Preparation method of rare earth fluoride

The rare earth fluoride preparation method comprises the following steps: (1) putting potassium fluoborate and rare earth carbonate into a reaction container, and adding water to prepare slurry; (2) diluting the rare earth chloride feed liquid with water, dropwise adding the diluted rare earth chloride feed liquid into the reaction container, and heating the materials in the reactor to 70-95 DEG C; (3) keeping the temperature to react for 1-3 hours, and finishing the fluorination reaction when the pH value of the slurry is 0.5-3; and (4) heating the slurry to 90 DEG C or above, carrying out first solid-liquid separation to obtain a fluorinated supernatant and a filter cake, and then washing the filter cake, carrying out second solid-liquid separation and drying to obtain the rare earth fluoride product. According to the method, the fluorination rate is the same as that of ammonium fluoride and hydrofluoric acid fluorination, meanwhile, the precipitation amount of rare earth chloride is reduced, refined contro