Sulfo-phosphoric attack of the phosphate ore: energetic contribution of each phenomenon intervening during the attack and effect of the time of addition of the sulfuric acid

ABSTRACT The energetic contribution of various phenomena involved in the reaction between the Tunisia phosphate ore and a mixture of phosphoric and sulfuric acids was studied calorimetrically. The enthalpies of the sulfuric acid ionization ( ), the H2PO4 − neutralization ( ), and the phosphate ore dissolution in phosphoric acid alone ( ) or in the mixture of the latter with sulfuric acid ( ) were determined and equal to −58.7 ± 0.7 kJ mol−1, 12.7 ± 1.3 kJ mol−1H2SO4, −186.2 ± 2.2 J g−1 and – 425.6 ± 3.3 J g−1, respectively. The addition time of the sulfuric acid was systematically investigated to reduce the loss of P2O5 in gypsum and the optimal condition for a better yield was deduced.