Synthesis and thermal characterization of glass bonded Ca-chloroapatite matrices for pyrochemical chloride waste immobilization

Ca-chloroapatite (CaApCl), glass-bonded CaApCl compositions loaded with 16–32 wt.% simulated pyrochemical chloride waste were prepared by mixing and heating (773–1023 K) apatite and borosilicate glass (BSG) forming reagents in appropriate ratios. The compositions were characterized by XRD, TGA/DTA, SEM, and EDAX. Among the products, 16–27 wt.% chloride waste loaded composition yielded phase pure Ca-chloroapatite and were resistant to leaching of Cl− and other ions. In case of 28–32 wt.% waste loaded compositions, even though formation of phase pure Ca-Chloroapatites was observed by XRD, the leaching of Cl− and other ions was found to be significant. Bulk thermal expansion behavior of the samples was studied by dilatometry. The 16 wt.% chloride waste loaded matrix showed nearly the same thermal expansion compared to pure Ca-Chloroapatites. The % linear thermal expansion of the matrices decrease on increasing the chloride waste loading; however, Ca-chloroapatite mixed with 20 wt.% BSG mixed matrix showed slightly higher thermal expansion. The coefficient of thermal expansion of borosilicate glass is the lowest among all the matrices measured. The coefficient of thermal expansion (CTE) is found to be 12.76 ± 0.64 × 10− 6 K− 1 for CaApl and 12.18 ± 0.63 × 10− 6 K− 1 for 16 wt.% waste loaded BSG-encapsulated CaApl in the temperature range of 298–780 K. The glass transition temperature of the waste loaded matrices is lower than that of the bare BSG and 20 wt.% BSG encapsulated Ca-chloroapatite.

► Chloride waste loaded glass bonded Ca-chloroapatites were prepared by solid state reaction.
► Compositions were characterized by XRD, TGA/DTA, SEM and EDAX.
► Thermal expansion and glass transition temperature of the matrices were investigated by dilatometry.
► Preliminary leaching studies on the matrices were carried out.
► These studies suggest 16 wt.% waste loading may be possible in these BSG bonded Ca-chloroapatite glass ceramics matrix.