Kinetics of leaching of tunisian phosphate ore particles in dilute phosphoric acid solutions

Van der Sluis et al.'s model was used to determine the rate of the partial dissolution of a Tunisian phosphate rock with dilute phosphoric acid (1.5 mass% P2O5). When the temperature rises from 25 to 90 degrees C, for a given particle size, the mass-transfer coefficients, k(L)degrees, vary from 3 x 10(-3) to s x 10(-3) m.s(-1). The corresponding diffusion coefficients, D, lies between 6 x 10(-7) and 27 x 10(-7) m(2).s(-1). Activation energy is equal to 14 kJ.mol(-1) and values o(n)k(L)degrees, at 25 degrees C, are in the range of 0.25 x 10(-3) and 4 x 10(-3) m.s(-1) when the agitation speed goes from 220 to 1030 rpm, showing that the leaching process is controlled by diffusion rather than by chemical reaction.