Zinc adsorption by a lateritic podzolic soil was measured in the presence of 0 to 3 mmol/litre of acetate, oxalate, citrate, tricarballylate, salicylate, or catechol, or 0 to 3 mmolc/litre of humate. Zinc remaining in solution was measured by atomic absorption spectrometry after shaking the soil for 17 h at a soil/liquid ratio of 1:5 in a 0.003 mol/litre KCl solution containing 0 to 500 μmol/litre Zn and the ligands. In the absence of organic ligands, more than 95% of the zinc was adsorbed. The amount of adsorption was linearly correlated with pH and the concentration of ZnOH+ in solution after shaking (r² = 0.98). Zinc adsorption and pH decreased in the presence of each of the ligands except catechol. Seventy four percent of the variation in adsorption was accounted for by the combined effects of the concentration of zinc-ligand complex (Zn-L) and the concentration of ZnOH+ that were present in solution after adsorption. However, other factors such as changes in the number of sites available for adsorption, the point of zero salt effect of the soil, and the change of zinc species also contributed to the magnitude of zinc adsorption.
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