Flow-Assisted Selective Mineral Extraction from Seawater

• Published in: Environmental science & technology letters Vol. 9; no. 7; pp. 645 - 649
• Main Authors: Wang, Qingpu, Nakouzi, Elias, Ryan, Elisabeth A., Subban, Chinmayee V.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12.07.2022; American Chemical Society (ACS)
• Subjects: ENVIRONMENTAL SCIENCES; Magnesium; Mineral; Non-equilibrium; Seawater mining; Selectivity; Treatment and Resource Recovery; Mineral; Selectivity; Magnesium; Seawater mining; Nonequilibrium
• ISSN: 2328-8930; 2328-8930
• DOI: 10.1021/acs.estlett.2c00229

The sustainable production of critical materials from natural sources requires a paradigm shift away from currently used resource-intensive processes. We report a single-step, laminar coflow method (LCM) that leverages nonequilibrium conditions to selectively extract pure Mg­(OH)2 from natural seawater. Conventional seawater-based Mg extraction involves adding individual or a combination of precipitants to obtain Mg­(OH)2, but the coexistence of Ca2+ unavoidably results in CaCO3 impurities requiring additional purification steps. Here, we show that the nonequilibrium conditions in LCM achieved using a microfluidics device and by simply coinjecting a NaOH solution with seawater can result in improved selectivity for Mg­(OH)2 unlike in a conventional bulk mixing method. The resulting precipitates are characterized for composition, and the process yield and purity are optimized through systematic variations of the reaction time and the concentration of NaOH. This is the first demonstration of LCM for selective separation, and as a one-step process that does not rely on novel sorbents, membranes, or external stimuli, it is easy to scale up. LCM has the potential to be broadly relevant to selective separations from complex feed streams and diverse chemistries, enabling more sustainable materials extraction and processing.