Implementing the Mean Spherical Approximation Model in the Speciation Code CHEAQS Next at High Salt Concentrations


Speciation programs all struggle with the challenge of converting equilibrium constants to non-zero ionic strength. Equations like the Davies equation are semi-empirical and do not give satisfactory results at high salt concentrations. The Mean Spherical Approximation (MSA) model is a method with a solid theoretical basis that gives good results at high salt concentrations. We implemented the MSA model in a new 64-bit version of the speciation program CHEAQS Next which is under development. It was shown that the results obtained with this research version are identical to results obtained earlier by Simonin (Ind Eng Chem Res 56:9721–9733, 2017). This is the first time the MSA model has been implemented in a production program.

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We would like to thank an anonymous reviewer and the editor for their constructive suggestions.

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Correspondence to Wilko Verweij.

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Verweij, W., Simonin, JP. Implementing the Mean Spherical Approximation Model in the Speciation Code CHEAQS Next at High Salt Concentrations. J Solution Chem 49, 1319–1327 (2020).

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  • Speciation program
  • MSA model
  • Activity correction