CaCl2 addition effect and melt formation in low-temperature decomposition of chrysotile with CaCO3

Mixtures of chrysotile (Mg6Si4O10(OH)(8)) and CaCO3 were burned at temperatures ranging from 500 degrees C to 1000 degrees C; the decomposition temperature of chrysotile was lowered by adding CaCl2. Thermal analysis and succeeding SEM observation confirmed the formation of melts, which was supposed to be responsible for the effect of the added CaCl2. The melts were detected even when the added CaCl2 was as little as 1-5 mass% of the CaCO3; the quantity of the CaCl2 was smaller than that predicted from the phase diagram. Thermodynamic calculations of chemical equilibrium showed that forsterite (Mg2SiO4), which was a thermal decomposition product of chrysotile and had a fibrous shape, destructed at about MOT. In the common decomposition methods to convert asbestos-cement composites to oxides of Ca-Si system, the decomposition reaction occurs via a solid-solid reaction and reacts slowly. So to increase the reaction rate, a reaction temperature above 1000 degrees C is required. The present study has experimentally evidenced that the formation of melts enlarges the reaction interface between the chrysotile and the CaCO3 so that the decomposition reaction can proceed even at lower temperatures.