A method for simultaneously and deeply removing F, P and COD from wastewater

Abstract

The present invention belongs to the technical field of wastewater treatment, and discloses a method for simultaneously deeply removing F, P, and COD from wastewater. The method comprises the following steps: adjusting the pH of the wastewater to 4-6 for the first time, then adding aluminum salt, mixing and reacting, and then using an adsorbent for adsorption, adjusting the pH to 6-7 for the second time, filtering by pressure, and obtaining filter residue and filtrate; the wastewater comprises F, P, and COD; the mass ratio of the aluminum element in the aluminum salt to the mass ratio of the F element in the wastewater is 7-9:1; and no calcium-containing substances are used in the process of adjusting the pH. The method of the present invention can make the wastewater F <6mg / L, and P <0.8mg / L, and has high COD removal efficiency. The method of the present invention has low cost and good environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and particularly relates to a method for simultaneously and deeply removing F, P and COD from wastewater. Background Art

[0002] In the lithium battery recycling industry, fluorine-containing electrolytes have always been a worrying presence in the industry. In the treatment of fluorine-containing electrolytes and subsequent production processes, fluorine ion enrichment is an unavoidable problem. Excessive fluorine content poses serious hazards to human safety and the ecological environment. Therefore, from the perspective of green production and resource environmental protection, whether it is the problem of defluorination of brine raw materials or wastewater, it is urgent to solve it. The most widely used defluorination method on the market today is lime precipitation, also known as calcium salt precipitation, that is, adding calcium salt to brine or wastewater to react fluoride ions with calcium ions in calcium salts to form CaF2 precipitation, thereby removing fluoride from wastewater. However, defluorination using calcium oxide can only reduce fluorine to about 20 mg / L, which cannot meet the national emission standards (F<6 mg / L). There are also problems such as excessive calcium slag produced during the reaction and low production efficiency.

[0003] In recent years, researchers have also developed relevant defluorination resins for wastewater defluorination, using ion exchange resins to adsorb fluorine, but the effect is not obvious when the fluorine content in wastewater is high. In addition, the pretreatment and regeneration of ion exchange resins are expensive and not suitable for most companies on the market. Therefore, wastewater defluorination has always been a difficult problem in the industry.

[0004] With the gradual increase of industrial production, phosphorus pollution in water bodies is becoming increasingly serious. If a large amount of phosphorus-enriched wastewater is discharged into the natural environment, it will not only seriously affect industrial production, but also damage the ecological environment. Phosphorus-containing compounds in wastewater are divided into organic phosphorus and inorganic phosphorus. In hydrometallurgy or lithium battery industry, the main source of organic phosphorus in wastewater is extractants. Nowadays, widely used extractants such as P204, P507, C272, TBP (tributyl phosphate), etc. on the market will lead to the introduction of organic phosphorus during the extraction process. Inorganic phosphorus is introduced through phosphate or hypophosphorous acid added in the process. Since phosphorus-containing compounds will be introduced in the process production, how to deal with it has become an inevitable problem. The widely used method today is phosphorus removal by activated carbon adsorption combined with calcium salt precipitation. Activated carbon is used to adsorb organic matter to remove organic phosphorus, while inorganic phosphorus is removed by using the metal ions produced by calcium salts and phosphates to form insoluble phosphate precipitates. If hypophosphorous acid is present, hydrogen peroxide must be added first to oxidize trivalent phosphorus into pentavalent phosphorus for better removal. The disadvantages of this process are obvious. The first is the cost issue. In order to better adsorb organic phosphorus, a large amount of activated carbon is needed. At the same time, the pH of phosphorus removal using calcium salts must be controlled above 12, and the consumption of liquid alkali is large. Moreover, when using calcium salt precipitation to remove phosphorus, the total phosphorus can only be reduced to 2-3 mg / L, and it cannot be reduced to below 0.8 mg / L, let alone below 0.5 mg / L. In general, the processes currently on the market still cannot achieve low-cost and effective phosphorus removal.

[0005] Along with high phosphorus, the COD in the wastewater will also be high. COD refers to the amount of oxidant consumed when a certain strong oxidant is used to treat a water sample under certain conditions. That is, the more serious the pollution of substances in the water, the more organic matter there is, and the higher the COD. There are many methods to treat COD, and the most widely used ones are Fenton method, biochemical method, ozone method, activated carbon adsorption, etc. However, these methods have their own disadvantages. The Fenton method can only remove about 60% of COD, and the cost of hydrogen peroxide and ferrous sulfate reagents is high, and the cost of sludge treatment is high; the biochemical method cannot treat the high-salinity wastewater in the factory; if the ozone method wants to achieve a good treatment effect, it must be in accordance with O3:COD=1:1, but ozone will be affected by high-salinity wastewater. The solubility is affected, and it is not easy to reach the level of O3:COD=1:1 at the same time. Therefore, in the end, most companies still generally use the method of activated carbon adsorption, which is simple to operate, but the cost of activated carbon and the time cost of workers changing and installing carbon are not low, and the COD removal effect is also relatively general.

[0006] In the lithium battery production process, the wastewater generated often contains F, P and COD at the same time. However, there is no method in the prior art that can simultaneously make F < 6 mg / L, P < 0.8 mg / L and have high COD removal efficiency.

[0007] Therefore, there is an urgent need to provide a new wastewater treatment method that has a good removal effect on F, P and COD and keeps the treatment cost as low as possible. Summary of the invention

[0008] 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 proposes a method for simultaneously deeply removing F, P and COD from wastewater. The method of the present invention can make the wastewater F <6mg / L, and P <0.8mg / L (further, P <0.5mg / L), and has high COD removal efficiency. The method of the present invention has low cost and good environmental protection.

[0009] The inventive concept of the present invention is as follows: the method of the present invention adjusts the pH of the wastewater to 4-6 for the first time. Under this pH, the aluminum element is a free aluminum ion, which is conducive to the subsequent reaction with F to form AlF2(OH) precipitation; if the pH of the wastewater is 7, aluminum hydroxide precipitation is directly formed, and F cannot be removed; calcium-containing substances are not used in the process of adjusting the pH, because the solubility product of calcium fluoride leads to a high content of F and incomplete precipitation. Through the mass ratio of the aluminum element in the specific aluminum salt to the mass ratio of the F element in the wastewater, F can be completely precipitated, and AlF2(OH) can be formally formed by adjusting the pH for the second time, which not only plays a role in completely removing F, but also AlF2(OH) can adsorb P and COD, thereby achieving the effect of removing F, P, and COD from the wastewater at the same time. In addition to adsorbing COD, the activated carbon also has the function of assisting filtration. Since AlF2(OH) has the function of adsorbing P, there is no need to add too much activated carbon, thereby reducing production costs. The method of the present invention controls multiple process conditions and works together to ensure that after the wastewater is treated, the F in the filtrate obtained is less than 6 mg / L and the P is less than 0.8 mg / L, and the COD removal rate is high. The method of the present invention has low cost and good environmental protection.

[0010] A method for simultaneously and deeply removing F, P and COD from wastewater comprises the following steps:

[0011] The wastewater is first adjusted to a pH of 4-6, then aluminum salt is added, mixed and reacted, and then adsorbed using an adsorbent, and the pH is adjusted to 6-7 for the second time, and filtered to obtain a filter residue and a filtrate;

[0012] The wastewater includes F, P and COD;

[0013] The mass ratio of the aluminum element in the aluminum salt to the F element in the wastewater is 7-9:1;

[0014] No calcium-containing substances are used in the pH adjustment process.

[0015] Preferably, the mass ratio of the aluminum element in the aluminum salt to the F element in the wastewater is 8-8.5:1.

[0016] Optionally, when the pH of the wastewater is 4-6, the first pH adjustment operation can be omitted.

[0017] Preferably, the F content in the wastewater is 80-800 mg / L, more preferably 100-500 mg / L, and even more preferably 150.61-342.44 mg / L.

[0018] Preferably, the P content in the wastewater is 20-90 mg / L, more preferably 30-70 mg / L, and even more preferably 47.25-55.74 mg / L.

[0019] Preferably, the COD content in the wastewater is 400-1000 mg / L, more preferably 450-700 mg / L, and even more preferably 513.69-523.06 mg / L.

[0020] Preferably, the wastewater comes from raffinate liquid, saponified water and magnesium water in the lithium battery production process.

[0021] Preferably, the fluorine-containing wastewater comes from various wastewaters containing F, P and COD in industrial production, such as raffinate liquid, saponified water and magnesium water in the lithium battery production process, and some raffinate liquid in the metal (such as manganese, cobalt, nickel) preparation process.

[0022] Preferably, the raffinate liquid comprises F, P and COD, as well as sodium sulfate solution and potassium sulfate solution. The concentration of sodium ions and potassium ions in the raffinate liquid is 20-80 g / L, wherein the proportion of sodium ions exceeds that of potassium ions.

[0023] Preferably, the saponified water comprises F, P and COD, and a sodium sulfate solution. The concentration of sodium ions in the saponified water is 20-80 g / L.

[0024] Preferably, the magnesium water F, P and COD, and the magnesium sulfate solution. The concentration of magnesium ions in the magnesium water is 5-35 g / L.

[0025] Preferably, the aluminum salt is aluminum sulfate or aluminum sulfate 18hydrate.

[0026] Preferably, the temperature of the mixing reaction is 10-40° C. and the time is 15-180 minutes.

[0027] Optionally, the activated carbon adsorption is performed before the first pH adjustment.

[0028] Preferably, the pH is adjusted to 4.5-6 for the first time, and further preferably, the pH is adjusted to 5-6 for the first time.

[0029] Preferably, the second pH adjustment is to 6.1-6.8, and further preferably, the second pH adjustment is to 6.3-6.7.

[0030] Preferably, the first pH adjustment and the second pH adjustment use sodium hydroxide solution, potassium hydroxide solution or sulfuric acid solution to adjust the pH, and the mass fraction of the sodium hydroxide solution, potassium hydroxide solution or sulfuric acid solution is 5-50%.

[0031] Preferably, the adsorbent includes activated carbon and / or diatomaceous earth, more preferably activated carbon.

[0032] Preferably, the mass ratio of the aluminum salt to the adsorbent is 4.0-4.8:0.3, and more preferably 4.0-4.5:0.3.

[0033] Application of the above method in treating wastewater.

[0034] Preferably, the wastewater includes F, P, and COD.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) The method of the present invention adjusts the pH of the wastewater to 4-6 for the first time. At this pH, the aluminum element is a free aluminum ion, which is conducive to the subsequent reaction with F to form AlF2(OH) precipitation; if the pH of the wastewater is 7, aluminum hydroxide precipitation is directly formed, and F cannot be removed; calcium-containing substances are not used in the process of adjusting the pH, because the solubility product of calcium fluoride leads to a high content of F and incomplete precipitation. By adjusting the mass ratio of the aluminum element in the specific aluminum salt to the mass ratio of the F element in the wastewater, F can be completely precipitated, and AlF2(OH) can be formally formed by adjusting the pH for the second time, which not only plays a role in completely removing F, but also AlF2(OH) can adsorb P and COD, thereby achieving the effect of removing F, P, and COD from the wastewater at the same time. In addition to adsorbing COD, the activated carbon also has a filtering aid effect. Since AlF2(OH) has the function of adsorbing P, there is no need to add too much activated carbon, thereby reducing production costs. The method of the present invention controls multiple process conditions and works together to ensure that after the wastewater is treated, the F in the filtrate obtained is less than 6 mg / L and the P is less than 0.8 mg / L, and the COD removal rate is high. The method of the present invention has low cost and good environmental protection.

[0037] (2) The present invention utilizes the property that aluminum salt is easily hydrolyzed to form AlF2(OH) precipitate. The AlF2(OH) precipitate has a large specific surface area and can adsorb P, COD, etc. in the wastewater by adsorption and remove them by filter pressing, thereby reducing the P in the wastewater to meet national standards.

[0038] (3) The wastewater treatment effect is more significant than that of the methods on the market. The calcium salts on the market can only reduce F removal to 20-30 mg / L and P removal to 2-3 mg / L. Not only can they fail to meet the emission standards, but they also have to face the cost of treating a large amount of calcium slag.

[0039] (4) The activated carbon of the present invention can not only assist filtration and accelerate the filtration speed, but also adsorb COD and P at the same time.

[0040] (5) The method of the present invention is cost-controllable. Firstly, the method can greatly reduce the amount of liquid alkali used. Secondly, the dosage of aluminum sulfate can be controlled according to the F content in the wastewater. Thirdly, the amount of activated carbon added can be adjusted according to the P and COD in the wastewater. If the COD is high, the input amount is increased, otherwise it is reduced, so that the cost of wastewater treatment is greatly reduced and the economic benefit is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the process of simultaneously deeply removing F, P and COD from wastewater in Example 3;

[0042] Figure 2 This is a schematic flow chart of the method for simultaneously and deeply removing F, P and COD from wastewater in Example 4. DETAILED DESCRIPTION

[0043] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0044] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0045] The wastewater used in the following examples and comparative examples (hereinafter referred to as fluorine-containing wastewater) comes from three batches of wastewater in the production of lithium battery industry.

[0046] The F content in the first batch of wastewater was 150.61 mg / L, the P content was 55.74 mg / L, the COD content was 513.69 mg / L, and the pH was 5.04.

[0047] The second batch of wastewater had an F content of 342.44 mg / L, a P content of 65 mg / L, a COD content of 530 mg / L, and a pH of 1.52;

[0048] The F content in the third batch of wastewater was 253.44 mg / L, the P content was 47.25 mg / L, the COD content was 523.06 mg / L, and the pH was 1.88.

[0049] The above three batches of wastewater all contain sodium sulfate, potassium sulfate and magnesium sulfate. The above three batches of wastewater are obtained by mixing the raffinate liquid, saponified water and magnesium water in the lithium battery production process.

[0050] The first pH adjustment and the second pH adjustment use sodium hydroxide solution, potassium hydroxide solution or sulfuric acid solution to adjust the pH.

[0051] Example 1

[0052] A method for simultaneously and deeply removing F, P and COD from wastewater comprises the following steps:

[0053] Take 300 mL of the first batch of wastewater, then add 4.50 g of aluminum sulfate 18hydrate, mix and react at 25°C for 30 minutes, then add 0.3 g of activated carbon for adsorption for 30 minutes, adjust the pH to 6.48 with sodium hydroxide solution, filter press for 30 minutes, and obtain filter residue and filtrate;

[0054] The mass ratio of the aluminum element in aluminum sulfate 18hydrate to the F element in the first batch of wastewater is 8:1.

[0055] Comparative Examples 1-3

[0056] The difference between Comparative Examples 1-3 and Example 1 is only that the amount of aluminum sulfate 18hydrate added is different.

[0057] Some parameters corresponding to the above-mentioned Example 1 and Comparative Examples 1-3 and the removal effects of F, P and COD are shown in Table 1.

[0058] Table 1

[0059]

[0060] As can be seen from Table 1, in the technical solution of the present invention, when aluminum sulfate is added, the aluminum-fluorine mass ratio in the fluoride-containing wastewater is 8:1, which can make F < 6 mg / L and P < 0.5 mg / L to meet the discharge index. It can be seen that the addition of aluminum sulfate has a great influence on the removal of F and P.

[0061] Example 2

[0062] A method for simultaneously and deeply removing F, P and COD from wastewater comprises the following steps:

[0063] Take 400 mL of the second batch of wastewater, adjust the pH to 5.0 with sodium hydroxide solution, then add 13.50 g of aluminum sulfate 18hydrate, mix and react at 25°C for 2 hours, then add 0.9 g of activated carbon for adsorption for 30 minutes, adjust the pH to 6.53 with sodium hydroxide solution (mass fraction 32%), filter for 30 minutes, and obtain filter residue and filtrate.

[0064] Comparative Examples 4-7

[0065] The difference between Comparative Examples 4-7 and Example 2 is only that the second pH adjustment value is different.

[0066] Some parameters corresponding to the above-mentioned Example 2 and Comparative Examples 4-7 and the removal effects of F, P and COD are shown in Table 2.

[0067] Table 2

[0068]

[0069]

[0070] As can be seen from Table 2, the second pH adjustment, whether it is <6 or >7, the defluorination effect of aluminum sulfate 18hydrate is poor, while when the pH is 6-7, the defluorination effect is obvious, which can make F < 6 mg / L, proving that the optimal condition for the second pH adjustment of aluminum defluorination is 6-7.

[0071] Comparative Examples 8-10

[0072] Compared with Example 2, the difference between Comparative Examples 8-10 is that quicklime is used for the second pH adjustment (instead of using sodium hydroxide solution to adjust the pH). The amount of quicklime used and the F removal effect are shown in Table 3.

[0073] Table 3

[0074]

[0075]

[0076] As can be seen from Table 3, when the pH value of calcium salt is 6-7 for the second time, the defluorination effect is not obvious. When the pH is 10 and it is alkaline, there is a certain defluorination effect, but it fails to meet the emission standard. When the pH is 12 and it is alkaline, F is 15.92 mg / L, which proves that calcium salt defluorination can only play a better defluorination effect under alkaline conditions, but the defluorination capacity is limited, and fluorine can only be reduced to 15-20 mg / L, and it is impossible to remove fluorine to below 6 mg / L. In addition, the use of calcium salt for defluorination will produce a large amount of slag, and the waste slag needs to be processed in the production process, which is costly. Therefore, the cost performance of calcium salt defluorination is not high.

[0077] Example 3: Changing the order of adding activated carbon

[0078] A method for simultaneously and deeply removing F, P and COD from wastewater comprises the following steps:

[0079] Take 300 mL of the third batch of wastewater, adjust the pH to 4.6 with sodium hydroxide solution, then add 7.50 g of aluminum sulfate 18hydrate, mix and react at 25°C for 30 minutes, then add 0.3 g of activated carbon for adsorption for 30 minutes, adjust the pH to 6.55 with sodium hydroxide solution, filter press, and obtain filter residue and filtrate.

[0080] Example 4: Changing the order of adding activated carbon

[0081] A method for simultaneously and deeply removing F, P and COD from wastewater comprises the following steps:

[0082] Take 300 mL of the third batch of wastewater, add 0.3 g of activated carbon for adsorption for 30 minutes, adjust the pH to 4.6 with sodium hydroxide solution, add 7.50 g of aluminum sulfate 18hydrate, mix and react at 25°C for 30 minutes, then adjust the pH to 6.53, filter press, and obtain filter residue and filtrate.

[0083] from Figure 1 and Figure 2 It can be seen that the order of adding activated carbon in Example 3 and Example 4 is different.

[0084] Some parameters corresponding to the above-mentioned Examples 3-4 and the removal effects of F, P and COD are shown in Table 5.

[0085] Table 5

[0086]

[0087] As can be seen from Table 5, the addition of aluminum sulfate in Example 3-4 according to the aluminum-fluorine ratio of 8:1 has significant treatment effects on F, P, and COD in fluoride-containing wastewater, and the effect difference is not large. F and P can be reduced to below the emission standard. However, when aluminum sulfate is added in Example 4 and then filtered, due to the lack of activated carbon filtration, the aluminum in the solution to be filtered exists in a colloidal form, and the filtration rate is slow during filtration. The time required for filtration is about 25 minutes longer than that of Example 3. Therefore, by combining the treatment effect and the filtration time, the removal of F, P, and COD according to the order of activated carbon addition in Example 3 is more efficient.

[0088] Comparative Example 11

[0089] Compared with Example 1, the difference of Comparative Example 11 is that the pH of the first batch of wastewater is first adjusted to 6.5 (adjusted with sodium hydroxide solution), and the other processes are the same as Example 1 (i.e., before adding aluminum sulfate 18hydrate, the pH of the first batch of wastewater is first adjusted to 6.5).

[0090] The filtrate obtained in Comparative Example 11 had an F content of 55.2 mg / L, a P content of 1.5 mg / L, and a COD content of 250 mg / L.

Claims

1. A method for simultaneously and deeply removing F, P and COD from wastewater, characterized in that: The following steps are involved: The wastewater is first adjusted to a pH of 4-6, then aluminum salt is added, mixed and reacted, and then adsorbed using an adsorbent, and the pH is adjusted to 6.1-6.8 for the second time, and filtered to obtain a filter residue and a filtrate; The wastewater includes F, P and COD; The mass ratio of the aluminum element in the aluminum salt to the F element in the wastewater is 8-8.5:1; No calcium-containing substances are used in the pH adjustment process; The content of F in the wastewater is 80-800 mg / L; the content of P in the wastewater is 20-90 mg / L; the content of COD in the wastewater is 400-1000 mg / L; The aluminum salt is aluminum sulfate 18hydrate; The first pH adjustment and the second pH adjustment use sodium hydroxide solution, potassium hydroxide solution or sulfuric acid solution to adjust the pH.

2. The method according to claim 1, characterized in that The wastewater comes from raffinate liquid, saponified water and magnesium water in the lithium battery production process.

3. The method according to claim 1, characterized in that The adsorption of the adsorbent is performed before the first pH adjustment.

4. The method according to claim 1, characterized in that: The first pH adjustment is to 4.5-6.

5. The method according to any one of claims 1 to 4, characterized in that: The mass ratio of the aluminum salt to the adsorbent is 4.0-4.8:0.

3.

6. Use of the method according to any one of claims 1 to 5 in treating wastewater.

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