Recycling of metal-organic chemical vapor deposition waste of GaN based power device and LED industry by acidic leaching: Process optimization and kinetics study

What is it about?

Recovery of metal values from GaN, a metal-organic chemical vapor deposition (MOCVD) waste of GaN based power device and LED industry is investigated by acidic leaching. Leaching kinetics of gallium rich MOCVD waste are studied and the process is optimized. The gallium rich waste MOCVD dust is characterized by XRD and ICP-AES analysis followed by aqua regia digestion. Different mineral acids are used to find out the best lixiviant for selective leaching of the gallium and indium. Concentrated HCl is relatively better lixiviant having reasonably faster kinetic and better leaching efficiency. Various leaching process parameters like effect of acidity, pulp density, temperature and concentration of catalyst on the leaching efficiency of gallium and indium are investigated. Reasonably, 4 M HCl, a pulp density of 50 g/L, 100 oC and stirring rate of 400 rpm are the effective optimum condition for quantitative leaching of gallium and indium.

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Why is it important?

The gallium rich waste MOCVD dust is a biphasic material, contain two different phases like GaN and Ga0.97N0.9O0.09. The Ga0.97N0.9O0.09 phase of MOCVD dust can be leached easily by a cost effective method using 4 M HCl as lixiviant. Leaching efficiencies of 64.62 % and 99.99 % for gallium and indium, respectively, were achieved at their optimum condition, i.e. lixiviant of 4 M HCl, pulp density of 50 g/L, temperature of 100 oC, agitation speed of 400 rpm and time for 60 minutes. It was observed from the experiments and kinetic analysis that the kinetic model: C_t=C_max (1-〖exp〗^(-kt)) was the most suitable to describe the leaching process of the gallium rich waste MOCVD dust in the HCl solution. As Ga0.97N0.9O0.09 phase of MOCVD dust can be leached quantitatively, a cost effective, environment friendly hydrometallurgy process can be developed for the recycling of the gallium rich waste MOCVD dust. The GaN phase of the gallium rich waste MOCVD dust is hard to leach, a pretreatment process followed by leaching is recommended. The developed process can meet the national urban mining policy and international environmental directives.