Institute of Metallurgy of Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia:

K. V. Pikulin, Junior Researcher, Post-Graduate Student, e-mail: pikulin.imet@gmail.com
E. N. Selivanov, Head of Laboratory, e-mail: pcmlab@mail.ru
L. I. Galkova, Researcher, e-mail: galkowa@mail.ru
R. I. Gulyaeva, Senior Researcher, e-mail: pcmlab@mail.ru

We substantiated the treatment regimes for spent catalysts to obtain calcium tungstate. The technology, which allows to obtain calcium tungstate from low-quality raw materials, was taken as a basis. It provides for oxidative roasting, cinder sintering with soda, water leaching of sintered mass and precipitation of calcium tungstate from solution. The spent hydrotreating catalyst was taken as an initial sample. The composition of the catalyst is as follows, %: 13.7 W, 2.7 Ni, 28.2 Al, 7.8 S, 0.3 Si, 2.6 Fe and 20.0 C. According to X-ray phase analysis, the main phase of the catalyst is γ-Al₂O₃. Tungsten, nickel and iron are represented as oxides (WO₃, NiO, Fe₂O₃), sulfides (WS₂, NiS, FeS) and NiWO₄ compounds. High content of carbon complicates the hydrometallurgical processing of catalyst. And high sulfur content does not allow its use for direct alloying of steel. Oxidative firing of the catalyst was used to reduce the carbon and sulfur contents. According to the data of thermal and X-ray diffraction (XRD) analyzes, the features of phase formation during oxidative roasting (900 ^оC) of spent catalysts were established. The process was accompanied by oxidation of carbon and sulfides and the formation of oxides of tungsten, nickel, iron and Al₂(WO₄)₃. The formation of Al₂(WO₄)₃ prevented the complete extraction of tungsten in the solution during leaching. The transfer of tungsten into a water-soluble form is possible by sintering the calcined catalyst with sodium carbonate at a temperature of 800 ^оC. According to the XRF data, the basis of the sintered mass was sodium tungstate. Oxides of  aluminum, iron and nickel were also identified. After aqueous (90–100 ^оC) leaching (l : s = 4), the oxides of aluminum, nickel and iron were concentrated in the cake. Calcium tungstate was precipitated from the solution by calcium nitrate at a pH of 10–12 and a temperature of 90–95 ^оC. It contained, %: 58.9 W, 13.9 Ca, 0.37 S. The extraction of tungsten in a commercial product was close to 90%.

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