Immobilization of Chromate from 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). ZVI is effective at acid to circum-neutral pH but Cr(VI) reduction rates in hyperalkaline (>pH 10) effluent from chromite ore processing residue (COPR) wastes are unknown. 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 chromate solutions at pH 7.7-12.3 and a COPR leachate (pH ≈12.2). Green rust removes chromate from high pH solutions (pH 10-12.5) very rapidly (