Study of thermal behaviour of organic matter from natural phosphates (Youssoufia - Morocco)

Thermogravimetry (TG), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were used to study the thermal behaviour of the organic matter in the natural phosphate and its concentrate kerogen from the Moroccan deposit. The TG analysis showed that both the investigated samples exhibited a one-step thermal oxidation in the main mass loss area, between 160 and 540°C, attributed to the hydrocarbon material. When DSC analyses of oxidation as well as pyrolysis yielded two evolutionary stages of the hydrocarbon in this temperature range : the first one at 160-360°C and the second one above 360°C. Pyrolytic kerogen decomposition was monitored by measuring changes in the principal FTIR organic bands. The results showed, in the first stage, the progressive decrease of signals due to CH₂ and CH₃ vibrations as well as the carbonyl and carboxylic bands, and their subsequent disappearance at 300°C. In the second stage above 400°C, the signal due to the aromatic components (1600 cm^-1) appeared but decreased with increasing temperature up to 540°C. This revised version was published online in August 2006 with corrections to the Cover Date.