Method and equipment for preparing hydrofluoric acid by recycling fluorine ions in strong brine

Abstract

The invention belongs to the field of coking wastewater treatment, and particularly relates to a method and equipment for preparing hydrofluoric acid by recovering fluorine ions in strong brine. The method comprises the following steps of: adsorbing fluorine ions in the fluorine-containing wastewater of the water treatment plant by using fluoride removal special resin Haishi DF-1S, Dulheng CH32, Blue LX-760 and LX-860, resolving by using NaCl or AlCl3 and other solutions to obtain fluorine-containing saline water, mixing the fluorine-containing saline water with concentrated sulfuric acid, heating, collecting hydrogen fluoride gas by condensing because the boiling point of hydrogen fluoride is low (19.5 DEG C), and recycling the fluorine-containing saline water to obtain the fluorine-containing wastewater of the water treatment plant. The heated solution can be repeatedly used as a desorption solution. According to the method, fluorine ions in the wastewater are effectively removed, so that the fluorine content of the water is lower than 1ppm, the generation of fluorine-containing impurity salts is avoided, and the pollution to the environment is reduced. The recycling of fluorine resources is realized, and additional economic benefits are created. And the NaCl or AlCl3 solution can be recycled, so that the operation cost of the whole treatment process is reduced, and the method has good economical efficiency and environmental protection property.

Description

Technical Field

[0001] The invention belongs to the field of coking wastewater treatment, and particularly relates to a method and equipment for recovering fluoride ions in concentrated brine to produce hydrofluoric acid. Background Art

[0002] During the treatment of ammonia distillation wastewater from coking plants, high concentrations of fluoride ions are common. Traditionally, after separation through a membrane system, the filtered water is reused, while the resulting brine enters the evaporation and crystallization stages to produce dried sodium chloride, sodium sulfate, and other salts. Prior to RO membrane treatment, there was a lack of effective fluoride ion recovery methods. Fluoride, present as sodium fluoride within the salts, was treated as a hazardous waste, resulting in extremely high treatment costs and significant environmental pollution if discharged indiscriminately. Currently, the primary treatment method for fluoride-containing wastewater from coking plants involves using defluoridation agents such as calcium chloride to precipitate the calcium fluoride through sedimentation and other methods, converting it into sludge, which is then treated as a hazardous waste alongside other biochemical sludges.

[0003] Fluoride is highly corrosive to equipment. Currently, there is no effective process for separating and utilizing fluorine. Some companies simply extract fluorine from salt and dispose of it as hazardous waste. Furthermore, existing technologies fail to fully utilize the fluorine resources in wastewater, resulting in resource waste. Therefore, there is an urgent need to develop a device and process that can effectively recover fluoride ions in the upstream section of the RO membrane to address these issues. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and equipment for recovering fluoride ions in concentrated brine to produce hydrofluoric acid, which can transform fluoride from impurities into valuables and obtain high-value hydrofluoric acid.

[0005] The present invention adopts a resin adsorption tank to adsorb fluoride ions in fluoride-containing wastewater from a water treatment plant. The resin in the resin adsorption tank can be Haisi brand DF-1S, Dusheng CH32, Lanxiao LX-760, or LX-860. Then, a solution such as NaCl or AlCl3 is used for decomposition to obtain a fluoride-containing brine. The fluoride-containing brine is mixed with concentrated sulfuric acid and then heated. Since hydrogen fluoride has a low boiling point (19.5°C), the hydrogen fluoride gas is collected by condensation. The heated solution can be reused as a decomposition solution.

[0006] In the membrane workshop of the coking ammonia wastewater treatment plant, the fluoride ion recovery device of the RO membrane front section includes a resin adsorption tank and a fluoride recovery device connected in sequence; the fluoride recovery device includes an analytical solution storage unit, a reaction unit, a condensation unit and an analytical solution circulation unit.

[0007] The fluoride ion recovery process based on the above device has the following specific steps: (1) A new resin adsorption tank is added to the pipeline before entering the RO membrane. The fluorine-containing wastewater from the coking ammonia evaporation wastewater treatment plant is introduced into the resin adsorption tank. The fluoride ions in the wastewater are adsorbed by the special fluoride removal resin in the tank. The filtration rate of the wastewater is controlled at 1-50BV, the temperature is maintained at 5-45℃, and the pressure is not limited. After resin adsorption, purified water with a fluorine content of less than 1ppm is obtained. The purified water can directly enter the subsequent treatment process, and no fluorine-containing salts are generated in the evaporation and crystallization section. (2) When the resin adsorption reaches saturation, a saturated NaCl or AlCl3 solution is used as a decomposition liquid to decompose the resin. The fluorine-containing concentrated water produced by the decomposition enters the decomposition liquid storage unit of the fluoride recovery device; (3) 30% concentrated hydrochloric acid is introduced into the reaction unit as a raw material, and reacts with the fluorine-containing concentrated water in the analytical solution storage unit at a temperature of 50-100°C to generate hydrogen fluoride gas; (4) The generated hydrogen fluoride gas enters the condensation unit and is condensed to obtain the product anhydrous hydrofluoric acid; (5) The solution after the heating reaction in step (3) is a NaCl or AlCl3 solution, which is introduced into the decomposition liquid circulation unit and can be reused as the decomposition liquid of the resin in step (2).

[0008] The resin in the above-mentioned adsorption tank can be Haisi brand DF-1S, Dusheng CH32, Lanxiao LX-760, LX-860.

[0009] Compared with the existing technology, the present invention has the following advantages: This effectively removes fluoride ions from wastewater, reducing the fluoride content of the water entering the evaporation and crystallization process to less than 1 ppm. This prevents the formation of fluorine-containing salts, reduces the difficulty and cost of subsequent salt treatment, and minimizes environmental pollution. Fluorine resources are recycled. Through a series of processes, fluoride ions in wastewater are converted into anhydrous hydrofluoric acid, improving resource utilization and creating additional economic benefits. The NaCl or AlCl3 solution can be recycled, reducing chemical consumption and the operating cost of the entire treatment process, resulting in excellent economic and environmental performance. DETAILED DESCRIPTION

[0010] The technical solutions and effects of the present invention are further described below through specific embodiments. Example 1

[0011] In the membrane workshop of a coking ammonia wastewater treatment plant, a resin adsorption tank was installed in the pipeline before the RO membrane. The tank was filled with HiSilicon DF-1S fluoride-removing resin. Fluoride-containing wastewater was introduced into the resin adsorption tank at a filtration rate of 10 BV. The wastewater temperature was controlled at 25°C, and fluoride ion adsorption was carried out under normal pressure. Testing showed that the fluoride content of the purified water after adsorption was 0.8 ppm.

[0012] When the resin is saturated with adsorption, a saturated NaCl solution is used to decompose the resin. The fluorine-containing concentrated water produced by the decomposition enters the fluoride recovery device. 30% concentrated hydrochloric acid reacts with the fluorine-containing concentrated water at 70°C in the reaction unit. The generated hydrogen fluoride gas enters the condensation unit and is condensed to obtain anhydrous hydrofluoric acid product. The NaCl solution after the reaction is used as the decomposition liquid again through the decomposition liquid circulation unit, and the above decomposition process is repeated.

[0013] The specific process is as follows: (1) A new resin adsorption tank is added to the pipeline before the RO membrane. The special resin for removing fluoride, Haisi brand DF-1S, is used to adsorb fluoride ions in the fluoride-containing wastewater of the water treatment plant. The filtration rate is 10BV, the temperature is 25℃, and the pressure is unlimited. The clear water after resin adsorption is purified water with a fluoride content of less than 1ppm, and the evaporation and crystallization section no longer produces fluoride-containing salts. (2) After resin adsorption, the fluorine-containing concentrated water is decomposed and enters the fluoride recovery device. The decomposition liquid is a saturated NaCl solution; (3) Use concentrated hydrochloric acid (30% concentration) as raw material and fluorine-containing concentrated water to generate hydrogen fluoride gas at a temperature of 70°C; (4) The hydrogen fluoride gas is condensed to obtain anhydrous hydrofluoric acid; (5) The solution after heating in step (3) is a NaCl solution, which can be reused as the decomposition solution of the resin in step 2. Example 2

[0014] In the membrane workshop of another coking ammonia distillation wastewater treatment plant, a resin adsorption tank was filled with Dusheng CH32 special fluoride removal resin. Fluorine-containing wastewater entered the resin adsorption tank at a filtration rate of 20BV and a temperature of 30°C. The fluorine content of the purified water after adsorption was 0.6ppm. Subsequently, a saturated AlCl3 solution was used to decompose the resin. The fluorine-containing concentrated water produced by the decomposition reacted with 30% concentrated hydrochloric acid at 80°C to generate hydrogen fluoride gas, which was condensed to obtain anhydrous hydrofluoric acid. The AlCl3 solution after the reaction was recycled for resin decomposition. The specific steps were the same as those in Example 1. The entire process operated stably, achieving effective recovery of fluoride ions and recycling of the decomposition solution. Example 3

[0015] The resin adsorption tank is filled with Lanxiao LX-760 special fluoride removal resin. The fluoride-containing wastewater enters the resin adsorption tank at a filtration rate of 30BV and a temperature of 40°C. The fluoride content of the purified water after adsorption is 0.6ppm. The reaction temperature of concentrated hydrochloric acid and fluoride-containing concentrated water is 55°C. The rest is the same as Example 1. Example 4

[0016] The resin adsorption tank was filled with LX-860 fluoride removal resin. The fluoride-containing wastewater entered the resin adsorption tank at a filtration rate of 40 BV and a temperature of 45°C. The fluoride content of the purified water after adsorption was 0.7 ppm. The reaction temperature of concentrated hydrochloric acid and fluoride-containing concentrated water was 60°C. The rest was the same as in Example 2.

[0017] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for recovering fluoride ions from concentrated brine to produce hydrofluoric acid, characterized in that The specific method is as follows: (1) A new resin adsorption tank is added to the pipeline before entering the RO membrane. The fluorine-containing wastewater from the coking ammonia evaporation wastewater treatment plant is introduced into the resin adsorption tank. The fluoride ions in the wastewater are adsorbed by the special fluoride removal resin in the tank. The filtration rate of the wastewater is controlled at 1-50BV, the temperature is maintained at 5-45℃, and the pressure is not limited. After resin adsorption, purified water with a fluorine content of less than 1ppm is obtained. The purified water can directly enter the subsequent treatment process, and no fluorine-containing salts are generated in the evaporation and crystallization section. (2) When the resin adsorption reaches saturation, a saturated NaCl or AlCl3 solution is used as a decomposition liquid to decompose the resin. The fluorine-containing concentrated water produced by the decomposition enters the decomposition liquid storage unit of the fluoride recovery device; (3) 30% concentrated hydrochloric acid is introduced into the reaction unit as a raw material, and reacts with the fluorine-containing concentrated water in the analytical solution storage unit at a temperature of 50-100°C to generate hydrogen fluoride gas; (4) The generated hydrogen fluoride gas enters the condensation unit and is condensed to obtain the product anhydrous hydrofluoric acid; (5) The solution after the heating reaction in step (3) is a NaCl or AlCl3 solution, which is introduced into the decomposition liquid circulation unit and can be reused as the decomposition liquid of the resin in step (2).

2. The method for recovering fluoride ions from concentrated brine to produce hydrofluoric acid according to claim 1, characterized in that The resin includes Haisi brand DF-1S, Dusheng CH32, Lanxiao LX-760 or LX-860.

3. A device for implementing the method of recovering fluoride ions from concentrated brine to produce hydrofluoric acid according to any one of claims 1 to 2, characterized in that The fluoride ion recovery device of the RO membrane front section of the membrane workshop of the coking ammonia evaporation wastewater treatment plant includes a resin adsorption tank and a fluoride recovery device connected in sequence; the fluoride recovery device includes an analytical solution storage unit, a reaction unit, a condensation unit and an analytical solution circulation unit.