EFFECTS OF MAGNESIUM CONTENT ON THE RHEOLOGICAL BEHAVIOUR OF PHOSPHORIC ACID AND ON THE PERFORMANCES OF HIS INDUSTRIAL MANUFACTURING BY THE DIHYDRATE WET PROCESSES

The industrial manufacture of phosphoric acid (PA), by dihydrate-wet processes, has a major disadvantage of producing impure crude acids containing a wide variety of dissolved impurities, such as magnesium (MgO). It is one of the undesirable impurities. It increase the viscosity of the liquid phase in the reaction medium and decrease the kinetics and crystalline growth of gypsum. It also contributes to the formation of insoluble complex mineral phases, which generates with them fouling problems and considerable losses of phosphorus [1, 2]. The main purpose of this work is to determine, in the laboratory scale, in a semi-continuous pilot, the quantitative effects of magnesium content in phosphate rock on the performances of the wet phosphoric acid processes by doping the phosphate rock by the pure magnesium oxide. In order to study its effects on the rheological behaviours and the kinetics of clarification of the two acid grades: 29%P2O5 and 54%P2O5, we have also doped these acids by the pure MgO. The results of experimental tests have clearly shown that the content of magnesium reduces the filterability of the phosphoric slurry and leads in the two acid profiles studied to a decrease on the kinetics of the solid decantation and an increase in the apparent viscosity.