Non-thermal reduction of indium oxide and indium tin oxide by mechanochemical method

A non-thermal process for reducing indium(III) oxide (In₂O₃) and/or indium tin oxide (ITO) into indium-metal by milling with lithium nitride (Li₃N) under (NH₃) or nitrogen (N₂) gas environment is proposed in this paper. Milling operation causes mechanochemical reaction in the systems of In₂O₃/ITO and Li₃N, to form In and LiOH. The latter is soluble in water, so that the milled sample was subjected to washing with water, enabling us to recover indium-metal. According to the characterization of the milled products by X-ray diffraction (XRD), the reduction of In₂O₃/ITO can be achieved in a short period of time. Analytical data by inductively coupled plasma (ICP) from dissolution of the pellets in acidic solution clearly shows that indium-metal concentration is over 95% and the yield of In from the starting oxide sample is more than 97%, depending on the milling condition. The reaction mechanism between In₂O₃/Li₃N and NH₃/N₂ is also discussed in the paper, and this could be applied to recover indium-metal from electric device wastes containing ITO.