Preparation method of sodium tetrafluoroborate

The invention relates to the field of fine chemical engineering, in particular to a preparation method of sodium tetrafluoroborate. The sodium tetrafluoroborate is prepared from hydrofluoric acid, boric acid and sodium carbonate; sodium tetrafluoroborate is purified by adopting evaporation, polar organic solvent dissolution, separation, modified polytetrafluoroethylene membrane fine filter filtration, cooling crystallization and the like. The preparation method comprises the following steps: preparing a modified polytetrafluoroethylene membrane filter element from a polytetrafluoroethylene membrane filter element, vinyl guanamine, sodium acrylate, 1-allyl-3-ethylimidazolium tetrafluoroborate, an initiator and deionized water; according to the prepared modified polytetrafluoroethylene membrane filter element, the purity of sodium tetrafluoroborate can be effectively improved; the method has the characteristics of low cost, simple process, low toxicity, environmental friendliness and the like; the preparation p