Chromate sorption by acidic and alkaline soils

Abstract

The sorption and rate of reduction of chromium by acidic and alkaline soils was investigated. The results indicate that Cr(VI) sorbed more Cr 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 acidic soils in the order: Cl‐ < ClO4 ‐ < SO4 2‐. On the other hand, in the alkaline Si‐LO soils, these three electrolyte solutions showed slight difference in Cr(VI) sorption. In the experiment replacing phosphate by chromate in the Taoyuan acidic soils, the amount of chromate desorbed by phosphate increased with increasing Cr(VI) concentrations and decreased 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, caused maximal reduction of Cr(VI) to Cr(III), whereas the ability of reduction decreased with increase in the incubation time and also with increase in the incubation temperature. Amendments 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.