Synthesis of anhydrite from red gypsum and acidic wastewater treatment

One-step process of red gypsum leaching to produce anhydrite was proposed. The effects of sulfuric acid concentration, reaction temperature and reaction time on both the leaching rate of red gypsum, the phase and micro-morphology of the product were systematically investigated. The acid leaching solution was tried to use circularly. And the valuable components in the leaching solution were recovered by step precipitation. Anhydrous calcium sulfate powder with anhydrite crystal phase and smooth and serrate morphology was successfully produced. The leaching rate of red gypsum was 39.82% under optimized conditions. The optimum cycle number for the reuse of acid leaching solution was 5. Sulfate ions and iron ions in the leaching solution were recovered by adjusting the pH value. A preparation mechanism of anhydrite from red gypsum was also proposed by theoretical analysis. All of these indicated that the whole procedure setup showed potential application for red gypsum utilization. [Display omitted] •One-step process of red gypsum leaching to produce anhydrite was proposed.•Anhydrite II with smooth and serrate morphology was successfully produced.•The valuable components in the solution were recovered by step precipitation.•The optimum cycle number for the reuse of acid leaching solution was 5.