Evaluating Extraction of Magnesium and Lithium Compounds from Seawater Using Byproducts of Demonstration-Scale Bipolar Membrane Electrodialysis.

Seawater is an abundant source of critical minerals, but low concentrations make mining uneconomical. Coupling seawater mining with other ocean-based processes could improve economic feasibility. Here, we investigate coupling it to bipolar membrane electrodialysis (BPMED), an emerging technology developed for ocean alkalinity enhancement (OAE)-a marine carbon dioxide removal (mCDR) pathway. BPMED generates acid and base from seawater, which are key inputs for mineral extraction. Using a demonstration-scale BPMED system, we characterized and identified mineral-rich streams within the process for Li+ and Mg2+ recovery. Li+ was extracted using an inorganic sorbent (H2TiO3) regenerated with BPMED acid, while high-purity Mg(OH)2 was selectively precipitated using BPMED base via a laminar coflow method. Our results show that Li+ and Mg2+ extraction from natural seawater using BPMED-sourced acid/base streams provide performance comparable to that obtained using commercial acid/base solutions. Preliminary cost-benefit assessments show that Mg(OH)2 extraction could generate positive net revenue, but Li+ recovery is uneconomical relative to the value of Mg2+ recovery. Importantly, the alkaline effluent post-Mg(OH)2 recovery retains alkalinity relevant to OAE under tested conditions. Our study demonstrates, for the first time, the feasibility and benefits of integrating mCDR with seawater mining to advance sustainable ocean-based climate solutions.