Semi-batch evaporative crystallization and drying of cobalt sulphate hydrates

Jianxin Zhang, Arshe Said, Bing Han, Marjatta Louhi-Kultanen*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Semi-batch evaporative crystallization of CoSO4 was investigated at various underpressures and with different heating powers. The underpressures for boiling aqueous CoSO4 solutions at various temperatures and concentrations were measured and compared to predicted values obtained by the Aspen Plus Version 11 process simulation software. The presence of CoSO4 solute decreased the underpressure for boiling solution in comparison to pure water. In the evaporative crystallization experiments, CoSO4 crystallized as CoSO4.7H2O at evaporation temperatures of 30 °C and 40 °C, whereas CoSO4.6H2O crystallized at 60 °C and 80 °C. The crystals obtained at 30 °C and 40 °C were mainly agglomerates of octahedron shaped particles. Heating power and mixing speed had significant effects on the evaporation flux and particle size distribution of the products. Smaller crystals were produced with higher heating power and higher mixing speed due to the enhancement of evaporation. Dehydration of the formed cobalt sulfate heptahydrate in the drying process was also investigated with two variables: drying temperature and drying time. The crystallization at 40 °C yielded unstable CoSO4.7H2O, which tended to dehydrate in a temperature range between 23 °C and 60 °C; these crystals were used in the study of crystal drying. At a drying temperature of 23 °C, CoSO4.7H2O transferred and stabilized as CoSO4.6H2O. At drying temperatures of 40 °C and 60 °C, the stable hydrate form was CoSO4.H2O. Gravimetric analysis, crystal habit, XRD, and Raman analyses were successfully utilized for the investigation of the transformation of the hydrate form during drying.

Original languageEnglish
Article number105821
Number of pages9
Early online date28 Jan 2022
Publication statusPublished - Feb 2022
MoE publication typeA1 Journal article-refereed


  • Cobalt sulfate
  • Dehydration
  • Drying
  • Evaporative crystallization
  • Hydrates


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