Laboratory experiment reveals distinct pH-dependent retention mechanisms for zinc and copper in acid mineral soil, indicating adsorption rather than precipitation controls metal solubility.
Studies of the effect of pH and competing cations on Zn 2+ and Cu 2+ solubility in an acid mineral soil indicate the probable involvement of hydrous oxides of iron, aluminum, or manganese in the adsorption process. Adsorption on permanent charge sites of clays, or complexation with organic matter could not account for the apparent fixation of Zn 2+ in a nonexchangeable form in the pH range of 5 to 7. Nucleation of Zn hydroxide on clay mineral surfaces may have produced the strongly pH‐dependent retention in the soil; however, Cu 2+ showed more evidence of being controlled by organic complexation mechanisms. All soil solutions were undersaturated with respect to the least soluble hydroxides and carbonates of Cu 2+ and Zn 2+ , at least at pH values below 7, indicating that simple precipitation was not involved in metal retention in the soil.
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McBride et al. (1979) studied this question.
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