Green process for recovering indium and other precious metals from high-sulphur hot filter residues via sodium-hydroxide hydrothermal treatment

Indium (In) has vital applications in solar photovoltaic technology and light-emitting diodes. However, the resource for In production is low. Zinc smelting is an important source of In, but the average In recovery rate is only 20%. The annual economic loss due to the loss of In is as high as USD 199.7 million. In this study, a high-sulphur hot filter residue (HFR) was processed via sodium-hydroxide (NaOH) hydrothermal treatment (NAHT). By varying the amount of NaOH and using the dissolution exotherm of NaOH, sulphur element (S0) in HFR was transferred to a liquid phase. Thus, In and other precious metals originally wrapped in S0 were enriched in the slag phase (TLR). The In grade in TLR was as high as 1700 g/t, and the recovery rate was 99%. In addition, 10.94 g/t gold, 125.81 g/t silver, 15.18% zinc and 22.27% iron were incidentally recovered. The wastewater produced in the process showed better effects than industrial Na2S in flotation processes. Thus, NAHT is an effective green recovery technique for recovering In and other precious metals from HFR. Further, the recovered In can yield an annual revenue of USD 1,122,170 for the plant. Therefore, the treatment of HFR plays an important role in zinc hydrometallurgical smelting plants.