AN INVESTIGATION OF THE PHASE-TRANSFORMATIONS IN A CASO4 (NH4)(2)SO4/H2O SYSTEM, DIRECTED AT THE PREPARATION OF A FINE-DISPERSED PURIFIED PHOSPHOGYPSUM/

The process of recrystallization of apatite phosphogypsum (PHG) in a s olution of ammonium sulphate (AS) with the subsequent decomposition of the binary salt was investigated and the resulting highly dispersed p roducts with a low P2O5 content have been discussed. The following eff ects were examined: (NH4)(2)SO4 concentration, the quantity of ammoniu m sulphate, the reaction temperature of phosphogypsum with (NH4)(2)SO4 solution, the time of treatment of phosphogypsum with (NH4)(2)SO4 sol ution and the decomposition of the binary salt, as well as the liquid/ solid ratio for the binary salts. Based on the results of the chemical and X-ray analysis, it was established that, depending on the technol ogical conditions of the processes of recrystallization, binary salts of (NH4)(2)SO4 . CaSO4 . H2O and of (NH4)(2)SO4 . 5 CaSO4 . H2O were f ormed. As a result of the investigations carried out, a product with a low P2O5 content, suitable for direct processing to secondary product s has been prepared.