The precipitating agent is preferably a mass ratio of 1: 0.1 mixture of lime and caustic soda 0.15. In addition to the hydrofluoric acid since the hydrofluoric acid-containing wastewater, also contain small amounts of nitric acid, about 1% of nitric acid and 10% hydrofluoric acid wastewater and is used only when the milk of lime as a precipitating agent, hydrofluoric acid wastewater with lime will the nitric acid and will form calcium nitrate caused a significant increase in the hardness of the water, causing severe fouling reverse osmosis membrane, the added precipitant mass ratio of 1: 0.1 and 0.15 when the lime mixture of caustic soda, a mixture of caustic soda can make calcium nitrate produced by the reaction of sodium nitrate, and calcium ions were precipitated, to prevent large amounts of calcium ions into the reverse osmosis membrane, reducing the hardness of the treated water, will help improve the life of the reverse osmosis membrane, which to some extent reduce the hydrofluoric acid wastewater treatment costs. 

Among them, the milk of lime was prepared as follows: lime mixed with water to prepare a milk of lime. Preferably, a purity of 98% lime; particle size is preferably 200 mesh. Lime main ingredient is calcium hydroxide, calcium carbonate and a small amount of magnesium. Step S120: hydrofluoric acid solution was added in the upper layer of liquid water, adjusting the PH value to 68, followed by coagulation homogeneous U, mixed precipitation, the supernatant. By adding the supernatant liquid hydrofluoric acid wastewater, adjust the PH value of 68 allows the upper liquid short-tailed bird beggar ion sufficient precipitation. 

By adding a coagulant to accelerate the upper liquid coagulation and flocculation of colloidal particles into large particles, or easy to make the floc precipitation. Coagulant coagulant commonly used in the art can, preferably aluminum chloride, aluminum sulfate polyacrylamide or hydrated. Preferably, the coagulant is added at a concentration of IPPM 50PPM. Wherein the coagulant was added and sedimentation time is preferably 10 minutes 120 minutes. Step S130: The supernatant was sequentially filtered using a filter First, cross-flow ultrafiltration to obtain the concentration of water and filtered water, filtered water, scale inhibitor was added, and then the reverse osmosis membrane filtration to obtain waste and back to the water.