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1.
In this research, the equilibrium sorption of Zn(II) and Cu(II) by kaolinite was explained using the Freundlich, Langmuir and Redlich–Peterson isotherms, via both linear and non-linear regression analyses. In the case of non-linear regression method, the best-fitting model was evaluated using six different error functions, namely coefficient of determination (r 2), hybrid fractional error function (HYBRID), Marquardt’s percent standard deviation (MPSD), average relative error (ARE), sum of the errors squared (SSE) and sum of the absolute errors (EABS). The examination of error estimation methods showed that the Langmuir model provides the best fit for the experimental equilibrium data for both linear and non-linear regression analyses. The SSE function was found to be a better option to minimize the error distribution between the experimental equilibrium data and predicted two-parameter isotherms. In the case of three-parameter isotherm, HYBRID was found to be the best error function to minimize the error distribution structure between experimental equilibrium data and theoretical isotherms. Non-linear method was found to be more appropriate method for estimating the isotherm parameters.  相似文献   

2.
Removal of dyes by low-cost adsorbents is an effective method in wastewater treatment. Iranian natural clays were determined to be effective adsorbents for removal of a basic dye (methylene blue) from aqueous solutions in batch processes. Characterizations of the clays were carried out by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis and field-emission scanning electron microscopy. Effects of the operational parameters such as adsorbent dosage, initial dye concentration, solution pH and temperature were investigated on the adsorption performance. Adsorption isotherms like Langmuir, Freundlich and Temkin were used to analyze the adsorption equilibrium data and Langmuir isotherm was the best fit. Adsorption kinetics was investigated by pseudo-first-order, pseudo-second-order and intraparticle diffusion models and the results showed that the adsorption system conforms well to the pseudo-second-order model. The thermodynamic parameters of adsorption (ΔS°, ΔH° and ΔG°) were obtained and showed that the adsorption processes were exothermic.  相似文献   

3.
Amorphous tin(VI) hydrogen phosphate (ATHP) was synthesized using the liquid phase precipitation method and served as an adsorbent to remove Pb(II), Cu(II), and Zn(II) from aqueous solutions. The ATHP was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption techniques. Adsorption properties were evaluated as a function of pH, reaction time, concentration of reactants, and salinity. Their equilibrium adsorption data were modeled using Freundlich, Langmuir, and Dubinin–Kaganer–Radushkevich isotherms, respectively. The results revealed that adsorption equilibrium reached within 180 min. ATHP indicated good adsorption even below the pHZPC, and best adsorption at pH 5 for Pb(II) and Cu(II) and at pH 5.5 for Zn(II) was observed. Equilibrium data fitted better to the Langmuir model for Pb(II) and Cu(II) and fitted better to the Freundlich model for Zn(II). The saturated adsorption capacities deduced from the Langmuir model were 2.425, 1.801, and 0.600 mmol/g for Cu(II), Pb(II), and Zn(II), respectively, indicating an adsorption affinity order of Cu > Pb > Zn. There is a negative correlation between the concentration of NaCl and adsorption capacity of ATHP, yet ATHP still exhibited excellent adsorption having an adsorption capacity of 19.35, 15.16, 6.425 mg/g when the concentration of NaCl was 0.6 mol/L. The free energy (E) was 12.33, 10.70, and 14.74 kJ/mol for Pb(II), Cu(II), and Zn(II), respectively. An adsorption mechanism based on ion exchange between heavy metal ions and H+ in the ATHP is proposed. Furthermore, the used ATHP was regenerated by HCl solution and the adsorbent was used repeatedly.  相似文献   

4.
Here, a novel one-dimensional composite of poly(m-phenylenediamine)s coating on filamentous Streptomyces was successfully constructed via a controllable polymerization reaction. The synthesized composites were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Their adsorption isotherm and kinetics for aqueous hexavalent chromium were also systematically examined. The results of scanning electron microscopy analysis indicated that the obtained composites based on Streptomyces were showed a uniform and stable one-dimensional morphology with distinct core–shell configuration. Moreover, the Langmuir isotherm model (R 2 > 0.96) and pseudo-second-order equation (R 2 = 0.9996) described well the equilibrium adsorption behavior and kinetics of hexavalent chromium adsorption by the composites. In addition, bath adsorption experiments demonstrated the highest adsorption capacity of hexavalent chromium by the composites reached 320.03 mg g?1 in an acid solution, which was 5.6 times as that of the pure Streptomyces filaments. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses suggested that the adsorption of hexavalent chromium by the composites possibly involved the protonation, redox, and chelation reactions. Therefore, a promising application of these composites in treating acid hexavalent chromium-contaminated wastewater is expectable.  相似文献   

5.
Acacia nilotica was used for the adsorption of Reactive Black 5 (RB5) dye from an aqueous solution. Both the raw and activated (with H3PO4) carbon forms of Acacia nilotica (RAN and ANAC, respectively) were used for comparison. Various parameters (including dye concentration, contact time, temperature, and pH) were optimized to obtain the maximum adsorption capacity. RAN and ANAC were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The maximum experimental adsorption capacities for RAN and ANAC were 34.79 and 41.01 mg g?1, respectively, which agreed with the maximum adsorption capacities predicted by the Langmuir, Freundlich, and Dubinin–Radushkevich equilibrium isotherm models. The adsorption data of ANAC showed a good fit to the isotherm models based on the coefficient of determination (R 2): Langmuir type II (R 2 = 0.99) > Freundlich (R 2 = 0.9853) > Dubinin–Radushkevich (R 2 = 0.9659). This result suggested monolayer adsorption of RB5 dye. The adsorption of RB5 dye followed pseudo-second-order kinetics. The RAN adsorbent reflected an exothermic reaction (enthalpy change, ΔH = ?0.006 kJ mol?1) and increased randomness (standard entropy change, ΔS = 0.038 kJ mol?1) at the solid–solution interface. In contrast, ANAC reflected both exothermic [?0.011 kJ mol?1 (303–313 K)] and endothermic [0.003 kJ mol?1 (313–323 K)] reactions. However, the ΔS value of ANAC was lower when the RB5 adsorption increased from 313 to 323 K. The negative values for the Gibbs free energy change at all temperatures indicated that the adsorption of RB5 dye onto RAN and ANAC was spontaneous in the forward direction.  相似文献   

6.
The use of agricultural wastes as biosorbents is gaining importance in bioremediation of heavy metal-polluted water and soils, due to their effectiveness and low cost. This work assesses the Cd, Pb and Cu adsorption capacity of the raw materials used in the production of substrates for mushroom production (Agaricus bisporus and Pleurotus ostreatus) and the spent mushroom composted (SMC), based on the functional groups of their organic carbon. The raw materials studied included agricultural wastes (wheat straw, wheat and rice poultry litter, grape pomace) and inorganic substances (gypsum and calcareous sand). Organic carbon from wastes and their composting products were characterized by CP-MAS 13C NMR. Langmuir adsorption isotherms of metals were plotted for each raw material, composting step, spent A. bisporus and P. ostreatus substrates and the final SMC. The maximum adsorption capacities of SMC were 40.43, 15.16 and 36.2 mg g?1 for Cd, Pb and Cu, respectively. The composting process modified the adsorption properties of raw materials because of the enhanced adsorption of Cd and Cu and decreased adsorption capacity of Pb. CP-MAS 13C NMR and potentiometric titration were used to identify the functional groups of the organic carbon responsible for the metal adsorption. The content of cellulose was correlated with Pb adsorption (p < 0.001), alkyl and carboxyl carbon with Cd adsorption (p < 0.001), and N-alkyl (p < 0.001) and carboxyl (p < 0.010) groups with Cu adsorption. These results are valuable to develop new biosorbents based on agricultural wastes and demonstrate the high potential of SMC to adsorb heavy metals from polluted environments.  相似文献   

7.
In this study, nickel ions adsorption from zinc ingot factory wastewater by brown algae (Sargassum glaucescens) and chitosan/polyvinyl alcohol nano-fiber membrane at continuous system was studied. The continuous process included a biosorption reactor and fixed-bed reactor that were optimized by predicting two batch steps with response surface modeling, based on the Box–Behnken in the novel approach. Nano-biosorbent characterized by scanning electron microscopy, Brunauer–Emmett–Teller and Fourier transform infrared spectrometer analysis. Maximum biosorption in this continuous system was at pH 6, biosorbent doses 8 g L?1 S. glaucescens and 0.48 g L?1 nano-fiber. The study of the reaction rate showed kinetic data best fitted by pseudo-first-order model with R 2 > 0.95 than pseudo-second-order and intraparticle diffusion models. Biosorption equilibrium data were performed using Langmuir isotherm and Freundlich isotherm, Langmuir isotherm fit better with equilibrium data.  相似文献   

8.
The adsorption behavior study of diethyl and dibutyl phthalates was investigated onto a new activated carbon prepared from an abundant biomass “Albizia julibrissin pods,” treated chemically by H3PO4. A series of experiments were conducted in a batch system to estimate the effect of operating conditions such as the adsorbent nature, the dose of adsorbent, the contact time, the initial concentration and the temperature on the adsorption efficiency. The optimum operating conditions were found to be 0.1 and 0.05 g of adsorbent for diethyl and dibutyl phthalates, respectively, at 30 min equilibrium time, 150 mg g?1 and 293 K. The adsorption isotherms for both phthalates were fit at different temperatures using the nonlinear regression of Langmuir, Freundlich, Dubinin–Radushkevich and Redlich–Peterson. The pseudo-first order, pseudo-second order by nonlinear regression and intraparticle diffusion models were used to describe the adsorption kinetic. The results show that the intraparticle diffusion model is not the limiting step governing the adsorption mechanism. The structural and textural characteristics of adsorbent surface were investigated. FTIR analysis of unloaded and phthalates-loaded adsorbent revealed that the aliphatic groups attached to phthalate esters are involved in adsorption mechanism.  相似文献   

9.
Novel bionanocomposites, S. cerevisiae–AgNPs, were synthesized by in situ formation of AgNPs on S. cerevisiae surface using fulvic acids as reductants under simulated sunlight. S. cerevisiae–AgNPs were characterized using UV–Vis spectroscopy, scanning electron microscope, transmission electron microscope and Fourier transform infrared spectroscopy. These analyses showed that AgNPs were distributed on the surface of S. cerevisiae. The application of S. cerevisiae–AgNPs in bacteria killing and heavy metal removal was studied. S. cerevisiae–AgNPs effectively inhibited the growth of E. coli with increasing concentrations of S. cerevisiae–AgNPs. E. coli was killed completely at high concentration S. cerevisiae–AgNPs (e.g., 100 or 200 µg mL?1). S. cerevisiae–AgNPs as excellent heavy metal absorbents also have been studied. Using Cd2+ as model heavy metal, batch experiments confirmed that the adsorption behavior fitted the Langmuir adsorption isotherms and the Cd2+ adsorption capacity of S. cerevisiae–AgNPs was 15.01 mg g?1. According to adsorption data, the kinetics of Cd2+ uptake by S. cerevisiae–AgNPs followed pseudo second-order kinetic model. Moreover, S. cerevisiae–AgNPs possessed ability of different heavy metals’ removal (e.g., Cr5+, As5+, Pb2+, Cu2+, Mn2+, Zn2+, Hg2+, Ni2+). The simulated contaminated water containing E. coli, Cd2+ and Pb2+ was treated using S. cerevisiae–AgNPs. The results indicated that the bionanocomposites can be used to develop antibacterial agents and bioremediation agents for water treatment.  相似文献   

10.
In this research, the stems of Onopordom Heteracanthom which is a kind of weed were converted to biochar particles, and their characteristics were investigated. The morphology and purity of these particles were examined by SEM and EDX techniques, respectively. Specific surface area was obtained as 5.73 m2 g?1 by BET method. The biochar particles obtained from Onopordom Heteracanthom were evaluated as an adsorbent to remove Cr(VI) from aqueous environments. The effect of some parameters such as initial concentration of Cr(VI), dosage of adsorbent, and pH were investigated on the adsorption capacity of Cr(VI) onto the adsorbent. The equilibrium data were analyzed by various isotherm models. The results revealed that in this process, the adsorption isotherm and kinetics have more conformity with Langmuir isotherm and pseudo-second-order kinetics, respectively. The multi-linearity of the Weber and Morris adsorption kinetic model indicates that the intra-particle diffusion is not merely the rate-controlling step for the whole adsorption process.  相似文献   

11.
In the present experimental study, solid waste was used as an adsorbent and the effectiveness of the adsorbent was increased by novel treatment methods. Red mud, acid-treated activated red mud and iron oxide-coated acid-treated activated red mud were used for the removal of lead (II). The structural and functional groups were identified to confirm the removal of lead (II) by powder X-ray diffraction and Fourier transform infrared spectroscopy analyses. The enhancement of surface area was confirmed by Brunauer–Emmett–Teller analysis. Batch adsorption experiment was also conducted, and various parameters such as the effect of adsorbent dosage, pH, contact time and initial ion concentration were analyzed and reported. Adsorption equilibrium data were investigated using Langmuir, Freundlich and Dubinin–Radushkevich isotherm models with three parameters, and the rate of reaction was examined through kinetic models. The results indicate that in particular a novel modified form of red mud, namely iron oxide-coated acid-treated activated red mud was well fitted in lead (II) removal compared with reported adsorbents. The Langmuir isotherm shows that the maximum adsorption of adsorbate per gram was greater than other adsorbents (27.02 mg/g). In Freundlich isotherm, the Freundlich constant n values lie between 1 and 10 indicate the favorable adsorption. The calculated n values for normal red mud, acid-treated activated red mud and iron oxide-coated acid-treated activated red mud were found to be 1.9, 2.1 and 2.0 respectively. The correlation coefficient value was higher and the rate of reaction follows the pseudo-second-order kinetic model.  相似文献   

12.
Copper Adsorption by Chernozem Soils and Parent Rocks in Southern Russia   总被引：1，自引：0，他引：1  
Laboratory data in Cu2+ adsorption by chernozems and parent rocks in Rostov region show that adsorption isotherms can be approximated by the Langmuir equation, whose parameters (Kl and C∞) were calculated for all of the samples. The values of C∞ show a strong negative correlation with the values of cationexchange capacity (CEC) (r =–0.88 at Р = 0.95), and Kl is correlated with the content of physical clay (particles <0.01 mm) (r = 0.78) and with clay (particles <0.001 mm) content in ordinary chernozem and southern chernozems of various particle size distribution (r = 0.80). Even stronger correlations were detected between these parameters in southern chernozems (r = 0.89 for the physical clay (PC) and r = 0.91 for the silt). However, none of the samples displays a significant correlation of C∞ and Kl with the contents of physical clay and silt. This led us to conclude that the composition of the samples, for example, their organic matter, can affect Cu2+ adsorption by the soils and parent rocks. Acidification mechanisms of the equilibrium solutions during the Cu2+ adsorption by soils are discussed, as also are the reasons for the absence of balance between Cu2+ adsorbed by soils and exchangeable cations transferred into solution. Analysis of the fine structures of the XANES and EXAFS spectra suggests that Cu2+ can form coordinated chelate complex compounds with humic acids (HA) of soils and can substitute Al3+ at octahedral sites when interacting with clay minerals in soils.  相似文献   

13.
The alumina impregnated by the di-2-ethyl hexyl phosphoric acid was introduced to make more adsorption of strontium as well as to determine the optimal conditions. The influence of various parameters such as pH, equilibrium time, adsorbent mass, interfering ions, and various eluant agents for the desorption of the strontium ions, initial concentration, and temperature was investigated to find out the adsorption behavior of the adsorbent under different conditions. The adsorbent was characterized by the Fourier transform infrared spectroscopy. The experimental data were fitted on the two-parameter and three-parameter adsorption isotherm models. The Freundlich and Redlich–Peterson models have suitable fitting on the experimental data (R 2 = 0.9307). The kinetic models of adsorption were analyzed by the pseudo-first- and pseudo-second-order models. The results have been indicated that the pseudo-second-order kinetic model is more appropriate than the others. Advantages of our method were simple operation, less time for preparation of adsorbent, rapid phase separation, and capability to combine with various detection techniques. The method has been utilized to extract and the recovery of strontium ions in environmental aqueous samples.  相似文献   

14.
This work aimed to investigate the adsorption characteristics, both kinetically and thermodynamically, of Cu(II) and Pb(II) removal from aqueous solutions onto mixed-waste activated carbon, as well as to study the competitive behavior found in mixed heavy metal solution systems. This study shows that activated carbon prepared from mixed waste is an effective adsorbent for the removal of Cu(II) and Pb(II) from aqueous solutions, with the aim of detoxifying industrial effluents before their safe disposal onto water surfaces. The adsorption process was characterized in terms of kinetic and thermodynamic studies. In addition, the influence of presence of Cu(II) and Pb(II) in a competitive system was investigated. The results showed that the maximum adsorption capacities were gained at a pH of 6 with a contact time of 180 min, a metal solution concentration of 300 ppm, and an adsorbent dose of 0.3 g/L. The adsorption process was found to follow a pseudo-first-order kinetic model. Thermodynamic parameters such as ΔG o, ΔH o, and ΔS o showed that the sorption process was spontaneous and endothermic in nature. A competitive study demonstrated the applicability of mixed-waste activated carbon to adsorb Cu(II) and Pb(II) from a solution of mixed metals. In addition, the adsorption capacity was found to be as effective as other adsorbents reported in the literature. The developed adsorptive removal procedure was applied for treatment of real wastewater samples and showed high removal efficiency.  相似文献   

15.
In this study, teff (Eragrostis tef) straw has been chemically treated and tested as an adsorbent for Cr(VI) removal. Chemically treatment of teff straw was done by NaOH, H3PO4 and ZnCl2 solutions. Scanning electron micrograph and X-ray diffraction were used for anatomical characterization, whereas Fourier transform infrared spectroscopy was used for surface change characterization of adsorbents. Effects of different experimental parameters like pH (2–12), initial Cr(VI) concentration (100–900 mg/L), adsorbent dose (2.5–20 g/L), contact time (15–360 min) and temperature (288–318 K) were studied. Temperature increment was found to stimulate the adsorption process. Langmuir isotherm was found to give better representation over wide range of temperature for untreated, H3PO4- as well as ZnCl2-treated teff straw, and Freundlich isotherm best represented the isotherm data for NaOH-treated teff straw. Maximum Cr(VI) adsorption capacity of untreated, NaOH-, H3PO4- and ZnCl2-treated teff straw was found to be 86.1, 73.8, 89.3 and 88.9 mg/g, respectively. Respective values of average effective diffusion coefficient (D e) were found to be 2.8 × 10?13, 2.59 × 10?14, 1.32 × 10?13 and 1.14 × 10?13 m2/s, respectively. The negative value of ΔG o for all the adsorbents indicates Cr(VI) spontaneous adsorption. Isosteric heat of adsorption (ΔH st,a) was found to vary with surface coverage (θ). ΔH st,a increased for untreated, H3PO4- and ZnCl2-treated teff straw, and decreased steadily with θ for NaOH-treated teff straw.  相似文献   

16.
Mine residue and leachate were sampled from an acid mine drainage site near Arroyo San Pedro, which is one of the oldest abandoned mine districts in San Luis Potosi, Mexico, and characterized by X-ray diffraction and inductively coupled plasma-optical emission spectroscopy, confirming the presence of Fe, As, and SO4 2?. To address this problem, chitosan network (net-CS) and chitosan network-N-vinylcaprolactam/N–N-dimethylacrylamide (net-CS)-g-NVCL/DMAAm hydrogels were synthesized and used as adsorbents of the different ions present in the aforementioned leachate by batch equilibrium procedure. Kinetics, isotherms, and ions dissolved in leachate were evaluated. The gels showed the highest adsorption capacity for As and Fe ions. The adsorption capacity of the net-CS hydrogels for As (V) and Fe(III) was 0.786 and 76.85 mg/g, respectively, attained after 50 h. The surface of the hydrogels was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy, before and after the adsorption process, where the presence of a bond between the hydrogels and heavy metals ions, which is commonly observed in organic groups, was observed. In addition, Freundlich and Langmuir adsorption isotherms constants were determined for the As and Fe ions, and it was found that the Freundlich isotherm, with a first-order pseudo model, better fitted the adsorption process, indicating heterogeneous sorption, and the retention process occurred by chemisorption. The results from the Geochemist´s Workbench (GWB) software program revealed that arsenates, such as H3AsO4, H2AsO4 ?, as well as Fe++, FeSO4(aq) and FeOH+ were the common aqueous species found in the leachate at pH = 2.9.  相似文献   

17.
Graphene oxide nanosheets were synthesized by electrochemical exfoliation. X-ray diffraction, scanning electron microscopy, atomic force microscopy, Raman spectrometry and Fourier transform infrared spectrometry were used to characterize crystal structure, particle size, thickness and function groups of the nanosheets. The nanosheets were examined for adsorption of methyl orange, an anionic dye, in aqueous solution at different pHs and temperatures. The maximum adsorption capacity of methyl orange on graphene oxide nanosheets obtained from the Langmuir isotherm was 138.69 mg/g at pH 2.0, which is larger than that of other carbonaceous adsorbents. The large adsorption affinity of graphene oxide nanosheets to methyl orange might be due to the presence of hydrogen bonding and π–π interaction between methyl orange and graphene oxide nanosheets. Adsorption kinetics followed a pseudo-second-order kinetic model, and the isotherm adsorption results were fitted with Langmuir isotherm model in a monolayer adsorption manner. The thermodynamic studies indicated that the adsorption reaction was a spontaneous physisorption process.  相似文献   

18.
The purpose of this study is to quantify the magnitudes of surface conduction and pore water conduction from the measured electrical conductivity of kaolinite, with the ultimate goal of estimating the electrical conductivity of kaolinite with a wide range of pore water conductivities (σ w = 0.013–3.356 S/m) and porosities (n = 0.368–1.0). Therefore, the theoretical background of the electrical conductivity in soils was reviewed, and electrical conductivity measurements on kaolinite were performed using both slurry and consolidation tests in this study. The results of this study demonstrate that the variations of measured electrical conductivity (σ mix) with n are debatable according to the values of σ w, because a decrease in n results in both an increase in surface conduction (K s) and a decrease in pore water conduction (K w); this causes the relative magnitude of K s compared to that of K w to vary with σ w and n. Consequently, this study develops the relation between the porosity-normalized K s/K w and 1/σ w. Additionally, the surface conductivity of the tested kaolinite is back-calculated and compared with the previous relationship between K s and zeta potential of kaolinite. The measured and estimated σ mix values are compared with the varying pore water conductivity and porosity values.  相似文献   

19.
The biosorption characteristics of Cd(II) and Cu(II) ions from aqueous solutions obtained using submerged aquatic plant (Myriophyllum spicatum) biomass were investigated in terms of equilibrium, kinetics, thermodynamics, and cation competition. Langmuir and Freundlich models were applied to describe the biosorption isotherm of metal ions by M. spicatum biomass and isotherm constants considering the most important parameter, pH. The variation of sorption isotherm constants showed pH dependence. The Langmuir and Freundlich models fitted the equilibrium data well. The maximum biosorption capacity (q m) of M. spicatum biomass was determined to be 29.07 mg/g for the Cd(II) ion at pH 5.0 and 12.12 mg/g for the Cu(II) ion at pH 6.0. Chi square analysis showed that the Freundlich model fitted the equilibrium data better than the Langmuir isotherm. Competition of Cd(II) and Cu(II) in a binary solution showed that the Langmuir monolayer capacity of Cd(II) decreased from 29.07 mg/g with only Cd(II) in solution to 12.02 mg/g in the presence of Cu(II). Kinetics results showed that the biosorption processes of both metal ions followed the pseudo-second-order kinetics well. The calculated thermodynamic parameters (?G 0, ?H 0, and ?S 0) showed that biosorption of Cd(II) and Cu(II) ions onto M. spicatum biomass was feasible, spontaneous, and endothermic in nature. Fourier transform infrared spectroscopy spectrum analysis revealed that Cd(II) and Cu(II) sorption was mainly ascribed to carboxyl, hydroxyl, amine, and C–N groups in M. spicatum.  相似文献   

20.
Proton binding constants for the edge and basal surface sites of kaolinite were determined by batch titration experiments at 25 °C in the presence of 0.1 M, 0.01 M and 0.001 M solutions of NaNO3 and in the pH range 3-9. By optimizing the results of the titration experiments, the ratio of the edge sites to the basal surface sites was found to be 6:1. The adsorption of Cd(II), Cu(II), Ni(II), Zn(II) and Pb(II) onto kaolinite suspensions was investigated using batch adsorption experiments and results suggested that in the lower pH range the metallic cations were bound through non-specific ion exchange reactions on the permanently charged basal surface sites (X−). Adsorption on these sites was greatly affected by ionic strength. With increasing pH, the variable charged edge sites (SOH) became the major adsorption sites and inner-sphere specifically adsorbed monodentate complexes were believed to be formed. The effect of ionic strength on the extent of adsorption of the metals on the variable charged edge sites was much less than those on the permanently charged sites. Two binding constants, log K(X2Me) and log K(SOMe), were calculated by optimizing these constants in the computer program FITEQL. A model combining non-specific ion exchange reactions and inner-sphere specific surface complexations was developed to predict the adsorption of heavy metals onto kaolinite in the studied pH range. Linear free energy relationships were found between the edge site binding constants and the first hydrolysis constants of the metals.  相似文献   

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