Efficiently rejecting and concentrating Li+ by nanofiltration membrane under a reversed electric field

Efficiently concentrating dilute lithium ion (Li+) solution is very important for the synthesis of Li+ products after Li+ extraction from salt lake brine. In this work, a reversed electric field coupling nanofiltration membrane (RENF) was designed to reject and concentrate Li+ solution from a low concentration feed. The effects of membrane pore structure, electric field and electrode spacing, and feed properties on Li+ rejection of RENF process were investigated. The concentration performance and energy consumption of the RENF process were also explored. Results showed that the NF membrane with a small structural coefficient under an electric field of >8 V/cm exhibited high Li+ rejection. A Li+ rejection of 97.01% by RENF and a high permeation flux were achieved. Likewise, the RENF showed a stable concentrating performance with a high Li+ recovery for dilute Li+ solution. The energy consumption of the RENF process only has a 0.17% increase as compared with the NF process, an order of magnitude lower than that of the RO process. The high rejection performance of RENF was resulted from the synergistic effects of the reversed EF dragging force to cations and sieving effect of the NF membrane with a small structural coefficient.