Mineralogical and chemical investigation of Tunisian phosphate washing waste during calcination

Phosphate washing waste (PWW) is one of the wastes generated by the phosphate mine with a very high amount. This waste was investigated in this work to study the effect of the calcination of the PWW at four different temperatures 600 °C, 700 °C, 800 °C and 900 °C on its mineralogical and chemical composition. The samples were investigated by X-ray powder diffraction, Fourier transform infrared, differential scanning calorimetry and thermogravimetric analysis, solid-state magic angle spinning nuclear magnetic resonance of ²⁹Si, ²⁷Al and ³¹P and scanning electron microscope. The results show that the PWW presents a complex system and it suffers a significant change on its mineralogical and chemical composition after calcination. It reveals the presence of carbonate, natural zeolite, fluorapatite, quartz and clay. After calcination, the waste shows the disappearance of some of these phases and the appearance of others and some other phases remain steady.