Thermodynamic modelling of aqueous metal sulfate solutions

Petri Kobylin

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    Acid mine drainage has long been a significant environmental problem in coal and metal sulfide mining. The requirement to recycle and reuse materials has increased significantly, especially in the EU. Dumping and land-filling a neutralised deposit is not an option any more. Thus, efficient techniques for the recycling and reuse of sulfuric acid and/or metal sulfates from the side streams are needed. When developing alternative solutions, a better understanding of the thermodynamic behaviour of the MeSO4–H2SO4–H2O (Me = Mn, Ni, Fe) system is needed. In the present study a thermodynamic model of the FeSO4–H2SO4–H2O, NiSO4–H2SO4–H2O, and MnSO4–H2O systems has been developed, in order to yield a thermodynamically consistent set of values for the solubility of metal sulfate over a wide range of temperatures and concentrations. The Pitzer mean activity coefficient model has been used in the assessment to take into account the non-ideal behaviour of the aqueous solution. The thermodynamic properties of metal sulfate hydrates were also refined. These metal sulfate solutions have previously been modelled in the literature. Those models have been reviewed critically in this work. The current model presents the experimental data of metal sulfate water systems over temperature intervals of -2–220 °C (FeSO4), -3–220 °C (NiSO4), and -11–175 °C (MnSO4) and in concentrations from pure water to the solubility limit of metal sulfate hydrates. The model in this work presents solubilities, mean activity coefficients, activities of water, enthalpy, and heat capacity of solution and hydrate dissociation pressure, with good accuracy and consistently, but the model has limitations at temperatures higher than 100 °C as a result of the lack of experimental data. The experimental data that are available for the FeSO4–H2SO4–H2O, and NiSO4–H2SO4–H2O systems are also presented with a good accuracy and consistently up to 100 °C and sulfuric acid concentrations up to 10 mol/kg. The model also predicts well the solubility measurements available in dilute sulfuric acid solutions at 160–250 °C.
    Translated title of the contributionMetallisulfaattipitoisten vesiliuosten termodynaaminen mallinnus
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Taskinen, Pekka, Supervising Professor
    • Taskinen, Pekka, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-5055-3
    Electronic ISBNs978-952-60-5056-0
    Publication statusPublished - 2013
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • modelling
    • Pitzer model
    • metal sulfate
    • activity
    • CALPHAD method

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