Sulfate removal from chemical industries' wastewater using ettringite precipitation process with recovery of Al(OH)3

Abstract

Abstract The objective of this study was to investigate a simple and less expensive process for the removal of sulfate from Iranian Chemical Industries Investment Company' wastewater using the ettringite (a calcium aluminum sulfate (Ca6Al2(SO4)3(OH)12.26H2O)) precipitation process. The optimum experimental conditions for sulfate removal and Al(OH)3 recovery were determined using batch experiments. Using Ca(OH)2 allowed to achieve optimum pH (pH = 12–12.5) for ettringite precipitation. The final residual sulfate concentration is dependent upon the aging time and reagent dosage. Sulfate ions were entirely removed in the ettringite precipitation step using fresh (after heating aluminum hydroxide for 10 h at 350 °C) and recovered Al(OH)3 with a aging time of 61 and 46 h, respectively. The initial concentration of calcium ions in the wastewater sample was also reduced to less than 20.04 mg/l after the carbonation step with 95% removal efficiency. This method with the recovery of Al(OH)3 through the decomposition of precipitated ettringite under low pH conditions is highly feasible and cost-effective for sulfate removal from sulfate-containing industries' wastewater.

Keywords

• Sulfate removal
• Chemical industries' wastewater
• Ettringite precipitation
• Al(OH)3 recovery