A method for treating phosphoric iron wastewater and waste residue

Abstract

This application relates to the field of producing iron phosphate, and specifically discloses a method for treating iron phosphate wastewater and waste residue. The method recycles and dries the waste residue wastewater of ferrous phosphate wastewater and waste residue, the sludge wastewater in the mother liquor produced by producing iron phosphate, and the purified waste residue wastewater of ammonium sulfate in the mother liquor, and uses experiments to find the optimal drying ratio of sludge filter cake, ferrous filter cake, ammonium sulfate waste residue and ammonium sulfate mother liquor, solving the technical problems in the prior art that the waste residue generated in the treatment of iron phosphate wastewater is not dried, resulting in high transportation costs and not meeting the production requirements of downstream manufacturers.

Description

Technical Field

[0001] The invention relates to the field of ferric phosphate production, and in particular to a method for treating ferric phosphate wastewater and waste residue. Background Art

[0002] Among new energy batteries, lithium batteries have the advantages of high voltage, high energy density, small volume and mass, and are being used in large quantities in new energy vehicles, energy storage and other fields. Among the various positive electrode materials of lithium batteries, lithium iron phosphate has the advantages of low cost, good cycle performance, wide source of raw materials, and environmental friendliness. Therefore, the proportion of lithium iron phosphate in positive electrode materials is increasing year by year.

[0003] As a precursor for the synthesis of lithium iron phosphate, the demand for iron phosphate is also growing rapidly. A large amount of wastewater is generated during the production of iron phosphate. Basically, the preparation of 1t of iron phosphate will produce 16-32M3 of wastewater. The mainstream production processes of iron phosphate are divided into sodium method and ammonium method. Since the ammonium method consumes less phosphate than the sodium method in the production of iron sulfate, the cost is lower than the sodium method, and it has become the mainstream method of iron phosphate production. However, iron phosphate will go through synthesis, washing and other processes during the production process. The pH of the synthetic mother liquor and washing water produced is very low at 1-2, and contains a large amount of sulfate, phosphate, ammonium, magnesium ions, manganese ions and iron ions. The treatment of iron phosphate wastewater is difficult, and the discharge of wastewater will cause serious damage and impact on the surrounding environment.

[0004] At present, the mainstream methods for treating wastewater from iron phosphate production are divided into lime precipitation method, magnesium salt treatment method and membrane treatment method. Among them, the membrane treatment method and multi-effect evaporation combined process are used to filter the wastewater through membrane treatment to obtain reusable clean water, and the concentrated water produced is evaporated by multi-effect, which realizes the effective utilization of wastewater resources as a whole.

[0005] However, the waste residues generated in the wastewater treatment of the whole process, such as the titanium-containing waste residues produced by the treatment of ferrous sulfate, the sludge produced by the wastewater of ferrous phosphate production, and the ammonium sulfate impurity waste residues in the production of by-product ammonium sulfate, still contain a large amount of water. When transported to downstream manufacturers to produce fertilizers, the transportation cost generated by this water is too high, and the moisture content is too high to meet the production needs of downstream manufacturers. Summary of the invention

[0006] The purpose of the present invention is to provide a method for treating ferric phosphate wastewater and waste residue, so as to solve the technical problems mentioned above that the waste residue generated in the treatment of ferric phosphate wastewater in the prior art is not dried, has high transportation cost, and does not meet the production needs of downstream manufacturers.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is as follows: a method for treating iron phosphate wastewater and waste residue, comprising the following steps:

[0008] S1: The wastewater from the dissolution and impurity removal of ferrous raw materials is filtered through a plate and frame to produce ferrous wastewater and ferrous filter cake;

[0009] S2: adding the mother liquor produced in the ferric phosphate production reaction to the precipitate adjusted with ammonia water and filtering it through a plate and frame filter to obtain the first concentrated mother liquor and sludge filter cake;

[0010] S3: The first concentrated mother liquor in S2 is mixed with the wastewater in S1, and the mixed wastewater is subjected to membrane treatment to produce the second concentrated mother liquor and clean water. The second concentrated mother liquor is passed into the MVR evaporator to obtain ammonium bisulfate and distilled water, and the clean water and distilled water are reused;

[0011] S4: dissolving ammonium bisulfate in soft water and adding ammonia water to react to generate ammonium sulfate solution and precipitate ammonium sulfate waste residue containing magnesium, which is separated by a centrifuge to obtain ammonium sulfate waste residue and ammonium sulfate solution, and the ammonium sulfate solution is dried to obtain ammonium sulfate by-product.

[0012] S5: crushing the ferrous filter cake in S1, the sludge filter cake in S2 and the ammonium sulfate waste residue in S4 into powder respectively; and mixing the powdered ferrous impurities, sludge and ammonium sulfate impurities to obtain mixed waste residue;

[0013] S6: The mixed waste residue in S5 is added with the second concentrated mother liquor of S3 to mix into a slurry-like state, and then introduced into a granulation dryer to obtain dark green sand-like particles.

[0014] The beneficial effects of this embodiment are:

[0015] 1. The waste residue generated in the wastewater treatment method of the present invention is mixed and granulated, so that the water content of the treated waste residue sand and gravel particles is about 20%. Compared with the prior art, the water content of the untreated waste residue is 50%-60%, which greatly reduces the transportation cost when transporting it to downstream manufacturers to produce fertilizers in the later stage, and the downstream manufacturers do not need to additionally process the water in the waste residue, thereby improving the quality of the raw materials and supply quality of the waste residue as fertilizer.

[0016] 2. In the present invention, S4 also carries out an impurity removal process on ammonium sulfate, a byproduct of producing ferric phosphate by the ammonium process, thereby improving the purity of the byproduct and the quality of ammonium sulfate, thereby gaining an advantage in market competition.

[0017] Furthermore, the mixed wastewater in S3 is first subjected to an ultrafiltration process for removing precipitation in the mixed wastewater before the membrane treatment. The ultrafiltration is performed once before the membrane treatment, which protects the membrane in the membrane treatment process from being blocked and prolongs the service life of the membrane in the membrane treatment.

[0018] Furthermore, the ground ferrous impurities, sludge and ammonium sulfate impurities in S6 are mixed in a ratio of 4:3:1, and the mass of the second concentrated mother liquor added in S7 is 10%-20% of the mass of the mixed waste residue. Experimental data show that when the impurities are in a ratio of 4:3:1 and the amount of the second concentrated liquor added is 10%-20%, the fluidity after mixing is good and the solid and liquid do not separate.

[0019] Furthermore, the adjusted pH value in S2 is in the range of 6.0-6.5. Adjusting the pH value to 6.0-6.5 ensures that the manganese ions and iron ions in the iron phosphate wastewater are almost completely precipitated. If the pH value is too high, the cost will increase.

[0020] Furthermore, when adding ammonia water for reaction in S4, stirring is performed while adding ammonia water, and the addition of ammonia water is stopped after the pH value is greater than 9. Since an excess amount of ammonia water must be added later to ensure that ammonium bisulfate is reacted into ammonium sulfate, the magnesium ion impurities are precipitated at this time, so that the pH value does not need to be adjusted to 8 in the early stage, the amount of ammonia water used is saved, and thus the cost is saved. DETAILED DESCRIPTION

[0021] The following is further described in detail through specific implementation methods:

[0022] A method for treating iron phosphate wastewater and waste residue, the method steps are as follows:

[0023] S1: The wastewater from the dissolution and impurity removal of ferrous raw materials is filtered through a plate and frame to produce ferrous wastewater and ferrous filter cake;

[0024] In the enterprises that use the ammonium process to produce ferric phosphate, in order to save costs, most of them purchase ferrous sulfate raw materials that are usually by-products of titanium dioxide production enterprises. Therefore, the purchased ferrous sulfate contains titanium impurities, which need to be flocculated. The titanium impurities are then flocculated and the titanium mud obtained after flocculation is filtered out using a plate and frame filter to reduce its moisture content. However, since the precipitate particles in the titanium mud are small and have strong adsorption to water, the moisture is difficult to remove. After using the plate and frame filter, the water content is still 60% (±5%).

[0025] S2: adding the mother liquor produced in the ferric phosphate production reaction to the precipitate adjusted with ammonia water and filtering it through a plate and frame filter to obtain the first concentrated mother liquor and sludge filter cake;

[0026] The pH value of wastewater produced by ferric phosphate is 1-2, and its main components are a large amount of sulfate, phosphate, ammonium, magnesium, manganese and iron ions. Ammonia water is used to adjust the pH value to 6.0-6.5, so that most of the metal impurities are precipitated. Since iron and manganese ions begin to precipitate at a pH of about 5, when the pH value is controlled at 6.0-6.5, the manganese and iron ions in the ferric phosphate wastewater are almost completely precipitated. If the pH value is too high, it will increase the cost.

[0027] S3: The first concentrated mother liquor in S2 is mixed with the wastewater in S1, and the mixed wastewater is subjected to membrane treatment to produce the second concentrated mother liquor and clean water. The second concentrated mother liquor is passed into the MVR evaporator to obtain ammonium bisulfate and distilled water, and the clean water and distilled water are reused;

[0028] After obtaining the first concentrated mother liquor, the first concentrated mother liquor is mixed with the ferrous wastewater in S1, and then ultrafiltration is performed once. The ultrafiltration process is to pass the wastewater through a filter composed of multiple layers of molecular membranes. The pore size of the molecular membrane is relatively large, which can pass water molecules and other ions, and only remove the precipitates that are not separated, thereby ensuring that the membrane in the subsequent membrane treatment process is not blocked.

[0029] S4: dissolving ammonium bisulfate in soft water and adding ammonia water to react to generate ammonium sulfate solution and precipitate ammonium sulfate waste residue containing magnesium, which is separated by a centrifuge to obtain ammonium sulfate waste residue and ammonium sulfate solution, and the ammonium sulfate solution is dried to obtain ammonium sulfate by-product.

[0030] Since the pH value was only adjusted to 6.0-6.5 in the early stage, the mother liquor still contained magnesium ion impurities. In order to improve the purity of ammonium sulfate in the later stage, ammonium bisulfate was dissolved in soft water (so as not to introduce other metal impurities into the water body), and ammonia water was used to adjust the pH value to greater than 9, which can make the ammonium bisulfate completely react into ammonium sulfate and completely precipitate the magnesium ion impurities in the mother liquor, thereby improving the purity of ammonium sulfate.

[0031] S5: crushing the ferrous filter cake in S1, the sludge filter cake in S2 and the ammonium sulfate waste residue in S4 into powder respectively; and mixing the powdered ferrous impurities, sludge and ammonium sulfate impurities to obtain mixed waste residue;

[0032] After grinding, various impurities are mixed more evenly, and their metal ions interact with each other. It is easy to form a paste when the mother liquor is added later. Experiments have shown that the ratio of sludge filter cake: ferrous filter cake: ammonium sulfate waste residue in the mixed impurities is 4:3:1, and the water adsorption is best. After mixing, a stable slurry is formed without solid-liquid separation. Therefore, there is no need to worry about the particles causing the granulation dryer to get stuck during the treatment process. Ensure that the smoothness of the treatment process is not interrupted, avoid wear of the granulation dryer, and extend the service life of the granulation dryer.

[0033] The water adsorption capacity of mixed impurities is shown in Table 1, where the solid-liquid separation is observed 30 minutes after the addition of water. 0 means solid-liquid separation and poor mixing, 1 means good mixing but poor fluidity, and 2 means good solid-liquid mixing, no separation, and good fluidity.

[0034] Table 1

[0035]

[0036] It is not difficult to see from the above table that the sludge impurities have better adsorption to water, ferrous impurities and ammonium sulfate impurities cannot be mixed well with water, but the mixed impurities after the three are mixed have good adsorption to water. Therefore, in order to dry the ferrous impurities and ammonium sulfate impurity liquid through the granulation dryer, mixing and drying the three waste residues for granulation is the best choice.

[0037] According to the amount of waste residue produced by the production of ferric phosphate, the proportion of each component of the mixed impurities was adjusted and the optimal ratio and the amount of the second concentrated solution added were explored. The results are shown in Table 2

[0038] Table 2

[0039]

[0040] Since Table 1 shows that the addition amount of the second concentrated solution is more suitable when it is less than 30%, the second concentrated solution is selected in Table 2 to conduct experiments when it is less than 30%.

[0041] According to the data in Table 2, although all can be mixed, when the sludge content is greater than the ferrous content, the fluidity after mixing is good, and the optimal amount of the second concentrated liquid is between 10% and 20%.

[0042] S6: The mixed waste residue in S6 is added with the second concentrated mother liquor of S3 to mix into a slurry-like state, and then introduced into a granulating dryer to obtain dark green sand-like particles.

[0043] Granulating and drying machine processes various waste residues. The machine operation status:

[0044] The ratio of sludge filter cake: ferrous filter cake: ammonium sulfate waste residue: second concentrated liquid in Class A mixed sample is 3:4:0:1.

[0045] In Class B mixed samples, the ratio of sludge filter cake: ferrous filter cake: ammonium sulfate waste residue: second concentrated liquid is 3:4:1:1.

[0046] (1) Ferrous filter cake: Hang the ferrous filter cake (water content 57.06%) to the feed port of the dryer and feed it slowly and evenly.

[0047] Conclusion: The feed drum of the dryer is stuck and the test is terminated.

[0048] (2) Sludge filter cake: Hang the sludge filter cake (moisture content 69.01%) to the feed port of the dryer and feed it slowly and evenly.

[0049] Conclusion: The sludge filter cake formation effect is good. After drying, the waste residue is yellow fine sand and gravel, and the moisture content is 27.09%.

[0050] (3) Class A mixed sample (TDS: 38.58%): Hang the Class A mixed sample to the feed port of the dryer and feed it slowly and evenly.

[0051] Conclusion: The sludge filter cake effect is good, and the waste residue after drying is dark green fine sand and gravel, with a moisture content of 25.35%.

[0052] (4) Class B mixed sample (TDS: 47.00%): Hang the Class B mixed sample to the feed port of the dryer and feed it slowly and evenly.

[0053] Conclusion: The sludge filter cake effect is good, and the waste residue after drying is dark green fine sand and gravel, with a moisture content of 20.47%.

[0054] (5) Ammonium sulfate waste residue: Hang the waste residue mixed sample to the feed port of the dryer and feed it slowly and evenly.

[0055] Conclusion: The dryer is stuck and liquid is flowing into the drying chamber.

[0056] From the above experiments, it is not difficult to conclude that among the wastewater and waste residues generated by ferric phosphate production, the sludge filter cake can be treated by a granulator and dryer to form yellow sandy particles, and the moisture content is reduced by about 40%; the sludge filter cake: ferrous filter cake: ammonium sulfate mother liquor, mixed at a ratio of 4:3:1, can be treated by a granulator and dryer to form dark green sandy particles, and the moisture content is reduced by about 25%; the sludge filter cake: ferrous filter cake: ammonium sulfate waste residue: ammonium sulfate mother liquor, mixed at a ratio of 4:3:1:1, can be treated by a granulator and dryer to form dark green sandy particles, and the moisture content is reduced by about 20%.

[0057] Considering the amount of waste residue generated during ferric phosphate production, mixing the waste residue in a ratio of 4:3:1:1 and then processing it in a granulator and dryer is the optimal solution for the treatment of ferric phosphate wastewater and waste residue.

[0058] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for treating phosphoric acid iron wastewater and waste residue, characterized in that: It includes the following steps: S1: Filter the wastewater obtained by dissolving and removing impurities from ferrous raw materials through a plate and frame filter to produce ferrous wastewater and ferrous filter cake; S2: Add ammonia water to the mother liquor generated in the phosphoric acid iron production reaction to adjust the pH value. After adjustment, the generated precipitate is filtered through a plate and frame filter to obtain the first concentrated mother liquor and sludge filter cake; S3: Mix the first concentrated mother liquor in S2 with the ferrous wastewater in S1. The mixed wastewater after mixing is subjected to membrane treatment. After membrane treatment, the second concentrated mother liquor and clear water are generated. The second concentrated mother liquor is introduced into an MVR evaporator to obtain ammonium bisulfate and distilled water, and the clear water and distilled water are recycled; S4: Dissolve ammonium bisulfate in soft water and add ammonia water. React to generate ammonium sulfate solution and precipitate magnesium-containing ammonium sulfate waste residue. Use a centrifuge for separation to obtain ammonium sulfate waste residue and ammonium sulfate solution. Dry the ammonium sulfate solution to obtain ammonium sulfate by-product; S5: Crush the ferrous filter cake in S1, the sludge filter cake in S2, and the ammonium sulfate waste residue in S4 into powder form respectively; and mix the powdered ferrous impurities, sludge, and ammonium sulfate impurities to obtain a mixed waste residue; S6: Add the second concentrated mother liquor in S3 to the mixed waste residue in S5 for mixing and mix it into a slurry-like state. After mixing, introduce it into a granulating and drying machine to obtain dark green gravel-like particles.

2. The method for treating phosphoric acid iron wastewater and waste residue according to claim 1, characterized in that: Before the membrane treatment of the mixed wastewater in S3, an ultrafiltration process that can remove precipitates in the mixed wastewater is first passed through.

3. The method for treating phosphoric acid iron wastewater and waste residue according to claim 1, characterized in that: The powdered ferrous impurities, sludge, and ammonium sulfate impurities in S5 are mixed in a ratio of 4:3:1, and the mass of the second concentrated mother liquor added in S6 is 10%-20% of the mass of the mixed waste residue.

4. The method for treating phosphoric acid iron wastewater and waste residue according to claim 1, characterized in that: The adjusted pH value range in S2 is 6.0-6.

5.

5. The method for treating phosphoric acid iron wastewater and waste residue according to claim 1, characterized in that: When adding ammonia water for reaction in S4, add ammonia water while stirring until the pH value is greater than 9, and then stop adding ammonia water.

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