INFLUENCE OF ANION COMPETITION ON BORON ADSORPTION BY CLAYS AND SOILS

Abstract

Boron adsorption on the clay minerals, kaolinite and montmorillonite, and two arid zone soils was investigated as a function of solution pH (3-12) and presence of competing anions (nitrate, sulfate, molybdate, and phosphate) after 2 h of reaction time. Boron adsorption on all materials increased from pH 3 to 8, exhibited a peak at pH 8 to 10, and decreased from pH 10 to 12. Boron adsorption was greatest using a NaNO3 background electrolyte. The competitive anion effects on B adsorption increased in the order sulfate < molybdate < phosphate. The competitive effect on B adsorption was small even for the strongly adsorbing anion, phosphate. Our results suggest that B-adsorbing sites are, generally, specific to B and act independently of competing anions. This result will simplify the description of B transport in that changes in solution concentration of competing anions may not have to be considered.