Adsorption of Divalent Lead on a Montmorillonite−Illite Type of Clay

The Study of Optimal Adsorption Conditions of Phosphate on Fe-Modified Biochar by Response Surface Methodology

A batch of Fe-modified biochars MS (for soybean straw), MR (for rape straw), and MP (for peanut shell) were prepared by impregnating biochars pyrolyzed from three different raw biomass materials, i.e., peanut shell, soybean straw, and rape straw, with FeCl₃ solution in different Fe/C impregnation ratios (0, 0.112, 0.224, 0.448, 0.560, 0.672, and 0.896) in this research. Their characteristics (pH, porosities, surface morphologies, crystal structures, and interfacial chemical behaviors) and phosphate adsorption capacities and mechanisms were evaluated. The optimization of their phosphate removal efficiency (Y%) was analyzed using the response surface method. Our results indicated that MR, MP, and MS showed their best phosphate adsorption capacity at Fe/C ratios of 0.672, 0.672, and 0.560, respectively. Rapid phosphate removal was observed within the first few minutes and the equilibrium was attained by 12 h in all treatment. The optimal conditions for phosphorus removal were pH = 7.0, initial phosphate concentration = 132.64 mg L^-1, and ambient temperature = 25 °C, where the Y% values were 97.76, 90.23, and 86.23% of MS, MP, and MR, respectively. Among the three biochars, the maximum phosphate removal efficiency determined was 97.80%. The phosphate adsorption process of three modified biochars followed a pseudo-second-order adsorption kinetic model, indicating monolayer adsorption based on electrostatic adsorption or ion exchange. Thus, this study clarified the mechanism of phosphate adsorption by three Fe-modified biochar composites, which present as low-cost soil conditioners for rapid and sustainable phosphate removal.

Enhancing the remarkable adsorption of Pb2+ in a series of sulfonic-functionalized Zr-based MOFs: a combined theoretical and experimental study for elucidating the adsorption mechanism

A series of Zr-based metal-organic frameworks was prepared via the solvothermal route using sulfonic-rich linkers for the efficient capture of Pb²⁺ ions from aqueous medium. The factors affecting adsorption such as the solution pH, adsorbent dosage, contact time, adsorption isotherms, and mechanism were studied. Consequently, the maximum adsorption capacity of Pb²⁺ on the acidified VNU-23 was determined to be 617.3 mg g^-1, which is much higher than that of previously reported adsorbents and MOF materials. Furthermore, the adsorption isotherms and kinetics of the Pb²⁺ ion are in good accordance with the Langmuir and pseudo-second-order kinetic model, suggesting that the uptake of Pb²⁺ is a chemisorption process. The reusability experiments demonstrated the facile recovery of the H⁺⊂VNU-23 material through immersion in an HNO₃ solution (pH = 3), where its Pb²⁺ adsorption efficiency still remained at about 90% of the initial uptake over seven cycles. Remarkably, the adsorption mechanism was elucidated through a combined theoretical and experimental investigation. Accordingly, the Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy connected to energy-dispersive X-ray mapping (SEM-EDX-mapping), and X-ray photoelectron spectroscopy (XPS) analysis of the Pb⊂VNU-23 sample and comparison with H⁺⊂VNU-23 confirmed that the electrostatic interaction occurs via the interaction between the SO₃^- moieties in the framework and the Pb²⁺ ion, leading to the formation of a Pb-O bond. In addition, the density functional theory (DFT) calculations showed the effective affinity of the MOF adsorbent toward the Pb²⁺ ion via the strong driving force mentioned in the experimental studies. Thus, these findings illustrate that H⁺⊂VNU-23 can be employed as a potential adsorbent to eliminate Pb²⁺ ions from wastewater.

Ethylenediaminetetraacetate functionalized MgFe layered double hydroxide/biochar composites for highly efficient adsorptive removal of lead ions from aqueous solutions

The application of layered double hydroxides (LDHs) of MgFe and its composites with biochar of Eucalyptus camdulensis (Eb) and ethylenediaminetetraacetic acid (EDTA) was explored in a batch study to mitigate toxic lead ions (Pb²⁺) from synthetic wastewater solutions. SEM images revealed that MgFe/LDH composites with Eb were successfully formed, while FTIR spectra confirmed the successful adsorption of Pb²⁺ onto the MgFe/LDH and composite adsorbents. Batch equilibrium was attained after 60 min, then the adsorption capacity gradually increased. An increase in adsorption capacity (and a 60% decrease in the percentage removal) was observed by increasing the initial Pb²⁺ concentration, and the highest value was 136 mg g^-1 for MgFe/LDH-Eb_EDTA. A 50–60% increase in both the adsorption capacities and percent removal was seen in the pH range of 2–6. The second-order kinetic model had a nearly perfect fitting, suggesting that chemisorption was the mechanism controlling adsorption. The Langmuir isotherm model best presented the adsorption data, suggesting that the Pb²⁺ adsorption was monolayer, and predicted a better affinity between the adsorbent surface and absorbed Pb²⁺ for MgFe/LDH-Eb_EDTA in comparison to the other two adsorbents. The D–R isotherm suggested that the adsorption system was physical based on E values for all three adsorbents, while the Temkin isotherm model suggested that Pb²⁺ adsorption was heterogeneous. Finally, the Sips and R–P isotherms predicted that the adsorption of Pb²⁺ on the surface of the adsorbents was homogeneous and heterogeneous.

Adsorption characteristics of Pb(II), Cd(II) and Cu(II) on carbon nanotube-hydroxyapatite

Based on batch experiments, we investigate the adsorption characteristics of Pb(II), Cd(II) and Cu(II) on multi-walled carbon nanotube-hydroxyapatite (MWCNT-HAP) composites in detail and explore the effects of the solid-to-liquid ratio, pH, the ionic strength, reaction time and temperature on adsorption. The results show that the adsorption on MWCNT-HAP follows Pb(II)>Cu(II)>Cd(II). With an increasing solid-to-liquid ratio, the adsorption quantity of Pb(II), Cd(II) and Cu(II) on MWCNT-HAP decreases, whereas the removal efficiency increases. The optimal pH for adsorption is 4.0∼6.0. The effect of the ionic strength on the adsorption of Cd(II) is pronounced, whereas that on the adsorption of Pb(II) and Cu(II) is small. In the single-component system and ternary-component system, the adsorption processes for Pb(II), Cd(II) and Cu(II) on MWCNT-HAP have fast kinetics, and the pseudo-second-order kinetics model can well describe the adsorption kinetics of the three heavy metals. The adsorption of Pb(II), Cd(II) and Cu(II) on MWCNT-HAP is spontaneous and endothermic, and the Langmuir model can well simulate the isothermal adsorption of Pb(II) and Cu(II), whereas the Langmuir and Freundlich models can be used to describe the isothermal adsorption of Cd(II).

Anionic polyacrylamide influence on the lead(II) ion accumulation in soil - the study on montmorillonite

PURPOSE

Polymeric substances, as soil conditioners, limit the erosion process as well as improve the soil structure. The same macromolecular compounds may influence the heavy metal accumulation in soil environment. The main aim of this study was investigation of anionic polyacrylamide (AN PAM) effect on the lead(II) ion sorption on the montmorillonite surface. The effects of Pb(II) ion concentration, sequence of heavy metal and anionic polymer addition into the system as well as anionic group content in the PAM macromolecules were also studied.

MATERIALS AND METHODS

The study was performed on montmorillonite (clay mineral). Two types of polymers were used: AN PAM 5% and AN PAM 30% containing 5% and 30% of carboxylic groups, respectively. The adsorbed amounts of Pb(II) ions or AN PAM on the solid were determined spectrophotometrically. Electrokinetic properties of the examined systems were established using potentiometric titration and microelectrophoresis method. The montmorillonite aggregation without and with selected substances was described based on the sedimentation study.

RESULTS

At pH 5 the Pb(II) adsorbed amount on montmorillonite equaled 0.05 mg/m² (for the initial concentration 10 ppm). Anionic polyacrylamide increased this value significantly (it was 0.11 mg/m² with AN PAM 5% and 0.11 mg/m² with AN PAM 30%). The lead(II) ions presence causes a slight increase of the anionic PAM adsorption on the montmorillonite surface. For example, for the initial polymer concentration 100 ppm, the AN PAM 5% adsorbed amount without Pb(II) equaled 0.49 mg/m², whereas with Pb(II) - 0.57 mg/m². What is more, anionic polyacrylamide and lead(II) ions affected electrokinetic properties and stability of the montmorillonite suspension.

CONCLUSIONS

Anionic polyacrylamide makes the Pb(II) accumulation on the montmorillonite surface larger and, as a consequence, reduces the Pb(II) availability to organisms. Therefore, this macromolecular compound can certainly be used to remediate soils contaminated with heavy metals.

Nanoadsorbents for water and wastewater remediation

Water has a wide-ranging effect on all aspects of human life, such as health and food. However, the water has often become polluted by the waste of our industrial, agricultural, and day-to-day activities due to the impact of humans. Therefore, there is an urgent need for new technologies to remove the contaminants from water and wastewater. Thence, many ways and techniques have been developed for water and wastewater remediation. Among all the methods of water and wastewater remediation techniques, the adsorption process has gained tremendous importance as a suitable water and wastewater remediation. The application of nanoadsorbent materials is a growing solution to solving this environmental problem. The unique physical and chemical properties of nanoadsorbents enhance their application due to its higher in ranking, status, and quality and beneficial in different fields compared to traditional adsorbents. Recently, numerous studies reported that the nanosorbent materials have a great and quite promising effect on water and wastewater treatment such as carbon tube, polymeric, zeolites, metal and metal oxides nanosorbents. Thus, the aim of this review article is to provide new data on the study and the improvement in this specific field, and to provide a version of the uses, benefits and restrictions of nanosorbents in water and wastewater remediation.

Adsorption characteristics of Barmer bentonite for hazardous waste containment application

Low hydraulic conductivity and high chemical immobilization are the two characteristics that make bentonite a mandatory construction material for hazardous waste containment applications. We performed a comprehensive batch sorption study on Barmer bentonite (BB), an exclusive construction clay mined in India, using lead (Pb²⁺) as a model contaminant. The maximum adsorption capacity of BB was obtained as 55 mg g^-1 at pH 5 and 27 ± 2℃. Adsorption was extremely rapid, with equilibrium attained <5 min for the BB. Increased adsorbent dosage resulted in higher Pb²⁺ percentage removal, while adsorption capacity decreased. Ionic strength, salt concentration, valency and ionic radius played a critical role in suppressing the adsorption of Pb²⁺. Clay fabric change was observed to be dispersed at low ionic strength and gradually attained aggregated face-to-face structures at high ionic strength. The simultaneous presence of other metals/salts strongly influenced Pb²⁺ removal by BB, while divalent salt exhibited high suppression of adsorptive reaction at low concentrations. Sorption isotherm and kinetic modeling results indicated the possibility of chemisorption of Pb²⁺ on BB. Based on the thermodynamic analysis, it was noted that Pb²⁺ adsorption on BB is exothermic, spontaneous and adsorption reaction is less favorable at a higher temperature.

Zerovalent nickel nanoparticles performance towards Cr(VI) adsorption in polluted water

Heavy metals are one of the most common types of pollutants in ground water due to their wide sources, non-degradability and high toxicity. Many traditional wastewater treatments were not capable of removing enough such contaminants in order to meet quality standards. Nanosized zerovalent transition metals have emerged as a great candidate for ground water remediation, due to their simplicity and low fabrication cost, furthermore they can comply with simple chemical synthesis. Here, we present the synthesis of nano zerovalent nickel (nZVN) by a simple grinding reduction method. The obtained nZVN was characterized with XRD, SEM, EDS and BET surface area. The results confirms the formation of nZVN and the active particle cluster size ranges from 100 to 200 nm. N₂ adsorption isotherms revealed that the formation mesoporous cluster of nZVN with good surface area. The adsorption of Cr(VI) using nZVN showed 96% removal efficiency for 10 ppm concentration, and even up to 98% when the temperature is slightly raised to 36 °C (309 K). The removal efficiencies of Cr by zerovalent nickel was well fitted by the Langmuir-Hinshelwood first order reaction kinetic model with deceptive rate constant values of 0.6699, 0.7956 and 1.0251 min^-1 at temperature 200, 303 and 309 K, respectively. In total, our studies suggest that nanoscale zerovalent iron is a capable material for Cr(VI) remediation from groundwater.

Removal of Hazardous Contaminants from Water by Natural and Zwitterionic Surfactant-modified Clay

In this study, natural clay (NC) was collected from Saudi Arabia and modified by cocamidopropyl betaine (CAPB) at different conditions (CAPB concentration, reaction time, and reaction temperature). NC and modified clay (CAPB-NC) were characterized using X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and N2 adsorption at 77 K. The adsorption efficiency of NC and CAPB-NC toward Pb2+ and reactive yellow 160 dye (RY160) was evaluated. The adsorption process was optimized in terms of solution initial pH and adsorbent dosage. Finally, the adsorption kinetics and isotherms were studied. The results indicated that NC consists of agglomerated nonporous particles composed of quartz and kaolinite. CAPB modification reduced the specific surface area and introduced new functional groups by adsorbing on the NC surface. The concentration of CAPB affects the adsorption of RY160 tremendously; the optimum concentration was 2 times the cation exchange capacity of NC. The equilibrium adsorption capacity of CAPB-NC toward RY160 was about 6 times that of NC and was similar for Pb2+. The adsorption process followed the pseudo-second-order kinetics for both adsorptive. RY160 adsorption on CAPB-NC occurs via multilayer formation while Pb2+ adsorption on NC occurs via monolayer formation..

Highest and Fastest Removal Rate of PbII Ions through Rational Functionalized Decoration of a Metal-Organic Framework Cavity

To overcome the challenge of developing a multipurpose adsorbent for effective removal of toxic and carcinogenic Pb^II ions from aqueous solutions, a made-for-purpose functional group (N¹ ,N² -di(pyridine-4-yl)oxalamide) was rationally designed and incorporated into the cavities of a Zn metal-organic framework (MOF), namely, TMU-56. Large enough pore size along with high densities of strong metal chelating sites lead not only to the highest uptake capacity for Pb^II ions, but also the fastest removal rate that has ever been reported for functionalized MOFs, occurring in just 20 s. Moreover, high concentrations of lead ions favor the ion exchange reaction, resulting in a high degree of metal exchange. In addition, TMU-56 can be a practical adsorbent because of its notable performance in the simultaneous removal of several toxic and carcinogenic heavy metals from wastewater, which has rare precedence.

Crumpled graphene balls as rapid and efficient adsorbents for removal of copper ions

A novel, three-dimensional (3D), self-supporting material-the crumpled graphene ball-was developed using an aerosol capillary approach. The resultant crumpled-graphene-ball architecture showed a self-supporting, 3D network microstructure with plenty of ridges and wrinkles. Due to their unique structural characteristics, the 3D balls exhibited a rapid adsorption rate and superior adsorption capacity toward the copper ion (Cu²⁺). It was noted that the adsorption capacity for Cu²⁺ reached about 224.56 mg/g within 2 min. A high adsorption capacity, fast adsorption kinetics, excellent regeneration and reusability characteristics, and the ease of materials processing make these crumpled graphene balls ideal candidates for heavy metal ion decontamination in practical application.

Research on Lead (II) Adsorption Mechanism from Aqueous Solution by Calcium Carbonate Modified Diatomite Absorbent

In this study, calcium carbonate was used to coat and link the surface of diatomite for the formation of a novel modified adsorbent (referred to as Ca–diatomite). Various analytical techniques were used to characterize structure and mechanisms of modification and adsorption process, like Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD). Results showed that that Calcium carbonate had been successful grafted onto the surface of diatomite after modification, and Calcium carbonate modification improved the adsorption performance of diatomite for the removal of lead (II) ions from aqueous solution. Ca–diatomite adsorption isotherms and adsorption kinetics were also been studied. The adsorption isotherms and the kinetic data were best fitted with the Langmuir model and pseudo-second-order kinetics, respectively.

Lead and Chromium Adsorption from Water using L-Cysteine Functionalized Magnetite (Fe3O4) Nanoparticles

L-Cysteine functionalized magnetite nanoparticles (L-Cyst-Fe3O4 NPs) were synthesized by chemical co-precipitation using Fe2+ and Fe3+ as iron precursors, sodium hydroxide as a base and L-Cysteine as functionalized agent. The structural and morphological studies were carried out using X-ray powder diffraction, transmission electron microscopy, dynamic light scattering, scanning electron microscopy and energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and UV-Vis spectrophotometric techniques. The zeta potential of bare Fe3O4 and functionalized L-Cyst-Fe3O4 NPs were +28 mV and -30.2 mV (pH 7.0), respectively. The positive surface charge changes to negative imply the presence of L-Cyst monolayer at particle interface. Band gap energy of 2.12 eV [bare Fe3O4NPs] and 1.4 eV [L-Cyst-Fe3O4 NPs] were obtained. Lead and chromium removal were investigated at different initial pHs, contact time, temperatures and adsorbate-adsorbent concentrations. Maximum Cr6+ and Pb2+ removal occurred at pH 2.0 and 6.0, respectively. Sorption dynamics data were best described by pseudo-second order rate equation. Pb2+ and Cr6+ sorption equilibrium data were best fitted to Langmuir equation. Langmuir adsorption capacities of 18.8 mg/g (Pb2+) and 34.5 mg/g (Cr6+) at 45 °C were obtained. Regeneration of exhausted L-Cyst-Fe3O4 NPs and recovery of Pb2+/Cr6+ were demonstrated using 0.01 M HNO3 and NaOH. L-Cyst-Fe3O4 NPs stability and reusability were also demonstrated.

The effect of Paecilomyces catenlannulatus on removal of U(VI) by illite

The effect of Paecilomyces catenlannulatus (P. catenlannulatus) on removal of U(VI) onto illite as a function of contact time, pH, ionic strength, and solution concentration was conducted by batch techniques. The adsorption kinetics indicated that the removal of U(VI) on illite and illite coated P. catenlannulatus can be fitted by pseudo-second order kinetic model very well. The removal of U(VI) on illite and illite coated P. catenlannulatus increased with increasing pH from 1.0 to 7.0, whereas the decrease of U(VI) adsorption on illite and illite coated P. catenlannulatus was observed at pH > 7.5. The adsorption behavior of U(VI) on illite and illite coated P. catenlannulatus can be simulated by the double diffuse model under various pH conditions. The ionic strength-dependent experiments showed that the removal of U(VI) on illite was outer-sphere surface complexation, whereas the inner-sphere surface complexation predominated the U(VI) adsorption onto illite coated P. catenlannulatus at pH 5.0-7.0. The maximum adsorption capacity of U(VI) on illite and illite coated P. catenlannulatus calculated from Langmuir model at pH 5.0 and T = 298 K was 46.729 and 54.347 mg/g, respectively, revealing enhanced adsorption of U(VI) on illite coated P. catenlannulatus. This paper highlights the effect of microorganism on the removal of radionuclides from aqueous solutions in environmental pollution management.

Adsorption of metal ions by clays and inorganic solids

This review deals with adsorption of metal ions, particularly those considered as hazardous, on clays and some inorganic solids and covers the publication years 2000–2013 describing and quantifying the use of isotherms to obtain the adsorption capacities of the solids.

Adsorption of Pb(II) and Cd(II) from aqueous solutions using titanate nanotubes prepared via hydrothermal method

Titanate nanotubes (TNs) with specific surface areas of 272.31 m(2)g(-1) and pore volumes of 1.264 cm(3)g(-1) were synthesized by alkaline hydrothermal method. The TNs were investigated as adsorbents for the removal of Pb(II) and Cd(II) from aqueous solutions. The FT-IR analysis indicated that Pb(II) and Cd(II) adsorption were mainly ascribed to the hydroxyl groups in the TNs. Batch experiments were conducted by varying contact time, pH and adsorbent dosage. It was shown that the initial uptake of each metal ion was very fast in the first 5 min, and adsorption equilibrium was reached after 180 min. The adsorption of Pb(II) and Cd(II) were found to be maximum at pH in the range of 5.0-6.0. The adsorption kinetics of both metal ions followed the pseudo-second-order model. Equilibrium data were best fitted with the Langmuir isotherm model, and the maximum adsorption capacities of Pb(II) and Cd(II) were determined to be 520.83 and 238.61 mg g(-1), respectively. Moreover, more than 80% of Pb(II) and 85% of Cd(II) adsorbed onto TNs can be desorbed with 0.1M HCl after 3h. Thus, TNs were considered to be effective and promising materials for the removal of both Pb(II) and Cd(II) from wastewater.

Kinetics of adsorption of metal ions on inorganic materials: A review

It is necessary to establish the rate law of adsorbate-adsorbent interactions to understand the mechanism by which the solute accumulates on the surface of a solid and gets adsorbed to the surface. A number of theoretical models and equations are available for the purpose and the best fit of the experimental data to any of these models is interpreted as giving the appropriate kinetics for the adsorption process. There is a spate of publications during the last few years on adsorption of various metals and other contaminants on conventional and non-conventional adsorbents, and many have tried to work out the kinetics. This has resulted from the wide interest generated on using adsorption as a practical method for treating contaminated water. In this review, an attempt has been made to discuss the kinetics of adsorption of metal ions on inorganic solids on the basis of published reports. A variety of materials like clays and clay minerals, zeolites, silica gel, soil, activated alumina, inorganic polymer, inorganic oxides, fly ash, etc. have been considered as the adsorbents and cations and anions of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn as adsorbate have been covered in this review. The majority of the interactions have been divided into either pseudo first order or second order kinetics on the basis of the best fit obtained by various groups of workers, although second order kinetics has been found to be the most predominant one. The discussion under each category is carried out with respect to each type of metal ion separately. Application of models as given by the Elovich equation, intra-particle diffusion and liquid film diffusion has also been shown by many authors and these have also been reviewed. The time taken for attaining equilibrium in each case has been considered as a significant parameter and is discussed almost in all the cases. The values of the kinetic rate coefficients indicate the speed at which the metal ions adsorb on the materials and these are discussed in all available cases. The review aims to give a comprehensive picture on the studies of kinetics of adsorption during the last few years.

Adsorption of o-, m- and p-nitrophenols onto organically modified bentonites

Experiments were conducted on the adsorption characteristics of o-, m- and p-nitrophenols by organically modified bentonites at different temperatures. Two organobentonites (HDTMA-B and PEG-B) were synthesized using hexadecyltrimethylammonium bromide (HDTMABr) and poly(ethylene glycol) butyl ether (PEG). Synthesized HDTMA-B and PEG-B were characterized by XRD, FTIR and DTA-TG analyses and their specific surface area, particle size and pore size distributions were determined. BET surface areas and basal spacings (d(001)) of the HDTMA-B and PEG-B were found to be 38.71 m(2)g(-1), 69.04 m(2)g(-1) and 21.96 Å, 15.17 Å, respectively. Increased adsorption with temperature indicates that the process is endothermic for o-nitrophenol. On the other hand m- and p-nitrophenols exhibited lower rates of adsorption at higher temperatures suggesting a regular exothermic process taking place. Results were analyzed according to the Langmuir, Freundlich and Dubinin-Redushkevich (D-R) isotherm equations using linearized correlation coefficient at different temperatures. R(L) separation factors for Langmuir and the n values for Freundlich isotherms showed that m- and p-nitrophenols are favorably adsorbed by HDTMA-B and, p-nitrophenol is favored by PEG-B. Adsorption of o-, m- and p-nitrophenols as single components or from their binary mixtures on HDTMA-B and, p-nitrophenol on PEG-B are all defined to be physical in nature.

Impact of environmental conditions on the sorption behavior of Pb(II) in Na-bentonite suspensions

In this study, a local bentonite from Lin'an county (Zhejiang province, China) was converted to Na-purified form and the Na-bentonite sample was characterized by using FTIR and XRD to determine its chemical constituents and micro-structure. The removal of lead from wastewaters by Na-bentonite was studied as a function of various environmental parameters such as contact time, pH, ionic strength, foreign ions, humic substances and temperature under ambient conditions. The results indicated that the sorption of Pb(II) on Na-bentonite was strongly dependent on pH and ionic strength. The Langmuir, Freundlich and D-R models were used to simulate the sorption isotherms of Pb(II) at three different temperatures of 298, 318 and 338 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent sorption isotherms indicated that the sorption process of Pb(II) on Na-bentonite was endothermic and spontaneous. At low pH, the sorption of Pb(II) was dominated by outer-sphere surface complexation and ion exchange with Na(+)/H(+) on Na-bentonite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, it is possible to conclude that Na-bentonite has good potentialities for cost-effective disposal of lead bearing wastewaters.

Adsorption of Pb(II) ions from aqueous solution by native and activated bentonite: kinetic, equilibrium and thermodynamic study

In this study, the adsorption kinetics, equilibrium and thermodynamics of Pb(II) ions on native (NB) and acid activated (AAB) bentonites were examined. The specific surface areas, pore size and pore-size distributions of the samples were fully characterized. The adsorption efficiency of Pb(II) onto the NB and AAB was increased with increasing temperature. The kinetics of adsorption of Pb(II) ions was discussed using three kinetic models, the pseudo-first-order, the pseudo-second-order and the intra-particle diffusion model. The experimental data fitted very well the pseudo-second-order kinetic model. The initial sorption rate and the activation energy were also calculated. The activation energy of the sorption was calculated as 16.51 and 13.66 kJ mol(-1) for NB and AAB, respectively. Experimental results were also analysed by the Langmuir, Freundlich and Dubinin-Redushkevich (D-R) isotherm equations at different temperatures. R(L) separation factor for Langmuir and the n value for Freundlich isotherm show that Pb(II) ions are favorably adsorbed by NB and AAB. Thermodynamic quantities such as Gibbs free energy (DeltaG), the enthalpy (DeltaH) and the entropy change of sorption (DeltaS) were determined as about -5.06, 10.29 and 0.017 kJ mol(-1) K(-1), respectively for AAB. It was shown that the sorption processes were an endothermic reactions, controlled by physical mechanisms and spontaneously.