Preparation of Quaternary Modified Positive Charge Nanofiltration Membrane for Li+/Mg2+Separation
The effective separation of Mg2+and Li+is a major challenge for the extraction of lithium resources from salt-lake brines.In this work,the surface grafting method was applied to fabricate the nanofiltration membrane,which introduced 1-(2-pyridyl)piperazine(PDP)into the interfacial polymerization reaction to construct a polyamide membrane with pyridine groups.Then quaternization reaction of bromethylamine(BEA)with the pyridine group on the membrane surface transformed the pyridine group into a quaternary ammonium group,which produced a positively charged quaternary ammonium salt nanofiltration membrane(TFC-PDP-BEA membrane).The optimal reaction conditions were investigated by examining the effects of PDP concentration,BEA concentration,reaction temperature and reaction time on the membrane structure and performance.The prepared TFC-PDP-BEA membrane showed rejections of 90.21% for MgCl2 and 40.78% for LiCl under the optimal conditions,with a separation factor of 6.05 and a water permeation flux of 37.27 L/(m2·h).This work established a method to modify the surface of a polyamide composite nanofiltration membrane with a positive charge,and improved the lithium-magnesium separation performance,which provides a technical reference for the separation of Li+/Mg2+by nanofiltration membrane.
membrane separationquaternary ammonium saltlithium extraction from salt lakesubstitution reactionhalogenated hydrocarbons
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