Dissolution, Polymorphism Control And Thermal Stability Of Calcium Salts

In nature,calcium sulfate and calcium carbonate have huge reserves.Their dissolution,crystalline and thermal stability are closely related with their applications in various fields.There are four parts in present article:measurement of solubility and thermodynamic interpretation of CaSO₄?2H₂O in various aqueous chloride solutions;Influence of experimental condition to crystal phase of CaCO₃ in CO₂ sequestration;Diffusion control of gaseous CO₂ to facilitate CO₂ utilization and formation of vaterite.Additionally,thermal stability of Ca_xMg_y?CH₃COO?_2?x+y?were evaluated by using TG-DTG-DSC.The thermal decomposition of Ca_xMg_y?CH₃COO?_2?x+y?for production of CaO via CaCO₃ was investigated,and activity energy and decomposition mechanism were estimated accordingly.Under normal pressure and room temperature,CaSO₄?2H₂O is the most stable phase among calcium sulfate.In the nature,it is the main pollutant causing soil salinization.Besides,CaSO₄?2H₂O precipitates in many industrial process including water cleaning,flue gas desulfurization and production of phosphoric acid.Thus,it is worth to put emphasis on solid-liquid equilibrium of CaSO₄·2H₂O in electrolyte solutions.This paper adopt static equilibrium method to measure solubility of CaSO₄·2H₂O in NaCl,MgCl₂,CaCl₂ and AlCl₃solution at 278.15K-308.15K.The diverse behaviors of CaSO₄·2H₂O in NaCl,MgCl₂,CaCl₂,AlCl₃ solution were investigated from the view of thermodynamics.The dissolution difference of CaSO₄·2H₂O in NaCl,MgCl₂ and AlCl₃ solutions were evaluated from ion pair,water activity and pH changing.In addition,phase stability of CaSO₄·2H₂O in concentrated chloride solutions were examined by using X-rays diffraction.Heavy emission of greenhouse gases bringing in environmental change and climate disaster would threaten survival and long term development of human.CO₂ as main greenhouse gases aroused extensive concerns worldwide.As a result,technologies for effective fixation of CO₂ have developed significantly in recent years,among which carbon sequestration received great attention.This paper use aqueous Ca²⁺solution to mineralize CO₂ for production of CaCO₃.The effects of temperature,pH value and CO₂ flow rate on crystal phase of CaCO₃ were investigated by using FTIR,XRD and SEM.In general,utilization of CO₂ is relatively low in continuous CO₂ sequestration under normal air pressure.In order to enhance utilization of CO₂,an improved glass reactor was fabricated in which a baffle covering the solution for constraint of CO₂ gaseous.The conversion rate from gaseous CO₂ to ionic CO₂ was increased by using this method.COMSOL Multiphysics was used to display concentration distribution of CO₂ in solution influenced by the baffle.Kontoyannis equation was employed to study composition of CaCO₃ precipitates.Calculation show higher fraction of vaterite and CO₂ utilization can be obtained with the assistance of the baffle.CaO as high temperature CO₂ adsorbent can be obtained in many approaches.Calcination of CaCO₃ was traditionally a way to produce CaO.In present paper,calcium magnesium acetates?CMA?synthesized by using CaCO₃ and MgCO₃ reacting with CH₃?COOH?₂.Compared to CaCO₃ or other inorganic calcium salts,CMAs are excellent precursors for production of calcium-based CO₂ adsorbents.After thermal decomposition,CaO as final products with porous surface due to evaporation of a large amount of gaseous usually display high adsorption capacity for CO₂.Two calcium magnesium acetates,CMA?Ca:Mg=9:1?and CMA?Ca:Mg=7:3?,were synthesized in present article.TG method were used to investigate thermal decomposition of CaAc,MgAc,CMA?Ca:Mg=9:1?and CMA?Ca:Mg=7:3?under nitrogen atmosphere.Friedman and Flynn-Wall-Ozawa methods were employed to calculate apparent energy of four acetates.IKP method provided constant kinetic parameters A_invnv and E_inv,and distribution of decomposition mechanism of four acetates.