Ceramics-Silikáty 59 (1) 29-36 (2015)

INFLUENCE OF THE COMPOSITION OF PHOSPHATE ROCK ON THE AMOUNT OF WATER-INSOLUBLE PHOSPHATE IMPURITIES IN SEMI-HYDRATE PHOSPHOGYPSUM

In this work a chemical and mineral composition of phosphate rock and phosphogypsum was investigated in order to identify which impurities of phosphate rock prevent natural phosphates from decomposing in full during the production of phosphoric acid and increase the amount of water-insoluble phosphate impurities in phosphogypsum. The analysis of X-ray diffraction (XRF), X-ray fluorescence (XRD), scanning electron microscopy with energy dispersive X-Ray spectrometry (SEM-EDS) and granulometry was carried out. The results showed that phosphate rocks (Kovdor and Kirovsk apatites) and the semi-hydrate phosphogypsums differ by their chemical composition. The apatites and phosphogypsums differ in the amount of the major components, as well as other components (MgO, Al₂O₃, SrO, BaO, ZrO₂, Ln₂O₃). In phosphate rock, Ln₂O₃ can be found in the composition of the mineral monazite. The SEM-EDS analysis revealed that the minerals of the apatite group and monazite form aggregate crystals. Monazite dissolves in sulphuric and phosphoric acids very marginal, therefore it prevents the apatites from full decomposition, thus influencing the quantity of insoluble phosphates in semi-hydrate phosphogypsum. The higher is the amount of minerals containing Ln₂O₃ in phosphate rock, the more water-insoluble phosphates remain in phosphogypsum. It was found that influence of Ln₂O₃ impurity is significant higher than influence of particles size of apatite.

Keywords: Phosphate rock, Semi-hydrate phosphogypsum, Insoluble impurities, Water-insoluble phosphates