The Study Of Extraction Of Lithium With Polymer Inclusion Membrane And Drowning-out Crystallization Methods

There are abundant amount of lithium source in the salt lake brine in China, butthe extraction of lithium from lake is still a problem because of the high mass ratio ofmagnesium to lithium. As a result, the extraction of lithium will certainly be interferedby magnesium.In order to develop a lithium extraction technology with high efficiency, thetransport behavior of Li through the polymer inclusion membrane with facilitatedtransport by the carrier and the magnesium/lithium separation performance of thepolymer inclusion membrane have been investigated in this study. Meanwhile, aprocess for purifying lithium hydroxide by drowning-out crystallization was alsostudied. The main contents of this study are shown as follows:(1) The dibenzo-14-crown-4with high selectivity of lithium was synthesized, andthe polymer inclusion membranes were prepared which composed of plasticizer, basepolymer and the dibenzo-14-crown-4as the carrier. And then, the effect of variousfactors of the transport system on the transport of lithium through the polymerinclusion membrane were investigated. The factors involved the transport temperature,carrier concentration, plasticizer concentration, plasticizer types, stirring speed, initialLi concentration and pH in the source solution. Based on this, the competitiontransport experiment of Mg/Li ion through the polymer inclusion membrane wasperformed. The results show that the polymer inclusion membrane system with thedibenzo-14-crown-4as the carrier has good performance for the selective extractionof lithium over magnesium.(2) In order to solve the problems such as complicated operation, high energy cost,low efficiency and environmental pollution in the traditional purification processes oflithium hydroxide, a efficient and clean purification technique of drowning-outcrystallization with ethanol as drowning-out agent was investigated. The operation issimple and can be performed at room temperature, as a result, the energy cost is lowerthan the traditional purification processes. And the drowning-out agent of ethanol canbe recovered by the alcohol-permselective composite membrane after thedrowning-out crystallization process, and this recovered ethanol can be reused asdrowning-out agent, thus the process will take advantage of conserving raw materialsand reduced environmental pollution.