Low-salt closed-loop management of secondary gallium resources: From selective recovery to high-purity upgrading.

Gallium is essential for semiconductors, photovoltaics, optoelectronics, and wide-bandgap electronic devices, but its primary supply remains constrained by dispersed occurrence and by-product-dependent production. Secondary gallium-bearing wastes, including spent LEDs, printed circuit boards, CIGS modules, IGZO targets, integrated circuits, MOCVD residues, and wafer-processing wastes, are therefore becoming important alternative resources. Their utilization, however, is restricted by phase recalcitrance, physical encapsulation, impurity co-dissolution, reagent consumption, salt accumulation, and stringent product-purity requirements. This review evaluates secondary gallium recovery as an integrated low-salt closed-loop management process rather than a series of isolated leaching and separation operations. Representative wastes are compared according to gallium occurrence, impurity fingerprints, release barriers, and process priorities. Phase-engineering activation and selective separation technologies, including adsorption, ion exchange, solvent extraction, liquid membranes, and ionic-liquid-based systems, are assessed using a practical selective-window framework that considers gallium recovery, impurity rejection, regeneration stability, salt-load evolution, and downstream compatibility. Solution-end purification and metal-end refining are further integrated to connect waste-derived gallium intermediates with high-purity products. The analysis indicates that effective gallium recycling requires occurrence-guided activation, selective impurity control, stable salt management, and product-oriented purification rather than recovery-efficiency maximization alone.