Purpose The purpose of this work is to study the patterns of pigment colour formation and to develop metal compositions for obtaining spinels using the precipitation and heat treatment methods. Design/methodology/approach Precursor materials were prepared using co-precipitation method. Phase composition of pigments were determined by X-ray diffraction. Colour of pigments was determined spectrophotometry. Modelling of colour formation was performed using simplex method. Planning in the future to carry out full synthesis of pigments of blue, red and yellow colours. Findings The paper deals with the results of theoretical and experimental research on the synthesis pigments of blue, red and yellow colours based on Fe-Co-Al-O spinel. The influence of the chromophore cation content and the heat treatment temperature on optical and colour characteristics of pigments were studied. Originality/value The resulting composition-property diagrams make it possible to evaluate the effect of chromophore cations and heat treatment on the colour formation for Fe2O3-Al2O3-CoO system. Crystal-phase composition of the pigments is installed and its relationship with the optical colour characteristics. That makes it possible carry out targeted synthesis of pigments blue, red and yellow colours in further. The phase composition of pigments and its relationship with optical and colour properties has been established thus enabling the directed synthesis of blue, red and yellow pigments.

The possibility of obtaining brown pigments with the use of blast furnace slag from waste water containing nickel is justified. The scheme of the main reactions is proposed. The kinetics of the reactions is studied. The contribution of the chemical interaction into the overall degree of treatment is established by potentiometric titration. The influence of the main factors on the degree of nickel extraction is determined. The phase composition of the formed pigment is established with the help of X-ray analysis. Rheological properties of the pigment particles are set. The main color characteristics of the obtained products are identified by visual and spectrophotometric way. X-ray microanalysis indicated the presence of the two phases in the obtained precipitate. Dispersed and phase compositions of the original slag determine the rheological properties of the pigment. By varying the synthesis parameters, the obtained patterns provide us with possibility of receiving pigments of the color from light brown to deep brown.

Porous biochars obtained from coniferous woods, and magnetic biochars based on them, which showed high sorption properties when extracting Cr(III) from aqueous solutions (from 0.005 to 0.0125 mol/L), were studied. The adsorption properties of the magnetic biochar are compared with the initial biochar. It has been established that the preparation of materials by the method of pyrolysis and subsequent treatment in a plasma reactor makes it possible to bring the samples under study into a number of promising adsorbents for the extraction of chromium from aqueous solutions.

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Different grades of magnetic cobalt ferrite (CoxFe3−xO4) nanoparticles were synthesized with various molar ratios of Fe 2+ to Co 2+ ions in the initial salt solutions method with using contact non-equilibrium plasma. The crystal structure and morphology of the nanoparticles are obtained from X-ray diffraction and transmission electron microscopy studies. With an increase in the value of x, the saturation magnetization for the samples of CoFe2O4 has decreased from 150.9 emu/g to 1.2 emu/g. The dependence of the coercive force on x is extremal with a plateau maximum corresponding to the x = 0.5-1.25.

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Nano-sized manganese ferrites Mn х Fe 3 − х О 4 (х = 0-1.3) were prepared using contact non-equilibrium plasma (CNP) in two different pH (11.5 and 12.5). The influence of synthesis conditions (e.g., cation ratio and initial pH) on phase composition, crystallite size, and magnetic properties were investigated employing X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and magnetic measurement techniques. The formation of monodispersed faceted ferrite particles at х = 0-0.8 was shown. The FTIR spectra revealed reflection in region 1200-1700 cm −1 caused by the presence of water adsorbed on the surface of Fe 3 − x Mn x O 4 micro-granules or embedded into their crystal lattice. The most sensitivity of reflection spectra to the composition changes takes place within a 400-1200 cm ). The XRD results showed that the nanocrystalline Mn х Fe 3 − х О 4 (0 < x < 1.0) had cubic spinel crystal structure with average crystallite size 48-49 A. The decrease of crystalline size with the x increase was also observed.

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