Investigation of phase transformations in thermal processing of phosphate rock

The reaction mechanism of the hydrothermal sintering processing of hydroxyfluorapatite (HFA) was studied. Samples from an industrial rotary kiln and laboratory-made samples were investigated by thermal, X-ray and chemical analysis. It was found that HFA decomposes by a solid-solid reaction with Ca-Mg-phosphates and by interaction with fused clinker. Apatite decomposition is not accompanied by fluorine evaporation; it merely creates the main precondition for fluorine evolution from clinker.