Abstract
The kinetics of Cr(VI) reduction to Cr(III) by metallic iron (Fe) 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 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 addition and temperature but inversely with initial pH. The pseudo-first-order rate coefficients () were determined as 0.0024, 0.010, 0.0268 and 0.062 8 min 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 were obtained at the temperature range of 288–308 K. Different Fe types were compared in this study. The reactivity was in the order starch-stabilized Fe nanoparticles > Fe nano-particles > Fe powder > Fe filings. Electrochemical analysis of the reaction process showed that Cr(III) and Fe(III) hydroxides should be the dominant final products.
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