You are here:
TREATMENT OF HEXAVALENT CHROMIUM IN CHROMITE ORE PROCESSING SOLID WASTE USING A MIXED REDUCTANT SOLUTION OF FERROUS SULFATE AND SODIUM DITHIONITE
Citation:
Su, C. AND R Ludwig*. TREATMENT OF HEXAVALENT CHROMIUM IN CHROMITE ORE PROCESSING SOLID WASTE USING A MIXED REDUCTANT SOLUTION OF FERROUS SULFATE AND SODIUM DITHIONITE. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 39(16):6208-6216, (2005).
Description:
We developed a method for disseminating ferrous iron in the subsurface to enhance chemical reduction of hexavalent chromium (Cr(VI)) in a chromite ore processing solid waste derived from the production of ferrochrome alloy. The method utilizes ferrous sulfate (FeSO4) in combination with sodium dithionite (Na2S2O4) to inhibit premature precipitation of Fe in the subsurface. We conducted both laboratory and field tests to evaluate the performance of FeSO4/Na2S2O4 solutions in treating the chromite ore processing waste and associated impacted ground water. The high pH ground water (up to 11.5), buffered by minerals such as forsterite (Mg2SiO4), brucite (Mg(OH)2), and hydrocalumite [Ca4(Al, Fe)2(OH)12Xo6H2O), X = (OH)2-, SO42-, CrO42-] is characterized by dissolved Cr(VI) concentrations as high as 57 mg L-1. Laboratory batch tests using a 0.05 M FeSO4 + 0.05 M Na2S2O4 solution indicated rapid and complete reduction of dissolved Cr(VI) in chromite ore processing waste suspensions. Injection of 5700 liters of a 0.07 M FeSO4 + 0.07 M Na2S2O4 solution into a saturated chromite ore processing waste zone at the Macalloy Corporation Superfund site in North Charleston, SC indicated effective treatment of dissolved phase and solid phase Cr(VI) based on ground water sampling results and analyses of aqueous, phosphate, and alkaline digestion extracts from treated core samples. Post-injection analysis also indicated no measurable decrease in formation hydraulic conductivity as a result of the ferrous iron and dithionite injection process.