Currently, one of the most important problems of environmental protection is the deep and complex processing of mineral raw materials. This problem is especially relevant when processing substandard ores and production waste, one of which is phosphogypsum. This study examines the process of CaSO₄/CaS composite material formation during the reduction of phosphogypsum with citric acid. The composite structure formation mechanism is proposed. The resulting materials are characterized using various methods, including X-ray diffraction (XRD), transmission electron microscopy, the Scherrer method, thermogravimetric analysis (TGA), and FT-IR spectroscopy. The reduced sample emits orange radiation in the range of 500–750 nm with a quantum yield of 0.17. Experimental results showed that the sample decomposition process in the solid state consisted of two components with a predominant contribution from the long-lived component (~46 ns). The optimal conditions for producing luminescent materials by reducing phosphogypsum with citric acid were determined: a heat treatment temperature of 1073 K, a holding time of 60 min, and a reducing agent mole fraction of 37%. It was found that an increase in temperature with a simultaneous decrease in heat treatment time, as well as a decrease in temperature with a simultaneous increase in heat treatment time, led to a decrease in the luminescent properties of the synthesized material compared to optimal values. The results can be used to develop technology for recycling large-tonnage waste from the chemical industry into luminescent materials.

The article presents results for the magnetic nanoparticles sol–gel method synthesis of cobalt (II) ferrite and organic–inorganic composite materials based on it. The obtained materials were characterized using X-ray phase analysis, scanning and transmission electron microscopy, Scherrer, Brunauer–Emmett–Teller (BET) methods. A composite materials formation mechanism is proposed, which includes a gelation stage where transition element cation chelate complexes react with citric acid and subsequently decompose under heating. The fundamental possibility of obtaining an organo–inorganic composite material based on cobalt (II) ferrite and an organic carrier using the presented method has been proved. Composite materials formation is established to lead to a significant (5–9 times) increase in the sample surface area. Materials with a developed surface are formed: the surface area measured by the BET method is 83–143 m²/g. The resulting composite materials have sufficient magnetic properties to be mobile in a magnetic field. Consequently, wide possibilities for polyfunctional materials synthesis open up for various applications in medicine.

One of the priority goals of sustainable socio-economic development for the period up to 2030 is providing food for the planet’s population. This entails an increase in the output of mineral fertilizers and, consequently, an increase in the quantities of solid industrial waste. Phosphogypsum, a by-product of phosphate fertilizer production from apatite ore, is one example of such waste. The problem of solid industrial waste recycling is urgent. The present study examines the process of converting calcium sulfate, in the form of a reagent, and phosphogypsum into a composite material of calcium sulfate/sulfide. An environmentally friendly material, sucrose, is used as a reducing agent. Reduced phosphogypsum (as well as calcium sulfate) luminescence is suggested to be associated with the formation of a CaS/CaSO₄ composite material. The synthesized materials are characterized by X-ray phase analysis, X-ray photoelectron spectroscopy, elemental analysis, and calcium sulfide qualitative and quantitative content in the samples. It is shown that in the reduction process at the phase contact point, crystal grids are formed with a significant number of defects, which contributes to the convergence of some of the energy levels of the calcium cation and sulfide anion, facilitating the transitions of electrons from the valence zone to the core zone and the formation of luminescence centers (cross-luminescence). Both samples of reduced phosphogypsum and alkaline earth metal sulfates are found to exhibit luminescence properties under ultraviolet radiation. The data obtained open up broad prospects for the use of solid industrial waste for the synthesis of new materials.

The paper presents a comprehensive study of the processing possibilities for phosphogypsum, a large-tonnage chemical industry waste, into highly sought-after products, such as ultraviolet pigments, and alkalizing reagents for the preparation of organomineral fertilizers. The materials obtained were characterized by X-ray diffraction (XRD), transmission electron microscopy, and thermogravimetric analysis (TGA). It was found that the phosphogypsum thermal treatment process in the presence of a reducing agent (charcoal, sunflower husk) allowed us to obtain new products with a high added value. For the first time, the possibility of obtaining various products by varying process conditions was established. The process of thermal reduction of phosphogypsum in the presence of charcoal at temperatures of 800–900 °C and an isothermal holding time of 60 min resulted in us obtaining samples capable of glowing when irradiated with ultraviolet light. This effect is due to the formation of a composite material based on calcium sulfide and calcium sulfate in the system. The process of the regenerative heat treatment of phosphogypsum at temperatures of 1000–1200 °C resulted in us obtaining a composite material consisting of calcium oxide and sulfate, which can be used for fractionating liquid waste from livestock farming and to obtain organomineral fertilizer. The technological methods developed allow the usage of chemical industrial waste and agricultural waste in secondary processing to produce highly innovative products that will contribute to the achievement of the sustainable development goals, in particular, “Ensuring rational consumption and production patterns”.

This paper explores the feasibility of producing manganese- and lead-doped luminescent materials from phosphogypsum. For the first time, orange- and red-emitting ultraviolet pigments were obtained using a sulfide matrix reduced from phosphogypsum. The resulting materials were characterized using X-ray diffraction (XRD), transmission electron microscopy, Fourier transform infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy (XPS). Doping with manganese or lead cations is shown to produce luminophores whose luminescence shifts from orange to red–orange under UV radiation as lead cations replace manganese cations in the CaS:Mn_1-xPb_x solid solution. A sharp increase in red luminescence intensity was observed for CaS: Mn luminophores when they were irradiated with short-wavelength ultraviolet radiation. These results open up broad possibilities for using phosphogypsum, a high production volume (HPV) chemical waste product, to produce highly innovative products.

This paper examines the formation of cobalt (II) ferrite on the surface of an organic support in stages: mixing metal salts, interaction with ammonia and citric acid solutions, and the subsequent thermolysis of the intermediate products. The resulting materials were characterized by X-ray diffraction, electron microscopy, and elemental analysis. A comparative analysis of the materials’ morphological properties suggests the formation of a cobalt (II) ferrite film on the surface of the organic support. This film forms as small cubic crystals measuring 50–100 nm in size, with a simultaneous significant (2–5 times) increase in the specific surface area of the synthesized composite materials compared to the support surface. The typical pore diameter of the composites is 20–40 nm. The synthesized material of CoFe₂O₄/sunflower husk biochar exhibits high catalytic activity; dye is removed from the solution within 60 min. The material of CoFe₂O₄/sunflower husk ash is less active in this process: dye removal is observed 140 min after the start of the reaction. These data may be useful for developing catalytically active materials for wastewater and soil solution treatments to remove persistent pollutants.