Abstract:Co-pyrolysis process of calcium arsenate and carbon powder system was studied. Weight loss of mixture with mass ratio of 4︰1 of calcium arsenate to carbon powder in argon atmosphere at 30-1 200 ℃ was measured by thermogravimetric analyzer under different heating rates. Residues in each weight loss stage were characterized by XRD. The results show that weight loss process of mixed system is divided into three stages. At the first weightless stage at temperature of 240-325 ℃, Ca2As2O7?H2O dehydrates to produce Ca2As2O7; at the second weightless stage at temperature of 560-668 ℃, crystal form transition from Ca2As5O7 to Ca3(AsO4)2, and Ca5(AsO4)3OH and Ca(OH)2 loses water to produce Ca5(AsO4)3 and CaO; at the third weight loss stage at temperature of 904-1 120 ℃, calcium arsenate is reduced by carbon to form CaO and arsenic vapor. The results of kinetic model fitting show that reaction mechanism of third weight loss stage of co-pyrolysis of calcium arsenate and carbon powder can be explained with phase boundary reaction kinetic model.