CHROMATE SORPTION BY ACIDIC AND ALKALINE SOILS

The sorption and rate of reduction of chromium by acidic and alkaline soils was investigated. The results indicate that Cr(VI) sorbed more C r in Ca(NO3)(2)(0.01 M) electrolytes than in 0.001 M Ca(NO3)(2) soluti on. Nonspecific anions influenced Cr(VI) sorbed by the Taoyuan acidic soils in the order: Cl- < ClO4- < SO42-. On the other hand, in the alk aline Si-LO soils, these three electrolyte solutions showed slight dif ference in Cr(VI) sorption. In the experiment replacing phosphate by c hromate in the Taoyuan acidic soils, the amount of chromate desorbed b y phosphate increased with increasing Cr(VI) concentrations and decrea sed with increase in equilibration time. However, Cr(VI) desorption wa s 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 incre asing incubation time. However, incubation in saturated water slowed d own the sorption as well as reduction of chromium. Optimization of the amount of added FeSO4,, a reductant, caused maximal reduction of Cr(V I) to Cr(III), whereas the ability of reduction decreased with increas e in the incubation time and also with increase in the incubation temp erature. Amendments in the glucose content of soils accelerated the re ductive condition of soils, and made it more suitable for Cr(VI) reduc tion. Addition of phosphate decreased Cr(VI) sorption due to the compe tition for sorption sites.