FORMATION OF CRYSTAL STRUCTURE AND FILTRATION CHARACTERISTICS OF PHOSPHOGYPSUM IN DIHYDRATE AND HEMIHYDRATE METHODS OF WET-PROCESS PHOSPHORIC ACID PRODUCTION

The problem of utilization and storage of phosphogypsum generated during the production of wetprocess phosphoric acid (WPA) is extremely relevant due to environmental issues associated with the pollution of water bodies, land, and the atmosphere. The large-scale accumulation of phosphogypsum requires the development of effective methods for its processing. A key requirement for the chemical processing of phosphogypsum is its particle-size distribution, primarily the size and shape of crystals. This study investigates the influence of the WPA production mode and the liquid-to-solid ratio (L:S) on the chemical composition, crystal size and habit, and filtration properties of phosphogypsum. Phosphogypsum was produced by dihydrate and hemihydrate methods at L:S ratios of 2.5:1 and 3:1 under laboratory conditions and under industrial process conditions at the Taraz branch «Mineral Fertilizers» of Kazphosphate. The composition and morphology of the samples were examined using X-ray fluorescence and X-ray diffraction methods, as well as electron microscopy. X-ray diffraction analysis identified the presence of finely dispersed anhydrite, which reduces the filterability of phosphogypsum precipitate obtained under industrial conditions at temperatures of 90-95°C. It was established that extraction in the dihydrate mode at L:S ratio of 3:1 promotes to formation of larger, uniform-size, isometric crystals of gypsum and ensures the maximum filtration productivity. The research results can be used to optimize WPA production.

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