MOCVD leaching though mechanochemical oxidative process

What is it about?

Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga0.97N0.9O0.09 is a concern for the environment can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga0.97N0.9O0.09 of the MOCVD dust is leached at the optimum condition. Subsequently, the leach residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86 w/w % the gallium and Indium are leached using 4 M HCl, 100 oC and pulp density of 100 kg/m3, respectively. After mechanochemical oxidation, both these processes achieved 90 w/w % gallium and 1. 86 w/w % of indium leaching at their optimum condition.

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Why is it important?

The MOCVD dust is a mixture contains two different phases like GaN and Ga0.97N0.9O0.09, where the latter is easier to leach than the former. The GaN needs mechanochemical treatment process prior to proceed for leaching. Treatment of MOCVD dust and recovery of gallium is feasible through mechanochemical oxidation and leaching. Mixture of GaN of MOCVD dust and Na2CO3 completely oxidizes through annealing at 1200 oC. For total recycling of the MOCVD dust, the quantitative leaching goal can be achieved through mechanochemical pretreatment (mixed with Na2CO3 and ball milling) and oxidative annealing. Based on pretreatment, annealing, leaching and indium recovery interest two different processes are proposed for treatment of MOCVD waste dust. The first Scheme 1 represented complete leaching of Ga0.97N0.9O0.09 component of the waste MOCVD dust at the optimum condition. Subsequently, the leach residue was mixed with Na2CO3, ball milled, followed by annealing, then leached to recover gallium and indium. The second Scheme 2 is established based on pretreatment of the waste MOCVD dust by mixing it with Na2CO3, ball milling, and annealing, followed by the acidic leaching. Both of these processes are close looped processes and both the processes could achieve quantitative leaching. The proposed process in Scheme 1 can be an environment-friendly, techno economical process for quantitative leaching of the MOCVD dust. Both of these processes are competitive with each other, have the potential to be used in the industrial leaching process to recover required metal values. The proposed treatment processes are green and clean technology as minimum energy and no hazardous chemicals used for processing.

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