Optimizing the use of natural and synthetic magnetites with very small amounts of coarse Fe(0) particles for reduction of aqueous Cr(VI)

Remediation of highly toxic aqueous Cr(VI) includes its chemical reduction to the very insoluble Cr(III) species. In this work we investigated the Cr(VI) reduction performance of synthetic and natural magnetites of different particle size sat three pH values (4, 6, 8), with the purpose of cost-optimizing the procedure at the laboratory scale. Only the finest magnetite showed considerable Cr(VI) reduction yields, but rates were low and after 25 days no equilibrium was attained. Mechano chemical mixing of the finer magnetites with 5% micron-sized Fe(0) increased dramatically their reductive reactivity, especially at pH 4 and 6, and at pH 8 only for the finest sample, despite the fact that the same quantity of Fe(0) added by itself reducednegligible amounts of Cr(VI). Increasing Fe(0) concentrations in the mixtures to 10 and 15% allowed considerable improvements in the reactivity of the intermediate-sized magnetites (of ca. 7 m(2)/g), but not that of the coarser samples for up to 20% Fe(0). This promises to be an optimal technology for remediation or treatment of Cr(VI) polluted aqueous environments and residues, that may prove beneficial for industries and pollution clean-up government agencies, because it uses readily available solid mineral samples and minimizes the use of acid reagents. (C) 2014 Elsevier B.V. All rights reserved.