Studies On The Technics For Leaching And Separation Of Tellurium From Tellurium Slag

This work is the study of improving the leaching rate of tellurium of slag formed in pyro-refining of silver. According to the composition of the raw meterial, a leaching method of taking water first and then hydrochloric acid as the leaching agent was selected.The preliminary indicated that the leaching rate is below 80% when leaching is conducted in water, sulphuric acid, sodium hydroxide, sodium sulfide or the mixture of sodium hydroxide and sodium sulfide, in which leaching rate is relatively low. On the other hand, the leaching rate of tellurium can be more than 99% when hydrochloric acid is used as leaching agent. However, the cost is too high to be suitale for industrial production. As a result, the raw material is leached by water in the first step and then by hydrochloric acid.In this paper, the leaching by water is first studied.The effects of leaching temperature, leaching time and the liquid to solid ration on the leaching efficiencie of tellurium have been investigated. In the leaching by water, the optimum condition is leaching temperature of 25℃, leaching time of 1h and liquid to solid ration of 3:1. Under this condition, the leaching rate with water is 66.95%. Then the leaching with hydrochloric acid is studied. .The effects of leaching temperature, leaching time, the concentration of hydrochloric acid and the liquid to solid ration on the leaching efficiencie of tellurium have been investigated. The optimum condition is as follows: temperature of 75℃, leaching time of 4h, hydrochloric acid concentration of 6mol/L and liquid to solid ration of 5:1. Under this condition, the leaching rate with hydrochloric acid is 99.85% and the whole leaching rate is 99.95%.The sodium sulfite is adopted to reduce tellurium containing in the leaching solution. The effects of the dosage of sodium sulfite, reducing temperature, reducing time and potential on the reducing efficiency of tellurium have been investigated. Under the follow operation conditions: the dosage of alloys of sodium sulfite excessive coefficient 1.4, temperature 343K , time 1.5h and potential 300mV, the reducing ratio of tellurium can reach to 99%.