Extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder

Abstract

The application provides an extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder, comprising: an extraction unit, which is communicated with a three-time impurity removal filtrate tank of the lithium liquid, is used for extracting and separating to obtain lithium-loaded organic phase and raffinate; a carbon dioxide back-extraction unit and a sulfuric acid back-extraction unit arranged in parallel and respectively communicated with the extraction unit; a lithium bicarbonate back-extraction liquid oil removal unit connected with the carbon dioxide back-extraction unit and used for removing oil from lithium bicarbonate back-extraction liquid to finally obtain lithium bicarbonate solution; a lithium sulfate back-extraction liquid oil removal unit connected with the carbon dioxide back-extraction unit and used for removing oil from lithium sulfate back-extraction liquid; and a bipolar membrane unit connected with the lithium sulfate back-extraction liquid oil removal unit and used for separating lithium sulfate back-extraction liquid after oil removal to obtain lithium sulfate solution, sulfuric acid and lithium hydroxide monohydrate solution, wherein the obtained sulfuric acid and lithium hydroxide monohydrate solution are transferred to a leaching process and an impurity removal process.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery cathode recovery liquid extraction technology, and in particular to an extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder. Background Technology

[0002] With the explosive growth of the new energy vehicle industry, the amount of retired lithium iron phosphate batteries has surged. The efficient recovery of valuable lithium metal from waste lithium iron phosphate black powder has become a crucial link in ensuring resource security across the new energy industry chain. Currently, the industrial process commonly employs a "leaching-impurity removal-extraction-back-extraction-evaporation crystallization" route to recover battery-grade lithium salts. However, existing extraction systems generally suffer from prominent problems such as a single product route, uncontrolled back-extraction solution quality, and high costs associated with purchasing acids and alkalis.

[0003] First, traditional extraction systems typically only have a single back-extraction route (e.g., CO2 back-extraction to lithium bicarbonate or sulfuric acid back-extraction to lithium sulfate), making it impossible to flexibly switch routes based on fluctuations in lithium carbonate market orders and the need for self-sufficiency in intermediate raw materials. This results in poor capacity flexibility and weak resilience to market risks for enterprises. Second, the organic phase inevitably carries trace amounts of extractant (such as tributyl phosphate, sulfonated kerosene, etc.) during the back-extraction process. If the back-extraction solution is not thoroughly degreased before entering subsequent crystallization or membrane treatment processes, it will cause the lithium carbonate product to turn yellow and have irregular crystal forms. It will also lead to fouling of the bipolar membrane stack surface, a surge in transmembrane voltage, and a significant reduction in membrane life. Third, existing bipolar membrane systems lack targeted acid-resistant degreasing and pH stabilization measures at the front end. Residual oil and acid fluctuations in the lithium sulfate back-extraction solution directly threaten the safe operation of the membrane stack. More critically, the large amounts of sulfuric acid and lithium hydroxide required for the leaching and impurity removal processes in existing systems are entirely dependent on external procurement, failing to form an acid-base closed loop with the extraction-back-extraction-bipolar membrane section. This not only results in high operating costs but also increases transportation and storage risks. Therefore, there is an urgent need for a lithium iron phosphate black powder recovery and purification lithium extraction system that combines product route flexibility, deep purification of back-extraction solution, and acid-base self-sufficiency. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned problems by providing an extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder.

[0005] The technical solution of this application is implemented as follows: An extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder includes: An extraction unit, which is connected to the lithium liquid three-stage impurity removal filtrate tank, is used to extract and separate the lithium-supported organic phase and the raffinate; The carbon dioxide back-extraction unit and the sulfuric acid back-extraction unit are arranged in parallel and are respectively connected to the extraction unit. The carbon dioxide back-extraction unit is used to back-extract the lithium-supported organic phase to obtain lithium bicarbonate back-extraction solution, and the sulfuric acid back-extraction unit is used to back-extract the lithium-supported organic phase to obtain lithium sulfate back-extraction solution. The lithium bicarbonate back-extraction solution de-oiling unit is connected to the carbon dioxide back-extraction unit to de-oil the lithium bicarbonate back-extraction solution and finally obtain a lithium bicarbonate solution. A lithium sulfate back-extraction solution oil removal unit is connected to the carbon dioxide back-extraction unit for oil removal treatment of the lithium sulfate back-extraction solution; The bipolar membrane unit is connected to the lithium sulfate back-extraction solution de-oiling unit and is used to separate the lithium sulfate back-extraction solution after de-oiling to obtain lithium sulfate solution, sulfuric acid and lithium hydroxide monohydrate solution. The obtained sulfuric acid and lithium hydroxide monohydrate solution are transferred to the leaching process and the impurity removal process.

[0006] As a further improvement, the organic phase used in the extraction unit is a neutral phosphorus-oxygen-carboxylic acid synergistic extraction system, specifically composed of: Main extractant: 20%-35% tributyl phosphate or triisoamyl phosphate; Co-extractant: 5%-10% naphthenic acid or 2-ethylhexanoic acid; Diluent: 55%-70% of 260# sulfonated kerosene or dearomatic solvent oil; Modifier: 2%-5% isodecanol or 2-ethylhexanol.

[0007] As a further improvement, the newly prepared organic phase needs to be saponified with a 5%-8% sodium carbonate solution to a saponification rate of 40%-60% before use, and then subjected to saturated Li... + The solution is pre-equilibrated for 2-3 cycles.

[0008] As a further improvement, the extraction unit employs a countercurrent extraction section consisting of 3-5 stages of box-type mixing and clarifying extraction tanks connected in series, wherein each stage of the box-type mixing and clarifying extraction tank includes: The mixing chamber is equipped with mechanical agitator. Clarification chamber: Adjacent to the mixing chamber, with a cross-sectional area 1.5-2.5 times that of the mixing chamber, and equipped with an interface control weir plate and a light / heavy phase collection tank.

[0009] As a further improvement, the loaded organic phase output from the extraction unit first enters the loaded organic phase buffer tank. The main pipe of the loaded organic phase buffer tank is equipped with a three-way proportional regulating valve group to divert the loaded organic phase to two back-extraction units according to a set ratio. The system is also equipped with a central coordination controller to receive order demand signals from MES / ERP, liquid level signals from each buffer tank, production capacity status of the bipolar membrane unit 140, and real-time flow rate of the loaded organic phase in the extraction unit, and dynamically optimize the two-way diversion ratio to ensure the balance between lithium carbonate product output and the self-sufficiency of intermediate raw materials.

[0010] As a further improvement, the carbon dioxide back-extraction unit consists of 2-3 stages of box-type countercurrent mixing and clarification extraction tanks connected in series, arranged in a stepped or horizontal line, with each stage connected by an inter-stage connecting pipe; each stage consists of a combined mixing chamber and a clarification chamber, with the mixing chamber located at the front of the clarification chamber and a flow channel between the two chambers; the bottom of the mixing chamber of the carbon dioxide back-extraction unit is equipped with a titanium alloy powder sintered aeration disc, and the top is equipped with a double-layer six-bladed disc turbine propeller driven by a variable frequency reduction motor; the outer wall of the mixing chamber is equipped with a semi-pipe spiral jacket for circulating cooling water to maintain a temperature of 20-35°C; the tail of the clarification chamber is equipped with a sawtooth-shaped light phase overflow weir and a radio frequency admittance interface instrument, and a stainless steel wire mesh coalescing layer is provided in the upper part of the clarification chamber and in front of the light phase overflow weir to promote the coalescence and sedimentation of trace amounts of aqueous droplets entrained in the light phase.

[0011] As a further improvement, the sulfuric acid back-extraction unit 138 is composed of 2-3 stages of box-type countercurrent mixing, clarifying, and extraction tanks connected in series, arranged in a stepped or horizontal line, with each stage connected by an inter-stage connecting pipe; each stage consists of a combined mixing chamber and a clarifying chamber, with the mixing chamber located at the front end of the clarifying chamber, and a flow channel provided between the two chambers; the upper part of the mixing chamber of the sulfuric acid back-extraction unit is provided with an annular sulfuric acid distribution pipe, and the bottom is evenly distributed with 4-8 small holes at a downward 45° angle, with a stirring speed of 100-200 rpm, so that the sulfuric acid back-extraction agent is evenly sprayed into the organic phase, avoiding local over-acidification leading to local acidification and demulsification of the organic phase or the formation of a third phase; the outer wall of the mixing chamber is provided with a semi-pipe spiral jacket for circulating hot water to maintain a temperature of 40-60°C; the volume of the clarifying chamber of the sulfuric acid back-extraction unit is increased to 2.0-2.5 times that of the mixing chamber.

[0012] As a further improvement, the lithium bicarbonate back-extraction solution oil removal unit includes a dissolved air flotation oil removal tank, a coalescing separator, an activated carbon adsorption column, and a precision security filter connected in series along the process.

[0013] As a further improvement, the lithium sulfate back-extraction solution oil removal unit includes an acid-resistant dissolved air flotation oil removal tank, an acid-compatible coalescing separator, an acid-resistant activated carbon adsorption column, a precision security filter, and a pH fine-tuning buffer tank connected in series along the process.

[0014] The advantages or beneficial effects of the above technical solutions include at least the following: The extraction system for recovering and purifying lithium iron phosphate black powder provided in this application achieves flexible switching and coordinated control of lithium carbonate product and intermediate raw material routes by setting up carbon dioxide back-extraction units and sulfuric acid back-extraction units in parallel. On the one hand, the CO2 back-extraction route can produce high-quality lithium bicarbonate back-extraction solution, which, after deep oil removal, is thermally decomposed to obtain battery-grade lithium carbonate. On the other hand, the sulfuric acid back-extraction route can produce lithium sulfate back-extraction solution, which, after oil removal, enters the bipolar membrane unit to be converted in situ into sulfuric acid and lithium hydroxide monohydrate, which are directly recycled for the front-end leaching and impurity removal processes, significantly reducing the cost of purchased acids and alkalis and realizing a closed-loop circulation of acid and alkali resources within the system. At the same time, the two back-extraction solutions are each equipped with a dedicated oil removal unit (multi-stage series of air flotation-coalescing-adsorption-precision filtration), which can remove residual organic phases in the back-extraction solution to <<0.5ppm, ensuring the color and purity of lithium carbonate crystals, avoiding performance degradation of the bipolar membrane stack due to oil clogging, and extending the membrane's service life. In addition, the raffinate is returned to the front-end impurity removal system for reprocessing, resulting in extremely low lithium loss; the overall system combines the advantages of product flexibility, cost economy, and green operation. Attached Figure Description

[0015] The accompanying drawings illustrate exemplary embodiments of the present application and, together with the description thereof, serve to explain the principles of the present application. These drawings are included to provide a further understanding of the present application and are incorporated in and constitute a part of this specification.

[0016] Figure 1 A framework diagram of the lithium iron phosphate black powder leaching system provided in an embodiment of the present invention is shown.

[0017] Figure 2 A framework diagram of the lithium iron phosphate leaching lithium solution impurity removal system provided in an embodiment of the present invention is shown.

[0018] Figure 3 A framework diagram of a lithium iron phosphate leaching lithium solution impurity removal system according to another embodiment of the present invention is shown.

[0019] Figure 4 A framework diagram of an extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder, according to another embodiment of the present invention, is shown. Detailed Implementation

[0020] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While some embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this application. It should be understood that the drawings and embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0021] It should be noted that, where there is no conflict, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] The names of the messages or information exchanged between multiple devices in the embodiments of this application are for illustrative purposes only and are not intended to limit the scope of these messages or information.

[0023] Reference Figure 1 This invention provides a lithium iron phosphate black powder leaching system, comprising: Sulfuric acid dilution tank 101 is used to dilute sulfuric acid; The first black powder slurry tank 102 is used to mix lithium iron phosphate black powder with diluted sulfuric acid solution to form a first slurry mixture. The first black powder leaching tank 103 and the second black powder leaching tank 104 are respectively connected to the black powder slurry tank 102 and are used to introduce the first slurry mixture, hydrogen peroxide, steam, compressed air and pure water for primary leaching. The first filter press 105 is connected to the first black powder leaching tank 103 and the second black powder leaching tank 104 respectively, and is used to filter and form the first filter residue and the first filtrate. The first 1 / 10 to 1 / 5 volume of filtrate from the first filter press is back-pumped to the first black powder leaching tank 103 and the second black powder leaching tank 104 for backwashing and cleaning. The first filtrate tank 106 is used to store the first filtrate; The first iron-phosphorus precipitation tank 107 is connected to the first filtrate tank 106 and is used to introduce the first filtrate, ferrous sulfate solution, lithium hydroxide solution and hydrogen peroxide solution to precipitate iron-phosphorus. The first iron and phosphorus filter press 108 is connected to the first iron and phosphorus tank 107 and is used to filter and form the first iron and phosphorus filtrate and the first iron and phosphorus filter residue. The first 1 / 10 to 1 / 5 volume of the filtrate of the first iron and phosphorus filter press 108 is used to further backwash and clean the first iron and phosphorus tank 107. The first iron and phosphorus removal filtrate tank 109, the first iron and phosphorus filter residue washing tank 110, and the first iron and phosphorus filter residue water washing tank 111 are respectively connected to the first iron and phosphorus precipitation filter press 108. The first iron and phosphorus removal filtrate tank 109 is used to store the first iron and phosphorus removal filtrate, the first iron and phosphorus filter residue washing tank 110 is used to store the first iron and phosphorus filter residue, and the first iron and phosphorus filter residue water washing tank 111 is used to store the water washing liquid for cleaning the first iron and phosphorus precipitation filter press 108. The water washing liquid is also transported to the sulfuric acid dilution tank 101 to dilute the sulfuric acid.

[0024] The sulfuric acid dilution tank 101 is equipped with a concentrated sulfuric acid feed pipe, a washing liquid recycling pipe, and a pure water replenishment pipe. The feed volume flow ratio of the three is 1:(0.6-0.8):(0.4-0.6). The sulfuric acid concentration after dilution is controlled at around 20%, and the temperature during the dilution process is controlled to not exceed 40℃ through jacket cooling. This control method solves the problems of blindly reusing washing liquid and large fluctuations in diluted sulfuric acid concentration leading to unstable pH during pulping. It narrows the fluctuation range of diluted sulfuric acid concentration from ±0.3 mol / L to ±0.1 mol / L, and stabilizes the initial pH of pulping at 1.0-1.5, ensuring consistent leaching kinetics.

[0025] The first black powder slurry tank 102 is an ultrasonically coupled slurry tank. An ultrasonic transducer array is installed on the sidewalls and / or bottom of the tank. The ultrasonic frequency is 20-40kHz, and the power density is 150-400W / L. Ultrasonic cavitation is applied simultaneously with mechanical stirring, and the slurry time is controlled within 15-30 minutes. After the black powder is crushed, a dense carbon coating layer (conductive carbon black + graphite) and trace amounts of binder remain on the surface of the black powder particles, hindering direct contact between sulfuric acid and LiFePO4 grains. This results in the problem of uneven dispersion even after conventional slurrying takes more than one hour. This invention uses ultrasonic cavitation microjets to peel off the surface carbon layer and binder residue, allowing the surface of the black powder particles and microcracks to rapidly saturate and swell with the acid. This increases the specific surface area of ​​the black powder particles by 30%-50%, shortens the slurry time by more than 50%, and reduces the slurry viscosity, resulting in a 20%-30% decrease in the specific resistance of subsequent pressure filtration.

[0026] The bottom of the first black powder leaching tank 103 and the second black powder leaching tank 104 are both equipped with an annular gas distributor and a hydrogen peroxide atomizing spray pipe; the annular gas distributor simultaneously introduces steam and compressed air, with a volume flow ratio of steam to compressed air of 1:(2-4), and after mixing, forms a microbubble flow with an average diameter ≤2mm; the nozzle of the hydrogen peroxide atomizing spray pipe is located 5-15cm above the annular gas distributor, and the hydrogen peroxide is atomized to a particle size ≤200μm, with the spray direction opposing the rising bubble flow.

[0027] Traditional top-addition of hydrogen peroxide results in rapid decomposition into oxygen and water at the liquid surface due to the high-temperature, acidic environment, leading to the loss of the effective oxidant before it reaches the particle surface. Furthermore, simple steam bubbling produces large bubbles (>5mm) with high rising speeds, resulting in low gas-liquid mass transfer efficiency and violent slurry splashing. This invention uses a mixture of steam and compressed air to create microbubbles that provide uniform and gentle heating (avoiding localized overheating). During the microbubble's ascent, it breaks up in the hydrogen peroxide atomization zone, releasing localized turbulence and vibration waves that ensure thorough contact between the hydrogen peroxide droplets and the black powder particles, achieving primary physical fragmentation. The reverse-flush design increases the hydrogen peroxide penetration depth and prolongs the effective oxidant concentration maintenance time, reducing the time to lithium leaching equilibrium in the primary leaching stage from 60-90 minutes to 25-40 minutes. Additionally, the further oxidation of LiFePO4 to FePO4 by hydrogen peroxide causes lattice volume expansion (approximately 6.5%-7.2%), generating internal stress that causes spontaneous particle breakage along the microcrack direction, achieving in-situ chemical fragmentation.

[0028] More specifically, the annular gas distributor includes an annular main pipe and multiple radial branch pipes. The annular main pipe is equipped with a steam inlet and a compressed air inlet. The multiple radial branch pipes are evenly distributed circumferentially along the bottom of the leaching tank and communicate with the annular main pipe. Each radial branch pipe has micro-orifice nozzles evenly distributed at its bottom. The orifice diameter of the micro-orifice nozzles is 0.3-1.5 mm, and the nozzle axis forms an angle of 30°-60° with the vertical direction and is arranged tangentially circumferentially, so that the steam-air mixture rises in the form of swirling microbubbles. The hydrogen peroxide atomizing spray pipe includes a liquid supply pipe and at least two layers of annular atomizing branch pipes. Each layer of annular atomizing branch pipes is evenly distributed with atomizing nozzles. The atomizing nozzles are pressure-type fan-shaped nozzles or airflow-type mixing nozzles, with a spray angle of 60°-120°.

[0029] In the existing first filter press 105, the cleaning process generally uses either gas backflushing or liquid backwashing alone. However, although gas backflushing alone can remove large pieces of filter cake, it is ineffective against fine carbon powder and iron phosphate microcrystals embedded in the micropores of the filter cloth; while when backwashing with filtrate alone, the thick filter cake on the surface that has not been removed hinders the penetration of liquid, requiring a large amount of filtrate for a long time and resulting in uneven cleaning. Therefore, preferably, in other embodiments, the first filter press 105 is further provided with a backwashing system, which can be a gradient pulse backwashing device, including the following steps executed sequentially: using gradient pulse compressed air or nitrogen at 0.3-0.5 MPa for 3-8 minutes to remove residual filter cake and dry the surface of the filter cloth; then using the first 1 / 10 to 1 / 5 volume of the first filtrate, injected in reverse at a gradient pulse pressure of 0.6-0.8 MPa, with a pulse frequency of 15-30 times / min and a duration of 5-12 minutes, to clean the pores of the filter cloth; finally, using gradient pulse compressed air or nitrogen at 0.3-0.5 MPa for 3-8 minutes to remove residual filtrate and dry the surface of the filter cloth. In this invention, the filter cloth is subjected to periodic "expansion-contraction" mechanical vibration by gradient pulse waveform. Combined with pressure amplitude changes, deep-seated blockage particles are loosened and detached under alternating stress. After regeneration, the air permeability resistance recovery rate of the filter cloth is ≥90%, the service life of a single filter cloth is extended by 30%-50%, and the residual filter cake moisture content after backflushing is reduced from 12%-15% to 6%-10%, reducing the entrainment loss of lithium in wet slag.

[0030] As a further improvement, the first iron-phosphorus sinking tank 107 is divided along the axial direction into an upper reaction zone (occupying 30%-40% of the tank height), a middle growth zone (occupying 30%-40% of the tank height), and a lower settling zone (occupying 20%-30% of the tank height) by a heat-insulating ring plate. Each of the three sections is equipped with an independent jacket and a temperature-controlled medium inlet and outlet. The upper jacket is supplied with 0.3-0.5MPa steam to maintain 80-90℃, the middle jacket is supplied with hot water / cooling water to maintain 70-75℃, and the lower jacket is supplied with cooling water to maintain 55-65℃. The upper section is equipped with a high-speed agitator (100-200rpm), the middle section with a medium-speed agitator (50-100rpm), and the lower section with a low-speed anchor agitator (10-30rpm) or agitation is omitted. Traditional single-temperature zone iron-phosphorus sinking tanks cannot simultaneously meet the contradictory kinetic requirements of "high-temperature rapid nucleation" and "low-temperature crystal maturation," and the uniform agitation of the entire tank causes the crystals in the settling zone to be resuspended and broken. The above-mentioned technical solution of the present invention: the nucleation induction period of FePO4·2H2O is shortened to <10min by the high temperature of the upper section (85±3℃); the medium temperature of the middle section (72±3℃) controls the linear growth rate of crystals and avoids explosive agglomeration; the low temperature of the lower section (60±3℃) promotes Ostwald maturation by static aging, resulting in the dissolution of fine crystals and the perfection of large crystals; the three sections work together to shorten the total iron and phosphorus precipitation time from 3-5h to 1.5-2.5h, and the crystal integrity of the lower section is high and it is not easily broken by stirring and shearing.

[0031] Before backwashing and cleaning the first iron-phosphorus filter press 108, the first 1 / 10 to 1 / 5 volume of filtrate flows through a plate heat exchanger. The heat exchange mode is selected according to the type of scaling on the inner wall of the first iron-phosphorus filter press 107 after discharge: when the scaling is mainly FePO4·2H2O crystal deposition, the filtrate is backwashed directly at the original temperature (70-85℃) to enhance the dissolution of microcrystals by utilizing the high temperature solubility; when the scaling is mainly Fe(OH)2 colloidal adhesion, the filtrate is cooled to 45-60℃ before backwashing to inhibit the re-dehydration and hardening of colloids at high temperature; and the backwashing time is indirectly determined by a differential pressure sensor. When the heat transfer pressure difference between the tank wall and the jacket of the first iron-phosphorus filter press 107 increases by ≥15% compared with the new tank state, the backwashing time is automatically extended to 1.5-2.0 times the reference value. In existing technologies, backwashing at a fixed temperature is generally used. However, this fixed-temperature backwashing is clearly unable to adapt to the differences in scale composition caused by fluctuations in raw material batches (ferric phosphorus crystal scale vs. ferric hydroxide colloidal scale), and the fixed duration is insufficient for cleaning stubborn scale and excessively wasteful for minor scale. This invention adopts adaptive temperature control based on scale composition—high temperature dissolves crystalline scale and medium temperature softens colloidal scale, avoiding "one-size-fits-all" thermal shock that causes hardening of colloidal scale or recrystallization of crystalline scale; the heat transfer pressure difference serves as an indirect quantitative indicator of scale thickness, enabling on-demand adjustment of backwashing intensity, with a tank wall heat transfer coefficient recovery rate ≥85% and a 15%-20% reduction in backwashing energy consumption.

[0032] In other embodiments, when mixed scale is identified, a three-stage temperature-controlled pulse backflushing procedure can be executed collaboratively: First stage (medium temperature softening section): The filtrate is cooled to 50-60℃ through the low temperature heat exchange main circuit, and then pulsed sprayed at a pressure of 0.4-0.6MPa for 5-8 minutes with a pulse frequency of 20-30 times / min to soften the Fe(OH)3 colloidal scale. Second stage (high temperature dissolution section): Switch to high temperature direct bypass, and continuously spray the filtrate at 70-80℃ with a pressure of 0.3-0.5MPa for 8-12 minutes to dissolve FePO4·2H2O crystal scale; The third stage (medium-temperature purging section): The system switches back to the low-temperature heat exchange main circuit, using a 40-50℃ filtrate and a high-pressure pulse purging pressure of 0.6-0.9 MPa for 3-5 minutes to remove residual loose scale and carry away suspended particles. The switching between the three stages is determined by the real-time rate of change (d(ΔP) / dt) of the differential pressure sensor: when the differential pressure decrease rate in a certain stage is <0.5 kPa / min, it automatically enters the next stage; when the differential pressure decrease rate in the third stage is ≥2.0 kPa / min, that stage is automatically extended by 2-4 minutes.

[0033] Please see Figure 2 As shown, the present invention further provides a lithium iron phosphate leaching lithium solution impurity removal system, comprising: The first primary lithium liquid impurity removal tank 120 and the second primary lithium liquid impurity removal tank 121 are arranged in parallel, wherein the first primary lithium liquid impurity removal tank 120 and the second primary lithium liquid impurity removal tank 121 are used to pass in the first iron and phosphorus removal filtrate and the lithium hydroxide solution. The lithium liquid primary impurity removal filter press 122 is connected to the first primary lithium liquid impurity removal tank 120 and the second primary lithium liquid impurity removal tank 121 respectively, and is used to filter and form primary lithium liquid impurity removal filtrate and primary impurity removal filter residue. The first 1 / 10 to 1 / 5 volume of the filtrate of the lithium liquid primary impurity removal filter press 122 is used to further backwash and clean the first primary lithium liquid impurity removal tank 120 or the second primary lithium liquid impurity removal tank 121. The lithium liquid primary impurity removal filtrate tank 123 is connected to the lithium liquid primary impurity removal filter press 122 and is used to store the lithium liquid primary impurity removal filtrate. The phosphorus and fluoride removal resin tank 124 is connected to the lithium liquid primary impurity removal filtrate tank 123, and is used to introduce the lithium liquid primary impurity removal filtrate and perform phosphorus and fluoride removal. The lithium liquid tank 125, after primary purification and removal of phosphorus and fluorine, is connected to the phosphorus and fluorine removal resin tank 124 and is used to store the lithium liquid purified by the phosphorus and fluorine removal resin tank 124.

[0034] The main purpose of introducing lithium hydroxide solution into the first primary lithium impurity removal tank 120 and the second primary lithium impurity removal tank 121 is: 1. Neutralize the free acid and adjust the pH of the solution from strongly acidic to near neutral; Second, deep impurity removal, so that residual Fe, Al and other substances precipitate out in the form of hydroxide colloidal or flocculent precipitates; 3. Create suitable inlet water conditions for the subsequent phosphorus and fluoride removal resin tank (the resin is sensitive to pH and usually requires a neutral or weakly alkaline environment).

[0035] The concentration of lithium hydroxide solution should not be too high (>15%), because high-concentration LiOH solutions have increased viscosity and poor atomization / dispersion effects; in addition, local OH... - Excessive concentration can lead to Li + With residual PO4 3- / F - The formation of Li3PO4 or LiF coprecipitates can lead to lithium loss and may also cause the pH to jump abruptly beyond the target range, increasing the difficulty of pH readjustment. However, the concentration of the lithium hydroxide solution should not be too low (<3%), because a low concentration results in a large feed volume, diluting the lithium solution concentration and increasing subsequent evaporation energy consumption. In addition, during the switching of parallel dual tanks, a large volume of low-concentration alkaline solution causes system response lag and a decrease in pH control accuracy. Preferably, the concentration of the lithium hydroxide solution is 6wt%-10wt% (approximately 1.4-2.4 mol / L), more preferably 7wt%-8wt%; in addition, the preparation temperature can be 40-60℃ (LiOH solubility decreases with increasing temperature, but appropriate heating can improve fluidity); the addition method can be a two-stage addition of pre-neutralization + fine-tuning, combined with online pH closed-loop control (for example, in the pre-neutralization stage, 60%-80% of the designed maximum flow rate is rapidly added to pH 5.5-6.0, and in the fine-tuning stage, 5%-10% of the designed maximum flow rate is added dropwise to the final pH 6.8-7.5); the final pH: strictly controlled at 6.8-7.5, optimally 7.0±0.2.

[0036] Both the first primary lithium impurity removal tank 120 and the second primary lithium impurity removal tank 121 are vertical cylindrical pressure tanks with a design pressure of 0.3-0.6 MPa, a design temperature of ≤100℃, and a height-to-diameter ratio (H / D) of 2.2:1 to 2.8:1, preferably 2.5:1; the total height of the tanks is 3.5-5.0 m. The interior of both the first primary lithium impurity removal tank 120 and the second primary lithium impurity removal tank 121 is divided into three functional zones along the axial direction by two porous baffles: (a) Upper neutralization reaction zone (occupying 30%-35% of the tank height): The top is equipped with a lithium hydroxide atomizing spray ring pipe; between the bottom and the middle section, there is a first porous baffle: the opening rate is 25%-35%, the hole diameter is 20-30mm, arranged in an equilateral triangle, the plate thickness is 8-12mm, and the material is PTFE-coated carbon steel; 50-80mm above the baffle, there is a stainless steel wire mesh defoaming layer (wire diameter 0.2-0.3mm, mesh size 2-3mm) to prevent spray droplets from being carried into the middle section.

[0037] (II) Mid-section flocculation and aging zone (occupying 40%-45% of the tank height): The system is equipped with mechanical agitation, which is suitable for rapid sedimentation of high concentrations. A second porous baffle is installed between the bottom and the lower section: the opening rate is 15%-20%, the hole diameter is 10-15mm, and a 200-400 mesh stainless steel wire mesh (316L material) is laid on the top of the baffle to intercept large flocs that may float to the surface and prevent blockage of the lower section slag discharge.

[0038] (III) Lower Settlement Buffer Zone (occupying 20%-25% of the trench height): The sidewalls are free of internal components, allowing for open space to facilitate the free settling of the flocs; the angle between the bottom of the cone and the horizontal plane is ≥60° to ensure that the hydroxide flocs do not stick to the wall.

[0039] In one embodiment, the filter plate of the lithium liquid primary impurity removal filter press 122 is a polypropylene reinforced diaphragm filter plate, and the filter cloth is an alkali-resistant polyester long-fiber multifilament filter cloth (warp and weft density 260-340 threads / 10cm, air permeability 400-600L / m). 2 The filter cloth layers are arranged in a precision gradient along the feed direction. Specifically, the first 1 / 3 of the filter cloth layer near the feed side uses a twill weave with a nominal pore size of 20-30μm to quickly intercept coarse flocs; while the last 2 / 3 of the filter cloth layer near the liquid outlet side uses a satin weave with a nominal pore size of 10-15μm to deeply trap fine colloidal particles. Furthermore, the two layers are bonded together with hot melt adhesive dots to avoid interlayer slippage that could lead to precision failure.

[0040] The filter press 122 is equipped with an online turbidity diversion valve at the filtrate outlet. This valve is used to divert residual particles from the filtrate (typically 10-30 NTU) that flows out in the first 3-5 minutes after the filter press starts. This portion of the filtrate is then introduced into the first primary lithium liquid impurity removal tank 120 or the second primary lithium liquid impurity removal tank 121 for backwashing and cleaning.

[0041] The phosphorus removal fluorine resin tank 124 is a vertical cylindrical pressure vessel, and its interior is divided into the following sections from bottom to top along the axial direction: The lower support layer (accounting for 10%-15% of the tank height) is filled with a graded pad of quartz sand (particle size 1.0-2.0mm) and pebbles (particle size 8-16mm) to prevent resin loss and ensure uniform liquid distribution. The middle section, main reaction layer (occupying 55%-65% of the tank height): filled with a phosphorus and fluorine removal composite resin. This resin is a chelating resin with polystyrene-divinylbenzene as the backbone and loaded with hydrated zirconium oxide (ZrO(OH)2) and hydrated alumina (Al(OH)3) as dual active sites, and also has the effect of removing phosphate (PO4) ions. 3- / HPO4 2- ) and fluoride ions (F - Selective adsorption capacity of ) Upper protective layer (occupying 10%-15% of the tank height): filled with inert polypropylene fiber balls (3-5mm in diameter) to trap trace amounts of colloidal flocs that may penetrate from the upstream filter press, preventing clogging of the resin surface.

[0042] The dual-active-site mechanism is as follows: ZrO(OH)2 site: for F - It exhibits extremely high affinity, forming Zr-F bonds through ligand exchange, and selectively adsorbs F. - The Al(OH)3 site exhibits specific adsorption for phosphate ions, immobilizing PO4 in the form of Al-OP endospheres within the pH range of 6.5-7.5. 3- / HPO4 2- The coexistence of two sites prevents the resin from adsorbing Li in complex lithium liquid systems. + (Li) + As it is a hydrated ion, it has no coordination ability with the resin skeleton, ensuring a direct lithium recovery rate of >99.5%.

[0043] The top inlet pipe and bottom outlet pipe of the phosphorus removal fluoride resin tank 124 are both equipped with flow meters, pressure sensors, and automatic regulating valves. The operating parameters are controlled as follows: Empty tower velocity (SV): 4-8 BV / h (optimal 5-6 BV / h). Too high a velocity will cause the adsorption zone front to break through, while too low a velocity will result in insufficient equipment capacity. Operating differential pressure: Controlled between 0.05-0.15 MPa; backwashing procedure is triggered when differential pressure ≥ 0.20 MPa. Endpoint determination: An online phosphorus / fluoride ion selective electrode (or ICP online detection module) is installed at the outlet. When P > 5 mg / L or F > 3 mg / L in the outlet, it automatically switches to the standby tank and marks the tank as entering the regeneration program.

[0044] In one embodiment, the phosphorus removal fluoride resin tank 124 is preferably a first phosphorus removal fluoride resin tank and a second phosphorus removal fluoride resin tank arranged in parallel, connected by an inlet manifold and an outlet manifold, forming a flexible mode of "one in use and one on standby" or "two tanks in series / parallel": Single-tank operation mode: one tank adsorbs while the other tank regenerates or stands by; Dual-tank series mode: When the throughput is low but the quality requirement is high, two tanks are connected in series. The first tank is for coarse removal and the second tank is for fine removal, ensuring that the output liquid has P<<1mg / L and F<<0.5mg / L. Dual-tank parallel mode: When the processing capacity reaches its peak, the tanks operate in parallel, doubling the total processing capacity.

[0045] Please see Figure 3 As shown, in other embodiments, the lithium liquid tank 125 after primary purification and phosphorus and fluorine removal also includes a secondary lithium liquid purification unit and a tertiary lithium liquid purification unit.

[0046] The secondary lithium liquid impurity removal unit includes: The first and second secondary lithium liquid impurity removal tanks 126 and 127 are arranged in parallel, wherein the first and second secondary lithium liquid impurity removal tanks 126 and 127 are used to pass in the lithium liquid purified by the phosphorus and fluorine removal resin tank 124 and the lithium hydroxide solution. The lithium liquid secondary impurity removal filter press 128 is connected to the first secondary lithium liquid impurity removal tank 126 and the second secondary lithium liquid impurity removal tank 127 respectively, and is used to filter and form lithium liquid secondary impurity removal filtrate and secondary impurity removal filter residue. The first 1 / 10 to 1 / 5 volume of the filtrate of the lithium liquid secondary impurity removal filter press 128 is used to further backwash and clean the first secondary lithium liquid impurity removal tank 126 and the second secondary lithium liquid impurity removal tank 127. The lithium liquid secondary impurity removal filtrate tank 129 is connected to the lithium liquid secondary impurity removal filter press 128 and is used to store the lithium liquid secondary impurity removal filtrate.

[0047] After one purification process (pH 6.8-7.5) and resin-based phosphorus and fluoride removal, trace amounts of Fe still remain in the lithium solution. 3+ / Al 3+ / Cu 2+ Residual impurities need to be removed through secondary impurity removal. Specifically, the core purpose of secondary impurity removal is to allow the above-mentioned trace transition metal hydroxides and basic salts to fully precipitate in a higher and more precise pH range (8.0-8.5) by extending the aging time, while keeping the pH stable within the safe upper limit of lithium loss.

[0048] The first and second secondary lithium liquid impurity removal tanks 126 and 127 are slender tanks with a height-to-diameter ratio of 3.5:1 to 5:1 (the height-to-diameter ratio of the primary impurity removal tank is usually 2.2:1 to 2.8:1), and are connected by a porous baffle plate along the axial direction. The specific structure is as follows: Upper reaction zone (occupying 25%-30% of the tank height): equipped with lithium hydroxide micro-mist spray ring pipe and online pH closed-loop control, and is basically the same as the first primary lithium liquid impurity removal tank 120 and the second primary lithium liquid impurity removal tank 121; Mid-section flocculation zone (35%-40% of tank height): No stirring is installed, only 2-3 layers of vertical baffles: each baffle is 15%-20% of the tank diameter in width, with a spacing of 300-500mm between baffles, and is welded to the tank wall. The baffles are staggered at a 30°-45° angle to the radial direction, forming an "S"-shaped flow channel, which reduces the liquid flow velocity to 0.3-0.8cm / s, promoting the collision and aggregation of micro-flocs; the baffles can be made of polypropylene (PP) or fiberglass (FRP), with a surface finish Ra≤1.6μm to reduce floc adhesion; a second porous baffle is installed between the bottom and the lower section: the porosity is 15%-20%, the pore size is 10-15mm, and a 200-400 mesh stainless steel wire mesh (316L material) is laid on top of the baffle to intercept large-diameter flocs that accidentally float to the surface, preventing blockage of the lower section slag discharge; Lower settling zone (occupying 30%-35% of the tank height): Conical bottom design, cone angle 45°-60°, with a central slag discharge pipe at the bottom, and the supernatant enters the filter press through the overflow weir.

[0049] The primary impurity removal tank adopts a "stirring-reaction" mode, which is suitable for high-concentration rapid sedimentation. The secondary impurity removal is for trace amounts of low-concentration impurities and adopts a "micro-disturbance-long aging" mode, which allows the low-concentration floc particles to grow, reducing the specific resistance of subsequent pressure filtration by 40%-50%, and avoiding the breakage of micro-flocs caused by stirring and shearing.

[0050] The filter cloth of the lithium liquid secondary impurity removal filter press 128 adopts a three-layer composite structure of "support layer + deep filtration layer + surface interception layer": Support layer: Polyester monofilament base fabric (warp strength ≥2000N / 5cm); Deep filtration layer: Polypropylene microfiber needle-punched felt (fiber diameter 1-5μm, thickness 2-3mm), used for deep filtration to retain fine hydroxide flocs with a particle size of 1-10μm; Surface retention layer: Polyamide nanofiber coating layer (pore size 0.5-2μm), used for surface fine filtration.

[0051] The lithium liquid secondary impurity removal filter press 128 deals with submicron-sized flocs that may still exist after secondary aging. It requires a composite structure of deep filtration and surface coating to ensure that the effluent turbidity is stable at <<1 NTU, providing a feed with almost no suspended solids for subsequent tertiary impurity removal or evaporation crystallization.

[0052] The three-stage lithium liquid impurity removal unit includes: The first and second lithium liquid impurity removal tanks 130 and 131 are arranged in parallel, wherein the first and second lithium liquid impurity removal tanks 130 and 131 are used to introduce lithium liquid purified by the secondary lithium liquid impurity removal unit and lithium hydroxide solution. The lithium liquid three-stage impurity removal precision filter 132 is connected to the first and third lithium liquid impurity removal tanks 130 and 131 respectively, and is used for pressure filtration to form lithium liquid three-stage impurity removal filtrate and three-stage impurity removal filter residue. The lithium liquid three-stage impurity removal filtrate tank 133 is connected to the lithium liquid three-stage impurity removal precision filter 132 and is used to store the lithium liquid three-stage impurity removal filtrate.

[0053] The structure of the tertiary lithium liquid impurity removal unit is basically the same as that of the secondary lithium liquid impurity removal unit. The difference is that the tertiary lithium liquid impurity removal precision filter 132 is a vertical cylindrical pressure vessel, which is different from the plate and frame filter press used in the upstream primary / secondary impurity removal. Its design pressure is 0.4-0.8MPa, design temperature is ≤80℃, height-to-diameter ratio is 3:1 to 4:1, and the shell material is 316L stainless steel with overall electropolishing treatment (inner surface roughness Ra≤0.4μm), or carbon steel shell lined with 3mm PTFE and electropolished to prevent trace metal ions from dissolving and contaminating the battery-grade lithium liquid.

[0054] The lithium liquid triple impurity removal precision filter 132 has an upper and lower tube sheet internally, with the distance between the two plates being 95%-98% of the effective length of the filter element. Filter element mounting holes (with hole diameter matching the filter element interface, such as DN25-DN40) are arranged in an equilateral triangle pattern on the tube sheet. A single filter can be connected in parallel with 3-9 filter elements (configured according to the throughput, typically 5-7 elements). The effective filtration area of ​​a single filter element is 0.2-0.5 m². 2 .

[0055] Each filter element adopts a three-layer coaxial composite structure of "outer layer pre-filtration + middle layer fine filtration + inner layer support", and its solid parameters are shown in Table 1.

[0056] Table 1 shows the parameters of the filter element in the lithium liquid three-stage impurity removal precision filter.

[0057] The turbidity of the effluent from the upstream lithium liquid secondary impurity removal filter press 128 is typically << 1 NTU, but it may still contain subparticles of 0.5-5 μm. This precision filter first forms a "bridging layer" through a 5-10 μm metal felt pre-filtration layer, and then achieves precise terminal retention with a 0.5-2 μm PTFE pleated membrane. The effluent turbidity is stable at << 0.2 NTU, and the total amount of residual metal ions such as Fe, Cu, Ni, and Al in the effluent is << 0.5 mg / L, meeting the front-end quality requirements for battery-grade lithium salt evaporation and crystallization.

[0058] Please see Figure 4 The present invention further provides an extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder, comprising: Extraction unit 134, which is connected to lithium liquid three-stage impurity removal filtrate tank 133, is used to extract and separate lithium-supported organic phase and raffinate; The carbon dioxide back-extraction unit 136 and the sulfuric acid back-extraction unit 138, which are arranged in parallel, are respectively connected to the extraction unit 134. The carbon dioxide back-extraction unit 136 is used to back-extract the lithium-supported organic phase to obtain lithium bicarbonate back-extraction solution, and the sulfuric acid back-extraction unit 138 is used to back-extract the lithium-supported organic phase to obtain lithium sulfate back-extraction solution. The lithium bicarbonate back-extraction solution de-oiling unit 137 is connected to the carbon dioxide back-extraction unit 136 to de-oil the lithium bicarbonate back-extraction solution and finally obtain a lithium bicarbonate solution. The lithium sulfate back-extraction solution de-oiling unit 139 is connected to the carbon dioxide back-extraction unit 136 and is used to de-oil the lithium sulfate back-extraction solution. The bipolar membrane unit 140 is connected to the lithium sulfate back-extraction solution de-oiling unit 139 and is used to separate the lithium sulfate back-extraction solution after de-oiling to obtain lithium sulfate solution, sulfuric acid and lithium hydroxide monohydrate solution. The obtained sulfuric acid and lithium hydroxide monohydrate solution are transferred to the leaching process and the impurity removal process.

[0059] In one embodiment, the organic phase used in the extraction unit 134 is a neutral phosphorus-oxygen-carboxylic acid synergistic extraction system, specifically composed of: Main extractant: 20%-35% tributyl phosphate (TBP) or triisoamyl phosphate (TiAP), providing phosphorus-oxygen coordination atoms and Li + Formation of neutral coordination complexes; Co-extraction agent: 5%-10% naphthenic acid or 2-ethylhexanoic acid (Versatic 10) to enhance the extraction of Li. + Selectivity and significant inhibition of Na + K + Co-extraction of alkali metal ions; Diluent: 55%-70% of 260# sulfonated kerosene or dearomatic solvent oil, used to adjust the density, viscosity and surface tension of the organic phase, making it easy to separate into layers with the aqueous phase; Modifier: 2%-5% isodecanol or 2-ethylhexanol, to prevent the formation of a third phase under high load and improve interfacial tension.

[0060] It should be noted that the newly prepared organic phase needs to be saponified with a 5%-8% sodium carbonate solution to a saponification rate of 40%-60% before use, and then subjected to saturated Li. + The solution is pre-equilibrated for 2-3 cycles to remove trace acidic impurities and stabilize the phase interface, reducing the risk of emulsification during normal operation.

[0061] Extraction unit 134 can be composed of 3-5 stages of box-type mixing and clarifying extraction tanks connected in series to form a countercurrent extraction section, wherein each stage of box-type mixing and clarifying extraction tank includes: The mixing chamber can be a cuboid or a cylindrical shape, with an effective volume of 50-200L (matched according to the processing capacity), and is equipped with mechanical stirring. Clarification chamber: Adjacent to the mixing chamber, with a cross-sectional area 1.5-2.5 times that of the mixing chamber, and equipped with an interface control weir plate and a light / heavy phase collection tank.

[0062] The feed inlet of the mixing chamber allows the organic phase and the liquid (aqueous phase) to enter tangentially from the upper sides of the mixing chamber, respectively. The feed inlet of the mixing chamber can be further equipped with a guide bend to allow the two phases to form a swirling premix in the stirring zone, shortening the time to reach dispersion equilibrium. An overflow baffle is installed between the mixing chamber and the clarification chamber, with a flow hole at the bottom. The mixed phase overflows into the clarification chamber. The height of the baffle is 70%-80% of the height of the mixing chamber to prevent short-circuiting of insufficiently mixed fluids.

[0063] As a further improvement, an adjustable-height weir plate (manual or electric adjustment, accuracy ±1mm) is provided in the middle of the clarification chamber. The organic phase (light phase) overflows from the upper overflow weir to the next stage mixing chamber or the organic phase collection manifold, while the raffinate (heavy phase) is discharged from the lower underflow outlet to the previous stage mixing chamber. In one embodiment, the upper part of the clarification chamber can be further filled with stainless steel wire mesh coalescing packing (wire diameter 0.1-0.2mm, porosity 95%-98%, packing layer height 100-200mm) to promote the coalescence and sedimentation of aqueous droplets entrained in the organic phase. In addition, a long strip of glass sight glass (height covering the entire interface adjustment range) can be provided on the side wall of the clarification chamber for manual verification of the interface position.

[0064] In one embodiment, the loaded organic phase output from the extraction unit 134 first enters a loaded organic phase buffer tank. A three-way proportional control valve assembly is installed on the buffer tank's main discharge pipe to divert the loaded organic phase to two back-extraction units according to a set ratio. Furthermore, the system includes a central control unit (CCU) that receives order demand signals from the MES / ERP system, level signals from each buffer tank, the production capacity status of the bipolar membrane unit 140, and the real-time flow rate of the loaded organic phase from the extraction unit. This dynamically optimizes the two-way flow ratio to ensure a balance between lithium carbonate product output and the self-sufficiency of intermediate raw materials.

[0065] Specifically, under normal production mode, the split ratio is set in the CCU according to downstream demand, with a typical range of CO2 back-extraction path: sulfuric acid back-extraction path = 1:1 to 3:1 (adjustable). When lithium carbonate order demand surges or inventory is low, the lithium carbonate product priority mode is activated, and the CCU automatically increases the proportion of CO2 back-extraction circuit while reducing the proportion of sulfuric acid back-extraction circuit. When the system's sulfuric acid or lithium hydroxide recycling inventory is insufficient (e.g., the extraction conditioning pH is difficult to maintain, or the LiOH replenishment in the impurity removal tank is insufficient), it automatically enters the intermediate raw material self-sufficiency priority mode. The CCU automatically increases the proportion of sulfuric acid back-extraction path and prioritizes the activation of the bipolar membrane unit 140 to produce recycled acid and alkali.

[0066] Finally, the opening accuracy of the three-way proportional valve can be controlled within ±1%, the response time is << 10s, and the single-channel flow fluctuation is controlled within ±3% of the set value.

[0067] Existing CCUs prioritize process stability and do not consider the time-varying nature of electricity costs. However, the bipolar film unit 140 is a major power consumer (accounting for 35%-45% of total system power consumption). The TSD (Time-of-Use Dispatch Module) can further integrate with the grid's time-of-use pricing signals (peak, normal, and off-peak hours), reducing the unit lithium product power consumption cost by 15%-20% without sacrificing on-time order delivery rates. Specifically: The CCU adopts a three-layer nested architecture of "demand layer - economic layer - execution layer", integrating the original independent production prioritization mode with TSD peak-valley scheduling into a unified decision: α final =α base +Δα demand +Δα electricity , Wherein, α base Δα represents the baseline split ratio under the current production mode. demand Δα is the dynamic adjustment amount at the demand layer. electricity The adjustment amount for the economic level electricity price is determined by a weighted fusion with constraints, rather than a simple summation, to ensure that the following constraints are met at any given time: minimum lithium carbonate production (order delivery), intermediate raw material safety stock (system non-shutdown), and bipolar film current density (300-800 A / m). 2 ).

[0068] Electricity price embedding under normal production mode: Under normal production mode (CO2 back-extraction circuit: sulfuric acid back-extraction circuit = 1:1 to 3:1 adjustable), TSD is no longer an independent module, but rather an economic layer correction coefficient that adjusts the benchmark split ratio in real time, for example: 1. Off-peak electricity hours (22:00-8:00 the next day) Economic layer output λ valley = +0.15 to +0.25 (shift towards the sulfuric acid path); If α base = 0.60 (CO2 route accounts for 60%), then α final = 0.60 - 0.20 = 0.40 (CO2 path decreases to 40%, sulfuric acid path increases to 60%) At this time, the bipolar membrane is operating at full load (600-800 A / m). 2 Pre-charge the sulfuric acid and LiOH stockpiles to 75%-80% high liquid level; Meanwhile, the lithium carbonate production line maintains its output using pre-production inventory during the daytime, while lithium carbonate production during off-peak hours drops to 60%-70% of the daytime baseline, which is then absorbed by the crystallizer buffer tank.

[0069] 2. Peak power hours (9:00-12:00, 14:00-17:00) Economic layer output λ peak = -0.10 to -0.20 (offset towards CO2 path); If α base = 0.60, then α final = 0.60 + 0.15 = 0.75 (CO2 path increases to 75%, sulfuric acid path decreases to 25%) At this point, the bipolar membrane pressure drops to 200-300 A / m. 2 In case of low current density or shutdown, the acid and alkali inventory pre-charged overnight will be consumed first. The lithium carbonate production line is operating at full capacity, processing the pre-production back-extraction solution from the previous night.

[0070] 3. Normal period λ flat =0, α final =α base The economic layer does not intervene; the demand layer is completely in control.

[0071] Additionally, if a lithium carbonate priority mode is encountered during off-peak electricity hours, the conflict can be resolved through coordination and conflict mitigation as follows: 1. Collaborative Scenario: When orders surge during peak hours, the following steps should be taken. The demand side has determined to enter a lithium carbonate priority mode, α base Automatically adjusted to 0.75-0.85; The economic layer is at its peak power level, λ peak = -0.15 (should have further boosted CO2 levels); Both are superimposed in the same direction: α final = 0.80 + 0.15 = 0.95 (CO2 circuit accounts for 95%, sulfuric acid circuit only 5% to maintain the minimum operation of bipolar membrane); At this point, the bipolar film can operate at 300 A / m 2 Operating at the lowest current density, it only maintains membrane stack wetness to prevent scaling and the generation of acids and alkalis; however, the consumption of intermediate raw materials relies entirely on inventory. If inventory falls below the 25% safety line, a downgrade instruction is triggered on the demand side: α base The value was forcibly reduced from 0.80 to 0.65, and the system was switched to a hybrid mode of "lithium carbonate priority + inventory protection" to ensure that the system does not stop.

[0072] 2. Conflict Scenario: Order surge during off-peak hours, handled as follows. The requirements layer requires α base=0.80 (lithium carbonate preferred), economic level requires λ valley =+0.20 (sulfuric acid route preferred); Conflict arbitration logic: When the delivery cycle of a lithium carbonate order is less than 24 hours (urgent order), the demand layer weight w demand =0.7, economic layer weight w electricity = 0.3, α final = 0.80 - 0.20×0.3 = 0.74 (CO2 route still accounts for 74%, but it yields 6 percentage points compared to the pure demand model, while sulfuric acid route gets 26% to make moderate use of off-peak electricity). Bipolar films at 500-600 A / m 2 Operating at a medium load replenishes some inventory without completely crowding out lithium carbonate production capacity. When the order delivery cycle is greater than 72 hours (for regular orders), the economic layer weight increases to 0.6, and α... final = 0.80 - 0.20×0.6 = 0.68, making better use of off-peak electricity to produce intermediate raw materials, and then switching to lithium carbonate production during the day.

[0073] The carbon dioxide back-extraction unit 136 consists of 2-3 stages of box-type countercurrent mixing and clarifying extraction tanks connected in series, arranged in a stepped or horizontal line, with each stage connected by an inter-stage connecting pipe. Each stage consists of a combined mixing chamber and a clarifying chamber, with the mixing chamber located at the front of the clarifying chamber and a flow channel between the two chambers. The bottom of the mixing chamber of the carbon dioxide back-extraction unit 136 is equipped with a titanium alloy powder sintered aeration disc (pore size 10-30μm), and the top is equipped with a double-layer six-bladed disc turbine propeller driven by a variable frequency reduction motor, with a rotation speed of 80-150rpm. The outer wall of the mixing chamber is equipped with a semi-pipe spiral jacket for circulating cooling water to maintain a temperature of 20-35℃. The rear of the clarifying chamber is equipped with a sawtooth-shaped light phase overflow weir and a radio frequency admittance interface instrument. The upper part of the clarifying chamber, in front of the light phase overflow weir, is equipped with a stainless steel wire mesh coalescing layer (316L wire diameter 0.1-0.2mm, mesh size 1-2mm, filling height 100-200mm) to promote the coalescence and sedimentation of trace amounts of aqueous droplets entrained in the light phase.

[0074] The sulfuric acid back-extraction unit 138 is also composed of 2-3 stages of box-type countercurrent mixing, clarification, and extraction tanks connected in series, arranged in a stepped or horizontal line, with each stage connected by an inter-stage connecting pipe. Each stage consists of a combined mixing chamber and a clarification chamber, with the mixing chamber located at the front of the clarification chamber and a flow channel between the two chambers. The mixing chamber of the sulfuric acid back-extraction unit 138 has an annular sulfuric acid distribution pipe at the top and 4-8 small holes evenly distributed downwards at 45° at the bottom. The stirring speed is 100-200 rpm to ensure that the sulfuric acid back-extraction agent is evenly sprayed into the organic phase, avoiding local over-acidification that could lead to localized acidification, demulsification, or the formation of a third phase. The outer wall of the mixing chamber is equipped with a semi-pipe spiral jacket for circulating hot water to maintain a temperature of 40-60°C. The volume of the clarification chamber of the sulfuric acid back-extraction unit 138 is increased to 2.0-2.5 times that of the mixing chamber. This is because the sulfuric acid back-extraction system has low interfacial tension, is prone to emulsification, and requires a longer clarification time.

[0075] The lithium bicarbonate back-extraction solution oil removal unit 137 includes a dissolved air flotation oil removal tank, a coalescing separator, an activated carbon adsorption column, and a precision security filter connected in series along the process.

[0076] The dissolved air flotation oil removal tank is equipped with a titanium alloy powder sintered microporous release device at the bottom and a bridge-type rotary oil scraper at the top. Part of the oil-removed clear liquid is pressurized to 0.3-0.5MPa by a dissolved air pump at a 10%-20% reflux ratio and then released as dissolved air, removing floating oil and dispersed oil with a particle size >10μm. The coalescence separator is equipped with 2-4 sets of glass fiber-polyester fiber composite coalescence filter elements. The back-extraction liquid passes through the filter elements from bottom to top. After the emulsified oil droplets coalesce and grow, they float to the top oil collection bag, removing emulsified oil with a particle size of 1-10μm. The activated carbon adsorption column consists of two parallel vertical cylindrical adsorption columns, one in use and one on standby. It is filled with coconut shell activated carbon for water purification and has an empty tower flow rate of 5-8 BV / h to adsorb dissolved organic matter. The precision security filter is equipped with a 0.5μm or 1.0μm melt-blown polypropylene filter element or a pleated PTFE membrane filter element. Each unit outlet is equipped with an online turbidity meter, an infrared oil analyzer, or an ultraviolet fluorescence oil analyzer. When the oil content of the effluent exceeds the standard, it automatically switches to a backup branch or returns to the front end for reprocessing. The waste oil discharged from the flotation and coalescence separator is collected into a settling separation tank, and the upper organic phase is reused in the extraction unit.

[0077] The lithium sulfate back-extraction solution oil removal unit includes an acid-resistant dissolved air flotation oil removal tank, an acid-compatible coalescing separator, an acid-resistant activated carbon adsorption column, a precision security filter, and a pH fine-tuning buffer tank, all connected in series. The acid-resistant dissolved air flotation oil removal tank has a carbon steel shell lined with 5mm PTFE or an integral FRP structure. It features a ceramic microporous aeration pipe at the bottom and a PTFE-coated bridge-type rotary oil skimmer at the top. A cooling water jacket is installed on the outer wall of the feed pipe to reduce the temperature of the back-extraction solution from 40-60℃ to 30-40℃. The acid-compatible coalescing separator is a carbon steel shell lined with 3-5mm PTFE. The filter features a PTFE or integral PVDF structure, with an internal PTFE fiber and glass fiber composite coalescing filter element. The top oil collection area is equipped with a PTFE sight glass and a pneumatically operated fluoropolymer-lined ball valve. The acid-resistant activated carbon adsorption column consists of two parallel FRP vertical adsorption columns filled with acid-washed coconut shell activated carbon, with an acid-resistant ceramic ball pad at the bottom. It is regenerated by soaking in 1%-2% dilute sulfuric acid. The precision security filter contains a PTFE pleated membrane filter element or a PVDF melt-blown filter element with an accuracy of 0.45-0.5μm. The pH fine-tuning buffer tank has a capacity equivalent to 1.5-2.0 hours of bipolar membrane unit processing capacity. It is equipped with an acid-resistant online pH meter and a low-speed stirrer, and the pH is stabilized at 3.5-4.5 by injecting bipolar membrane recycled alkali. Each unit outlet is equipped with an online infrared oil analyzer, turbidity meter, and pH meter. When the oil content exceeds the standard, it is automatically returned to the front end for reprocessing.

[0078] Those skilled in the art should understand that the above embodiments are merely for illustrative purposes and are not intended to limit the scope of this application. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of this application.

Claims

1. An extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder, characterized in that: include: An extraction unit, which is connected to the lithium liquid three-stage impurity removal filtrate tank, is used to extract and separate the lithium-supported organic phase and the raffinate; The carbon dioxide back-extraction unit and the sulfuric acid back-extraction unit are arranged in parallel and are respectively connected to the extraction unit. The carbon dioxide back-extraction unit is used to back-extract the lithium-supported organic phase to obtain lithium bicarbonate back-extraction solution, and the sulfuric acid back-extraction unit is used to back-extract the lithium-supported organic phase to obtain lithium sulfate back-extraction solution. The lithium bicarbonate back-extraction solution de-oiling unit is connected to the carbon dioxide back-extraction unit to de-oil the lithium bicarbonate back-extraction solution and finally obtain a lithium bicarbonate solution. A lithium sulfate back-extraction solution oil removal unit is connected to the carbon dioxide back-extraction unit for oil removal treatment of the lithium sulfate back-extraction solution; The bipolar membrane unit is connected to the lithium sulfate back-extraction solution de-oiling unit and is used to separate the lithium sulfate back-extraction solution after de-oiling to obtain lithium sulfate solution, sulfuric acid and lithium hydroxide monohydrate solution. The obtained sulfuric acid and lithium hydroxide monohydrate solution are transferred to the leaching process and the impurity removal process.

2. The extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder according to claim 1, characterized in that: The organic phase used in the extraction unit is a neutral phosphorus-oxygen-carboxylic acid synergistic extraction system, specifically composed of: Main extractant: 20%-35% tributyl phosphate or triisoamyl phosphate; Co-extractant: 5%-10% naphthenic acid or 2-ethylhexanoic acid; Diluent: 55%-70% of 260# sulfonated kerosene or dearomatic solvent oil; Modifier: 2%-5% isodecanol or 2-ethylhexanol.

3. The extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder according to claim 2, characterized in that: The newly prepared organic phase needs to be saponified with a 5%-8% sodium carbonate solution to a saponification rate of 40%-60% before use, and then subjected to saturated Li. + The solution is pre-equilibrated for 2-3 cycles.

4. The extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder according to claim 1, characterized in that: The extraction unit employs a countercurrent extraction section consisting of 3-5 stages of box-type mixing and clarifying extraction tanks connected in series. Each stage of the box-type mixing and clarifying extraction tank includes: The mixing chamber is equipped with mechanical agitator. Clarification chamber: Adjacent to the mixing chamber, with a cross-sectional area 1.5-2.5 times that of the mixing chamber, and equipped with an interface control weir plate and a light / heavy phase collection tank.

5. The extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder according to claim 1, characterized in that: The loaded organic phase output from the extraction unit first enters the loaded organic phase buffer tank. The main pipe of the loaded organic phase buffer tank is equipped with a three-way proportional regulating valve group to divert the loaded organic phase to two back-extraction units according to a set ratio. The system is also equipped with a central coordination controller to receive order demand signals from MES / ERP, liquid level signals from each buffer tank, production capacity status of the bipolar membrane unit 140, and real-time flow rate of the loaded organic phase in the extraction unit, and dynamically optimize the two-way diversion ratio to ensure the balance between lithium carbonate product output and the self-sufficiency of intermediate raw materials.

6. The extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder according to claim 1, characterized in that: The carbon dioxide back-extraction unit consists of 2-3 stages of box-type countercurrent mixing and clarification extraction tanks connected in series, arranged in a stepped or horizontal line, with each stage connected by an inter-stage connecting pipe. Each stage consists of a combined mixing chamber and a clarification chamber, with the mixing chamber located at the front of the clarification chamber and a flow channel between the two chambers. The bottom of the mixing chamber of the carbon dioxide back-extraction unit is equipped with a titanium alloy powder sintered aeration disc, and the top is equipped with a double-layer six-bladed disc turbine propeller driven by a variable frequency reduction motor. The outer wall of the mixing chamber is equipped with a semi-pipe spiral jacket for circulating cooling water to maintain a temperature of 20-35°C. The tail of the clarification chamber is equipped with a sawtooth-shaped light phase overflow weir and a radio frequency admittance interface instrument. A stainless steel wire mesh coalescence layer is installed in the upper part of the clarification chamber and in front of the light phase overflow weir to promote the coalescence and sedimentation of trace water droplets entrained in the light phase.

7. The extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder according to claim 1, characterized in that: The sulfuric acid back-extraction unit 138 consists of 2-3 stages of box-type countercurrent mixing, clarification, and extraction tanks connected in series, arranged in a stepped or horizontal line, with each stage connected by an inter-stage connecting pipe. Each stage consists of a combined mixing chamber and a clarification chamber, with the mixing chamber located at the front of the clarification chamber and a flow channel between the two chambers. The mixing chamber of the sulfuric acid back-extraction unit has an annular sulfuric acid distribution pipe at the top and 4-8 small holes at a downward 45° angle evenly distributed at the bottom. The stirring speed is 100-200 rpm to ensure that the sulfuric acid back-extraction agent is evenly sprayed into the organic phase, avoiding local over-acidification that could lead to localized acidification, demulsification, or the formation of a third phase. The outer wall of the mixing chamber is equipped with a semi-pipe spiral jacket for circulating hot water to maintain a temperature of 40-60°C. The volume of the clarification chamber of the sulfuric acid back-extraction unit is increased to 2.0-2.5 times that of the mixing chamber.

8. The extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder according to claim 1, characterized in that: The lithium bicarbonate back-extraction solution oil removal unit includes a dissolved air flotation oil removal tank, a coalescing separator, an activated carbon adsorption column, and a precision security filter connected in series along the process.

9. The extraction system for recovering and purifying lithium liquid from lithium iron phosphate black powder according to claim 1, characterized in that: The lithium sulfate back-extraction solution oil removal unit includes an acid-resistant dissolved air flotation oil removal tank, an acid-compatible coalescing separator, an acid-resistant activated carbon adsorption column, a precision security filter, and a pH fine-tuning buffer tank connected in series along the process.

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