Rate of decomposition of phosphorite in sulphuric acid-sodium sulphate solutions

This article presents a series of studies on the rate of decomposition of phosphorite in H2SO4 - Na2SO4 solutions of various concentrations at temperatures of 40 to 80 degrees C in order to elucidate the mechanism of phosphorus dissolution from this mineral. The dissolution rate was directly influenced by the reagent concentration and temperature but was inversely proportional to the average initial particle size of the phosphorite grains. The reaction rate was significantly improved by the addition of sodium sulphate and by stirring. The experimental data fitted well into an expression based on a kinetic model for diffusion-controlled reactions. The enhanced kinetics in H2SO4 - Na2SO4 solutions could be attributed to the relatively lower activation energy obtained, compared to that in H2SO4 alone. In both cases, the activation energy was less than 20 kJ.mol(-1), suggesting a transport process to be the rate controlling step.