A method for removing fluorine from fluorine-containing hydrochloric acid

Abstract

The present invention relates to a method for removing fluorine from fluorine-containing hydrochloric acid, comprising the following steps: 1) adding a siliceous adsorption material to the fluorine-containing hydrochloric acid and allowing the reaction to proceed for a period of time; 2) dropwise adding a calcium chloride solution to the fluorine-containing hydrochloric acid, and filtering the solution after the reaction is complete to obtain a filtrate. The method utilizes waste glass slag as an adsorbent to accelerate precipitation, thereby improving production efficiency. Furthermore, the waste glass slag is low in cost, has good economic benefits, and is suitable for industrial applications.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorine chemical industry, in particular to a method for removing fluorine from fluorine-containing hydrochloric acid. Background Art

[0002] Fluorine-containing hydrochloric acid (HF) is produced in large quantities during the fluorine chemical production process. This byproduct, 0.1-2 wt% fluoride ion content, makes the extraction and recovery of fluorine from HF uneconomical. It is typically sold directly or through distributors to consumers. However, improper use by consumers can lead to safety hazards and accidents, such as equipment corrosion and leakage. Other consumers discharge substandard fluorine-containing wastewater, causing fluorine pollution in the surrounding environment. This raises safety and environmental concerns, necessitating the development of effective methods for removing HF from HF.

[0003] Chinese patent CN113428886A discloses a method for producing high-purity calcium fluoride and concentrating waste hydrochloric acid using waste acid, comprising the following steps: Step 1: filtering a mixed acid containing hydrofluoric acid and hydrochloric acid, heating the filtered mixed acid to a constant temperature of 50-60°C and stirring; Step 2: adding a calcium chloride solution dropwise to the mixed acid solution obtained in Step 1, stirring the reaction to obtain a mixed solution, vacuum filtering the mixed solution to obtain a hydrochloric acid solution and a precipitate; Step 3: adding a sodium hydroxide solution to the precipitate, stirring the reaction to obtain a mixture, filtering the mixture to separate a filter residue and an alkaline filtrate, rinsing the filter residue with deionized water, and then drying and crushing it to obtain high-purity calcium fluoride. The addition of the calcium chloride solution in Step 2 generates a calcium fluoride precipitate, but the calcium fluoride particles generated by using calcium chloride alone are fine and difficult to precipitate, resulting in low filtration and separation efficiency.

[0004] Chinese patent CN113200519B utilizes a self-developed aluminum silicate and fluorine-removing resin combination to effectively remove fluoride from high-fluorine hydrochloric acid. The aluminum silicate is prepared using an oil column molding method: sodium silicate, aluminum sulfate, and alkali are mixed and sprayed to form the mixture, which is then aged in a special oil to produce the aluminum silicate. This manufacturing process is complex and costly. Summary of the Invention

[0005] The purpose of the present invention is to improve the defluorination efficiency of fluorine-containing hydrochloric acid, reduce the defluorination cost, and improve the utilization value of fluorine-containing hydrochloric acid. The specific scheme is:

[0006] A method for defluoridating fluorine-containing hydrochloric acid comprises the following steps:

[0007] 1) Add siliceous adsorption material to fluorine-containing hydrochloric acid and react for a period of time;

[0008] 2) Add calcium chloride solution dropwise to the fluorine-containing hydrochloric acid, and filter after the reaction is complete to obtain a filtrate.

[0009] Since hydrofluoric acid is corrosive to siliceous materials, the addition of the siliceous adsorbent material corrodes the adsorbent, increasing its specific surface area and improving its adsorption capacity. At this point, a measured amount of calcium chloride solution is added dropwise. The calcium ions combine with fluoride ions to form fine calcium fluoride particles, which then adsorb onto the adsorbent material. The accumulation of calcium fluoride on the adsorbent material reduces its concentration in the solution, further promoting its formation. The calcium fluoride quickly precipitates and adsorbs onto the adsorbent material, promoting precipitation and improving filtration efficiency, effectively removing the majority of fluoride ions.

[0010] The siliceous adsorption material can be selected from granular materials whose main component is silicon dioxide, such as glass slag, quartz sand, etc.

[0011] The chemical reactions involved in the above process are:

[0012] 6HF+SiO2→H2SiF6+2H2O

[0013] 2HF+CaCl2→CaF2↓+2HCl

[0014] Preferably, in step 2), after the calcium chloride solution is added dropwise, the fluorine-containing hydrochloric acid is heated to 80-100° C., and then cooled and filtered.

[0015] At the beginning, some fluorosilicic acid is generated by the reaction between the siliceous adsorption material and hydrofluoric acid. At this time, there is still fluorosilicic acid impurities in the solution. At this time, the solution is heated to 80-100℃ to decompose the fluorosilicic acid and react with calcium ions to generate calcium fluoride and silicon dioxide. The two precipitates are aggregated with the precipitate of the aforementioned adsorption material. Then the solution is cooled and filtered to obtain fluoride-free hydrochloric acid with a fluoride ion concentration of less than 20ppm.

[0016] The chemical reactions involved in the above process are:

[0017] H2SiF6+2H2O+3CaCl2→3CaF2↓+SiO2↓+6HCl

[0018] Preferably, in step 2), the filtrate after filtration is distilled. Distillation can further reduce the fluoride ion concentration in the hydrochloric acid.

[0019] Preferably, in step 2), the filtrate after filtration is subjected to reduced pressure distillation. During the reduced pressure distillation, the vacuum degree is -0.01 to -0.02 MPa. This can produce hydrochloric acid with a lower fluoride content, with a fluoride ion concentration of less than 1 ppm.

[0020] Preferably, the particle size of the adsorption material in step 1) is 20-80 microns. If the particle size is too small, the adsorption capacity will be poor after being corroded by hydrofluoric acid. If the particle size is too large, it will easily settle and the suspension time will be short, which is not conducive to the adsorption effect.

[0021] Preferably, the adsorption material in step 1) is obtained by crushing and screening waste glass slag. Using waste glass slag to process and prepare the adsorption material can reduce the cost of the adsorption material.

[0022] Preferably, the amount of the adsorption material used in step 1) is 5-15% by weight of the fluorine-containing hydrochloric acid.

[0023] Preferably, the concentration of the calcium chloride solution in step 2) is 20-40 wt%.

[0024] Preferably, the amount of calcium chloride solution added in step 2) is 0.5-0.51 times the molar number of hydrofluoric acid in the fluorine-containing hydrochloric acid.

[0025] The present invention utilizes waste glass slag as an adsorbent to accelerate precipitation, thereby improving production efficiency. Meanwhile, the waste glass slag has low cost, good economic benefits, and is suitable for industrial application. DETAILED DESCRIPTION

[0026] The fluorine-containing hydrochloric acid used in the following examples has a hydrofluoric acid content of 0.24% and is sourced from a domestic chemical company.

[0027] Example 1

[0028] Take 200g of fluorine-containing hydrochloric acid in a container, add 10g of glass slag with a particle size distribution of 20-60μm, stir slowly for 2h, then add 6.66g of 20wt% calcium chloride solution dropwise, continue stirring slowly at 10rpm for 3h, then heat to 80°C, stir slowly for another 1h, cool to room temperature, and filter to obtain 202g of fluorine-free hydrochloric acid. The fluoride ion concentration was tested to be 17ppm.

[0029] Example 2

[0030] Take 200g of fluorine-containing hydrochloric acid in a container, add 30g of glass slag with a particle size distribution of 40-80μm, stir slowly for 1h, then add 6.78g of 20wt% calcium chloride solution dropwise, continue stirring slowly at 10rpm for 5h, then heat to 100℃, stir slowly for another 1h, cool to room temperature, and filter to obtain 201g of fluorine-free hydrochloric acid. The fluoride ion concentration was tested to be 9ppm.

[0031] Example 3

[0032] Take 200g of fluorine-containing hydrochloric acid in a container, add 15g of glass slag with a particle size distribution of 30-70μm, stir slowly for 1h, then add 6.78g of 20wt% calcium chloride solution dropwise, continue stirring slowly at 10rpm for 4h, then heat to 90°C, stir slowly for another 1h, cool to room temperature, filter to obtain fluorine-free hydrochloric acid, and then distill at 110°C to obtain 190g of pure hydrochloric acid. The fluoride ion concentration was tested to be 0.6ppm.

[0033] Example 4

[0034] Take 200g of fluorine-containing hydrochloric acid in a container, add 15g of glass slag with a particle size distribution of 30-70μm, stir slowly for 1h, then add 3.39g of 40wt% calcium chloride solution dropwise, continue stirring slowly at 10rpm for 4h, then heat to 90℃, stir slowly for another 1h, cool to room temperature, filter to obtain fluorine-free hydrochloric acid, and then distill under reduced pressure at 60℃ with a vacuum degree of -0.08MPa to obtain 180g of pure hydrochloric acid. The fluoride ion concentration is tested to be 0.4ppm.

[0035] Example 5

[0036] Take 200g of fluorine-containing hydrochloric acid in a container, add 10g of glass slag with a particle size distribution of 20-60μm, stir slowly for 2h, then add 6.66g of 20wt% calcium chloride solution dropwise, continue stirring slowly at 10rpm for 3h, filter to obtain 202g of fluorine-free hydrochloric acid, and the fluoride ion concentration is 16ppm and the fluorosilicate ion concentration is 220ppm after testing.

[0037] Table of impurity ion contents of hydrochloric acid obtained in Examples 1-5 (ppm)

[0038] <![CDATA[F - ]]> <![CDATA[Ca 2+ ]]> <![CDATA[SiF6 2- ]]> <![CDATA[Na + ]]> Example 1 17 27 13 60 Example 2 9 48 11 56 Example 3 0.6 7 ND 8 Example 4 0.4 3 ND 8 Example 5 16 32 220 58

[0039] In the above examples, the use of waste glass slag as an adsorption material effectively removed fluoride ions from fluorine-containing hydrochloric acid, resulting in a fluoride ion content of less than 20 ppm in the treated hydrochloric acid. In Examples 3 and 4, further distillation treatment reduced the fluoride ion solubility in the hydrochloric acid to below 1 ppm. In Example 5, no heating or distillation treatment was performed, resulting in a higher fluorosilicate ion concentration.

Claims

1. A method for removing fluorine from fluorine-containing hydrochloric acid, characterized in that: The following steps are involved: 1) Add siliceous adsorption material to fluorine-containing hydrochloric acid and react for 1 hour or 2 hours; 2) adding a calcium chloride solution dropwise to the fluorine-containing hydrochloric acid, filtering after the reaction is complete to obtain a filtrate; The adsorption material in step 1) is obtained by crushing and screening waste glass slag, with a particle size of 20-80 microns, and the amount used is 5-15% by weight of the fluorine-containing hydrochloric acid, and the hydrofluoric acid content of the fluorine-containing hydrochloric acid is 0.24%; In step 2), after the calcium chloride solution is added dropwise, the fluorine-containing hydrochloric acid is heated to 80-100° C., and then cooled and filtered.

2. The method for defluoridating fluorine-containing hydrochloric acid according to claim 1, wherein: Step 2) distilling the filtered filtrate.

3. The method for removing fluorine from fluorine-containing hydrochloric acid according to claim 2, wherein: Step 2) The filtered filtrate is subjected to reduced pressure distillation.

4. The method for defluoridating fluorine-containing hydrochloric acid according to claim 1, wherein: In step 2), the concentration of the calcium chloride solution is 20-40 wt%.

5. The method for defluoridating fluorine-containing hydrochloric acid according to claim 4, wherein: In step 2), the amount of calcium chloride solution added is 0.5-0.51 times the molar number of hydrofluoric acid in the fluorine-containing hydrochloric acid.