The Research On Separation Of Magnesium And Lithium From Brine By Electrodialysis

The salt lake brine contains abundant lithium resource in our country,however,the majority of them present the characteristic of high Mg²⁺/Li⁺ratio,which is the key obstacle to realize the separation of magnesium and lithium.The traditional precipitation method is not suitable for the lithium recovery from this kind of brine.It is a difficult technical problem of extracting lithium from high Mg²⁺/Li⁺ratio（in the mass concentration style）brine.Electrodialysis is a new type of membrane separation technology,in which anion and cation exchange membranes have selectivity for corresponding ions in the solution under direct current electric field.Electrodialysis has characteristic of simple process,low energy consumption,economical and environmental protection,etc.It has been widely used in seawater desalination,chemical separation and other fields.The separation process of magnesium and lithium by electrodialysis was studied in this paper.On the one hand,the operating voltage,the feed flow rate,the Mg²⁺/Li⁺ratio and the pH value were investigated.The results showed that the increase of operating voltage could improve the separation coefficient and the recovery ratio of Li⁺,but energy consumption would also increase.With the increase of feed flow rate,the separation coefficient had a rinsing trend,but too large flow rate would enlarge energy consumption.When the Mg²⁺/Li⁺ratio was in the range of 5-92,electrodialysis showed good separation efficiency of magnesium and lithium.The Mg²⁺and Li⁺separation coefficient reached77.59 and the recovery ratio of Li⁺was 72.10%in the pH=4.7 which was the optimal value in this research.According to the comprehensive analysis of the experimental results,the optimal operation conditions of electrodialysis device was that the operating voltage was5V and the flow rate was 130 L/h.When the brine with a Mg²⁺/Li⁺ratio of 60 was treated by electrodialysis under this condition,the concentration of Li⁺was concentrated to 0.210g/L from 0.148 g/L.The recovery ratio of Li⁺and the current efficiency were 72.46%and8.68%,respectively.And the separation coefficient was 12.48 and the specific energy consumption was 0.17 kWh/mol Li.On the other hand,the concentration effect of Na⁺and K⁺on the separation of magnesium and lithium in brine was investigated respectively.The results showed that with the increase of Na⁺concentration,the rejection of Li⁺increased gradually,but the separation coefficient and the recovery ratio of Li⁺decreased gradually.The greater concentration of Na⁺in brine was not conducive to the separation of magnesium and lithium.The effect of K⁺was some as that of Na⁺.The rejection of Li⁺and Mg²⁺were increased with the increase of K⁺concentration,while both the separation coefficient and the recovery ratio of Li⁺were decreased.It indicated that the higher the concentration of Na⁺and K⁺in brine,the lower the migration amount of Li⁺.It led to more obvious competition with Li⁺through the membrane and adverse impact on the separation of magnesium and lithium.