Catalytic Effect of Tropical Clay Minerals on the Organic Reduction of Hexavalent Chromium

Abstract

The organic reduction of hexavalent chromium in the presence of clay minerals found in some areas of the Eastern part of Nigeria has been studied. Remediation of chromium contaminated environment like soil, land, fills, sewage and plant bodies, can be effected by reducing hexavalent chromium to the trivalent analogue, which makes it unstable and less harmful to the environment since it cannot act on its own, but can be combined with other compounds which are insoluble such as calcium, magnesium which it can than been extracted from them. Results show that the overall reduction rate increased with increase in the mass of the clay mineral 1.0 – 5.0 g. However, the rate was higher in bentonite 0.043 – 0.014 g/dm3 and lower in kaolin 0.049 – 0.022 g/dm3 for corresponding mass of clay. The rate was also higher in bentonite with increasing concentration of the reductant – oxalic acid 0.043 – 0.012 g/dm3 and lower in kaolin 0.049 – 0.015 g/dm3 for corresponding reductant concentration. From experiment, it can be deduced that from the values obtained, the catalytic effect of bentonite is greatest (fastest) and that of kaolinite is slow, that is to say that the rate of catalysis of bentonite > kaolinite. These result suggest that Cr(VI) reduction rate in subsurface environments rich in organic compound may be elevated through catalysis of surface-bound metals and/or soluble species from the clay minerals, and as a result, higher than those expected from aqueous phase reaction alone.