IR spectroscopic study of high energy activated Tunisian phosphorite

The IR spectra of natural Tunisian phosphorite before and after high energy milling recorded at ambient and liquid nitrogen temperatures are presented and thoroughly interpreted in respect to the vibrations of the main entities: phosphate and carbonate ions, OH groups and water molecules. The detailed interpretation of the IR spectra gives valuable information on the structural changes accompanying the milling process, which are responsible in a large degree for the increased almost three times solubility of the as-activated samples. It is established that the most significant structural changes are caused by the very fast inclusion in the apatite structure of additional carbonate species from air. The distribution of CO32− between B and A sites is analysed on the basis of Gaussian fitted spectra in the region of carbonate ν3 and ν2 bands. The carbonate ions are primarily distributed over the two B and A sites with slight preference for the A sites, but the prolonged milling leads to a subsequent migration of the carbonate ions from the B sites to the A sites. The relative part of the A carbonates increases progressively with the prolonged milling, which contribute to the increased solubility of the milled samples.