Development of Technology for Processing Pyrite–Cobalt Concentrates to Obtain Pigments of the Composition Fe2O3 and Fe3O4

This paper presents the results of a study on the development of a processing technology for pyrite–cobalt concentrates to obtain iron oxide pigments (Fe2O3 and Fe3O4) via high-temperature hydrolysis. It was found that, in a single operation, the concentrate can be effectively purified from lead, zinc, and copper, yielding an iron–nickel–cobalt product suitable for further processing by standard technologies, such as smelting into ferronickel. The scientific originality of research concludes in a mechanism of stepwise selective chloride volatilization, which was established as follows: stage I (500–650 °C)—removal of lead; stage II (700–750 °C)—chlorination of copper and iron; stage III (850–900 °C)—volatilization of nickel and cobalt. Microprobe analysis of the powders obtained from high-temperature hydrolysis of FeCl2·4H2O and FeCl3·6H2O revealed the resulting Fe3O4 and Fe2O3 powders with particle sizes 50 μm and 100 μm. A visual color palette was created, corresponding to different Fe3O4/Fe2O3 ratios in the pigment composition—ranging from black (magnetite) to red (hematite)—and potential application areas. For the first time, the new technological scheme was proposed of pigments Fe2O3 and Fe3O4 production from pyrite–cobalt concentrates via combination of oxidized roasting with subsequent chlorination and high-temperature hydrolysis of the products.