The paper proposes a simple one-stage synthesis of organic-inorganic composite materials based on oxide compounds of iron (III) and cobalt (II) with a developed surface. The process of cobalt(II) ferrite (CoFe2O4) structure formation on the biochar surface was studied. As an organic component, biochar was obtained from agricultural waste, including sunflower husks, rice husks, and pea kernels. Composite materials cobalt ferrite/biochar were obtained for the first time using these wastes. The obtained materials were characterized using X-ray phase analysis, fourier transform infrared spectroscopy (FTIR), transmission electron microscopy, and N2 adsorption-desorption. A mechanism for forming composite materials is proposed, including the stage of formation of chelate complexes of transition element cations with citric acid on the biochar surface and their subsequent thermal decomposition. High adsorption activity of the synthesized materials in the process of removing chromium (VI) ions from aqueous solutions was established. The sunflower husk biochar composite material based on CoFe2O4 has the highest adsorption capacity of 6.98 mg/g. The results suggest that biochar composites based on CoFe2O4 have great potential for the practical industrial wastewater treatment.

A simple one-step synthesis of developed surface zinc ferrite is proposed (S BET = 453.1 m2 g−1). The formation of zinc ferrite, zinc chromite (S BET = 53.6 m2 g−1), and mixed zinc ferrite-chromite (S BET = 37.4 m2 g−1) structures is studied. The resulting materials are analysed using x-ray phase and x-ray fluorescence analysis, IR spectrometry, electron microscopy, TGA and BET method. Single-phase sample formation mechanism is proposed, which includes transition element cation chelate complex formation stage in the presence of citric acid and subsequent thermal decomposition of the complexes formed. The synthesised materials exhibited photocatalytic activity in the decomposition of an organic dye under the action of hydrogen peroxide. The highest catalytic activity is demonstrated by zinc ferrite in acidic medium; the calculated reaction rate constant is 0.010 min−1 for ZnFe2O4, 0.008 min−1 for ZnFeCrO4, 0.007 min−1 for ZnCr2O4. The results can be applied to obtain materials suitable for wastewater treatment processes at industrial enterprises where organic dyes are used in production cycles.

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The article studies the technological features of calcium sulfide production from phosphogypsum. To ensure the environmental safety of industrial enterprises, closed production cycles creation is necessary. One of the criteria for “green” technologies is industrial waste recycling. Phosphogypsum formed during the orthophosphoric acid production from apatite raw materials by sulfuric acid method can be classified as large-tonnage waste. Phosphogypsum can be considered a mineral with zero mining costs and zero feedstock to produce valuable products. The synthesized materials are characterized using a complex of modern methods such as X-ray phase analysis, and electron microscopy. An environmentally friendly precursor, sucrose, is used as a reducing agent for calcium sulfate. The recovered material is a mixture of calcium sulfate and sulfide. When illuminated with ultraviolet light, it glows yellow-orange. The article presents an integrated approach to the problem of phosphoric acid production waste disposal by marketable products production.