The Study Of Cerium Sulfate Containing Fluorine Rare Earth Solution Thermodynamic Properties

Bastnasite is an important rare earth mineral,and is an important raw material to extractcerium.The "oxidizing roasting-sulfuric acid leaching-solvent extraction" process is the most promising rare earth separation and extraction technology.The fluoride ions can enter into the leaching solution together with rare earth ions,which will seriously affect the separation and purification of rare earths and the subsequent studies,and restrict the industrialization of the process because of the strong coordination ability of fluorine.Therefore,it is important to study the physiochemistry property of bastnasite leaching solution.Based on the reality demand,taking fluorine bearing rare earth sulfate solution as the research object to simulate bastnasite sulfuric acid leaching solution,using Nernst equation and Pitzer theory,the average activity coefficients of Ce(SO4)2 and H2SO4 were determined according to the change of electromotive force,which is expected to lay a foundation for the study of fluorine bearing solution and provide ideas and data for extensive wider range of rare earth metallurgy.This paper aims to the thermodynamic properties of the fluorine-containing rare earth cerium sulfate solution,and following four parts were researched.Firstly,the electromotive forces were detected with pH glass electrode and Pt electrode.The results show that:the EMF values of pH glass electrode increase with the increase of sulfuric acid concentration,decrease first and then increase with the increase of cerium sulfate concentration,decrease with the addition of fluorine,and increase with the increase of temperature;the EMF values of Pt electrode increase with the increase of cerium sulfate concentration,increase with the increase of sulfuric acid concentration when the acidity lower than 1 mol/L,and barely affected by acidity when the acidity higher than 1 mol/L.The EMF values of Pt electrode also decrease with the increase of ratio of fluorine and cerium and the increase of sulfuric acid concentration,and increase slightly with the increase of temperature.Secondly,according to the EMF values of pH glass electrode and Pt electrode,the Pitzer parameters and E0 were obtained and the average activity coefficients of H2SO4 and Ce(SO4)2 were calculated.The average activity coefficients both decrease with the increase of sulfuric acid concentration and cerium sulfuric concentration,indicating that the cerium sulfate solution becomes complicated with the increase of solute concentration.The Pitzer parameters provide a theoretical model for the later study of rare earth electrolyte solution.Thirdly,the refractive index and conductivity of Ce(SO4)2-H2SO4-H2O ternary system and Ce(SO4)2-H2SO4-NaF-H2O quaternary system were detected.The results show that:the refractive index decreases with the increase of temperature,and increases with the increase of sulfuric acid and sulfuric acid cerium concentrations.The Ce4+ is the most influential factor,that the more free Ce4+,the greater refractive index.The conductivity increases with the increase of cerium sulfate concentration,and increases with the increase of sulfuric acid concentration when the concentration lower than 0.4 mol/L,and barely affected by sulfuric acid concentration when the concentration higher than 0.4 mol/L.The conductivity also decreases with the increase of temperature.In the fluorine-containing system,the conductivity decreases with the increase of ratio of fluorine and cerium when the acidity lower than 0.5 mol/L,and most affected by sulfuric acid concentration when the acidity higher than 0.5 mol/L.Lastly,the Ce4+ selective electrodes were studied and prepared.The results show that:the best response effect of PVC membrane electrode is obtained at the ratio of PVC 0.075 g,tetrahydrofuran 3 ml,phthalic acid dibutyl 0.33 g,P204 0.1 ml as surfactant,oleic acid 5mg as additive and acidity of internal reference solution 0.5 mol/L;the best response effect of film coated Pt electrode is obtained at the ratio of blue dimethylanilide 15 mg and oleic acid 5 mg.