With the rapid expansion of the market scale for indium phosphide (InP) semiconductors in high-tech industries such as optoelectronics and solar energy, the generation of hazardous waste InP has also increased dramatically, and the task of recycling waste InP is urgent. However, InP as a representative phosphide semiconductor is prone to produce highly toxic substances such as yellow phosphorus and PH3 in the recycling process, which discourages most companies from using it. In this study, a safe and efficient method of "vacuum decomposition-directional condensation (VD-DC)" is proposed to recover valuable materials from waste InP. In this method, briquetting pretreatment is used to improve thermal conductivity. At a decomposition temperature of 1123 K, system pressure of 30 Pa, and holding time of 3.5 h, indium with a purity of 99.43 wt% is obtained, and the direct yield reaches 98.54%. Non-toxic and stable red phosphorus with a purity of 98.14 wt% is recovered by converting the condensed yellow phosphorus at 573 K. Vacuum technology significantly reduces the decomposition temperature of InP and avoids the emission of waste water and waste gas, thus operating in an environmentally friendly manner.

Vacuum volatilization is a clean and efficient method for metal purification, alloy separation, and comprehensive recovery of secondary resources. The evaporation kinetics of In and In–Sn alloys were investigated to better understand the evaporation mechanism during the vacuum volatilization of In. The evaporation rates of the In and In–Sn alloys at 1173–1373 K and 5 Pa increased significantly with increasing temperature in accordance with the equation ω = e(a+b∙T). The evaporation rates at 1323 K and 5 Pa decreased with increasing crucible depth in accordance with the equation ω = a2+(a1-a2)/(1+e(h-b)/c). For In and In–Sn, the total mass-transfer coefficients of In were obtained at different temperatures and crucible depths. A theoretical kinetic model of In was established and limiting links were obtained vacuum volatilization of In and In–Sn.