Nanofiltration as pretreatment for lithium recovery from salt lake brine

J Zhai and A Balogun and S Bhattacharjee and RJ Vogler and R Khare and M Malmali and A Deonarine and YX Shen, JOURNAL OF MEMBRANE SCIENCE, 710, 123150 (2024).

DOI: 10.1016/j.memsci.2024.123150

Nanofiltration (NF) membranes have been used extensively for lithium extraction pretreatment from salt lake brine. However, the separation of lithium from divalent cations by NF membranes under high salinity conditions is technically challenging. Here, Salton Sea geothermal brine, a promising lithium enriched resource in the U.S., was used to conduct comprehensive experiments to evaluate NF as a potential pretreatment approach under different feed salinity and pH levels. Among the 3 most popular commercial membranes (NF270, DL, and NF90), poor rejection, low Li/Mg selectivity (1 2), and low flux (28 42 L m- 2 h- 1 , LMH) were found at 30 bars at higher salinity. With the feed concentration being diluted from 200 g/L to 20 g/L, the rejection of divalent ions (68.5 79.1 %) and flux (75 135 LMH) improved significantly. pH only influenced the selectivity when the feed concentration was low. Our molecular dynamics simulation confirmed that the hydrogen bond dynamics at high salinities reduced the water mobility, while the salt mobility deterioration was found to be relatively insignificant. Therefore, the rejection was decreased at high feed salinity. These are critical findings to be considered if NF is employed to pretreat brine for lithium extraction. A preliminary economic assessment was conducted using combined NF and crystallization to recover Li from geothermal brine. With enormous high content of calcium in the Salton Sea geothermal brine, we suggest placing crystallization upstream of NF to remove most of divalent cations. Then, the treated brine required to be diluted to a range of 18 30 g/L followed by three-stages of NF that can achieve the final molar Li/Mg and Li/Ca ratios upward 99.

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