Thermodynamic Modeling of Calcium Sulfate Hydrates in the CaSO4-H2O System from 273.15 to 473.15 K with Extension to 548.15 K

Leiting Shen; Hannu Sippola; Xiaobin Li; Daniel Lindberg; Pekka Taskinen

doi:10.1021/acs.jced.9b00112

Thermodynamic Modeling of Calcium Sulfate Hydrates in the CaSO₄-H₂O System from 273.15 to 473.15 K with Extension to 548.15 K

J Chem Eng Data. 2019 Jun 13;64(6):2697-2709. doi: 10.1021/acs.jced.9b00112. Epub 2019 Apr 9.

Authors

Leiting Shen^{1

2}, Hannu Sippola^{1

3}, Xiaobin Li², Daniel Lindberg¹, Pekka Taskinen¹

Affiliations

¹ School of Chemical Engineering, Metallurgical Thermodynamics and Modeling Research Group, Aalto University, Espoo 02150, Finland.
² School of Metallurgy and Environment, Central South University, Changsha 410083, China.
³ FCG Design and Engineering, Osmontie 34, Helsinki FI-00601, Finland.

Abstract

Calcium sulfate is one of the most common inorganic salts with a high scaling potential. The solubility of calcium sulfate was modeled with the Pitzer equation at a temperature range from 273.15 to 473.15 K from published solubility data, which was critically evaluated. Only two Pitzer parameters, β⁽¹⁾ and β⁽²⁾, with simple temperature dependency are required to model the solubility with excellent extrapolating capabilities up to 548.15 K. The stable temperature range for gypsum is 273.15-315.95 K, whereas above 315.95 K the stable phase is anhydrite. Hemihydrate is in the metastable phase in the whole temperature range, and the obtained metastable invariant temperature from gypsum to hemihydrate is 374.55 K. The obtained enthalpy and entropy changes at 298.15 K for the solubility reactions are in good agreement with literature values yielding solubility products of 2.40 × 10^-05, 3.22 × 10^-05, and 8.75 × 10^-05 for gypsum, anhydrite, and hemihydrate, respectively. The obtained Pitzer model for the CaSO₄-H₂O system is capable of predicting the independent activity and osmotic coefficient data with experimental accuracy. The mean absolute average error of activity coefficient data at 298.15 K is less than 2.2%. Our model predicts the osmotic coefficient on the ice curve within 1.5% maximum error.