Selenite Adsorption on Alluvial Soils: II. Solution Composition Effects

The adsorption envelope for selenite on two alluvial soils from the San Joaquin Valley, California, was investigated with respect to variations in solution composition. Sodium‐saturated soil pastes were mixed with solutions containing sulfate, phosphate, and Ca ions in a background electrolyte of 50 mol NaCl m−3. The effects of increasing chloride concentration were investigated at 100 mol NaCl m−3. No discernible change in the amount of selenite adsorbed was found as a result of increased chloride concentration or through the addition of 16 mmol Na2SO4kg−1. In contrast, an initial concentration of phosphate comparable to that of selenite resulted in a decrease of selenite adsorbed by approximately one‐half. The addition of 100 mol CaCl2m−3resulted in significant increases in selenite adsorption on both soils above pH 5, which could be attributed to precipitation or an increase of surface charge through Ca adsorption.