Defluorination of bastnaesite by steam roasting process

Abstract

The bastnaesite was defluorinated by steam roasting process, and fluorine was removed in the form of hydrogen fluoride to realize the separation from rare earth. The effects of particle size of raw material, roasting temperature and time on defluorination rate of bastnaesite were studied. The suitable conditions of steam roasting process are that the particle size of raw material is less than 74 μm, the roasting temperature is 1000 °C and the roasting time is 4 h. The defluorination rate of bastnaesite is close to 100% under above these conditions. When the temperature rises to 1000 °C, the voids on the surface of the particles increase obviously, and there is a developed network of voids, which indicates that the fluorine oxides in bastnaesite react fully with the saturated water vapor at this stage, and a large amount of fluorine escapes in the form of hydrogen fluoride from the surface and inside of the mineral. X-ray diffraction results show that there are only rare-earth oxides in the form of Ce0.33La0.33Ca0.33O1.5 and Ce7O12 in the slag. The results of energy spectra and chemical analysis show that the fluorine in the baking sand was basically completely removed.