Method for recycling hydrofluoric acid from wastewater containing fluorosilicic acid

The invention provides a method for recycling hydrofluoric acid from wastewater containing fluorosilicic acid. Ammonia or ammonium is added into the wastewater containing the fluorosilicic acid and the fluorosilicic acid is decomposed into sediments of ammonium fluoride and silicon dioxide; magnesium sulfate is added into a solution containing the ammonium fluoride and fluorine in the solution is precipitated and separated out in a magnesium fluoride form; the solution is filtered to obtain magnesium fluoride and a fluoride precipitation post-solution; then the magnesium fluoride is thermally decomposed by sulfuric acid; thermally decomposed steam is condensed and absorbed to obtain the hydrofluoric acid; residues of thermal decomposition are returned back to a fluoride precipitation and separation procedure and are circularly utilized. Lime is added into the fluoride precipitation post-solution, stirring and a mixed solution is evaporated to recycle the ammonia; the recycled ammonia is returned back to a fluorosilicic acid ammonolysis procedure for circular utilization; the method has the advantages of simple process, simplicity and convenience for operation, high fluorine recovery rate, low recovery cost, good working environment and the like.