THERMOGRAVIMETRIC STUDIES OF THE SYNTHESIS OF CAS FROM GYPSUM, CASO4-CENTER-DOT-2H(2)O AND PHOSPHOGYPSUM

Using a heating rate of 2 degrees C min(-1), CaS reacts with oxygen in air from 700 degrees C to form CaSO4, with a complete conversion at 1 100 degrees C. Synthesis of CaS from the reaction between CaSO4 contai ning compounds and carbon compounds in air would not be possible, as t he carbon reacts from 600 degrees C with oxygen in the air to give CO2 . Heating stoichiometric amounts of carbon and pure CaSO4, synthetic g ypsum or phosphogypsum in a nitrogen atmosphere, results in the format ion of CaS from 850 degrees C. Using a heating rate of 10 degrees C mi n(-1), the formation of CaS is completed at 1080 degrees C. Addition o f 5% Fe2O3 as a catalyst lowers the starting temperature of the reacti on to 750 degrees C. Activation energy values at different fraction re action values (alpha) differ between 340 and 400 kJ mol(-1). The relat ionship between the activation energy values and conversion (alpha) in dicates that the reaction proceeds via multiple steps.