Adsorption behavior of co-existing Mn(II) and Cr(III) in loess soil

Heavy metal is one of the most important pollutants in soil, and heavy metal-combined pollution is the most common form. Behavior of Mn(II) and Cr(III) adsorption in loess soil is studied through a series of experiments in laboratory. Adsorption of Mn(II) is found to be inhibited in Mn(II)-Cr(III)-combined system and the adsorption capacity decreases by 14.6%~46.5%, while adsorption of Cr(III) is basically not influenced. Mn(II) adsorption agrees well with that of the Langmuir model but not with that of the Freundlich and D-R models, while Cr(III) adsorption still agrees well with that of the Freundlich and D-R models. At pH around 5~7, removal of Mn(II) becomes more efficient, and that of Cr(III) becomes less efficient. Under alkaline condition, Cr(III) is almost completely removed, but Mn(II) removal is inhibited greatly. The physical property of heavy metal (i.e., hydrolysis constant) and minerals in loess soil both are found to play important roles in adsorption of Mn(II) and Cr(III).