Study on the recovery of purified MgSO4·7H2O crystals from industrial solution by eutectic freezing

C. Himawan, H. J.M. Kramer, G. J. Witkamp*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


Eutectic freezing, characterized by a simultaneous crystallization of ice and salt, was applied to recover magnesium sulphate heptahydrate from a magnesium sulphate industrial stream emitted from flue gas desulphurization. Key aspects of the recovery process for further pilot-scale investigation were studied in a laboratory-scale batch crystallizer with focus on discovering the type of the hydrate product and the quality of the ice and salt crystals. MgSO4·12H2O was formed in the crystallizer and the recrystallization into magnesium sulphate heptahydrate (MgSO4·7H2O) occurred spontaneously during the subsequent filtration and drying above 0.4 °C. The ice and salt crystal products were reasonably pure (only a small amount of Mn was built into the heptahydrate crystals). Ice crystals were disk-shaped with an average size of 300 μm. The MgSO4·7H2O crystals were rather needle-like with an average size of 275 μm. Both products were easily filtered. The characteristics of the eutectic freezing process, i.e. the working area and the dynamics of the simultaneous crystallization, are demonstrated experimentally.

Original languageEnglish (US)
Pages (from-to)240-248
Number of pages9
JournalSeparation and Purification Technology
Issue number2
StatePublished - Jun 15 2006
Externally publishedYes

Bibliographical note

Funding Information:
The authors wish to thank the Ministry of Economic Affairs, the Ministry of Housing, Spatial Planning and Environment, and the Ministry of Education and Science of The Netherlands through the Economy, Ecology, and Technology (EET) program, Pannevis Solid Liquid Separation, Kemira Agro Ventures, Nedmag, and DSM Research for their (financial) support. Robert Gaertner for his calculation of the calcium ion solubilities.


  • Eutectic crystallization
  • Eutectic freezing
  • Ice
  • Industrial stream
  • Magnesium sulphate
  • Recovery

ASJC Scopus subject areas

  • Analytical Chemistry
  • Filtration and Separation


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