Modelling and experimental measurement of the closed equilibrium systems of CaS–H2O and SrS–H2O
Date
2023-07-11
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Abstract
Eesti põlevkivitööstuses tekkivad ohtlikud jäätmed avaldavad negatiivset mõju keskkonna kvaliteedile ja inimeste tervisele. Näiteks poolkoksijäägi koosmõjul veega (keeruliste keemiliste reaktsioonide tulemusena) tekib väga aluseline väävlirikas nõrgvesi. Lisaks paiskub osa sellest pärinevast väävlist anaeroobsetes tingimustes atmosfääri toksilise gaasilise divesiniksulfiidi (H2Sg) kujul.
Käesoleva doktoritöö eesmärkideks oli uurida CaS või SrS lahustumisprotsessi ülipuhtas (MilliQ) vees ja määrata nende suletud tasakaaluliste süsteemide olulised parameetrid (nt pH, vesilahustuvus või KSP väärtus, ioonide sisaldus), ning kirjeldada neid struktuurskeemina. Eesmärkide hulka kuulus ka mitte-termodünaamiliste matemaatiliste mudelite väljatöötamine, mis võtavad arvesse kõiki konjugeeritud happe-aluse protsesse, et arvutada vastavad pH väärtused, moodustatud ioonide ja molekulide sisaldused iteratsioonimeetodi abil. CaS–H2O või SrS–H2O süsteemide pH-väärtused ja moodustunud sulfiidse väävli liikide sisaldus määrati potentsiomeetriliselt, spektrofotomeetriliselt ja jodomeetrilise tiitrimisega.
Lisaks uuriti nanoosakeste jälgimise- ja analüüsisüsteemi (NTA) abil CaS või SrS vesilahuses moodustunud osakeste suurust ja keskmist sisaldust, kusjuures väiksemad osakesed lahustusid paremini. Seega on võimalik antud printsiibist lähtudes arvutada erinevates suletud tasakaalulistes süsteemides esinevate nanomõõtmetega osakeste jaoks vastav KSP väärtus kasutades selleks NTA meetodit, mis sobib nii mono- kui ka polüdisperssetest süsteemidest võetud proovide jaoks, kuna selle lahutusvõime on oluliselt parem võrreldes teiste sarnaste meetoditega nende iseloomustamiseks ja analüüsimiseks.
Kokkuvõtteks on vaja teha täiendavaid uuringuid CaS ja SrS lahustumise kirjeldamiseks vees lähtudes uuest prootonikesksest mudelist, mida saab kasutada nii inimtegevusest tulenevate mõjude hindamiseks looduslikele veekogudele kui ka tööstuslike protsesside (sh reoveepuhastuse) modelleerimiseks.
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.
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.
Description
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Keywords
hazardous waste, calcium sulphide, strontium sulphide, solubility, dissolution