Chemical and Structural Changes of Raw Phosphate during Heat Treatment

In the wet phosphoric acid production using calcined phosphate particles, physical structure and chemical composition of used material have an impact on the reaction speed. In this study, porous properties of phosphate fraction size 125-200 mum after heating at different temperature between 240degreesC to 940degreesC were investigated. Fluorapatite, carbonate fluorapatite (Francolite), dolomite and calcite constitute the major minerals of the phosphate rock used. The results of TG/DTA, CRTA, IP, and ESEM observations were used to understand the chemical changes observed. The decline of the specific surface area (SSA) from 16.61 m(2)/g down to 0.81 m(2)/g was interpreted according to the thermal results. The increasing of the linear shrinkage % by sintering process is observed. This process begins near 240degreesC and reaches a maximum near 940degreesC. These results are in agreement with those in the literature. Some kinetic tests were undertaken at laboratory scale to elucidate the relationship between reactivity and porous properties of phosphate particles.