Reductive capacity of soils for chromium

A standard batch procedure was developed to measure soil reductive capacity (SRC) based on the ability of soil to reduce Cr(VI). Parameters that were investigated and optimized included extractant (sulfate) concentration, rea ction temperature. types of reductants, reductant contact time and Cr(VI) c ontact time. 0.1 M sulfate was used as the extracting solution as a measure of safety. Reaction temperature did not have a significant influence on th e reduction kinetics of Cr(VI). Dithionite was selected as a standard reduc tant due to its efficiency in increasing SRC by reducing labile soil compon ents in the soil itself. A time period of 2 days was optimum contact time t o achieve full reduction and oxidation. Soil treated with Fe(II) and the co mbination of Fe(II) and dithionite showed a constant SRC regardless of the frequency of reduction/oxidation cycle, whereas the intrinsic reductive cap acity and total reductive capacity of the soil treated with dithionite were exhausted within several cycles. Column tests were conducted using soil wi th measured intrinsic and total reductive capacities. Differences observed between Cr(VI) breakthrough and that predicted from batch studies are likel y to have benn caused by slow Cr(VI) reduction kinetics and heterogeneity o f the soil. The relative behavior of the column tests agreed with observati ons of the reactants in the batch experiments. The tests demonstrate that s oils can be used to develop an in situ treatment process in which soils are reduced by the addition of reductants and groundwater contaminated with Cr (VI) is passed through the reduced soil zone.