Selective Lithium Separation by Hydrophobic Polymer Modified Cation Exchange Membrane
Open AccessLithium is a promising element that has been widely applied in various fields. It has been estimated that lithium consumption will exceed the manufacturing amount in the future decades. Considering the rising demand and the decreasing land resources of lithium, novel technologies for lithium extraction from identified aqueous sources have gained increasing attention. Several lithium-extraction methods have been developed from water resources, including precipitation, solvent extraction, sieves ion-exchange sorbent, membrane-based separation method, and electrochemical extraction method. Membrane capacitive deionization (MCDI) is an electrochemical desalination method using ion exchange membranes to remove ions from the liquid by applying an electrical potential between two porous electrodes. This research studied the lithium selectivity performance by MCDI with the hydrophobic polymer-modified Cation Exchange Membranes (CEM). We successfully modified commercial CEMs via an optimized procedure with different polymer layers (PPyCl, PPyTS, and PPyDS) to investigate how the surface hydrophobicity affected the selectivity of lithium in Li/Na solution and Li/Ca solution. PPyDS CEM presents the highest hydrophobicity than other modified membranes. Its water contact angle increased up to 89.5˚ ± 3.5˚. The effect of dopants and dosage on polymer hydrophobicity was investigated as well. In comparison, dopant type is more significant for CEMs modification with PPy coating than dosage. Moreover, the MCDI experimental results showed that Lithium selectivity over Na stays from 0.60 ± 0.03 to 0.64 ± 0.02. While the selectivity performance of lithium over calcium increases from 0.58 ± 0.06 to 0.99 ± 0.07.
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