The Research On Separation And Purification Of Lithium From Brine/Seawater By Electrodialysis

With the speed development of high-tech enterprises,such as green car,wind power,nuclear power and so on,more and more lithium metals are needed.Nowadays,the focus of people forward to salt lake brines.This pathway will ease the shortage of lithium resource,effectively.But the precipitation process which was used widely at present need a large area of salt pan and a certain amount of chemicals.To some extent,the precipitation method caused the waste of the resources because of high Mg²⁺/Li⁺in multiple salt lake brines of our country.So,some new technologies of recovering lithium from brine,which is high-efficiency,low-cost and environment-friendly,are urgent need to develop.Membrane separation technologies have many advantages in industrial production:higher separating efficiency,lower energy consumption,straightforward operation and integrated conveniently.As one of the electric membrane technologies,electrodialysis?ED?can be achieved the directional migration of target ion in liquid phase under an electric field.Then,the target ions were separated and purified.In order to provide the relevant research of recovering lithium from brine or seawater with theoretical basis and technological support,some studies were carried out are as follows:?1?The influence of co-existing ions(Na⁺,K⁺,Ca²⁺,Mg²⁺)under different concentrations and feed temperatures were studied under binary chloride system which contain lithium ions.The results show that the competitive migration between co-existing ions and lithium ion have complicated relativity in their concentration and composition:the higher the co-existing ion concentration,the greater the competitive migration of co-existing ion;high concentration of co-existing can lead to low-grade current efficiency and excessive specific energy consumption of recovering lithium process;the influence order of co-existing ions with the same concentration on lithium migration was:K⁺>Na⁺>Ca²⁺>Mg²⁺,and this is consistent with the order of hydrated ionic radius size of those ions.Based on this,the migration process of cations through monovalent selective cation exchange membrane was investigated in theory.And we propose that ions migration process was achieved by the method of dehydrating partially.Then the partial dehydration conceptual model was obtained.?2?The purification process of lithium in concentrate seawater and three kinds of salt lake brines were also investigated.And the influence of polybasic co-existing ions on the separation and purification process of lithium by selectrodialysis?SED?technology were discussed.The results show that the lithium ions in all saltwater system have been purified;the migration rate of Ca²⁺,Mg²⁺and SO₄^2-under a low level;the migrated mass of Li⁺and purification result of LiCl were enhanced with increased of applied voltage.However,the Na⁺/Li⁺and K⁺/Li⁺were also increased.And,the appropriate voltages of concentrate seawater and practical salt lake brines were 7 V and 10 V,respectively.Moreover,the ions migration resistance was increased with the decreasing of V_C/V_D,i.e.,V_C/V_D shouldn't be too lowest,and appropriate VC/VD value was 0.8.