Method for removing heavy metal zinc from wet-process phosphoric acid

Abstract

The application discloses a method for removing heavy metal zinc from wet-process phosphoric acid, which comprises the following steps: complexing trace zinc ions in the wet-process phosphoric acid with an additive, and then adsorbing the zinc ions in the wet-process phosphoric acid by using a strong acid cation exchange resin, so as to remove the heavy metal zinc ions in the wet-process phosphoric acid; and the strong acid cation exchange resin after adsorption is regenerated and then continuously used. The method has low cost, does not generate solid waste residues and harmful gases, and avoids potential safety hazards to the environment; the method is simple to operate, can be combined with a production process of refined phosphoric acid and the like, and meets the requirements of raw material acid indexes of refined phosphoric acid or a lithium iron phosphate battery product, and is easy to be applied in industrialization.

Description

Technical Field

[0001] This invention relates to the field of wet phosphoric acid treatment technology, and in particular to a method for purifying and removing heavy metal zinc from wet phosphoric acid. Background Technology

[0002] With the widespread adoption and application of power batteries, lithium-ion batteries are being used more and more extensively. Among them, lithium iron phosphate (LFP) cathode materials have seen a significant increase in market demand due to their excellent thermal stability, good cycle life, and electrochemical stability. As a crucial raw material for LFP production, the market demand for iron phosphate is also rapidly increasing. However, the preparation of iron phosphate mainly uses soluble iron salts and phosphoric acid as raw materials through a co-precipitation method. During the production process, the high impurity content of the raw materials leads to the product easily carrying impurities, resulting in poor quality iron phosphate. Among these, Zn... 2+ This can cause chemical side reactions in lithium iron phosphate batteries during use, affecting battery capacity balance. This process is irreversible, and as the lithium iron phosphate battery cycles through charging and discharging, this process gradually accumulates, leading to capacity decay and reduced lifespan. Therefore, reducing the content of heavy metal zinc impurities in the raw material phosphoric acid is crucial for lithium iron phosphate to accelerate its development in the new energy sector and is key to promoting the sustainable, high-quality, and refined development of the fine phosphate chemical industry.

[0003] Currently, there are two main methods for producing phosphoric acid: the thermal process and the wet process. The thermal process produces yellow phosphoric acid using an electric furnace, followed by oxidation and absorption to obtain relatively pure industrial phosphoric acid. The wet process involves decomposing phosphate rock with strong acids such as sulfuric acid or hydrochloric acid, followed by liquid-solid separation to obtain phosphoric acid containing various impurities. However, the thermal process requires high-quality raw materials, consumes a lot of energy, and generates significant dust and harmful gases that cause serious environmental pollution. The wet process, on the other hand, has advantages such as low power consumption and lower requirements for the grade of the phosphate rock, and has a history of production spanning over a century, with increasingly sophisticated technology. However, with the decreasing grade and impurities of phosphate rock, the extraction process between sulfuric acid and phosphate rock increases the risk of Zn contamination. 2+ Heavy metal impurities can enter the phosphoric acid extract, causing the phosphoric acid product to fail to meet requirements. Therefore, to meet the acid requirements for refined phosphoric acid or raw materials for lithium iron phosphate batteries, wet-process phosphoric acid is used, which is then concentrated after defluorination to obtain raw phosphoric acid with 40%–48% P2O5. After conventional heavy metal removal steps, the zinc ion content in the raw phosphoric acid is still around 450 ppm. Although the content is low, it still seriously affects the quality of lithium iron phosphate batteries, requiring further purification of the Zn in the wet-process phosphoric acid. 2+ .

[0004] For Zn 2+The removal of zinc ions from zinc-containing wastewater is primarily studied in the mining, metallurgical, and electroplating industries. No reports have been found specifically on the removal of zinc ions from wet-process phosphoric acid. Common methods for treating zinc-containing wastewater include neutralization precipitation, oxidation-reduction, and ion exchange. Sussesse et al. used membrane separation to treat low-concentration zinc-containing wastewater. The membrane module consisted of an ultrafiltration membrane and a low-pressure reverse osmosis membrane. The ultrafiltration membrane primarily works by sieving, retaining larger molecules. The low-pressure reverse osmosis membrane has a smaller pore size and primarily uses interfacial phenomena and adsorption to deposit zinc-containing pollutants on its surface. This method is only suitable for wastewater purification and cannot achieve the desired effect in strongly acidic environments. Meanwhile, according to literature, Liu Lei et al. used a combination of Na2S and a heavy metal scavenger to treat acidic zinc-containing wastewater. Na2S solution and the heavy metal scavenger were added sequentially to the wastewater to reduce H2S gas production and simultaneously remove Zn from the acidic zinc-containing wastewater. 2+ This process causes the generated metal sulfides to flocculate into large flocs, facilitating separation and removal. Patent CN109399592A provides a method for removing heavy metals from phosphoric acid, utilizing sodium sulfide to combine with heavy metal ions in phosphoric acid to form insoluble compounds. None of the above methods are suitable for removing zinc from wet-process phosphoric acid, mainly because Zn₂S precipitate dissolves in wet-process phosphoric acid.

[0005] In summary, under strongly acidic conditions, the neutralization-precipitation method significantly increases phosphorus loss in wet-process phosphoric acid due to the presence of zinc ions. Furthermore, because wet-process phosphoric acid has a complex composition and Zn₂S precipitate dissolves in it, chemical precipitation is also unsuitable for removing zinc ions. Therefore, there is an urgent need to develop a method for removing zinc ions from wet-process phosphoric acid. Summary of the Invention

[0006] This invention provides a method for purifying and removing heavy metal zinc from wet phosphoric acid, solving the problem that existing methods for removing zinc ions are difficult to apply to wet phosphoric acid.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for purifying and removing heavy metal zinc from wet-process phosphoric acid involves using an additive to complex trace amounts of zinc ions in the wet-process phosphoric acid, followed by adsorption of these zinc ions using a strongly acidic cation exchange resin. The adsorbed zinc ions are then regenerated and reused multiple times.

[0009] As a preferred technical solution, the additive is at least one of acrylamide graft copolymer, amphoteric polyacrylamide polymer, active silica flocculant and polyethylenediaminetetraacetic acid.

[0010] As a preferred technical solution, the auxiliary agent is prepared into a solution with a mass concentration of 1‰, and the amount of the auxiliary agent added is 0.5% to 1% of the mass of the wet-process phosphoric acid.

[0011] As a preferred technical solution, the wet-process phosphoric acid is stirred for 10-20 minutes after adding the auxiliary agent at a temperature of 65-85°C.

[0012] As a preferred technical solution, the strongly acidic cation exchange resin is a cross-linked polystyrene copolymer containing sulfonic acid groups and possessing a macroporous structure. The macroporous polymeric resin is a precursor to the sulfonic acid-based resin and has the ability to absorb heavy metal ions from strong acids. The sulfonic acid groups in the strongly acidic cation exchange resin facilitate the complexation of heavy metal ion groups in the phosphoric acid medium. -SO3H (sulfonic acid group) reacts with Zn... 2+ Chemisorption occurs under strongly acidic conditions, thus providing sufficient space for the adsorption of heavy metal ions on strongly acidic cation exchange resins.

[0013] As a preferred technical solution, the strong acid cation exchange resin has an acid resistance of 90% to strong acids, including phosphoric acid, nitric acid and sulfuric acid.

[0014] As a preferred technical solution, the amount of the strong acid cation exchange resin added is 2-5% of the mass of the wet-process phosphoric acid.

[0015] As a preferred technical solution, the adsorption conditions of the strong acid cation exchange resin for zinc ions in wet-process phosphoric acid are as follows: adsorption temperature of 65-85℃, shaking time of 15-30 min, shaking rate of 100-150 r / min, and pH of 0-0.2. After adsorption, the wet-process phosphoric acid is separated from the strong acid cation exchange resin by filtration.

[0016] As a preferred technical solution, the strongly acidic cation exchange resin is regenerated by sulfuric acid solution, the loaded zinc ions are desorbed, and the strongly acidic cation exchange resin can be reused.

[0017] The above-mentioned technical solution is a method for purifying and removing heavy metal zinc from wet phosphoric acid. An auxiliary agent is used to complex with trace amounts of zinc ions in wet phosphoric acid, and then a strong acid cation exchange resin is used to adsorb the zinc ions in the wet phosphoric acid, thereby achieving the purpose of removing heavy metal zinc ions from wet phosphoric acid. After adsorption, the strong acid cation exchange resin is regenerated and reused.

[0018] Working Mechanism: This method utilizes an additive to complex with trace amounts of zinc ions in wet-process phosphoric acid, followed by adsorption of these zinc ions using a strongly acidic cation exchange resin, thus removing zinc ions from the wet-process phosphoric acid. Incomplete swelling of the resin leads to poor kinetics and weak absorption capacity for metal ions. The addition of the additive enhances the resin's swelling capacity in a strongly acidic medium, and also causes the trace zinc ions to aggregate, making them easily adsorbed by the strongly acidic cation exchange resin. The method for purifying and removing heavy metal zinc from wet-process phosphoric acid provided by this invention, when combined with production processes such as refined phosphoric acid, meets the acid requirements for raw materials in refined phosphoric acid or lithium iron phosphate battery products.

[0019] Compared with the prior art, the method described in this invention has the following advantages:

[0020] 1. This invention utilizes an additive to complex with trace amounts of zinc ions in wet-process phosphoric acid, and then uses a strongly acidic cation exchange resin to remove heavy metal zinc ions from the wet-process phosphoric acid, achieving significant results.

[0021] 2. The present invention enables the resin to have high swelling properties in a strongly acidic medium by adding additives, and the additives make trace amounts of zinc ions easily adsorbed by the strongly acidic cation exchange resin by agglomerating them.

[0022] 3. The method of the present invention is low in cost, produces no solid waste or harmful gases, and avoids potential safety hazards to the environment;

[0023] 4. This invention is simple to operate and, when combined with production processes such as refined phosphoric acid, meets the acid index requirements for raw materials of refined phosphoric acid or lithium iron phosphate battery products, making it easy to apply in industrial applications. Detailed Implementation

[0024] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0025] Example 1

[0026] Take 200g of 45% (P2O5) wet-process phosphoric acid, first add 1g of acrylamide graft copolymer with a mass concentration of 1‰, the wet-process phosphoric acid temperature is 85℃, stir for 10min, then add 4g of sulfonic acid-based strong acid cation exchange resin with macroporous structure, shake for 30min at a shaking rate of 150r / min, pH is 0.09, filter and separate, the removal rate of zinc ions in wet-process phosphoric acid reaches 48.27%, add sulfonic acid-based strong acid cation exchange resin to sulfuric acid solution and stir for 30min, then wash with deionized water multiple times to recover.

[0027] Example 2

[0028] Take 200g of 46% (P2O5) wet-process phosphoric acid, first add 1g of amphoteric polyacrylamide polymer with a mass concentration of 1‰, the wet-process phosphoric acid temperature is 70℃, stir for 20min, then add 6g of sulfonic acid-based strong acid cation exchange resin with macroporous structure, shake for 20min at a shaking rate of 120r / min, pH is 0.16, filter and separate, the removal rate of zinc ions in wet-process phosphoric acid reaches 47.93%, add sulfonic acid-based strong acid cation exchange resin to sulfuric acid solution and stir for 30min, then wash with deionized water several times to recover.

[0029] Example 3

[0030] Take 200g of 47% (P2O5) wet-process phosphoric acid, first add 1g of active silica flocculant with a mass concentration of 1‰, the wet-process phosphoric acid temperature is 75℃, stir for 15min, then add 8g of sulfonic acid-based strong acid cation exchange resin with macroporous structure, shake for 25min at a shaking rate of 100r / min, pH is 0.12, filter and separate, the removal rate of zinc ions in wet-process phosphoric acid reaches 49.95%, add sulfonic acid-based strong acid cation exchange resin to sulfuric acid solution and stir for 30min, then wash with deionized water several times to recover.

[0031] Example 4

[0032] Take 200g of 48% (P2O5) wet-process phosphoric acid, first add 1g of polyethylenediaminetetraacetic acid with a mass concentration of 1‰, the wet-process phosphoric acid temperature is 65℃, stir for 20min, then add 10g of sulfonic acid-based strong acid cation exchange resin with macroporous structure, shake for 15min at a shaking rate of 130r / min, pH is 0.07, filter and separate, the removal rate of zinc ions in wet-process phosphoric acid reaches 48.44%, add sulfonic acid-based strong acid cation exchange resin to sulfuric acid solution and stir for 30min, then wash with deionized water several times to recover.

[0033] test:

[0034] The test results of using the four additives in combination are shown in Table 1. Table 1 shows that the method provided by this invention significantly removes heavy metal ions from wet-process phosphoric acid. Compared with the results of adsorption tests using a strong acid cation exchange resin without any additives, the addition of additives makes the resin highly swellable in a strong acid medium, and the additives cause trace amounts of zinc ions to aggregate and be easily adsorbed by the strong acid cation exchange resin.

[0035] Table 1

[0036] Test Plan Heavy metal zinc removal rate / % No additives added 25.62 0.5% Acrylamide graft copolymer + 0.5% Active silica flocculant 49.62 0.5% Acrylamide graft copolymer + 0.5% Polyvinyl diaminetetraacetic acid 48.35 0.5% amphoteric polyacrylamide polymer + 0.5% active silica flocculant 44.37 0.5% active silica flocculant + 0.5% polyethylenediaminetetraacetic acid 48.69

[0037] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for removing heavy metal zinc by wet phosphoric acid purification, characterized in that: The additive complexes with trace amounts of zinc ions in wet-process phosphoric acid, and then the zinc ions in the wet-process phosphoric acid are adsorbed by a strong acid cation exchange resin, thereby achieving the purpose of removing heavy metal zinc ions from the wet-process phosphoric acid. After adsorption, the strong acid cation exchange resin is regenerated and reused. The additive is at least one of acrylamide graft copolymer, amphoteric polyacrylamide polymer, active silica flocculant, and polyethylenediaminetetraacetic acid; the additive is prepared as a solution with a mass concentration of 1‰, and the amount of additive added is 0.5% to 1% of the mass of the wet-process phosphoric acid; the wet-process phosphoric acid is stirred for 10 to 20 min after adding the additive at a temperature of 65 to 85℃; the adsorption conditions of the strong acid cation exchange resin for zinc ions in the wet-process phosphoric acid are: adsorption temperature of 65 to 85℃, shaking time of 15 to 30 min, shaking rate of 100 to 150 r / min, and pH of 0 to 0.2; after adsorption, the wet-process phosphoric acid is separated from the strong acid cation exchange resin by filtration.

2. The method for removing heavy metal zinc by wet phosphoric acid purification as described in claim 1, characterized in that: The strongly acidic cation exchange resin is a cross-linked copolymer of polystyrene containing sulfonic acid groups and having a macroporous structure.

3. The method for removing heavy metal zinc by wet phosphoric acid purification as described in claim 1, characterized in that: The strong acid cation exchange resin has a 90% acid resistance to strong acids, including phosphoric acid, nitric acid, and sulfuric acid.

4. The method for removing heavy metal zinc by wet phosphoric acid purification as described in claim 1, characterized in that: The amount of the strong acid cation exchange resin added is 2 to 5% of the mass of the wet-process phosphoric acid.

5. The method for removing heavy metal zinc by wet phosphoric acid purification as described in claim 1, characterized in that: The strongly acidic cation exchange resin is regenerated by sulfuric acid solution, and the loaded zinc ions are desorbed, allowing the strongly acidic cation exchange resin to be reused.