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The purpose of this study was to the low-temperature synthesis of cobalt-containing diopside pigments based on granulated blast furnace slag and to study the characteristics of the mineral formation processes, changes in the structure and colour indices.

Synthesis of cobalt-containing diopside pigments based was carried out by the directional formation of the mineralogical composition with the introduction of part of the components using granulated blast-furnace slag.

It has been established that the formation of the diopside phase in pigments containing blast-furnace slag as the main component proceeds at low temperatures (1,100°C–1,150 °C). The colour of diopside pigments is formed because of the isomorphic substitution of Si4+ ions for Al3+ ions and Mg2+ ions for Co2+ ions. It is expedient to add CoO in an amount of 0.9 mol (18 Wt.%) into the composition of diopside pigments based on blast-furnace slag to obtain defect-free violet glazes.

The developed diopside pigments enable obtaining of high-quality violet glazes for ceramics. The application of the obtained results can significantly reduce the consumption of traditional raw materials in the composition of silicate ceramic pigments, as well as reduce their firing temperature.

Calcium, magnesium and silicon oxides are the main components of blast-furnace slag. In addition, granulated blast furnace slag is mainly represented by the glassy phase, which determines its high activity during the firing process. These factors are prerequisites for using the blast-furnace slag as a valuable substitute for chemically pure or natural raw materials in silicate pigments and reducing their firing temperature.

The purpose of this paper is to conduct the directed synthesis of blue-colour aluminate spinel pigments based on spent aluminium–cobalt–molybdenum (ACM) catalyst and to study peculiar features of mineral formation processes and changes in their colour indices depending on composition and firing temperature.

Aluminate spinel ceramic pigments with specified colour indices were synthesised by directed formation of their mineral composition and identification of the most rational technological parameters of production. Mineral composition of synthesised pigments was evaluated by X-ray phase analysis. The colour indices of pigments and pigment-containing glaze coatings were studied on the comparator colour. The chemical resistance of pigments was determined by loss of their weight loss after boiling in 1 N hydrochloric acid solution and 1 N sodium hydroxide solution.

Peculiar features of formation of the mineral composition of aluminate spinel pigments based on the ACM catalyst were studied. The expediency of using magnesium and zinc oxides in their composition has been proved. It is found that for the formation of stable pigments of intense blue colour, a concentration of cobalt (II) oxide in the amount of 0.5 mol is sufficient, which is 23.1 Wt.%. The colour of such pigments is determined by the ratios of cobalt, magnesium and zinc aluminates, which form a spinel solid solution.

The use of developed aluminate spinel pigments provides obtaining of high-quality glass coatings of blue colour, in particular, for ceramics.

Aluminium oxide in the spent ACM catalyst is predominantly in the active form (of amorphous aluminium hydroxide and y-Al₂O₃). This is a prerequisite for the use of this waste material as a complete substitute for chemically pure Al₂O₃ in the technology of aluminate spinel pigments and reduction of their firing temperature. Besides, spent ACM catalyst already contains 5 Wt.% of expensive cobalt (II) oxide in the form of stable colour-bearing phase CoAl₂O₄.