Kinetics of hexavalent chromium reduction by scrap iron

The kinetics of Cr(VI) reduction by scrap iron was investigated in batch system, for aqueous solutions having low buffering capacities, as a function of pH (2.10–7.10), temperature (10–40 °C) and Cr(VI) concentration (19.2–576.9 μM). The results obtained using only the experimental data at initial times indicate zero-order kinetics at pH 2.10 and first-order kinetics over the pH range of 2.98–7.10. The reaction order with respect to H+ concentration, over the pH range of 4.17–7.10 and Cr(VI) concentration range of 19.2–38.4 μM, was found to be 0.31. The effects of pH, Cr(VI) initial concentration and temperature were investigated; the observed Cr(VI) reduction rates increased with decreasing pH, increasing temperature and decreasing initial Cr(VI) concentration. The observed and overall rate coefficients were determined, and a kinetic expression was developed to describe reduction of chromium by scrap iron over the pH range of 4.17–7.10 and Cr(VI) concentration range of 19.2–38.4 μM.