A fluorine recovery method for fluorine-containing waste acid and its application

Abstract

The invention discloses a fluorine recovery method for fluorine-containing waste acid and its application, the fluorine recovery method comprises the following steps: S1: adding a sulfiding agent to the waste acid for reaction, collecting the supernatant, and obtaining a sulfided liquid; S2: taking the sulfided liquid described in step S1 and adding a defluorinating agent until the pH value of the reaction system is adjusted to 5-7, collecting the solid phase after the reaction, and obtaining a crude calcium fluoride product; S3: taking the sulfided liquid described in step S1 and mixing with the crude calcium fluoride product described in step S2 for slurry pickling, collecting the solid phase and washing with water, and obtaining a finished calcium fluoride product. The fluorine recovery method provided by the present invention can effectively recover fluorine from fluorine-containing waste acid, prepare a high-purity calcium fluoride product, and the process is simple and easy to operate, the reaction conditions are mild, and each step is easy to control, and can be widely used in actual production.

Description

Technical Field

[0001] The invention belongs to the technical field of waste acid treatment, and in particular relates to a fluorine recovery method for waste acid containing fluorine and application thereof. Background Art

[0002] The non-ferrous smelting industry produces a large amount of polluted acid wastewater during the flue gas acid production process. The polluted acid is highly harmful and contains high levels of fluorine, chlorine and sulfate. At present, the industry mainly uses neutralization, sulfide-neutralization and lime-iron salt methods to treat polluted acid. The above methods first remove heavy metals from the polluted acid, and then use neutralization to remove the fluorine element from the polluted acid, which will cause fluoride ions and sulfate to co-precipitate, forming fluorine-containing waste slag in the form of calcium fluoride-calcium sulfate co-precipitation, resulting in the inability to efficiently recover fluorine resources.

[0003] In addition, calcium fluoride is a strategic resource, known as the "second rare earth". Calcium fluoride with high purity can be used in metallurgy, aluminum smelting and other industries. Therefore, recovering high-purity calcium fluoride from fluorine-containing waste slag has good environmental and economic benefits. At present, the main methods for purifying calcium fluoride are flotation and chemical methods. These methods have the disadvantages of high energy consumption, complicated purification steps, many pollutants, low yield and high cost. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a fluorine recovery method for fluorine-containing waste acid, which can effectively recover fluorine from fluorine-containing waste acid to prepare a high-purity calcium fluoride product, and the process is simple and easy to operate, the reaction conditions are mild, and each step is easy to control, and can be widely used in actual production.

[0005] The present invention also proposes the application of the fluorine recovery method.

[0006] According to a first aspect of the present invention, a method for recovering fluorine from fluorine-containing waste acid is provided, the method comprising the following steps:

[0007] S1: adding a sulfiding agent to the dirty acid to react, collecting the supernatant to obtain a sulfided liquid;

[0008] S2: taking the sulfided liquid in step S1 and adding a defluorinating agent, adjusting the pH value of the reaction system to 5-7 for reaction, collecting the solid phase, and obtaining a crude calcium fluoride product;

[0009] S3: taking the sulfided liquid in step S1 and mixing it with the crude calcium fluoride product in step S2, performing slurry acid washing, collecting the solid phase and washing it with water to obtain a finished calcium fluoride product.

[0010] In some embodiments of the present invention, the sulfiding agent in step S1 includes at least one of hydrogen sulfide, sodium sulfide and sodium hydrosulfide.

[0011] In some embodiments of the present invention, the molar ratio of sulfur element in the vulcanizing agent in step S1 to heavy metal ions in the waste acid is (1-3):1.

[0012] In some embodiments of the present invention, the molar ratio of sulfur element in the vulcanizing agent in step S1 to heavy metal ions in the waste acid is (1-2):1.

[0013] In some embodiments of the present invention, the defluorination agent in step S2 includes at least one of calcium oxide, calcium hydroxide and calcium carbonate.

[0014] In some embodiments of the present invention, the reaction time in step S2 is 1-3 hours.

[0015] In some embodiments of the present invention, the reaction time in step S2 is 1-2 hours.

[0016] In some embodiments of the present invention, the mixed liquid-to-solid ratio of the sulfided liquid and the crude calcium fluoride in step S3 is (4-20): 1 mL / g.

[0017] In some embodiments of the present invention, the mixed liquid-to-solid ratio of the sulfided liquid and the crude calcium fluoride in step S3 is (5-20): 1 mL / g.

[0018] In some embodiments of the present invention, when the molar ratio of fluoride ions to sulfate ions in the waste acid in step S1 is less than or equal to 25, step S3 further includes the step of adjusting the pH value of the sulfided liquid to 6-8 using sodium hydroxide.

[0019] In step S3, calcium sulfate in the low-grade crude calcium fluoride can react with hydrofluoric acid to be replaced by calcium fluoride with lower solubility, and the effect of calcium sulfate being converted into calcium fluoride near neutral is better, so when the calcium sulfate content in the calcium fluoride is high, it is necessary to adjust the pH value of the sulfided liquid to 6-8; step S3 mixes the crude calcium fluoride with the sulfided liquid for reaction, which can convert calcium sulfate impurities into calcium fluoride to improve the purity of calcium fluoride on the one hand, and consume fluoride ions in the sulfided liquid on the other hand, reduce the amount of defluoridation agent used, and further reduce the production cost of the fluorine recovery method.

[0020] In some embodiments of the present invention, the slurry pickling time in step S3 is 1-3 hours.

[0021] In some embodiments of the present invention, the slurry pickling time in step S3 is 1-2 hours.

[0022] In some embodiments of the present invention, the liquid-to-solid ratio of the water washing in step S3 is (3-10): 1 mL / g.

[0023] In some embodiments of the present invention, the liquid-to-solid ratio of the water washing in step S3 is (4-6): 1 mL / g.

[0024] The calcium fluoride slag after pulping and acid washing has a high water content and will carry some soluble impurities on its surface, such as chloride ions. These soluble impurities can be removed after water washing, further improving the purity of calcium fluoride.

[0025] In some embodiments of the present invention, the waste acid in step S1 includes acidic wastewater generated when acid is produced from flue gas during metal smelting.

[0026] In some embodiments of the invention, the waste acid contains fluoride ions, chloride ions and sulfate ions.

[0027] In some embodiments of the present invention, the pH value of the waste acid is 1-3.

[0028] According to the second aspect of the present invention, the application of the fluorine recovery method as described in the first aspect of the present invention in the resource treatment of fluorine-containing waste acid is proposed.

[0029] The present invention has at least the following beneficial effects:

[0030] The fluorine recovery method provided by the present invention solves the problem that fluorine in waste acid cannot be effectively recovered and utilized in smelting production. The recovery method can prepare calcium fluoride with a purity greater than 80% based on fluorine-containing waste acid, and the calcium fluoride reaches product-grade purity; and the fluorine recovery method provided by the present invention only needs to add a small amount of sulfiding agent and defluoriding agent to achieve the purification of calcium fluoride, and has low cost, simple steps, mild reaction conditions, and easy control of each step; the crude calcium fluoride obtained by the fluorine recovery method can be used as a new defluoridating agent to reduce the fluoride ion concentration in the liquid after sulfidation, thereby saving the amount of defluoridating agent used in the reaction process and further reducing the processing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0032] Figure 1 A schematic flow chart of the fluorine recovery method provided in Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0034] Example 1

[0035] This embodiment provides a method for recovering fluorine from fluorine-containing waste acid, and its flow diagram is as follows: Figure 1 As shown, the specific steps include:

[0036] 1) The waste acid used in this embodiment comes from a smelter, and the water quality of the waste acid is shown in Table 1;

[0037] Table 1 Water quality of the waste acid used in Example 1

[0038]

[0039]

[0040] 2) Take 1000 mL of the waste acid, add 6.49 g of sodium hydrosulfide to the waste acid to react and remove heavy metal ions, collect the supernatant to obtain a sulfided liquid, and the pH of the sulfided liquid is 3.04;

[0041] 3) taking the sulfided liquid obtained in step 2) and adding 59.6 g of 30% lime milk, mixing evenly, adjusting the pH to 7, and stirring for reaction for 1 hour; after the reaction, performing solid-liquid separation to obtain 58.64 g of crude calcium fluoride (wet residue) and filtrate, the purity of the crude calcium fluoride is 56.59%;

[0042] 4) taking 20 g of the crude calcium fluoride (wet slag) obtained in step 3), adding 100 mL of the sulfided liquid obtained in step 2) to slurry, and stirring the reaction at room temperature for 1 hour; after the reaction, performing solid-liquid separation to obtain a filtrate and purified calcium fluoride slag, wherein the concentration of fluoride ions in the filtrate is 8.77 g / L;

[0043] 5) washing the purified calcium fluoride slag obtained in step 4) with water at a liquid-to-solid ratio of 5:1 for 20 min, and performing solid-liquid separation after washing to obtain a solid phase, which is a finished calcium fluoride product with a purity of 87.62% and a dry weight of 8.94 g.

[0044] Example 2

[0045] This embodiment provides a method for recovering fluorine from fluorine-containing waste acid, which specifically comprises the following steps:

[0046] 1) The waste acid used in this example comes from a smelter, and the water quality of the waste acid is shown in Table 2;

[0047] Table 2 Water quality of the waste acid used in Example 2

[0048]

[0049] 2) Take 1000 mL of waste acid, add 9.19 g of hydrogen sulfide to the waste acid for reaction to remove heavy metal ions, collect the supernatant to obtain a sulfided liquid, and the pH of the sulfided liquid is 2.15;

[0050] 3) taking the sulfided liquid obtained in step 2) and adding 55.92 g of 30% lime milk, mixing evenly, adjusting the pH to 6, and stirring for reaction for 1 hour; after the reaction, performing solid-liquid separation to obtain 54.57 g of crude calcium fluoride (wet residue) and filtrate, the purity of the crude calcium fluoride is 51.09%;

[0051] 4) taking 20 g of the crude calcium fluoride (wet slag) obtained in step 3), adding 400 mL of the sulfided liquid obtained in step 2) to slurry (the pH of the sulfided liquid was adjusted to 7 with sodium hydroxide), and stirring the reaction at room temperature for 1 hour; after the reaction, performing solid-liquid separation to obtain a filtrate and purified calcium fluoride slag, wherein the concentration of fluoride ions in the filtrate was 0.226 g / L;

[0052] 5) washing the purified calcium fluoride slag obtained in step 4) with water at a liquid-to-solid ratio of 5:1 for 20 min, and performing solid-liquid separation after washing to obtain a solid phase, which is a finished calcium fluoride product with a purity of 81.02% and a dry weight of 9.06 g.

[0053] Comparative Example 1

[0054] This comparative example provides a fluorine recovery method for fluorine-containing waste acid, which differs from Example 2 only in that the step of adjusting the pH value in step 4) is omitted, and the other steps are consistent with Example 2. Among them, the concentration of fluorine ions in the filtrate obtained after step 4) is 4.5 g / L, and the purity of the calcium fluoride product after step 5) is 62.74%, and the dry weight is 9.43 g.

[0055] Comparative Example 2

[0056] This comparative example provides a fluorine recovery method for fluorine-containing waste acid, which is different from Example 2 only in that the sulfided liquid in step 4) is adjusted to pH=5 with sodium hydroxide solution, and the other steps are consistent with Example 2. Among them, the concentration of fluoride ions in the filtrate obtained after step 4) is 2.216 g / L, and the purity of the calcium fluoride product after step 5) is 73.85%, and the dry weight of the product is 9.28 g.

[0057] Comparative Example 3

[0058] This comparative example provides a fluorine recovery method for fluorine-containing waste acid, which is different from Example 1 only in that the amount of the post-sulfurization liquid added in step 4) is adjusted to 60 mL (i.e., liquid-to-solid ratio = 3:1), and the other steps are consistent with Example 1. Among them, the concentration of fluoride ions in the filtrate obtained after step 4) is 10.98 g / L, and the purity of the calcium fluoride product after step 5) is 77.05%, and the dry weight of the product is 9.05 g.

[0059] Comparative Example 4

[0060] This comparative example provides a fluorine recovery method for fluorine-containing waste acid, which is different from Example 2 only in that the amount of 30% lime milk added in step 3) is adjusted to 58.59 g, so that the pH value of the mixed system is 8, and the other steps are consistent with Example 2. After step 3), 57.69 g (wet residue) and filtrate of crude calcium fluoride are obtained, and the purity of the crude calcium fluoride is 48.25%; after step 4), the concentration of fluoride ions in the filtrate is 0.443 g / L, and after step 5), the purity of the finished calcium fluoride is 78.27%, and the dry weight of the product is 9.15 g.

[0061] It can be seen from the purity test results of the finished calcium fluoride products obtained in Example 1, Example 2 and Comparative Examples 1-4 that the present invention achieves an excellent calcium fluoride recovery effect by using a sulfiding agent, a defluorinating agent and adjusting the reaction system to a specific pH value condition, and the purity of the obtained calcium fluoride exceeds 80%; the present invention solves the problems that the waste acid is of little use in the smelting production process and is difficult to process and recycle, and the process is simple and easy to operate, the reaction conditions are mild, and each step is easy to control, so that the fluorine resources in the waste acid can be effectively recovered.

[0062] The above is a detailed description of the embodiments of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for recovering fluorine from fluorine-containing waste acid, characterized in that: The fluorine recovery method comprises the following steps: S1: adding a sulfiding agent to the dirty acid to react, collecting the supernatant to obtain a sulfided liquid; S2: taking the sulfided liquid in step S1 and adding a defluorinating agent until the pH value of the reaction system is adjusted to 5-7, collecting the solid phase after the reaction to obtain a crude calcium fluoride product; S3: taking the sulfided liquid in step S1 and mixing it with the crude calcium fluoride product in step S2, performing slurry acid washing, collecting the solid phase and washing it with water to obtain a finished calcium fluoride product.

2. The fluorine recovery method according to claim 1, characterized in that: The sulfiding agent in step S1 includes at least one of hydrogen sulfide, sodium sulfide and sodium hydrosulfide.

3. The fluorine recovery method according to claim 1, characterized in that: In step S1, the molar ratio of sulfur element in the vulcanizing agent to heavy metal ions in the waste acid is (1-3):

1.

4. The fluorine recovery method according to claim 1, characterized in that: The defluoridating agent in step S2 includes at least one of calcium oxide, calcium hydroxide and calcium carbonate.

5. The fluorine recovery method according to claim 1, characterized in that: The reaction time in step S2 is 1-3 hours.

6. The fluorine recovery method according to claim 1, characterized in that: The mixed liquid-solid ratio of the sulfided liquid and the crude calcium fluoride in step S3 is (4-20): 1 mL / g; And / or, when the molar ratio of fluoride ions to sulfate ions in the waste acid in step S1 is less than or equal to 25, step S3 further includes the step of adjusting the pH value of the sulfided liquid to 6-8 using sodium hydroxide.

7. The fluorine recovery method according to claim 1, characterized in that: The slurry pickling time in step S3 is 1-3 hours.

8. The fluorine recovery method according to claim 1, characterized in that: The liquid-to-solid ratio of the water washing in step S3 is (3-10): 1 mL / g.

9. The fluorine recovery method according to claim 1, characterized in that: The waste acid in step S1 includes acid wastewater generated when acid is produced from flue gas during metal smelting; Preferably, the waste acid contains fluoride ions, chloride ions and sulfate ions; Preferably, the pH value of the dirty acid is 1-3.

10. Application of the fluorine recovery method as claimed in any one of claims 1 to 9 in resource treatment of fluorine-containing waste acid.

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