Optimization Of Crystallization Process Of Yttrium Oxalate

The size of yttrium oxide determines the effect of its application.Yttrium oxide with different sizes can be used to produce materials needed in different fields.At present,most of the researches on yttrium oxide at home and abroad are on small particles,but few on large particles.Oxalic acid precipitation method is a way to prepare yttrium oxide with large particle size.As a good precursor of yttrium oxide,the size of yttrium oxalate particle directly determines the size of yttrium oxide particle after calcination.Therefore,in order to prepare large particles of yttrium oxalate,the crystallization thermodynamics and kinetics of yttrium oxalate were studied in this paper.On the basis of this study,the influence of various factors on the crystallization process of yttrium chloride precipitated by oxalic acid was studied and analyzed,and the optimal crystallization condition of yttrium chloride precipitated by oxalic acid was obtained.The main research contents are as follows:In terms of thermodynamics,The solubility data of 318.15 K~343.15 K yttrium oxalate in different concentrations of oxalic acid solution at atmospheric pressure were determined by dynamic method.Apelblat equation and polynomial empirical equation are used to fit the experimental data,and the correlation results are good,in which the empirical equation is better than the Apelblat equation.The solution enthalpy and entropy of yttrium oxalate in different oxalic acid solutions were calculated by Van't Hoff equation.The results show that the dissolution process of yttrium oxalate in different concentrations of oxalic acid solution is a non-spontaneous exothermic process,and the enthalpy change has a great influence on this process.In terms of crystallization kinetics,the reaction crystallization process of yttrium oxalate was studied by batch dynamic method.The nucleation rate equation and growth rate equation of yttrium oxalate in oxalic acid solution were obtained by regression.The effects of supersaturation and temperature on the crystallization kinetics of yttrium oxalate were discussed.The results show that the growth rate and nucleation rate increase with the increase of temperature,and the growth is easier to occur;The growth rate and nucleation rate will increase with the increase of supersaturation;The nucleation rate will increase with theincrease of suspension density.On the basis of the above research,response surface method was used to determine the optimal operation conditions by investigating the influence of temperature,feeding speed,oxalic acid concentration,stirring speed and other conditions on the particle size of yttrium oxalate.The optimal parameters obtained by response surface method are as follows: reaction temperature is 60 ?,feeding speed of oxalic acid is 1.01ml/min,concentration of precipitant oxalic acid is 1.5 mol/L.Under the optimized conditions,the D50 of yttrium oxalate is53?m.The average value of the actual D50 of the actual yttrium oxalate was 51.8?m after tests under optimal conditions.which shows that the regression equation of yttrium oxalate D50 established by response surface method has good prediction effect and certain guiding significance.