Preparation of high-purity tellurium powder by hydrometallurgical method

This hydrometallurgical method consists of oxidation leaching, sulfide impurities removing, and sulfur dioxide reduction. The crude tellurium powder was treated by H2O2 oxidation for 2.0 h at pH 2.5 when adding 50 ml H2O2 (30 %) per 100 g raw material, a tellurium recover rate around 91 % is achieved. The tellurium leaching ratio can reach 98.9 % under 3.75 mol·L−1 NaOH concentration in liquid–solid ratio of 5:1 at 80 °C for 1.5 h. The overall separation of tellurium and other heavy metals is optimum at sulfide dosages of about 1.1 times of the theoretical values. The removal rates of Ag, Ni, Pb, and Cu from the solution are greater than 99.8 %, and As and Se removal rates are 98.6 % and 97.2 %, respectively. Over 99.5 % tellurium can be recovered by SO2 reaction when the operation is conducted at 85 °C in 6 mol·L−1 HCl solution. The tellurium powder with size of <5 μm and purity of >99.999 % is obtained.