Thermochemical and kinetic investigations of the phosphoric attack of Tunisian phosphate ore

Abstract

A thermochemical study of the attack of Tunisian phosphate ore by aqueous phosphoric acid was investigated using a differential reaction calorimeter “DRC”. The influence of the liquid-to-solid ratio, reaction temperature, acid concentration and particle size on the attack reaction was studied. The results obtained for various liquid-to-solid ratios showed three domains, each one corresponding to particular phenomena. The enthalpy of phosphate dissolution, the solubility and the enthalpy of precipitation of mono-calcium phosphate mono-hydrate were deduced as − 182.1 ± 0.6 kJ mol−1, 5.2 g(phosphate)/kg(acid) and − 69.7 J g−1, respectively. The effect of the other parameters was studied in the latter domain. The kinetic study performed at 25 °C shows that the attack rate increased with increasing acid concentration and stirring speed. But, increasing the size of the particles and the liquid-to-solid ratio decreases the rate of reaction. The expression of the attack kinetics determined previously was rewritten that depends on the parameters given above.