Selective Recovery of Gallium (Indium) from Metal Organic Chemical Vapor Deposition DustA Sustainable Process

Gallium (indium)-containing dust as a hazardous waste generated from light-emitting diode (LED) epitaxial wafer manufacturing attracts worldwide attention because of both resources and environmental importance. Oxidative roasting combined with acidic leaching is frequently utilized to recover the corresponding metals from such dust, while the recovery rate is usually low because of the rather inert physicochemical properties of gallium compounds. Simultaneously, the selectivity of leaching is low, which results in complex separation or purification is required in order to obtain the required product (e.g., metallic gallium, Ga­(OH)3). In this research, it is demonstrated that the selectivity of leaching can be achieved via properly controlling the physicochemical properties of the leaching solution and the leaching conditions. The leaching rate of gallium can reach 90.01% through optimizing the effects of different parameters, including leaching reagent concentration, solid-to-liquid ratio, reaction temperature, reaction time, and rotation rate, which is about 16% higher than the conventional method. Moreover, the corresponding leaching mechanisms and kinetics were also evaluated, and the apparent activation energy of the reaction is determined as 24.33 kJ/mol. Without further purification, 99.8% of gallium and 99.1% of indium can be further recovered as Ga­(OH)3 and In­(OH)3 from the leaching solutions, respectively. In the whole process, the effective recycling rates of gallium and indium are 89.83% and 92.42%, respectively. This study provides bases for developing an effective recycling process of such waste with high recovery rate, advanced selectivity, and low environmental impacts.