Thermogravimetric Study of Oxidation Firing of Rhenium- and Osmium-Containing Lead Sludge

Results are provided for thermal and thermogravimetric studies of lead sludge in the presence of and without oxidizing agents in order to determine the thermally active part of the charge composition. It is shown that during oxidation firing of lead sludge the process begins with charge dewatering and organic compound decomposition, and rare metal oxidation commences after complete destruction of organic compounds. Addition of sodium nitrate or calcium hypochlorite oxidizing agents provides complete oxidation of rhenium and osmium in the range of 400–650°C with the subsequent extraction of osmium into sublimate and concentration of rhenium in the form of perrhenate compounds in the ash. In this case decomposition of organic substances proceeds in parallel with oxidation reactions of rare metals without affecting their oxidation.