Adsorption of Pb(II) and Ni(II) From Aqueous Solution by a High-Capacity Industrial Sewage Sludge-Based Adsorbent

In the present study, adsorption of Ni(II) and Pb(II) from aqueous solution was investigated using activated carbon synthesized with industrial wastewater sludge. The synthesized adsorbent was analyzed using nitrogen adsorption–desorption and Fourier transfer infrared (FTIR) techniques. Batch adsorption mode was used to evaluate the effect of solution pH, contact time, adsorbent dose, initial metal ion concentration, and temperature on the adsorption capacity of the synthesized adsorbent. The kinetic data were analyzed using different kinetic models. The pseudo-second-order equation gave the best fit to the experimental data for both metal ions. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherm models. The results showed that the data obtained for the Ni(II) and Pb(II) adsorption are in good agreement with the Langmuir model. The Langmuir mono-layer maximum adsorption capacities for Ni(II) and Pb(II) ions were estimated to be 74.06 and 88.76 mg g^?1 at 25°C, respectively. In addition, the thermodynamic studies proved that the adsorption process of both metals could be considered endothermic.     

Highly efficient removal of toxic lead ions from aqueous solutions using a new magnetic metal‐organic framework nanocomposite

A magnetic metal‐organic framework (MOF) nanocomposite was successfully prepared by a new and green strategy through reasonable design. Magnetic MOF of Fe₃O₄‐NHSO₃H@HKUST‐1 nanocomposite use for removal of lead ions as an environmental pollutant. The experimental results indicated that the nano adsorbent of Fe₃O₄‐NHSO₃H@HKUST‐1 can removed lead ions under optimum operational conditions. The dosage of the nanocomposite, pH of the sample solution, and contact time were obtained to be 10 mg, 7.0, and 90 min, respectively, while the initial concentration of Pb(II) ions of 400 mg/L was used. A kinetic study indicated that a pseudo‐second‐order model agreed well with the experimental data. The isotherm experiments revealed that the Langmuir model attained better fits to the equilibrium data than the Freundlich model. The maximum adsorption capacity of the adsorbent for the removal of lead under the optimum operational conditions of pH 7.0 and temperature 25°C was found to be 384.6 mg/g. The thermodynamic parameters indicate that the adsorption of lead is spontaneous and endothermic. The magnetic MOF nanocomposite could be recovered easily and reused many times without significant loss of its nano‐adsorbent activity. The proposed method is simple, eco‐friendly, low cost, and efficient in the removal of lead ions from aqueous solutions.     

Adsorption of Pb(II) on a composite material prepared from polystyrene-alumina and activated carbon: Kinetic and thermodynamic studies

The ability of polystyrene-alumina-activated carbon composite as a synthetic adsorbent was investigated for the removal of Pb(II) ions from aqueous solutions. Various physico-chemical parameters such as pH, initial metal ion concentration, adsorbent dosage and contact time were studied. The optimum solution pH for the maximum adsorption of Pb(II) was found to be 4. Kinetic data were best described by pseudo-second-order model. The adsorption process followed both Langmuir and Freundlich adsorption isotherms at 30 °C. Thermodynamic studies indicated that the adsorption was spontaneous and endothermic in nature. Desorption studies were carried out by batch and column operations and it was found that 97% Pb(II) could be recovered by the column process using 0.1 M HCl as eluent.     

Sequestration of Aqueous Lead(II) Using Modified and Unmodified Red Onion Skin

The efficacy of onion skins, both unmodified and chemically modified with thioglycolic acid, was investigated as alternative low-cost adsorbents for the sequestration of aqueous lead(II) ions from aqueous solution. The adsorbents were characterised using Fourier transform infrared spectroscopy and scanning electron microscopy – energy dispersive X-ray spectroscopy. Adsorption experiments were performed using batch sorption processes. The effects of contact time, pH, initial Pb(II) concentration, adsorbent dose, and temperature were investigated. Optimum sorption conditions were found at pH 4 and a 150?min equilibrium time for the modified onion skin and unmodified onion skin. The Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models were used to characterize the equilibrium experimental results. The equilibrium process was best described by the Freundlich isotherm. The maximum adsorption capacities of 4.878 and 6.173?mg/g were obtained for modified and unmodified adsorbents, respectively, using the Langmuir model. Kinetic studies indicated that the sorption of Pb(II) ions followed a pseudo-second-order model. Thermodynamic parameters such as standard enthalpy change (ΔH°), entropy change (ΔS°), and free energy change (ΔG°) were evaluated from the sorption experimental measurements. The results showed that the sorption process of Pb(II) ions on unmodified and modified onion skins was feasible and exothermic under the conditions used in this study. The sorption process followed the mechanism of physisorption.     

Efficient Removal of Pb(II) from Aqueous Medium Using Chemically Modified Silica Monolith

The adsorptive removal of lead (II) from aqueous medium was carried out by chemically modified silica monolith particles. Porous silica monolith particles were prepared by the sol-gel method and their surface modification was carried out using trimethoxy silyl propyl urea (TSPU) to prepare inorganic–organic hybrid adsorbent. The resultant adsorbent was evaluated for the removal of lead (Pb) from aqueous medium. The effect of pH, adsorbent dose, metal ion concentration and adsorption time was determined. It was found that the optimum conditions for adsorption of lead (Pb) were pH 5, adsorbent dose of 0.4 g/L, Pb(II) ions concentration of 500 mg/L and adsorption time of 1 h. The adsorbent chemically modified SM was characterized by scanning electron microscopy (SEM), BET/BJH and thermo gravimetric analysis (TGA). The percent adsorption of Pb(II) onto chemically modified silica monolith particles was 98%. An isotherm study showed that the adsorption data of Pb(II) onto chemically modified SM was fully fitted with the Freundlich and Langmuir isotherm models. It was found from kinetic study that the adsorption of Pb(II) followed a pseudo second-order model. Moreover, thermodynamic study suggests that the adsorption of Pb(II) is spontaneous and exothermic. The adsorption capacity of chemically modified SM for Pb(II) ions was 792 mg/g which is quite high as compared to the traditional adsorbents. The adsorbent chemically modified SM was regenerated, used again three times for the adsorption of Pb(II) ions and it was found that the adsorption capacity of the regenerated adsorbent was only dropped by 7%. Due to high adsorption capacity chemically modified silica monolith particles could be used as an effective adsorbent for the removal of heavy metals from wastewater.     

Biosorption of lead from aqueous solution by seed powder of Strychnos potatorum L.

In the present study, Pb(II) removal efficiency of Strychnos potatorum seed powder (SPSP) from aqueous solution has been investigated. Batch mode adsorption experiments have been conducted by varying pH, contact time, adsorbent dose and Pb(II) concentration. Pb(II) removal was pH dependent and found to be maximum at pH 5.0. The maximum removal of Pb(II) was achieved within 360 min. The Lagergren first-order model was less applicable than pseudo-second-order reaction model. The equilibrium adsorption data was fitted to Langmuir and Freundlich adsorption isotherm models to evaluate the model parameters. Both models represented the experimental data satisfactorily. The monolayer adsorption capacities of SPSP as obtained from Langmuir isotherm was found to be 16.420 mg/g. The FTIR study revealed the presence of various functional groups which are responsible for the adsorption process.     

Adsorption of Cu(II) from aqueous phase by Cedar bark

The capability of Cedar bark (Cedrus atlantica Manetti) (CB) for the adsorption of Cu(II) from aqueous solutions was examined. Adsorption isotherm and kinetics of Cu(II) by CB were investigated through a number of batch adsorption experiments. The effect of experimental parameters such as initial Cu(II) concentration, adsorbent mass, initial pH and ionic strength on the removal of metal ions was examined. Equilibrium data were fitted to the Langmuir, Freundlich and Harkins–Jura isotherm models. Experimental equilibrium data were best represented by the Langmuir and Harkins–Jura isotherms. The findings revealed that the CB has the potential to be used as an adsorbent for the removal of heavy-metal ions from aqueous solutions.     

Preparation and characterization of nanocomposite,silica aerogel,activated carbon and its adsorption properties for Cd (II) ions from aqueous solution

A novel composite adsorbent, silica aerogel activated carbon was synthesized by sol-gel process at ambient pressure drying method. The composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Nitrogen adsorption/desorption isotherms (BET).In the present study, the mentioned adsorbent was used moderately for the removal of cadmium ions from aqueous solutions and was compared with two other adsorbents of cadmium, activated carbon and silica aerogel. The experiments of Cd adsorption by adsorbents were performed at different initial ion concentrations, pH of the solution, adsorption temperature, adsorbent dosage and contact time. Moreover, the optimum pH for the adsorption was found to be 6.0 with the corresponding adsorbent dosage level of 0.1 g at 60 °C temperature. Subsequently, the equilibrium was achieved for Cd with 120 min of contact time.Consequently, the results show that using this composite adsorbent could remove more than 60% of Cd under optimum experimental conditions. Langmuir and Freundlich isotherm model was applied to analyze the data, in which the adsorption equilibrium data were correlated well with the Freundlich isotherm model and the equilibrium adsorption capacity (q_e) was found to be 0.384 mg/g in the 3 mg/L solution of cadmium.     

Removal of Cd(II) and Pb(II) from aqueous solution by modified attapulgite clay

Three low-cost adsorbents (purified raw attapulgite (A-ATP), high-temperature-calcined attapulgite (T-ATP), and hydrothermal loading of MgO (MgO-ATP)) were prepared as adsorbents for the removal of Cd(II) and Pb(II). By evaluating the effect of the initial solution pH, contact time, initial solution concentration, temperature and coexistence of metal ions on Cd(II) and Pb(II) adsorption, the experimental results showed that MgO-ATP was successfully prepared by hydrothermal reaction and calcination as well as appearing to be a promising excellent adsorbent. At an initial pH of 5.0, A-ATP, T-ATP and MgO-ATP reached maximum adsorption amounts of 43.5, 53.9 and 127.6 mg/g for Pb(II) and 10.9, 11.2, and 25.3 mg/g for Cd(II) at 298 K, respectively. The Cd(II) adsorption on A-ATP was fitted by the Freundlich model, while the adsorption of Pb(II) and Cd(II) on T-ATP and MgO-ATP as well as Pb(II) adsorption on A-ATP agreed with the Langmuir model. All kinetic experimental data favored pseudo second-order model. The calculated thermodynamic parameters suggested that Pb(II) adsorption onto MgO-ATP was spontaneous and exothermic. When considering foreign metal ions, the three adsorbents all presented preferential adsorption for Pb (II). Chemical adsorption had a high contribution to the removal of Cd(II) and Pb(II) by modified attapulgite. In summary, the adsorption was greatly enhanced by the hydrothermal loading of MgO. It aimed to provide insights into the MgO-ATP, which could be able to efficiently remove Cd(II) and Pb(II) and serve as an economic and promising adsorbent for heavy metal-contaminated environmental remediation.     

Biosorption of Pb(II) and Cd(II) ions by Agave sisalana (sisal fiber)

The present work proposes the use of Agave sisalana (sisal fiber) as an natural adsorbent for ions Pb(II) and Cd(II) biosorption from natural waters. The flame atomic absorption spectrometry was used for quantitative determination and study of the ions Pb(II) and Cd(II) adsorption on the solid phase. The Fourier transform infrared spectroscopy (FT IR) was used to investigate the sisal structure and the specific BET surface area was analyzed. The biosorption potential of sisal as biosorbent for the removal of the ions Pb(II) and Cd(II) from aqueous solution was investigate considering the followings parameters: pH, biomass amount and contact time. Langmuir and Freundlich isotherms were used to evaluate adsorption behavior of the ions on this solid phase. The results showed that sisal has a surface area to adsorption of 0.0233 m² g^{− 1}, and the OH and CO functional groups are the main involved in the biosorption. The best interpretation for the experimental data was given by Freundlich isotherm that proposes a monolayer sorption with a heterogeneous energetic distribution of active sites, accompanied by interactions between sorbed molecules. The maximum monolayer biosorption capacity was found to be 1.85 mg g^{− 1} for Cd (II) and 1.34 mg g^{− 1} for Pb (II) at pH 7 and 296 K. This phase solid can be used for biosorption of cadmium and lead in polluted natural waters.     

Copper (II) adsorption from aqueous solution by herbaceous peat

In this research, the herbaceous peat collected from Gavurgolu peatlands, one of the biggest Turkish peatlands, was utilized as an adsorbent for the removal of copper (II) ions from aqueous solution. Adsorption experiments were conducted under various conditions, i.e., initial concentration, temperature, and pH. While the amount of Cu (II) adsorbed on the peat increased with increasing concentration of Cu (II) ions, it was not markedly affected by temperature and pH. Percentage removal was higher at lower concentration. For example, the maximum percentage removal of Cu (II) ions for initial concentration of 3 x 10(-4) M was 97.04% at 21 degrees C and pH 5.5. The adsorption capacity (Q(0)) of the peat was 4.84 mgg(-1) from Langmuir adsorption isotherm for the concentration range of 3 x 10(-4)-6 x 10(-4) M at 21 degrees C and pH 5.5. The equilibrium time of adsorption of Cu (II) ions was 150 min and independent of concentration and temperature. The amount of Cu (II) adsorbed at equilibrium time did not considerably change with temperature and pH. It was also determined that adsorption isotherm followed both Freundlich and Langmuir. Uptake mechanism of Cu (II) ions by the peat occurs via cation exchange (especially by means of Ca(2+) and Mg(2+)) as well as copper/peat complexation. Adsorption kinetic was consistent with the pseudo-second-order model.     

Enhancement of Cd2+ removal on CuMgAl-layered double hydroxide/montmorillonite nanocomposite: Kinetic,isotherm, and thermodynamic studies

In recent decades, great progress has been made in the application of adsorption processes to mitigate water pollution by hazardous metals. However, developing a highly efficient adsorbent is essential if the adsorption process is to be successfully applied in practical applications. In this study, a CuMgAl-layered double hydroxides/montmorillonite nanocomposite (CuMgAl-LDH/MMt) was prepared, characterized, and then used as a novel adsorbent for adsorption of Cd²⁺ ions from wastewater. The effects of initial pH, adsorbent dosage, agitation speed, particle size, contact time, initial Cd²⁺ concentration, and temperature on the pollutant removal efficiency were analyzed. An isotherm model reading revealed that the results of the experimental work were a good fit with the Freundlich model. The maximum adsorption capacity was reached at 174.87 mg/g under optimal conditions (pH 5, dosage of 0.02 g/l, agitation speed of 150 rpm, and particle size of 87 μm) at 50 ppm after 120 min of adsorption time. Kinetic studies showed that pseudo-second-order models were best fitted to the adsorption data, indicating heterogeneous adsorption of Cd²⁺ ions onto multilayer CuMgAl-LDH/MMt sites, and that the adsorption process is primarily chemical adsorption. Thermodynamic parameters (ΔS^o, ΔH^o, and ΔG^o) demonstrated that Cd²⁺ adsorption onto adsorbent was exothermic and spontaneous. Moreover, the synthesized adsorbent can be recovered after five consecutive cycles with a minimal reduction in the adsorption ability of 29.56 %. The study showed that specific heavy metals can be removed from aqueous solution by a newly prepared adsorbent due to its excellent morphology, high stability under a wide range of conditions, recyclability, and high adsorption capacity.     

Removal of heavy metal ions from water by using poly(ethyleneglycol dimethacrylate-co-acrylamide) beads

Poly(ethyleneglycol dimethacrylate-co-acrylamide) (poly(EDGMA-co-AAm)) copolymer beads have been prepared for use in the separation Pb(II), Hg(II), and Cd(II), metal ions in aqueous solution by a batch equilibration technique. Adsorption capacity were increased with pH for Pb(II), Cd(II) and Hg(II) and then reached almost plateau value around 6.0. The high initial rate of metal ions uptake (<10 min) suggests that the adsorption occurs mainly at the bead surface. The metal uptake results show that poly(EGDMA-co-AAm) can be used for the adsorption of the following metals in the indicated order: Pb(II) > Cd(II) > Hg(II) expressed on a molar basis. However, when the uptake was expressed in terms of the amount of metal removed from solution was as follows: Pb(II) > Hg(II) > Cd(II). The beads still showed preference toward Pb(II) when this metal was in a mixture with Hg(II) and Cd(II). A linearized form of the Freundlich and the Langmuir isotherm model fits the experimental equilibrium concentration data of Hg(II) and Cd(II) better than isotherm type model of Pb(II). The recovery of the metal ions after adsorption and the regeneration of the adsorbent can be carried out by treatment of the loaded beads with either 0.5 M NaCl, or 1 M HNO₃.     

Adsorption of Hazardous Azorhodanine Dye from an Aqueous Solution Using Rice Straw Fly Ash

The potential of using rice straw fly ash (RSFA) as low-cost adsorbents for the removal of hazardous azorhodanine (AR) dye from aqueous solution was investigated. The effects of different variables in the batch method as a function of solution pH, contact time, concentration of adsorbate, adsorbent dosage, and temperature were investigated, and optimal experimental conditions were ascertained: 0.05 g for initial dye concentration of 20–100 mg/L at pH 2. The experimental equilibrium data were tested by the isotherm models, namely the Langmuir and Freundlich adsorption and the isotherm constants were determined. The kinetic models, pseudo-first-order and pseudo-second-order, were employed to analyze the kinetic data. The activation energy of adsorption was also evaluated and found to be +10.89 kJ.mol^?1, indicating that the adsorption is physisorption. Various thermodynamic parameters, such as Gibbs free energy, entropy, and enthalpy of the ongoing adsorption process, have been calculated and found to be spontaneous and exothermic, respectively.     

Removal of Chromium(III) and Cadmium(II) Heavy Metal Ions from Aqueous Solutions Using Treated Date Seeds: An Eco-Friendly Method

The aim of the research was to prepare low-cost adsorbents, including raw date pits and chemically treated date pits, and to apply these materials to investigate the adsorption behavior of Cr(III) and Cd(II) ions from wastewater. The prepared materials were characterized using SEM, FT-IR and BET surface analysis techniques for investigating the surface morphology, particle size, pore size and surface functionalities of the materials. A series of adsorption processes was conducted in a batch system and optimized by investigating various parameters such as solution pH, contact time, initial metal concentrations and adsorbent dosage. The optimum pH for achieving maximum adsorption capacity was found to be approximately 7.8. The determination of metal ions was conducted using atomic adsorption spectrometry. The experimental results were fitted using isotherm Langmuir and Freundlich equations, and maximum monolayer adsorption capacities for Cr(III) and Cd(II) at 323 K were 1428.5 and 1302.0 mg/g (treated majdool date pits adsorbent) and 1228.5 and 1182.0 mg/g (treated sagai date pits adsorbent), respectively. It was found that the adsorption capacity of H₂O₂-treated date pits was higher than that of untreated DP. Recovery studies showed maximal metal elution with 0.1 M HCl for all the adsorbents. An 83.3–88.2% and 81.8–86.8% drop in Cr(III) and Cd(II) adsorption, respectively, were found after the five regeneration cycles. The results showed that the Langmuir model gave slightly better results than the Freundlich model for the untreated and treated date pits. Hence, the results demonstrated that the prepared materials could be a low-cost and eco-friendly choice for the remediation of Cr(III) and Cd(II) contaminants from an aqueous solution.     

Adsorption of some bivalent heavy metal ions from aqueous solutions by manganese nodule leached residues

The leached residue, generated after selective extraction of Cu, Ni, and Co in sulfur dioxide-ammonia leaching of manganese nodules, was characterized and batch isothermal adsorption experiments were conducted at ambient temperature to evaluate the effectiveness of the water-washed leached residue for removal of different bivalent metal ions from aqueous synthetic solutions. The effects of pH, initial metal ion concentrations, amount of adsorbent, interfering ions, and heat treatment were also investigated. The uptake of metal ions increased with increasing pH. Under identical conditions the adsorption capacity increased in the order Cd(2+)相似文献   

Integrated approaches for reducing sample size for measurements of trace elemental impurities in plutonium by ICP-OES and ICP-MS

A novel microsphere adsorbent based upon carboxymethyl cellulose sodium/prussian blue composite loaded with Lanthanum(III) (CMC/PB-La) was successfully synthesized via electrostatic ejection device for removal of cesium from contaminated water, and characterized by FT-IR, SEM, EDX and XPS. Influencing factors to adsorption cesium were investigated, including solution pH, adsorbent dosage, contact time, initial concentration, temperature and competing ions. Linear Freundlich isotherm was fitted satisfactorily to the adsorption data, and the adsorption kinetic data was fitted well with pseudo-second-order model. Moreover, the results of γ-irradiation experiments indicate that CMC/PB-La has good radiation stability.     

Chemically activated Ipomoea carnea as an adsorbent for the copper sorption from synthetic solutions

An indigenously prepared zinc chloride activated Ipomoea carnea (morning glory), a low-cost and abundant adsorbent, was used for removal of Cu(II) ions from aqueous solutions in a batch adsorption system. The chemical activating agent ZnCl₂ was dissolved in deionised water and then added to the adsorbent in two different ratios 1:1 and 1:0.5 adsorbent to activating agent ratio by weight. Studies were conducted as a function of contact time, initial metal concentration, dose of adsorbent, and pH. Activated Ipomoea carnea (AIC) were characterised using scanning electron microscopy (SEM), iodine number and methylene blue number. High iodine numbers indicates development of micro pores with zinc chloride activation. Maximum adsorption was noted within pH range 6.0(±0.05). Adsorption process is fast initially and reaches equilibrium after about 4 hours. The kinetic data were analysed using pseudo-first-order and pseudo-second-order models. The pseudo-second-order kinetic model was found to agree well with the experimental data. Adsorption equilibrium data were analyzed using Langmuir and Freundlich isotherm models. The Langmuir model represented the sorption process better than the Freundlich model. Based on the Langmuir isotherm, the monolayer adsorption capacity of Cu(II) ions was 7.855 mg?g^?1 for AIC (1:1) and 6.934 mg?g^?1 for AIC (1:0.5).     

Optimization of adsorption parameters for Fe (III) ions removal from aqueous solutions by transition metal oxide nanocomposite

Manganese oxide nanocomposite (Mn₂O₃/Mn₃O₄) was prepared by sol-gel technique and used as an adsorbent. Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FE-SEM) were used to characterize the adsorbent. The response surface methodology (RSM) was employed to evaluate the effects of solution pH, initial Fe (III) ions concentration, adsorbent weight, and contact time on the removal ratio of the Fe (III) ions. A total of 27 adsorption experimental runs were carried out employing the detailed conditions designed based on the Box-Behnken design (BBD). Results showed that the pH of the solution and initial Fe (III) ions concentration were the most significant parameters for Fe (III) ions removal. In process optimization, the maximal value of the removal ratio of Fe (III) was achieved as 95.80%. Moreover, the corresponding optimal parameters of adsorption process were as: contact time?=?62.5?min, initial Fe (III) concentration?=?50?mg/L, adsorbent weight?=?0.5?g, and pH?=?5. The experimental confirmation tests showed a strong correlation between the predicted and experimental responses (R²?=?0.9803). The fitness of equilibrium data to common isotherm equations such as Langmuir, Freundlich, and Temkin were also tested. The sorption isotherm of adsorbent was best described by the Langmuir model. The kinetic data were analyzed using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models. The adsorption kinetics of Fe (III) ions were well fitted with the pseudo-second-order kinetic model.     

Removal of Cd(II), Cu(II), and Pb(II) by adsorption onto natural clay: a kinetic and thermodynamic study

In this work, we study the elimination of three bivalent metal ions (Cd²⁺, Cu²⁺, and Pb²⁺) by adsorption onto natural illitic clay (AM) collected from Marrakech region in Morocco. The characterization of the adsorbent was carried out by X-ray fluorescence, Fourier transform infrared spectroscopy and X-ray diffraction. The influence of physicochemical parameters on the clay adsorption capacity for ions Cd²⁺, Cu²⁺, and Pb²⁺, namely the adsorbent dose, the contact time, the initial pH imposed on the aqueous solution, the initial concentration of the metal solution and the temperature, was studied. The adsorption process is evaluated by different kinetic models such as the pseudo-first-order, pseudo-second-order, and Elovich. The adsorption mechanism was determined by the use of adsorption isotherms such as Langmuir, Freundlich, and Temkin models. Experiments have shown that heavy metals adsorption kinetics onto clay follows the same order, the pseudo-second order. The isotherms of adsorption of metal cations by AM clay are satisfactorily described by the Langmuir model and the maximum adsorption capacities obtained from the natural clay, using the Langmuir isotherm model equation, are 5.25, 13.41, and 15.90 mg/g, respectively for Cd(II), Cu(II), and Pb(II) ions. Adsorption of heavy metals on clay is a spontaneous and endothermic process characterized by a disorder of the medium. The values of ΔH are greater than 40 kJ/mol, which means that the interactions between clay and heavy metals are chemical in nature.