A short-range pretreatment method for lithium battery production wastewater

Abstract

This invention discloses a short-range pretreatment method for lithium battery production wastewater. The method involves adjusting the pH value of the wastewater, adding persulfate and ferrous sulfate to oxidize and remove NMP, and then adding polyacrylamide to the NMP-removed wastewater for flocculation. The rate gradient of the flocculation reaction is controlled, and nano-graphite is precipitated and separated to obtain pretreated lithium battery production wastewater. This method utilizes the reaction between nano-graphite and Fe... 2+ A co-activated persulfate oxidation method was used to oxidize NMP in lithium battery production wastewater, improving the removal rate and biodegradability of NMP. Based on this, nanofiltration graphite was used for flocculation and sedimentation separation. This method utilizes nano-graphite and Fe... 2+ The co-activated persulfate oxidation method was used to oxidize NMP in lithium battery production wastewater, improving the removal rate and biodegradability of NMP; and it also improved the flocculation and sedimentation separation effect of nanofiltration graphite, shortening the process flow and reducing energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment and relates to a short-range, high-efficiency pretreatment method for lithium battery production wastewater. Background Technology

[0002] Since the beginning of the 21st century, the global environmental carrying capacity has been declining, and energy shortages have begun to emerge. To address these issues, the development and application of new energy sources have gradually attracted the attention of governments worldwide, with lithium batteries becoming a key project in this development. With the booming development of the lithium battery industry, a large amount of production wastewater is inevitably generated. This wastewater mainly originates from the production of positive and negative electrodes and the cleaning of raw material storage tanks. Because lithium battery production wastewater contains high concentrations of nano-graphite and N-methylpyrrolidone (NMP), it results in high concentrations of chemical oxygen demand (COD), total suspended solids (TSS), and total nitrogen (TN), exhibiting poor biodegradability and biotoxicity. Therefore, pretreatment of the pollutants nano-graphite and NMP is necessary.

[0003] Previous pretreatment methods treated the two pollutants separately, resulting in high energy consumption and long process durations. Evaporation is commonly used for nano-graphite in wastewater; while achieving good separation, it is extremely energy-intensive, with treatment costs approaching 200 yuan per ton of water. Furthermore, evaporation equipment is prone to clogging and damage, often affecting the normal operation of subsequent water treatment systems. After graphite separation, advanced oxidation methods, such as Fenton oxidation, are often used. While this improves biodegradability, its removal efficiency for NMP is poor, typically below 30%. In summary, the pretreatment of lithium battery production wastewater suffers from high energy consumption and long process durations. Shortening the process, reducing energy consumption, and improving treatment performance are key issues that urgently need to be addressed in this field. Summary of the Invention

[0004] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a short-range, high-efficiency pretreatment method for lithium battery production wastewater. This method utilizes nano-graphite and Fe... 2+ The co-activated persulfate oxidation method was used to oxidize NMP in lithium battery production wastewater, improving the removal rate and biodegradability of NMP; and it also improved the flocculation and sedimentation separation effect of nanofiltration graphite, shortening the process flow and reducing energy consumption.

[0005] The present invention is achieved through the following technical solution.

[0006] This invention provides a short-range pretreatment method for lithium battery production wastewater, comprising:

[0007] The pH value of the lithium battery production wastewater was adjusted, and persulfate and ferrous sulfate were added to the wastewater to oxidize and remove NMP.

[0008] Polyacrylamide was added to the NMP removal wastewater to induce a flocculation reaction. The rate gradient of the flocculation reaction was controlled, and the nano-graphite was precipitated and separated to obtain pretreated lithium battery production wastewater.

[0009] Preferably, the pH is adjusted using sodium hydroxide with a concentration of 0.01-0.1 mmol / L to adjust the pH to 9.0-11.0.

[0010] Preferably, the dosage of ferrous sulfate is 10-15 mmol / L, and the dosage of persulfate is 18-22 mmol / L.

[0011] Preferably, the persulfate is either sodium persulfate or potassium persulfate.

[0012] Preferably, the oxidation time of NMP is 20-30 min.

[0013] Preferably, the concentration of the polyacrylamide is 0.5-1%, and the dosage of polyacrylamide is 90-100 mg / L.

[0014] Preferably, the flocculation reaction time is 1-5 min.

[0015] Preferably, the rate gradient of the flocculation reaction is 40-60 s. -1 .

[0016] Preferably, the sedimentation time is 5-10 minutes.

[0017] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0018] Existing technologies for treating lithium battery production wastewater involve pretreatment with nano-graphite and NMP separately. This results in drawbacks such as long process flows, high treatment costs, and poor treatment efficiency. Compared to existing technologies, the advantages of this invention are:

[0019] 1. Improved removal efficiency: Utilizing nano-graphite to enhance Fe removal efficiency. 2+ Activated persulfate oxidation of NMP fully considers the synergistic effect between the two pollutants, thereby improving the removal efficiency and biodegradability of NMP by persulfate oxidation. This can increase the removal rate by 20-30% and the biodegradability by 10-20%. The pretreatment of lithium battery production wastewater achieves a COD removal rate of no less than 57%, and the nano-graphite separation removal rate is no less than 96%.

[0020] 2. Shortened process flow: The pretreatment of lithium battery production wastewater is divided into two steps: persulfate oxidation and flocculation separation. Moreover, only one flocculant, PAM, is added during the flocculation process, which shortens the process flow and simplifies the process operation steps.

[0021] 3. Reduced treatment costs: The treatment cost per ton of water using this method is less than 30 yuan, which is only 15% of the cost of traditional evaporation separation methods. It also reduces costs by more than 30% compared to the traditional method of coagulation followed by Fenton oxidation. Attached Figure Description

[0022] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings:

[0023] Figure 1 The mechanism of persulfate oxidation of organic matter;

[0024] Figure 2 The functional group distribution curves on the surface of nano-graphite in lithium battery production wastewater;

[0025] Figure 3 The changes in nano-graphite flocs in lithium battery production wastewater are shown; where a represents nano-graphite in raw lithium battery wastewater, b represents nano-graphite flocs in wastewater with added iron salts, and c represents nano-graphite flocs in wastewater with added polyacrylamide. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0027] The short-range, high-efficiency pretreatment method for lithium battery production wastewater provided in this invention includes the following steps:

[0028] Step 1, Nitrogen oxide methylpyrrolidone (NMP):

[0029] Wastewater from lithium battery production enters the reaction tank. The pH of the wastewater is adjusted to 9.0-11.0 using sodium hydroxide at a concentration of 0.01-0.1 mmol / L. Then, 18-22 mmol / L of persulfate and 10-15 mmol / L of ferrous salt are added to the pH-adjusted wastewater. The persulfate is either sodium persulfate or potassium persulfate, and the ferrous salt is either ferrous sulfate or ferrous chloride. An oxidation reaction is carried out for 20-30 minutes, passing through Fe... 2+ It is used in conjunction with nano-graphite to activate persulfate oxidation and remove NMP.

[0030] In step 1, persulfate oxidation can be achieved through different activation methods (such as heat, alkali, transition metal ions (Fe)). 2+ (etc.), ultrasound, ultraviolet, etc., generate sulfate free radicals (SO4-·, E, etc.) with stronger oxidizing power than their own. 0 =2.6V), indirectly generating hydroxyl radicals (·OH, E). 0 =2.8V), to oxidize and degrade organic pollutants, the mechanism of which is as follows: Figure 1 As shown, a persulfate oxidation system is formed by adding persulfate and ferrous salt.

[0031] In persulfate oxidation systems, pH affects the types of free radicals and thus the removal efficiency of organic matter. Typically, under acidic conditions, the main active free radicals in activated sodium persulfate systems are... Under neutral to weakly alkaline conditions While coexisting with ·OH, ·OH is the main reactive free radical under strongly alkaline conditions. Our research group found that the degradation effect of NMP is optimal under weakly alkaline conditions (pH = 9.0-11.0), i.e., when both reactive free radicals coexist in the system.

[0032] The surface of nanographite contains abundant oxygen-containing functional groups (C=O, -COOH and C-OH) (see...) Figure 2 More importantly, these functional groups can act as active sites, meaning that persulfate gains electrons from the surface of the graphite nanoparticles to break the OO bonds, forming... and through interaction with OH - The reaction generates OH· which participates in the oxidation reaction, achieving the continuous degradation and mineralization of NMP. Results showed that nano-graphite can enhance the activation effect of persulfate, increasing the removal rate of NMP (based on COD removal rate) by 20-30% and its biodegradability by 10-20% compared to the oxidation effect of persulfate after graphite separation.

[0033] Step 2, Separate the nano-graphite:

[0034] The solution treated in step 1 is then introduced into a flocculation sedimentation tank. Polyacrylamide (PAM) at a concentration of 0.5-1% (90-100 mg / L) is added to the tank. The flocculation reaction takes 1-5 minutes, with a rate gradient of 40-60 seconds. -1 5-10 min of precipitation to separate and remove nano-graphite.

[0035] In step 2, coagulation effectively removes colloidal or colloidal substances from water and typically involves two steps: coagulation and flocculation. Coagulation usually involves adding ferrous or aluminum salts to destabilize the colloids, while flocculation usually involves adding flocculants (such as polyacrylamide) to form larger flocs from the destabilized colloids. These flocs then separate and remove pollutants through adsorption bridging or scavenging. The solution contains ferrous salts, which are oxidized to ferric salts by persulfate, thus contributing to coagulation.

[0036] The GT value is an important parameter affecting coagulation performance. Controlling a reasonable GT value can result in larger floc size, which is beneficial for further sedimentation and separation. Here, T is the coagulation time; for nano-graphite, 1-5 minutes is sufficient for good coagulation. G is the velocity gradient; given a coagulation time of 1-5 minutes, controlling the velocity gradient of the flocculation reaction (40-60 seconds) is crucial. -1 Larger floc sizes can be obtained. See the results below. Figure 3 Therefore, the method of this invention can effectively improve the COD removal rate and the separation efficiency of nano-graphite when treating lithium battery production wastewater.

[0037] The present invention will be further described in detail below with reference to specific embodiments.

[0038] Example 1

[0039] (1) Nitrogen oxide methylpyrrolidone (NMP):

[0040] Wastewater from lithium battery production enters the reaction tank. The pH is adjusted to 10.0 with 0.01 mmol / L sodium hydroxide, and 20 mmol / L sodium persulfate and 10 mmol / L ferrous sulfate are added. The mixture is stirred, and Fe... 2+ Sodium persulfate was activated together with nano-graphite to oxidize and remove NMP, and the reaction lasted for 20 min;

[0041] (2) Separation of nano-graphite:

[0042] The wastewater from step (1) enters the flocculation sedimentation tank, and 1% polyacrylamide (PAM) at 95 mg / L is added for flocculation reaction for 2 min. The flocculation reaction rate gradient is 40 s. -1 The nano-graphite was separated and removed after 8 minutes of precipitation.

[0043] Example 2

[0044] (1) Nitrogen oxide methylpyrrolidone (NMP):

[0045] Wastewater from lithium battery production enters the reaction tank. The pH is adjusted to 9.5 with 0.02 mmol / L sodium hydroxide, and 18 mmol / L sodium persulfate and 12 mmol / L ferrous sulfate are added. The mixture is stirred, and Fe... 2+ Sodium persulfate was activated together with nano-graphite to oxidize and remove NMP, and the reaction lasted for 25 min;

[0046] (2) Separation of nano-graphite:

[0047] The wastewater from step (1) enters the flocculation sedimentation tank, and 0.8% polyacrylamide (PAM) at 95 mg / L is added for flocculation reaction for 2 min. The flocculation reaction rate gradient is 60 s. -1The nano-graphite was separated and removed after 5 minutes of precipitation.

[0048] Example 3

[0049] (1) Nitrogen oxide methylpyrrolidone (NMP):

[0050] Wastewater from lithium battery production enters the reaction tank. The pH is adjusted to 10.0 with 0.05 mmol / L sodium hydroxide, and 19 mmol / L sodium persulfate and 12 mmol / L ferrous chloride are added. The mixture is stirred, and Fe... 2+ The sodium persulfate was activated together with nano-graphite to oxidize and remove NMP, and the reaction lasted for 23 minutes.

[0051] (2) Separation of nano-graphite:

[0052] The wastewater from step (1) enters the flocculation sedimentation tank, and 0.5% polyacrylamide (PAM) at 94 mg / L is added for flocculation reaction for 3 min. The flocculation reaction rate gradient is 50 s. -1 The nano-graphite was separated and removed after precipitation for 6 minutes.

[0053] Example 4

[0054] (1) Nitrogen oxide methylpyrrolidone (NMP):

[0055] Wastewater from lithium battery production enters the reaction tank. The pH is adjusted to 10.5 with 0.06 mmol / L sodium hydroxide, and 20 mmol / L sodium persulfate and 13 mmol / L ferrous sulfate are added. The mixture is stirred, and Fe... 2+ Sodium persulfate was activated together with nano-graphite to oxidize and remove NMP, and the reaction lasted for 24 min;

[0056] (2) Separation of nano-graphite:

[0057] The wastewater from step (1) enters the flocculation sedimentation tank, and 1% polyacrylamide (PAM) at 90 mg / L is added for flocculation reaction for 4 min. The rate gradient of the flocculation reaction is 55 s. -1 The nano-graphite was separated and removed after 5 minutes of precipitation.

[0058] Example 5

[0059] (1) Nitrogen oxide methylpyrrolidone (NMP):

[0060] Wastewater from lithium battery production enters the reaction tank. The pH is adjusted to 11 with 0.07 mmol / L sodium hydroxide, and 22 mmol / L potassium persulfate and 14 mmol / L ferrous chloride are added. The mixture is stirred, and Fe... 2+ Sodium persulfate was activated together with nano-graphite to oxidize and remove NMP, and the reaction lasted for 20 min;

[0061] (2) Separation of nano-graphite:

[0062] The wastewater from step (1) enters the flocculation sedimentation tank, and 1% polyacrylamide (PAM) at 100 mg / L is added for flocculation reaction for 5 min. The rate gradient of the flocculation reaction is 45 s. -1 The nano-graphite was separated and removed after 5 minutes of precipitation.

[0063] Example 6

[0064] (1) Nitrogen oxide methylpyrrolidone (NMP):

[0065] Wastewater from lithium battery production enters the reaction tank. The pH is adjusted to 9.0 with 0.1 mmol / L sodium hydroxide, and 20 mmol / L potassium persulfate and 15 mmol / L ferrous sulfate are added. The mixture is stirred, and Fe... 2+ Sodium persulfate was activated together with nano-graphite to oxidize and remove NMP, and the reaction lasted for 30 min;

[0066] (2) Separation of nano-graphite:

[0067] The wastewater from step (1) enters the flocculation sedimentation tank, and 0.7% polyacrylamide (PAM) at 90 mg / L is added to carry out the flocculation reaction for 1 min. The flocculation reaction rate gradient is 50 s. -1 The nano-graphite was separated and removed after precipitation for 10 minutes.

[0068] The following table (Table 1) illustrates the COD removal rate of wastewater and the removal rate of nano-graphite in Examples 1-6 of this invention.

[0069] Table 1. COD and nano-graphite removal rates obtained in Examples 1-6

[0070]

[0071] As can be seen from the comparison of Examples 1-6 and the comparative examples above, this invention introduces a short-range, high-efficiency pretreatment method for lithium battery production wastewater. By controlling the dosage of ferrous sulfate and sodium persulfate, as well as the reaction time, the activation performance of persulfate is enhanced by nano-graphite in the wastewater, effectively improving the removal efficiency of NMP. By controlling the dosage of PAM as a flocculant and the rate gradient of the flocculation reaction, iron ions in the solution synergistically coagulate with PAM to separate and remove nano-graphite. After the entire process, the COD removal rate is not less than 57%, and the nano-graphite separation efficiency is not less than 96%. This method significantly improves the COD removal rate and nano-graphite separation efficiency of lithium battery production wastewater, and greatly reduces the cost of wastewater treatment. It is an effective method for reducing energy consumption and improving treatment efficiency in the field of wastewater treatment.

[0072] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A short-range pretreatment method for lithium battery production wastewater, characterized in that, Includes the following steps: The pH of the lithium battery production wastewater was adjusted to 9.0-11.0, and persulfate and ferrous sulfate were added to the wastewater to carry out an oxidation reaction, through which Fe... 2+ Co-activation with nano-graphite to remove NMP by persulfate oxidation; Persulfate is either sodium persulfate or potassium persulfate; Coagulation removes colloidal or colloidal substances from water, and includes two steps: coagulation and flocculation. Ferrous salts are oxidized to ferric salts by persulfate and undergo a coagulation reaction; Flocculation was initiated by adding polyacrylamide to the NMP removal wastewater. The flocculation reaction time was 1-5 minutes, and the rate gradient of the flocculation reaction was controlled at 40-60 seconds. -1 The process involves precipitation and separation to remove nano-graphite, with a separation efficiency of no less than 96%, resulting in pretreated lithium battery production wastewater.

2. The short-range pretreatment method for lithium battery production wastewater according to claim 1, characterized in that, The pH was adjusted using sodium hydroxide at a concentration of 0.01-0.1 mmol / L.

3. The short-range pretreatment method for lithium battery production wastewater according to claim 1, characterized in that, The dosage of ferrous sulfate is 10-15 mmol / L, and the dosage of persulfate is 18-22 mmol / L.

4. The short-range pretreatment method for lithium battery production wastewater according to claim 1, characterized in that, The oxidation time for NMP is 20-30 min.

5. The short-range pretreatment method for lithium battery production wastewater according to claim 1, characterized in that, The concentration of the polyacrylamide is 0.5-1%, and the dosage of polyacrylamide is 90-100 mg / L.

6. The short-range pretreatment method for lithium battery production wastewater according to claim 1, characterized in that, The settling time is 5-10 min.

7. A short-range pretreatment method for lithium battery production wastewater according to any one of claims 1-6, characterized in that, The COD removal rate of pretreated lithium battery production wastewater shall not be less than 57%.

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