Abstract

APSEY, G  and  LEWIS, A.E. Selenium impurity in sodium sulphate decahydrate formed by eutectic freeze crystallization of industrial waste brine. J. S. Afr. Inst. Min. Metall. [online]. 2013, vol.113, n.5, pp.00-00. ISSN 2411-9717.

Eutectic freeze crystallization (EFC) is a novel technique for the recovery of pure salt and pure water from hypersaline waste brines. It is therefore a promising technology for the treatment of industrial waste waters. The impurities caused by crystallizing salt out of multi-component brines by EFC have not yet been investigated, however. To these ends, the selenium impurity found in sodium sulphate, produced from the waste brine of a platinum operation, was investigated. It was believed that the similarity between sulphate and selenate ions allowed isomorphous substitution of selenate ions into the sodium sulphate crystals, which was the likely cause of impurity uptake. It was found that the presence of sodium chloride in the industrial brine promotes the uptake of selenium, while ionic strength of the brine and mass deposition rate of sodium sulphate did not have a significant effect on the selenium uptake. Isomorphous substitution is predicted to be the most significant mechanism by which all impurities will be taken up when applying EFC to other industrial waste brines.

Keywords : eutectic freeze crystallization; impurity; salt; brine; sodium sulphate; waste water; isomorphous.

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