This study focuses on developing a method for utilizing phosphogypsum, a large-tonnage waste product from phosphate raw material processing, whose disposal sites are sources of complex negative impacts on the environment. As a promising approach to the utilization of gypsum-containing waste, the study considers the interaction of phosphogypsum with a sodium carbonate solution (carbonate conversion), which yields calcium carbonate, a marketable product referred to as phosphochalk. Existing technologies typically produce a fine-grained material, which hinders filtration and restricts the potential applications of phosphochalk. This study aims to determine the carbonate conversion parameters that enable the production of phosphochalk with tailored particle size characteristics while maintaining a high degree of feedstock conversion. A series of single-factor experiments was carried out to evaluate the influence of reaction conditions – temperature, Na₂CO₃ concentration in the carbonate solution, liquid-to-solid (L:S) ratio, and phase contact time – on the conversion of CaSO₄·2H₂O. The results showed that raising the conversion temperature to 90-100 °C and increasing the L:S ratio to 10 promote intensive nucleation of CaCO₃ crystals and the formation of large agglomerates. A Na₂CO₃ concentration of 250 g/dm³ and a phase contact time of up to 3 h together yield phosphochalk with a particle size of D90 = 45 μm at a conversion degree of 98.8 %. In terms of its characteristics, the resulting product is suitable for use in the metallurgical industry as a raw material for flux production, which demonstrates its competitiveness in the secondary raw materials market. The recommendations developed in this work enable the design of a low-waste technology for processing technogenic raw materials, consistent with the principles of sustainable development and helping to reduce the environmental burden.

The study is devoted to the development of a method for the technogenic raw materials utilization. Special attention is paid to the prospect of involving products based on them in the production of new building materials. The results of Russian and foreign studies on the reuse of wastes, such as phosphogypsum, metallurgical slag, waste from municipal and industrial wastewater treatment, etc., in the building materials industry are considered. It has been established that the use of incinerated sewage sludge ash in construction is a promising direction in terms of environmental and economic efficiency. The research confirmed the compliance of the lightweight ash-based concrete components to the regulatory documentation requirements for a number of indicators. As a result of the research, the composition of the raw mixture for the lightweight concrete production with incinerated sewage sludge ash as a replacement for a part of the cement has been developed. In terms of parameters, the developed concrete corresponds to standard lightweight concrete, marked in accordance with the regulatory documents of the Russian Federation as D1300 (density not less than 1.3 g/cm3), Btb2 (flexural strength not less than 2 MPa), M200/B15 (compressive strength not less than 15 MPa). Lightweight ash-based concrete is suitable for use in construction, repair of roads and improvement of urban areas.