Competitive Adsorption Of Heavy Metals Research Articles

Kinetics comparison on simultaneous and sequential competitive adsorption of heavy metals in red soils

To compare the adsorption kinetics of Cu, Zn and Cd introduced into red soils simultaneously and sequentially as well as their distribution coefficients, the ability of red soils to retain heavy metals was evaluated by performing batch experiments. The results indicate that Cu is preferentially adsorbed by red soils no matter in simultaneous or in sequential situation. The adsorption amount of Cd is the minimum in simultaneous competitive adsorption experiment. As heavy metals are added into red soils sequentially, the heavy metal adsorptions are relatively hard to reach equilibrium in 2 h. Red soils retain more Cd than Zn, which is opposite to the result in simultaneous adsorption. The addition sequences of heavy metals affect their adsorbed amounts in red soils to a certain extent. The joint distribution coefficients of metals in simultaneous adsorption are slightly higher than those in sequential adsorption.

Competitive adsorption of heavy metal by extracellular polymeric substances (EPS) extracted from sulfate reducing bacteria.

Competitive adsorption of heavy metals by extracellular polymeric substances (EPS) extracted from Desulfovibrio desulfuricans was investigated. Chemical analysis showed that different EPS compositions had different capacities for the adsorption of heavy metals which was investigated using Cu(2+) and Zn(2+). Batch adsorption tests indicated that EPS had a higher combined ability with Zn(2+) than Cu(2+). This was confirmed and explained by Fourier transform infrared (FTIR) and excitation-emission matrix (EEM) spectroscopy analysis. FTIR analysis showed that both polysaccharides and protein combined with Zn(2+) while only protein combined with Cu(2+). EEM spectra further revealed that tryptophan-like substances were the main compositions reacted with the heavy metals. Moreover, Zn(2+) had a higher fluorescence quenching ability than Cu(2+).

Experimental Study of Competitive Adsorption of Heavy Metals and Organic Matter for the Phosphoric Acid Purification

The program articulated around the experimental study of the effect of several parameters on the elimination of the cations: copper, cadmium and zinc, and the organic matter present in the phosphoric acid by using the bentonite, actived carbon and carbon of olives as supports, and on the other hand to show the effect of several parameters on this keeping back such as: the effect of the time (kinetic) of contact, speed of excitement, initial concentration of the pollutant, Solid report /liquid, the isotherms. At selected best parameters for better one capacity we calculated the capacity of purification for the different supports, the sawdust and the waste of cereal. The kinetic study of the keeping back of existing pollutants in the phosphoric acid is still presented.

Poly(hydroxyethyl methacrylate) nanobeads containing imidazole groups for removal of Cu(II) ions

Poly(hydroxyethyl methacrylate) (PHEMA) nanobeads with an average size of 300 nm in diameter and with a polydispersity index of 1.156 were produced by a surfactant free emulsion polymerization. Specific surface area of the PHEMA nanobeads was found to be 996 m 2/g. Imidazole containing 3-(2-imidazoline-1-yl)propyl(triethoxysilane) (IMEO) was used as a metal-chelating ligand. IMEO was covalently attached to the nanobeads. PHEMA-IMEO nanobeads were used for the removal of copper(II) ions from aqueous solutions. To evaluate the degree of IMEO loading, the PHEMA nanobeads were subjected to Si analysis by using flame atomizer atomic absorption spectrometer and it was estimated as 973 µmol IMEO/g of polymer. The PHEMA nanobeads were characterized by transmission electron microscopy and fourier transform infrared spectroscopy. Adsorption equilibrium was achieved in about 8 min. The adsorption of Cu 2+ ions onto the PHEMA nanobeads was negligible (0.2 mg/g). The IMEO attachment into the PHEMA nanobeads significantly increased the Cu 2+ adsorption capacity (58 mg/g). Adsorption capacity of the PHEMA-IMEO nanobeads increased significantly with increasing concentration. The adsorption of Cu 2+ ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing Cu +, Cd 2+, Pb 2+ and Hg 2+ was also investigated. The adsorption capacities are 61.4 mg/g (966.9 µmol/g) for Cu 2+; 180.5 mg/g (899.8 µmol/g) for Hg 2+; 34.9 mg/g (310.5 µmol/g) for Cd 2+ and 14.3 mg/g (69 µmol/g) for Pb 2+. The affinity order in molar basis is observed as Cu 2+ > Hg 2+ > Cd 2+ > Pb 2+. These results may be considered as an indication of higher specificity of the PHEMA-IMEO nanobeads for the Cu 2+ comparing to other ions. Consecutive adsorption and elution operations showed the feasibility of repeated use for PHEMA-IMEO nanobeads.

A New Competitive Adsorption Isothermal Model of Heavy Metals in Soils

Abstract A new competitive adsorption isothermal model (CAIM) was developed for the coexistent and competitive binding of heavy metals to the soil surface. This model extended the earlier adsorption isothermal models by considering more than one kind of ion adsorption on the soil surface. It was compared with the Langmuir model using different conditions, and it was found that CAIM, which was suitable for competitive ion adsorption at the soil solid-liquid surface, had more advantages than the Langmuir model. The new competitive adsorption isothermal model was used to fit the data of heavy metal (Zn and Cd) competitive adsorption by a yellow soil at two temperatures. The results showed that CAIM was appropriate for the competitive adsorption of heavy metals on the soil surface at different temperatures. The fitted parameters of CAIM had explicit physical meaning. The model allowed for the calculation of the standard molar Gibbs free energy change, the standard molar enthalpy change, and the standard molar entropy change of the competitive adsorption of the heavy metals, Zn and Cd, by the yellow soil at two temperatures using the thermodynamic equilibrium constants.

Competitive adsorption of heavy metals in soil underlying an infiltration facility installed in an urban area

Accumulation of heavy metals at elevated concentration and potential of considerable amount of the accumulated heavy metals to reach the soil system was observed from earlier studies in soakaways sediments within an infiltration facility in Tokyo, Japan. In order to understand the competitive adsorption behaviour of heavy metals Zn, Ni and Cu in soil, competitive batch adsorption experiments were carried out using single metal and binary metal combinations on soil samples representative of underlying soil and surface soil at the site. Speciation analysis of the adsorbed metals was carried out through BCR sequential extraction method. Among the metals, Cu was not affected by competition while Zn and Ni were affected by competition of coexisting metals. The parameters of fitted 'Freundlich' and 'Langmuir' isotherms indicated more intense competition in underlying soil compared to surface soil for adsorption of Zn and Ni. The speciation of adsorbed metals revealed less selectivity of Zn and Ni to soil organic matter, while dominance of organic bound fraction was observed for Cu, especially in organic rich surface soil. Compared to underlying soil, the surface soil is expected to provide greater adsorption to heavy metals as well as provide greater stability to adsorbed metals, especially for Cu.

Adsorption isotherms of copper, lead, nickel, and zinc in two Chilean soils in single- and multi-component systems: sewage sludge impact on the adsorption isotherms of Diguillin soil

The potential impact of the addition of sewage sludge from domestic waste water treatment plants on agricultural soils is a worldwide concern. A proportion of heavy metals in sewage sludge will be present in the soil solution; their equilibria can be modified by the competitive interactions between them, changing not only their mobility but also their adsorption pattern. The competitive adsorption of heavy metals by soils has been studied by several authors in simple model substrates and synthetic minerals, and also in soils but restricted to binary adsorption. In the present paper the modification of the Cu, Pb, Ni, and Zn interactions with soils as a consequence of a competitive adsorption on the available adsorption sites on Andisols were determined.The single- and multi-component adsorption of Cu, Pb, Ni, and Zn were carried out at constant ionic strength (0.1 m KNO3). The adsorption was monitored by ICP-OES and the Langmuir model was applied to fit the adsorption isotherms.Competitive adsorption isotherms indicate a reduction of the adsorption in the control soils when compared to the single adsorption isotherms. The maximum adsorption constants for single- and multi-component isotherms for Diguillín soil were 38.2 and 33.3 mmol/kg for Cu, 48.1 and 30.0 mmol/kg for Pb, 5.4 and 2.1 mmol/kg for Ni, and 18.0 and 8.1 mmol/kg for Zinc, respectively. With Ralun soil, lower values were obtained, but the same tendency was observed.The maximum adsorption and the affinity constant increased for all cations, after the addition of sewage sludge to Diguillin soil.

Competitive Adsorption of Heavy Metals in Humic Substances by a Simple Ligand Model

Proton and metal ion binding to humic acids has been recognized as an important factor in controlling metal speciation and mobility in aqueous and soil environments. The binding and competition behavior of humics has not been fully described, however, due to the polydisperse mixtures of natural organic polyelectrolytes with different functional groups. The simplified discrete binding group type of model (Model A) was used in this study. Model A was applied to describe three single metals and their competitive binding on the humic acids. Model A considers only a single carboxyl group type and a single phenolic hydroxyl group type with a variable electrostatic interaction factor that is expressed as a polynomial equation. Metal binding experiments were performed using a batch‐type dialysis equilibration method, and mass and charge balance expressions were used to calculate individual components of the system. The fit of Model A suggested that the major binding site for the three metal ions tested (Cd, Zn, and Cu) was a bidentate chelate of the carboxyl groups. Model A described two‐ and three‐metal competition on the humic acids using the intrinsic stability constant for the single metal ion. The model used in this study adequately described the competition of two metals; however, it showed weaknesses when applied to more complex systems, especially when metals with substantially different binding characteristics were present. Model A presented a better prediction with adjusted Cu concentration (2:1:1 Cu/Cd/Zn).

Monometal and competitive adsorption of heavy metals by sewage sludge-amended soil

Sewage sludge-amended soils may alter their ability to adsorb heavy metals over time, due to the decomposition of sludge-borne organic matter. Thus, we studied Cd, Ni, and Zn adsorption by a sewage sludge-amended soil (Typic Xerofluvent) before and after one-year incubation in both monometal and competitive systems. In the monometal system, the order of decreasing sorption was Zn>Cd>Ni. Competition significantly reduced metal K(d), especially that of Cd which decreased by nearly 50%. Over the course of the incubation there was a 31% reduction of soil organic matter content. At the same time, in competitive systems Cd K(d) significantly decreased, while Zn K(d) significantly increased, and Ni K(d) remained unaffected. This study shows that sewage sludge-amended soils may change in their ability to sorb heavy metals over time at high metal concentrations. The data suggest that Cd is likely to be of most environmental significance in such soils, since it exhibited decreased sorption under competitive conditions and as the organic matter content of the soil was reduced. The potential for long-term release of metals should be considered in the risk assessment associated with sewage sludge addition to soils, particularly in climates where degradation of organic matter is likely to be enhanced.

Alanine containing porous beads for mercury removal from artificial solutions

AbstractN‐methacryloyl‐(L)‐alanine (MALA) was synthesized by using methacryloyl chloride and alanine as a metal‐complexing ligand or comonomer. Spherical beads with an average diameter of 150–200 μm were obtained by suspension polymerization of MALA and 2‐hydroxyethyl methacrylate (HEMA) conducted in an aqueous dispersion medium. Poly(HEMA–MALA) beads were characterized by SEM, swelling studies, surface area measurement, and elemental analysis. Poly(HEMA–MALA) beads have a specific surface area of 68.5 m2/g. Poly(HEMA–MALA) beads with a swelling ratio of 63%, and containing 247 μmol MALA/g were used in the removal of Hg2+ from aqueous solutions. Adsorption equilibrium was achieved in about 60 min. The adsorption of Hg2+ ions onto PHEMA beads was negligible (0.3 mg/g). The MALA incorporation into the polymer structure significantly increased the mercury adsorption capacity (168 mg/g). Adsorption capacity of MALA containing beads increased significantly with pH. The adsorption of Hg2+ ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing Cd2+, Cu2+, Pb2+, and Hg2+ was also investigated. The adsorption capacities are 44.5 mg/g for Hg2+, 6.4 mg/g for Cd2+, 2.9 mg/g for Pb2+, and 2.0 mg/g for Cu2+ ions. These results may be considered as an indication of higher specificity of the poly(HEMA–MALA) beads for the Hg2+ comparing to other ions. Consecutive adsorption and elution operations showed the feasibility of repeated use for poly(HEMA–MALA) chelating beads. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1222–1228, 2006

Comment on 'Biosorption of Cadmium Using the Fungus Aspergillus niger.' by Barros, L.M., Macedo, G.R., Duarte, M.M.L., Silva, E.P. and Lobato, A.K.C.L.

In a recent publication Macedo et al. (2003), the section Results and Discussions, authors mentioned a pseudo-second-order Lagergren equation in Eq. (3). In fact, it is Ho (1995) who first developed a pseudo-second order kinetic expression for the adsorption systems of divalent metal ions using sphagnum moss peat. The earlier application of the pseudo-second order equation to the kinetic studies of competitive heavy metal adsorption by sphagnum moss peat was undertaken by Ho et al. (1996). The pseudo-second order rate expression of Ho has also been applied to the sorption of metal ions, dyes, and organic substances from aqueous solutions (Table 1). In addition, discussion of the reaction order has been reported such as the comparison of chemisorption kinetic models (Ho and McKay, 1998a) and pseudo-second order model (Ho and McKay, 1999a). Furthermore, Ho’s kinetic expression has also been applied to a multi-stage batch sorption design (Ho and McKay, 1999b) and a two-stage batch sorption optimized design (Ho and McKay, 1998b). Numerous applications of Ho’s kinetic expression have been reported in recent years. A list of pseudo-second order systems is given in Table 1. I suggest that Macedo et al. cite Ho’s original pseudo-second order kinetic expression paper.

Competitive adsorption of heavy metals and uranium on soil constituents and microorganism

Measurements were made of the adsorption of lead, cadmium, zinc, nickel and uranium per unit surface area of microorganisms, two clays (reference smectite, kaolinite), and two soils (untreated Vertisol and treated Vertisol) to quantify the selective affinity. The adsorption of heavy metals and uranium by the samples was influenced by soil constituents, and increased with increasing Pb, Ni, Zn, Cd and U concentrations. Microorganisms were also compared with these abiotic soil constituents for their ability to adsorb these metals. Dead cells adsorbed the largest quantity of all heavy metals than live cells and other soil components. At pH 6.0, the uptake percentage of U(VI) by dead cells was higher than that of any of the other metal ions. On the basis of amounts of adsorption on adsorbents, the selectivity sequences were varied. The most common sequences were U≫Pb>Cd≈Zn>Ni. The results verified the importance of geochemical parameters of soils such as type of clay mineral, oxide mineral content, and organic content, for controlling metal uptake. The results also suggest that bacterial membrane cells can be successfully used in the treatment of mixed metal-contaminated wastes.

The Competitive Adsorption of Heavy Metals under Various Incineration Conditions.

The main objective of this study is to investigate the competitive adsorption behavior of multiple components on sorbents (silica sand with limestone) at different operating conditions (temperature, additives of chloride, operating time). Moreover, the Toxicity Characteristic Leaching Process (TCLP) analyzed the leaching rates of metals from the spent sorbents.The results show that the adsorption capacities of Pb and Cd are better among those four metals on the sorbents. At 850°C, the adsorption of Pb and Cd can reach the adsorption saturation points. However, the adsorption amounts on the sorbents will increase as the operating temperature increases. X-ray powder diffract meter (XRD) analysis revealed the adsorption components on the sorbents had metal fusion formations. The TCLP tests show that the leaching rate of metals are significantly lower at 600°C, however, as the operating temperature increases (700°C and 850°C), the sorbents became more stable. At the same temperature, increasing the operating time on the incinerator shows a decreasing leaching rate on the sorbent. Adding PVC or NaCl will decrease the adsorption amounts of Pb and Cd, but increase the leaching rates of all metals on the sorbent. Competitive effects were analyzed by comparing single-component adsorption and multiple-component adsorption cases. The result shows that a multiple-component case has a better adsorption capacity than that of a single-component case.

Simultaneous competitive adsorption of heavy metals by the mineral matrix of tropical soils

Disposal of sewage sludge, composts and industrial wastes onto agricultural lands is commonly and increasingly used in Brazil, potentially adding multi-component heavy metal solutions. Soil organic matter was removed from representative Brazilian soils and the simultaneous competitive adsorption on the mineral matrix of Cr, Ni, Cu, Zn, Cd and Pb was determined. The competition affected the behavior of heavy metal cations in such a way that the soils adsorbed less Ni, Zn and Cd and more Cr, Cu and Pb with increasing total concentrations, regardless of the molar concentration applied. On the other hand, the occupancy of the adsorption complex by the heavy metals was proportional to the relative concentration applied. As the applied concentrations increased Cr, Cu and Pb adsorption increased, while Ni, Zn and Cd adsorption decreased. The maximum adsorption capacity for the heavy metal cations was calculated, with the soils differing markedly. Ultisol and Alfisol soils showed the highest maximum adsorption values, in the order of 50.76 and 64.52 mmol kg −1, whereas some Oxisols showed the lowest values, in the order of 23.92 and 30.86 mmol kg −1. The results suggest that the first two soil types are capable of receiving and holding higher heavy metal loadings compared to the Oxisols, which are more vulnerable to heavy metal contaminant inputs.

Metal-complexing ligand methacryloylamidocysteine containing polymer beads for Cd(II) removal

Different metal-complexing ligands carrying synthetic and natural adsorbents have been reported in the literature for heavy metal removal. We have developed a novel and new approach to obtain high metal adsorption capacity utilizing 2-methacryloylamidocysteine (MAC) as a metal-complexing ligand and/or comonomer. MAC was synthesized by using methacryloyl chloride and cysteine. Spherical beads with an average size of 150–200 μm were obtained by the radical suspension polymerization of MAC and 2-hydroxyethylmethacrylate (HEMA) conducted in an aqueous dispersion medium. Poly(2-hydroxyethylmethacrylate–methacryloylamidocysteine) p(HEMA–MAC) beads have a specific surface area of 18.9 m2 g−1. p(HEMA–MAC) beads were characterized by swelling studies, FTIR and elemental analysis. The p(HEMA–MAC) beads with a swelling ratio of 72%, and containing 3.9 mmol MAC g−1 were used in the removal of cadmium(II) ions from aqueous solutions. Adsorption equilibrium was achieved in about 15 min. The adsorption of Cd(II) ions onto pHEMA beads was negligible. The MAC incorporation significantly increased the Cd(II) adsorption capacity. Adsorption capacity of MAC incorporated beads increased significantly with pH. Competitive heavy metal adsorption from aqueous solutions containing Cd(II), Cr(III), Pb(II), Hg(II) and As(III) was also investigated. The adsorption capacities are 254 mg g−1 for Cd(II); 90.9 mg g−1 for Cr(III); 150.4 mg g−1 for Hg(II), 91.2 mg g−1 for Pb(II) and 6.7 mg g−1 for As(III) ions. These results are an indication of higher specificity of the p(HEMA–MAC) beads for the Cd(II) ions compared with other ions. Consecutive adsorption and desorption operations showed the feasibility of repeated use for p(HEMA–MAC) chelating beads.

Selectivity Sequence and Competitive Adsorption of Heavy Metals by Brazilian Soils

Heavy‐metal cations can be introduced into agricultural soils by application of fertilizers, liming materials, sewage sludge, composts, and other industrial and urban waste materials. Therefore, heavy‐metal adsorption reactions, in a competitive system, are important to determine heavy‐metal availability to plants and their mobility throughout the soil. This study was conducted to evaluate the selectivity sequence and estimate the competitive adsorption of several heavy metals in seven soils with different chemical and mineralogical characteristics. Distribution coefficients (Kd), which represent the sorption affinity of metals for the solid phase, were obtained for each soil and heavy‐metal cation. On the basis of these Kd, the selectivity sequence was evaluated. The most common sequences were Cr > Pb > Cu > Cd > Zn > Ni and Pb > Cr > Cu > Cd > Ni > Zn. Chromium, Pb, and Cu were the heavy‐metal cations most strongly adsorbed by all soils, whereas Cd, Ni, and Zn were the least adsorbed, in the competitive situation. Selectivity sequences related to valence for the trivalent Cr. For metals of the same valence, sequences did not exactly follow the order of electronegativity. For individual elements, the Misono softness parameter and hydrolysis properties of the heavy‐metal cations may have influenced the sequences. Correlation analysis showed that soil characteristics that may have affected the heavy‐metals adsorption, represented by the distribution coefficients, were pH and cation‐exchange capacity (CEC) for Cd and Cr; organic carbon, clay, and gibbsite contents for Cu; pH and CEC for Ni and Pb.

Poly(vinylalcohol) coated/Cibacron Blue F3GA-attached polypropylene hollow fiber membranes for removal of cadmium ions from aquatic systems

Dye-affinity adsorption is increasingly used for heavy metal removal from aquatic systems. Synthetic hollow fiber membranes have advantages as support matrices in comparison to conventional microbead adsorbents because they are not compressible and they eliminate internal diffusion limitations. The aim of this study was to explore in detail the performance of polyvinyl alcohol coated/Cibacron Blue F3GA-attached polypropylene hollow fibers for removal of Cd(II) ions. The internal matrix was characterized by scanning electron microscopy. Commercially available polypropylene hollow fiber membranes were coated with polyvinyl alcohol (PVA). The PVA adsorption conditions were optimized to increase the amount of PVA by changing the initial concentration of PVA, and adding NaCl. The maximum PVA adsorption capacity was 22.6 mg/g. These hollow fiber membranes carrying Cibacron Blue F3GA (87.9 μmol/g) were used in the Cd(II) removal from aqueous solutions containing different amounts of ions (10–500 mg/l) and at different pH values (2.0–8.0). Cd(II) adsorption capacity increased with time during the first 40 min and then leveled off toward the equilibrium adsorption capacity. Adsorption of Cd(II) ions on the PVA coated polypropylene hollow fiber membranes was 1.2 mg/g. Cibacron Blue F3GA-attachment significantly increased the Cd(II) adsorption (46 mg/g polymer). The adsorption of Cd(II) ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing Cd(II), Cu(II), Pb(II) and Hg(II) was also investigated. The adsorption capacities are 1.75 mg/g for Cu(II); 3.46 mg/g for Hg(II); 5.86 mg/g for Pb(II) and 18.45 mg/g for Cd(II) ions. These results may be considered as an indication of higher specificity of the Cibacron Blue F3GA-attached polypropylene hollow fibers for the Cd(II) comparing to other ions. Modified hollow fibers can be regenerated by washing with a solution of nitric acid (0.1 M). The maximum regeneration value was as high as 95%. These modified membranes are suitable for repeated use for more than three adsorption–desorption cycles without considerable loss of Cd(II) adsorption capacity.

Kinetic Studies of Competitive Heavy Metal Adsorption by Sphagnum Moss Peat

Much of the work on the adsorption of metals by low-cost, natural biosorbents has focussed on the uptake of single metals. In practice, wastewaters are polluted with multiple metals. In addition, the kinetics of adsorption, which are important in the design of treatment systems, have largely been neglected. This paper describes the results of an examination into the adsorption by peat of copper and nickel from both mono and bi-solute systems. These showed that, in general, pore diffusion appeared to be the rate-controlling step and that the presence of ‘contaminant’ copper ions reduced the binding of nickel. In fact, the best interpretation which could be placed on the data was that the behaviour of nickel was unusual. The results also showed that the kinetics of adsorption were best described by a second-order expression rather than a first-order model.

Competitive Adsorption of Heavy Metals by Soils

AbstractThe competitive adsorption of Cd, Cu, Pb, and Zn from 0.025 M NaClO4 solutions onto four soils with differing chemical properties was investigated with batch adsorption experiments. For two mineral soils, adsorption under acidic conditions (pH 5.0) followed the sequence Pb > Cu > Zn > Cd, which corresponds to the order of increasing pK for the first hydrolysis product (e.g., PhOH+) of the metal ions. In contrast, the order of selectivity for two soils containing 20 to 40 g kg−1 organic C was Pb > Cu > Cd > Zn, suggesting that organic matter (OM) increased Cd retention preferentially over that of Zn. When accompanied by a sizable reduction in cation exchange capacity (CEC), extraction of soil OM markedly reduced adsorption of all four metals. However, only Cd and Cu adsorption were appreciably smaller for a soil that maintained a sizable CEC following OM removal. Lead, and possibly Zn, adsorption by soils with substantial inorganic exchange sites may be unresponsive to organic waste amendments. For Cd and Cu, increased soil OM should restrict mobility and bioavailability, at least under acidic conditions where soluble metal complex formation is limited.