A method for recycling fluorine-containing waste residue

Abstract

This article belongs to the technical field of fluorine-containing waste residue recycling, specifically a method for recycling fluorine-containing waste residue. This article uses alkaline leaching to treat fluoride salt-containing waste residues. This method is simple, efficient, and low-cost, and can recover sodium fluoride for utilization, reducing the pressure on waste residue treatment.

Description

Technical Field

[0001] This article belongs to the technical field of recycling and utilizing fluorine-containing waste residues, and specifically relates to a method for recycling and utilizing fluorine-containing waste residues. Background Art

[0002] As a precursor to the popular cathode material lithium iron phosphate, iron phosphate is playing an increasingly important role in the rapidly developing new energy industry. Phosphoric acid is a key reactant in its preparation, and its production and purification processes are gaining increasing attention.

[0003] Currently, phosphoric acid is produced primarily through the pyrometallurgical and wet-process methods. Pyrometallurgical phosphoric acid offers high purity but remains expensive. Wet-process phosphoric acid is less expensive, but contains more impurities, requiring further purification before use in the production of synthetic ferric phosphate. Extraction and ammoniation methods are commonly used in the industry to remove impurities from wet-process phosphoric acid, but these methods often result in significant phosphorus losses and low byproduct value. The double salt method, due to its advantages such as low purification costs and ease of operation, is increasingly being used in phosphoric acid purification. The fluoride salt method, a specific type of double salt method, utilizes a fluoride-containing double salt to precipitate and remove impurities such as Al, Ca, and Mg from phosphoric acid. While this method is effective in purifying phosphoric acid and offers high phosphorus recovery rates, it produces a significant amount of fluoride-containing waste residue during the reaction, posing a significant environmental risk. Currently, there is no comprehensive method for resource-recovery of this fluoride-containing waste residue. Recycling the fluorine in this fluoride-containing waste residue could alleviate the burden of waste disposal while also generating significant economic value. Summary of the Invention

[0004] In response to the problem of how to recycle fluorine-containing waste residues involved in the above-mentioned related technologies, this article will provide a method for recycling fluorine-containing waste residues.

[0005] To achieve the above objectives, the following technical solutions are specifically included:

[0006] A method for recycling fluorine-containing waste residues comprises the following steps:

[0007] Primary alkaline leaching: alkali leaching the fluorine-containing waste residue to obtain primary leaching residue and primary leachate, wherein the primary leachate is used to recover sodium fluoride;

[0008] Secondary alkaline leaching: subjecting the primary leaching residue to alkali leaching to obtain secondary leaching residue and secondary leachate;

[0009] Mixing the secondary leaching residue with water and performing countercurrent washing to obtain waste residue and washing liquid;

[0010] In the primary alkali leaching and the secondary alkali leaching, the alkaline solutions used for the alkali leaching are each independently selected from at least one of a sodium hydroxide solution and a potassium hydroxide solution.

[0011] In addition to forming insoluble precipitates with fluoride ions, metal ions in fluoride-containing waste residues can also form insoluble hydroxide precipitates with hydroxide ions. Therefore, this paper utilizes the principle of precipitation conversion through alkaline leaching to release fluoride ions from the fluoride-containing slag. Furthermore, aluminum, one of the main elements in fluoride slag, is soluble in strong alkaline solutions, further promoting structural destruction and fluoride leaching. The primary leachate obtained from alkaline leaching is a sodium fluoride solution. Sodium fluoride has low solubility in aqueous solutions and easily precipitates crystals, which can be concentrated by evaporation to obtain a solid product. The sodium fluoride product extracted and recovered by the method described in this paper is of high purity and can be recycled or used as a raw material for other production processes. Its economic value is higher than the alkali used for leaching itself. The filter residue after alkaline leaching is mainly composed of hydroxides such as magnesium and aluminum, and the weight of the residue is approximately 45% of the weight before alkaline leaching, which reduces the pressure on waste residue treatment and is far less hazardous than the original fluoride-containing waste residue.

[0012] In one embodiment, the secondary leachate is used for primary alkaline leaching of new fluorine-containing waste residue, and the specific steps are as follows:

[0013] Primary alkaline leaching: placing new fluorine-containing waste residue in the secondary leachate for alkaline leaching to obtain primary leaching residue and primary leachate, wherein the primary leachate is used to recover sodium fluoride;

[0014] Secondary alkaline leaching: subjecting the primary leaching residue to alkali leaching to obtain secondary leaching residue and secondary leachate;

[0015] The secondary leaching residue is mixed with water and subjected to countercurrent washing to obtain waste residue and washing liquid.

[0016] The method herein utilizes a two-stage alkali leaching process consisting of a primary alkali leaching and a secondary alkali leaching. The primary leachate obtained from the initial alkali leaching has a high sodium fluoride concentration and is used to recover the sodium fluoride. The secondary leachate is then used as the alkali solution for the primary alkali leaching in the next cycle. After the primary alkali leaching, a new secondary alkali solution is used for the secondary alkali leaching, and the resulting secondary leachate is then used as the alkali solution for the primary alkali leaching in the next cycle. Therefore, the method herein is a cyclic alkali leaching process, utilizing a unique two-stage alkali leaching process to improve the efficiency of the alkali solution and save on the amount of alkali solution used.

[0017] This paper uses alkaline leaching to treat fluoride salt-containing waste residues for secondary alkaline leaching. This method is simple, efficient, and low-cost. It can recycle sodium fluoride and reduce the pressure of waste residue treatment. It has prospects for further research and development.

[0018] In one embodiment, in the primary alkaline leaching, the fluorine-containing waste residue includes at least one of phosphoric acid purification residue, fluorosilicate purification residue, and fluorochlorate purification residue.

[0019] In one embodiment, in the first alkali leaching, the alkali leaching temperature is 60-90°C.

[0020] In one embodiment, the alkali leaching time in the one alkali leaching is 1-12 hours.

[0021] In one embodiment, in the first alkali leaching, the concentration of the alkaline solution used in the alkali leaching is 0.5-5 mol / L.

[0022] In one embodiment, in the one alkali leaching, the alkali leaching is carried out under stirring, and the stirring rate is 200-600 rpm.

[0023] In one embodiment, in the primary alkaline leaching, the ratio of the volume of the alkaline solution to the mass of the fluorine-containing waste residue (ie, the liquid-to-solid ratio) is 10-20 mL / g.

[0024] In one embodiment, in the secondary alkali leaching, the alkali leaching temperature is 60-90°C.

[0025] In one embodiment, in the secondary alkali leaching, the alkali leaching time is 1-6 hours.

[0026] In one embodiment, in the secondary alkaline leaching, the concentration of the alkaline solution used in the alkali leaching is 1-5 mol / L.

[0027] In one embodiment, in the secondary alkali leaching, the alkali leaching is carried out under stirring, and the stirring rate is 200-600 rpm.

[0028] In one embodiment, in the secondary alkaline leaching, the secondary leachate can be used again to prepare the alkaline solution used in the alkali leaching.

[0029] In one embodiment, the temperature of the countercurrent washing is 60-90°C.

[0030] In one embodiment, the countercurrent washing time is 0.5-3 hours.

[0031] In one embodiment, the countercurrent washing is performed 2-5 times.

[0032] In one embodiment, in the secondary alkaline leaching, the ratio of the volume of the alkaline solution to the mass of the primary leaching residue (ie, the liquid-solid ratio) is 10-20 mL / g.

[0033] In one embodiment, the washing liquid can be reused to prepare the alkaline solution used in the alkaline leaching.

[0034] Compared with the related art, this paper has the following beneficial effects:

[0035] (1) Since the solubility products of magnesium hydroxide and fluoride contained in the phosphoric acid purification slag are not much different, the driving force of the precipitation conversion reaction is enhanced by the second-stage alkaline leaching, thereby improving the dissolution and conversion of the fluorine element. At the same time, the property of aluminum salt being soluble in alkali is utilized to promote the dissolution and conversion of aluminum fluoride, so that the fluorine element can be completely leached into the solution, thereby achieving the purpose of efficiently recovering sodium fluoride from the fluorine-containing waste slag, and the fluorine element content remaining in the filter residue is extremely small.

[0036] (2) The alkaline leaching method used in this paper can not only be applied to the recycling of phosphoric acid purification slag, but also can be used for the treatment and recycling of other fluorine-containing waste slags (such as fluorosilicate purification slag, fluorochlorate purification slag, etc.), and has wide applicability.

[0037] (3) This paper comprehensively utilizes fluorine-containing waste residues through a simple secondary alkaline leaching and separation method. While efficiently extracting the fluorine element from the waste residues, it also greatly reduces the final amount of waste residues produced and reduces the cost of waste residue treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic flow chart of the method for recycling fluorine-containing waste residues in this article.

[0039] Figure 2 FIG. 1 is an XRD spectrum of the dilute phosphoric acid purification slag in one embodiment.

[0040] Figure 3 is an XRD spectrum of the filter residue in one embodiment.

[0041] Figure 4 The XRD patterns of the filter residues in one pair are shown in FIG. DETAILED DESCRIPTION

[0042] To better illustrate the purpose, technical solutions and advantages of this article, this article will be further described below through specific embodiments.

[0043] The schematic flow diagram of the method for recycling fluorine-containing waste residues in the following embodiment is shown in the attached figure. Figure 1 shown.

[0044] The filter residue obtained by purifying and removing impurities from the crude phosphate fluoride salt method of the dilute phosphoric acid purification residue used below mainly consists of fluoride salts of impurity elements and sodium fluorosilicate.

[0045] Example 1

[0046] A method for recycling fluorine-containing waste residues specifically comprises the following steps:

[0047] (1) 50 g of dilute phosphoric acid purification residue was placed in a beaker, 800 mL of 1 mol / L sodium hydroxide low-concentration alkali solution was added, and the mixture was placed in an 85°C water bath. The stirring blade speed was adjusted to 300 rpm, and the alkali leaching reaction was carried out under stirring for 2 h. After the reaction was completed, the mixture was filtered to collect the primary leachate and the primary leachate residue; the primary leachate entered the fluorine recovery process and was concentrated by evaporation to obtain a sodium fluoride product;

[0048] (2) mixing the primary leaching residue in step (1) with 800 mL of 3 mol / L freshly prepared sodium hydroxide high-concentration alkali solution, performing alkaline leaching reaction for 2 h at a water bath temperature of 85° C. and a stirring rate of 300 rpm, filtering after the reaction to collect the secondary leachate and secondary leach residue; the secondary leachate is used for the primary leaching of the next batch of purified residue;

[0049] (3) The secondary alkali leaching residue was mixed with deionized water at a liquid-to-solid ratio of 10:1, and three countercurrent washings were performed in a water bath at 85°C to dissolve a large amount of sodium fluoride remaining in the secondary alkali leaching residue into the washing liquid. Each washing lasted half an hour, and the washing liquid was collected to prepare a high-concentration alkali solution. The filter residue was treated as hazardous waste.

[0050] (4) Repeat the above steps (1)-(2) for 3 times, specifically:

[0051] (4-1) 50 g of the purified slag was added to the secondary leachate from step (2) and placed in an 85°C water bath. The stirring speed was adjusted to 300 rpm, and the alkali leaching reaction was carried out under stirring for 2 h. After the reaction was completed, the leaching solution and the primary leachate were collected by filtration.

[0052] (4-2) mixing the primary leaching residue of step (4-1) with 800 mL of 3 mol / L freshly prepared sodium hydroxide high-concentration alkali solution, performing an alkali leaching reaction at a water bath temperature of 85° C. and a stirring rate of 300 rpm for 2 h, filtering after the reaction, and collecting a secondary leachate and secondary leaching residue;

[0053] (4-3) 50 g of the purified residue was added to the secondary leachate obtained in step (3-2) and placed in an 85°C water bath. The stirring speed was adjusted to 300 rpm, and the mixture was stirred for 2 h for alkaline leaching. After the reaction was completed, the mixture was filtered to collect the primary leachate and the primary leachate residue.

[0054] (4-4) mixing the secondary leaching residue from step (4-3) with 800 mL of 3 mol / L freshly prepared sodium hydroxide high-concentration alkali solution, performing an alkali leaching reaction at a water bath temperature of 85° C. and a stirring rate of 300 rpm for 2 h, filtering after the reaction, and collecting the secondary leaching solution and secondary leaching residue;

[0055] (4-5) 50 g of the purified residue was added to the secondary leachate in step (4-4) and placed in an 85°C water bath. The stirring speed was adjusted to 300 rpm. The mixture was stirred for 2 h and then filtered to collect the primary leachate and primary leachate residue.

[0056] (4-6) The secondary leaching residue of step (4-5) was mixed with 800 mL of 3 mol / L freshly prepared sodium hydroxide high concentration alkali solution, and the alkali leaching reaction was carried out at a water bath temperature of 85° C. and a stirring rate of 300 rpm for 2 h. After the reaction was completed, the mixture was filtered to collect the secondary leachate and secondary leaching residue.

[0057] Example 2

[0058] The difference between this embodiment and embodiment 1 is that the concentration of the high alkali solution in step (1) is 1.5 mol / L.

[0059] Example 3

[0060] The difference between this embodiment and embodiment 1 is that the concentration of the high alkali solution in step (1) is 2.3 mol / L.

[0061] Example 4

[0062] The difference between this embodiment and embodiment 1 is that the concentration of the high alkali solution in step (1) is 5 mol / L.

[0063] Example 5

[0064] The difference between this embodiment and embodiment 1 is that the temperature of the alkali leaching reaction in steps (1)-(2) is 60°C.

[0065] Example 6

[0066] The difference between this embodiment and embodiment 1 is that the temperature of the alkali leaching reaction in steps (1)-(2) is 90°C.

[0067] Example 7

[0068] The difference between this embodiment and embodiment 1 is that the time of the alkali leaching reaction in steps (1)-(2) is 1 hour.

[0069] Example 8

[0070] The difference between this embodiment and embodiment 1 is that the time of the alkali leaching reaction in steps (1)-(2) is 6 hours.

[0071] Example 9

[0072] The difference between this embodiment and embodiment 1 is that the alkali used in the alkali leaching in steps (1)-(2) is a potassium hydroxide solution of equal concentration.

[0073] Example 10

[0074] The difference between this embodiment and embodiment 1 is that the stirring rate in steps (1)-(2) is 600 rpm.

[0075] Example 11

[0076] The difference between this embodiment and embodiment 1 is that the stirring rate in steps (1)-(2) is 200 rpm.

[0077] Example 12

[0078] The difference between this embodiment and embodiment 1 is that the temperature of the countercurrent washing in step (3) is 60°C.

[0079] Example 13

[0080] The difference between this embodiment and embodiment 1 is that the number of countercurrent washing in step (3) is 2 times.

[0081] Example 14

[0082] The difference between this embodiment and embodiment 1 is that the number of countercurrent washing in step (3) is 5 times.

[0083] Example 15

[0084] The difference between this embodiment and embodiment 1 is that the liquid-to-solid ratio in the secondary alkaline leaching in step (2) is 10 mL / g.

[0085] Example 16

[0086] The difference between this embodiment and embodiment 1 is that the liquid-to-solid ratio in the secondary alkaline leaching in step (2) is 20 mL / g.

[0087] Comparative Example 1

[0088] Weigh 159g of sodium carbonate and dissolve it in 800mL of deionized water (1.5mol / L). Mix the obtained sodium carbonate solution with 50g of dilute phosphoric acid purification residue to form a slurry. Heat and stir in a water bath at 85℃ for 4h. After the reaction is completed, filter, wash the precipitate, and dry it to obtain a filter residue. Detect the content of each element in the filter residue and its XRD spectrum. The results are shown in Table 2-3 and the attached Figure 4 .

[0089] Comparative Example 2

[0090] Compared with Example 1, this embodiment differs in that only one alkali leaching is performed with a high-concentration alkali solution, specifically:

[0091] (1) 50 g of dilute phosphoric acid purification residue was placed in a beaker, 800 mL of 3 mol / L sodium hydroxide solution was added, and the mixture was placed in a water bath at 85°C. The stirring speed was adjusted to 300 rpm, and the mixture was subjected to alkaline leaching reaction for 4 h under stirring. After the reaction was completed, the mixture was filtered and the primary leachate and primary leach residue were collected. The primary leachate entered the fluorine recovery process and was concentrated by evaporation to obtain a sodium fluoride product.

[0092] (2) The primary alkali leaching residue was mixed with deionized water at a liquid-to-solid ratio of 10:1, and countercurrent washing was performed three times in a water bath at 85°C to dissolve a large amount of sodium fluoride remaining in the primary alkali leaching residue into the washing liquid. Each washing was conducted for half an hour, and the washing liquid was collected and evaporated to obtain the sodium fluoride product. The filter residue was treated as hazardous waste.

[0093] The original dilute phosphoric acid purification slag and the filter residue obtained after alkali leaching used in Examples 1-16 and Comparative Examples 1-2 were tested for Na, Mg, Al, P, Si, and Ca elemental contents using ICP-AES equipment, and the F elemental content was tested using an ion chromatograph. The test results are shown in Tables 1-2. The weight of the original dilute phosphoric acid purification slag and the filter residue obtained after alkali leaching were weighed, and the results are shown in Table 3.

[0094] The dilute phosphoric acid purification slag used in Examples 1-16 and Comparative Examples 1-2 is the same, and its components are shown in Table 1. Its XRD spectrum is shown in the attached figure. Figure 2 The XRD spectrum of the filter residue obtained after alkali leaching in Example 1 is shown in the attached figure. Figure 3 shown.

[0095] Table 1 Element mass percentage of original dilute phosphoric acid purification slag %

[0096] Na Mg Al F P Si Ca 12.1715 7.6448 11.5552 43.8840 2.1931 3.3641 0.4360

[0097] Table 2 Comparison of elemental composition before and after alkali leaching of purified slag

[0098]

[0099] Table 3 Filter residue mass (dry residue)

[0100]

[0101] As shown in Table 2, after the purified slag was alkali-leached in Examples 1-16, the fluorine content in the slag was significantly reduced, and there was very little residual fluorine in the filter residue.

[0102] By the attached Figure 2-4It can be seen from the XRD spectrum that the component of the purification slag, sodium magnesium aluminum fluoride, has been completely destroyed after alkaline leaching with sodium hydroxide solution, and the hydroxide in the alkali replaces the fluoride ion, so that sodium fluoride can be extracted; while in Comparative Example 1, when the same amount of sodium carbonate solution is used for leaching, due to its insufficient alkalinity, the structure of the purification slag is not destroyed, and effective leaching of fluorine cannot be achieved.

Claims

1. A method for recycling fluorine-containing waste residues, characterized in that: The steps include: Primary alkaline leaching: alkali leaching the fluorine-containing waste residue to obtain primary leaching residue and primary leachate, wherein the primary leachate is used to recover sodium fluoride; Secondary alkaline leaching: alkali leaching the primary leaching residue to obtain secondary leaching residue and secondary leachate; in the secondary alkali leaching, the concentration of the alkaline solution used in the alkali leaching is 3-5 mol / L; Mixing the secondary leaching residue with water and performing countercurrent washing to obtain waste residue and washing liquid; In the primary alkali leaching and the secondary alkali leaching, the alkaline solution used for the alkali leaching is independently selected from at least one of a sodium hydroxide solution and a potassium hydroxide solution; The secondary leachate is used for primary alkaline leaching of new fluorine-containing waste residue, and the cycle is repeated at least 3 times. The specific steps are: Primary alkaline leaching: placing new fluorine-containing waste residue in the secondary leachate for alkaline leaching to obtain primary leaching residue and primary leachate, wherein the primary leachate is used to recover sodium fluoride; Secondary alkaline leaching: subjecting the primary leaching residue to alkali leaching to obtain secondary leaching residue and secondary leachate; The secondary leaching residue is mixed with water and subjected to countercurrent washing to obtain waste residue and washing liquid.

2. The method for recycling fluorine-containing waste residue according to claim 1, characterized in that: In the first alkali leaching, the alkali leaching temperature is 60-90°C; And / or, in the secondary alkali leaching, the alkali leaching temperature is 60-90°C.

3. The method for recycling fluorine-containing waste residues according to claim 1, wherein: In the first alkali leaching, the alkali leaching time is 1-6h; And / or, in the secondary alkali leaching, the alkali leaching time is 1-6 hours.

4. The method for recycling fluorine-containing waste residue according to claim 1, wherein: In the first alkali leaching, the concentration of the alkaline solution used in the alkali leaching is 0.5-5 mol / L.

5. The method for recycling fluorine-containing waste residue according to claim 1, characterized in that: In the first alkali leaching, the alkali leaching is carried out under stirring, and the stirring rate is 200-600 rpm; And / or, in the secondary alkali leaching, the alkali leaching is carried out under stirring, and the stirring rate is 200-600 rpm.

6. The method for recycling fluorine-containing waste residue according to claim 1, characterized in that: The temperature of the countercurrent washing is 60-90°C.

7. The method for recycling fluorine-containing waste residue according to claim 1, characterized in that: The countercurrent washing is repeated 2-5 times.

8. The method for recycling fluorine-containing waste residue according to claim 1, characterized in that: In the first alkaline leaching, the ratio of the volume of the alkaline solution to the mass of the fluorine-containing waste residue is 10-20 mL / g. And / or, in the secondary alkaline leaching, the ratio of the volume of the alkaline solution to the mass of the primary leaching residue is 10-20 mL / g.

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