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.

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.

In this work, we introduce the novel possibility of producing blue fluorescent ultraviolet pigments from phosphogypsum. The obtained materials are characterized by X-ray diffraction (XRD), transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). The formation of the CaS phase in the sample during the reduction of calcium sulfate was established. Thermal treatment of phosphogypsum in the presence of a reducing agent (potato starch) under environmental isolation conditions is found to yield high-quality products with high added value. The highest luminosity is established in samples containing 0.6 mol. %, which were heat-treated under a temperature of 1100 °C for 60 min. The synthesized CaS:Cu materials are shown to emit light in the blue region of the spectrum, with an emission maximum at a wavelength of 480–490 nm. The developed technological methods open the possibility to recycle chemical industry waste, which contributes to the achievement of sustainable development goals, in particular, the goal of ensuring rational consumption and production patterns.

Relevance. The need to develop a technology for the disposal of solid and liquid industrial waste to obtain organic-inorganic fertilizer. The growth of industrial production is accompanied by an increase in waste. In modern society, considerable attention is paid to the problem of processing man-made waste to obtain demanded products. Phosphogypsum is the main by-product of the production of fertilizers and phosphoric acid, it is a multi-tonnage waste, its storage leads to the withdrawal of vast territories from circulation. Liquid waste from pig farms also needs to be processed into organic fertilizers. Aim. To study the process of heat treatment of phosphogypsum in the presence of a reducing agent to obtain an alkalizing reagent. This will make it possible to further organize processing liquid and solid agricultural and industrial waste and produce domestic organic fertilizers Methods. Heat treatment of phosphogypsum in the presence of a reducing agent, followed by the preparation of an aqueous suspension to obtain an agent that reduces the acidity of livestock effluents. The samples of heat-treated phosphogypsum obtained during the study were characterized by X-ray phase analysis, electron microscopy. Suspensions with different pH values were obtained on their basis. Results and conclusions. The authors have studied heat treatment of large-tonnage inorganic waste of the chemical industry – phosphogypsum. It was found that the suspension of phosphogypsum heat-treated in the presence of a reducing agent has increased values of the hydrogen index, which can be used to obtain an alkalizing reagent for treating agricultural waste. The authors revealed the optimal technological modes of obtaining a reagent having the maximum pH value of the suspension: the amount of the introduced reducing agent is 0.16 mol/mol CaSO4, the heat treatment temperature is 1000 °C.