Removal of Pb2+ and Cd2+ from drinking water using polysaccharide extract isolated from cactus pads (Opuntia ficus indica)

The use of a polysaccharide extract isolated from cactus pads (Opuntia ficus indica) as a low‐cost adsorbent for the removal of Pb²⁺ and Cd²⁺ from water was investigated. The Brunauer?Emmett?Teller study showed that the surface area of the extract powder was approximately 2.373 m²/g. Inductively coupled plasma optical emission spectrometry was used to monitor changes in ion concentrations during the adsorption. The adsorption mechanism was studied as a function of physicochemical variables such as initial metal ion concentration, adsorbent dosage, contact time, and pH of the solution. The results indicated that the adsorption percentage of the two cations increased with contact time, attaining equilibrium at 150 and 120 min for Cd²⁺ and Pb²⁺, respectively. At these optimal times, the adsorption capacity of Pb²⁺ and Cd²⁺ increased with increasing pH. Langmuir, Freundlich, Toth, Dubinin–Radushkevich, Sips, and Redlich–Peterson isotherm models were thereafter applied to understand the adsorption mechanism. The qe plot against C_e for the Toth isotherm model had the best fit with low error values and the highest correlation coefficient (R²) values of 0.9973 and 0.9953 for Pb²⁺ and Cd²⁺, respectively. Therefore, the isotherm study reveals that the adsorption mechanism involved is complex because of the presence of different interactions (such as ionic exchange and coagulation), yielding maximum adsorption capacities of 256 and 151 gm/L for Pb²⁺ and Cd²⁺, respectively. Generally, the polysaccharide extract exhibited higher adsorption capacity of Pb²⁺ than of Cd²⁺ under similar conditions. Besides the removal capacities reported in this study, the adsorbent regeneration and its reusability was also investigated. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43913.     

Comparative Study of Zn2+, Cd2+, and Pb2+ Removal From Water Solution Using Natural Clinoptilolitic Zeolite and Commercial Granulated Activated Carbon. Equilibrium of Adsorption

Abstract

The aim of this work is to study the effectiveness of regional, low-cost natural clinoptilolitic zeolite tuff in heavy metal ions removal from aqueous solution, through comparative study with commercial granulated activated carbon. The equilibrium of adsorption of Cd²⁺, Pb²⁺, and Zn²⁺ on both adsorbents have been determined at 25, 35, and 45°C in batch mode. The granulated activated carbon has shown around three times higher adsorption capacity for Cd²⁺ and Zn²⁺ than natural zeolite, and almost the same adsorption capacity for Pb²⁺ as the natural zeolite. The metal ion selectivity series Pb²⁺ > Cd²⁺ > Zn²⁺, on a mass basis, has been obtained on both adsorbents. The Langmuir and Freundlich model have been used to describe the adsorption equilibrium. The thermodynamic parameters were calculated from the adsorption isotherm data obtained at different temperatures. The study of the influence of the acidity of the metal ion aqueous solution has shown an increase of metal ion uptake with increase of the pH. The sorption mechanism of Cd²⁺, Pb²⁺, and Zn²⁺ on natural zeolite changes from ion-exchange to ion-exchange and adsorption of metal-hydroxide with increase of the pH from 2 to 6 (and 7 for Zn²⁺). The preliminary cost calculation, based on adsorbents maximum adsorption capacity and their price, have revealed the potential of natural zeolite as an economic alternative to the granulated activated carbon in the treatment of heavy metal polluted wastewater.     

Synthesis of magnetic Fe3O4@SiO2-(-NH2/-COOH) nanoparticles and their application for the removal of heavy metals from wastewater

In this work, Fe₃O₄@SiO₂-(-NH₂/-COOH) nanoparticles were synthesized for the removal of Cd²⁺, Pb²⁺ and Zn²⁺ ions from wastewater. The results of characterization showed that Fe₃O₄@SiO₂-(-NH₂/-COOH) was superparamagnetic with a core–shell structure. The surface of Fe3O4 was successfully coated with silica and modified with amino groups and carboxyl groups through the use of a silane coupling agent, polyacrylamide and polyacrylic acid. The dispersion of the particles was improved, and the surface area of the Fe3O4@SiO2-(-NH2/-COOH) nanoparticles was 67.8 m²/g. The capacity of Fe₃O₄@SiO₂-(-NH₂/-COOH) to adsorb the three heavy metals was in the order Pb²⁺ > Cd²⁺ > Zn²⁺, and the optimal adsorption conditions were an adsorption dose of 0.8 g/L, a temperature of 30°C and concentrations of Pb²⁺, Cd²⁺ and Zn²⁺ below 120, 80 and 20 mg/L, respectively. The maximum adsorption capacities for Pb²⁺, Cd²⁺ and Zn²⁺ were 166.67, 84.03 and 80.43 mg/g. The adsorption kinetics followed a pseudo-second-order model and Langmuir isotherm model adequately depicted the isotherm adsorption process. Thermodynamic analysis showed that the adsorption of the three metal ions was an endothermic process and that increasing the temperature was conducive to this adsorption.     

Investigation of synergistic adsorption between methyl orange and Cd(II) from binary mixtures on magnesium hydroxide modified clinoptilolite

The simultaneous removal of Methyl orange (MO) and Cd²⁺ (mainly from organo-metallic dyes) onto magnesium hydroxide modified clinoptilolite (MHMC) was described and compared to a single adsorbate situation. The adsorption performance was studied by batch experiments. The adsorption mechanism of MO and Cd²⁺ on MHMC was investigated. Langmuir and Dubinin-Raduskevich (D-R) isotherm successfully predicted the adsorption of MO and Cd²⁺ in single and binary systems. Maximum adsorption capacity calculated from Langmuir isotherm equation in single solution for MO and Cd²⁺ was 0.305 and 0.282mmol/g, respectively. In a binary system of MO/Cd²⁺, the adsorption capacity for both MO and Cd²⁺ was higher than in single solutions. The results indicated that the adsorption system of MO/Cd²⁺ presented a synergistic effect, not competitive adsorption, which suggested that MHMC can be used as an adsorbent for removal of dyes and heavy metal in the multi-solute system.     

Removal of Cd2+ ions from aqueous solution using cassava starch–based superabsorbent polymers

A comprehensive feasibility study on the adsorption of Cd²⁺ ions by cassava starch–based superabsorbent polymers (CST‐SAPs) as the biosorbent was investigated as a function of adsorbent dosage, pH, initial concentration, contact time, and temperature. An orthogonal experiment and range analysis were applied to optimize the adsorption conditions. Adsorbent dosage and initial concentration were the most sensitive variables for adsorption capacity. The maximum adsorption value of Cd²⁺ ions was determined as 347.46 mg/g at pH 6.0, initial concentration of 200 mg/L, and contact temperature and time of 323 K and 6 h, respectively, with 0.1 g adsorbent dosage. The equilibrium data were well described by a Langmuir model, and the adsorption process was well fitted by pseudo‐second‐order kinetics. The Fourier transform infrared spectroscopy (FTIR) data confirmed that acrylic acid and acrylic amide grafted onto the cassava starch. The X‐ray diffraction and FTIR results for the Cd²⁺‐absorbed CST‐SAP (CST‐SAP‐Cd²⁺) samples showed that the CST‐SAP could effectively adsorb Cd²⁺ ions and that the characteristic groups were translocated by chelation. The scanning electron microscopy results for the CST‐SAP revealed that the surface of the polymer was rough, and the layered structure that was full of folds caused an enhanced specific surface; such conditions were beneficial to Cd²⁺ ion adsorption. It was concluded that the CST‐SAP was an excellent adsorbent for Cd²⁺ ion removal from aqueous solution. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44758.     

Adsorption of Lead and Cadmium on Ca-Deficient Hydroxyapatite

A Ca-deficient hydroxyapatite(d-HAp) has been used to remove lead and cadmium from their mixed ions solution. The effect of pH, coexistent calcium and magnesium ions, and humic acid on the adsorption efficiency were investigated. The results showed that this d-HAp adsorbed both Cd²⁺ and Pb²⁺ efficiently within a wide pH range. The existence of humic acid reduced the removal efficiency of Cd²⁺ and Pb²⁺. The addition of Ca²⁺ and Mg²⁺ with a concentration of 500 mg/L only slightly reduced the removal efficiency. The adsorption kinetics was described by pseudo-second-order reaction model and the adsorption isotherm followed the Langmuir model.     

Functionalized nanostructured silica by tetradentate-amine chelating ligand as efficient heavy metals adsorbent : Applications to industrial effluent treatment

Organofunctionalized nanostructured silica SBA-15 with tri(2-aminoethyl)amine tetradentate-amine ligand was synthesized and applied as adsorbent for the removal of Cu²⁺, Pb²⁺, and Cd²⁺ from both synthetic wastewater and real paper mill and electroplating industrial effluents. The prepared materials were characterized by XRD, N₂ adsorption-desorption, TGA, and FT-IR analysis. The Tren-SBA-15 was found to be a fast adsorbent for heavy metal ions from single solution with affinity for Cu²⁺, Pb²⁺, than for Cd²⁺ due to the complicated impacts of metal ion electronegativity. The kinetic rate constant decreased with increasing metal ion concentration due to increasing of ion repulsion force. The equilibrium batch experimental data is well described by the Langmuir isotherm. The maximum adsorption capacity was 1.85 mmol g^?1 for Cu²⁺, 1.34 mmol g^?1 for Pb²⁺, and 1.08 mmol g^?1 for Cd²⁺ at the optimized adsorption conditions (pH=4, T=323 K, t=2 h, C₀=3 mmol L^?1, and adsorbent dose=1 g L^?1). All Gibbs energy was negative as expected for spontaneous interactions, and the positive entropic values from 103.7 to 138.7 J mol^?1 K^?1 also reinforced this favorable adsorption process in heterogeneous system. Experiment with real wastewaters showed that approximately a half fraction of the total amount of studied metal ions was removed within the first cycle of adsorption. Hence, desorption experiments were performed by 0.3M HCl eluent, and Tren-SBA-15 successfully reused for four adsorption/desorption cycles to complete removal of metal ions from real effluents. The regenerated Tren-SBA-15 displayed almost similar adsorption capacity of Cu²⁺, Pb²⁺, and Cd²⁺ even after four recycles. The results suggest that Tren-SBA-15 is a good candidate as an adsorbent in the removal of Cu²⁺, Pb²⁺, and Cd²⁺ from aqueous solutions.     

Application of non-fluorescent carbon particles as scavengers for heavy metal ions: A waste utilisation approach

In the preparation of fluorescent carbon nanoparticles, formation of non-fluorescent carbon particles (CPs) as waste matter is indispensible. This work is introducing CPs as adsorbents for some toxic metal ions in aqueous medium. CPs were characterised and their particle size, surface area, porosity, morphology etc. were compared with their parent material (charcoal). The effects of the initial metal ion concentration, contact time and pH on adsorption were undertaken. Adsorption data were evaluated for Langmuir and Freundlich isotherm models. The adsorption capacities (mg/g) of Ni²⁺, Pb²⁺, Zn²⁺, Co^2+, Cd²⁺ and Cu²⁺ were 85, 76, 75, 67, 58 and 46, respectively.     

L-cystein modified bentonite-cellulose nanocomposite (cellu/cys-bent) for adsorption of Cu2+, Pb2+, and Cd2+ ions from aqueous solution

In this study, L-cystein modified bentonite-cellulose (cellu/cys-bent) nanocomposite was synthesized and characterized by XRD, FTIR, SEM with EDS, TGA, and TEM techniques. In order to optimize the process the effect of various operational parameters such as pH, adsorbent dosage, contact time, and temperature were also investigated. The adsorption experiments were carried out in initial concentrations range of 20-100 mg L^?1and the adsorbent affinity for metal ions was found to be in order of Cu²⁺ > Pb²⁺ > Cd²⁺. The optimum pH for adsorption of Cu²⁺ and Cd²⁺ was observed at 5 while for Pb²⁺ it was pH 6. Based on the Langmuir model, the maximum adsorption capacity of Cu²⁺, Pb²⁺, and Cd²⁺ at 50^?C was found to be 32.36, 18.52, and 16.12 mg g^?1, respectively. The Langmuir isotherm and pseudo-second order model were found to be better fitted than the other isotherms and kinetic models. The results of thermodynamic parameters confirmed the process to be endothermic and spontaneous in nature.     

Synthesis of novel copper ion-selective material based on hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimethacrylate)

A novel hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimethacrylate) using a double-imprinting approach for the Cu²⁺ selective separation from aqueous medium was prepared. In the imprinting process, both Cu²⁺ ions and surfactant micelles (cetyltrimethylammonium bromide – CTAB) were employed as templates. The hierarchically imprinted organic polymer named (IIP-CTAB), single-imprinted (IIP-no CTAB) and non-imprinted (NIP-CTAB and NIP-no CTAB) polymers were characterized by SEM, FTIR, TG, elemental analysis and textural data from BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda). Compared to these materials, IIP-CTAB showed higher selectivity, specific surface area and adsorption capacity toward Cu²⁺ ions. Good selectivity for Cu²⁺ was obtained for the Cu²⁺/Cd²⁺, Cu²⁺/Zn²⁺ and Cu²⁺/Co²⁺ systems when IIP-CTAB was compared to the single-imprinted (IIP-no CTAB) and non double-imprinted polymer (NIP-CTAB), thereby confirming the improvement in the polymer selectivity due to double-imprinting effect. For adsorption kinetic data, the best fit was provided with the pseudo-second-order model for the four materials, thereby indicating the chemical nature of the Cu²⁺ adsorption process. Cu²⁺ adsorption under equilibrium was found to follow dual-site Langmuir–Freundlich model isotherm, thus suggesting the existence of adsorption sites with low and high binding energy on the adsorbent surface. From column experiments 600 adsorption–desorption cycles using 1.8 mol L⁻¹ HNO₃ as eluent confirmed the great recoverability of adsorbent. The synthesis approach here investigated has been found to be very attractive for the designing of organic ion imprinted polymer and can be expanded to the other polymers to improve performance of ion imprinted polymers in the field of solid phase extraction.     

Highly ordered macroporous γ-alumina prepared by a modified sol-gel method with a PMMA microsphere template for enhanced Pb2+, Ni2+ and Cd2+ removal

The adsorption performance of three-dimensionally ordered macroporous (3DOM) γ-alumina was investigated for enhanced Pb²⁺, Ni²⁺ and Cd²⁺ removal. The synthesis was based on a modified sol-gel method using a colloidal crystal template (CCT) method based on PMMA microspheres. The structure was characterized by means of FTIR spectroscopy and XRD analysis. The three-dimensional structure was examined by scanning electron microscopy, which enabled image analysis that showed significantly low shrinkage (8.77%) after calcination at 800 °C. The influential parameters, including contact time and adsorbent dosage, were investigated in a batch adsorption study. The adsorption equilibrium and kinetic data were found to be in agreement with the Freundlich isotherm for Pb²⁺ removal and the Dubinin-Radushkevich isotherm for Ni²⁺ and Cd²⁺ removal. The time-dependent adsorption was best described by a pseudo-second-order kinetic model and the Weber-Morris model. High adsorption capacities: 95.39, 23.32 and 25.39 mg/g were obtained for Pb²⁺, Cd²⁺ and Ni²⁺ removal at 45 °C, respectively. The existence of interconnected macroporous and mesoporous structures of highly ordered γ-alumina enabled a higher adsorption capacity in comparison with literature data for others alumina-based adsorbents.     

Adsorption from aqueous solution by δ-manganese dioxide II. Adsorption of some heavy metal cations

The adsorption isotherms of M²⁺ ions (M²⁺ = Ni²⁺, Co²⁺, Cd²⁺, Zn²⁺ and Mn²⁺) on the K⁺-form of δ-MnO₂, at pH 6 and at different temperatures, fitted the Langmuir equation and an apparent heat of adsorption, Q, was found to be - 78, - 33, - 34, - 19 and - 15 kJ mol^?1 respectively. The adsorption capacity of δ-MnO₂ increased in the series: Ni²⁺ < Co²⁺ < Cd²⁺ ± Zn²⁺ < Mn²⁺. This was nearly the order of decrease in the radii, r′, of the hydrated ions, estimated from hydration enthalpies. An ionexchange mechanism between hydrated K⁺ ions in the outer Helmholtz layer and hydrated M²⁺ ions in the solution, suggests positive entropy contributions which offset the endothermic Q. The proposed mechanism is in agreement with the observed sequence of adsorption capacity and with the decrease in Q in the above series, except for Co²⁺ adsorption (possibly complicated by the oxidation of Co²⁺ by δ-MnO²). The adsorption of the cations is probably accompanied by the exchange with Mn ions from the solid. There was evidence of specific adsorption below the point of zero charge (pH 3.3). The adsorption isotherms of Mn²⁺ ions at pH 7 were higher than those at pH 6 and Q was found to be - 19 kJ mol^?1. As the ionic strength increased, the adsorption isotherm of Mn²⁺ ions at pH 7 and 298 K shifted to lower values. Adsorption isotherms of Cu(II)ions at pH 3.5 and of Fe(III) at pH 2 represent specific adsorption and Q was found to be - 74 and - 13 kJ mol^?1 respectively.     

Adsorption of Pb2+ and Cd2+ onto a Novel Activated Carbon‐Chitosan Complex

A novel activated carbon‐chitosan complex adsorbent (ACCA) was prepared via the crosslinking of glutaraldehyde and activated carbon‐(NH₂‐protected) chitosan complex under microwave irradiation. The surface morphology of this adsorbent was characterized. The adsorption of ACCA for Pb²⁺ and Cd²⁺ was investigated. The results demonstrate that ACCA has higher adsorption capacity than chitosan. The adsorption follows pseudo first‐order kinetics. The isotherm adsorption equilibria are better described by Freundlich and Dubinin‐Radushkevich isotherms than by the Langmuir isotherm. The adsorbent can be recycled. These results have important implications for the design of low‐cost and effective adsorbents in the removal of heavy metal ions from wastewaters.     

One-step hydrothermal synthesis of a green NiCo-LDHs-rGO composite for the treatment of lead ion in aqueous solutions

Herein, we have synthesized a microspherical nickel-cobalt-layered double hydroxides-reduced graphene oxide composite (NiCo-LDHs-rGO) through a one-step hydrothermal method and then used it as an adsorbent for the removal of Pb²⁺ from aqueous solutions. Fourier transform infrared spectrophotometry (FT-IR), field emission scanning electron microscopy (FESEM), mapping elemental analysis, electron dispersive x-ray spectroscopy (EDX), x-ray diffraction analysis (XRD), and the Brunauer–Emmett–Teller (BET) method were used for the characterization of the adsorbent. Factors affecting the adsorption of Pb²⁺ ion such as solution pH, adsorbent dosage, contact time, competing ion, and regeneration were investigated in batch mode by the NiCo-LDHs-rGO. Under optimized conditions based on the Taguchi method (pH = 5.0, adsorbent dosage = 20 mg, and contact time = 30 min), the highest removal percentage was found to be 99.7% for 100 mg L⁻¹ of Pb²⁺. According to the results, NiCo-LDHs-rGO exhibited a high preference for Pb²⁺ over Cu²⁺, Zn²⁺, and Cd²⁺. This adsorbent was regenerated for several cycles (using 0.01 M HCl) with no significant deterioration in performance. Analyses of the adsorption isotherm models revealed that the adsorption of Pb²⁺ follows Freundlich isotherm with a maximum adsorption capacity of 200 mg g⁻¹. Also, the kinetic data confirmed that pseudo second order kinetic equation is the best model for predicting the kinetics. Furthermore, the Simulink modelling illustrated that the adsorption kinetics of Pb²⁺ onto NiCo-LDHs-rGO is done with high accuracy in a continuous stirred-tank reactor. Finally, dual interactions of the effective parameters can be modelled by polynomial equations in MATLAB, and according to the Taguchi model, pH is clearly the most important feature among all effective parameters.     

Novel magnetic polyamic hydrazide nanocomposite: Preparation,characterization, and application for the removal of cd2+ and pb2+ from industrial wastes

In this work, a novel polymer polyamic hydrazide (PAH) was synthesized via the reaction of terephthalohydrazide with pyromelitic dianhydride. The obtained PAH was characterized with nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT‐IR) spectroscopy and elemental analysis. Finally, a novel magnetic nanocomposite was prepared by immobilization of PAH on the Fe₃O₄ nanoparticles in water. The prepared magnetic nanocomposite was successfully used for selective removal of Pb²⁺ and Cd²⁺ ions from industrial wastes and the effects of affecting parameters on the adsorption capacity of the magnetic nanocomposite adsorbent for the removal of Pb²⁺ and Cd²⁺ from model aqueous solutions were investigated. The maximum adsorption capacities of Pb²⁺ and Cd²⁺ were found to be 138.9 and 103.1 mg g^?1, respectively. The kinetics and mechanism of the adsorption of Pb²⁺ and Cd²⁺ on the surface of the prepared nanocomposite were studied and it was found that complex formation between active sites of the surface of the nanocomposite and metal ions is the possible mechanism for adsorption of metal cations. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42538.     

Reusability and selective adsorption of Pb<Superscript>2+</Superscript> on chitosan/P(2-acrylamido-2-methyl-1-propanesulfonic acid-<Emphasis Type="Italic">co</Emphasis>-acrylic acid) hydrogel

Reusability and selective adsorption toward Pb²⁺ with the coexistence of Cd²⁺, Co²⁺, Cu²⁺ and Ni²⁺ ions on chitosan/P(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylic acid) [CS/P(AMPS-co-AA)] hydrogel, a multi-functionalized adsorbent containing –NH₂, –OH, –COOH and –SO₃H groups was studied. The CS/P(AMPS-co-AA) was prepared in aqueous solution by a simple one-step procedure using glow discharge electrolysis plasma technique. The reusability of adsorbent in HNO₃, EDTA-2Na and EDTA-4Na was investigated in detail. The competitive adsorption of the metal ions at the initial stage was compared between their equal mass concentration and equal molar concentration. In addition, the adsorption mechanism of the adsorbent for adsorption of Pb²⁺ was also analyzed by XPS. The results showed that the optimum pH of adsorption was 4.8, and time of adsorption equilibrium was about 180 min. Adsorption kinetics fitted well in the pseudo second-order model. The equilibrium adsorption capacities of Pb²⁺, Cd²⁺, Co²⁺, Cu²⁺, and Ni²⁺ at pH 4.8 were obtained as 673.3, 358.3, 176.7, 235.0 and 171.7 mg g^?1, in their given order. The adsorbent displayed an excellent reusability using 0.015 mol L^?1 EDTA-4Na solution as the eluent, and the desorption ratio could not correctly reflect the true characteristics of adsorption/desorption process. Moreover, the adsorbent showed good adsorption selectivity for Pb²⁺. The molar adsorption capacity at the initial stage with equal molar concentration was more reliable than the mass adsorption capacity during the study of selective adsorption. According to the XPS results, the adsorption of Pb²⁺ ions by the CS/P(AMPS-co-AA) absorbent could be attributed to the coordination between N atom and Pb²⁺ and ion-exchange between Na⁺ and Pb²⁺.     

Adsorption of heavy metals and methylene blue from aqueous solution with citric acid modified peach stone

Peach stones (PS) modified by citric acid (MPS) were used to remove heavy metals and methylene blue (MB) from wastewater. The effects of experimental factors such as pH, adsorbent dosage and contact time, etc. were conducted. Moreover, the adsorption kinetics and isotherm studies also were investigated. According to the Langmuir isotherm model, the maximum adsorption capacities of Pb²⁺, Cd²⁺, Cu²⁺ and MB were 118.76, 37.48, 32.22 and 178.25 mg/g, respectively. Finally, column experiments were also carried out to investigate the adsorption of Pb²⁺ and MB. All results indicated that PS has a good potential for the treatment of wastewater.     

Thiourea modified hyper‐crosslinked polystyrene resin for heavy metal ions removal from aqueous solutions

A hyper‐crosslinked resin chemically modified with thiourea (TM‐HPS) was synthesized, characterized, and evaluated for the removal of heavy metal ions (Pb²⁺, Cd²⁺, and Cu²⁺) from aqueous solutions. The structural characterization results showed that a few thiourea groups were grafted on the surface of the resin with a big BET surface area and a large number of narrow micropores. Various experimental conditions such as pH, contact time, temperature, and initial metal concentration of the three heavy metal ions onto TM‐HPS were investigated systematically. The results indicated that the prepared resin was effective for the removal of the heavy metal ions from aqueous solutions. The isotherm data could be better fitted by Langmuir model, yielding maximum adsorption capacities of 689.65, 432.90, and 290.69 mg/g for Pd²⁺, Cd²⁺, and Cu²⁺, respectively. And the adsorption kinetics of the three metal ions followed the pseudo‐second‐order equation. FTIR and XPS analysis of TM‐HPS before and after adsorption further revealed that the adsorption mechanism could be a synergistic effect between functional groups and metal ions and electrostatic attraction, which may provide a new insight into the design of highly effective adsorbents and their potential technological applications for the removal of heavy metal ions from aqueous solutions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45568.     

Modeling of cadmium(II) adsorption on kaolinite-based clays in the absence and presence of humic acid

Cadmium adsorption on kaolinite-based clays in the absence and presence of humic acid was modeled with the aid of the FITEQL 3.2 computer program using a modified Langmuir approach for capacity calculations. Formation of surface–metal ion and surface–humate–metal ion complexes was assumed using the DLM approach. As Cd(II) adsorption was ionic strength-dependent, the adsorption experiments were carried out in solutions containing two different concentrations of an inert electrolyte (0.1 M and 0.005 M NaClO₄). The surface sites responsible for the adsorption were assumed to be the permanent charges, ≡S₁OH silanol groups and carboxyl groups having pK_a values close to that of the silanol groups, and ≡S₂OH aluminol groups and phenol groups with pK_a values close to that of the aluminol groups, because the studied clays (partly composed of clay soil) contained organic carbon. Cd²⁺ ions were assumed to bind to the surface in the form of outer-sphere X₂²⁻ Cd²⁺ and inner-sphere ≡SOCd⁺ monodentate complexes. When humic acid was added, Cd(II) adsorption was modeled using a multi-site binding model by the aid of FITEQL3.2. The fit between model and experimental values was excellent in each case. Since the stability of the ternary surface complexes in the presence of humic acid was higher than that of the corresponding binary surface–cadmium ion complexes, the adsorption vs. pH curves were much steeper (and distinctly S-shaped) compared to the tailed curves observed in binary clay–cadmium ion systems. The clay mineral in the presence of humic acid probably behaved more like a chelating ion-exchanger for heavy metal ions than as a simple inorganic ion exchanger.     

Kinetics of zinc adsorption on charcoal

The kinetics of zinc adsorption on charcoal was carried out. In order to study the kinetics of adsorption various parameters were studied such as pH, particle size of charcoal, temperature, amount of charcoal as well as initial Zn²⁺ ion concentration. The adsorption kinetics followed a Freundlich adsorption isotherm. Good correlation of the theoretical and experimental equilibrium concentrations of Zn²⁺ ions was observed for the isotherm model. A mathematical model was developed to explain the kinetic data. The rate determining step for adsorption was found to be diffusion controlled.