Thermodynamic Modeling On The Solubility Of CO₂,Quartz And Other Minerals In Common Water-Salt Systems

CO₂ capture and sequestration?CCS?in water-rich deep saline aquifers is an effective way to reduce the amount of CO2 emissions to the atmosphere.Storage capacity of CO₂ in different saline aquifers is a key problem of CCS.Water-rich fluid and rocks interact all the time in the deep Earth.The solubilities of quartz and other minerals constrain the transferred element mass,and then influence the formation of some ore deposits.Therefore,the study on the solubilities of CO₂ and minerals like quartz in water-salt systems is very important to CCS and deposit formation.By collecting and evaluating a great amount of solubility data of CO₂ and quartz in water and aqueous solutions,we have developed the solubility models of them based on thermodynamic relations.1.Based on the Pitzer electrolyte theory for activity coefficient and the equation of state of Span and Wagner?1996?for vapor fugacity,an improved activity-fugacity model is developed to calculate CO2 solubility in aqueous KCl,MgCl₂,CaCl₂,Na₂SO₄,K₂SO₄ and MgSO₄ solutions,respectively.The valid range of temperature,pressure and ion strength is up to 450 K,500 bar and 5 mol kg^-1.Average absolute deviation of CO₂ solubility is about 5%compared to a large number of experimental data available,within or close to experimental uncertainties.By combining the interaction parameters of CO₂ and ions developed here with those of CO₂ and Na⁺ and Cl^–from an earlier study of Mao et al.?2013?,this model can be used to accurately predict CO₂ solubility in aqueous mixed-salt solution containing Na⁺,K⁺,Mg²⁺,Ca²⁺,Cl^–and SO₄^2-under conditions of CCS.2.Based on the pressure-volume-temperature-composition?PVTx?model of Mao et al.?2010?,an semi-empirical density-based model is developed for the solubility of quartz in aqueous NaCl and/or CO₂ solution up to 1273 K and 20 kbar.Compared to a large number of experimental data,the average absolute deviations of calculated quartz solubilities in water,aqueous NaCl solution and aqueous CO₂solution are 5.50%,5.24% and 7.55%,respectively,which are within experimental uncertainties,and are much better than the most competitive models in literature.Particularly,this model can predict the solubility of quartz in aqueous NaCl and CO₂ solution without using any additional parameter.The hydration numbers of silica in different temperatures and pressures calculated from this model are generally reasonable and consistent with some previous results.In principle,the thermodynamic theories and empirical formulae are applicable to other insoluble minerals.According to this approach,the solubility models of corundum and rutile are established,where most of the experimental data used in the parametrization can be reproduced well.