Immobilization of chromate in hyperalkaline waste streams by green rusts and zero-valent iron

Zero-valent iron (ZVI) and green rusts can be used as reductants to convert chromium from soluble, highly toxic Cr(VI) to insoluble Cr(III). This study compared the reduction rates of Cr(VI) by ZVI and two carbonate green rust phases in alkaline/hyperalkaline solutions. Batch experiments were carried out with synthetic chromate solutions at pH 7.7–12.3 and a chromite ore processing residue (COPR) leachate (pH ≈ 12.2). Green rust removes chromate from high pH solutions (pH 10–12.5) very rapidly (