Recovering Critical Metals from Brines: Technology Landscape, Circular Economy, and Future Trends

The accelerating demand for critical metals (CMs) such as lithium, cobalt, and rare earth elements has intensified interest in alternatives to conventional mining. Brines, including geothermal fluids, produced water, and desalination reject streams, represent a chemically diverse and underutilized resource, but their exploitation is constrained by complex ion compositions, high salinity, and strong variability across sources. This review synthesizes recent advances in brine-based CM recovery technologies, spanning electrochemical, membrane, adsorbent, and hybrid thermal–separation platforms, with an emphasis on how brine chemistry, selectivity mechanisms, and system integration govern performance beyond laboratory conditions. Across technology classes, the review reveals that selectivity and efficiency gains demonstrated under simplified brines frequently degrade under realistic multicomponent chemistries, helping explain the limited translation of many promising concepts to pilot scale. Beyond individual processes, the review evaluates CM recovery from brines through a circular economy lens, highlighting how system-level design choices influence resource retention and supply resilience. Ecological network analysis (ENA) is examined as a design-stage tool to quantify circularity potential and identify how upstream brine sourcing and downstream coupling to energy, water, or material users shape overall system value. While ENA enables early assessment without detailed operational data, the review identifies critical limitations arising from coarse network resolution, data scarcity, and weak coupling to experimentally measured performance, underscoring the need for tighter integration between laboratory results and system-level models. Drawing on these insights, the review argues that progress toward scalable CM recovery from brines will depend less on isolated material improvements and more on mechanistic validation under realistic chemistries, harmonized performance metrics, and deliberate codesign of extraction technologies with downstream utilization pathways. Integrating techno-economic, life-cycle, and policy considerations at early design stages is shown to be essential for distinguishing concepts with true deployment potential from those limited to proof-of-concept demonstrations. Collectively, these findings provide a structured framework for prioritizing research and design choices that can translate brine-based CM recovery from promising experiments to robust, circular, and supply relevant technologies.