Research On Extraction Of Tellurium From Neutralization Sludge And Electrolytic Preparation Of High Purity Tellurium

With the energy shortage of the world, people pay more attention to solar energy, which is called clean and pollution-free renewable energy. High purity tellurium is a raw material of preparation telluride cadmium which is widely used for solar cells, it’s quantity demand is more and more big. In this study, neutralization sludge was chosen as a raw material which is produced after recovery of platinum and palladium from anode slime of copper. The aim is that high purity tellurium is prepared by electrolysis after recovery of tellurium from the neutralization sludge. Cyclic voltammetry and steady-state polarization curves were used to analyze the electrochemical behavior in the process of the cathode electrolytic.Neutralization sludge contains a large amount of copper, zinc, sodium, and the dried neutralization sludge contains11.24%of tellurium.With sulflfuric acid leaching neutralization sludge, the dosage of sulfuric acid, acid concentration, reaction temperature and reaction time on the influence of leaching rate of tellurium were researched. Appropriate conditions is as follows:sulphuric acid concentration is53.9g·L-1, the amount of sulfuric acid is1.5times, reaction temperature is30℃, the reaction time is30min, and the leaching rate of tellurium and copper are100%.Leaching liquor was reduced by SO2at the condition of the catalyst of hydrochloric acid, considering the condition of hydrochloric acid concentration, reaction temperature, reaction time and the way of ventilation on the influence of reduction rate of tellurium. Appropriate conditions is as follows:hydrochloric acid concentration is3.2mol·L-1, reaction temperature is75℃, reaction time is2h and the intermission ventilation time is30min, tellurium with purity of98.27%was obtained and the morphologic of the elemental tellurium is aciculiform.When raw tellurium powder was oxidated by hydrogen peroxide oxident, the ratio of amount of substance of hydrogen peroxide and tellurium, the ratio of amount of substance of sulfuric acid and tellurium,reaction temperature on oxidation rate and loss rate of tellurium were studied. It is found that the ratio of amount of substance of hydrogen peroxide and tellurium is5.72:1, the ratio of amount of substance of sulfuric acid and tellurium is0.47:1, reaction temperature is50℃, the oxidation rate of tellurium is95%.Hydrochloric acid was used to dissolve tellurium dioxide, then reduced by sulfur dioxide, the purity of tellurium is up to99.9%,tellurium powder was turned to tellurium dioxide by hydrogen peroxide. Sodium hydroxide was chosen to dissolve tellurium dioxide for preparation sodium tellurite. For preparation of high purity tellurium by the method of electrolysis, effect of tellurium concentration, sodium hydroxide concentration, temperature electrolysis, electrolyte cycle speed and current density on the purity of tellurium and the current efficiency were investigated. Appropriate experimental conditions is tellurium concentration of150g·L-1, sodium hydroxide concentration of100g·L-1, electrolysis temperature of45℃, electrolyte cycle speed of1mL·min-1, current density of50A·m-2, the purity of tellurium reachs99.99%. The result of cycle electrolytic experiment shows that the purity of tellurium still can arrive to99.99%, and the current efficiency is98.14%, but the oxidation rate of TeO32-is as high as11.42%.The method of steady state cathode polarization curve and circulation current-voltage curve were adopted to research the process of electrolysis. The experimental results shows that the apparent transfer coefficient of the cathode reaction is0.195, exchange current density is8.08×10-4A·cm-2, activation energy is44KJ·mol-1, and the rate determined step for reducing TeO32-is electrochemical reaction. Cycle current-voltage curves suggest that the electrochemical reaction is quasi reversible process, peak current increasing and the peak of the corresponding potential moving to in the direction of increase electrochemical polarization with the increase of number of scanning. The spectrum of reduction of TeO32-shows that the reaction is the charge transfer reaction of catalysis.