Recovery Of Tellurium From The Tellurium Caustic Sludge Process

Tellurium slag is a by-product generated from the refining process of crude lead, which contains tellurium, lead, copper and other valuable elements. Therefore, it not only improves the comprehensive utilization ratio of resources, but also had important social and economic benefits to recovery tellurium from tellurium slag. And it is also in line with the requirements of clean production.The research progress on treating tellurium slag were introduced in this thesis, and the advantages and disadvantages of various methods were analyzed. According. to the particularity of the raw material and the low recovery ratio of extraction process of tellurium, a new process in the recycling of tellurium from tellurium slag was developed which consists of water leaching, acid leaching, purification and hydrolysis of tellurium.In this paper, the thermodynamic processes in the leaching, purification and hydrolysis of tellurium slag was first analyzed. On this basis, the leaching process of tellurium slag was investigated experimentally, and the effects of leaching temperature, leaehing time, endpoint pH and the L/S on the leaching effieiencie of tellurium had been investigated. In the leaching by water, the optimum conditions are leaching temperature of80℃, leaching time of45minutes and L/S of4:1. Under those conditions, the leaching ratio with water is75%. In the leaching with sulfuric acid, the optimum conditions are listed as followed temperature of80℃, leaching time of20minutes, the endpoint pH of0.5to1.0and L/S of5:1.Under those conditions, the leaching ratio with sulfuric acid was75.4%. The whole leaching ratio of tellurium was93.85%through the two-stage leaching.Second, the purification process of leaching solution of tellurium was investigated experimentally by sulfide precipitation method. The effects of purifying temperature, purifying time and the theoretic amount of Na2S on the removal ratio of impurities and tellurium had been investigated. The optimum conditions are purifying temperature of60℃, purifying time of20minutes and the excess ratio of Na2S is1.2. Under those conditions, the removal ratio of Pb was87.12%, Cu was100%and recovery ratio of tellurium was99.93%.Finally, the hydrolysis process of tellurium in the purification liquid was studied. The effects of hydrolysis temperature, hydrolysis time and the endpoint pH on the hydrolysis ratio of tellurium have been investigated. The optimum conditions are hydrolysis temperature of90℃, the endpoint pH=3.9～4.1and hydrolysis time of10minutes. Under those conditiona, the hydrolysis ratio of tellurium was94.40%and the purity of tellurium dioxide was86.32%.Under above optimum conditions, the hydrolysis ratio of tellurium was89.06%and the purity of tellurium dioxide was84.45%, reaching the experimental purpose.