A mixture of phosphoric and sulfuric acid was used to investigate the dissolution kinetics of phosphate ore by Differential Reaction Calorimetry (DRC). The effect of the solid-to-iquid ratio, concentration, stirring speed, particle size and temperature of the reaction is examined. It was established that the dissolution rate increased with stirring speed and particle size. However, rising the olid-to-iquid ratio, temperature and concentration decreased the dissolution rate. It was determined that the dissolution rate fits in the first order of the pseudo-homogeneous reaction model. Two negative values of apparent activation energies were found in the range of 25 to 60°C. The experimental data were tested by graphical and statistical methods and it was found that the following models were best fitted for the experimental data and an empirical equation for the process was developed. -ln (1 -x) = [2,2 E-09((S/L)0.75C -0.461G0.447(SS) 0.471exp (2671/T)]t. T≤ 40°C -ln (1 -x) = [2,2 E-09((S/L)0.75C -0.461G0.447(SS) 0.471exp (6959/T)]t. T > 45°C

A calorimetric, Differential Reaction Calorimetry (DRC), study of the thermochemical of the attack of a phosphate ore from Gafsa region (Tunisia) by a mixture of sulfuric and phosphoric acid is undertaken at different solid-liquid ratio and different temperature. The plot of the quantity of heat measured by integrating the raw signal as a function of the dissolved mass in the same volume solution at 25˚C presents three straight segments attributed at the formation of the hemihydrate (CaSO 4 •1/2H 2 O:HH), the dihydrate (CaSO 4 •2H 2 O:DH) or a mixture of these two products checked by X-ray diffraction, infrared spectroscopy and thermal analysis (Differential Scanning Calorimeter: DSC). The attack by the acid mixture was performed at higher temperature and showed in addition the formation of another form of calcium sulfate:anhydrous (CaSO 4 :AH). Moreover, the variation of mass enthalpy versus temperature presents a break at the T = 45˚C. According to our results, it seems that the effect of the temperature on the sulfo-phosphoric attack reaction on the natural phosphate (NP) generates a change of mechanism at around 45˚C.

Mixture of phosphoric and sulfuric acid solutions has been used to investigate the dissolution of natural phosphates (PN) by DRC. The effect of concentration, particle size and stirring speed reaction is examined. Thermochimique properties of each kinetic parameters reaction are determined. It was found that these parameters have a considerable effect on the thermochemical aspect of the attack reaction. It is known that the process of PN sulphophosphoric acid attack leads to the formation of dihydrate (CaSO 4 •2H 2 O: DH). The present work shows the precipitation of other residues their formula depends on factors studied. The increase in concentration leads to the formation of hemihydrate (CaSO 4 v1/2H 2 O:HH) beside DH for the low values of% H 2 SO 4 due to the solubility of dihydrate on the etching solution and the precipitation of (Ca (H 2 PO 4) 2 •2H 2 O) next of DH for low agitation values because of the lack of turbulence between the liquid phase and the solid phase which favors the precipitation of this latter compound.