CN117545718A - Method for recycling fluorine-containing waste residues - Google Patents

Abstract

The method belongs to the technical field of fluorine-containing waste residue recycling, and particularly relates to a fluorine-containing waste residue recycling method. The fluoride salt fluorine-containing waste residue is subjected to secondary alkaline leaching treatment by an alkaline leaching method, and the method is simple, efficient and low in cost, and can recover sodium fluoride therefrom for utilization, so that the waste residue treatment pressure is reduced.

Description

Method for recycling fluorine-containing waste residues

Technical Field

The method belongs to the technical field of fluorine-containing waste residue recycling, and particularly relates to a fluorine-containing waste residue recycling method.

Background

Iron phosphate is used as a precursor of hot cathode material lithium iron phosphate, and has increasingly important position in the new energy industry which is rapidly developed at present. Phosphoric acid is an important reactant for preparing ferric phosphate, and the production and purification processes of the phosphoric acid are also increasingly emphasized.

At present, the production mode of phosphoric acid mainly comprises a fire method and a wet method, and the purity of the fire method phosphoric acid is high, but the production cost is high; the wet-process phosphoric acid has low cost, but contains more impurities, and can be used for preparing the synthetic ferric phosphate only by further removing impurities and purifying. The wet phosphoric acid is usually subjected to impurity removal by an extraction method, an ammonification method and the like in industry, but the problems of high phosphorus loss, low utilization value of byproducts and the like are generally caused. The double salt method has the advantages of lower purification cost, simple and convenient operation and the like, and is increasingly widely applied to the field of phosphoric acid purification. The fluoride salt method in the double salt method is a method for precipitating and removing impurities such as Al, ca, mg and the like in phosphoric acid by utilizing fluoride-containing double salt. Although the method has good effect of purifying the phosphoric acid and high phosphorus recovery rate, a certain amount of fluorine-containing waste residues are generated in the reaction process, and the method has certain harm to the environment. Up to now, there is no method for recycling and comprehensively utilizing the fluorine-containing purification slag. If the fluorine in the fluorine-containing waste residue can be recycled, certain economic value can be obtained while the pressure of waste residue treatment is reduced.

Disclosure of Invention

In view of the above-mentioned problems related to how to recycle the fluorine-containing waste residue, a method for recycling the fluorine-containing waste residue will be provided herein.

In order to achieve the above purpose, the method specifically comprises the following technical scheme:

a method for recycling fluorine-containing waste residues comprises the following steps:

primary alkaline leaching: alkaline leaching is carried out on fluorine-containing waste residues to obtain primary leaching residues and primary leaching liquid, and the primary leaching liquid is used for recycling sodium fluoride;

secondary alkaline leaching: alkaline leaching is carried out on the primary leaching residues to obtain secondary leaching residues and secondary leaching solutions;

mixing the secondary leaching residue with water for countercurrent washing to obtain waste residue and washing liquid;

in the primary alkaline leaching and the secondary alkaline leaching, the alkaline solution used in the alkaline leaching is at least one of sodium hydroxide solution and potassium hydroxide solution independently.

The metal ions in the fluorine-containing waste residue can form insoluble precipitates with fluorine ions and also can form insoluble hydroxide precipitates with hydroxide, so that the purpose of releasing the fluorine ions in the fluorine-containing slag is achieved by utilizing the principle of precipitation conversion in an alkaline leaching mode; and aluminum, which is one of the main elements of the fluorinated slag, is soluble in strong alkali solution, which can further promote the destruction of the structure and leaching of fluorine. The primary leaching solution obtained by alkaline leaching is sodium fluoride solution, sodium fluoride has low solubility in aqueous solution and is easy to precipitate crystals, a solid product can be obtained by evaporation and concentration, the purity of the sodium fluoride product obtained by extraction and recovery in the method is higher, the sodium fluoride product can be recycled or used as other production raw materials, and the economic value of the sodium fluoride product is higher than that of alkali used for leaching. The main components of the filter residue after alkaline leaching are hydroxides of magnesium, aluminum and the like, the weight of the residue is about 45 percent before alkaline leaching, the pressure of waste residue treatment is reduced, and the harm of the filter residue is far lower than that of the original fluorine-containing waste residue.

In one embodiment, the secondary leaching solution is used for primary alkaline leaching of new fluorine-containing waste residues, and the specific steps are as follows:

primary alkaline leaching: placing new fluorine-containing waste residues into the secondary leaching solution for alkaline leaching to obtain primary leaching residues and primary leaching solution, wherein the primary leaching solution is used for recycling sodium fluoride;

secondary alkaline leaching: alkaline leaching is carried out on the primary leaching residues to obtain secondary leaching residues and secondary leaching solutions;

and mixing the secondary leaching residue with water for countercurrent washing to obtain waste residue and washing liquid.

In the method, a two-stage alkaline leaching mode of primary alkaline leaching and secondary alkaline leaching is used, wherein the primary leaching liquid is obtained by primary alkaline leaching at first, and contains high sodium fluoride concentration for recovering sodium fluoride; because the secondary leaching liquid is used as alkali liquid for primary alkali leaching in the next circulation process, after primary alkali leaching, new alkali liquid is used for secondary impregnation, and then the obtained secondary leaching liquid is used as alkali liquid for primary alkali leaching in the next circulation. Therefore, the whole method is a circulating alkaline leaching process, and the unique two-stage alkaline leaching is utilized, so that the use effect of alkali liquor is improved, and the consumption of the alkali liquor is saved.

The fluoride salt fluorine-containing waste residue is subjected to secondary alkaline leaching treatment by an alkaline leaching method, and the method is simple, efficient and low in cost, can recycle sodium fluoride from the fluoride salt waste residue, reduces the waste residue treatment pressure, and has the prospect of further research and development.

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

In one embodiment, the primary alkaline leaching is performed at a temperature of 60-90 ℃.

In one embodiment, the time of the primary alkaline leaching is 1-12h.

In one embodiment, the concentration of the alkaline solution used in the alkaline leaching is 0.5 to 5mol/L.

In one embodiment, the primary alkaline leaching is performed with agitation at a rate of 200-600rpm.

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

In one embodiment, the secondary alkaline leaching is performed at a temperature of 60-90 ℃.

In one embodiment, the time of the secondary alkaline leaching is 1-6 hours.

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

In one embodiment, the secondary alkaline leaching is performed with agitation at a rate of 200-600rpm.

In one embodiment, in the secondary alkaline leaching, the secondary leach solution may be reused to configure the alkaline solution used in the alkaline leaching.

In one embodiment, the countercurrent washing temperature is 60-90 ℃.

In one embodiment, the counter-current wash time is 0.5 to 3 hours.

In one embodiment, the number of counter current washes is 2-5.

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

In one embodiment, the wash liquor may be reused to formulate the alkaline solution used in the alkaline leaching.

With respect to the related art, the following benefits are provided herein:

(1) Because the solubility product of magnesium hydroxide and fluoride contained in the phosphoric acid purification slag is not large, the driving force of precipitation conversion reaction is enhanced through two-stage alkaline leaching, and the dissolution and conversion of fluorine element are improved; meanwhile, the dissolution and conversion of aluminum fluoride are promoted by utilizing the property that aluminum salt is soluble in alkali, so that fluorine element can be thoroughly leached into the solution, the purpose of efficiently recovering sodium fluoride from fluorine-containing waste residues is achieved, and the content of fluorine element remained in the filter residues is very small.

(2) The alkaline leaching method adopted in the method not only can be applied to recycling of phosphoric acid purification slag, but also can be used for treating and recycling of other fluorine-containing waste residues (such as fluorosilicate purification slag, fluorite purification slag and the like), and has wide applicability.

(3) The fluorine-containing waste residue is comprehensively utilized by a simple secondary alkaline leaching and separating method, so that the fluorine element in the waste residue is efficiently extracted, the final yield of the waste residue is greatly reduced, and the treatment cost of the waste residue is reduced.

Drawings

FIG. 1 is a schematic flow chart of a method for recycling fluorine-containing waste residues.

Fig. 2 is an XRD spectrum of the diluted phosphoric acid purification slag in an embodiment.

Fig. 3 is an XRD spectrum of the filter residue in an embodiment.

Fig. 4 is an XRD spectrum of the filter residue in a comparative example.

Detailed Description

For a better description of the objects, technical solutions and advantages herein, the following description will further explain the same by means of specific examples.

A schematic flow chart of the method for recycling fluorine-containing waste residues in the following embodiment is shown in the attached figure 1.

The residue obtained by purifying and removing impurities from the dilute phosphoric acid purified residue by a crude phosphoric acid fluoride salt method is mainly composed of fluoride salt of impurity elements and sodium fluosilicate.

Example 1

The method for recycling the fluorine-containing waste residues specifically comprises the following steps:

(1) Taking 50g of dilute phosphoric acid purification slag, adding 800mL of 1mol/L sodium hydroxide concentration low-concentration alkali liquor into a beaker, placing into a water bath at 85 ℃, adjusting the rotating speed of a stirring paddle to 300rpm, carrying out alkaline leaching reaction for 2 hours under stirring, filtering after the reaction is finished, and collecting primary leaching liquid and primary leaching slag; the primary leaching solution enters a fluorine recovery process, and sodium fluoride products are obtained through evaporation and concentration;

(2) Mixing the primary leaching residue obtained in the step (1) with 800mL of 3mol/L sodium hydroxide high-concentration alkali liquor, performing alkaline leaching reaction for 2 hours at the water bath temperature of 85 ℃ and the stirring speed of 300rpm, filtering after the reaction is finished, and collecting secondary leaching solution and secondary leaching residue; the secondary leaching solution is used for primary leaching of the next batch of purified slag;

(3) The weight ratio is as follows: and (3) mixing the secondary alkaline leaching residue with deionized water according to the liquid-solid ratio, performing countercurrent washing for three times under the water bath at the temperature of 85 ℃ to dissolve a large amount of sodium fluoride remained in the secondary alkaline leaching residue into washing liquid, washing for half an hour each time, and collecting washing liquid for preparing high-concentration alkali liquor and treating filter residues as hazardous waste.

(4) Cycling the steps (1) - (2) 3 times, specifically:

(4-1) taking 50g of purified slag, adding the secondary leaching solution obtained in the step (2) into a water bath at 85 ℃, adjusting the rotating speed of a stirring paddle to 300rpm, carrying out alkaline leaching reaction for 2 hours under stirring, filtering after the reaction is finished, and collecting primary leaching solution and primary leaching slag;

(4-2) mixing the primary leaching residue obtained in the step (4-1) with 800mL of 3mol/L sodium hydroxide high-concentration alkali liquor, performing alkaline leaching reaction for 2 hours at the water bath temperature of 85 ℃ and the stirring speed of 300rpm, filtering after the reaction is finished, and collecting secondary leaching solution and secondary leaching residue;

(4-3) adding 50g of purified slag into the secondary leaching solution obtained in the step (3-2), placing the secondary leaching solution in a water bath at 85 ℃, adjusting the rotating speed of a stirring paddle to 300rpm, carrying out alkaline leaching reaction for 2 hours under stirring, filtering after the reaction is finished, and collecting primary leaching solution and primary leaching slag;

(4-4) mixing the secondary leaching residue obtained in the step (4-3) with 800mL of 3mol/L sodium hydroxide high-concentration alkali liquor, performing alkaline leaching reaction for 2 hours at the water bath temperature of 85 ℃ and the stirring speed of 300rpm, filtering after the reaction is finished, and collecting secondary leaching solution and secondary leaching residue;

(4-5) adding 50g of purified slag into the secondary leaching solution obtained in the step (4-4), placing the secondary leaching solution in a water bath at 85 ℃, adjusting the rotating speed of a stirring paddle to 300rpm, carrying out alkaline leaching reaction for 2 hours under stirring, filtering after the reaction is finished, and collecting primary leaching solution and primary leaching slag;

(4-6) mixing the secondary leaching residue obtained in the step (4-5) with 800mL of 3mol/L sodium hydroxide high-concentration alkali liquor, performing alkaline leaching reaction for 2 hours at the water bath temperature of 85 ℃ and the stirring speed of 300rpm, filtering after the reaction is finished, and collecting the secondary leaching solution and the secondary leaching residue.

Example 2

This example is different from example 1 in that the high alkali solution concentration in step (1) is 1.5mol/L.

Example 3

This example is different from example 1 in that the high alkali solution concentration in step (1) is 2.3mol/L.

Example 4

This example is different from example 1 in that the high alkali solution concentration in step (1) is 5mol/L.

Example 5

This example is different from example 1 in that the alkaline leaching reaction in steps (1) - (2) is carried out at a temperature of 60 ℃.

Example 6

This example is different from example 1 in that the temperature of the alkaline leaching reaction in steps (1) - (2) is 90 ℃.

Example 7

This example is different from example 1 in that the time of the alkaline leaching reaction in steps (1) to (2) is 1h.

Example 8

This example is different from example 1 in that the time of the alkaline leaching reaction in steps (1) to (2) is 6 hours.

Example 9

This example is different from example 1 in that the alkali used for the alkaline leaching in steps (1) to (2) is an aqueous potassium hydroxide solution of equal concentration.

Example 10

This example differs from example 1 in that the stirring rate in steps (1) - (2) was 600rpm.

Example 11

This example is different from example 1 in that the stirring rate in steps (1) - (2) is 200rpm.

Example 12

This example differs from example 1 in that the countercurrent washing in step (3) is at a temperature of 60 ℃.

Example 13

This example is different from example 1 in that the number of countercurrent washing in step (3) is 2.

Example 14

This example is different from example 1 in that the number of countercurrent washing in step (3) is 5.

Example 15

This example is different from example 1 in that the liquid-solid ratio in the secondary alkaline leaching in the step (2) is 10mL/g.

Example 16

This example is different from example 1 in that the liquid-solid ratio in the secondary alkaline leaching in the step (2) is 20mL/g.

Comparative example 1

Weighing 159g of sodium carbonate and dissolving in 800mL of deionized water (1.5 mol/L), mixing the obtained sodium carbonate solution with 50g of dilute phosphoric acid purification slag to form slurry, reacting for 4 hours under the condition of heating and stirring in a water bath at 85 ℃, filtering, washing the precipitate after the reaction is finished, and drying to obtain filter residues; the content of each element in the filter residue and XRD spectrum thereof are detected, and the results are shown in tables 2-3 and figure 4.

Comparative example 2

This example is different from example 1 in that the alkaline leaching is performed only once with a high concentration of alkaline solution, specifically:

(1) Taking 50g of dilute phosphoric acid purification slag, adding 800mL of 3mol/L sodium hydroxide solution into a beaker, placing the beaker in a water bath at 85 ℃, adjusting the rotation speed of a stirring paddle to 300rpm, carrying out alkaline leaching reaction for 4 hours under stirring, filtering after the reaction is finished, and collecting primary leaching liquid and primary leaching slag; the primary leaching solution enters a fluorine recovery process, and sodium fluoride products are obtained through evaporation and concentration;

(2) The weight ratio is as follows: and (3) mixing the primary alkaline leaching residue with deionized water according to the liquid-solid ratio, carrying out countercurrent washing for three times under the water bath at the temperature of 85 ℃ to dissolve a large amount of sodium fluoride remained in the primary alkaline leaching residue into washing liquid, washing for half an hour each time, collecting washing liquid, evaporating and concentrating to obtain a sodium fluoride product, and treating filter residues as hazardous waste.

The filter residues obtained after the alkaline leaching of the raw diluted phosphoric acid-purified slag used in examples 1 to 16 and comparative examples 1 to 2 were tested for the content of Na, mg, al, P, si, ca element by using an ICP-AES apparatus, the content of F element by using an ion chromatograph, the test results are shown in tables 1 to 2, and the weights of the filter residues obtained after the alkaline leaching of the raw diluted phosphoric acid-purified slag are measured, and the results are shown in table 3.

The diluted phosphoric acid purification slag used in examples 1 to 16 and comparative examples 1 to 2 were the same, the component contents thereof were shown in Table 1, the XRD patterns thereof were shown in FIG. 2, and the XRD patterns of the filter residues obtained after alkaline leaching in example 1 were shown in FIG. 3.

Table 1 the mass percent of the elements of the original dilute phosphoric acid purification slag is%

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

TABLE 2 comparison of elemental composition of purified slag before and after alkaline leaching

TABLE 3 quality of residue (Dry residue)

As is clear from Table 2, in examples 1 to 16, after alkaline leaching of the purified slag, the fluorine content in the slag was significantly reduced, and the residual fluorine in the residue was very small.

As can be seen from XRD patterns of figures 2-4, the components of the purified slag sodium aluminum fluoride are completely destroyed after alkaline leaching by sodium hydroxide solution, and the hydroxide radical in the alkali replaces fluorine ions, so that sodium fluoride is extracted; in contrast, in comparative example 1, when leaching was performed with the same amount of sodium carbonate solution, the purified slag structure was not destroyed due to insufficient alkalinity, and thus effective leaching of fluorine could not be achieved.

Claims (9)

1. The method for recycling the fluorine-containing waste residues is characterized by comprising the following steps:

primary alkaline leaching: alkaline leaching is carried out on fluorine-containing waste residues to obtain primary leaching residues and primary leaching liquid, and the primary leaching liquid is used for recycling sodium fluoride;

secondary alkaline leaching: alkaline leaching is carried out on the primary leaching residues to obtain secondary leaching residues and secondary leaching solutions;

mixing the secondary leaching residue with water for countercurrent washing to obtain waste residue and washing liquid;

in the primary alkaline leaching and the secondary alkaline leaching, the alkaline solution used in the alkaline leaching is at least one of sodium hydroxide solution and potassium hydroxide solution independently.

2. The method for recycling fluorine-containing waste residue according to claim 1, wherein in the primary alkaline leaching, the temperature of the alkaline leaching is 60-90 ℃;

and/or, in the secondary alkaline leaching, the alkaline leaching temperature is 60-90 ℃.

3. The method for recycling fluorine-containing waste residue according to claim 1, wherein the time of alkaline leaching in the primary alkaline leaching is 1-6h;

and/or, in the secondary alkaline leaching, the time of the alkaline leaching is 1-6h.

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

And/or, in the secondary alkaline leaching, the concentration of the alkaline solution used in the alkaline leaching is 1-5mol/L.

5. The method for recycling fluorine-containing waste residue according to claim 1, wherein in the primary alkaline leaching, the alkaline leaching is performed under stirring, and the stirring speed is 200-600rpm;

and/or, in the secondary alkaline leaching, the alkaline leaching is carried out under stirring, and the stirring speed is 200-600rpm.

6. The method for recycling fluorine-containing waste residue according to claim 1, wherein the countercurrent washing temperature is 60-90 ℃.

7. The method for recycling fluorine-containing waste residue according to claim 1, wherein the number of countercurrent washing is 2 to 5.

8. The method for recycling fluorine-containing waste residue according to claim 1, wherein the ratio of the volume of the alkaline solution to the mass of the fluorine-containing waste residue in the primary alkaline leaching is 10-20mL/g,

and/or, in the secondary alkaline leaching, the ratio of the volume of the alkaline solution to the mass of the primary leaching slag is 10-20mL/g.

9. The method for recycling fluorine-containing waste residues according to claim 1, wherein the secondary leaching solution is used for primary alkaline leaching of new fluorine-containing waste residues, and comprises the following specific steps:

primary alkaline leaching: placing new fluorine-containing waste residues into the secondary leaching solution for alkaline leaching to obtain primary leaching residues and primary leaching solution, wherein the primary leaching solution is used for recycling sodium fluoride;

secondary alkaline leaching: alkaline leaching is carried out on the primary leaching residues to obtain secondary leaching residues and secondary leaching solutions;

and mixing the secondary leaching residue with water for countercurrent washing to obtain waste residue and washing liquid.