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.