Method for producing gypsum as byproduct in preparation of lithium carbonate by using lepidolite from tantalum-niobium tailings

The invention provides a method for producing gypsum which is a byproduct in preparation of lithium carbonate by using lepidolite from tantalum-niobium tailings. The method comprises an acid dipping step in which a dilute sulfuric acid solution is added to a lepidolite raw material and a neutralization fluoride removal step. The invention is characterized in that the method comprises the following steps: pulverizing lepidolite to form lepidolite powders with a particle size of about 200 meshes; feeding the lepidolite powders into a reactor together with a sulfuric acid solution with a concentration of 30% to 70%, with a solid-liquid mass ratio of 1:(2-8); allowing fluoride removal reactions to take place for 3 to 10 hours under such a condition that the reaction temperature ranges from 60 DEG C to 200 DEG C; separating the produced hydrofluoric acid under vacuum after the reactions are completed to form a solid-liquid mixture; filtering off residues to form a mother liquid; performing neutralization fluoride removal, which is implemented by adding equivalent amount of water to the hydrofluoric acid solution that is separated under vacuum into the solid-liquid mixture and then adding calcium hydroxide; adjusting the pH of the liquid within the range from 5 to 7; and filtering to obtain high-purity gypsum.