Adsorption of Lead, Copper, Zinc, Cobalt, and Cadmium by Soils That Differ in Cation‐exchange Materials

Abstract

The adsorption of Zn2+, PbZ+. Cu2+, Co2+, and CdZ+ (Mz+) by soils was measured at concentrations ranging from lo-' to M in to 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 varicd 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. IntroductionT H E A D S O R P T I O N of heavy metal cations by soils has importance in determining their availability to the plant and their movement through the soil. Earlier we found that selective adsorption of Zn by soils is dependent on their major cation-exchange materials (Wada and Abd-Elfattah, 1979). The present paper reports the results of studies along the same lines on the adsorption of Pb, Cu, Co, and Cd by soils. The main interest is in the effects of kind of heavy metal cation and of cation-exchange material, and the effect of soil pH, on the selective adsorption of heavy metal cations by soils. The evaluation of these effects is important in estimating the heavy metal retention by the soil and in order to elucidate the reaction mechanism.

Fractionation of zinc in greenhouse soils

“…I). These results indicate that Pb 2+ effectively replaced the specifically adsorbed Zn a~ at pH 6.0, and therefore, that Pb 2+ had a higher affinity to the specific adsorption sites than Zn 2+ as reported by Abd-Elfattah and Wada (1981).…”

Caracterização química e física de vermicomposto e avaliação de sua capacidade em adsorver cobre e zinco

“…No entanto, a análise das porcentagens extraídas (tabela 2), mostra a não-totalização de 100%. Tal observação pode ser atribuída ao fato de o material analisado, além dos sítios de adsorção em razão da matéria orgâ-nica, apresentar, também, sítios provenientes dos argilo-minerais (caulinita e outros), responsáveis pela adsorção de cátions, como chumbo, cobre, zinco e cádmio 34 . O uso de água oxigenada como oxidante da matéria orgânica deve ser cauteloso, visto que problemas de natureza analítica podem ocorrer, já que nem toda a matéria orgânica pode ser oxidada e a formação de áci-do oxálico deve ser considerada, conduzindo à formação de oxalato de chumbo 25 .…”

Removal of Heavy Metals from Aqueous Solution by Zeolite in Competitive Sorption System

“…According to [32], selective metal retention can be explained by the differences in electronegativity, which, in this case, is higher for Cu (2.0) than Zn (1.6). However, other investigators pointed out that the first hydrolysis constant is most predictive for metal adsorption selectivity by specimen Fe oxides and soil colloids [33]. The first hydrolysis constant (pK1) for Cu varies between 7.3 and 8.0, whereas the pK1 for Zn ranges from 9.0 to 9.4 [33].…”

“…However, other investigators pointed out that the first hydrolysis constant is most predictive for metal adsorption selectivity by specimen Fe oxides and soil colloids [33]. The first hydrolysis constant (pK1) for Cu varies between 7.3 and 8.0, whereas the pK1 for Zn ranges from 9.0 to 9.4 [33]. Furthermore, Misono et al derived a softness parameter to predict metal affinity sequences or preferential retention of metals by soil colloids.…”