Ultrasonic-induced water-oil interface of microdroplets: A selective and rapid green approach for gold recovery from...

Developing sustainable and efficient methods for gold recovery is of vital importance for resource recycling and environmental protection. However, conventional extraction methods are often hindered by complex material synthesis requirements, cumbersome operational procedures, poor selectivity, and limited adsorption capacity in complex acidic leachate matrices. Herein, we report a novel green strategy utilizing ultrasonic-induced water-in-oil microdroplets for the rapid and highly selective extraction of gold from electronic waste (e-waste). This unique microreactor system exhibits exceptional performance: achieving over 99 % Au(III) removal within merely 10 min across a remarkably wide pH range (1 to 10) and a broad initial gold concentration span (0.01 to 1 mM). Crucially, this method demonstrates outstanding selectivity and recyclable for Au(III), maintaining high extraction efficiency (>95 %) even in the presence of high concentrations of common interfering ions and over 10 consecutive extraction cycles. Mechanistic investigations reveal that the Au(III) was effectively reduced to Au(0) precipitates by the electrons (e^-) and superoxide free radicals (·O₂^-) generated at the water-oil interface of microdroplets. More importantly, the microdroplets method was applied in an experiment for recovering gold from the waste printed circuit board (WPCB) leachates, achieving an impressive extraction efficiency of over 90 %. This ultrasonic-induced water-in-oil microdroplets extraction method demonstrates remarkable efficiency, selectivity, simplicity, low-cost and eco-friendly for gold, providing a revolutionary approach for sustainable and efficient recovery of precious metals.