Chromate sorption by acid and alkaline soils

Abstract

Cr (VI) sorbed more Cr in Cr (VI) in Ca (NO₃)₂ (0.01 M) electrolytes than in 0.001 M Ca(NO₃)₂ solution. Nonspecific anions influenced Cr (VI) sorbed by the Taoyuan acid soils in the order: Cl^- < ClO₄ ^- < SO₄ ^2-. On the other hand, in the alkaline soils, these three electrolyte solutions showed slight differences in Cr(VI) sorption. In the experiment replacing phosphate by Chromate in the Taoyuan acid soils, the amount of Chromate desorbed by phosphate increased with increasing Cr (VI) concentrations and decrease with increase in equilibration time. However, Cr (VI) desorption was not affected by equilibration time in the alkaline Si-Lo soils.

When Cr (VI) was incubated at various soil water contents, sorption of Cr and reduction of Cr (VI) to Cr (III) was observed to increase with increasing incubation time. However incubation in saturated water slowed down the sorption as well as reduction of chromium. Optimization of the amount of added FeSO₄, a reductant, maximal reduction Cr (VI) to Cr (III), whereas the ability of reduction decreased with increase in incubation time and also with incrcrease in incubation temperature. Increasing in the glucose content of soils accelerated the reductive condition of soils, and made it more suitable for Cr (VI) reduction. Addition of phosphate decreased Cr (VI) sorption due to the competition for sorption sites.