Thermogravimetric analysis of the reaction between carbon and CaSO4 centerdot 2H(2)O, gypsum and phosphogypsum in an inert atmosphere

Heating stoichiometric amounts of carbon and pure CaSO4, synthetic gypsum o r phosphogypsum in a nitrogen atmosphere, results in the formation of CaS b etween 700 degrees C and 1100 degrees C. Different heating rates were used to investigate the reaction, and the amount of CaS formed depends on the he ating rate used. A quantitative XRD method was used to determine the amount s of CaSO4, CaS, CaO and C in the samples. More CaS formed with increasing heating rate. Addition of 5% Fe2O3 and 5% ZnO as catalysts lowers the tempe rature range, as well as the activation energy of the reaction. The relatio nship between the activation energy values and degree of conversion (alpha) for the reaction between carbon and CaSO4 indicates that it is a complex r eaction, and that simultaneous competitive reactions are taking place. (C) 1999 Elsevier Science B.V. All rights reserved.