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ADSORPTION OF LEAD, COPPER, ZINC, COBALT, AND CADMIUM BY SOILS THAT DIFFER IN CATION-EXCHANGE MATERIALS 总被引:4,自引:0,他引:4
The adsorption of Zn2+, Pb2+, Cu2+, Co2+, and Cd2+ (M2+) by soils was measured at concentrations ranging from 10-7 to 10-2 M in 10-3 to 10-2 M CaCI2. Exchange between Ca2+ and M2+, and solubility products [M2+][OH?]2 indicate that M2+ is not precipitated as hydroxide but is adsorbed on cation-exchange sites. The proportion of selective adsorption sites with specified values of the selectivity coefficient calculated using Ca as reference ion, increased in the order montmorillonite < humus, kaolinite, < allophane. imogolite < halloysite, iron oxides. Raising the soil pH by Ca-saturation increased both the amount and affinity of adsorption. Selectivity of adsorption increased in the order Mg, Ca < Cd, Co < Zn < Cu, Pb, and the selectivity coefficient varied from < 1 to > 10 000. The formation of the coordination complexes of heavy metal with deprotonoted OH and COOH groups as ligands is suggested as a possible mechanism of selective adsorption. 相似文献
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The adsorption of Zn by soils which are different in their major cation-exchange materials was measured at equilibrium Zn concentrations up to 10?2 M in 10?2 to 10?3 M CaCl2. The results are interpreted on KZnCa[Zn]soil plots, where KZnCa is the selectivity coefficient defined by the equation All natural samples except those containing halloysite exhibited no or very small specific Zn adsorption. All Ca-saturated samples exhibited specific Zn adsorption dependent on cation-exchange materials. The cation-exchange sites with high selectivities for Zn (KZnCa > 10) constitute more than 40 per cent of the total exchange sites in soils containing allophane, imogolite, and halloysite, whereas those with moderate to low selectivities for Zn (KZaCa < 10) predominate in montmorillonitic, vermiculitic, and humic soils. Differences in the contribution of the respective cation-exchange materials to specific Zn adsorption are discussed relating to differences in the origin of their negative charge. 相似文献
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