A recycling method and a recycling device

Abstract

The application provides a recovery method and a recovery device. The recovery method comprises the following steps: performing trivalent iron-electrolytic reduction treatment on a delithiated phosphorus-iron slag system to obtain a reduction system; performing impurity removal treatment on the reduction system to obtain a divalent iron system; and performing divalent iron-electrolytic oxidation treatment on the divalent iron system to obtain a trivalent iron system. The recovery method can efficiently remove and recover iron elements in delithiated oxidation products of lithium iron phosphate at a lower cost.

Description

Technical Field

[0001] This invention relates to a recycling method and a recycling device, belonging to the field of material recycling technology. Background Technology

[0002] With the development of my country's lithium-ion battery industry, the effective recycling and disposal of waste batteries is a crucial issue for the healthy and sustainable development of this industry. A lithium-ion battery typically includes a positive electrode, negative electrode, electrolyte, separator, casing, and cover plate. Among these, the positive electrode material is the core of the lithium battery, accounting for more than 30% of the battery cost.

[0003] Currently, some researchers electrolyze spent lithium iron phosphate to induce oxidation at the anode, releasing lithium ions and the oxidation product, iron phosphate. The lithium ions can be recycled into lithium hydroxide or lithium carbonate as a lithium source for lithium cathode active materials, while the iron phosphate oxidation product is calcined with the recovered lithium source to produce recycled lithium iron phosphate cathode active materials. However, the recycled iron phosphate often contains significant amounts of impurities such as aluminum and titanium, which inevitably reduces the purity of the recycled lithium iron phosphate cathode active material, making it unsuitable for battery applications.

[0004] Therefore, it is essential to develop an economical, environmentally friendly, and efficient recycling method suitable for recycling cathode materials from waste batteries. Summary of the Invention

[0005] This invention provides a recycling method that can recover iron from waste lithium iron phosphate with high purity and low cost.

[0006] The present invention also provides a recycling device that can be used to implement the above-described recycling method.

[0007] This invention provides a recycling method, comprising the following steps:

[0008] The lithium-free phosphorus iron slag system was subjected to trivalent iron-electrolytic reduction treatment to obtain a reduced system.

[0009] The reduction system is subjected to impurity removal treatment to obtain a divalent iron system;

[0010] The divalent iron system was subjected to divalent iron-electrolytic oxidation treatment to obtain a trivalent iron system.

[0011] In the recycling method described above, the impurity content in the divalent iron system is less than 100 ppm. The impurities mentioned here are aluminum, titanium, and copper impurities.

[0012] The recycling method described above, wherein the impurity removal process includes at least one of a titanium ion removal step, an aluminum ion removal step, and a copper ion removal step.

[0013] The recovery method described above is characterized in that the impurity removal treatment includes at least one of impurity metal resin adsorption treatment, reduction treatment, and pH adjustment treatment.

[0014] In the recovery method described above, the trivalent iron-electrolytic reduction treatment and the divalent iron-electrolytic oxidation treatment are the cathode-side reduction reaction and the anode-side oxidation reaction of the same electrolytic treatment, respectively.

[0015] In the recycling method described above, the trivalent iron-electrolytic reduction treatment and the divalent iron-electrolytic oxidation treatment are the cathode-side reduction reaction and the anodic-side oxidation reaction of different electrolytic treatments, respectively.

[0016] The recycling method described above further includes the step of using the trivalent iron system as an iron source to generate iron phosphate, lithium iron phosphate, or lithium manganese iron phosphate.

[0017] In the recycling method described above, the delithiated iron phosphate slag system is a delithiated iron phosphate slag leachate or an electrode containing delithiated iron phosphate slag.

[0018] In the recycling method described above, wherein the lithium-phosphorus-iron slag system,

[0019] The molar concentration of ferric ions is not less than 0.001 M; and / or,

[0020] The iron content by mass is not less than 0.1%.

[0021] In the recycling method described above, wherein, in the divalent iron system,

[0022] The molar concentration of ferrous ions is not less than 0.001 M; and / or,

[0023] The iron content by mass is not less than 0.1%.

[0024] In the recycling method described above, the voltage of the trivalent iron-electrolytic reduction treatment is 1~10V.

[0025] In the recycling method described above, wherein the trivalent iron-electrolytic reduction treatment and / or divalent iron-electrolytic oxidation treatment,

[0026] The anode is a titanium plate or a titanium electrode with an anode coating, wherein the anode coating includes at least one selected from ruthenium-iridium alloy, ruthenium-iridium coating, iridium-tantalum alloy, ruthenium-iridium-tantalum alloy, titanium suboxide, platinum, gold, and silver; and / or,

[0027] The cathode is a stainless steel electrode, a copper plate, a nickel plate, or a stainless steel electrode with a cathode coating, wherein the cathode coating includes at least one of tin-iron alloy and carbon material; and / or,

[0028] The membrane separating the cathode and anode is a proton membrane or an ion membrane.

[0029] This invention provides a recycling device, comprising a first electrolysis unit, a purification unit, and a second electrolysis unit;

[0030] The cathode chamber outlet of the first electrolysis unit is connected to the inlet of the impurity removal unit, and the outlet of the impurity removal unit is connected to the anode chamber inlet of the second electrolysis unit.

[0031] In the recycling device described above, the first electrolysis unit and the second electrolysis unit are the same electrolysis unit.

[0032] In the recycling device described above, the first electrolysis unit and the second electrolysis unit are different electrolysis units.

[0033] The recovery device described above further includes a monitoring unit and an electronic control unit; the monitoring unit is used to monitor at least one of the following: the content of ferric ions in the first electrolysis unit, the content of ferrous ions in the second electrolysis unit, the liquid level in the first electrolysis unit, the liquid level in the second electrolysis unit, and the content of metal ions in the impurity removal unit.

[0034] The electrical control unit is electrically connected to the monitoring unit, the inlet and outlet of the first electrolysis unit, the inlet and outlet of the impurity removal unit, and the inlet and outlet of the second electrolysis unit, respectively.

[0035] The recycling method of this invention first reduces the lithium-phosphorus iron slag system by electrolysis, efficiently and at low cost reducing ferric iron to ferrous iron, thereby differentiating iron from other impurity elements. Because the impurity metals are different from iron, the subsequent impurity removal process can effectively remove impurity metal ions without affecting the iron, resulting in a high-purity ferrous iron system. The high-purity ferrous iron system is then oxidized to ferric iron by electrolysis, facilitating the recycling of iron and enabling its application in fields with high requirements for impurities, thus broadening the application range of iron-containing materials. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of one embodiment of the recycling device of the present invention;

[0037] Figure 2 This is a schematic diagram of another embodiment of the recycling device of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] The first aspect of this invention provides a recycling method, comprising the following steps:

[0040] The lithium-free phosphorus iron slag system was subjected to trivalent iron-electrolytic reduction treatment to obtain a reduced system.

[0041] The reduction system is subjected to impurity removal treatment to obtain a divalent iron system;

[0042] The divalent iron system was subjected to divalent iron-electrolytic oxidation treatment to obtain a trivalent iron system.

[0043] The recycling method of this invention can be used as a downstream process after lithium recovery from waste lithium iron phosphate, efficiently removing iron from the waste lithium iron phosphate to facilitate iron recovery. The delithiated iron phosphate slag is the residual iron phosphate residue after lithium recovery. In addition to iron, the delithiated iron phosphate slag also contains impurity metals such as titanium, aluminum, and copper. This invention's recycling method achieves efficient separation of iron from impurity metals at a lower cost, ultimately recovering a highly stable trivalent iron system with a significant iron recovery rate.

[0044] Specifically, the ferric ions in the delithiated phosphorus iron slag system are subjected to ferric electrolytic reduction treatment to reduce the ferric ions in the delithiated phosphorus iron slag to ferrous ions, thus obtaining a reduced system.

[0045] It is understandable that as the ferric electrolytic reduction process proceeds, a large number of ferric ions in the delithiated ferric slag system are reduced to ferrous ions, and the resulting reduced system is a system containing a large number of ferrous ions.

[0046] Subsequently, by removing impurities from the reduction system, a ferrous iron system is obtained. This invention does not limit the specific method of impurity removal, as long as it achieves the separation of iron and phosphorus elements from impurities. The specific method depends on the differences between ferrous iron and the impurity metal elements. For example, differences in valence, oxidation potential, etc., can be used to separate ferrous iron from other impurity metal elements.

[0047] Subsequently, the ferrous iron system undergoes ferrous iron-electrolytic oxidation treatment to oxidize ferrous iron to ferric iron, obtaining a ferric iron system and achieving iron recovery from the lithium-phosphorus iron slag. This invention is not limited to the location where the above-mentioned ferric iron-electrolytic reduction treatment is performed; for example, it can be carried out in an electrolytic cell including an anode chamber and a cathode chamber. The cathode chamber is used to contain the cathode electrolyte and the cathode, and the anode chamber is used to contain the anolyte and the anode.

[0048] In this process, the lithium-free phosphorus-iron slag system gains electrons in the cathode chamber and undergoes trivalent iron electrolytic reduction. The invention does not specifically limit the type of system in the corresponding anode chamber, as long as it possesses reducing properties and can lose electrons to undergo an oxidation reaction. For example, it could be one or more reactions such as oxygen evolution reaction, chlorine evolution reaction, oxidation of low-valence ions, reactions generating metal ion oxides, methanol oxidation, and formic acid oxidation.

[0049] In detail, using water as an electrolyte allows the oxygen evolution reaction to occur in the anode chamber, where water is oxidized to produce oxygen and hydrogen ions, as shown in the following ionic equation.

[0050]

[0051] The oxygen generated by the oxygen evolution reaction can be collected and used not only for the chemical oxidation of ferrous iron, but also as a combustion aid in a range of applications that require oxygen as a combustion environment.

[0052] Alternatively, an electrolyte solution containing chloride ions can be used as the electrolyte in the anode chamber to undergo a chlorine evolution reaction, where chloride ions are oxidized to chlorine gas. The ionic equation is as follows.

[0053]

[0054] The chlorine gas generated by the chlorine evolution reaction can be collected and used as a raw material for the chlorination treatment of fine organic chemicals.

[0055] Alternatively, an electrolyte solution containing reducing low-valence ions can be used as the electrolyte in the anode chamber to induce a low-valence ion oxidation reaction. For example, sulfate ions (… ) is oxidized to persulfate ( ) or persulfate free radical ( These free radicals can further participate in various chemical reactions, such as in wastewater treatment, to oxidize organic pollutants and promote their degradation.

[0056] Alternatively, a solution containing metal ions can be used as the anolyte. The metal ions will not only deposit as metal, but may also combine with oxygen or other anions to form metal oxides or composite oxide layers. The resulting metal oxides or composite oxides can be used to manufacture semiconductor materials and ceramic coatings, thus enabling their application in sensor manufacturing or semiconductor manufacturing.

[0057] Alternatively, methanol (CH3OH) can be used as the anolyte to undergo oxidation, producing formaldehyde (HCHO) or other basic raw materials used in organic synthesis.

[0058] Alternatively, formic acid (HCOOH) can be used as an anolyte to oxidize the anode, converting it into carbon dioxide (CO2) and other oxidation products, thus providing a key reaction intermediate for the synthesis of chemical products.

[0059] It's understandable that to obtain a high-purity ferric iron system, the lower the impurity content, the better. The inventors' research shows that when the impurity content in the ferrous iron system is less than 100 ppm, it basically meets the requirements for downstream applications of the recovered ferric iron. Here, impurities mainly refer to aluminum, titanium, and copper impurities.

[0060] Generally, the impurity removal process includes at least one of the following steps: titanium ion removal, aluminum ion removal, and copper ion removal.

[0061] The present invention does not limit the specific method of impurity removal treatment, and may include at least one of impurity metal resin adsorption treatment, reduction treatment and pH adjustment treatment.

[0062] In one specific embodiment, since the oxidation states of iron in the ferrous iron system differ from those of some impurity metal elements (trivalent aluminum, trivalent titanium, and tetravalent titanium), this difference in oxidation states can be used to separate high-valence impurity metal ions from the reduction system. In practical applications, a metal ion adsorption resin can be used to adsorb the impurity metals into the reduction system, thereby separating the high-valence metal ions from the ferrous iron by adsorbing them into the resin.

[0063] Alternatively, the pH value of the divalent system can be adjusted. For example, a pH adjuster can be added to the divalent ferric ion solution to adjust the pH to 2, so that Ti, Al, etc. can form hydroxide precipitates with smaller Ksp values, thereby achieving removal.

[0064] For divalent or monovalent impurity metal ions, in one embodiment, a reducing agent can be added to the divalent iron system for reduction treatment. During the reduction treatment, the reducing agent reduces the divalent metal impurity ions, which have a higher oxidation potential than divalent iron, to elemental form, which is then separated by filtration. For example, taking copper ions as an example, the divalent iron system is reduced using a reducing agent, and the copper ions are reduced to elemental copper, which is then separated from the divalent iron system.

[0065] After the impurity removal process is completed, the ferrous iron system undergoes ferrous iron-electrolytic oxidation treatment. Similarly, the present invention is not limited to the location where the above-mentioned ferrous iron-electrolytic oxidation treatment is performed; for example, it can be carried out in an electrolytic cell including an anode chamber and a cathode chamber. The cathode chamber is used to contain the cathode electrolyte and the cathode, and the anode chamber is used to contain the anolyte and the anode.

[0066] In this process, the ferrous iron system loses electrons in the anode chamber, resulting in ferrous iron electrolytic oxidation. The type of system in the corresponding cathode chamber is not specifically limited in this invention, as long as it is a reaction that can gain electrons and undergo reduction. For example, it could be one or more reactions such as hydrogen evolution reaction, high-valence ion reduction, or metal deposition.

[0067] In detail, using an acidic solution as an electrolyte allows a hydrogen evolution reaction to occur in the cathode chamber, where hydrogen ions are reduced to produce hydrogen gas. The ionic equation is as follows.

[0068]

[0069] The hydrogen gas produced by the hydrogen evolution reaction can be collected and used as a reducing agent or as hydrogen energy storage.

[0070] Alternatively, reduction of high-valence ions may occur, for example... Restored to The ionic equations are as follows:

[0071]

[0072] For example, after high-valence ions are reduced to low-valence ions in the cathode chamber, the low-valence ions can be used to generate specific hydrolysis products or oxides.

[0073] Alternatively, a metal deposition reaction may occur, such as the precipitation of metallic Cu, with the following ionic equation:

[0074]

[0075] The aforementioned metal deposition reaction can be used for metal recovery, cathode surface treatment, and other applications.

[0076] This invention uses the lithium-removed iron-phosphate slag system as the cathode reduction target. By maximizing the reduction of ferric ions in the lithium-removed iron-phosphate slag, and then utilizing the differences between ferrous iron and other impurity elements (such as differences in valence and oxidation potential) to remove other impurity metals, it lays the foundation for high-purity iron recovery. Finally, electrolytic oxidation is used to oxidize ferrous iron to ferric iron, achieving the recovery of stable ferric ions at low cost.

[0077] Furthermore, the above-mentioned ferric iron-electrolytic reduction treatment and ferrous iron-electrolytic oxidation treatment are the cathode-side reduction reaction and the anode-side oxidation reaction of the same electrolytic treatment, respectively.

[0078] In detail, the ferric iron-electrolytic reduction treatment and the ferrous iron-electrolytic oxidation treatment can occur separately in the cathode chamber and anode chamber of the same electrolytic cell. Specifically, at the beginning of the ferric iron-electrolytic reduction treatment in the lithium-phosphorus slag system, any one of the aforementioned reactions can occur in the anode chamber, such as oxygen evolution reaction, chlorine evolution reaction, oxidation of low-valence ions, reaction to generate metal ion oxides, methanol oxidation, and formic acid oxidation. As the ferric iron-electrolytic reduction treatment and impurity removal treatment proceed, after the ferrous iron system is generated, it can be transferred to the anode chamber of the electrolytic cell where the ferric iron-electrolytic reduction treatment is taking place for ferrous iron-electrolytic oxidation treatment to obtain the ferric iron system.

[0079] At this time, in the same electrolytic cell, the cathode undergoes trivalent iron electrolytic reduction treatment, and the anode undergoes divalent iron electrolytic oxidation treatment. The recovery method of the present invention realizes the reduction of trivalent iron and the oxidation of divalent iron in the recovery steps of the lithium-free phosphorus iron slag system by applying a cell voltage to one electrolytic cell only once, thereby achieving the recovery of iron elements in the lithium-free phosphorus iron slag system with high recovery rate, high purity and low cost.

[0080] In this invention, the delithiated iron phosphate slag system continuously enters the cathode side, and after successively completing the trivalent iron-electrolytic reduction treatment and impurity removal treatment, the divalent iron system then enters the anode side corresponding to the cathode side for divalent iron-electrolytic oxidation treatment. This cyclic method also realizes the continuous recycling of the delithiated iron phosphate slag system, improves the recycling efficiency of the delithiated iron phosphate slag, and reduces the application cost of recycled iron.

[0081] Alternatively, the ferric iron-electrolytic reduction treatment and the ferrous iron-electrolytic oxidation treatment are respectively the cathode-side reduction reaction and the anode-side oxidation reaction of different electrolytic processes. That is, the ferric iron-electrolytic reduction treatment and the ferrous iron-electrolytic oxidation treatment occur in different electrolytic cells. In this case, the ferric iron-electrolytic reduction treatment occurs at the cathode of one electrolytic cell, while the anode of that electrolytic cell can undergo any one of the aforementioned reactions such as oxygen evolution reaction, chlorine evolution reaction, oxidation of low-valence ions, reaction to generate metal ion oxides, methanol oxidation, and formic acid oxidation. After the reduction system in the cathode is purified to obtain the ferrous iron system, the ferrous iron system enters the anode of another electrolytic cell to undergo the ferrous iron-electrolytic oxidation treatment, while the cathode of that electrolytic cell can undergo one or more of the aforementioned reactions such as hydrogen evolution reaction, reduction of high-valence ions, and metal deposition.

[0082] Furthermore, after the divalent iron-electrolytic oxidation treatment, the present invention also includes the step of using trivalent iron as an iron source to generate iron phosphate, lithium iron phosphate, or lithium manganese iron phosphate.

[0083] Specifically, by adding phosphorus sources and other metal sources (such as manganese sources) to the trivalent iron system, iron phosphate or iron phosphate doped with other metals can be prepared, and then used as a precursor to undergo a reduction reaction with lithium sources to obtain lithium iron phosphate, lithium manganese iron phosphate, etc.

[0084] In the recycling method of the present invention, the delithiated iron phosphate slag system can participate in the trivalent iron-electrolytic reduction treatment in any form, such as using the delithiated iron phosphate slag leachate as the electrolyte or using the delithiated iron phosphate slag as the electrode.

[0085] In detail, the aforementioned delithiated iron phosphate slag leachate refers to the solution system obtained by dissolving and leaching the delithiated iron phosphate slag with a solvent. For example, an acidic solvent can be used to dissolve the delithiated iron phosphate slag to maximize the leaching of metals in ionic form, resulting in a leaching system including phosphate, ferric, copper, titanium, and aluminum ions. The leaching system is then filtered to remove insoluble substances, yielding the delithiated iron phosphate slag leachate. This delithiated iron phosphate slag leachate participates in the electrolysis reaction as an electrolyte in a conventional electrolysis process.

[0086] When lithium-free phosphorus iron slag is required as an electrode, the electrolysis method is not specifically limited. For example, it can be ordinary electrolysis, solid-phase electrolysis, or suspension electrolysis.

[0087] For example, a solid cathode sheet can be obtained by mixing lithium-free iron phosphate slag with a conductive agent and solvent to form a slurry, and then coating the slurry onto a conductive substrate and drying it; or by coating the slurry onto a substrate, drying it, pressing it into a sheet, and then placing the sheet onto the conductive substrate to obtain a cathode sheet. This cathode sheet is then subjected to a trivalent iron-electrolytic reduction treatment with a solid electrolyte (such as zirconium oxide, polymer electrolyte, etc.) to obtain a reduced divalent iron electrode sheet, which is then leached with acid to obtain a leachate rich in divalent iron.

[0088] Alternatively, ferric phosphate or lithium iron phosphate waste residue can be dispersed in a solution containing a supporting electrolyte (a conductive inorganic salt solution, such as a sulfate solution, sodium chloride solution, etc.) to form a suspended electrode. This method typically requires a stirring device to keep the particles suspended and requires electrode materials with good conductivity as the working and counter electrodes. Specifically, ferric phosphate or lithium iron phosphate microparticles are prepared, ensuring they have suitable particle size and morphology; the microparticles are then mixed with a solution containing a supporting electrolyte to form a stable suspension. The working and counter electrodes are placed in an electrolytic cell, ensuring that the distance between them is appropriate. A magnetic or mechanical stirring device is used to maintain uniform dispersion of the waste residue in the solution. A constant voltage or current is applied by an electrochemical workstation to achieve the electrolytic reduction of ferric iron. After the reaction is complete, the leachate rich in ferrous iron is collected by methods such as filtration and centrifugation.

[0089] To improve the efficiency of ferric iron electrolytic reduction treatment, the molar concentration of ferric ions in the delithiated ferric phosphate slag system can be controlled to be no less than 0.001 M. This results in faster reduction of ferric iron, higher Faraday efficiency, and lower reduction energy consumption. For example, concentrations can be 0.002 M, 0.05 M, 0.1 M, 0.5 M, 1 M, 2 M, 3 M, or any range of molar concentrations.

[0090] Of course, the reduction efficiency of ferric iron can also be improved by limiting the mass percentage of iron. When the mass percentage of iron is not less than 0.1%, it is beneficial to further achieve efficient reduction of ferric iron. Here, the mass percentage of iron refers to the mass percentage of iron in the lithium-phosphorus iron slag.

[0091] During the ferric iron-electrolytic reduction process, the concentration of ferric ions in the cathode electrolyte (current reduction system) can be monitored in real time to determine the current degree of electrolysis. It is understood that a higher concentration of ferrous ions in the reduction system indicates a more thorough ferric iron-electrolytic reduction process; conversely, a lower concentration of ferric ions in the reduction system indicates a more thorough ferric iron-electrolytic reduction process.

[0092] When performing electrolytic oxidation treatment on a purified ferrous iron (Fe2+) system, to improve the efficiency of this treatment and ensure more ferrous ions are oxidized to ferric ions, the molar concentration of ferrous ions in the system can be controlled to be no less than 0.001 M. For example, this can be within the range of 0.005 M, 0.02 M, 0.05 M, 0.1 M, 0.5 M, 1 M, 2 M, 3 M, or any other molar concentration. Alternatively, the oxidation efficiency can be improved by limiting the mass percentage of iron. A mass percentage of iron of no less than 0.1% is beneficial for achieving even higher efficiency in the oxidation of ferrous iron. Here, the mass percentage of iron refers to the mass percentage of iron in the anolyte.

[0093] As for the content of ferrous ions and ferric ions in the ferric system, the present invention does not make specific limitations. Those skilled in the art can determine the degree of ferrous ion electrolytic oxidation treatment according to the specific needs of downstream applications.

[0094] The above-mentioned detection of the content or molar concentration of ferrous and ferric iron can all be performed using redox potentiometric titration.

[0095] Furthermore, the voltage for electrolytic treatment is 1-10V.

[0096] This invention does not limit the specific selection of electrode materials. For example, the anode is a titanium plate, or a titanium electrode with an anode coating, and the anode coating includes at least one of ruthenium-iridium alloy, ruthenium-iridium coating, iridium-tantalum alloy, ruthenium-iridium-tantalum alloy, titanium suboxide, platinum, gold, and silver; the cathode is a stainless steel electrode, a copper plate, a nickel plate, or a stainless steel electrode with a cathode coating, and the cathode coating includes a tin-iron alloy and carbon materials.

[0097] Furthermore, the cathode and anode can be separated by a diaphragm, which can be a proton membrane or an ion membrane, such as polybenzimidazole (PBI), perfluorosulfonic acid (PFSA), sulfonated polyether ether ketone (SPEEK), nonwoven fabric, polyphenylene ether (PPO), etc.

[0098] Of course, a diaphragm may not be required between the anode and cathode chambers. In this case, other compensation methods are needed to suppress unnecessary material migration between the chambers. These methods include, but are not limited to, optimizing electrode arrangement, selecting electrode materials, adjusting electrode spacing, controlling flow rate and stirring speed, setting up in-tank flow guides, and adjusting electrolysis parameters through online analysis.

[0099] A second aspect of the present invention provides a recycling apparatus for performing the aforementioned recycling method of the first aspect. For example... Figure 1 As shown, the recycling device includes a first electrolysis unit 1a, a purification unit 2, and a second electrolysis unit 1b; the cathode chamber outlet of the first electrolysis unit 1a is connected to the inlet of the purification unit 2, and the outlet of the purification unit 2 is connected to the anode chamber inlet of the second electrolysis unit 1b.

[0100] The first electrolysis unit 1a includes at least a cathode chamber for performing ferric iron electrolytic reduction treatment. The second electrolysis unit 1b includes at least an anode chamber for performing ferrous iron electrolytic oxidation treatment; the impurity removal unit 2 is used to remove impurities from the reduction system from the first electrolysis unit 1a, so that the impurity elements are separated from the ferrous iron.

[0101] In practical applications, by applying voltage to the first electrolysis unit 1a, the delithiated iron-phosphorus slag system undergoes ferric iron electrolytic reduction treatment in the cathode chamber, gradually reducing the ferric iron content to obtain a reduced system containing ferrous ions. After exiting the cathode chamber, the reduced system enters the impurity removal unit 2 through the inlet for further impurity removal, yielding a ferrous iron system. After exiting the impurity removal unit 2, the ferrous iron system enters the second electrolysis unit 1b for ferrous iron electrolytic oxidation treatment, yielding a ferric iron system.

[0102] The present invention does not limit the specific material selection of the cathode and anode in the first electrolysis unit 1a and the second electrolysis unit 1b, or the specific selection of the impurity removal unit 2, as long as the above-mentioned processing can be completed efficiently.

[0103] In one specific embodiment, the first electrolysis unit 1a and the second electrolysis unit 1b are both common electrolytic cells in the art. The specific materials of the cathode and anode are the same as those described above. The impurity removal unit 2 is, for example, a metal adsorption resin, which includes, but is not limited to, cation exchange resin or chelating resin.

[0104] Furthermore, such as Figure 2 As shown, the aforementioned first electrolysis unit 1a and second electrolysis unit 1b are the same electrolysis unit 1.

[0105] Specifically, the outlet of the cathode chamber 1A of the electrolysis unit 1 is connected to the inlet of the impurity removal unit 2, the outlet of the impurity removal unit 2 is connected to the inlet of the anode chamber 1B of the same electrolysis unit 1, and the cathode chamber 1A and the anode chamber 1B are separated by a diaphragm 1C.

[0106] At this point, the trivalent iron electrolytic reduction treatment and the divalent iron electrolytic oxidation treatment are carried out separately in the cathode chamber 1A and anode chamber 1B of the same electrolysis unit 1, which helps to reduce the footprint of the recovery device and reduce recovery costs. It can be understood that, at this point, the first electrolysis unit 1a and the second electrolysis unit 1b are the cathode chamber and anode chamber of the same electrolytic cell, respectively.

[0107] Furthermore, the first electrolysis unit 1a and the second electrolysis unit 1b can also be different electrolysis units. It can be understood that, in this case, the first electrolysis unit 1a is the cathode chamber of one electrolysis cell, and the second electrolysis unit 1b is the anode chamber of another electrolysis cell.

[0108] It is understood that, in order to improve recycling efficiency, the above-mentioned device may also include an electrical control unit and a monitoring unit. The monitoring unit is used to monitor at least one of the following: the content of ferric ions in the first electrolysis unit 1a, the content of ferrous ions in the second electrolysis unit 1b, the liquid level in the first electrolysis unit 1a, the liquid level in the second electrolysis unit 1b, and the content of metal ions in the impurity removal unit 2. The electrical control unit is electrically connected to the monitoring unit, the inlet and outlet of the first electrolysis unit 1a, the inlet and outlet of the impurity removal unit 2, and the inlet and outlet of the second electrolysis unit 1b.

[0109] For example, when the monitoring unit detects that the content of ferric ions in the first electrolysis unit 1a (or cathode chamber 1A) has decreased to the target content, it will release an electrical signal to the electronic control unit. After receiving the electrical signal, the control unit will control the outlet of the first electrolysis unit 1a (or cathode chamber 1A) and the inlet of the impurity removal unit 2 to be in the open state, so that the reduction system of the first electrolysis unit 1a (or cathode chamber 1A) enters the impurity removal unit 2 for impurity removal treatment.

[0110] Of course, the monitoring unit can also be used to monitor the liquid level of the first electrolysis unit 1a (or cathode chamber 1A). When the liquid level of the first electrolysis unit 1a (or cathode chamber 1A) is lower than the target liquid level, an electrical signal can be released to make the electronic control unit open the inlet of the first electrolysis unit 1a (or cathode chamber 1A) so that more fresh lithium-phosphorus iron slag system to be treated can enter the first electrolysis unit 1a (or cathode chamber 1A) for trivalent iron-electrolytic reduction treatment.

[0111] Of course, flow pumps can also be installed between the first electrolysis unit 1a (or cathode chamber 1A) and the impurity removal unit 2, and between the second electrolysis unit 1b (or anode chamber 1B) and the impurity removal unit 2. While driving the flow of the material, the flow rate of the material can also be further monitored to further improve the impurity removal efficiency.

[0112] The recycling method of the present invention will be described below through specific embodiments.

[0113] Example 1

[0114] The recycling method in this embodiment includes the following steps:

[0115] 1) The delithiated lithium iron phosphate slag was mixed with sulfuric acid at a molar ratio of 1:1.2, dissolved, and filtered to obtain a delithiated lithium iron phosphate slag leachate with a trivalent iron molar concentration of 1M; the composition of the delithiated lithium iron phosphate slag leachate was shown in Table 1 by ICP analysis.

[0116] 2) The leaching solution of lithium-free phosphorus iron slag is placed in the cathode chamber of the electrolytic cell as the cathode electrolyte, and 1M ferrous sulfate solution is placed in the anode chamber of the electrolytic cell as the initial anode electrolyte. Electrolysis is performed by applying a cell voltage of 4V.

[0117] In the electrolytic cell, the cathode is a stainless steel plate, and the anode is a ruthenium-iridium coated titanium plate; the diaphragm separating the cathode chamber and the anode chamber is a perfluorosulfonic acid proton exchange membrane;

[0118] 3) When the molar concentration of ferric iron C2 in the cathode chamber is 0.001M, electrolysis is stopped, and a reduced system is obtained;

[0119] 4) The reduction system was purified using a metal adsorption resin column (Tulsimer® T-62MP resin was used) to obtain a solution of ferrous iron system.

[0120] 5) The solution of the ferrous iron system was fed into the anode chamber of the electrolytic cell for ferrous iron electrolytic oxidation treatment to obtain the ferric iron system. Testing showed that the molar concentration of ferric iron in the ferric iron system was 1 M, and the mass of ferrous iron per kilogram of the ferric iron system was less than 10 mg.

[0121] Table 1

[0122]

[0123] Example 2

[0124] The recovery method in this embodiment is basically the same as that in embodiment 1. The difference is that in step 4), iron powder is added to the reduction system at a ratio of 2 g iron powder per liter of reduction system for reduction treatment so that some impurities are reduced and precipitated. After filtration, the solution is then adsorbed and removed by a metal adsorption resin column to obtain a solution of ferrous iron system.

[0125] Example 3

[0126] The recycling method in this embodiment is basically the same as that in Embodiment 2, except that the delithiated iron phosphate slag is replaced. The composition of the leachate from the delithiated iron phosphate slag in this embodiment is shown in Table 2.

[0127] Table 2

[0128]

[0129] Example 4

[0130] The recycling method in this embodiment uses the same apparatus as in Embodiment 1. The main difference lies in the cathode electrolyte, requiring adaptive adjustments to the electrolysis method. Specifically, the method includes the following steps:

[0131] 1) The same delithiated iron phosphate residue as in Example 1 was added to a 1 M sulfuric acid solution and stirred thoroughly to form a solid suspension slurry. This suspension slurry was used as the cathode electrolyte, and ferrous sulfate solution was used as the anode electrolyte. Stainless steel was used as the reduction electrode for the cathode, and titanium electrode was used as the anode. Electrolysis was carried out at 4V.

[0132] 2) When the concentration of ferric iron in the solution is detected to be 0.001M, electrolysis is stopped; the leachate rich in ferrous iron is collected by filtration and centrifugation to obtain the reduced system;

[0133] 3) After removing impurities from the reduction system using the method described in Example 1, a solution of the divalent iron system is obtained after the impurity removal treatment;

[0134] 4) The solution of the ferrous iron system was fed into the anode chamber of the electrolytic cell for ferrous iron electrolytic oxidation treatment to obtain the ferric iron system. Testing showed that the molar concentration of ferric iron in the ferric iron system was 1 M, and the mass of ferrous iron per kilogram of the ferric iron system was less than 10 mg.

[0135] Comparative Example 1

[0136] The leaching solution of the delithiated iron phosphate slag in Table 1 is recycled using a method of iron powder reduction and hydrogen peroxide oxidation. The specific method includes the following steps:

[0137] 1) Add 7.8g of reduced iron powder to 100 mL of ferric phosphate slag leachate to carry out a reduction reaction, and obtain a reduction system with a ferric ion molar concentration of 0.001 M;

[0138] 2) The reduction system was purified according to the purification method in Example 1 to obtain a divalent iron system;

[0139] 3) The divalent iron system was oxidized with hydrogen peroxide to obtain a 1M trivalent iron system, and the mass of divalent iron in each kilogram of trivalent iron system was less than 10mg.

[0140] Treating 1 ton of ferric phosphate slag leachate using the above method, the cost of iron powder reduction is approximately 308 yuan, and the cost of hydrogen peroxide oxidation is approximately 192.5 yuan. Converted to recovering each ton of trivalent iron, the cost of iron powder reduction is approximately 5130 yuan, and the cost of hydrogen peroxide oxidation is approximately 3206 yuan. The price of reduced iron powder is 4700 yuan / ton, and the price of hydrogen peroxide is 950 yuan / ton.

[0141] Comparative Example 2

[0142] The lithium-free phosphorus iron slag leachate in Table 2 is recycled using a method of iron powder reduction and hydrogen peroxide oxidation. The specific method includes the following steps:

[0143] 1) Add 6g of reduced iron powder to 100 mL of ferric phosphate slag leachate to carry out a reduction reaction, and obtain a reduction system with a ferric ion molar concentration of 0.001 M;

[0144] 2) The reduction system was purified according to the purification method in Example 1 to obtain a divalent iron system;

[0145] 3) The divalent iron system was oxidized with hydrogen peroxide to obtain a 1M trivalent iron system, and the mass of divalent iron in each kilogram of trivalent iron system was less than 10mg.

[0146] Treating 1 ton of ferric phosphate slag leachate using the above method, the cost of iron powder reduction is approximately 235 yuan, and the cost of hydrogen peroxide oxidation is approximately 146.9 yuan. Converted to recovering 1 ton of trivalent iron, the cost of iron powder reduction is approximately 4895 yuan, and the cost of hydrogen peroxide oxidation is approximately 2447.4 yuan. The price of reduced iron powder is 4700 yuan / ton, and the price of hydrogen peroxide is 950 yuan / ton.

[0147] Comparative Example 3

[0148] The impurity removal method in this comparative example includes the following steps:

[0149] NaOH solution was added to the delithiated phosphorus iron slag leachate with the composition shown in Table 1 to adjust the pH of the system to 3. After precipitation, the solution was filtered to obtain the purified system solution.

[0150] Test case

[0151] 1. The energy consumption and energy cost of recovering a unit mass of trivalent iron in the examples were calculated, and the results are shown in Table 3.

[0152] The energy consumption E (kW·h· / ton) refers to the electrical energy consumed to recover 1 ton of ferric iron. E is calculated according to Equation 1. Since the reduction rate of ferric iron is less than the oxidation rate of ferrous iron, the energy consumption for ferric iron reduction is greater than that for ferrous iron oxidation. Therefore, when ferrous iron oxidation and ferric iron reduction are carried out simultaneously in an electrolytic cell, E in Equation 1 is calculated based on the mass of ferric iron reduced per unit time.

[0153] In the cost of electricity, electricity is calculated at 0.67 yuan / kWh.

[0154] Formula 1

[0155] 2. The iron content in the purified system solutions of the examples and comparative examples was determined by ICP, and the iron recovery rate w was calculated according to the following formula. The results are shown in Table 4.

[0156] w(%) = Iron content in the solution of the ferrous iron system after impurity removal / Iron content in the reduced system

[0157] 3. Ferric phosphate was prepared using the trivalent iron system of each embodiment and comparative example as the iron source. The method for preparing ferric phosphate was implemented using existing technology, and details are not elaborated here. The impurity metals in the prepared ferric phosphate solid phase were detected by ICP, and the composition is shown in Table 4 below.

[0158] Table 3

[0159]

[0160] Table 4

[0161]

[0162] As shown in Tables 3 and 4, the recovery method of the present invention can achieve efficient recovery of ferric iron at a lower cost and with higher purity. In Examples 2 and 3 and Comparative Examples 1 and 2, iron powder was added during the recovery process, resulting in an iron recovery rate higher than 100% calculated according to the above formula. Furthermore, since the addition of sulfuric acid solution to the delithiated iron phosphate slag as a cathode electrolyte not only causes the reduction of ferric iron, but also continuously leaches iron from the delithiated iron phosphate slag, the iron content in the reduction system is determined to be higher than that in Example 1, based on the iron content in the delithiated iron phosphate slag. The iron content in the reduction system of Example 4 in Table 4 is the result of ICP testing of the delithiated iron phosphate slag and calculation based on the mass of the sulfuric acid solution.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A recycling method, characterized in that, Includes the following steps: The lithium-free phosphorus iron slag system was subjected to trivalent iron-electrolytic reduction treatment to obtain a reduced system. The reduction system is subjected to impurity removal treatment to obtain a divalent iron system; The divalent iron system was subjected to divalent iron-electrolytic oxidation treatment to obtain a trivalent iron system.

2. The recycling method according to claim 1, characterized in that, The impurity content in the divalent iron system is less than 100 ppm.

3. The recycling method according to claim 1 or 2, characterized in that, The impurity removal process includes at least one of the following steps: titanium ion removal, aluminum ion removal, and copper ion removal.

4. The recycling method according to any one of claims 1-3, characterized in that, The impurity removal treatment includes at least one of the following: impurity metal resin adsorption treatment, reduction treatment, and pH adjustment treatment.

5. The recycling method according to any one of claims 1-4, characterized in that, The trivalent iron-electrolytic reduction treatment and the divalent iron-electrolytic oxidation treatment are the cathode-side reduction reaction and the anodic-side oxidation reaction of the same electrolytic treatment, respectively.

6. The recycling method according to any one of claims 1-4, characterized in that, The ferric iron-electrolytic reduction treatment and the ferrous iron-electrolytic oxidation treatment are the cathode-side reduction reaction and the anodic-side oxidation reaction of different electrolytic treatments, respectively.

7. The recycling method according to any one of claims 1-6, characterized in that, The recycling method also includes the step of using the trivalent iron system as an iron source to generate iron phosphate, lithium iron phosphate, or lithium manganese iron phosphate.

8. The recycling method according to any one of claims 1-7, characterized in that, The delithiated iron phosphate slag system is a delithiated iron phosphate slag leachate or an electrode containing delithiated iron phosphate slag.

9. The recycling method according to any one of claims 1-8, characterized in that, In the lithium-free phosphorus-iron slag system The molar concentration of ferric ions is not less than 0.001 M; and / or, The iron content by mass is not less than 0.1%.

10. The recycling method according to any one of claims 1-9, characterized in that, In the aforementioned divalent iron system The molar concentration of ferrous ions is not less than 0.001 M; and / or, The iron content by mass is not less than 0.1%.

11. The recycling method according to any one of claims 1-10, characterized in that, The voltage for the trivalent iron-electrolytic reduction treatment is 1~10V.

12. The recycling method according to any one of claims 1-11, characterized in that, In the aforementioned ferric iron-electrolytic reduction treatment and / or ferrous iron-electrolytic oxidation treatment The anode is a titanium plate or a titanium electrode with an anode coating, wherein the anode coating includes at least one selected from ruthenium-iridium alloy, ruthenium-iridium coating, iridium-tantalum alloy, ruthenium-iridium-tantalum alloy, titanium suboxide, platinum, gold, and silver; and / or, The cathode is a stainless steel electrode, a copper plate, a nickel plate, or a stainless steel electrode with a cathode coating, wherein the cathode coating includes at least one of tin-iron alloy and carbon material; and / or, The membrane separating the cathode and anode is a proton membrane or an ion membrane.

13. A recycling device, characterized in that, It includes a first electrolysis unit, a purification unit, and a second electrolysis unit; The cathode chamber outlet of the first electrolysis unit is connected to the inlet of the impurity removal unit, and the outlet of the impurity removal unit is connected to the anode chamber inlet of the second electrolysis unit.

14. The recycling device according to claim 13, characterized in that, The first electrolysis unit and the second electrolysis unit are the same electrolysis unit.

15. The recycling device according to claim 13, characterized in that, The first electrolysis unit and the second electrolysis unit are different electrolysis units.

16. The recycling apparatus according to any one of claims 13-15, characterized in that, It also includes a monitoring unit and an electronic control unit; the monitoring unit is used to monitor at least one of the following: the content of ferric ions in the first electrolysis unit, the content of ferrous ions in the second electrolysis unit, the liquid level in the first electrolysis unit, the liquid level in the second electrolysis unit, and the content of metal ions in the impurity removal unit; The electrical control unit is electrically connected to the monitoring unit, the inlet and outlet of the first electrolysis unit, the inlet and outlet of the impurity removal unit, and the inlet and outlet of the second electrolysis unit, respectively.

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