on dynamic Cd(II) uptake was examined by injecting 100 mg·L -1 solutions of varying acidity through the micro-column at 3 mg·min -1 (Fig. 6 b). From pH 1 to 6, removal efficiency increases monotonically, attaining ~ 90% in the narrow window pH 5.5–6.5. At pH < 3, excess H + ions compete directly with Cd(II) for the deprotonated Si-O - sites, lowering the surface charge and suppressing adsorption. As the pH rises, progressive deprotonation of Si-OH generates negatively charged Si-O - ligands that electrostatically attract Cd(II), maximising capacity ( Nebagha et al. 2015 ). Above pH 6.5, the slight decline in removal is attributed to the onset of Cd(OH) 2 precipitation, which decreases the activity of free Cd(II) in the liquid phase. Thus, the optimum operational pH is fixed at 5.5–6.5 to ensure maximum surface complexation while avoiding bulk precipitation. 2.7 Effect of loading flow rate on adsorption In fixed-bed operation, the loading flow-rate directly controls the residence time of Cd(II) ions within the sand bed and therefore dictates the extent of adsorption. To identify the optimum flow-rate, a 100 mg·L -1 Cd(II) solution (pH 6.0) was percolated through the micro-column at 0.5-5.0 mL/minwhile effluent concentrations were monitored on-line (Fig. 6 c). Between 0.5 and 3 mL/min, removal efficiency plateaus at ~ 90%, indicating that equilibrium is attained within the available contact window. Beyond 3.5 mL·min -1 , efficiency declines steeply because the reduced residence time (< 15 s) is insufficient for Cd(II) to diffuse to the internal binding sites, resulting in premature breakthrough. Consequently, a loading flow-rate of 3 mL·min -1 was adopted for all subsequent dynamic experiments as the best compromise between capacity and throughput. 2.8 Effect of Temperature on Adsorption The influence of temperature on adsorption is fundamentally governed by thermodynamic principles. During the adsorption process, temperature affects both the chemical reaction rate and the diffusion rate of heavy metal ions on the adsorbent surface, thereby influencing the overall adsorption rate. This study investigated the effect of temperature (ranging from 298 K to 313 K) on the adsorption performance of natural sand particles toward Cd(II). As shown in Fig. 6 (d), the adsorption capacity of natural sand for Cd(II) at 298 K was 7.58 mg/g. With increasing temperature, no significant change in adsorption capacity was observed. The relevant thermodynamic parameters for the adsorption process were calculated using Equations (4) and (5)( Li et al. 2024 ). $$\:\begin{array}{c}\text{ln}{\text{K}}_{\text{d}}\text{=}\text{−}\frac{\text{∆}{\text{H}}^{\text{0}}}{\text{RT}}\text{+}\frac{\text{∆}{\text{S}}^{\text{0}}}{\text{R}}\#\text{}\text{}\text{(}\text{4}\text{)}\end{array}$$ $$\:\begin{array}{c}\text{Δ}{\text{G}}^{\text{0}}\text{=}\text{−}\text{R}\text{T}\text{ln}{\text{K}}_{\text{d}}\#\text{(}\text{5}\text{)}\end{array}$$ The adsorption of Cd(II) onto natural sand particles was evaluated through thermodynamic analysis, where K d represents the equilibrium constant, R the ideal gas constant, ΔG 0 (kJ·mol -1 ) the Gibbs free energy change, ΔH 0 (kJ·mol -1 ) the enthalpy change, ΔS 0 (J·mol -1 ·K -1 ) the entropy change, and T (K) the absolute temperature. Table 1 Kinetic Parameters for Cd(II) Adsorption onto Natural Sand Particles ΔG 0 (kJ/mol − 1 ) ΔS 0 (J/mol·K) ΔH 0 (kJ/mol) 298K 303K 308K 313K \(\:\text{−}\) 0.375 \(\:\text{−}\) 0.381 \(\:\text{−}\) 0.388 \(\:\text{−}\) 0.394 1.328 0.021 As summarized in Table 1 , the calculated thermodynamic parameters reveal that ΔH 0 > 0, indicating an endothermic adsorption process. The positive value of ΔS 0 suggests an increase in randomness at the solid-liquid interface during adsorption. Furthermore, the negative ΔG 0 confirms the spontaneity of the process. 2.9 Discussion of adsorption model Adsorption isotherms were fitted using adsorption isotherm equations to investigate the adsorption behavior of cadmium ions on solid phases packed with sand particles. Commonly used equations include the Langmuir and Freundlich adsorption isotherms. Adsorption isotherm fitting curves were established based on the Langmuir and Freundlich adsorption isotherm equations (6) ,(7)and (8)( Dagang et al. 2023 ): $$\:\begin{array}{c}{\text{Q}}_{\text{e}}\text{=}\frac{{\text{Q}}_{\text{m}}{\text{K}}_{\text{L}}{\text{C}}_{\text{e}}}{\text{1+}{\text{K}}_{\text{L}}{\text{C}}_{\text{e}}}\#\text{(}\text{6}\text{)}\end{array}$$ $$\:\begin{array}{c}{\text{R}}_{\text{L}}\text{=}\frac{\text{1}}{\text{1+}{\text{K}}_{\text{L}}{\text{C}}_{\text{0}}}\#\text{(}\text{7}\text{)}\end{array}$$ $$\:\begin{array}{c}{\text{Q}}_{\text{e}}\text{=}{\text{K}}_{\text{F}}{\text{C}}_{\text{e}}^{\frac{\text{1}}{\text{n}}}\#\text{(}\text{8}\text{)}\end{array}$$ Table 2 Basic Information about the Freundlich and Langmuir Models Langmuir isotherm Freundlich isotherm K L Q m (mg·g − 1 ) R 2 R L K F 1/n R 2 0.0057 10.23 0.84 0.59 0.41 0.75 0.94 Where C e is the cadmium ion concentration at adsorption equilibrium, Q e is the adsorption capacity at equilibrium, Q m is the maximum adsorption capacity, K represents the Langmuir constant, Kf represents the Freundlich constant, and a is the adsorption exponent. Results are shown in Fig. 7 (a) and Table 2 . Fitting the experimental data using the Langmuir and Freundlich models yielded correlation coefficients R 2 of 0.84 and 0.94, respectively. The Freundlich isotherm fit demonstrated significantly better correlation than the Langmuir fit. Therefore, the adsorption behavior of sand particles toward cadmium ions better conforms to the Freundlich adsorption model. The adsorption energies at different sites on the sand particle surface are non-uniform [14] , and the adsorption of cadmium ions is dominated by a process involving multiple layers of physical adsorption based on loose monolayer chemical adsorption. 2.10 Analysis of Adsorption Kinetics The adsorption mechanism of Cd(II) on natural sand particles was analyzed using pseudo-first-order and pseudo-second-order kinetic models, elucidating the patterns of its adsorption behavior. The equations for the pseudo-first-order and pseudo-second-order kinetic models are shown in (9) and (10)( Yang et al. 2025 ): $$\:\begin{array}{c}\text{ln}\text{(}{\text{Q}}_{\text{e}}\text{−}{\text{Q}}_{\text{t}}\text{)}\text{=}\text{ln}{\text{Q}}_{\text{e}}\text{−}{\text{k}}_{\text{1}}\text{t}\#\text{(}\text{9}\text{)}\end{array}$$ $$\:\begin{array}{c}\frac{\text{t}}{{\text{Q}}_{\text{t}}}\text{=}\frac{{\text{k}}_{\text{2}}}{{\text{Q}}^{\text{2}}}\text{+}\frac{\text{t}}{{\text{Q}}_{\text{c}}}\#\text{(}\text{10}\text{)}\end{array}$$ The pseudo-first-order and pseudo-second-order kinetic models were applied to fit the adsorption behavior of Cd(II) onto natural sand particles. Table 3 Parameters of Pseudo-First-Order and Pseudo-Second-Order Kinetic Models for Cd(II) Adsorption Pseudo-first-order kinetics Pseudo-second-order kinetics Q e,cal (mg·g − 1 ) K 2 (min − 1 ) R 2 Q e,cal (mg·g − 1 ) K 2 (min − 1 ) R 2 7.48 0.055 0.848 8.36 0.010 0.966 The adsorption behavior of Cd(II) onto natural sand particles was analyzed using pseudo-first-order and pseudo-second-order kinetic models. The corresponding parameters for the adsorption process were calculated, and the results are summarized in Table 3 . As shown in Fig. 7 (b), the correlation coefficient (R²) for the pseudo-first-order model was 0.848, while that for the pseudo-second-order model reached 0.966. The higher R² value of the pseudo-second-order model indicates that it provides a better fit for the experimental data, suggesting that the adsorption process is predominantly governed by chemical interaction mechanisms. 3 Conclusion This study systematically investigated the dynamic adsorption performance and mechanism of natural sand grains (NSGs) from the Taklamakan Desert for Cd(II) in aqueous solutions. Online monitoring via flame atomic absorption spectrometry (FAAS) combined with characterization by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) clarified the adsorption characteristics and structural basis of NSGs. The characterization results confirmed that NSGs are mainly composed of SiO₂, with a hierarchically rough and porous surface rich in Si-OH and Si-O-Si functional groups. These inherent properties provide sufficient active sites and binding foundations for Cd(II) adsorption. Single-factor optimization experiments determined the optimal adsorption conditions: at ambient temperature, with a pH range of 5.5–6.5 and a feed flow rate of 3 mL·min⁻¹, the dynamic saturated adsorption capacity of NSGs for Cd(II) reached 10.2 mg·g⁻¹, with a removal efficiency as high as 90.2%. The adsorption equilibrium data were better fitted by the Freundlich isotherm model (R²=0.938), indicating a heterogeneous multilayer adsorption process. Kinetic fitting results showed that the pseudo-second-order kinetic model had a higher correlation coefficient (R²=0.966), confirming that the adsorption process is mainly controlled by chemical interactions. Thermodynamic analysis revealed that the adsorption process is endothermic (ΔH⁰>0), spontaneous (ΔG⁰0). Regeneration experiments demonstrated that 0.01 mol·L⁻¹ hydrochloric acid can achieve 98.4% desorption of Cd(II), and the regenerated NSGs showed no significant loss in adsorption capacity, indicating excellent recyclability. In summary, natural desert sand grains, as a low-cost, abundant, and unmodified adsorbent, exhibit advantages of high efficiency, renewability, and easy large-scale application in the treatment of Cd(II)-containing wastewater. Their adsorption mechanism originates from the coordination and electrostatic attraction between surface functional groups and Cd(II), providing new ideas and experimental basis for the development of low-cost heavy metal wastewater treatment technologies with important environmental application value. Declarations Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Ethical Approval: This is not applicable. Consent to Participate: This is not applicable. Consent to Publish: Therefore, all authors have agreed to publish their articles in your journal. Competing Interests: All authors have no competing interests to declare regarding the publication of this article. Funding: This work is financially supported by the National Natural Science Foundation of China (No. 52163030). Author Contributions: All authors contributed to the conception and design of this study. The preparation of experimental materials, data collection and analysis were completed by Jiaxiang Qi, Yixin Sui and Shuaibing Gao. The first draft of the manuscript was written by Jiaxiang Qi. Professor Shawket Abliz, as the project leader and supervisor, provided financial support, venue access and outline guidance for the experiment. LinLin Chai participated in the later-stage manuscript review and offered suggestions for the manuscript writing. All authors commented on the previous versions of the manuscript. All authors have read and approved the final version of the manuscript. Acknowledgments: This work is financially supported by the National Natural Science Foundation of China (No. 52163030). We are grateful to the College of Chemical Engineering, Xinjiang University for providing the experimental venue and shared instrument facilities. We would like to thank the laboratory technicians and engineers for their guidance on experimental operations, equipment maintenance and technical support for data analysis. Special thanks are extended to Mr. Chenqi Peng for his valuable suggestions on experimental design, and to Mr. Liyang Nan for his technical assistance in sample testing. Data Availability Statement: The datasets including laboratory experimental data and other detection results used and/or analyzed during the current study are not yet deposited in a public repository but are available free of charge from the corresponding author upon reasonable request. References Amjlef A, Khrach S, Ait El Fakir A, El Rhazi M, Bakasse M, El Hassani A, Qourzal S (2021) Nano-engineered materials for environmental remediation: a review. Nanotechnol Environ Eng 6:26. https://doi.org/10.1186/s40580-021-00283-3 Ayach J, El Malti W, Duma L, Lalevée J, Al Ajami M, Hamad H, Hijazi A (2024) Comparing conventional and advanced approaches for heavy metal removal in wastewater treatment: an in-depth review emphasizing filter-based strategies. Polymers 16(14):1959. https://doi.org/10.3390/polym16141959 Aziz KHH, Mustafa FS, Hamarawf RF, Omer KM (2025) Adsorptive removal of toxic heavy metals from aquatic environment by metal organic framework (MOF): a review. J Water Process Eng 70:106867. https://doi.org/10.1016/j.jwpe.2024.106867 Chen BB, Zhang L, He M, Li Q, Jiang X, Yu H, Liu Y, Wang C (2020) Determination of Cd by flame AAS after dispersive solid-phase extraction with modified silica. Spectrochim Acta Part B 164:105751. https://doi.org/10.1016/j.sab.2020.105751 Díez AM, Moreira FC, Marinho BA, Espíndola JCA, Paulista LO, Sanromán MA, Pazos M, Boaventura RAR, Vilar VJP (2018) A step forward in heterogeneous photocatalysis: Process intensification by using a static mixer as catalyst support. Chem Eng J 343:597–606. https://doi.org/10.1016/j.cej.2018.03.041 Feng XF, Long RX, Wang LL, Liu CC, Bai ZX, Liu XB (2022) A review on heavy metal ions adsorption from water by layered double hydroxide and its composites. Sep Purif Technol 284:120099. https://doi.org/10.1016/j.seppur.2021.120099 Hong J, Ko D, Hwang Y (2020) Magnetic biochar for rapid removal of cadmium from wastewater. J Hazard Mater 399:123060. https://doi.org/10.1016/j.jhazmat.2020.123060 Huang M, Qi WY, Pang B, Ding CC, Zhu FP, Song C, Wang SG (2025) Adsorption of calcium ion in cooling water using ion-imprinted adsorbents for scale inhibition. ACS Appl Polym Mater 7(17):11549–11557. https://doi.org/10.1021/acsapm.5c00876 Jomova K, Alomar SY, Nepovimova E, Kuca K, Valko M (2025) Heavy metals: toxicity and human health effects. Arch Toxicol 99(1):153–209. https://doi.org/10.1007/s00204-024-03903-2 Lee SM, Kim WG, Laldawngliana C, Hwang YH, Lee JS (2010) Isotherm and kinetic studies of Cd(II) adsorption on natural zeolite. J Chem Eng Data 55(9):3089–3094. https://doi.org/10.1021/je1001195 Li S, Ye S, Zhang W, He H, Zhang Y, Xiong M, Chen Y, Wang M, Nie Z (2024) Magnetic ion-imprinted materials for selective adsorption of Cr(VI): adsorption behavior and mechanism study. Molecules 29:1952. https://doi.org/10.3390/molecules29091952 Ma LQ, Li S, Wang YZ, Zhang Y, Liu J, Chen W (2020) Preparation of a low-cost adsorbent from desert sand for heavy-metal removal. New Chem Mater 48(10):290–293 (in Chinese). https://doi.org/10.14028/j.cnki.1003-3726.2020.10.052 Ma Y, Guo F, Zhu H, Wu Y, Guo B, Yang J, Wu F (2024) Risk assessment and impact prediction of associated heavy metal pollution in selenium-rich farmland. Sci Total Environ 950:175321. https://doi.org/10.1016/j.scitotenv.2023.175321 Medine A, Nurulla I, Abliz S (2015) FTIR and XRD characterization of Taklamakan sand. Spectrosc Spectral Anal 35(2):539–542 (in Chinese). https://doi.org/10.3964/j.issn.1000-0593(2015)02-0539-04 Mitra S, Chakraborty AJ, Tareq AM, Emran TB, Nainu F, Khusro A, Idris AM, Khandaker MU, Osman H, Alhumaydhi FA, Simal-Gandara J (2022) Impact of heavy metals on the environment and human health: Novel therapeutic insights to counter the toxicity. J King Saud Univ Sci 34:101865. https://doi.org/10.1016/j.jksus.2022.101865 Nan H, Wang C, Wang G, Wei HM (2015) Surface modification of nano-TiO₂ by in-situ coating with silane coupling agent and its application in PVC functional modification. Chem Res Appl 27(2):189–194 (in Chinese). https://doi.org/10.3969/j.issn.1004-1656.2015.02.015 Nebagha KC, Ziat K, Rghioui L, El Haddad M, Benhammou A (2015) Clay minerals as natural adsorbents for Cd(II) and Pb(II). J Mater Environ Sci 6(11):3022–3033. https://doi.org/10.4314/jmes.v6i11.17 Qasem NAA, Mohammed RH, Lawal DU (2021) Author Correction: Removal of heavy metal ions from wastewater: a comprehensive and critical review. npj Clean Water 4(1):1–3. https://doi.org/10.1038/s41545-021-00148-4 Qi DG, Zhang HW, Zhou ZY, Ren ZQ (2023) Cadmium ion-imprinted polymers for adsorption and detection of cadmium ions. J Environ Chem Eng 11(5):110804. https://doi.org/10.1016/j.jece.2023.110804 Radha E, Gomathi T, Sudha PN, Sashikala S (2021) Chitosan-based composites for selective removal of cadmium. Polym Bull 78:1109–1132. https://doi.org/10.1007/s00289-020-03274-5 Wang H, Gan X, Tang Y (2024) Mechanisms of heavy metal cadmium (Cd)-induced malignancy. Biol Trace Elem Res 203:608–623. https://doi.org/10.1007/s12011-024-04189-2 Yang Q, Zheng Z, Shu C, Xie Q, Gao X (2025) Mechanistic study of selective adsorption of As(V) by a surface ion-imprinted diatomite-based adsorbent. Langmuir 41(36):24671–24682. https://doi.org/10.1021/acs.langmuir.5c01234 Cite Share Download PDF Status: Published Journal Publication published 07 Apr, 2026 Read the published version in Environmental Science and Pollution Research → Version 1 posted Editorial decision: Major Revision 03 Feb, 2026 Reviewers agreed at journal 06 Jan, 2026 Reviewers invited by journal 06 Jan, 2026 Editor invited by journal 06 Jan, 2026 Editor assigned by journal 24 Dec, 2025 First submitted to journal 21 Dec, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-8364648","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":570366695,"identity":"0052f588-63c2-4982-a134-5f6d16dc21d3","order_by":0,"name":"Jiaxiang Qi","email":"","orcid":"","institution":"Xinjiang University College of Chemical Engineering: Xinjiang University School of Chemical Engineering","correspondingAuthor":false,"prefix":"","firstName":"Jiaxiang","middleName":"","lastName":"Qi","suffix":""},{"id":570366696,"identity":"728a356e-561f-4e34-b13a-30772a961d28","order_by":1,"name":"Yixin 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2","display":"","copyAsset":false,"role":"figure","size":1257828,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSEM images( a,b:before adsorption ; c,d:after adsorption)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8364648/v1/e2d459af259afe21ae4609f6.png"},{"id":99812328,"identity":"7972a186-9a8e-4842-bd02-10a846e202ae","added_by":"auto","created_at":"2026-01-08 14:36:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":98532,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFTIR spectra of natural sand\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8364648/v1/a491cc9392a30738eb19b35d.png"},{"id":99812472,"identity":"46a3af42-6abb-441a-9b2c-cc582b44638c","added_by":"auto","created_at":"2026-01-08 14:37:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":157387,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eXRD pattern of natural sand\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8364648/v1/211b78547dc9d95804b42805.png"},{"id":99812412,"identity":"5aa15c21-f8eb-446b-a5b6-0bc9f7129a50","added_by":"auto","created_at":"2026-01-08 14:36:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":65971,"visible":true,"origin":"","legend":"\u003cp\u003ePore structure characteristics of natural sand particles.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8364648/v1/72828414690afb887b263167.png"},{"id":99812352,"identity":"2918ca79-42f9-464b-ba35-fe6d6753a4af","added_by":"auto","created_at":"2026-01-08 14:36:53","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":611322,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure (a) Isothermal adsorption curve of Cd(II) onto natural sand grains;Figure (b) Effect of solution pH on adsorption;Figure (c) Effect of loading flow rate on adsorption;Figure (d) Effect of Temperature on Adsorption.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8364648/v1/981a83dddb8062b5f38a8a79.png"},{"id":99812534,"identity":"f43b490d-1d04-404d-bf3e-15e36dabc233","added_by":"auto","created_at":"2026-01-08 14:37:24","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":293960,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure (a) Fitting of natural sand adsorption behavior to the Langmuir and Freundlich models;Figure (b) Fitting of natural sand adsorption behavior to adsorption kinetic models.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8364648/v1/a275afc20b87b9c63e9c1179.png"},{"id":106809950,"identity":"e9b7004b-f203-497f-a894-f602c601c84d","added_by":"auto","created_at":"2026-04-13 16:13:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4169150,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8364648/v1/230d4b0a-fedd-4575-aa7c-69d111b7c77b.pdf"}],"financialInterests":"","formattedTitle":"Performance Research of the natural sand grains for adsorption enrichment and removal of Cd(II) from aqueous solution","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCadmium is introduced into the environment through both geochemical weathering and a wide range of industrial activities such as electroplating, base-metal smelting, Ni-Cd battery manufacture, pigment and plastic production, and the formulation of phosphate fertilisers and pesticides (\u003cem\u003eWang 2024; Chi et al. 2018; Radha et al. 2021\u003c/em\u003e). Once released, Cd(II) accumulates in soils and aquatic systems, enters the food chain via irrigation water and crops, and persists in human soft tissues-particularly the kidneys and liver-for decades. Because cadmium is non-essential and classified as a human carcinogen, even trace concentrations represent a serious environmental and public-health risk (\u003cem\u003eChen et al. 2020; Hong et al. 2020; Ma et al. 2024\u003c/em\u003e). Consequently, the efficient removal of Cd(II) from water and wastewater is imperative.\u003c/p\u003e \u003cp\u003eAmong the technologies available (chemical precipitation, solvent extraction, ion exchange, membrane separation and adsorption (\u003cem\u003eMa et al. 2020; Jomova et al. 2024\u003c/em\u003e)), adsorption is especially attractive for low-to-medium strength effluents because it can be implemented at ambient temperature and pressure, does not generate sludge volumes requiring further treatment, and is capable of reducing Cd(II) to sub-ppm levels (\u003cem\u003eAyach et al. 2024\u003c/em\u003e). Although activated carbons, synthetic resins and engineered nanomaterials exhibit high capacities, their cost and/or complex synthesis limit large-scale application (\u003cem\u003eQasem et al. 2021; Feng et al. 2021; Aziz et al. 2025\u003c/em\u003e). There is therefore growing interest in the use of raw or minimally processed natural solids-clays, zeolites, peat, rice husk, etc.-that already possess favourable surface area, porosity and surface functionality (\u003cem\u003eAwual et al. 2018\u003c/em\u003e).\u003c/p\u003e \u003cp\u003eHere, we evaluated the potential of untreated sand from China's largest desert-the Taklamakan Desert-as a low-cost, abundant, and non-toxic Cd(II) adsorbent. Previous mineralogical investigations indicate that these sand grains contain over 90% silica (wt%) and exhibit a hierarchically rough microporous structure with terminal silanol (Si-OH) and siloxane (Si-O-Si) groups-features theoretically favorable for metal ion binding (\u003cem\u003eAmjlef et al. 2021; Lee et al. 2010; Medine et al. 2015; Nan H et al. 2015\u003c/em\u003e). This study employed a miniature packed-bed column filled with natural sand grains (NSGs) coupled online with flame atomic absorption spectroscopy (FAAS) for real-time monitoring of adsorption kinetics. By systematically varying pH, flow rate, and feed concentration, the saturation capacity and rate-limiting steps were successfully quantified.The schematic diagram of the serial connection is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e below.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eStructural changes in samples before and after Cd(II) adsorption were verified using SEM, FTIR, and XRD techniques. Equilibrium data successfully fit the Freundlich adsorption model and pseudo-second-order kinetic model, indicating a heterogeneous multilayer adsorption mechanism where the process is primarily chemically controlled. Adsorption thermodynamics analysis confirmed the process is endothermic and spontaneous. These findings demonstrate that Taklamakan natural sand grains serve as an efficient, renewable, and genuinely low-cost biosorbent for Cd(II) removal from aqueous media.\u003c/p\u003e"},{"header":"1 Experimental part","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1.1 Instruments and Reagents\u003c/h2\u003e \u003cp\u003eFlame atomic absorption spectrometer (AA-6880, Shimadzu); Fourier transform infrared spectrometer (type EQUINOX55, BRUKER, Germany); Scanning electron microscope (LEO-1430VP, Zeiss AG, Germany); X-ray powder diffractometer (D8 Advance, AXS GmbH, Bruker, Germany); Electric constant temperature drying oven (DHG-9140A, Shanghai Jinghong Experimental Equipment Co, Ltd.); Vacuum drying oven (DZF-6020, Shanghai Anting Scientific Instrument Factory); Electronic balance (JY302, Shanghai METTLER TOLEDO Instrument Co, Ltd.); Peristaltic pump (BTOO-300M type; Beijing Baoding Town Lange Constant Flow Pump Co, Ltd.); cadmium hollow cathode lamp; grains of sand (grains of sand collected at different points in the Taklamakan Desert); Cadmium carbonate (Tianjin Beilian Fine Chemical Development Co, Ltd.); Ethanol, acetic acid (Tianjin Damao Chemical Reagent Factory); hydrochloric acid, sodium hydroxide (Urumqi Dicheng Chemical Co, Ltd.); Deionized water (deionized water supply room, School of Chemical Engineering, Xinjiang University).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e1.2 Preparation of sand pretreatment and adsorption separation microcolumns\u003c/h2\u003e \u003cp\u003eAn appropriate amount of sand grains were weighed, deionized water was washed repeatedly and repeatedly to remove dust and water-soluble components on the surface of the sand particles, and then dried at a constant temperature of 80℃ in an oven for 24 h. A certain mass of sand particles as a solid-phase adsorption material was added to a 4\u0026times;50 mm glass microcolumn, and the separation microcolumn was used in conjunction with a peristaltic pump for dynamic adsorption and desorption experiments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e1.3 Verify the adsorption of Cd(II) ions by sand particles\u003c/h2\u003e \u003cp\u003eAfter the Cd(II) ion standard solution passed through the adsorption separation microcolumn at a certain flow rate, 0.010 mol\u0026middot; L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e hydrochloric acid was eluted, and the Cd(II) ion solution and desorption solution flowing from the microcolumn were quantitatively collected, respectively. The concentration of Cd(II) ions in the original solution, Cd(II) ion solution and desorption solution was determined by FAAS method. Compared with the original solution, the decrease of Cd(II) ion concentration in the column solution indicates that the sand particles have adsorption effect on the Cd(II) ion solution, and the larger the concentration decrease, the better the adsorption effect. The determination of Cd(II) ions in the desorption solution can further prove the adsorption performance of Cd(II) ions by sand particles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e1.4 Dynamic adsorption and desorption experiments\u003c/h2\u003e \u003cp\u003eAt room temperature, a Cd(II) ionic solution or sample with pH\u0026thinsp;=\u0026thinsp;6 was passed through the adsorption separation microcolumn at an appropriate flow rate, and then 0.010 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e hydrochloric acid was eluted through the microcolumn at a natural flow rate, and the concentration of Cd(II) ions in solution was determined by FAAS method. The relevant adsorption parameters are calculated according to equations (1), (2) and (3) (\u003cem\u003eHuang et al. 2025\u003c/em\u003e).\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\text{Q}\\text{=}\\frac{\\text{(}{\\text{C}}_{\\text{0}}\\text{\u0026minus;}{\\text{C}}_{\\text{e}}\\text{)}\\text{V}}{\\text{W}}\\#\\text{(}\\text{1}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\text{E}\\text{(}\\text{%}\\text{)}\\text{=}\\frac{\\text{(}{\\text{C}}_{\\text{0}}\\text{-}{\\text{C}}_{\\text{e}}\\text{)}}{{\\text{C}}_{\\text{0}}}\\text{\u0026times;}\\text{100}\\text{%}\\text{}\\text{}\\#\\text{(}\\text{2}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\text{B}\\text{(}\\text{%}\\text{)}\\text{=}\\frac{{\\text{C}}_{\\text{d}}{\\text{V}}_{\\text{d}}}{\\text{(}{\\text{C}}_{\\text{0}}\\text{-}{\\text{C}}_{\\text{e}}\\text{)}\\text{V}}\\text{\u0026times;}\\text{100}\\text{%}\\text{}\\#\\text{(}\\text{3}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eC\u003csub\u003e0\u003c/sub\u003e is the concentration of Cd(II) ions in the original solution before adsorption, C\u003csub\u003ee\u003c/sub\u003e is the concentration of Cd(II) ions in the column solution, C\u003csub\u003ed\u003c/sub\u003e is the concentration of Cd(II) ions in the desorption solution (mg/L), V is the volume of the solution passing through the microcolumn, V\u003csub\u003ed\u003c/sub\u003e is the volume of the desorption solution (ml), and W is the dry weight (g) of the adsorbent added.\u003c/p\u003e \u003c/div\u003e"},{"header":"2 Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.1 SEM characterization\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSurface morphology of natural sand particles before and after adsorption was analyzed using SEM. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a,b), the pre-adsorption images reveal that sand particles, as granular natural products, exhibit diverse and irregular shapes with a dense, porous, and rough surface morphology. This characteristic enhances the specific surface area of the sand particles, thereby increasing the number of adsorption sites available on their surfaces during the adsorption process. Comparing with Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c,d), it is evident that the overall particle contours remain largely unchanged after cadmium ion loading. However, high-magnification images reveal partial blockage of numerous surface pores and smoothing of localized protrusions. These subtle yet discernible morphological changes provide direct qualitative evidence for the successful immobilization of cadmium ions on the surface of natural sand particles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.2 FTIR Analysis\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe composition and functional groups of the sand particles were characterized by Fourier transform infrared (FTIR) spectroscopy. Analysis of the peak assignments in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e indicates that the natural sand particles are primarily composed of silica, with silanol (Si-OH) and siloxane (Si-O-Si) groups being the predominant functional groups.\u003c/p\u003e \u003cp\u003eThe broad absorption peaks at 3618 cm\u003csup\u003e-1\u003c/sup\u003e and 3424.8 cm\u003csup\u003e-1\u003c/sup\u003e are attributed to the O-H stretching vibrations of water molecules (H-O-H) adsorbed on the sand particle surface. The absorption peaks observed at 2982.8 cm\u003csup\u003e-1\u003c/sup\u003e and 2876.2 cm\u003csup\u003e-1\u003c/sup\u003e correspond to the C-H stretching vibrations from trace organic matter present in the natural sand. The peak at 1796.9 cm\u003csup\u003e-1\u003c/sup\u003e is assigned to a combination band of the Si-O bond. The strong absorption at 1006.3 cm\u003csup\u003e-1\u003c/sup\u003e is attributed to the asymmetric stretching vibration of the siloxane (Si-O-Si) covalent bond. The peak at 875.3 cm\u003csup\u003e-1\u003c/sup\u003e is associated with the symmetric stretching vibration of the Si-O-Si bond, while the absorption at 710.9 cm\u003csup\u003e-1\u003c/sup\u003e corresponds to the bending vibration of the silanol (Si-OH) group. All these characteristic peaks are indicative of the quartz phase of SiO\u003csub\u003e2\u003c/sub\u003e in the natural sand.The coordinating atoms present in the functional groups of sand particles contribute to their adsorption capacity through coordination interactions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.3 XRD Analysis\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe composition and functional groups of the natural sand particles were further characterized using X-ray diffraction (XRD), and the results are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The strong diffraction peaks observed at 2θ\u0026thinsp;=\u0026thinsp;20.76\u0026deg;,26.60\u0026deg;,36.51\u0026deg;,50.09\u0026deg;,59.92\u0026deg; are attributed to SiO\u003csub\u003e2\u003c/sub\u003e. The diffraction peaks appearing at 2θ\u0026thinsp;=\u0026thinsp;19.84\u0026deg;,20.79\u0026deg;,21.95\u0026deg;,26.68\u0026deg;,27.96\u0026deg;,36.50\u0026deg;,39.49\u0026deg;,59.98\u0026deg;,67.64\u0026deg; correspond to CaAl\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO. Additionally, the peaks at 2θ\u0026thinsp;=\u0026thinsp;19.84\u0026deg;,20.79\u0026deg;,21.95\u0026deg;,26.68\u0026deg;,27.96\u0026deg;,36.50\u0026deg;,39.49\u0026deg;,59.98\u0026deg;,67.64\u0026deg; are identified as CaCO\u003csub\u003e3\u003c/sub\u003e. The results indicate that the main components of the natural sand particles include SiO\u003csub\u003e2\u003c/sub\u003e, Si(OH)\u003csub\u003en\u003c/sub\u003e, Mn(SiO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, among others. Combined characterization by XRD and FTIR demonstrates that the sand particles, serving as a carrier abundant in silanol and siloxane functional groups, possess certain adsorption capabilities.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Isothermal adsorption curves\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe pore structure characteristics of natural sand particles were characterized by nitrogen adsorption-desorption measurements. The specific surface area was determined to be 3.1731 m\u0026sup2;/g, with an average pore width of 8.3451 nm. Mesopores close to the average pore size were found to dominate the porosity contribution (0.00589 cm\u003csup\u003e3\u003c/sup\u003e/g). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the adsorption-desorption isotherm can be classified as Type IV according to the IUPAC classification. At low relative pressures (p/p\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.8), the adsorption quantity increased gradually, corresponding to monolayer-to-multilayer physical adsorption of nitrogen on the particle surfaces and within the pore channels. As the relative pressure approached 1.0, a sharp increase in adsorption quantity was observed, which is characteristic of capillary condensation occurring in mesopores (2\u0026ndash;50 nm). The adsorption and desorption branches form an H\u003csub\u003e3\u003c/sub\u003e-type hysteresis loop in the medium-to-high relative pressure range (p/p\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;0.8-1.0). This type of hysteresis is associated with slit-shaped pores, which is consistent with the physical nature of natural sand particles\u0026mdash;primarily composed of dense mineral grains such as quartz, where the porosity originates not from intrinsic intraparticle pores but from interparticle voids formed during accumulation, thus exhibiting typical slit-like pore features of a packed structure.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Isothermal adsorption curves\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA 0.01 g portion of acid-washed natural sand grains was packed into a 4 mm i.d. micro-column and challenged with Cd(II) standard solutions (20\u0026ndash;200 mg\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e) at 25 ℃ and a constant loading flow rate of 3 mg\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e. Effluent fractions were collected and analysed by on-line FAAS to construct the equilibrium isotherm shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a). Uptake increases monotonically with inlet Cd(II) concentration as the enhanced concentration gradient drives mass transfer. A plateau is reached at \u0026ge;\u0026thinsp;120 mg\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e, signalling saturation of the surface binding sites; the corresponding maximum capacity is 10.2 mg\u0026middot;g\u003csup\u003e-1\u003c/sup\u003e, in good agreement with the value predicted by the Freundlich model.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Effect of solution acidity on adsorption\u003c/h2\u003e \u003cp\u003eThe influence of pH on dynamic Cd(II) uptake was examined by injecting 100 mg\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e solutions of varying acidity through the micro-column at 3 mg\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). From pH 1 to 6, removal efficiency increases monotonically, attaining\u0026thinsp;~\u0026thinsp;90% in the narrow window pH 5.5\u0026ndash;6.5. At pH\u0026thinsp;\u0026lt;\u0026thinsp;3, excess H\u003csup\u003e+\u003c/sup\u003e ions compete directly with Cd(II) for the deprotonated Si-O\u003csup\u003e-\u003c/sup\u003e sites, lowering the surface charge and suppressing adsorption. As the pH rises, progressive deprotonation of Si-OH generates negatively charged Si-O\u003csup\u003e-\u003c/sup\u003e ligands that electrostatically attract Cd(II), maximising capacity (\u003cem\u003eNebagha et al. 2015\u003c/em\u003e). Above pH 6.5, the slight decline in removal is attributed to the onset of Cd(OH)\u003csub\u003e2\u003c/sub\u003e precipitation, which decreases the activity of free Cd(II) in the liquid phase. Thus, the optimum operational pH is fixed at 5.5\u0026ndash;6.5 to ensure maximum surface complexation while avoiding bulk precipitation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Effect of loading flow rate on adsorption\u003c/h2\u003e \u003cp\u003eIn fixed-bed operation, the loading flow-rate directly controls the residence time of Cd(II) ions within the sand bed and therefore dictates the extent of adsorption. To identify the optimum flow-rate, a 100 mg\u0026middot;L\u003csup\u003e-1\u003c/sup\u003e Cd(II) solution (pH 6.0) was percolated through the micro-column at 0.5-5.0 mL/minwhile effluent concentrations were monitored on-line (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). Between 0.5 and 3 mL/min, removal efficiency plateaus at ~\u0026thinsp;90%, indicating that equilibrium is attained within the available contact window. Beyond 3.5 mL\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e, efficiency declines steeply because the reduced residence time (\u0026lt;\u0026thinsp;15 s) is insufficient for Cd(II) to diffuse to the internal binding sites, resulting in premature breakthrough. Consequently, a loading flow-rate of 3 mL\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e was adopted for all subsequent dynamic experiments as the best compromise between capacity and throughput.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e2.8 Effect of Temperature on Adsorption\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eThe influence of temperature on adsorption is fundamentally governed by thermodynamic principles. During the adsorption process, temperature affects both the chemical reaction rate and the diffusion rate of heavy metal ions on the adsorbent surface, thereby influencing the overall adsorption rate. This study investigated the effect of temperature (ranging from 298 K to 313 K) on the adsorption performance of natural sand particles toward Cd(II). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d), the adsorption capacity of natural sand for Cd(II) at 298 K was 7.58 mg/g. With increasing temperature, no significant change in adsorption capacity was observed. The relevant thermodynamic parameters for the adsorption process were calculated using Equations (4) and (5)(\u003cem\u003eLi et al. 2024\u003c/em\u003e).\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\text{ln}{\\text{K}}_{\\text{d}}\\text{=}\\text{\u0026minus;}\\frac{\\text{∆}{\\text{H}}^{\\text{0}}}{\\text{RT}}\\text{+}\\frac{\\text{∆}{\\text{S}}^{\\text{0}}}{\\text{R}}\\#\\text{}\\text{}\\text{(}\\text{4}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\text{\u0026Delta;}{\\text{G}}^{\\text{0}}\\text{=}\\text{\u0026minus;}\\text{R}\\text{T}\\text{ln}{\\text{K}}_{\\text{d}}\\#\\text{(}\\text{5}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe adsorption of Cd(II) onto natural sand particles was evaluated through thermodynamic analysis, where K\u003csub\u003ed\u003c/sub\u003e represents the equilibrium constant, R the ideal gas constant, ΔG\u003csup\u003e0\u003c/sup\u003e (kJ\u0026middot;mol\u003csup\u003e-1\u003c/sup\u003e) the Gibbs free energy change, ΔH\u003csup\u003e0\u003c/sup\u003e (kJ\u0026middot;mol\u003csup\u003e-1\u003c/sup\u003e) the enthalpy change, ΔS\u003csup\u003e0\u003c/sup\u003e (J\u0026middot;mol\u003csup\u003e-1\u003c/sup\u003e\u0026middot;K\u003csup\u003e-1\u003c/sup\u003e) the entropy change, and T (K) the absolute temperature.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eKinetic Parameters for Cd(II) Adsorption onto Natural Sand Particles\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eΔG\u003csup\u003e0\u003c/sup\u003e(kJ/mol\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eΔS\u003csup\u003e0\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(J/mol\u0026middot;K)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eΔH\u003csup\u003e0\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e(kJ/mol)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e298K\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e303K\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e308K\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e313K\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{\u0026minus;}\\)\u003c/span\u003e\u003c/span\u003e0.375\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{\u0026minus;}\\)\u003c/span\u003e\u003c/span\u003e0.381\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{\u0026minus;}\\)\u003c/span\u003e\u003c/span\u003e0.388\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{\u0026minus;}\\)\u003c/span\u003e\u003c/span\u003e0.394\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.328\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.021\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAs summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the calculated thermodynamic parameters reveal that ΔH\u003csup\u003e0\u003c/sup\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0, indicating an endothermic adsorption process. The positive value of ΔS\u003csup\u003e0\u003c/sup\u003e suggests an increase in randomness at the solid-liquid interface during adsorption. Furthermore, the negative ΔG\u003csup\u003e0\u003c/sup\u003e confirms the spontaneity of the process.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e2.9 Discussion of adsorption model\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAdsorption isotherms were fitted using adsorption isotherm equations to investigate the adsorption behavior of cadmium ions on solid phases packed with sand particles. Commonly used equations include the Langmuir and Freundlich adsorption isotherms. Adsorption isotherm fitting curves were established based on the Langmuir and Freundlich adsorption isotherm equations (6) ,(7)and (8)(\u003cem\u003eDagang et al. 2023\u003c/em\u003e):\u003cdiv id=\"Equf\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equf\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\text{Q}}_{\\text{e}}\\text{=}\\frac{{\\text{Q}}_{\\text{m}}{\\text{K}}_{\\text{L}}{\\text{C}}_{\\text{e}}}{\\text{1+}{\\text{K}}_{\\text{L}}{\\text{C}}_{\\text{e}}}\\#\\text{(}\\text{6}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equg\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equg\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\text{R}}_{\\text{L}}\\text{=}\\frac{\\text{1}}{\\text{1+}{\\text{K}}_{\\text{L}}{\\text{C}}_{\\text{0}}}\\#\\text{(}\\text{7}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equh\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equh\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}{\\text{Q}}_{\\text{e}}\\text{=}{\\text{K}}_{\\text{F}}{\\text{C}}_{\\text{e}}^{\\frac{\\text{1}}{\\text{n}}}\\#\\text{(}\\text{8}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBasic Information about the Freundlich and Langmuir Models\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e \u003cp\u003eLangmuir isotherm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eFreundlich isotherm\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003csub\u003eL\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eQ\u003csub\u003em\u003c/sub\u003e(mg\u0026middot;g\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR\u003csub\u003eL\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eK\u003csub\u003eF\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1/n\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.0057\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWhere C\u003csub\u003ee\u003c/sub\u003e is the cadmium ion concentration at adsorption equilibrium, Q\u003csub\u003ee\u003c/sub\u003e is the adsorption capacity at equilibrium, Q\u003csub\u003em\u003c/sub\u003e is the maximum adsorption capacity, K represents the Langmuir constant, Kf represents the Freundlich constant, and a is the adsorption exponent. Results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Fitting the experimental data using the Langmuir and Freundlich models yielded correlation coefficients R\u003csup\u003e2\u003c/sup\u003e of 0.84 and 0.94, respectively. The Freundlich isotherm fit demonstrated significantly better correlation than the Langmuir fit. Therefore, the adsorption behavior of sand particles toward cadmium ions better conforms to the Freundlich adsorption model. The adsorption energies at different sites on the sand particle surface are non-uniform \u003csup\u003e[14]\u003c/sup\u003e, and the adsorption of cadmium ions is dominated by a process involving multiple layers of physical adsorption based on loose monolayer chemical adsorption.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e2.10 Analysis of Adsorption Kinetics\u003c/h2\u003e \u003cp\u003eThe adsorption mechanism of Cd(II) on natural sand particles was analyzed using pseudo-first-order and pseudo-second-order kinetic models, elucidating the patterns of its adsorption behavior. The equations for the pseudo-first-order and pseudo-second-order kinetic models are shown in (9) and (10)(\u003cem\u003eYang et al. 2025\u003c/em\u003e):\u003cdiv id=\"Equi\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equi\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\text{ln}\\text{(}{\\text{Q}}_{\\text{e}}\\text{\u0026minus;}{\\text{Q}}_{\\text{t}}\\text{)}\\text{=}\\text{ln}{\\text{Q}}_{\\text{e}}\\text{\u0026minus;}{\\text{k}}_{\\text{1}}\\text{t}\\#\\text{(}\\text{9}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equj\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equj\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\frac{\\text{t}}{{\\text{Q}}_{\\text{t}}}\\text{=}\\frac{{\\text{k}}_{\\text{2}}}{{\\text{Q}}^{\\text{2}}}\\text{+}\\frac{\\text{t}}{{\\text{Q}}_{\\text{c}}}\\#\\text{(}\\text{10}\\text{)}\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe pseudo-first-order and pseudo-second-order kinetic models were applied to fit the adsorption behavior of Cd(II) onto natural sand particles.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParameters of Pseudo-First-Order and Pseudo-Second-Order Kinetic Models for Cd(II) Adsorption\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003ePseudo-first-order kinetics\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c4\"\u003e \u003cp\u003ePseudo-second-order kinetics\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ\u003csub\u003ee,cal\u003c/sub\u003e(mg\u0026middot;g\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003e(min\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eQ\u003csub\u003ee,cal\u003c/sub\u003e(mg\u0026middot;g\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003e(min\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.055\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.848\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.966\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe adsorption behavior of Cd(II) onto natural sand particles was analyzed using pseudo-first-order and pseudo-second-order kinetic models. The corresponding parameters for the adsorption process were calculated, and the results are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b), the correlation coefficient (R\u0026sup2;) for the pseudo-first-order model was 0.848, while that for the pseudo-second-order model reached 0.966. The higher R\u0026sup2; value of the pseudo-second-order model indicates that it provides a better fit for the experimental data, suggesting that the adsorption process is predominantly governed by chemical interaction mechanisms.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Conclusion","content":"\u003cp\u003eThis study systematically investigated the dynamic adsorption performance and mechanism of natural sand grains (NSGs) from the Taklamakan Desert for Cd(II) in aqueous solutions. Online monitoring via flame atomic absorption spectrometry (FAAS) combined with characterization by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) clarified the adsorption characteristics and structural basis of NSGs. The characterization results confirmed that NSGs are mainly composed of SiO₂, with a hierarchically rough and porous surface rich in Si-OH and Si-O-Si functional groups. These inherent properties provide sufficient active sites and binding foundations for Cd(II) adsorption.\u003c/p\u003e \u003cp\u003eSingle-factor optimization experiments determined the optimal adsorption conditions: at ambient temperature, with a pH range of 5.5\u0026ndash;6.5 and a feed flow rate of 3 mL\u0026middot;min⁻\u0026sup1;, the dynamic saturated adsorption capacity of NSGs for Cd(II) reached 10.2 mg\u0026middot;g⁻\u0026sup1;, with a removal efficiency as high as 90.2%. The adsorption equilibrium data were better fitted by the Freundlich isotherm model (R\u0026sup2;=0.938), indicating a heterogeneous multilayer adsorption process. Kinetic fitting results showed that the pseudo-second-order kinetic model had a higher correlation coefficient (R\u0026sup2;=0.966), confirming that the adsorption process is mainly controlled by chemical interactions. Thermodynamic analysis revealed that the adsorption process is endothermic (ΔH⁰\u0026gt;0), spontaneous (ΔG⁰\u0026lt;0), and accompanied by an increase in randomness at the solid-liquid interface (ΔS⁰\u0026gt;0).\u003c/p\u003e \u003cp\u003eRegeneration experiments demonstrated that 0.01 mol\u0026middot;L⁻\u0026sup1; hydrochloric acid can achieve 98.4% desorption of Cd(II), and the regenerated NSGs showed no significant loss in adsorption capacity, indicating excellent recyclability. In summary, natural desert sand grains, as a low-cost, abundant, and unmodified adsorbent, exhibit advantages of high efficiency, renewability, and easy large-scale application in the treatment of Cd(II)-containing wastewater. Their adsorption mechanism originates from the coordination and electrostatic attraction between surface functional groups and Cd(II), providing new ideas and experimental basis for the development of low-cost heavy metal wastewater treatment technologies with important environmental application value.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting Interests:\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eEthical Approval:\u003c/h2\u003e \u003cp\u003eThis is not applicable.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent to Participate:\u003c/strong\u003e \u003cp\u003eThis is not applicable.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent to Publish:\u003c/strong\u003e \u003cp\u003eTherefore, all authors have agreed to publish their articles in your journal.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompeting Interests:\u003c/strong\u003e \u003cp\u003eAll authors have no competing interests to declare regarding the publication of this article.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThis work is financially supported by the National Natural Science Foundation of China (No. 52163030).\u003c/p\u003e\u003ch2\u003eAuthor Contributions:\u003c/h2\u003e \u003cp\u003eAll authors contributed to the conception and design of this study. The preparation of experimental materials, data collection and analysis were completed by Jiaxiang Qi, Yixin Sui and Shuaibing Gao. The first draft of the manuscript was written by Jiaxiang Qi. Professor Shawket Abliz, as the project leader and supervisor, provided financial support, venue access and outline guidance for the experiment. LinLin Chai participated in the later-stage manuscript review and offered suggestions for the manuscript writing. All authors commented on the previous versions of the manuscript. All authors have read and approved the final version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments:\u003c/h2\u003e \u003cp\u003eThis work is financially supported by the National Natural Science Foundation of China (No. 52163030). We are grateful to the College of Chemical Engineering, Xinjiang University for providing the experimental venue and shared instrument facilities. We would like to thank the laboratory technicians and engineers for their guidance on experimental operations, equipment maintenance and technical support for data analysis. Special thanks are extended to Mr. Chenqi Peng for his valuable suggestions on experimental design, and to Mr. Liyang Nan for his technical assistance in sample testing.\u003c/p\u003e\u003ch2\u003eData Availability Statement:\u003c/h2\u003e \u003cp\u003eThe datasets including laboratory experimental data and other detection results used and/or analyzed during the current study are not yet deposited in a public repository but are available free of charge from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003cp\u003eAmjlef A, Khrach S, Ait El Fakir A, El Rhazi M, Bakasse M, El Hassani A, Qourzal S (2021) Nano-engineered materials for environmental remediation: a review. Nanotechnol Environ Eng 6:26. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1186/s40580-021-00283-3\u003c/span\u003e\u003cspan address=\"10.1186/s40580-021-00283-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eAyach J, El Malti W, Duma L, Lalev\u0026eacute;e J, Al Ajami M, Hamad H, Hijazi A (2024) Comparing conventional and advanced approaches for heavy metal removal in wastewater treatment: an in-depth review emphasizing filter-based strategies. Polymers 16(14):1959. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/polym16141959\u003c/span\u003e\u003cspan address=\"10.3390/polym16141959\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eAziz KHH, Mustafa FS, Hamarawf RF, Omer KM (2025) Adsorptive removal of toxic heavy metals from aquatic environment by metal organic framework (MOF): a review. J Water Process Eng 70:106867. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jwpe.2024.106867\u003c/span\u003e\u003cspan address=\"10.1016/j.jwpe.2024.106867\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eChen BB, Zhang L, He M, Li Q, Jiang X, Yu H, Liu Y, Wang C (2020) Determination of Cd by flame AAS after dispersive solid-phase extraction with modified silica. Spectrochim Acta Part B 164:105751. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.sab.2020.105751\u003c/span\u003e\u003cspan address=\"10.1016/j.sab.2020.105751\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eD\u0026iacute;ez AM, Moreira FC, Marinho BA, Esp\u0026iacute;ndola JCA, Paulista LO, Sanrom\u0026aacute;n MA, Pazos M, Boaventura RAR, Vilar VJP (2018) A step forward in heterogeneous photocatalysis: Process intensification by using a static mixer as catalyst support. Chem Eng J 343:597\u0026ndash;606. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cej.2018.03.041\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2018.03.041\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eFeng XF, Long RX, Wang LL, Liu CC, Bai ZX, Liu XB (2022) A review on heavy metal ions adsorption from water by layered double hydroxide and its composites. Sep Purif Technol 284:120099. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.seppur.2021.120099\u003c/span\u003e\u003cspan address=\"10.1016/j.seppur.2021.120099\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eHong J, Ko D, Hwang Y (2020) Magnetic biochar for rapid removal of cadmium from wastewater. J Hazard Mater 399:123060. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2020.123060\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2020.123060\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eHuang M, Qi WY, Pang B, Ding CC, Zhu FP, Song C, Wang SG (2025) Adsorption of calcium ion in cooling water using ion-imprinted adsorbents for scale inhibition. ACS Appl Polym Mater 7(17):11549\u0026ndash;11557. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acsapm.5c00876\u003c/span\u003e\u003cspan address=\"10.1021/acsapm.5c00876\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eJomova K, Alomar SY, Nepovimova E, Kuca K, Valko M (2025) Heavy metals: toxicity and human health effects. Arch Toxicol 99(1):153\u0026ndash;209. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00204-024-03903-2\u003c/span\u003e\u003cspan address=\"10.1007/s00204-024-03903-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eLee SM, Kim WG, Laldawngliana C, Hwang YH, Lee JS (2010) Isotherm and kinetic studies of Cd(II) adsorption on natural zeolite. J Chem Eng Data 55(9):3089\u0026ndash;3094. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/je1001195\u003c/span\u003e\u003cspan address=\"10.1021/je1001195\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eLi S, Ye S, Zhang W, He H, Zhang Y, Xiong M, Chen Y, Wang M, Nie Z (2024) Magnetic ion-imprinted materials for selective adsorption of Cr(VI): adsorption behavior and mechanism study. Molecules 29:1952. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/molecules29091952\u003c/span\u003e\u003cspan address=\"10.3390/molecules29091952\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eMa LQ, Li S, Wang YZ, Zhang Y, Liu J, Chen W (2020) Preparation of a low-cost adsorbent from desert sand for heavy-metal removal. New Chem Mater 48(10):290\u0026ndash;293 (in Chinese). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.14028/j.cnki.1003-3726.2020.10.052\u003c/span\u003e\u003cspan address=\"10.14028/j.cnki.1003-3726.2020.10.052\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eMa Y, Guo F, Zhu H, Wu Y, Guo B, Yang J, Wu F (2024) Risk assessment and impact prediction of associated heavy metal pollution in selenium-rich farmland. Sci Total Environ 950:175321. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2023.175321\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2023.175321\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eMedine A, Nurulla I, Abliz S (2015) FTIR and XRD characterization of Taklamakan sand. Spectrosc Spectral Anal 35(2):539\u0026ndash;542 (in Chinese). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3964/j.issn.1000-0593(2015)02-0539-04\u003c/span\u003e\u003cspan address=\"10.3964/j.issn.1000-0593(2015)02-0539-04\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eMitra S, Chakraborty AJ, Tareq AM, Emran TB, Nainu F, Khusro A, Idris AM, Khandaker MU, Osman H, Alhumaydhi FA, Simal-Gandara J (2022) Impact of heavy metals on the environment and human health: Novel therapeutic insights to counter the toxicity. J King Saud Univ Sci 34:101865. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jksus.2022.101865\u003c/span\u003e\u003cspan address=\"10.1016/j.jksus.2022.101865\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eNan H, Wang C, Wang G, Wei HM (2015) Surface modification of nano-TiO₂ by in-situ coating with silane coupling agent and its application in PVC functional modification. Chem Res Appl 27(2):189\u0026ndash;194 (in Chinese). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3969/j.issn.1004-1656.2015.02.015\u003c/span\u003e\u003cspan address=\"10.3969/j.issn.1004-1656.2015.02.015\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eNebagha KC, Ziat K, Rghioui L, El Haddad M, Benhammou A (2015) Clay minerals as natural adsorbents for Cd(II) and Pb(II). J Mater Environ Sci 6(11):3022\u0026ndash;3033. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.4314/jmes.v6i11.17\u003c/span\u003e\u003cspan address=\"10.4314/jmes.v6i11.17\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eQasem NAA, Mohammed RH, Lawal DU (2021) Author Correction: Removal of heavy metal ions from wastewater: a comprehensive and critical review. npj Clean Water 4(1):1\u0026ndash;3. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41545-021-00148-4\u003c/span\u003e\u003cspan address=\"10.1038/s41545-021-00148-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eQi DG, Zhang HW, Zhou ZY, Ren ZQ (2023) Cadmium ion-imprinted polymers for adsorption and detection of cadmium ions. J Environ Chem Eng 11(5):110804. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jece.2023.110804\u003c/span\u003e\u003cspan address=\"10.1016/j.jece.2023.110804\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eRadha E, Gomathi T, Sudha PN, Sashikala S (2021) Chitosan-based composites for selective removal of cadmium. Polym Bull 78:1109\u0026ndash;1132. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00289-020-03274-5\u003c/span\u003e\u003cspan address=\"10.1007/s00289-020-03274-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eWang H, Gan X, Tang Y (2024) Mechanisms of heavy metal cadmium (Cd)-induced malignancy. Biol Trace Elem Res 203:608\u0026ndash;623. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12011-024-04189-2\u003c/span\u003e\u003cspan address=\"10.1007/s12011-024-04189-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003cp\u003eYang Q, Zheng Z, Shu C, Xie Q, Gao X (2025) Mechanistic study of selective adsorption of As(V) by a surface ion-imprinted diatomite-based adsorbent. Langmuir 41(36):24671\u0026ndash;24682. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acs.langmuir.5c01234\u003c/span\u003e\u003cspan address=\"10.1021/acs.langmuir.5c01234\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Natural sand grains, Cadmium ions, Flame atomic absorption spectroscopy, Adsorption model","lastPublishedDoi":"10.21203/rs.3.rs-8364648/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8364648/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the performance of natural sand particles from the Taklamakan Desert as a low-cost adsorbent for removing Cd(II) from water. SEM, FTIR, and XRD characterization revealed a multi-porous silica structure with abundant Si\u0026ndash;OH and Si\u0026ndash;O\u0026ndash;Si groups. Using a microcolumn coupled with FAAS under optimal conditions (pH 5.5\u0026ndash;6.5, flow rate 3 mL\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, room temperature), the sand particles exhibited a dynamic saturation adsorption capacity of 10.2 mg\u0026middot;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Cd(II) ions, achieving an adsorption rate of 90.2%. Equilibrium data conformed to the Freundlich model (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.938), indicating heterogeneous multilayer adsorption. Kinetic data followed pseudo-second-order kinetics (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.966), revealing a chemically controlled mechanism. Thermodynamic analysis confirmed the process as a spontaneous, endothermic reaction. After desorption using 0.01 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e hydrochloric acid, the desorption rate reached 98.4% with no significant loss of adsorption capacity. This demonstrates that natural sand particles represent a sustainable and highly efficient adsorbent for Cd(II) remediation.\u003c/p\u003e","manuscriptTitle":"Performance Research of the natural sand grains for adsorption enrichment and removal of Cd(II) from aqueous solution","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-08 13:56:10","doi":"10.21203/rs.3.rs-8364648/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revision","date":"2026-02-03T05:05:48+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2026-01-06T21:01:27+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-01-06T17:34:56+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2026-01-06T14:18:56+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-24T05:33:42+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2025-12-21T22:27:47+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f9c668d8-823a-4749-98f8-bcfea0869642","owner":[],"postedDate":"January 8th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-04-13T16:10:42+00:00","versionOfRecord":{"articleIdentity":"rs-8364648","link":"https://doi.org/10.1007/s11356-026-37696-x","journal":{"identity":"environmental-science-and-pollution-research","isVorOnly":false,"title":"Environmental Science and Pollution Research"},"publishedOn":"2026-04-07 15:59:24","publishedOnDateReadable":"April 7th, 2026"},"versionCreatedAt":"2026-01-08 13:56:10","video":"","vorDoi":"10.1007/s11356-026-37696-x","vorDoiUrl":"https://doi.org/10.1007/s11356-026-37696-x","workflowStages":[]},"version":"v1","identity":"rs-8364648","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8364648","identity":"rs-8364648","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}