Fundamentals of the wet-process phosphoric acid production .1. Kinetics and mechanism of the phosphate rock dissolution

This paper is devoted to the fundamentals of natural phosphate rock dissolution under conditions close to those in the industry of the wet-process phosphoric acid production. The dissolution kinetics and mechanism of single crystals of natural fluorapatite at micro- and nanolevels have been studied for the first time. Methods of optical and scanning electron microscopy and Auger electron and IR reflection spectroscopy were used for the investigations. As a result, effects of dislocation acceleration of dissolution rate (increasing to 1.6 times) and random fluctuations of crystal size with parameter 1.15 +/- 0.05 mu m were discovered. Both phenomena have been described as a micromechanism of dissolution. A new system of five chemical equations for the acidic dissolution of fluorapatite has also been proposed and described as a nanomechanism of dissolution. The obtained results are useful for elaboration of new technological and ecological principles of wet-process phosphoric acid production.