Experimental study and simulation on nanofiltration separation of lithium and magnesium from sulfate desorption solution
In order to explore the feasibility of lithium extraction from salt lake brine by"adsorption-membrane"method,experimental study and"concentration-diafiltration"simulation calculation of lithium-magnesium separation in sulfuric acid desorption solution obtained from brine were carried out by using NF270 nanofiltration membrane.First,the basic structure and separation characteristics of NF270 membranes were determined,and the effects of pressure and pH on the flux and retention of Li2SO4 and MgSO4 for the single salt solution were initially investigated.Secondly,the separation of magnesium and lithium at different pH and Li+mole fraction(xLi+)was evaluated and an analysis of the separation was performed.The results showed that under neutral conditions,the strong electrostatic repulsion between the NF270 membrane and SO4-resulted in high retention rates of Li+and Mg2+.The separation could only be achieved by lowering the pH below the isoelectric point.Compared with xLi+,the effect of pH on the separation of lithium and magnesium was more significant.When xLi+was 0.40 and pH was 1.7,the separation factor could reach more than 10.Then,the separation performance of the NF270 membrane on lithium and magnesium for the simulated desorption solution with other ions was studied.It was found that ions of Na+,K+and Ca2+with low concentrations did not affect the separation factors of lithium and magnesium,and the membrane could achieve high retention to Ca2+and Mg2+,reducing the risk of scaling in subsequent treatment.Finally,based on the composition and retention rate of the simulated adsorption solution,the selective separation of Li+and Mg2+by the NF diafiltration was simulated for the binary solution containing 0.023 mol/L MgSO4 and 0.125 mol/L Li2SO4.After pre-concentration and diafiltration,the concentrations of Mg2+and Li+were 0.20 mol/L and 0.66 mol/L in the feed solution,and 0.0025 mol/L and 0.17 mol/L in the permeate,respectively.At this time,the Li+recovery could be up to 75％,proving the feasibility of realizing the separation of magnesium and lithium in the desorption solution by the NF diafiltration process.
nanofiltrationmagnesium and lithium separationdesorption solutionspre-concentration and diafiltration
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