Recovery of Na2SO4·10H2O from a reverse osmosis retentate by eutectic freeze crystallisation technology

S. T. Reddy*, A. E. Lewis, G. J. Witkamp, H. J.M. Kramer, J. van Spronsen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


The increasing amount of waste water and effluent from South Africa's mining industry forms a growing problem, which processing requires sustainable solutions in which both the water and the dissolved component can be re-used. Eutectic freeze crystallisation (EFC) has been identified as a key technology that is not only energy efficient, but also produces ice and salt products of high quality. Unlike reverse osmosis membrane systems, EFC can treat both dilute and concentrated systems minimising waste water volumes. In this paper it is shown that freeze and eutectic freeze crystallisation can be used for the processing of a reverse osmosis retentate stream containing 4% NaSO4 and a number of impurities (F, Cl, K, Li, Mg, Ca, NO3 and NH4), producing both pure water and NaSO4·10H2O crystals. The influence of the impurities on the eutectic point and on the crystal structure of mirabilite was investigated using EFC technology investigated for a pure binary system, for a synthetic reverse osmosis retentate as well as for a concentrated NaCl system. In addition, investigations into the recovery and purity of mirabilite for these streams were conducted.

Original languageEnglish (US)
Pages (from-to)1153-1157
Number of pages5
JournalChemical Engineering Research and Design
Issue number9
StatePublished - Sep 2010
Externally publishedYes


  • Brine
  • Crystallisation
  • Eutectic freeze crystallisation
  • Sodium sulphate decahydrate

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering


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