Optimization of process on electrodeposition of 4N tellurium from alkaline leaching solutions

Abstract The purification of tellurium (Te) has received considerable attention as the cadmium telluride (CdTe) photovoltaic modules have become one of the lowest-cost products of solar electricity. An optimum tellurium (Te) purification process consists impurity separation, electrodeposition, and ultrasonic cleaning was proposed first time for preparing 99.99% (4N) purity of Te from alkaline leaching solution which contains high level impurities. The main metallic impurities copper (Cu), lead (Pb), iron (Fe), and bismuth (Bi) were effectively separated from the solution by adding appropriate quantity of sodium sulfide nonahydrate (Na 2 S·9H 2 O) before electrodeposition. The impurities arsenic (As) and selenium (Se) were further removed by ultrasonic cleaning. Under the optimum process, 4N-Te powder was prepared, meanwhile, the impurity contents of Cu, Se, As, Pb, Fe, Bi, magnesium (Mg), and sulfur (S) in the Te product all met the 4N-Te standard, along with the impurity contents of As and Se in the Te product were lower than 2 ppm after ultrasonic cleaning. The chemical composition of the Te product was identified by inductively coupled plasma optical emission spectrometer (ICP-OES). Furthermore, the electrochemical behavior of Te on the titanium (Ti) plate in the alkaline leaching solution was studied by linear sweep voltammogram (LSV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry (CP). The morphology, structure and purity of Te product were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-rays (EDX). 4N-Te product with hexagonal single crystal structure was obtained by the optimum Te purification process based on electrodeposition method.