SELENITE ADSORPTION BY MANGANESE OXIDES

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Abstract
Selenite adsorption by Mn oxides was investigated using syntheitc manganese oxides (birnessite, cryptomelane and amorphous Mn oxide), which were not expected to adsorb much selenite because of the development of a negative surface charge. Selenite adsorption by Mn oxides increased with decreasing pH, indicating that adsorption was dependent on the variable charge developed on the surface of the Mn oxides. The large increase in negative charge on the particle surfaces and the small proton consumption were characteristically observed in the ligand exchange reactions with selenite adsorption by the Mn oxides. Binding force between Mn oxides and selenite was weaker than between goethite and selenite. Selenite adsorption by the Mn oxide was greater than that of phosphate adsorption in all ranges of pH. The competition sequence with selenite adsorption on the Mn oxide for a given anion concentration ration was molybdate > phosphate > citrate > oxalate > fluoride > sulfate = acetate. These results indicate the possibility that selenite behavior in soils would be affected by Mn oxides, which have a higher surface negative charge than Al or Fe oxides. © Williams & Wilkins 1995. All Rights Reserved.

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