Investigation of Vanadium-Containing Sludge Oxidation Roasting Process for Vanadium Extraction

Vanadium containing sludge is a by-product of vanadium pentoxide obtained by hydrometallurgical methods from vanadium slag that can be estimated as a promising technogeneous raw material for vanadium production. The phase analysis of vanadium-containing sludge by the X-ray diffraction method showed that it contains vanadium in spinel form (FeO∙V2O3). The various oxidation roasting methods for sludge treatment were studied for increasing vanadium extraction into the solution. It showed that the most effective additive is 1% CaCO3 at a roasting temperature of 1000 °C. Oxidation roasting of vanadium-containing sludge with the additive led to an increase in the acid-soluble form of V2O5 from 1.5% to 3.7% and a decrease in the content of FeO∙V2O3 from 3% to 0.4%. These results confirm the efficiency of the application of oxidation roasting to convert vanadium compounds into acid-soluble forms. The conversion mechanism of spinel to acid-soluble phases during oxidation roasting with additives was investigated by thermogravimetric analysis and thermodynamic simulation. It showed that the formation of acid-soluble calcium vanadates during oxidation roasting without additives occurs at temperatures above 800 °C while CaCO3 addition allows one to reduce this temperature to 600 °C.