A pilot study: Efficient electrowinning of tellurium from alkaline solution by cyclone electrowinning technology

Efficient electrowinning is critical for industrial tellurium (Te) production. To overcome the bottlenecks of a low production rate and low recovery in conventional processes, Te electrowinning tests with three different current densities were conducted in an industrial pilot-scale cyclone electrowinning cell. A numerical simulation of the flow field and electric field in the electrowinning cell was undertaken and the results were visualized by finite-element analysis using COMSOL Multiphysics. The cathode Te purity and production parameters were compared with those of the traditional technology. The numerical simulations and pilot-scale test results indicated that the electrolyte flow rate near the cathode wall remained above 0.15 m·s−1 because of the high flow velocity at the base. A feasible condition for Te electrowinning with high current densities was provided based on the electrode reaction kinetics. Te was deposited stably at a large scale and at high current densities up to 200 A·m−2. Efficient Te electrowinning was achieved with a high current efficiency of 97.1% on an industrial scale. The production rate was increased from 0.88 kg·m−2·d−1 to 5.04 kg·m−2·d−1 and the final electrolyte concentration was reduced from 80 g·L−1 to 30 g·L−1. A 2 N Te product was obtained with a recovery of 85.22%, and the Te purity after casting increased to 4 N. The excessive current density at the edge of the cathode sheet that was caused by the edge effect resulted in the formation of prominent nodules. The cathode sheet disintegrated because of an excessive deposition current and uneven edge current density.