Low temperature synthesis of 12CaO·7Al2O3 from calcium sulfite waste

Abstract

One of the calcium aluminate, 12CaO·7Al2O3, was synthesized from calcium sulfite hemihydrate waste which was produced as a by-product of calcium polysulfide. The calcium sulfite waste was at first pre-treated by sodium salts, Na2CO3 and Na 2C2O4. Then, the waste was converted to the CaCO3 and CaC2O4, respectively. From these pre-treated sample, 12CaO·7Al2O3 phase was formed at 850°C for the converted CaCO3 from Na2CO 3 and at 6507deg;C for the converted CaC2O4 from Na2C2O4. These crystallization temperatures are much lower than from reagent CaCO3 and CaC 2O4 at 1250 and 850°C, respectively. The reason of such reduction of crystallized temperature may result from impurity Fe 2O3 including in the by-product. Actually, addition of Fe2O3 into the reagent CaCO3 posed decrease of crystallization temperature of 12CaO·7Al2O3 from 1250 to 10507deg;C. © 2013 The Ceramic Society of Japan.