Adsorption of Cd and Mn from neutral mine effluents using bentonite, zeolite, and stabilized dewatered sludge

Adsorption of Cd and Mn from neutral mine effluents using bentonite, zeolite, and stabilized dewatered sludge | 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 Adsorption of Cd and Mn from neutral mine effluents using bentonite, zeolite, and stabilized dewatered sludge Veronika Prepilková, Juraj Poništ, Anna Ďuricová, Jozef Salva, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3852913/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study aimed to investigate the adsorption efficiency of Cd and Mn using natural sorbents - bentonite, zeolite and stabilized digested dewatered waste sludge. The main contributions of the scientific article are in adding to the scientific knowledge of the use of natural and waste sorbents in the removal of heavy metals from neutral mine effluents. Current studies mainly focus on metal removal by sorption using natural sorbents from acid mine drainage. Our study investigates sorption in neutral mine drainage. The maximum efficiency of Mn removal by bentonite at the end of the test was approximately 90%. The removal of Mn by zeolite was considerably lower - about 20% compared to the use of sludge - 80%. Based on the sorption efficiency, the sludge was suitable for sorption. Much higher levels of Cd sorption were achieved using sludge compared to using natural bentonite and zeolite. The main novelty of the work lies in the sorption of metals using dewatered digested sludge. Previous studies have focused on metal sorption using activated sludge. Another novelty of our scientific paper is the comparison of the sorption of this waste sorbent with natural sorbents. adsorption cadmium manganese neutral mine drainage stabilized digested dewatered sludge heavy metal removal Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction The industrial sector is the source of a large amount of wastewater that needs to be disposed of before being discharged into the environment (Saadi et al., 2015 ). Multiple damage to living systems can occur if the threshold is exceeded (Luo et al., 2011 ). Cadmium (Cd) is one of the major pollutants, a non-essential metal that is harmful to organisms at relatively low concentrations of about 0.001–0.1 mg .dm − 3 (Alkorta et al., 2004 ; Tang et al., 2018 ). Cadmium (Gray, 1998 ) and Manganese (Mn) (Das, 2018 ), (Favas et al., 2016 ; US EPA, 2015 ) occur as one of the heavy metals in mine effluents. Generally, mine drainage treatment aims to raise the pH while removing metals and sulphates before it is discharged into natural streams. The removal mechanisms for most metals in mine drainage are sorption and precipitation (Skousen et al., 2017 ). Current methods for the treatment of wastewater containing heavy metal ions are the ferrite method, chemical precipitation, electrochemical method, reverse osmosis method, ion exchange method, and adsorption methods (Wang et al., 2022 ). Frequently used natural sorbents for heavy metal sorption include bentonites (Gitari, 2014 ) (Enslin et al., 2010 ) (Orakwue et al., 2016a ) (Masindi et al., 2015a ) (Gumede and Musonge, 2022 ) (Enslin et al., 2010 ) a zeolite (Balintova et al., 2012 ) (Ryu et al., 2019 ) a zeolite (Feng et al., 2019 ) (Olegario-Sanchez and Pelicano, 2017 ) (Wulandari et al., 2020a ) (Ryu et al., 2019 ) (Varvara et al., 2013 ) (Motsi, 2010a ). Bentonites for sorption have also been used in mixtures with other materials to increase their efficiency (Ntwampe, 2023 ). Other materials with a confirmed Cd sorption effect include, for example, charcoal (Strugała-Wilczek et al., 2020 ). In addition to natural materials, by-products from production can be used for sorption (Kaartinen et al., 2017 ). In recent years, many readily economically available biosorption materials have been used and have shown promise as methods for heavy metal removal (Ahad et al., 2017 ; Bailey et al., 1999 ; Kratochvil and Volesky, 1998 ). Waste digested activated sludge (WDAS) is also a waste material that can be used as a biosorbent for the purpose of metal removal. WDAS is produced in wastewater treatment plants where excess activated sludge is used to produce biogas in an anaerobic digester (Appels et al., 2008 ). Activated sludge has been used in the past as a sorbent for heavy metals (Arican et al., 2002 ). In the removal of metals from mine effluents by sorption, previous studies have mainly used natural sorbents due to their low cost (Aguiar et al., 2013 ; Akbari Dehkharghani, 2019 ; Farsi et al., 2019 ; Masindi et al., 2015b ; Motsi, 2010b ; Motsi et al., 2009 ; Orakwue et al., 2016b ; Wulandari et al., 2020b ). In this work, we investigated the removal of Cd and Mn by adsorption using SDDS, bentonite, and zeolite. As a sorbent, it could find use in the treatment of mine drainage as opposed to landfilling. Using zeolite, efficiencies of more than 89% were achieved for Cu (Balintova et al., 2012 ); (Feng et al., 2019 ); (Balintova et al., 2014 ), Fe (Varvara et al., 2013 ), 47% for Cd (Mokgehle et al., 2019 ) and for Mn ∼100% (Motsi, 2010a ). Using bentonite, the sorption was more than 89% for Fe (Enslin et al., 2010 ) (Masindi et al., 2015a ), the same for Cd (Mokgehle et al., 2019 ) as well as for Mn (Masindi et al., 2015a ), even according to another study a sorption of ∼100% was found for Mn (Masindi et al., 2015a ). Biosorption by activated sludge for heavy metals has also been studied in the past. Cd uptake by activated sludge has been confirmed to be greater than 95% (Gourdon et al., 1990a ). Another study reported Cd sorption by activated sludge and a level of 50% (Sterritt and Lester, 1981 ). Activated sludge was studied for Ni sorption (39.7%) (Arican et al., 2002 ) Sorption for Cd and Pb capture by activated sludge has also been carried out (Wang et al., 2006 ). Biosorption isotherms show that Cd can be biosorbed up to more than 20,000-fold above water concentrations using free cells at 30°C and pH 6.6 (Gourdon et al., 1990b ). According to the study (Çeçen and Gürsoy, 2001 ) activated sludge had a high biosorption capacity and equilibrium was reached in a short time with respect to copper, iron, manganese, zinc and chromium from landfill leachate. The use of surplus sludge from wastewater treatment plants is very limited in Slovakia, e.g. due to its confirmed microplastic content (“Hnojivá zo splaškového kalu obsahujú znepokojujúce množstvo mikroplastov, hovorí nová štúdia,” ). The current regulatory framework for sewage sludge is set out in several instruments at EU level. However, these primarily focus on the waste dimension and not on the reuse of valuable resources (“Nastal čas, aby sme sa na kaly z ČOV pozerali ako na cenný zdroj,” ). The view of sludge use in Slovakia focuses mainly as a fertilizer. However, for its application on agricultural land as a fertilizer is bound by restrictions regulated by the Act of the National Assembly of the Slovak Republic No. 188/2003 Coll. and the subsequent Manual for the application of sewage sludge to agricultural land, issued by the Research Institute of Soil Science and Soil Protection, Bratislava. According to this manual from the law in question, the application of sewage sludge and bottom sediments is prohibited to agricultural land or forest land, - the pH value of which is lower than 5.0; in the protection zone of water supply sources of I. degree and II. Grade I or II; with a slope above 12°, if the groundwater level is less than 0.5 m from the soil surface (or other restrictions defined by law). The use of surplus sewage sludge, for example also in sorption methods, is one of the paths towards a circular economy, which is currently being strongly emphasised throughout the European Union. The above studies mainly focused on the removal of metals by sorption from acid mine drainage. Our study investigates sorption in neutral mine effluents. The novelty of this study was the simplicity of the technique and low equipment costs; the process can be operated by any well-trained technician. The reagents occur naturally and do not require sophisticated engineering processing. Another novelty is in the sorption of metals from neutral mine effluents, instead of sorption from acid mine effluents in other studies. Material and methods In this work, ground-digested dewatered sludge, bentonite, and zeolite were used as adsorbent. Description of the sorbents and neutral mine drainage Stabilized digested dewatered sludge was used in the study. Stabilized sludge was used specifically to remove pathogenic microorganisms that could cause hygienic complications when this sorbent is applied to the aquatic ecosystem. The sludge was dried and ground with a ball mill to a fraction below 200 µm. Ground fine bentonite was used for better contact between the sorbent and the sample. Bentonite was obtained from the Kopernica site (Table 1 ). The bentonite was ball milled to a fraction below 200 µm. Ground fine zeolite was used for better contact between the sorbent and the sample. The zeolite was ball milled to a fraction below 200 µm. Zeolite was obtained from Nižný Hrabovec (Table 1 ). The mineral composition of the zeolite used is Klinoptilolite 82–84% (“VSK Pro-Zeo - Úprava, spracovanie a balenie zeolitu.,” ). Neutral mine drainage was taken from the Voznická dedičná stôlňa adit – Central Slovakia. The average pH over 2 years in neutral mine drainage was 7.24. Aqueous solutions were used for sorption. The concentration of cadmium and manganese in them was modified with selected Cd and Mn salts for the needs of 5 input concentrations. Table 1 Chemical and mineral composition of bentonite and zeolite Sorbent Chemical composition [%] Source SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO TiO 2 Na 2 O K 2 O MnO P 2 O 5 SO 3 Bentonite 59.02–74.6 12.07–26.67 2.01–3.29 0.99–1.74 1.03–3.47 0.13–0.24 0.16–0.88 0.68–1.28 – – – Supplier 66.09 23.96 2.69 1.9 2.93 0.15 0.43 1.68 0.05 0.01 0.11 Deliova et al., 2015 Zeolite 70.37 11.98 1.76 3.57 0.31 – – – – – – Supplier 64.18–75.5 10.93–14.80 0.12–2.45 1.43–11.68 0.29–1.43 0.10–2.97 1.24–4.24 – – – VSK Pro-Zeo, Mineral composition [%] Sorbent Montmorillonite Plagioclase K-feldspar Biotite Quartz-cristobalite Volcanic glass loss by annealing Smektite Feldspar Kaolinite Clinoptilolite Source Bentonite 50–98 2.53 1.89 5.33 13.44 5.13 0.48 – – – – Supplier – – 2.5 1.5 – – 80 8 2 – Deliova et al., 2015 Zeolite 82–84 VSK Pro-Zeo, Sorption of heavy metals Adsorption experiments were carried out in closed Erlenmeyer flasks at laboratory temperature by mixing the sorbent with 100 cm 3 of neutral mine drainage solution. Sorbent concentrations of 5 g.dm − 3 were used in the experiment. The samples were periodically mixed at a constant speed (200 rpm) using an electromagnetic stirrer. Sorption was carried out at a laboratory temperature of 20°C. The sorption experiment was carried out in parallel samples. The first represented the input concentration. At minute intervals, sorption was gradually interrupted in individual samples. After stopping the sorption in a 100 ml sample, the solution was filtered, and the concentration of manganese/cadmium was determined in it. This experiment was repeated 6 times for the same input concentrations and the sorption results were averaged. 5 different inlet concentrations were achieved by adding manganese/cadmium salt to neutral mine drainage. In four of the five samples, the sorbent concentration was the same at 5 g. dm − 3 . The range of input – zero concentration of manganese/cadmium was chosen depending on the measuring range of the instrument used for the determination of metals. Determination of heavy metal concentration Metal concentrations were determined by atomic absorption spectrometry (AAS). For the determination of metals, we used an AAS AVANTA Σ flame atomization spectrometer (GBC Scientific). A hollow cathode lamp with a supply current of 3.00 mA was used as the radiation source. Air/acetylene was used as the flame type at flow rates of 11.50 dm 3 .min − 1 for air and 1.10 dm 3 .min − 1 for acetylene. The relative errors of the AAS measurements were less than 5%. The instrument operation as well as the evaluation of the results was carried out with the GBC Avanta software ver. 2.0. Determination of heavy metal concentrations of sorbents and neutral mine drainage The AES-ICP atomic emission spectrometry with inductively coupled plasma method was used to determine copper, manganese, iron, lead, cadmium, and aluminum. The EA-TCD - elemental analysis with thermal conductivity detection method was used to determine zinc. Calculations Adsorption capacity From the measured concentrations, the adsorption capacity at equilibrium (qe), the amount of metal adsorbed per unit sorbent at time t (qt), and the percent removal efficiency of Mn 2+ and Cd 2+ ions from the solution (Ads. %) were calculated. The adsorption capacity at equilibrium and at time t, respectively, was calculated according to Eq: $${\text{q}}_{\text{e}}=\frac{\left({\text{c}}_{\text{o}}-{\text{c}}_{\text{e}}\right)\bullet \text{V}}{\text{m}}$$ 1 where co is the initial concentration of ions in solution (mg.dm − 3 ), ce is the equilibrium concentration of ions in solution or the concentration of ions in solution at time t (mg.dm − 3 ), V is the volume of solution (dm − 3 ) and m is the mass of adsorbent added (g). Percentage of metal ion removal efficiency The percentage removal efficiency of metal ions from the solution was calculated according to Eq: $$\text{A}\text{d}\text{s}.\text{%}=\frac{\left({\text{c}}_{0}-{\text{c}}_{\text{e}}\right)}{{\text{c}}_{\text{o}}}\text{*}100 \left[\text{%}\right]$$ 2 Experiments focusing on the adsorption of Mn and Cd were carried out with natural unmodified adsorbents and waste-stabilized digested dewatered sludge in a closed system under constant stirring of the suspension at laboratory temperature. We monitored the progress of sorption depending on the sorbent used. Freundlich and Langmuir adsorption isotherms To express the dependence of the adsorbed amount of a metal ion on its equilibrium concentration in solution, Freundlich and Langmuir's isotherms were constructed for all adsorbents used. The isotherms were evaluated at 5 input concentrations. Freundlich adsorption isotherm The effect of initial metal concentration on adsorption is described by adsorption isotherms. Several empirical and semiempirical relationships have been proposed for the analytical expression of the isotherms, of which either the Freundlich or Langmuir isotherm is the most suitable for adsorption from solutions. The Freundlich isotherm is usually valid for physical adsorption and for adsorption on heterogeneous surfaces with different active sites. It can be expressed by the relation: $${\text{q}}_{\text{e}}={\text{K}}_{\text{f}}\bullet {\text{c}}_{\text{e}}^{\frac{1}{\text{n}}}$$ 3 To verify that the experimental data fit this isotherm, the relation is linearized: $${\text{l}\text{o}\text{g}\text{q}}_{\text{e}}={\text{l}\text{o}\text{g}\text{K}}_{\text{f}}+\frac{1}{\text{n}}{\text{l}\text{o}\text{g}\text{c}}_{\text{e}}$$ 4 where Kf (mg.g − 1 ) is a constant related to the adsorption capacity and n is an empirical parameter expressing the adsorption intensity, which varies with the heterogeneity of the adsorbent. Langmuir adsorption isotherm The Langmuir isotherm is usually valid for chemisorption or electrostatic adsorption, where only a monomolecular layer is formed on the adsorbent surface and all active centers are equivalent. The Langmuir isotherm is expressed by the relation: $${\text{q}}_{\text{e}}=\frac{{\text{q}}_{\text{m}}\bullet \text{b}\bullet {\text{c}}_{\text{e}}}{1+\text{b}\bullet {\text{c}}_{\text{e}}}$$ 5 or in the linearized form: $$\frac{{\text{c}}_{\text{e}}}{{\text{q}}_{\text{e}}}=\frac{1}{\text{b}\bullet {\text{q}}_{\text{m}}}+\frac{1}{{\text{q}}_{\text{m}}}\bullet {\text{c}}_{\text{e}}$$ 6 where q m (mg.g − 1 ) gives the maximum monolayer adsorption capacity and b is the equilibrium constant dependent on the sorption energy. Results First, the background concentrations of metals in the sorbents and the mine water were verified (Table 2 ). The concentrations of Mn and Cd in neutral mine water several times exceed their concentrations in sorbents. Table 2 Metal content in sorbents and neutral mine drainage Sample Copper Manganese Zinc Iron Lead Cadmium Aluminium µg.kg − 1 / µg.L − 1 µg.kg − 1 / µg.L − 1 µg.kg − 1 / µg.L − 1 µg.kg − 1 / µg.L − 1 µg.kg − 1 / µg.L − 1 µg.kg − 1 / µg.L − 1 µg.kg − 1 / µg.L − 1 Bentonite 2.70 106 13.8 4121 25.2 0.068 8929 Zeolite 3.32 115 39.6 5352 9.28 0.147 39375 SDDS 415 182 1348 19034 38.5 1.89 17335 Neutral mine drainage 117 3090 6130 8810 94 24 3060 The parameters of adsorption isotherms present the ability and conditions for the sorption of individual sorbents. The selected parameters are also used for mutual comparison between sorbents. These findings can then be confronted with the adsorption capacity of the monolayer q m as seen in Table 3 . Table 3 Parameters of Freundlich and Langmuir adsorption isotherms for bentonite, zeolite, and sludge Adsorbent Density (kg/m 3 ) Metal Langmuir´s parameters Freundlich´s parameters q m (mg.g − 1 ) B (dm 3 .mg − 1 ) R 2 k f n R 2 Bentonite 1944.2 Cd 0.0542 0.1149 0.6905 0.6002 1.3426 0.9747 Mn 3.992 0.3240 0.8190 1.3060 2.6330 0.9210 Zeolite 1456.5 Cd -1.4302 -0.0127 0.0776 0.0187 0.9888 0.9863 Mn 0.5360 0.3366 0.9908 0.2757 5.6818 0.9840 SDDS 1194.1 Cd 0.1450 0.4170 0.8485 0.0486 2.1268 0.9182 Mn 4.2194 0.4034 0.8189 1.5014 2.6709 0.8260 qm (mg.g-1) indicates the maximum monolayer adsorption capacity B = equilibrium constant dependent on sorption energy kf (mg.g − 1 ) = adsorption capacity related constant n = empirical parameter expressing the adsorption intensity, which varies depending on the heterogeneity of the adsorbent The fitting of the Langmuir isotherm was carried out according to the above equations at time t 120 - the end of the experiment. We assumed that at the end of the experiment, after 120 min of sorption, the trends of the isotherm curves would reach a steady-state character, which would be indicative of a state of reaching equilibrium. In some cases, the fitting of the Langmuir isotherm at t 120 corresponded to a linear trend (e.g. bentonite - Mn; zeolite - Mn; sludge - both Cd and Mn. In other cases, the fitting of the isotherms at t120 resulted in very low R 2 , e.g. for Cd sorption using zeolite. The fitting of the Freundlich isotherm also took place at time t 120 - at the end of the sorption experiment. In this case, the R 2 refers to a more linear trend than was the case for the Langmuir adsorption isotherms. Also when fitting the Freundlich isotherms at time t 120 , some deviations in the real versus linearized values were observed. However, these deviations were much smaller than for the fitting of the Langmuir isotherms at time t 120 . In the case of Mn sorption, the highest value of adsorption capacity qm was observed when sludge was used. The bentonite level for Mn sorption reached a similar value, on the other hand, qm when zeolite was used was in the low range. The highest sorption intensity for Mn sorption was observed when zeolite was used. The sorption intensity for Mn sorption using bentonite and sludge was at similar levels. The maximum monolayer capacity for Cd sorption was generally maintained at low values for all three sorbents. The highest sorption intensity for Cd sorption was observed using dewatered excess sludge. Sorption intensities for Cd sorption using bentonite and zeolite reached similar levels. The equilibrium constant dependent on the sorption energy reached the highest values when excess dewatered sludge was used. The highest value of kf, which is also related to adsorption capacity, was observed to be the highest for Mn sorption using excess dewatered sludge. Metal removal depending on contact time The adsorption efficiency greatly increases by increasing the time of contact between pollutants and adsorbent due to the increase of interaction time between active sites of chelation and metals. Normally, at the beginning of the adsorption, the removal efficiency occurs quickly and then increases gradually. This occurs because of the availability of the free active sites at initial adsorption that are gradually occupied with time by chelated metals (Tahoon et al., 2020). According to obtained data, we can conclude that the adsorption process is the most rapid between 30 and 90 minutes. After 120 minutes, equilibrium starts to occur in the solutions, probably due to the filling monolayer. This correlates with the results of Bhatti et al. (2015) that more than 50% of the total metal content in solution is adsorbed within the first 60 minutes of adsorption. Alexander et al. (2019) determined the adsorption intensity n at the level of 5.8. Compared with calcined bentonite, we determined a higher monolayer adsorption capacity by a factor of about 8. We see the reason as the fineness of the fraction that was used in our study. Metal removal depending on the initial concentration The percentage of Mn removal was evaluated in the concentration range of 8–22 mg.L − 1 and Cd removal in the concentration range approximately of 1–5 mg.L − 1 (Fig. 7 , 8 ). The concentration-dependent decrease in Mn removal efficiency was similar to that observed with zeolite and bentonite. Sorption using sludge was approximately 60% higher compared to zeolite. This indicates that digested sludge is a better adsorbent for Mn removal than zeolite. The experiment did not confirm a direct dependence between the input concentration and the percentage of Cd removal efficiency. Therefore, it is necessary to experimentally determine the optimum level of input concentration and not rely on the application of a mathematical relationship (linear or otherwise). The results confirmed decreasing levels of Cd removal from increasing concentrations of this metal ion in the solution. However, the level of sorption is several times higher than that of using bentonite and zeolite. We can conclude that SDDS could be used as an effective low-cost sorbent for metal removal. Also, with increasing initial concentration of metal in solution metal removal efficiency slightly decreased. According to Tahoon et al. (2020) above a particular initial concentration, ions with an equal amount of adsorption locations are available, which therefore decreases their elimination adsorption capacity. Discussion Pradas et al. studied the sorption of cadmium using natural and activated bentonite. The maximum monolayer adsorption capacity q m using natural bentonite reached 3.32 mg.g − 1 and 4.54 mg.g − 1 , respectively. The level of equilibrium constant b was at 1.61 and 1.86 dm 3 .mg − 1 (Pradas et al., 1994 ). These values are much higher than ours – q m 0.0542 mg.g − 1 and b 0.1149. Alexander et al. ( 2017 ) present the sorption capacity of natural bentonite at 1.4 and 2.4 for input Cd concentrations of 10 and 50 mg.dm − 3 , respectively(Alexander et al., 2017 ). Again, as in the previous case, a lower average value (by about 1 order of magnitude) was obtained by our experiment. The differences with the compared studies may be due to the length of the test or to the particular composition of the bentonite used. Using zeolite, Rao et al. (2006) determined Cd adsorption intensities of 4.382 and 3.690. The sorption intensity n in our study was approximately 1. Rao et al. performed their sorption at 30°C, which may have increased the sorption intensity. Therefore, one possible way to increase the sorption intensity may be to increase the temperature (within observed and controlled levels, of course). The Langmuir adsorption isotherm was found to be unsuitable for evaluating Cd sorption using zeolite. Therefore, it will not be considered in this study. Hu et al. (2012) tested Cd sorption on dewatered sludge from a wastewater treatment plant. By constructing the Langmuir isotherm, a q m of 28.336 mg.g − 1 was obtained. By treating the sludge, they achieved an improvement in q m with the addition of 0.125 mol.l − 1 NaOH; 0.25 mol.dm − 3 NaOH; 2.5 mol.dm − 3 NaOH; 7.5 mol.dm − 3 NaOH q m at the level of 85.232 mg.g − 1 ; 70.336 mg.g − 1 ; 86.128 mg.g − 1 ; 108.192 mg.g − 1 . In our case, a much lower monolayer capacity (approximately 100-fold lower) was obtained. By Freundlich isotherm using sludge, Hu et al. (2012) achieved a sorption intensity n of 3.25 and an adsorption capacity K f of 28 mg.g − 1 . The sorption intensity, in this case, was comparable to our experiments. In contrast, the sorption capacity K f was again incomparably lower compared to the study of Hu et al. (2012). We assume that the above differences were due to the heterogeneous composition of the sludge. Therefore, as we can see, the sorption properties are incomparable for different sludge types in terms of their chemistry. Pradas et al. using natural bentonite achieved % Cd removal of 99.3–100% (Pradas et al., 1994 ). By our sorption, much lower values were achieved. It should be justified that Pradas et al. heat-treated their bentonite to a temperature of 110°C. Furthermore, in Prads' study, sorption lasted 72 h, i.e. 36 times longer than in our case. At the same time, the concentration of added bentonite was 100 g.dm − 3 in Pradas' study, which is 20 times higher than in our experiment. This indicates that adsorption time has no inconsiderable effect on the removal efficiency. Our results indicate that SDDS could be a promising low-cost adsorbent for the removal of Mn and Cd from neutral mine drainage. Muhammad et al. (2015) have confirmed good removal efficiency (88.15%) when using a mixture of limestone, activated sludge, spent mushroom compost, and woodchips. However, the contact time should be 12 hours. Fuchida et al. (2020) have studied the removal of Mn and Cd in the subsurface limestone beds. They have confirmed that except from adsorption also microorganism activity of the manganese-oxidizing bacteria plays a crucial role in Cd and Mn removal. When thinking about cadmium and manganese removal we need to take into account not only the dosage of adsorbent but also contact time and the possibility of bacteria interference, which could strengthen removal efficiency. Summary Based on the tests performed, stabilized digested dewatered sludge appears as a good low-cost sorbent for Cd and Mn removal. However, when comparing with other studies, usually for effective removal longer contact time is needed, from 4–8 hours up to 72 hours. Differences in metal sorption may be due to different sorbent compositions or other test conditions (thermal and chemical pre-treatment of the sorbent). Mn sorption results using zeolite according to other studies are comparable to our results. Comparable sorption results were found for sorption using sludge compared to bentonite, and even better when using zeolite. Much higher levels of Cd sorption were achieved using sludge compared to using natural bentonite and zeolite. To improve the sorption, the sorbent dosage needs to be increased and at the same time, the contact time should be extended. As manganese-oxidizing bacteria could contribute to both Mn and Cd removal, in next study should be investigated if they are naturally occurring in mine drainage or digested sludge and how to support their activity for better heavy metals uptake. Declarations Supplementary Information: not necessary Author Contributions All authors contributed to the study conception and design. Data collection, analysis, and writing the first draft were performed by Prepilková, Mordáčová and Schwarz provided detailed comments and revised the previous versions of the manuscript. All authors read and approved the final manuscript. Funding: This work was supported by Comprehensive research of determinants for ensuring environmental health (ENVIHEALTH), ITMS 313011T721 supported by the Operational Programme Integrated Infrastructure (OPII) funded by the ERDF Data availability: not applicable. Ethical approval: This article does not contain studies with human participants or animals by any of the authors. Consent to Participate: This article does not contain studies with human participants. Consent to Publish: All authors of this study agree to publish this paper in Environmental Science and Pollution Research. Competing Interests : The authors declare that they have no confict of interest. Acknowledgments This publication is the result of the project implementation: Comprehensive research of determinants for ensuring environmental health (ENVIHEALTH), ITMS 313011T721 supported by the Operational Programme Integrated Infrastructure (OPII) funded by the ERDF. References Aguiar, A.O., Duarte, R.A., Ladeira, A.C.Q.: The Application of MnO2 in the Removal of Manganese from Acid Mine Water. Water Air Soil Pollut. 224 , 1690 (2013). https://doi.org/10.1007/s11270-013-1690-2 Ahad, R.I.A., Goswami, S., Syiem, M.B.: Biosorption and equilibrium isotherms study of cadmium removal by Nostoc muscorum Meg 1: morphological, physiological and biochemical alterations. 3 Biotech. 7 , 104 (2017). https://doi.org/10.1007/s13205-017-0730-9 Akbari Dehkharghani, A.: Exfoliated Graphitic Carbon Nitride for the Fast Adsorption of Metal Ions from Acid Mine Drainage: A Case Study from the Sungun Copper Mine. 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URL https://www.vskpro-zeo.sk/ (accessed 1.10.23) Wang, Q., Zhu, S., Xi, C., Zhang, F.: A Review: Adsorption and Removal of Heavy Metals Based on Polyamide-amines Composites. Front. Chem. 10 , 814643 (2022). https://doi.org/10.3389/fchem.2022.814643 Wang, X., Xia, S., Chen, L., Zhao, J., Chovelon, J., Nicole, J.: Biosorption of cadmium(II) and lead(II) ions from aqueous solutions onto dried activated sludge. J. Environ. Sci. 18 , 840–844 (2006). https://doi.org/10.1016/S1001-0742(06)60002-8 Wulandari, E., Hidayat, A.E., Moersidik, S.S.: Comparison of copper adsorption effectivity in acid mine drainage using natural zeolite and synthesized zeolite. IOP Conf. Ser. : Earth Environ. Sci. 473 , 012143 (2020a). https://doi.org/10.1088/1755-1315/473/1/012143 Wulandari, E., Hidayat, A.E., Moersidik, S.S.: Comparison of copper adsorption effectivity in acid mine drainage using natural zeolite and synthesized zeolite. IOP Conf. Ser. : Earth Environ. Sci. 473 , 012143 (2020b). https://doi.org/10.1088/1755-1315/473/1/012143 Additional Declarations No competing interests reported. Supplementary Files GA.jpg Graphical abstract Cite Share Download PDF Status: Posted Version 1 posted 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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adsorbed\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-3852913/v1/a16e7392f71aead3f61c1121.png"},{"id":50014042,"identity":"e1f72e4c-e935-42c7-bce8-9750188dcf75","added_by":"auto","created_at":"2024-01-23 06:04:55","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":12098,"visible":true,"origin":"","legend":"\u003cp\u003eDependence of the amount of Cd adsorbed\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-3852913/v1/51cde9831937ba32185bfce5.png"},{"id":51326488,"identity":"a1eac256-1161-43fd-a61d-07897ff4d13a","added_by":"auto","created_at":"2024-02-19 16:15:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":696254,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3852913/v1/4bc663c1-d21f-4bed-a098-19b3b9921bf4.pdf"},{"id":50014040,"identity":"6ae97dcf-ba69-4e7b-8e49-4e47a507742d","added_by":"auto","created_at":"2024-01-23 06:04:55","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":127944,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical abstract\u003c/p\u003e","description":"","filename":"GA.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3852913/v1/e576f2edc5cfc732c2c23e71.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Adsorption of Cd and Mn from neutral mine effluents using bentonite, zeolite, and stabilized dewatered sludge","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe industrial sector is the source of a large amount of wastewater that needs to be disposed of before being discharged into the environment (Saadi et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Multiple damage to living systems can occur if the threshold is exceeded (Luo et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCadmium (Cd) is one of the major pollutants, a non-essential metal that is harmful to organisms at relatively low concentrations of about 0.001\u0026ndash;0.1 mg .dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e (Alkorta et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Tang et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Cadmium (Gray, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1998\u003c/span\u003e) and Manganese (Mn) (Das, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), (Favas et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; US EPA, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) occur as one of the heavy metals in mine effluents.\u003c/p\u003e \u003cp\u003eGenerally, mine drainage treatment aims to raise the pH while removing metals and sulphates before it is discharged into natural streams. The removal mechanisms for most metals in mine drainage are sorption and precipitation (Skousen et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Current methods for the treatment of wastewater containing heavy metal ions are the ferrite method, chemical precipitation, electrochemical method, reverse osmosis method, ion exchange method, and adsorption methods (Wang et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFrequently used natural sorbents for heavy metal sorption include bentonites (Gitari, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) (Enslin et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) (Orakwue et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2016a\u003c/span\u003e) (Masindi et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e) (Gumede and Musonge, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) (Enslin et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) a zeolite (Balintova et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) (Ryu et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) a zeolite (Feng et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) (Olegario-Sanchez and Pelicano, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) (Wulandari et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e) (Ryu et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) (Varvara et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) (Motsi, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2010a\u003c/span\u003e). Bentonites for sorption have also been used in mixtures with other materials to increase their efficiency (Ntwampe, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Other materials with a confirmed Cd sorption effect include, for example, charcoal (Strugała-Wilczek et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In addition to natural materials, by-products from production can be used for sorption (Kaartinen et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn recent years, many readily economically available biosorption materials have been used and have shown promise as methods for heavy metal removal (Ahad et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Bailey et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Kratochvil and Volesky, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Waste digested activated sludge (WDAS) is also a waste material that can be used as a biosorbent for the purpose of metal removal. WDAS is produced in wastewater treatment plants where excess activated sludge is used to produce biogas in an anaerobic digester (Appels et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Activated sludge has been used in the past as a sorbent for heavy metals (Arican et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the removal of metals from mine effluents by sorption, previous studies have mainly used natural sorbents due to their low cost (Aguiar et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Akbari Dehkharghani, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Farsi et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Masindi et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2015b\u003c/span\u003e; Motsi, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2010b\u003c/span\u003e; Motsi et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Orakwue et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016b\u003c/span\u003e; Wulandari et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e). In this work, we investigated the removal of Cd and Mn by adsorption using SDDS, bentonite, and zeolite. As a sorbent, it could find use in the treatment of mine drainage as opposed to landfilling. Using zeolite, efficiencies of more than 89% were achieved for Cu (Balintova et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2012\u003c/span\u003e); (Feng et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); (Balintova et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), Fe (Varvara et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), 47% for Cd (Mokgehle et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) and for Mn \u0026sim;100% (Motsi, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2010a\u003c/span\u003e). Using bentonite, the sorption was more than 89% for Fe (Enslin et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) (Masindi et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e), the same for Cd (Mokgehle et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) as well as for Mn (Masindi et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e), even according to another study a sorption of \u0026sim;100% was found for Mn (Masindi et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e). Biosorption by activated sludge for heavy metals has also been studied in the past. Cd uptake by activated sludge has been confirmed to be greater than 95% (Gourdon et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1990a\u003c/span\u003e). Another study reported Cd sorption by activated sludge and a level of 50% (Sterritt and Lester, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e1981\u003c/span\u003e). Activated sludge was studied for Ni sorption (39.7%) (Arican et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) Sorption for Cd and Pb capture by activated sludge has also been carried out (Wang et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Biosorption isotherms show that Cd can be biosorbed up to more than 20,000-fold above water concentrations using free cells at 30\u0026deg;C and pH 6.6 (Gourdon et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1990b\u003c/span\u003e). According to the study (\u0026Ccedil;e\u0026ccedil;en and G\u0026uuml;rsoy, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) activated sludge had a high biosorption capacity and equilibrium was reached in a short time with respect to copper, iron, manganese, zinc and chromium from landfill leachate.\u003c/p\u003e \u003cp\u003eThe use of surplus sludge from wastewater treatment plants is very limited in Slovakia, e.g. due to its confirmed microplastic content (\u0026ldquo;Hnojiv\u0026aacute; zo splaškov\u0026eacute;ho kalu obsahuj\u0026uacute; znepokojuj\u0026uacute;ce množstvo mikroplastov, hovor\u0026iacute; nov\u0026aacute; št\u0026uacute;dia,\u0026rdquo; ). The current regulatory framework for sewage sludge is set out in several instruments at EU level. However, these primarily focus on the waste dimension and not on the reuse of valuable resources (\u0026ldquo;Nastal čas, aby sme sa na kaly z ČOV pozerali ako na cenn\u0026yacute; zdroj,\u0026rdquo; ). The view of sludge use in Slovakia focuses mainly as a fertilizer. However, for its application on agricultural land as a fertilizer is bound by restrictions regulated by the Act of the National Assembly of the Slovak Republic No. 188/2003 Coll. and the subsequent Manual for the application of sewage sludge to agricultural land, issued by the Research Institute of Soil Science and Soil Protection, Bratislava. According to this manual from the law in question, the application of sewage sludge and bottom sediments is prohibited to agricultural land or forest land, - the pH value of which is lower than 5.0; in the protection zone of water supply sources of I. degree and II. Grade I or II; with a slope above 12\u0026deg;, if the groundwater level is less than 0.5 m from the soil surface (or other restrictions defined by law). The use of surplus sewage sludge, for example also in sorption methods, is one of the paths towards a circular economy, which is currently being strongly emphasised throughout the European Union.\u003c/p\u003e \u003cp\u003eThe above studies mainly focused on the removal of metals by sorption from acid mine drainage. Our study investigates sorption in neutral mine effluents. The novelty of this study was the simplicity of the technique and low equipment costs; the process can be operated by any well-trained technician. The reagents occur naturally and do not require sophisticated engineering processing. Another novelty is in the sorption of metals from neutral mine effluents, instead of sorption from acid mine effluents in other studies.\u003c/p\u003e"},{"header":"Material and methods","content":"\u003cp\u003eIn this work, ground-digested dewatered sludge, bentonite, and zeolite were used as adsorbent.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eDescription of the sorbents and neutral mine drainage\u003c/h2\u003e \u003cp\u003eStabilized digested dewatered sludge was used in the study. Stabilized sludge was used specifically to remove pathogenic microorganisms that could cause hygienic complications when this sorbent is applied to the aquatic ecosystem. The sludge was dried and ground with a ball mill to a fraction below 200 \u0026micro;m.\u003c/p\u003e \u003cp\u003eGround fine bentonite was used for better contact between the sorbent and the sample. Bentonite was obtained from the Kopernica site (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The bentonite was ball milled to a fraction below 200 \u0026micro;m.\u003c/p\u003e \u003cp\u003eGround fine zeolite was used for better contact between the sorbent and the sample. The zeolite was ball milled to a fraction below 200 \u0026micro;m. Zeolite was obtained from Nižn\u0026yacute; Hrabovec (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The mineral composition of the zeolite used is Klinoptilolite 82\u0026ndash;84% (\u0026ldquo;VSK Pro-Zeo - \u0026Uacute;prava, spracovanie a balenie zeolitu.,\u0026rdquo; ).\u003c/p\u003e \u003cp\u003eNeutral mine drainage was taken from the Voznick\u0026aacute; dedičn\u0026aacute; st\u0026ocirc;lňa adit \u0026ndash; Central Slovakia. The average pH over 2 years in neutral mine drainage was 7.24. Aqueous solutions were used for sorption. The concentration of cadmium and manganese in them was modified with selected Cd and Mn salts for the needs of 5 input concentrations.\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\u003eChemical and mineral composition of bentonite and zeolite\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"21\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c16\" colnum=\"16\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c17\" colnum=\"17\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c18\" colnum=\"18\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c19\" colnum=\"19\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c20\" colnum=\"20\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c21\" colnum=\"21\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSorbent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"19\" nameend=\"c20\" namest=\"c2\"\u003e \u003cp\u003e\u003cem\u003eChemical composition [%]\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c21\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMgO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e \u003cp\u003eMnO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c19\" namest=\"c18\"\u003e \u003cp\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c20\"\u003e \u003cp\u003eSO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c21\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eBentonite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e59.02\u0026ndash;74.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e12.07\u0026ndash;26.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e2.01\u0026ndash;3.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.99\u0026ndash;1.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.03\u0026ndash;3.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e \u003cp\u003e0.13\u0026ndash;0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e \u003cp\u003e0.16\u0026ndash;0.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e \u003cp\u003e0.68\u0026ndash;1.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c19\" namest=\"c18\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c21\"\u003e \u003cp\u003eSupplier\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e66.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e23.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e2.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e \u003cp\u003e1.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c19\" namest=\"c18\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c21\"\u003e \u003cp\u003eDeliova et al., 2015\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eZeolite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e70.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e11.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e1.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c19\" namest=\"c18\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c21\"\u003e \u003cp\u003eSupplier\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e64.18\u0026ndash;75.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e10.93\u0026ndash;14.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e0.12\u0026ndash;2.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.43\u0026ndash;11.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.29\u0026ndash;1.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e \u003cp\u003e0.10\u0026ndash;2.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c15\" namest=\"c14\"\u003e \u003cp\u003e1.24\u0026ndash;4.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c17\" namest=\"c16\"\u003e \u003cp\u003e\u003cb\u003e\u0026ndash;\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c19\" namest=\"c18\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c21\"\u003e \u003cp\u003eVSK Pro-Zeo,\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"21\" nameend=\"c21\" namest=\"c1\"\u003e \u003cp\u003eMineral composition [%]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSorbent\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eMontmorillonite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e\u003cb\u003ePlagioclase\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e\u003cb\u003eK-feldspar\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e\u003cb\u003eBiotite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003eQuartz-cristobalite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e\u003cb\u003eVolcanic glass\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e\u003cb\u003eloss by annealing\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e \u003cp\u003e\u003cb\u003eSmektite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e \u003cp\u003e\u003cb\u003eFeldspar\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c18\" namest=\"c17\"\u003e \u003cp\u003e\u003cb\u003eKaolinite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c20\" namest=\"c19\"\u003e \u003cp\u003e\u003cb\u003eClinoptilolite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c21\"\u003e \u003cp\u003e\u003cb\u003eSource\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eBentonite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50\u0026ndash;98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e2.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e1.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e5.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e13.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e5.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e0.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c18\" namest=\"c17\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c20\" namest=\"c19\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c21\"\u003e \u003cp\u003eSupplier\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c18\" namest=\"c17\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c20\" namest=\"c19\"\u003e \u003cp\u003e\u0026ndash;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c21\"\u003e \u003cp\u003eDeliova et al., 2015\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eZeolite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c14\" namest=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c16\" namest=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c18\" namest=\"c17\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c20\" namest=\"c19\"\u003e \u003cp\u003e82\u0026ndash;84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c21\"\u003e \u003cp\u003eVSK Pro-Zeo,\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eSorption of heavy metals\u003c/h2\u003e \u003cp\u003eAdsorption experiments were carried out in closed Erlenmeyer flasks at laboratory temperature by mixing the sorbent with 100 cm\u003csup\u003e3\u003c/sup\u003e of neutral mine drainage solution. Sorbent concentrations of 5 g.dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e were used in the experiment. The samples were periodically mixed at a constant speed (200 rpm) using an electromagnetic stirrer. Sorption was carried out at a laboratory temperature of 20\u0026deg;C. The sorption experiment was carried out in parallel samples. The first represented the input concentration. At minute intervals, sorption was gradually interrupted in individual samples. After stopping the sorption in a 100 ml sample, the solution was filtered, and the concentration of manganese/cadmium was determined in it. This experiment was repeated 6 times for the same input concentrations and the sorption results were averaged. 5 different inlet concentrations were achieved by adding manganese/cadmium salt to neutral mine drainage. In four of the five samples, the sorbent concentration was the same at 5 g. dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. The range of input \u0026ndash; zero concentration of manganese/cadmium was chosen depending on the measuring range of the instrument used for the determination of metals.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of heavy metal concentration\u003c/h2\u003e \u003cp\u003eMetal concentrations were determined by atomic absorption spectrometry (AAS). For the determination of metals, we used an AAS AVANTA Σ flame atomization spectrometer (GBC Scientific). A hollow cathode lamp with a supply current of 3.00 mA was used as the radiation source. Air/acetylene was used as the flame type at flow rates of 11.50 dm\u003csup\u003e3\u003c/sup\u003e.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for air and 1.10 dm\u003csup\u003e3\u003c/sup\u003e.min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for acetylene. The relative errors of the AAS measurements were less than 5%. The instrument operation as well as the evaluation of the results was carried out with the GBC Avanta software ver. 2.0.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of heavy metal concentrations of sorbents and neutral mine drainage\u003c/h2\u003e \u003cp\u003eThe AES-ICP atomic emission spectrometry with inductively coupled plasma method was used to determine copper, manganese, iron, lead, cadmium, and aluminum. The EA-TCD - elemental analysis with thermal conductivity detection method was used to determine zinc.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eCalculations\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003eAdsorption capacity\u003c/h2\u003e \u003cp\u003eFrom the measured concentrations, the adsorption capacity at equilibrium (qe), the amount of metal adsorbed per unit sorbent at time t (qt), and the percent removal efficiency of Mn\u003csup\u003e2+\u003c/sup\u003e and Cd\u003csup\u003e2+\u003c/sup\u003e ions from the solution (Ads. %) were calculated.\u003c/p\u003e \u003cp\u003eThe adsorption capacity at equilibrium and at time t, respectively, was calculated according to Eq:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${\\text{q}}_{\\text{e}}=\\frac{\\left({\\text{c}}_{\\text{o}}-{\\text{c}}_{\\text{e}}\\right)\\bullet \\text{V}}{\\text{m}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere co is the initial concentration of ions in solution (mg.dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), ce is the equilibrium concentration of ions in solution or the concentration of ions in solution at time t (mg.dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), V is the volume of solution (dm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) and m is the mass of adsorbent added (g).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003ePercentage of metal ion removal efficiency\u003c/h2\u003e \u003cp\u003eThe percentage removal efficiency of metal ions from the solution was calculated according to Eq:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\text{A}\\text{d}\\text{s}.\\text{%}=\\frac{\\left({\\text{c}}_{0}-{\\text{c}}_{\\text{e}}\\right)}{{\\text{c}}_{\\text{o}}}\\text{*}100 \\left[\\text{%}\\right]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eExperiments focusing on the adsorption of Mn and Cd were carried out with natural unmodified adsorbents and waste-stabilized digested dewatered sludge in a closed system under constant stirring of the suspension at laboratory temperature. We monitored the progress of sorption depending on the sorbent used.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eFreundlich and Langmuir adsorption isotherms\u003c/h2\u003e \u003cp\u003eTo express the dependence of the adsorbed amount of a metal ion on its equilibrium concentration in solution, Freundlich and Langmuir's isotherms were constructed for all adsorbents used. The isotherms were evaluated at 5 input concentrations.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eFreundlich adsorption isotherm\u003c/h2\u003e \u003cp\u003eThe effect of initial metal concentration on adsorption is described by adsorption isotherms. Several empirical and semiempirical relationships have been proposed for the analytical expression of the isotherms, of which either the Freundlich or Langmuir isotherm is the most suitable for adsorption from solutions.\u003c/p\u003e \u003cp\u003eThe Freundlich isotherm is usually valid for physical adsorption and for adsorption on heterogeneous surfaces with different active sites. It can be expressed by the relation:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${\\text{q}}_{\\text{e}}={\\text{K}}_{\\text{f}}\\bullet {\\text{c}}_{\\text{e}}^{\\frac{1}{\\text{n}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eTo verify that the experimental data fit this isotherm, the relation is linearized:\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$${\\text{l}\\text{o}\\text{g}\\text{q}}_{\\text{e}}={\\text{l}\\text{o}\\text{g}\\text{K}}_{\\text{f}}+\\frac{1}{\\text{n}}{\\text{l}\\text{o}\\text{g}\\text{c}}_{\\text{e}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere Kf (mg.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is a constant related to the adsorption capacity and n is an empirical parameter expressing the adsorption intensity, which varies with the heterogeneity of the adsorbent.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eLangmuir adsorption isotherm\u003c/h2\u003e \u003cp\u003eThe Langmuir isotherm is usually valid for chemisorption or electrostatic adsorption, where only a monomolecular layer is formed on the adsorbent surface and all active centers are equivalent. The Langmuir isotherm is expressed by the relation:\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$${\\text{q}}_{\\text{e}}=\\frac{{\\text{q}}_{\\text{m}}\\bullet \\text{b}\\bullet {\\text{c}}_{\\text{e}}}{1+\\text{b}\\bullet {\\text{c}}_{\\text{e}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eor in the linearized form:\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$$\\frac{{\\text{c}}_{\\text{e}}}{{\\text{q}}_{\\text{e}}}=\\frac{1}{\\text{b}\\bullet {\\text{q}}_{\\text{m}}}+\\frac{1}{{\\text{q}}_{\\text{m}}}\\bullet {\\text{c}}_{\\text{e}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere q\u003csub\u003em\u003c/sub\u003e (mg.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) gives the maximum monolayer adsorption capacity and b is the equilibrium constant dependent on the sorption energy.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eFirst, the background concentrations of metals in the sorbents and the mine water were verified (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The concentrations of Mn and Cd in neutral mine water several times exceed their concentrations in sorbents.\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\u003eMetal content in sorbents and neutral mine drainage\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCopper\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eManganese\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eZinc\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eIron\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLead\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCadmium\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAluminium\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026micro;g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e/ \u0026micro;g.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026micro;g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e/ \u0026micro;g.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026micro;g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e/ \u0026micro;g.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026micro;g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e/ \u0026micro;g.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026micro;g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e/ \u0026micro;g.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026micro;g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e/ \u0026micro;g.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u0026micro;g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e/ \u0026micro;g.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBentonite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e106\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4121\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e25.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.068\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e8929\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eZeolite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e115\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e39.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5352\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e9.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.147\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e39375\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSDDS\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e415\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e182\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1348\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e19034\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e38.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e17335\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNeutral mine drainage\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e117\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3090\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6130\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8810\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3060\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 parameters of adsorption isotherms present the ability and conditions for the sorption of individual sorbents. The selected parameters are also used for mutual comparison between sorbents. These findings can then be confronted with the adsorption capacity of the monolayer q\u003csub\u003em\u003c/sub\u003e as seen in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\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 Freundlich and Langmuir adsorption isotherms for bentonite, zeolite, and sludge\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eAdsorbent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eDensity (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMetal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c7\" namest=\"c4\"\u003e \u003cp\u003eLangmuir\u0026acute;s parameters\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c10\" namest=\"c8\"\u003e \u003cp\u003eFreundlich\u0026acute;s parameters\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eq\u003csub\u003em\u003c/sub\u003e (mg.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eB\u003c/p\u003e \u003cp\u003e(dm\u003csup\u003e3\u003c/sup\u003e.mg\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 \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003ek\u003csub\u003ef\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eBentonite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003e1944.2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eCd\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.0542\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.1149\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.6905\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e0.6002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.3426\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.9747\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eMn\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.992\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.3240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.8190\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e1.3060\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.6330\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.9210\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eZeolite\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003e1456.5\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eCd\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1.4302\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-0.0127\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0776\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e0.0187\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.9888\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.9863\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eMn\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.3366\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.9908\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e0.2757\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e5.6818\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.9840\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eSDDS\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003e1194.1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eCd\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1450\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.4170\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.8485\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e0.0486\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.1268\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.9182\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eMn\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.2194\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.4034\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.8189\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e1.5014\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.6709\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.8260\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\u003eqm (mg.g-1) indicates the maximum monolayer adsorption capacity\u003c/p\u003e \u003cp\u003eB\u0026thinsp;=\u0026thinsp;equilibrium constant dependent on sorption energy\u003c/p\u003e \u003cp\u003ekf (mg.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u0026thinsp;=\u0026thinsp;adsorption capacity related constant\u003c/p\u003e \u003cp\u003en\u0026thinsp;=\u0026thinsp;empirical parameter expressing the adsorption intensity, which varies depending on the heterogeneity of the adsorbent\u003c/p\u003e \u003cp\u003eThe fitting of the Langmuir isotherm was carried out according to the above equations at time t\u003csub\u003e120\u003c/sub\u003e - the end of the experiment. We assumed that at the end of the experiment, after 120 min of sorption, the trends of the isotherm curves would reach a steady-state character, which would be indicative of a state of reaching equilibrium. In some cases, the fitting of the Langmuir isotherm at t\u003csub\u003e120\u003c/sub\u003e corresponded to a linear trend (e.g. bentonite - Mn; zeolite - Mn; sludge - both Cd and Mn. In other cases, the fitting of the isotherms at t120 resulted in very low R\u003csup\u003e2\u003c/sup\u003e, e.g. for Cd sorption using zeolite.\u003c/p\u003e \u003cp\u003eThe fitting of the Freundlich isotherm also took place at time t\u003csub\u003e120\u003c/sub\u003e - at the end of the sorption experiment. In this case, the R\u003csup\u003e2\u003c/sup\u003e refers to a more linear trend than was the case for the Langmuir adsorption isotherms. Also when fitting the Freundlich isotherms at time t\u003csub\u003e120\u003c/sub\u003e, some deviations in the real versus linearized values were observed. However, these deviations were much smaller than for the fitting of the Langmuir isotherms at time t\u003csub\u003e120\u003c/sub\u003e. In the case of Mn sorption, the highest value of adsorption capacity qm was observed when sludge was used. The bentonite level for Mn sorption reached a similar value, on the other hand, qm when zeolite was used was in the low range. The highest sorption intensity for Mn sorption was observed when zeolite was used. The sorption intensity for Mn sorption using bentonite and sludge was at similar levels.\u003c/p\u003e \u003cp\u003eThe maximum monolayer capacity for Cd sorption was generally maintained at low values for all three sorbents. The highest sorption intensity for Cd sorption was observed using dewatered excess sludge. Sorption intensities for Cd sorption using bentonite and zeolite reached similar levels. The equilibrium constant dependent on the sorption energy reached the highest values when excess dewatered sludge was used. The highest value of kf, which is also related to adsorption capacity, was observed to be the highest for Mn sorption using excess dewatered sludge.\u003c/p\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eMetal removal depending on contact time\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe adsorption efficiency greatly increases by increasing the time of contact between pollutants and adsorbent due to the increase of interaction time between active sites of chelation and metals. Normally, at the beginning of the adsorption, the removal efficiency occurs quickly and then increases gradually. This occurs because of the availability of the free active sites at initial adsorption that are gradually occupied with time by chelated metals (Tahoon et al., 2020). According to obtained data, we can conclude that the adsorption process is the most rapid between 30 and 90 minutes. After 120 minutes, equilibrium starts to occur in the solutions, probably due to the filling monolayer. This correlates with the results of Bhatti et al. (2015) that more than 50% of the total metal content in solution is adsorbed within the first 60 minutes of adsorption. Alexander et al. (2019) determined the adsorption intensity n at the level of 5.8. Compared with calcined bentonite, we determined a higher monolayer adsorption capacity by a factor of about 8. We see the reason as the fineness of the fraction that was used in our study.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eMetal removal depending on the initial concentration\u003c/h2\u003e \u003cp\u003eThe percentage of Mn removal was evaluated in the concentration range of 8\u0026ndash;22 mg.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and Cd removal in the concentration range approximately of 1\u0026ndash;5 mg.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe concentration-dependent decrease in Mn removal efficiency was similar to that observed with zeolite and bentonite. Sorption using sludge was approximately 60% higher compared to zeolite. This indicates that digested sludge is a better adsorbent for Mn removal than zeolite. The experiment did not confirm a direct dependence between the input concentration and the percentage of Cd removal efficiency. Therefore, it is necessary to experimentally determine the optimum level of input concentration and not rely on the application of a mathematical relationship (linear or otherwise). The results confirmed decreasing levels of Cd removal from increasing concentrations of this metal ion in the solution. However, the level of sorption is several times higher than that of using bentonite and zeolite. We can conclude that SDDS could be used as an effective low-cost sorbent for metal removal.\u003c/p\u003e \u003cp\u003eAlso, with increasing initial concentration of metal in solution metal removal efficiency slightly decreased. According to Tahoon et al. (2020) above a particular initial concentration, ions with an equal amount of adsorption locations are available, which therefore decreases their elimination adsorption capacity.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003ePradas et al. studied the sorption of cadmium using natural and activated bentonite. The maximum monolayer adsorption capacity q\u003csub\u003em\u003c/sub\u003e using natural bentonite reached 3.32 mg.g\u003csup\u003e− 1\u003c/sup\u003e and 4.54 mg.g\u003csup\u003e− 1\u003c/sup\u003e, respectively. The level of equilibrium constant b was at 1.61 and 1.86 dm\u003csup\u003e3\u003c/sup\u003e.mg\u003csup\u003e− 1\u003c/sup\u003e (Pradas et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). These values are much higher than ours – q\u003csub\u003em\u003c/sub\u003e 0.0542 mg.g\u003csup\u003e− 1\u003c/sup\u003e and b 0.1149. Alexander et al. (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) present the sorption capacity of natural bentonite at 1.4 and 2.4 for input Cd concentrations of 10 and 50 mg.dm\u003csup\u003e− 3\u003c/sup\u003e, respectively(Alexander et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Again, as in the previous case, a lower average value (by about 1 order of magnitude) was obtained by our experiment. The differences with the compared studies may be due to the length of the test or to the particular composition of the bentonite used.\u003c/p\u003e \u003cp\u003eUsing zeolite, Rao et al. (2006) determined Cd adsorption intensities of 4.382 and 3.690. The sorption intensity n in our study was approximately 1. Rao et al. performed their sorption at 30°C, which may have increased the sorption intensity. Therefore, one possible way to increase the sorption intensity may be to increase the temperature (within observed and controlled levels, of course). The Langmuir adsorption isotherm was found to be unsuitable for evaluating Cd sorption using zeolite. Therefore, it will not be considered in this study.\u003c/p\u003e \u003cp\u003eHu et al. (2012) tested Cd sorption on dewatered sludge from a wastewater treatment plant. By constructing the Langmuir isotherm, a q\u003csub\u003em\u003c/sub\u003e of 28.336 mg.g\u003csup\u003e− 1\u003c/sup\u003e was obtained. By treating the sludge, they achieved an improvement in q\u003csub\u003em\u003c/sub\u003e with the addition of 0.125 mol.l\u003csup\u003e− 1\u003c/sup\u003e NaOH; 0.25 mol.dm\u003csup\u003e− 3\u003c/sup\u003e NaOH; 2.5 mol.dm\u003csup\u003e− 3\u003c/sup\u003e NaOH; 7.5 mol.dm\u003csup\u003e− 3\u003c/sup\u003e NaOH q\u003csub\u003em\u003c/sub\u003e at the level of 85.232 mg.g\u003csup\u003e− 1\u003c/sup\u003e; 70.336 mg.g\u003csup\u003e− 1\u003c/sup\u003e; 86.128 mg.g\u003csup\u003e− 1\u003c/sup\u003e; 108.192 mg.g\u003csup\u003e− 1\u003c/sup\u003e. In our case, a much lower monolayer capacity (approximately 100-fold lower) was obtained. By Freundlich isotherm using sludge, Hu et al. (2012) achieved a sorption intensity n of 3.25 and an adsorption capacity K\u003csub\u003ef\u003c/sub\u003e of 28 mg.g\u003csup\u003e− 1\u003c/sup\u003e. The sorption intensity, in this case, was comparable to our experiments. In contrast, the sorption capacity K\u003csub\u003ef\u003c/sub\u003e was again incomparably lower compared to the study of Hu et al. (2012). We assume that the above differences were due to the heterogeneous composition of the sludge. Therefore, as we can see, the sorption properties are incomparable for different sludge types in terms of their chemistry.\u003c/p\u003e \u003cp\u003ePradas et al. using natural bentonite achieved % Cd removal of 99.3–100% (Pradas et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). By our sorption, much lower values were achieved. It should be justified that Pradas et al. heat-treated their bentonite to a temperature of 110°C. Furthermore, in Prads' study, sorption lasted 72 h, i.e. 36 times longer than in our case. At the same time, the concentration of added bentonite was 100 g.dm\u003csup\u003e− 3\u003c/sup\u003e in Pradas' study, which is 20 times higher than in our experiment. This indicates that adsorption time has no inconsiderable effect on the removal efficiency.\u003c/p\u003e \u003cp\u003eOur results indicate that SDDS could be a promising low-cost adsorbent for the removal of Mn and Cd from neutral mine drainage. Muhammad et al. (2015) have confirmed good removal efficiency (88.15%) when using a mixture of limestone, activated sludge, spent mushroom compost, and woodchips. However, the contact time should be 12 hours. Fuchida et al. (2020) have studied the removal of Mn and Cd in the subsurface limestone beds. They have confirmed that except from adsorption also microorganism activity of the manganese-oxidizing bacteria plays a crucial role in Cd and Mn removal. When thinking about cadmium and manganese removal we need to take into account not only the dosage of adsorbent but also contact time and the possibility of bacteria interference, which could strengthen removal efficiency.\u003c/p\u003e "},{"header":"Summary","content":"\u003cp\u003eBased on the tests performed, stabilized digested dewatered sludge appears as a good low-cost sorbent for Cd and Mn removal. However, when comparing with other studies, usually for effective removal longer contact time is needed, from 4–8 hours up to 72 hours. Differences in metal sorption may be due to different sorbent compositions or other test conditions (thermal and chemical pre-treatment of the sorbent). Mn sorption results using zeolite according to other studies are comparable to our results. Comparable sorption results were found for sorption using sludge compared to bentonite, and even better when using zeolite. Much higher levels of Cd sorption were achieved using sludge compared to using natural bentonite and zeolite. To improve the sorption, the sorbent dosage needs to be increased and at the same time, the contact time should be extended. As manganese-oxidizing bacteria could contribute to both Mn and Cd removal, in next study should be investigated if they are naturally occurring in mine drainage or digested sludge and how to support their activity for better heavy metals uptake.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSupplementary Information:\u0026nbsp;\u003c/strong\u003enot necessary\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u0026nbsp;\u003c/strong\u003eAll authors contributed to the study conception and design. Data collection, analysis, and writing the first draft were performed by Prepilkov\u0026aacute;, Mord\u0026aacute;čov\u0026aacute; and Schwarz \u0026nbsp;provided detailed comments and revised the previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding: \u0026nbsp;\u003c/strong\u003eThis work was supported by Comprehensive research of determinants for ensuring environmental health (ENVIHEALTH), ITMS 313011T721 supported by the Operational Programme Integrated Infrastructure (OPII) funded by the ERDF\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u0026nbsp;\u003c/strong\u003enot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval:\u0026nbsp;\u003c/strong\u003eThis article does not contain studies with human participants or animals by any of the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate:\u0026nbsp;\u003c/strong\u003eThis article does not contain studies with human participants.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish:\u0026nbsp;\u003c/strong\u003eAll authors of this study agree to publish this paper in Environmental Science and Pollution Research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e: The authors declare that they have no confict of interest.\u003c/p\u003e\n\u003ch2\u003eAcknowledgments\u003c/h2\u003e\n\u003cp\u003eThis publication is the result of the project implementation: Comprehensive research of determinants for ensuring environmental health (ENVIHEALTH), ITMS 313011T721 supported by the Operational Programme Integrated Infrastructure (OPII) funded by the ERDF.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAguiar, A.O., Duarte, R.A., Ladeira, A.C.Q.: The Application of MnO2 in the Removal of Manganese from Acid Mine Water. 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Sci. \u003cb\u003e473\u003c/b\u003e, 012143 (2020b). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1088/1755-1315/473/1/012143\u003c/span\u003e\u003cspan address=\"10.1088/1755-1315/473/1/012143\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"adsorption, cadmium, manganese, neutral mine drainage, stabilized digested dewatered sludge, heavy metal removal","lastPublishedDoi":"10.21203/rs.3.rs-3852913/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3852913/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"This study aimed to investigate the adsorption efficiency of Cd and Mn using natural sorbents - bentonite, zeolite and stabilized digested dewatered waste sludge. The main contributions of the scientific article are in adding to the scientific knowledge of the use of natural and waste sorbents in the removal of heavy metals from neutral mine effluents. Current studies mainly focus on metal removal by sorption using natural sorbents from acid mine drainage. Our study investigates sorption in neutral mine drainage. The maximum efficiency of Mn removal by bentonite at the end of the test was approximately 90%. The removal of Mn by zeolite was considerably lower - about 20% compared to the use of sludge - 80%. Based on the sorption efficiency, the sludge was suitable for sorption. Much higher levels of Cd sorption were achieved using sludge compared to using natural bentonite and zeolite. The main novelty of the work lies in the sorption of metals using dewatered digested sludge. Previous studies have focused on metal sorption using activated sludge. Another novelty of our scientific paper is the comparison of the sorption of this waste sorbent with natural sorbents.","manuscriptTitle":"Adsorption of Cd and Mn from neutral mine effluents using bentonite, zeolite, and stabilized dewatered sludge","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-23 06:04:51","doi":"10.21203/rs.3.rs-3852913/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"19ec8535-fca3-40a5-8717-da8533cdcdfd","owner":[],"postedDate":"January 23rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-02-19T16:15:40+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-23 06:04:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3852913","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3852913","identity":"rs-3852913","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}