TITLE:
Attack of Tunisian Phosphate Ore by a Mixture of Sulfuric and Phosphoric Acid: Thermochemical Study by Means of Differential Reaction Calorimetry
AUTHORS:
Olfa Lachkar-Zamouri, Khemaies Brahim, Feten Bennour-Mrad, Ismail Khattech
KEYWORDS:
Dissolution, Thermochemistry, Differential Reaction Calorimeter, Phosphate Ore, Liquid/Solid, Temperature
JOURNAL NAME:
Advances in Materials Physics and Chemistry,
Vol.8 No.10,
October
26,
2018
ABSTRACT: 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℃ presents three straight segments attributed at the formation of the
hemihydrate (CaSO4·1/2H2O:HH), the dihydrate (CaSO4·2H2O: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
(CaSO4:AH). Moreover, the
variation of mass enthalpy versus temperature presents a break at the T = 45℃.
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℃.