Calcium Chromates’ Formation Behaviors in the Oxidative Roasting Process and Their Leachability in Ammonium Carbonate Solutions

A novel process based on calcified roasting and ammonia solution leaching was proposed to realize the recycling of auxiliary materials in the chromate salt production process. This paper investigated the formation of calcium-chromium compounds by oxidation roasting Cr₂O₃ with CaCO₃ and their leachability in (NH₄)₂CO₃ solution. Thermodynamic analysis and experimental results showed that Ca₃(CrO₄)₂ and Ca₅(CrO₄)₃O_0.5 were main phases by oxidation roasting chromite with CaCO₃; additionally, high temperature and Ca/Cr molar ratio would promote formation of Ca₃(CrO₄)₂ and Ca₅(CrO₄)₃O_0.5. CaC_rO₄ had an excellent leaching performance in (NH₄)₂CO₃ solution while the leaching of chromium in Ca₃(CrO₄)₂ and Ca₅(CrO₄)₃O_0.5 should be assisted by adding H₂O₂. The chromium leaching of clinker could reach 90% in (NH₄)₂CO₃–NH₃·H₂O solution with adding H₂O₂. The present work is favorable for developing a cleaner technique of chromate salts production with recycling auxiliary materials.