Calcium-induced sulfate adsorption by soils

The effect of Ca²⁺ on the adsorption of SO₄^2- in variable-charge soils was examined. The increase in SO₄^2- adsorption per unit increase in Ca²⁺ adsorption was 12 times more in soils containing Fe and Al hydrous oxides as the major variable-charge component than in soils dominated by organic matter. In soils containing Fe and Al hydrous oxides, specific adsorption of Ca²⁺ increased the positive charge and thereby induced further adsorption of SO₄^2-. In soils with organic matter as the major variable-charge component, Ca²⁺ is complexed by organic ligands. Calcium complex formation through electrostatic attraction does not create positive sites and this may be the reason for the absence of Ca²⁺-induced SO₄^2- adsorption in these soils. -from Authors