Clean and efficient sulfuric acid roasting - vacuum thermal reduction process for extracting 4N tellurium from high value - added crude tellurium resource

Abstract

4N tellurium is a crucial material for modern high-tech appliances and a key precursor for producing 7 - 8N ultra - high - purity tellurium. Crude tellurium slag, derived from copper anode slime, is a key intermediate material with high value, containing 95.13 % tellurium and significant impurities including Se, Cu, Pb, Na and S. This study offered a clean and efficient process for extracting 4N tellurium from crude tellurium slag, which integrated sulfuric acid roasting pretreatment with vacuum carbon reduction. The process is based on Gibbs free energy, E - pH diagrams, saturated vapor pressure theory and phase diagram. Under optimally sulphated roasting conditions, 98.85 % of Se was removed. Under the optimal wet purification conditions, 97.30 % of Cu and 97.28 % of Na were removed. High purity tellurium of 99.994 % can be produced under optimal vacuum carbon reduction conditions with a direct yield of 96.13 % tellurium, 99.9 % of the S was removed. Direct tellurium yield of 95.83 % for the overall process, removal rates greater than 97 % for all impurities. This study demonstrated a highly effective impurity removal process and offered a sustainable, clean, and efficient method for extracting 4N tellurium from high - value crude tellurium resources, thereby offering significant implications for the tellurium metallurgy industry.