CHROMIUM CONTAMINATION FROM CHROMITE MINE

Among the dominant species of chromium, the trivalent form widely occu rs in nature in chromite ores or in silicate minerals and is extremely immobile. The higher oxidation state Cr(VI), is, however, rarely foun d in nature, is more mobile, and several times more toxic than Cr(III) . Cr(VI) occurs in chromates and dichromates manufactured from chromit e ores. The hexavalent state is stable in an oxidizing alkaline enviro nment, whereas the trivalent state is stable in a reducing acidic envi ronment. Serpentinization and Mg release during deuteric alteration of ultramafic rocks create alkaline pore water and lateritization is an intensive oxidation process. Chromite ore bodies in oxidized serpentin ite therefore may generate hexavalent chromium from the inert chromite s and cause hazardous chromium pollution of the water. With this end i n view, a combined field and laboratory study has been made on chromit e-bearing oxidized serpentinite rocks of Sukinda in Orissa, India. Lab oratory leaching studies on mine overburden samples, chemical analyses of streamwater, and hydrolysate incrustation on detrital grains taken from stream beds have indicated the possibility of chromium mobilizat ion from the chromite ores into the waterbodies.