Application of alternative reducing reagents in the technology of technical selenium production in the Copper Plant`s metallurgical shop

During the processing of copper electrolytic sludge in the metallurgical shop of the Copper Plant of the JSC MMC Norilsk Nickel, in addition to the main commercial product — platinum metal concentrates — technical selenium is also produced (GOST 10298). The technology for its production is based on the capture of selenium dioxide by alkaline solutions from gases formed during the roasting of copper sludge. Its further isolation from gas cleaning solutions is carried out by the hydrometallurgical selenide method; hydrazine hydrate is used to reduce selenium. The use of this reagent, despite its effectiveness, significantly increases the cost of producing technical selenium; in addition, due to the explosion and fire hazard and toxicity of the compound, it is necessary to comply with special industrial safety requirements when using it in technology. Currently, a search is underway for alternative reagents to replace hydrazine hydrate with more affordable and safe reducing agents. The article presents the results of studies of selenium precipitation from gas cleaning solutions using sodium bisulfite and glucose. Optimal process parameters were experimentally selected. It was determined that when testing both reagents, the extraction of selenium from solutions into the sediment was more than ~90%; the differences lie in the physicochemical characteristics of the resulting product. When using sodium bisulfite, the sediment is contaminated with sulfur impurities, and to bring selenium to the requirements of GOST 10298, it is necessary to carry out additional cleaning operations (repulping in a sodium hydroxide solution, refining smelting followed by grinding of the smelt). Experiments with glucose showed the possibility of selenium precipitation of the required purity, but finer dispersed, with a predominance of a fraction less than 0.040 mm (62.9%). The differences revealed in the precipitation processes of the element in question by hydrazine hydrate and alternative reagents allowed to develop recommendations for adapting the process and equipment schemes of the current production to the use of each of the tested reagents.