Effect of heat treatment on grindabilities of celestite and gypsum and separation of heated mixture by differential grinding

This study was conducted to determine thermal decomposition of gypsum (CaSO4 · 2H2O) and celestite (SrSO4), to examine the effect of heating on grindability and the possibility of celestite–gypsum separation by differential grinding after heating. The results indicated that no significant decomposition reaction was observed in celestite up to 900 °C whereas the decomposition of gypsum occurred within 100–450 °C. ndices (Wi) of celestite and gypsum were found as 6.76 and 5.18 kWh/shton, respectively. Wi of celestite did not change significantly after heating at 200 °C where that of gypsum decreased to 4.00 kWh/shton. The difference in grindabilities makes it possible to separate celestite from gypsum by differential grinding. This method has the advantage that celestite–gypsum beneficiation and production of plaster of Paris are achieved in a single stage.