Selective isolation of gallium and indium from waste photovoltaic modules facilitated by extractant-mesoporous activated carbon composites

Abstract

With the expanded installation and decommission of photovoltaic modules, the recovery of critical metals involved, such as gallium (Ga) and indium (In), is becoming an important issue. Liquid–liquid extraction, as a conventional recovery method, is always accompanied by serious emulsification, poor phase-separation, and huge volatile organic solvent consumption. Here, a more efficient and environmentally benign solid adsorbent was innovatively prepared by combining P507 with coconut shell-derived mesoporous activated carbon (P507@MAC) for Ga and In recovery. Surprisingly, P507@MAC retained an excellent selectivity for In3+ from the coexisting ions (Al3+, Zn2+, Cd2+, Cu2+, and Mg2+), and the selectivity for Ga3+ was actually increased compared to P507. Unexpectedly high adsorption capacities of P507@MAC for Ga3+ (67.0 mg·g−1) and In3+ (52.6 mg·g−1) were found to be 1.85 and 1.23 times the accumulation of MAC and P507, respectively, and much superior to that of P507-impregnated resin (11.8 mg·g−1 (Ga3+) and 36.5 mg·g−1 (In3+)). Moreover, the adsorption capacity of this novel adsorbent demonstrated no significant decrease over 6 cycles. Such desirable capture capability of Ga3+ and In3+ was ascribed to the rich mesopores and high surface area of MAC, providing adequate adsorption sites for phosphoryl groups and metal ions. Going forward, by demonstrating successful Ga3+ and In3+ separation from the leaching solution of waste CIGS photovoltaic modules, the extractant-MAC composites might provide a promising and industry-compatible approach for valuable metal recovery.