Solid-liquid Equilibrium In The Processes Of Lithium Hydroxide Produced From Lithium Sulfate And Purification

High-purity lithium hydroxide is an important source of lithium in the defense industry,the battery industry and the aerospace industry.The design,optimization and control of conversion process for production of lithium hydroxide,and how to improve the purity of lithium hydroxide require the support of phase equilibrium data and the guidance of phase diagram.For this purpose,the solid-liquid phase equilibrium study of the production of lithium hydroxide by lithium sulfate conversion and its purification process was carried out,and the relevant basic data and phase equilibrium laws were obtained.The following conclusions were obtained:The solid-liquid phase equilibrium of LiOH-Na2SO4-H2O system at 283.15K,298.15K and 323.15K was obtained,and the relevant phase diagrams were drawn.There are four solid phases in the system,namely Na2SO4·10H2O,Na2SO4·2.5H2O,Na2SO4 and LiOH·H2O,without double salts.At 298.15K,an unknown solid phase exists in the system.The chemical analysis,Karl Fischer water titration,XRD,TG and DSC determinations determine that the new solid phase is Na2SO4·2.5H2O.The experimental results show that the solubility of lithium hydroxide in the system changes little with the change of temperature,and the solubility of sodium sulfate changes significantly.The solid-liquid phase equilibrium of LiOH-C2H5OH-H2O system at 273.15K,283.15K,298.15K,308.15K and 323.15K was obtained,and the relevant phase diagrams were drawn.At the same temperature,the saturated solubility of lithium hydroxide decreases significantly with the increase of the ethanol/water mass ratio;for the same ethanol/water mass ratio,the saturation solubility of lithium hydroxide changes little with temperature.The change in the ethanol/water mass ratio can significantly affect the solubility of lithium hydroxide relative to temperature.When the ethanol/water mass ratio is below 1,the saturated solubility of lithium hydroxide decreases significantly with the increase of ethanol mass ratio;when the ethanol/water mass ratio is above 1.0,the decrease of lithium hydroxide solubility is obviously slowed down.The phase equilibrium of LiOH-NaOH-C2H5OH-H2O system at 273.15K,283.15K,298.15K,308.15K and 323.15K was obtained,and the relevant phase diagrams were drawn.For the same ethanol/water mass ratio,the saturation solubility of lithium hydroxide varies little with temperature and decreases significantly with increasing NaOH content.When the ethanol/water mass ratio is less than 1,a small amount of NaOH has a great influence on the solubility of LiOH.The addition of NaOH will significantly reduce the solubility of LiOH.When the ethanol/water mass ratio is greater than 1,NaOH has little effect on the solubility of LiOH..According to the results of phase equilibrium study,taking lithium sulfate as the raw material,the optimized process plan and process parameters of producing lithium hydroxide at high temperature and removing sodium sulfate at low temperature were put forward.