Chemical Behavior of Chromium in Soils: Ⅲ. Mechanism of Cr(Ⅵ) Adsorption by Soils

An analysis of Cr (Ⅵ)-sorbed surface of the soils by using a scanning electron microscope and an electron probe microscope has proved that aluminium is the chief element affecting Cr (Ⅵ) adsoption. As the ionic strength of the solution increased, the amounts of Cr (Ⅵ) adsorbed by goethite and soils decreased. Cr (Ⅵ) adsorption was greatly depressed in the presence of SO₄^2-, WO₄^2-, MoO₄^2-, HPO₄^2- and H₂PO^4- which competed for anion adsorption sites. The depressing extent of these anions was found to follow the sequence: HPO₄^2-, H₂PO^4->MoO₄^2->WO₄^2->SO₄^2->>Cl^-, NO^3-. The amounts of Cr (Ⅵ) desorption varied with different extractants.