<p>This paper investigates the possibility of heat treatment of phosphogypsum, a waste product of the chemical industry. Partial dehydration of dihydrous calcium sulfate occurs when phosphogypsum is dried, and complete dehydration occurs when it is calcined at temperatures of 600 – 1200°C. The samples were found to actively absorb water after heat treatment below 800°C. During the heat treatment of phosphogypsum in the presence of a reducing agent, two endothermic effects related to the sequential dehydration of CaSO₄· 2H₂O were observed, as well as a broad peak of exothermic effect due to the heat degradation of the reducing agent and the formation of calcium sulfide from phosphogypsum. Heat-treated phosphogypsum samples in the presence of the reducing agent acquire the ability to emit yellow-orange luminescence under the action of ultraviolet radiation. Synthesized pigments can be used to produce water-based paints and varnishes.</p>