Platov South-Russian State Polytechnic University (NPI) (Novocherkassk, Russia):

Shabelskaya N. P., Head of Chair, Doctor of Engineering Sciences, Associate Professor, nina_shabelskaya@mail.ru
Medennikov O. A., Postgraduate Student
Khliyan Z. D., Postgraduate Student
Ulyanova V. A., Student

This paper presents the results of a comprehensive study on the possibility of processing the large-tonnage phosphogypsum waste generated in the manufacture of orthophosphoric acid to obtain an inorganic luminescent material. The main process parameters for the thermal reduction of phosphogypsum into the target product are analyzed. It is shown that heat treatment in the presence of a reducing agent generates a composite material containing a phase of anhydrous calcium sulfate and calcium sulfide and is accompanied by partial destruction of the structure; the boundaries of lamellar crystals become less clear and clusters of reduced material form on their surface; when heat-treated in the presence of a number of reducing agents, such as activated carbon, vegetable oil, citric acid, starch, and sucrose, phosphogypsum becomes luminescent due to the presence of calcium sulfide. The luminescence is observed under ultraviolet irradiation; the samples emit light in the yellow-orange part of the spectrum. The luminescence of the material changes with variations in the processing methods. The best process conditions include heat treatment temperatures of 800–900 °C, the treatment time of 60 minutes, and the amount of reducing agent introduced at 7–14 wt%. Sucrose in the amount of 7 wt% was the most effective reducing agent under the conditions studied. It has been suggested that the relatively low luminosity of the samples obtained using coal as a reducing agent may be due to the kinetics of the reduction process as the process is solid-phase in the case of coal and involves a liquid phase of oxygen-containing reducing agents at elevated temperatures. The research conducted opens up wide possibilities for the comprehensive use of mineral raw materials with the manufacture of a high-demand inorganic product.

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