Kinetics of hexavalent chromium reduction by iron metal

The kinetics of Cr(VI) reduction to Cr(III) by metallic iron (Fe 0 ) was studied in batch reactors for a range of reactant concentrations, pH and temperatures. Nearly 86.8% removal efficiency for Cr(VI) was achieved when Fe 0 concentration was 6 g/L (using commercial iron powder (< 200 mesh) in 120 min). The reduction of hexavalent chromium took place on the surface of the iron particles following pseudo-first order kinetics. The rate of Cr(VI) reduction increased with increasing Fe 0 addition and temperature but inversely with initial pH. The pseudo-first-order rate coefficients ( k obs ) were determined as 0.0024, 0.010, 0.0268 and 0.062 8 min −1 when iron powder dosages were 2, 6, 10 and 14 g/L at 25°C and pH 5.5, respectively. According to the Arrehenius equation, the apparent activation energy of 26.5 kJ/mol and pre-exponential factor of 3 330 min −1 were obtained at the temperature range of 288–308 K. Different Fe 0 types were compared in this study. The reactivity was in the order starch-stabilized Fe 0 nanoparticles > Fe 0 nanoparticles > Fe 0 powder > Fe 0 filings. Electrochemical analysis of the reaction process showed that Cr(III) and Fe(III) hydroxides should be the dominant final products.