Sulphate removal from mine water by precipitation as ettringite by newly developed electrochemical aluminium dosing method

Precipitation as ettringite (Ca6Al2(SO4)(3)(OH)(12)center dot 26H(2)O) is an effective method for sulphate removal from mine water. The addition of calcium hydroxide and aluminium to sulphate-containing mine water in stoichiometric amounts induces an increase in pH to approximately 12.5, leading to the precipitation of ettringite. Typically, aluminium salts are used as the source of aluminium; however, in this research, an electrochemical dosage of aluminium was used, and the results were compared with the results of chemical ettringite precipitation as well as the results of computational simulations of sulphate removal. The mine water sulphate concentration was reduced 99.0% and 98.6% from the initial 1,060 +/- 20 mg L-1 using a current density of 28 mA cm(-2) in electrochemical aluminium dosing and chemical aluminium dosing, respectively, which was close to the theoretical 100% sulphate removal. When using the current density of 28 mA cm(-2) in the electrochemical aluminium dosing, the recovered ettringite purity was 92.5%, which was almost the same as the 92.6% purity in the chemical aluminium dosing characterised with X-ray diffraction and Rietveld analysis. The results indicate that the electrochemical dosing of aluminium could be an alternative to aluminium salt application in ettringite precipitation.