Sulphate removal from aqueous solutions: State-of-the-art technologies and future research trends

Sulphate (SO42−) is a common anion nutrient naturally occurs in water bodies, and considered not toxic when presented in low concentration. However, the presence of large amounts of SO42− induces sour taste in household water and scaling in pipe lines. A concentration of 500 to 750 mg(SO42−)/L causes laxative effect, dehydration, and gastrointestinal irritation in human bodies. Hence, strict limitation was imposed on SO42− discharge, to conform with regulatory bodies standards. Several techniques were developed to eliminate or minimize the SO42− content in wastewater discharges. Generally, chemical precipitation method widely utilized for SO42− mitigation from high SO42− concentration sources particularly mine wastewater. However, the drawback of this process is that the theoretically obtainable minimum sulphate concentration with lime precipitation is 1500 mg/L SO42− at ambient temperature due to high solubility of gypsum. In the present review, the traditional and recently developed sulphate removal techniques are discussed by addressing their merits/drawbacks and potential further improvements. Moreover, novel integrated system which combines one or more advanced techniques in parallel with the established methods are reviewed that could pave the way towards the development of suitable technology. Finally, the life cycle assessment and techno-economic analysis are discussed for the various technologies.