A novel and clean process for extracting tellurium and bismuth from Dashuigou tellurium ore by oxidizing leaching

Abstract

As the only independent tellurium deposit in the world, the exploitation and utilization of Dashuigou tellurium deposit has attracted more and more attention in recent years. Phase analyses show that the mineral composition of tellurium ores is complex. Tellurium and bismuth in tellurium ores are of low grade and sulfur is of high grade. We proposed a process of oxidative leaching followed by selective reduction to recover tellurium and bismuth from Dashuigou tellurium ores. The leaching behavior of tellurium ores in Fe3+-H2SO4 media has been studied systematically in the present work. Before leaching, tellurium and bismuth exist in the form of Bi2Te2S and BiTe in the raw tellurium ores. After leaching, tellurium and bismuth exist in the lixivium in the form of Te4+ or HTeO2+ and Bi3+, respectively. The effects of particle size, H2SO4 concentration, Fe3+ concentration, reaction temperature, reaction time and liquid-solid ratio on the leaching rate of tellurium and bismuth are discussed in detail. The leaching ratios of tellurium and bismuth reach 95.61% and 95.77%, respectively, under the suitable conditions of 40 min, 104–150 μm, 90 °C, 150 g/L H2SO4, 60 g/L Fe3+ and liquid-solid ratio of 6:1 mL/g. The apparent activation energies are <13 kJ·mol−1, which implies that the leaching process is controlled by diffusion through the product layer. Sulfur exists in lixivium as SO42− ion or in residue as elemental sulfur, avoiding the formation of toxic gases to pollute the environment. Most of the calcium elements in tellurium ores enter the residue in the form of CaSO4. Thus, the lixivium can be directly used to obtain the tellurium by reduction reaction with Na2SO3 or SO2. The process described in this work is proven to be an efficient and environmentally friendly extraction process for the treatment of low-grade tellurium ores with high sulfur content.