Mineral processing: leaching process of chromium and recovery of platinum group elements from Northwestern Saudi Arabian Ophiolitic chromite

The current strategy reports the recovery of precious group metals (PGMs) from Na2CO3 roast of Saudi Arabian ophiolitic chromite ore at 1160 °C under atmospheric O2. The influence of roasting temperature (960–1200 °C) and leaching agents (H2O, HCl, H2SO4) and their concentrations on the recovery of PGMs was studied. Chromite roast concentrates a reasonable percentage of approximately 45% with an overall 43% Cr2O3. PGMs in the original ore was petitioned and ends up in Na2CrO4 liquor whereas the liquor and a solid roast residues contained the rest of chromite components (Fe2O3, Al2O3, others). Na2CrO4 in the water or H2SO4 leachate was reduced with SO2 gas to give crystalline basic chrome sulfate with excellent yield (> 99%) and purity (Fe < 0.1%). PGMs in the Na2CrO4 liquor were extracted into methylisobutylketone (MIBK) after shaking with ammonium pyrrolidine dithiocarbamate (APDC). In MIBK extract, the PGMs species was then stripped by shaking with HgCl2–HNO3 (1.0 mol L−1). Ir and Pt in the produced PGEs cake were found up to 4.0 and 0.5 µg/g, respectively whereas the majority of Ni (0.5% as NiO) was retained in the solid roast residues. The proposed method offers a simple approach with good cost-effectiveness for PGEs recovery and production of basic chrome sulfate with Fe content less than 0.1%. Leaching with water offers a simple, an eco-friendly and cost-effectiveness approach for the production of a basic chromium sulfate product with high quality yield of PGEs as a byproduct with minimum Fe content (< 0.1% m/m) required for the tanning industry compared to the method reported.