Treatment methods for lithium recovery and targeted removal of heavy metals in lithium battery production wastewater

Abstract

This invention discloses a method for lithium recovery and targeted removal of heavy metals from lithium battery production wastewater. The technology includes: pre-treatment and oxidation regulation of wastewater using NO2-containing industrial tail gas to create a self-powered environment; selective adsorption of lithium ions using a modified lithium-ion sieve under a DC electric field to separate lithium from heavy metals such as nickel, cobalt, and manganese; targeted removal of heavy metals from the effluent through electrocoagulation or chelation precipitation; and finally, recovery of high-purity lithium salts through field-enhanced desorption. This invention achieves a lithium recovery rate ≥98% and a heavy metal removal rate ≥99%, offering advantages such as waste-to-waste treatment, low energy consumption, no secondary pollution, and high resource recovery value. It is suitable for the deep treatment and resource utilization of lithium-ion battery production wastewater.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource recycling technology, and in particular to a treatment method for lithium recovery and targeted removal of heavy metals from lithium battery production wastewater. Background Technology

[0002] Wastewater generated during the production of lithium-ion batteries typically contains high concentrations of lithium ions (Li₂O₃). + This wastewater contains heavy metal ions such as nickel (Ni), cobalt (Co), and manganese (Mn), as well as complex components such as fluorides and organic solvents. With the explosive growth of the new energy vehicle industry, the amount of this type of wastewater has increased dramatically. If not treated properly, it will cause serious harm to the ecological environment and also waste valuable lithium resources.

[0003] Existing technologies for treating lithium battery wastewater mainly include chemical precipitation, membrane separation, adsorption, and evaporation crystallization. However, these methods have the following significant problems in practical applications:

[0004] (1) Low lithium recovery rate and poor purity: Traditional precipitation methods have difficulty separating lithium from other divalent heavy metal ions (such as Ni²⁺). + Co² + Effective separation results in low purity of recovered lithium salts, making them unsuitable for direct reuse in battery production; membrane separation is prone to contamination and clogging, and lacks the selective retention capacity for monovalent lithium ions.

[0005] (2) High energy consumption and serious secondary pollution: Evaporation crystallization method has extremely high energy consumption and high operating cost; Chemical method requires the addition of a large amount of acid and alkali reagents to adjust pH, generating a large amount of sludge containing heavy metals, which poses a risk of secondary pollution.

[0006] (3) Lack of coordination mechanism: Existing processes often separate "pollutant removal" from "resource recycling", resulting in a lengthy process that cannot achieve simultaneous water purification and high-value resource recycling.

[0007] (4) High energy dependence: Traditional electrochemical or membrane treatment processes rely entirely on external power input, resulting in high operating costs and a lack of innovative mechanisms for energy self-sufficiency by utilizing industrial by-products (such as exhaust gas).

[0008] Therefore, developing an integrated lithium battery wastewater treatment technology that can utilize industrial exhaust gas to achieve highly selective adsorption and desorption of lithium ions, efficiently remove heavy metals, and possess self-powered characteristics has become an urgent technical challenge to be solved. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a treatment method for lithium recovery and targeted removal of heavy metals in lithium battery production wastewater. The aim is to achieve a lithium resource recovery rate of ≥98% and a heavy metal removal rate of ≥99%, and to use industrial exhaust gas to build a self-powered system to reduce operating costs.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: The present invention relates to a method for lithium recovery and targeted removal of heavy metals from lithium battery production wastewater, characterized by comprising the following steps: Step 1: Pretreatment and Oxidation Regulation After removing large particulate suspended solids from lithium battery production wastewater through a screen, it is introduced into a reaction tank. Industrial tail gas containing nitrogen oxides (NO2) is introduced into the reaction tank. By utilizing the dissolution and oxidation properties of NO2 in water, the low-valence metal ions in the wastewater are oxidized to high-valence states. At the same time, the pH value of the wastewater is adjusted to a weakly acidic range to create a self-powered oxidation environment. Step 2: Electrochemical synergistic adsorption Pretreated wastewater is pumped into an electrochemical adsorption reactor filled with modified lithium-ion sieves. A DC electric field is applied across the reactor, with the voltage controlled at 1.5V-3.0V and the current density at 5mA / cm²-15mA / cm². Under the influence of the electric field, lithium ions (Li...) in the wastewater... + Lithium ions migrate directionally to the cathode area and undergo specific intercalation and adsorption within the sieve channels, while divalent heavy metal ions such as nickel, cobalt, and manganese are excluded from the adsorption sites due to differences in hydration radius and charge, thus achieving the initial separation of lithium from heavy metals. Step 3: Targeted removal of heavy metals After adsorption, the effluent enters the heavy metal deep purification unit, where specific chelating agents are added or electrocoagulation is used to form insoluble precipitates or complexes of residual heavy metal ions such as nickel, cobalt, and manganese. These precipitates are then removed by a solid-liquid separation device to ensure that the heavy metal concentration in the effluent meets the discharge standards. Step 4: Electric Field Enhanced Desorption and Lithium Resource Recovery When the lithium ion sieve is saturated, the electrode polarity of the electrochemical adsorption reactor is switched or a reverse pulse voltage is applied, while dilute acid eluent is introduced. Under the effect of electric field enhancement, lithium ions are rapidly desorbed from the lithium ion sieve channels and enter the eluent to obtain a high-concentration lithium-rich solution. Step 5: Product Synthesis and System Self-Circulation The lithium-rich solution is reacted with the nitrate ions formed by the absorption of nitrogen oxides in step one to synthesize a high-purity lithium nitrate product; the treated wastewater is discharged or reused after passing the test, and the adsorption material is recycled after regeneration.

[0011] As a preferred embodiment of the present invention, in step one, the volume concentration of NO2 in the industrial exhaust gas is 500ppm-2000ppm, the ventilation rate is 0.5L / min-2.0L / min, and the reaction time is 20 minutes-40 minutes. The nitric acid generated by the reaction of NO2 and water provides an acidic environment and oxidant, without the need to add additional acid or oxidant.

[0012] As a preferred embodiment of the present invention, in step two, the modified lithium ion sieve is a titanium-based or manganese-based ion sieve with a particle size of 0.5mm-1.2mm, a specific surface area ≥300m² / g, and a selectivity coefficient for lithium ions K(Li / Na)≥50 and K(Li / Mg)≥100; the hydraulic residence time of the electrochemical adsorption reactor is 30 minutes-60 minutes.

[0013] As a preferred technical solution of the present invention, in step three, the heavy metal deep purification unit adopts an electrocoagulation reactor, with an iron plate or aluminum plate as the sacrificial anode, a current density of 10A / m²-20A / m², a reaction time of 15 minutes-25 minutes, and a heavy metal removal rate of ≥99%.

[0014] As a preferred embodiment of the present invention, in step four, the frequency of the reverse pulse voltage is 0.5Hz-2.0Hz, the duty cycle is 30%-70%, the eluent is 0.05mol / L-0.2mol / L dilute hydrochloric acid or dilute nitric acid, the desorption time is 15 minutes-30 minutes, and the desorption rate of lithium ions is ≥95%.

[0015] In a preferred embodiment of the present invention, in step five, lithium nitrate is synthesized by reacting the nitrate ions generated in step one with a lithium-rich solution.

[0016] As a preferred technical solution of the present invention, it also includes an intelligent control system, which monitors the lithium concentration, heavy metal concentration, pH value and conductivity of the influent in real time, and automatically adjusts the industrial exhaust gas flow rate, electric field voltage intensity and elution cycle to ensure that the system always operates in the state of optimal energy efficiency ratio.

[0017] As a preferred technical solution of the present invention, the intelligent control system monitors the lithium concentration, heavy metal concentration, pH value and conductivity of the influent in real time, and automatically adjusts the industrial exhaust gas flow rate, electric field voltage intensity and elution cycle.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: High recovery rate and high purity: By utilizing the selective adsorption mechanism of lithium-ion sieve enhanced by electric field, the lithium ion is efficiently separated from impurities such as nickel, cobalt, and manganese. The lithium recovery rate is ≥98%, and the purity of the recovered product reaches battery-grade standards.

[0019] Waste-to-waste treatment and self-sustaining energy: This innovative approach utilizes NO2 from industrial exhaust gas as an oxidant and acid source, which not only reduces exhaust gas emissions but also decreases the amount of chemical reagents required. This creates a self-sustaining reaction system that treats waste with waste, significantly reducing operating costs.

[0020] Synergistic and efficient: Resource recycling and water purification are coupled in the same system. Electrochemical means are used to enhance the mass transfer process, shorten the process flow, achieve a heavy metal removal rate of ≥99%, and ensure that the effluent water quality meets the standards.

[0021] Environmentally friendly: The entire process generates no secondary sludge, avoiding the solid waste disposal problems of traditional chemical precipitation methods, and meeting the requirements of green manufacturing and circular economy. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of the processing steps; Figure 2 This invention relates to an integrated process flow for lithium recovery and heavy metal removal from lithium battery wastewater. Figure 3 This is a schematic diagram of the selective adsorption principle of lithium ion sieve enhanced by electric field in the electrochemical adsorption reactor of the present invention; Figure 4 This is a diagram illustrating the structure and reaction mechanism of the industrial exhaust gas-driven self-powered system of the present invention. Detailed Implementation

[0023] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0024] In the attached diagram, all identical reference numerals refer to the same components.

[0025] Example 1: like Figure 1 As shown, the treatment method for lithium recovery and targeted removal of heavy metals in lithium battery production wastewater includes the following steps: Preprocessing: Take initial Li + The concentration is 800 mg / L, Ni² + The concentration is 50 mg / L, Co² + 50L of simulated lithium battery wastewater with a concentration of 40mg / L was introduced. Industrial exhaust gas containing 1000ppm NO2 was passed through at a rate of 1.0L / min, and the reaction lasted for 30 minutes. At this point, the pH of the wastewater naturally dropped to around 4.5, and some low-valence metals were oxidized.

[0026] Electrochemical adsorption: Wastewater was pumped into an electrochemical adsorption column packed with titanium-based lithium ion sieves (0.8 mm particle size). A DC voltage of 2.0 V, a current density of 10 mA / cm², and a hydraulic retention time of 45 minutes were applied. Under these conditions, Li... + Ni² is selectively adsorbed. + Co² + It flows out with the water.

[0027] Heavy metal removal: Adsorbed effluent enters the electrocoagulation unit, using an iron plate as the anode, with a current density of 15 A / m², and a reaction time of 20 minutes. The generated Fe(OH)₃ flocs adsorb and encapsulate residual heavy metals. After precipitation and filtration, the effluent contains Ni²⁺. + Co² + The concentrations were all below 0.5 mg / L, and the removal rate was >99%.

[0028] Desorption and recovery: A reverse pulse voltage (frequency 1 Hz, duty cycle 50%) was applied to the adsorption-saturated ion sieve, and 0.1 mol / L dilute nitric acid was introduced for elution for 20 minutes. The eluent was collected, and Li was measured. + The concentration is approximately 4500 mg / L, and the desorption rate is 96.5%.

[0029] Product synthesis: The lithium-rich eluent was concentrated and crystallized to obtain high-purity lithium nitrate crystals.

[0030] Experimental data: Lithium recovery rate: 98.2%; Heavy metal (Ni, Co) removal rate: 99.4%; System energy consumption: 65% lower than traditional evaporation crystallization method; Chemical savings: Due to the use of exhaust gas acidification, acid consumption is reduced by 80%.

[0031] Example 2: Adjust the process parameters: NO2 concentration in industrial exhaust gas 1500ppm, electrochemical adsorption voltage 2.5V, eluent concentration 0.15mol / L.

[0032] Experimental data: Lithium recovery rate: 98.5%; Heavy metal removal rate: 99.6%; Desorption rate: 97.1%.

[0033] The results show that appropriately increasing the voltage and eluent concentration can further improve the desorption efficiency, but the energy consumption will increase slightly, and a comprehensive balance needs to be made.

[0034] Comparative Example 1: The same wastewater is treated using static adsorption without applying an electric field.

[0035] Experimental data: Lithium recovery rate: 82.4%; Adsorption equilibrium time: extended to 120 minutes; The selectivity coefficient decreased significantly, Ni² + The co-adsorption amount increases.

[0036] This demonstrates that electric field enhancement is crucial for improving adsorption rate and selectivity.

[0037] Comparative Example 2: Instead of introducing industrial exhaust gas, sulfuric acid is used to adjust the pH to 4.5, and hydrogen peroxide is added for oxidation.

[0038] Experimental data: The treatment effect is comparable to that of Example 1, but the operating cost increases by about 45% (mainly due to the cost of acid and oxidant), and there is no benefit of waste gas resource recovery.

[0039] Table 1. Performance Comparison of Examples and Comparative Examples

[0040] As can be seen from Table 1, the technology of this invention significantly reduces operating costs and chemical reagent consumption while ensuring high recovery and removal rates.

[0041] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for lithium recovery and targeted removal of heavy metals from lithium battery production wastewater, characterized in that, Includes the following steps: Step 1: Pretreatment and oxidation control. Industrial tail gas containing nitrogen oxides is introduced into the wastewater to adjust the pH and oxidize low-valence metal ions by utilizing its dissolution and oxidation properties. Step 2: Electrochemical synergistic adsorption. Wastewater is pumped into an electrochemical adsorption reactor filled with modified lithium-ion sieves. A DC electric field is applied to cause lithium ions to migrate directionally and be embedded in the adsorption, while heavy metal ions are repelled. Step 3: Targeted removal of heavy metals, deep purification of the adsorbed water to remove residual heavy metal ions; Step 4: Electric field enhanced desorption and lithium resource recovery. Switch electrode polarity or apply reverse pulse voltage, and introduce eluent to desorb lithium ions to obtain a lithium-rich solution. Step 5: Product synthesis, converting the lithium-rich solution into lithium salt products.

2. The processing method as described in claim 1, characterized in that: In step one, the main component of the industrial exhaust gas is NO2, with a volume concentration of 500ppm-2000ppm. The acidic environment is provided by the nitric acid generated by the reaction of NO2 with water, without the need to add additional acid.

3. The processing method as described in claim 1, characterized in that: In step two, the modified lithium-ion sieve is a titanium-based or manganese-based ion sieve, and a DC voltage of 1.5V-3.0V and a current density of 5mA / cm²-15mA / cm² are applied.

4. The processing method as described in claim 1, characterized in that: In step three, the deep purification of heavy metals adopts electrocoagulation or specific chelation precipitation, and the heavy metal removal rate is ≥99%.

5. The processing method as described in claim 1, characterized in that: In step four, the reverse pulse voltage frequency is 0.5Hz-2.0Hz, the eluent is 0.05mol / L-0.2mol / L dilute acid, and the lithium ion desorption rate is ≥95%.

6. The processing method as described in claim 1, characterized in that: In step five, lithium nitrate is synthesized by reacting the nitrate ions generated in step one with a lithium-rich solution.

7. The processing method as described in claim 1, characterized in that: It also includes an intelligent control system that automatically adjusts the exhaust gas flow rate, electric field parameters, and elution cycle based on the influent water quality.

8. A processing apparatus for implementing the method according to any one of claims 1-7, characterized in that: It includes an exhaust gas absorption unit, an electrochemical adsorption reaction unit, a heavy metal deep purification unit, a desorption regeneration unit, and a product synthesis unit. Each unit is connected in series through pipelines and is equipped with a central control module.

9. The processing apparatus as described in claim 8, characterized in that: The intelligent control system monitors the lithium concentration, heavy metal concentration, pH value and conductivity of the influent in real time, and automatically adjusts the industrial exhaust gas flow rate, electric field voltage intensity and elution cycle.

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