Doctoral defence: Kalev Uiga "Modelling and experimental measurement of the closed equilibrium systems of CaS–H2O and SrS–H2O“

On 8 September at 10:15 Kalev Uiga will defend his doctoral thesis "Modelling and experimental measurement of the closed equilibrium systems of CaS–H2O and SrS–H2O" for obtaining the degree of Doctor of Philosophy (in Environmental Technology).


Research Fellow in Colloidal and Environmental Chemistry Ivar Zekker, University of Tartu

Specialist in Environmental Chemistry Ergo Rikmann, University of Tartu

professor Toomas Tenno, PhD (1940-2022)


professor Marina Valentukevičienė, Vilnius Gediminas Technical University (Lithuania)


Hazardous wastes from oil-shale industry in Estonia have negative impact to the quality of environment and human health. For example, the interaction of semi-coke residue with water (as a result of complex chemical reactions) generates highly alkaline sulphur-rich leachate, from where a toxic gaseous hydrogen sulphide (H2Sg) is emitted into the atmosphere. The aims of current thesis were to investigate the dissolution process of CaS or SrS in ultrapure MilliQ water in order to determine the important parameters (e.g., pH, water solubility or KSP value, ion content) of these closed equilibrium systems (CaS–H2O or SrS–H2O) and to describe them as a structural scheme. The objectives also included developing non-thermodynamic mathematical models, which are taking into consideration all conjugated acid-base processes in order to calculate the pH values, concentrations of formed ions and molecules by using an iteration method. The pH values of these closed equilibrium systems and the concentration of sulphide sulphur species were determined potentiometrically, spectrophotometrically and by iodometric titration. Besides, the size, distribution and concentration of formed particles in aqueous CaS or SrS solutions at equilibrium state were investigated by using a nanoparticle tracking analysis (NTA). Based on the experimental results, the solubility of CaS or SrS in MilliQ water also depended on the pH and the concentration of formed particles. Therefore, based on this principle, it is possible to calculate more accurately the corresponding KSP value for nano-sized ones present in different closed equilibrium systems using the NTA method. In summary, the present thesis suggests that further investigations are needed for describing CaS and SrS solubilization in water by using our novel proton-centric model, which can be used both to assess the effects of human activities on natural water bodies and to model industrial processes (e.g., wastewater treatment) more efficiently.


Defence can be also followed in Zoom

Meeting ID: 971 0644 9449

Passcode: 501970