Study On The Preparation Process Of Lithium Hydroxide From Separated Brine By Membrane In West Taijinar Salt Lake

Lithium,as an important strategic resource,plays an important role in promoting the development of national economy.Lithium hydroxide belongs to a basic lithium product,which was an important raw material for the preparation of lithium grease,lithium-ion batteries and electrode materials.Due to the advantages of large reserves and low production cost,saline brine has become the main development direction of lithium resource.Therefore,there is important theoretical and practical meanings to study the preparation of lithium hydroxide from saline brine.This thesis was carried on the production of lithium hydroxide by electrolysis process from the separated brine by membrane in West Taijinar Salt Lake.The technological process is divided into three parts: brine refining,ion-exchange membrane electrolysis and product preparation.The main contents are as follows.The brine refining part includes four stages: magnesium removal,boron removal,boron and magnesium removal depth,and sodium removal from brine.Fisrtly,chemical precipitation was used to separate most magnesium in the brines,and the removal rate of magnesium is 96.87%,the recovery rate of lithium is 97.95%.Then,using LSC-800 resin as ion exchange resin to remove boron from brine,the effects of factors,such as adsorption time,p H value,quantum of resin,reaction temperature etc,were investigated.Langmuir model and Freundlich model were applied to investigate adsorption behavior about LSC-800 resin.The removal rate of boron and the recovey rate of lithium are respectively 96.18% and 92.90%.Thirdly,LSC-800 resin and D469 resin were used for the deep adsorption of boron and magnesium from brine,through adjusted the mass ratio of resins to achieve a better co-adsorption effect,which can reduce boron and magnesium concentration less than 1 mg/L.Lastly,according to the phase equilibrium theory,forced evaporation was used to remove sodium from brine by controlling the evaporation conditions.The sodium removal rate is 90%,and the lithium loss rate is 4?6%.The refining brine can be used for ion-exchange membrane electrolysis.In the process of ion-exchange membrane electrolysis,one membrane and two chambers were used for the electrolysis experiment,the membrane was a cation exchange membrane,and the two chambers were an anode chamber and a cathode chamber.The anode and cathode solution were respectively refined brine and low-concentration lithium hydroxide solution.The influence of factors,such as current density,Li Cl concentration of anode solution,p H value of anode solution,Li OH concentration of cathode solution and circular flow rate have been analyzed briefly,the effects of experimental factors on performance parameters,including the type of cation exchange membrane,current density,Li Cl concentration of anode solution,circular flow rate were investigated by univariate experiment,the change of performance parameters such as average voltage,current efficiency and direct power consumption were also investigated.lithium hydroxide solution with mass fraction of 8?10% was obtained by ion-exchange membrane electrolysis.The product preparation process included two parts: evaporative crystallization process,washing and drying process.By controlling the evaporation temperature and concentration ratio of lithium hydroxide solution during the evaporative crystallization process,and controlling the ratio of solid to liquid,washing times,drying temperature,drying time and other conditions during the washing and drying process,the product of battery grade lithium hydroxide,which is accordance with the national standard of battery grade lithium hydroxide monohydrate(GB/T 26008-2010)can be prepared.Summarizing the process.Finally,the total process flow from saline brine to lithium hydroxide product has been designed.