The aim of this study was to develop alternative techniques for removing sulfate ions from mining/metallurgy effluents. Sulfate removal processes are generally expensive and show low removal efficiency. Two alternatives to treat sulfate-rich solutions were studied in this work. The first alternative was sulfate removal in acidic pH, as jarosite. Moreover, the second precipitating alternative was tested in alkaline conditions, as ettringite. Sulfate removal as ettringite was considered the preferable form for treating sulfate-containing wastewaters due to its low solubility in water, close to 10 mg/L at the pH of 11.5. Chemical precipitation of sulfate in synthetic solutions containing 1,500 mg/L sulfate, at the temperature of 22±1º C, was thus investigated, and removals close to 85% in continuous precipitation systems were observed. This study showed sulfate reduction to final concentration values below 250 mg/L - lower than that recommended by environmental regulations.
sulfate removal; acid mining drainage; ettringite; jarosite
