Recovery of tellurium from high tellurium-bearing materials by alkaline pressure leaching process: Thermodynamic evaluation and experimental study

• Technical roadmap analysis by Pourbaix diagram of Cu-Te-Se-H2O.
• Thermodynamic simulation based on raw material compositions using Factsage 6.3.
• Optimization of experimental conditions for selective leaching of tellurium.

This paper focuses on the recovery of tellurium from high tellurium-bearing material with similar compositions to the anode slime of copper electrorefining, containing about 50% of copper and 34% of tellurium in several different phases. Based on the Pourbaix diagram (Eh-pH) of Cu–Te–Se–H2O in certain conditions, an alkaline pressure leaching process with NaOH as leaching agent was proposed to separate tellurium and selenium selectively from the raw material. Further heterogeneous thermodynamic simulation of the leaching was performed by Factsage 6.3 and the behavior of different species was predicted. The experimental results agree with the simulation results and prove that about 90% of the tellurium can be oxidized to soluble sodium tellurite, while the copper stays in the residue. It is found that selenium is difficult to dissolve with a leaching efficiency of only 20%, which needs more detailed research in the future. For the leaching of tellurium, the established optimal leaching conditions were as follows: L/S ratio of 6:1, free concentration of NaOH of 30–40 g/L, time of 6 h, total pressure of compressed air of 1.0 MPa, temperature of 120 ± 5 °C, and agitation speed of 400 rpm.