A recycling method and a recycling device

Abstract

The application provides a recovery method and a recovery device, the recovery method comprising the following steps: performing chlorine ion electrolytic oxidation treatment on a phosphorus-iron system to obtain a dechlorinated phosphorus-iron residue system; performing trivalent iron electrolytic reduction treatment on the dechlorinated phosphorus-iron residue 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 provided by the application takes the phosphorus-iron system as a recovery object, realizes the separation of trivalent iron and impurity elements to the greatest extent, has low recovery cost, and is helpful to the popularization and application in the industrial field.

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] Batteries are currently widely used in various fields. However, since the average lifespan of a battery is 5-8 years, improper disposal of used batteries can lead to serious environmental and safety problems. Meanwhile, due to the scarcity of energy metals and the continuous growth in market demand, the lithium, iron, and other energy metals abundant in used batteries will become an important source of supplementary energy. Therefore, the recycling of used batteries has become one of the research hotspots in recent years. However, battery performance is closely related to the quality of materials. Therefore, the battery industry has high requirements for materials, such as requiring that the content of certain impurities (e.g., aluminum, titanium, copper) in the cathode material be less than 100 ppm, which further increases the difficulty of recycling metal elements.

[0003] Currently, some researchers oxidize waste lithium iron phosphate to release lithium ions and the oxidation product iron phosphate. The lithium ions can react with a precipitant and be used as a lithium source to participate in the preparation of positive electrode active materials. However, the composition of the oxidation product iron phosphate is too complex, making it difficult to obtain high-purity iron phosphate that meets the purity requirements of fine chemical raw materials through low-cost purification. Therefore, it is often directly used as a raw material for basic chemicals, which undoubtedly leads to inefficient use of resources.

[0004] Therefore, how to achieve efficient purification of the oxidation product ferric phosphate at a lower cost is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention provides a recycling method that uses the ferrophosphorus system as the recycling target. It not only achieves a high degree of separation between ferric iron and impurity elements, but also has low recycling costs, which is conducive to its widespread application in the industrial field.

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

[0007] The recycling method of the present invention includes the following steps:

[0008] The phosphorus-iron system was subjected to chloride ion electrolytic oxidation treatment to obtain a dechlorinated phosphorus-iron slag system;

[0009] The dechlorinated phosphorus slag system was subjected to electrolytic reduction treatment with trivalent iron to obtain a reduced system;

[0010] The reduction system is subjected to impurity removal treatment to obtain a divalent iron system;

[0011] The divalent iron system was subjected to divalent iron electrolytic oxidation treatment to obtain a trivalent iron system.

[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, wherein 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 chloride ion electrolytic oxidation treatment and the trivalent iron electrolytic reduction treatment are respectively the anode-side electrolytic oxidation reaction and the cathode-side electrolytic reduction reaction of the first electrolytic treatment.

[0015] In the recycling method described above, the electrolytic oxidation treatment of ferrous iron and the electrolytic reduction treatment of ferric iron are respectively the anodic side electrolytic oxidation reaction and the cathode side electrolytic reduction reaction of the second electrolytic treatment.

[0016] In the recycling method described above, at least 2n electrolytic circuits are connected in parallel under one cell voltage, where n≥1; each pair of electrolytic circuits shares a cathode, wherein the cathode performs the electrolytic reduction treatment of ferric iron, and the two anodes perform the electrolytic oxidation treatment of chloride ions and the electrolytic oxidation treatment of ferrous iron, respectively.

[0017] The recovery method described above further includes, in the chloride ion electrolytic oxidation treatment, the step of introducing an inert gas into the ferrophosphorus system; or, the step of reducing the pressure of the ferrophosphorus slag system.

[0018] The recovery method described above further includes a step of absorbing and treating the chlorine gas generated during the chloride ion electrolytic oxidation process using an absorbent.

[0019] The recycling method described above further includes the step of using the trivalent iron system obtained from the oxidation treatment as an iron source to generate iron phosphate, lithium iron phosphate, or lithium manganese iron phosphate.

[0020] In the recycling method described above, the phosphorus iron slag is a delithiated phosphorus iron slag leachate or a lithium iron phosphate slag leachate.

[0021] In the recovery method described above, the concentration of chloride ions in the phosphorus-iron system is not higher than 10,000 ppm; and / or,

[0022] In the dechlorinated phosphorus slag system, the chloride ion content is less than 30 ppm; and / or,

[0023] The impurity content in the divalent iron system is less than 100 ppm.

[0024] In the recovery method described above, the chloride ion electrolytic oxidation treatment is constant current electrolysis, with a voltage of 1~10V and a current density not exceeding 1A / cm². 2 ; and / or,

[0025] The electrolytic oxidation treatment of divalent iron is a constant current electrolysis, with a voltage of 1~10V and a current density not exceeding 1A / cm. 2 ;

[0026] The electrolytic reduction of ferric iron is performed using constant current electrolysis with a voltage of 1~10V and a current density not exceeding 1A / cm². 2 .

[0027] In the recycling method described above, in the chloride ion electrolytic oxidation treatment and the 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 alloy, iridium-tantalum alloy, ruthenium-iridium-tantalum alloy, titanium suboxide, platinum, gold, and silver; and / or,

[0028] In the electrolytic reduction of ferric iron, the cathode is a stainless steel electrode, a copper plate, a titanium plate, or a nickel plate; or, a stainless steel electrode with a cathode coating, wherein the cathode coating includes a tin-iron alloy or a carbon material; and / or,

[0029] The membrane separating the cathode and anode is a proton membrane or an ion membrane.

[0030] This invention provides a recycling device, comprising a chloride ion electrolytic oxidation unit, a ferrous iron electrolytic oxidation unit, a ferric iron electrolytic reduction unit, and a purification unit;

[0031] The outlet of the chloride ion electrolytic oxidation unit is connected to the inlet of the ferric ion electrolytic reduction unit, the outlet of the ferric ion electrolytic reduction unit is connected to the inlet of the impurity removal unit, and the outlet of the impurity removal unit is connected to the inlet of the ferrous ion electrolytic oxidation unit.

[0032] The recycling device described above includes an electrolytic cell, which is separated into Q cathode chambers and N+M anode chambers by a diaphragm.

[0033] The chloride ion electrolytic oxidation unit includes N chloride ion electrolytic oxidation sub-units, the ferrous iron electrolytic oxidation unit includes M ferrous iron electrolytic oxidation sub-units, and the ferric iron electrolytic reduction unit includes Q ferric iron electrolytic reduction sub-units; N≥1, M≥1, Q≥1;

[0034] Wherein, Q cathode chambers are Q ferric electrolytic reduction sub-units, and N+M anode chambers are N chloride ion electrolytic oxidation sub-units and M ferrous electrolytic oxidation sub-units, respectively; wherein, there is at least one ferric electrolytic reduction sub-unit between adjacent chloride ion electrolytic oxidation sub-units and ferrous electrolytic oxidation sub-units.

[0035] In the recycling device described above, the anodes in the N anode chambers and the cathodes in the Q cathode chambers form an electrolytic circuit, and the anodes in the M anode chambers and the cathodes in the Q cathode chambers form an electrolytic circuit.

[0036] In the recycling device described above, N+M anode chambers are electrically connected to the positive electrode of the electrolytic cell, and Q cathode chambers are electrically connected to the negative electrode of the electrolytic cell.

[0037] In the recycling device described above, N, M, and Q are all 1.

[0038] In the recycling device described above, the impurity removal unit includes K impurity removal sub-units, the outlet of each of the trivalent iron electrolytic reduction sub-units is connected to the inlet of at least one of the impurity removal sub-units, and the outlet of each of the impurity removal sub-units is connected to at least one of the divalent iron electrolytic oxidation sub-units, where K ≥ 1.

[0039] The recovery device described above further includes an absorption unit, the inlet of which is connected to the chlorine outlet of the chloride ion electrolytic oxidation unit.

[0040] The recovery method of the present invention involves sequentially subjecting the ferrophosphorus system to chloride ion electrolytic oxidation treatment, ferric ion electrolytic reduction treatment, impurity removal treatment, and ferrous ion electrolytic oxidation treatment to obtain a ferric ion system with high ferric ion content and low impurity element content. This recovery method not only has excellent recovery rate and recovery purity, but also low recovery cost, which greatly expands the downstream application range of the ferrophosphorus system. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of one embodiment of the recycling device of the present invention;

[0042] Figure 2 This is a schematic diagram of another embodiment of the recycling device of the present invention;

[0043] Figure 3 This is a schematic diagram of another embodiment of the recycling device of the present invention;

[0044] Figure 4 A schematic diagram of another embodiment of the recycling device of the present invention. Detailed Implementation

[0045] 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.

[0046] The first aspect of this invention provides a recycling method, comprising the following steps:

[0047] The phosphorus-iron system was subjected to chloride ion electrolytic oxidation treatment to obtain a dechlorinated phosphorus-iron slag system;

[0048] The dechlorinated phosphorus slag system was subjected to electrolytic reduction treatment with trivalent iron to obtain a reduced system;

[0049] The reduction system is subjected to impurity removal treatment to obtain a divalent iron system;

[0050] The divalent iron system was subjected to divalent iron electrolytic oxidation treatment to obtain a trivalent iron system.

[0051] The phosphorus-iron system of the present invention refers to a compound that includes at least iron, phosphorus and chlorine elements, such as iron phosphate or lithium iron phosphate containing chlorine impurities and other non-ferrous metal impurities such as copper impurities and titanium impurities.

[0052] In one specific embodiment, the phosphorus-iron system of the present invention can be phosphorus-iron slag after delithiation. More specifically, the recycling method of the present 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. In the process of recycling waste lithium iron phosphate, the waste lithium iron phosphate is usually oxidized to obtain free lithium ions and delithiated phosphorus-iron slag. The free lithium ions will form lithium salt precipitates under the action of a precipitant and be recovered as a lithium source. The remaining delithiated phosphorus-iron slag is the lithium-recovered phosphorus-iron phosphate residue.

[0053] In one specific embodiment, the phosphorus-iron system of the present invention can be lithium iron phosphate slag, which can be derived from lithium iron phosphate, the positive electrode active material of waste secondary batteries.

[0054] Generally, the metallic elements in the delithiated phosphorus iron slag include not only iron, but also impurity metallic elements such as titanium, aluminum, and copper.

[0055] The recycling method of the present invention can not only efficiently separate iron from impurity metal elements, but also minimize iron loss and reduce recycling costs, making it suitable for widespread application in the industrial recycling field.

[0056] In detail, this invention first performs chloride ion electrolytic oxidation treatment on the ferrophosphate system, oxidizing the chloride ions into chlorine gas for discharge, thus preventing chloride ion corrosion of subsequent equipment. Subsequently, the dechlorinated ferrophosphate slag system undergoes ferric ion electrolytic reduction treatment, reducing the ferric ion to ferrous ion. This separation of ferrous ion and impurity metals is achieved through the difference between ferrous ion and impurity metals. Finally, a high-purity ferric ion system (ferric phosphate) is obtained through ferrous ion electrolytic oxidation treatment. The recovery method of this invention uses electrolysis, avoiding the increased recovery costs and the risk of introducing new impurity elements associated with using oxidants or reducing agents. Furthermore, the inventors discovered that performing chloride ion electrolytic oxidation treatment before ferric ion electrolytic reduction treatment promotes the reduction of more ferric ion to ferrous ion, thereby achieving a more thorough separation of iron and impurity metals, improving iron recovery efficiency and purity.

[0057] It is understood that electrolysis can be carried out in an electrolytic cell that includes an anode chamber and a cathode chamber. The cathode chamber contains the cathode electrolyte and the cathode, while the anode chamber contains the anolyte and the anode. The cathode chamber can be used for reduction reactions, and the anode chamber can be used for oxidation reactions.

[0058] This invention does not specifically limit the impurity removal process, as long as it can separate iron and phosphorus elements from impurities. The specific method depends on the differences between ferrous iron and impurity metal elements. For example, differences in valence or solubility can be used to separate ferrous iron from other impurity metal elements.

[0059] Generally, the impurity removal process includes at least one of the following steps: titanium ion removal, aluminum ion removal, and copper ion removal.

[0060] As mentioned above, 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.

[0061] 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.

[0062] Alternatively, the pH value of the divalent system can be adjusted. For example, a pH adjuster can be added to the divalent iron ion solution to adjust the pH to 2, so that Ti, Al, etc. can form precipitates with smaller Ksp values, thereby achieving removal.

[0063] 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 metal impurity ions with a higher oxidation potential than divalent iron to elemental form, which is then separated by filtration. For example, by using a reducing agent to reduce the divalent iron system, copper ions are reduced to elemental copper and then separated from the divalent iron system.

[0064] It is understandable that when the above-mentioned recovery method is carried out by electrolysis, the chloride ion electrolytic oxidation treatment is the anode-side reaction, the trivalent iron electrolytic reduction treatment is the cathode-side reaction, and the divalent iron electrolytic oxidation post-treatment is the anode-side reaction.

[0065] When the reaction on the anode side is chloride ion electrolytic oxidation or ferrous electrolytic oxidation, this invention does not limit the type of reduction reaction on the cathode side of the electrolysis device, as long as the oxidizing substance can gain electrons and undergo a reduction reaction. For example, it can be one or more reactions such as hydrogen evolution reaction, high-valence ion reduction, and metal deposition.

[0066] 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.

[0067] 2H + +2e − →H2

[0068] The hydrogen gas produced by the hydrogen evolution reaction can be collected and used as a reducing agent or as hydrogen energy storage.

[0069] Alternatively, reduction of high-valence ions, such as Ni, may occur. 3+ Reduced to Ni 2+ The ionic equations are as follows:

[0070] Ni 3+ + e - → Ni 2+

[0071] 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.

[0072] Alternatively, a metal deposition reaction may occur, such as the precipitation of metallic Cu, with the following ionic equation:

[0073] Cu 2+ + 2e - → Cu

[0074] The aforementioned metal deposition reaction can be used for metal recovery, cathode surface treatment, and other applications.

[0075] When the cathode-side reaction is a trivalent iron electrolytic reduction process, this invention does not limit the type of oxidation reaction on the anode side of the electrolytic device. The anode side can be any oxidizable substance. For example, the anode side can be a system capable of undergoing one or more of the following reactions: oxygen evolution reaction, chlorine evolution reaction, oxidation of low-valence ions, reaction to generate metal ion oxides, methanol oxidation, formic acid oxidation, etc.

[0076] 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.

[0077] 2H₂O → O₂ + 4H + + 4e −

[0078] 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.

[0079] 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.

[0080] 2Cl - → Cl2 + 2e −

[0081] 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.

[0082] 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 (SO42-) can be used. 2− ) is oxidized to persulfate (S2O8) 2− ) or sulfate free radicals (SO4) − These free radicals can further participate in various chemical reactions, such as in wastewater treatment, to oxidize organic pollutants and promote their degradation.

[0083] 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.

[0084] Alternatively, methanol (CH3OH) can be used as the anolyte to undergo oxidation, producing formaldehyde (HCHO) or other basic raw materials used in organic synthesis.

[0085] 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.

[0086] In one specific embodiment, the chloride ion electrolytic oxidation treatment and the trivalent iron electrolytic reduction treatment are respectively the anodic side electrolytic oxidation reaction and the cathode side electrolytic reduction reaction of the first electrolytic treatment.

[0087] In detail, the chloride ion electrolytic oxidation treatment and the ferric iron electrolytic reduction treatment occur in the anode chamber and cathode chamber of the first electrolytic cell, respectively, whereby the first electrolytic cell is used to perform the first electrolytic treatment. Specifically, at the beginning of the chloride ion electrolytic oxidation treatment of the phosphorus-iron system in the anode chamber of the first electrolytic cell, any one of the aforementioned hydrogen evolution reaction, high-valence ion reduction, and metal deposition reactions can occur in the cathode chamber of the first electrolytic cell. As the chloride ion electrolytic oxidation treatment proceeds and the dechlorinated phosphorus-iron slag system is generated, the dechlorinated phosphorus-iron slag system is transported to the cathode chamber of the first electrolytic cell where the chloride ion electrolytic oxidation treatment occurs, replacing the hydrogen evolution reaction, high-valence ion reduction, or metal deposition reaction, so that the cathode chamber undergoes ferric iron electrolytic reduction treatment to obtain the reduced system.

[0088] At this point, in the first electrolytic cell, chloride ion electrolysis occurs in the anode chamber, while the cathode chamber receives the dechlorinated ferrophosphate slag system from the anode chamber for ferric iron electrolytic reduction. The recovery method of this invention achieves the removal of chloride ions and the reduction of ferric iron in the ferrophosphate system by applying a single cell voltage to one electrolytic cell, thus recovering iron from the ferrophosphate system at a lower cost and with higher efficiency.

[0089] In this invention, the phosphorus-iron system continuously enters the anode side and completes the chloride ion electrolytic oxidation treatment. Then, the dechlorinated phosphorus-iron slag system enters the cathode side corresponding to the anode side for trivalent iron electrolytic reduction treatment. This cyclic method realizes the continuous recovery of the phosphorus-iron system, which not only improves the recovery efficiency of the delithiated phosphorus-iron slag, but also reduces the application cost of recovering trivalent iron.

[0090] In one specific embodiment, the divalent iron electrolytic oxidation treatment and the trivalent iron electrolytic reduction treatment are respectively the anodic side electrolytic oxidation reaction and the cathode side electrolytic reduction reaction of the second electrolytic treatment.

[0091] In detail, the electrolytic oxidation treatment of ferrous iron and the electrolytic reduction treatment of ferric iron occur in the anode chamber and cathode chamber of the second electrolytic cell, respectively, whereby the second electrolytic cell is used for the second electrolytic treatment. Specifically, at the beginning of the ferric iron electrolytic reduction treatment of the dechlorinated phosphorus slag system in the cathode chamber of the first electrolytic cell, any one of the aforementioned reactions—oxygen evolution reaction, chlorine evolution reaction, oxidation of low-valence ions, reaction to generate metal ion oxides, methanol oxidation, and formic acid oxidation—can occur in the anode chamber of the second electrolytic cell. As the ferric iron electrolytic reduction treatment proceeds, a reduction system is generated and, after impurity removal, a ferrous iron system is obtained. The ferrous iron system is then transferred to the anode chamber of the second electrolytic cell where the ferric iron electrolytic reduction treatment occurs, replacing the oxygen evolution reaction, chlorine evolution reaction, oxidation of low-valence ions, reaction to generate metal ion oxides, methanol oxidation, or formic acid oxidation, thus causing the ferrous iron electrolytic oxidation treatment to occur in the anode chamber of the second electrolytic cell, yielding a ferric iron system.

[0092] At this point, in the second electrolytic cell, the cathode chamber undergoes electrolytic reduction of ferric iron, while the anode chamber receives the purified ferrous iron system from the cathode chamber for electrolytic oxidation of ferrous iron. The recovery method of this invention achieves both the reduction of ferric iron and the oxidation of ferrous iron by applying a single cell voltage to only one electrolytic cell, thus recovering iron from the ferrophosphorus system at a lower cost and higher efficiency.

[0093] In this invention, the ferric iron system continuously enters the cathode side, and after completing the ferric iron electrolytic reduction and impurity removal treatment, the ferrous iron system then enters the anode side corresponding to the cathode for ferrous iron electrolytic oxidation treatment. This cyclic method realizes the continuous recovery of the phosphorus iron system, which not only improves the recovery efficiency of lithium-free phosphorus iron slag, but also reduces the application cost of recovering ferric iron.

[0094] In another embodiment, at least 2n electrolytic circuits are connected in parallel under one cell voltage, where n≥1; each pair of electrolytic circuits shares a cathode, wherein the cathode performs the electrolytic reduction treatment of ferric iron, and the two anodes perform the electrolytic oxidation treatment of chloride ions and the electrolytic oxidation treatment of ferrous iron, respectively.

[0095] Specifically, the above implementation uses only one electrolytic cell to simultaneously complete chloride ion electrolytic oxidation, ferric ion electrolytic reduction, and ferrous ion electrolytic oxidation under the condition of applying a single cell voltage. For example, the electrolytic cell is divided into 2n anode chambers and n cathode chambers by 2n proton exchange membranes, with the cathode chambers located between two anode chambers. Each anode chamber is electrically connected to the positive terminal of an external power supply, and each cathode chamber is electrically connected to the negative terminal of an external power supply. Of the 2n anode chambers, a portion is used for chloride ion electrolytic oxidation, and the anodes in this portion of the anode chambers and the cathodes in the n cathode chambers form a partial electrolytic circuit; the remaining portion of the 2n anode chambers is used for ferrous ion electrolytic oxidation, and the anodes in this portion of the anode chambers and the cathodes in the n cathode chambers form the remaining electrolytic circuit. Thus, 2n electrolytic circuits are formed under a single cell voltage.

[0096] Taking n=1 as an example, in an electrolytic cell, two proton exchange membranes divide the cell into two anode chambers and one cathode chamber, with the cathode chamber located between the two anode chambers. Each anode chamber is electrically connected to the positive terminal of an external power supply, and each cathode chamber is electrically connected to the negative terminal of the external power supply. Of the two anode chambers, one is used for chloride ion electrolytic oxidation, and the anode in this chamber and the cathode in the cathode chamber form one electrolytic circuit; the remaining anode chamber is used for ferrous ion electrolytic oxidation, and the anode in this chamber and the cathode in the cathode chamber form another electrolytic circuit. Thus, two electrolytic circuits are formed under one cell voltage.

[0097] Specifically, during electrolysis, the ferrophosphorus system first undergoes chloride ion electrolytic oxidation treatment in part of the anode chambers to obtain a dechlorinated ferrophosphorus slag system. Subsequently, this dechlorinated ferrophosphorus slag system is fed into the central cathode chamber for ferric iron electrolytic reduction treatment to obtain a reduced system. After impurity removal treatment, the ferrous iron system then enters the remaining anode chambers for ferrous iron electrolytic oxidation treatment. In this recovery method, the anode chambers on both sides and the central cathode form 2n parallel complete electrolytic circuits. Under the same cell voltage, the voltage of the two electrolytic circuits is the same. This helps to further reduce energy consumption.

[0098] Furthermore, during the chloride ion electrolytic oxidation process, chloride ions are continuously converted into chlorine gas. To prevent chlorine gas from dissolving again in the system, this invention also includes a step of introducing an inert gas into the ferrophosphorus system, or a step of reducing the pressure of the ferrophosphorus slag system. This operation helps to reduce the solubility of chlorine gas in the system, ensuring efficient removal of chloride ions.

[0099] It is understandable that, in order to maximize resource utilization, absorbents can be used to absorb and treat the generated chlorine gas. The specific absorbent can be selected according to the needs of downstream applications. For example, water or aqueous solutions of alkali metal or alkaline earth metal hydroxides (sodium hydroxide, potassium hydroxide) can be used to generate hypochlorous acid or hypochlorite.

[0100] This invention does not limit the specific application of the trivalent iron system. Furthermore, the trivalent iron system can be used as an iron source to generate iron-containing materials, such as iron phosphate, lithium iron phosphate, lithium manganese iron phosphate, etc.

[0101] Specifically, iron phosphate can be prepared by adding phosphorus and other metal sources (such as manganese) to the trivalent iron system. Then, iron phosphate is used as a precursor and undergoes a reduction reaction with lithium to obtain lithium iron phosphate, lithium manganese iron phosphate, etc.

[0102] In the recycling method of the present invention, when dechlorination is achieved by chloride ion-electrolytic oxidation treatment, the ferrophosphorus system can participate in chloride ion-electrolytic oxidation treatment in any form, for example, ferrophosphorus leachate can be used as electrolyte.

[0103] Taking delithiated iron phosphate slag as an example, the aforementioned iron phosphate leaching solution refers to the solution system obtained by dissolving and leaching the delithiated iron phosphate slag with a solvent. For example, an acidic solvent (such as sulfuric acid) 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 ions, copper ions, titanium ions, aluminum ions, and chloride ions. The leaching system is then filtered to remove insoluble matter, yielding the delithiated iron phosphate slag leaching solution. This delithiated iron phosphate slag leaching solution participates in the electrolysis reaction as an electrolyte in a conventional electrolysis process. It should be emphasized that sulfuric acid is commonly used to dissolve the delithiated iron phosphate slag at present. However, since this invention can achieve efficient removal of chloride ions, hydrochloric acid can also be used as an acidic solvent to dissolve the delithiated iron phosphate slag when using the recovery method of this invention. When preparing lithium iron phosphate leaching solution from lithium iron phosphate slag, the process is basically the same as for delithiated iron phosphate slag, but an additional oxidant, such as hydrogen peroxide, needs to be added.

[0104] This invention does not impose a specific limit on the concentration of chloride ions in the phosphorus-iron system; for example, it may not exceed 10,000 ppm.

[0105] Furthermore, when the chloride ion content in the dechlorinated phosphorus-iron slag system is less than 30 ppm, electrolytic reduction of ferric iron can be performed. It is understandable that to obtain a high-purity ferrous iron system, the lower the impurity content, the better. Through the inventors' research, controlling the chloride ion content in the dechlorinated phosphorus-iron slag system to less than 30 ppm is more conducive to the separation of iron from other impurity metallic elements.

[0106] In addition, when the impurity content in the divalent iron system is less than 100 ppm, the impurities here mainly refer to aluminum, iron and copper impurities, and the iron source can be recovered with high purity, which can meet the downstream demand for high-purity iron sources.

[0107] Furthermore, the chloride ion-electrolytic oxidation treatment is a constant current electrolysis process with a voltage of 1~10V and a current density not exceeding 1A / cm². 2 .

[0108] Furthermore, the electrolytic oxidation treatment of ferrous iron is a constant current electrolysis process with a voltage of 1~10V and a current density not exceeding 1 A / cm². 2 .

[0109] Furthermore, the electrolytic reduction of ferric iron is performed using constant current electrolysis, with a voltage of 1~10V and a current density not exceeding 1A / cm². 2 .

[0110] In the chloride ion electrolytic oxidation treatment and the ferrous iron electrolytic oxidation treatment, the present 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, wherein the anode coating includes at least one of ruthenium-iridium alloy, ruthenium-iridium alloy, iridium-tantalum alloy, ruthenium-iridium-tantalum alloy, titanium suboxide, platinum, gold, and silver.

[0111] For example, in the electrolytic reduction of ferric iron, the cathode is a stainless steel electrode, a copper plate, a titanium plate, a nickel plate, or a stainless steel electrode with a cathode coating, wherein the cathode coating includes a tin-iron alloy or a carbon material.

[0112] Furthermore, when the cathode and anode are in the same electrolytic cell, they 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.

[0113] 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 recovery device includes a chloride ion electrolytic oxidation unit 1, a ferrous iron electrolytic oxidation unit 2, a ferric iron electrolytic reduction unit 3, and a purification unit 4; the outlet of the chloride ion electrolytic oxidation unit 1 is connected to the inlet of the ferric iron electrolytic reduction unit 3, the outlet of the ferric iron electrolytic reduction unit 3 is connected to the inlet of the purification unit 4, and the outlet of the purification unit 4 is connected to the inlet of the ferrous iron electrolytic oxidation unit 2.

[0114] The system comprises: a chloride ion electrolytic oxidation unit 1 for receiving the ferrophosphorus system and performing chloride ion electrolytic oxidation treatment to obtain a dechlorinated ferrophosphorus slag system; a ferric iron electrolytic reduction unit 3 for receiving the dechlorinated ferrophosphorus slag system from the chloride ion electrolytic oxidation unit 1 and performing ferric iron electrolytic reduction treatment on the ferric iron to reduce it to ferrous iron, thus obtaining a reduced system; a purification unit 4 for purifying the reduced system from the ferric iron electrolytic reduction unit 3 to separate the impurity metal elements from the ferrous iron ions, thus obtaining a ferrous iron system; and a ferrous iron electrolytic oxidation unit 2 for receiving the ferrous iron system and performing electrolytic oxidation treatment on the ferrous iron, thus obtaining a ferric iron system.

[0115] It is understood that, in order to improve the recovery efficiency, the above-mentioned device may further include a monitoring unit and an electronic control unit; the monitoring unit is used to monitor at least one of the following: the chloride ion content in the chloride ion electrolytic oxidation unit 1, the liquid level in the chloride ion electrolytic oxidation unit 1, the liquid level in the ferrous iron electrolytic oxidation unit 2, the liquid level in the ferric iron electrolytic reduction unit 3, the ferric iron content in the ferrous iron electrolytic oxidation unit 2, the ferrous iron content in the ferric iron electrolytic reduction unit 3, and the impurity metal ion content in the impurity removal unit 4;

[0116] The electrical control unit is electrically connected to the monitoring unit, the inlet and outlet of the chloride ion electrolytic oxidation unit 1, the inlet and outlet of the ferrous ion electrolytic oxidation unit 2, the inlet and outlet of the ferric ion electrolytic reduction unit 3, and the inlet and outlet of the impurity removal unit 4.

[0117] For example, when the monitoring unit detects that the chloride ion content in the chloride ion electrolytic oxidation unit 1 has decreased to the target content, it will release an electrical signal to the electrical control unit. After receiving the electrical signal, the electrical control unit will control the outlet of the chloride ion electrolytic oxidation unit 1 and the inlet of the ferric iron electrolytic reduction unit 3 to be in the open state, so that the dechlorinated phosphorus iron slag system of the chloride ion electrolytic oxidation unit 1 enters the ferric iron electrolytic reduction unit 3 for ferric iron reduction treatment.

[0118] Alternatively, the monitoring unit can also be used to monitor the liquid level of the chloride ion electrolytic oxidation unit 1. When the liquid level of the chloride ion electrolytic oxidation unit 1 is lower than the target liquid level, an electrical signal can be released to make the electronic control unit open the inlet of the chloride ion electrolytic oxidation unit 1, so that more fresh phosphorus-iron system to be treated can enter the chloride ion electrolytic oxidation unit 1 for dechlorination treatment.

[0119] In one specific embodiment, an electrolytic cell is included, which is separated into Q cathode chambers and N+M anode chambers by a diaphragm; the chloride ion electrolytic oxidation unit includes N chloride ion electrolytic oxidation sub-units, the ferrous iron electrolytic oxidation unit includes M ferrous iron electrolytic oxidation sub-units, and the ferric iron electrolytic reduction unit includes Q ferric iron electrolytic reduction sub-units; N≥1, M≥1, Q≥1; wherein, the Q cathode chambers are Q ferric iron electrolytic reduction sub-units, and the N+M anode chambers are respectively N chloride ion electrolytic oxidation sub-units and M ferrous iron electrolytic oxidation sub-units; wherein, there is at least one ferric iron electrolytic reduction sub-unit between adjacent chloride ion electrolytic oxidation sub-units and ferrous iron electrolytic oxidation sub-units.

[0120] Furthermore, the anodes in the N anode chambers and the cathodes in the Q cathode chambers form an electrolytic circuit, and the anodes in the M anode chambers and the cathodes in the Q cathode chambers form an electrolytic circuit.

[0121] It is understood that an anode is provided in the anode chamber and a cathode is provided in the cathode chamber. This invention achieves multiple parallel electrolytic circuits under one cell voltage by forming N electrolytic circuits with N anodes and Q cathodes, and M electrolytic circuits with M anodes and Q cathodes, thereby completing multiple electrolytic oxidation and electrolytic reduction processes and reducing the internal consumption of the system.

[0122] In one specific embodiment, N+M anode chambers can be electrically connected to the positive electrode of the electrolytic cell, and Q cathode chambers can be electrically connected to the negative electrode of the electrolytic cell, thereby constructing multiple parallel electrolytic circuits in one electrolytic cell.

[0123] For example, Figure 2 In the electrolytic cell 100, there are three sub-cells: anode chamber 1a, anode chamber 2a, and cathode chamber 3a, where M=N=Q=1. Anode chamber 1a is a sub-unit for chloride ion electrolysis and oxidation, anode chamber 2a is a sub-unit for ferrous ion electrolysis and oxidation, and cathode chamber 3a is a sub-unit for ferric ion electrolysis and reduction. Figure 2 As shown, under an external power supply of 100a, the anode chamber 1a is used for chloride ion electrolytic oxidation treatment to obtain a dechlorinated phosphorus iron slag system; the dechlorinated phosphorus iron slag system enters the cathode chamber 3a for trivalent iron electrolytic reduction treatment to obtain a reduced system; the reduced system enters the impurity removal unit 4 for impurity removal treatment, and then enters the anode chamber 2a for divalent iron electrolytic oxidation treatment to obtain a trivalent iron system.

[0124] For example, Figure 3 In the electrolytic cell 200, there are anode chambers 1a, 1b, 2a, 3a, and 3b, i.e., N=Q=2, M=1. Anode chambers 1a and 1b are chloride ion electrolysis oxidation subunits, anode chamber 2a is a ferrous ion electrolysis oxidation subunit, and cathode chambers 3a and 3b are ferric ion electrolysis reduction subunits. Figure 3 As shown, under an external power supply 200a, cathode chambers 1a and 1b are used for chloride ion electrolytic oxidation treatment to obtain a dechlorinated phosphorus iron slag system; the dechlorinated phosphorus iron slag system enters cathode chambers 3a and 3b respectively for trivalent iron electrolytic reduction treatment to obtain a reduced system; after the reduced system enters the impurity removal unit 4 for impurity removal treatment, the divalent iron system enters the anode chamber 2a for divalent iron electrolytic oxidation treatment to obtain a trivalent iron system.

[0125] Furthermore, the impurity removal unit includes K impurity removal sub-units, the outlet of each of the trivalent iron electrolytic reduction sub-units is connected to the inlet of at least one of the impurity removal sub-units, and the outlet of each of the impurity removal sub-units is connected to at least one of the divalent iron electrolytic oxidation sub-units, where K≥1.

[0126] Figure 4 In the middle, K=2, in Figure 3 On this basis, Figure 4 The electrolytic cell 300 also includes two impurity removal sub-units 4a and 4b. After the reduction system in the cathode chambers 3a and 3b enters the impurity removal sub-units 4a and 4b for impurity removal, the ferrous iron system enters the anode chamber 2a from the impurity removal sub-units 4a and 4b for ferrous iron electrolytic oxidation to obtain the ferric iron system.

[0127] Furthermore, the recovery device of the present invention also includes an absorption unit; the inlet of the absorption unit is connected to the chlorine outlet of the chloride ion electrolytic oxidation unit. This absorption unit is used to absorb the chlorine gas released from the chloride ion electrolytic oxidation unit.

[0128] The recycling method of the present invention will be described below through specific embodiments.

[0129] Example 1

[0130] The recycling method in this embodiment adopts... Figure 2 The electrolytic cell shown is used for the following steps:

[0131] 1) The lithium iron phosphate residue after delithiation was mixed with sulfuric acid solution at a mass ratio of 1:3, dissolved and filtered to obtain a lithium iron phosphate residue leachate with a trivalent iron molar concentration of 1 M and a pH of 1.53; the composition of the lithium iron phosphate residue leachate was shown in Table 1 by ICP analysis.

[0132] 2) The leaching solution of delithiated iron phosphate slag was placed in the anode chamber 1a of the electrolytic cell 100 as the anode electrolyte, and ferric sulfate was placed in the cathode chamber 3a of the electrolytic cell 100 as the cathode electrolyte. A cell voltage of 4V was applied, and chloride ion electrolytic oxidation treatment was carried out under constant voltage. After 6 hours, a dechlorinated iron phosphate slag solution with a chloride ion content of 8.31ppm was obtained. At the same time, nitrogen gas was introduced into the anode chamber, and water was used to absorb the chlorine gas escaping from the anode chamber.

[0133] In the electrolytic cell, the cathode in cathode chamber 3a is a stainless steel plate, and the anode in anode chamber 1a is a ruthenium-iridium coated titanium plate; the diaphragm separating cathode chamber 3a and anode chamber 1a is a perfluorosulfonic acid proton exchange membrane;

[0134] 3) The dechlorinated phosphorus iron slag solution from step 2) is introduced into the cathode chamber 3a of the electrolytic cell 100 as the cathode electrolyte for the electrolytic reduction of ferric iron; the delithiated phosphorus iron slag leachate is introduced into the anode chamber 1a for simultaneous oxidative dechlorination treatment. When the molar concentration C2 of ferric iron in the cathode chamber 3a is less than 0.001M, a reduction system is obtained.

[0135] 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;

[0136] 5) The solution of the divalent iron system in step 4) is introduced into the anode chamber 2a of the electrolytic cell 100 as the anode electrolyte for divalent iron electrolytic oxidation treatment. The dechlorinated phosphoric acid leaching solution is introduced into the cathode chamber 3a for trivalent iron electrolytic reduction treatment. When the molar concentration of divalent iron C3 in the anode chamber 2a is less than 0.001M, the trivalent iron system is obtained.

[0137] The anode in anode chamber 2a is a ruthenium-iridium coated titanium plate; the diaphragm separating cathode chamber 3a and anode chamber 2a is a perfluorosulfonic acid proton exchange membrane.

[0138] Table 1

[0139]

[0140] Example 2

[0141] The recovery method in this embodiment is basically the same as that in Example 1, except that the delithiated iron phosphate slag is replaced. The composition of the delithiated iron phosphate slag leachate in this embodiment is shown in Table 2. Based on the same electrolysis time, current density and cell voltage as in step 2) of Example 1, a dechlorinated iron phosphate slag solution with a chloride ion content of 7.61 ppm was obtained.

[0142] Table 2

[0143]

[0144] Example 3

[0145] The recovery method in this embodiment is basically the same as that in Embodiment 1, except that the cell voltage is 7V in step 2). Based on the same electrolysis time and current density as in step 2) of Embodiment 1, a dechlorinated phosphorus slag solution with a chloride ion content of 5.84 ppm is obtained.

[0146] Example 4

[0147] The recycling method in this embodiment is basically the same as that in Embodiment 1, except that in step 2), the current density is 0.5 A / cm². 2 Based on the same electrolysis time and cell voltage as in step 2) of Example 1, a dechlorinated phosphorus slag solution with a chloride ion content of 5.36 ppm was obtained.

[0148] Example 5

[0149] The recycling method in this embodiment is basically the same as that in Embodiment 1, except that in step 2), the current density is 0.7 A / cm². 2 Based on the same electrolysis time and cell voltage as in step 2) of Example 1, a dechlorinated phosphorus slag solution with a chloride ion content of 4.19 ppm was obtained.

[0150] Example 6

[0151] The difference between the recycling method in this embodiment and that in Embodiment 1 is that in the electrolytic cell 100, the cathode is a titanium plate, and both anodes are ruthenium-iridium-tantalum coated titanium plates. Based on the same electrolysis time, current density, and cell voltage as in step 2) of Embodiment 1, a dechlorinated phosphorus slag solution with a chloride ion content of 9.3 ppm is obtained in step 2).

[0152] Example 7

[0153] The difference between the recycling method in this embodiment and that in Embodiment 1 is that in the electrolytic cell 100, the cathode is a stainless steel plate and the two anodes are titanium plates. Based on the same electrolysis time, current density and cell voltage as in step 2) of Embodiment 1, a dechlorinated phosphorus slag solution with a chloride ion content of 9.85 ppm is obtained in step 2).

[0154] Example 8

[0155] The recycling method in this embodiment includes the following steps:

[0156] 1) The delithiated iron phosphate slag was mixed with sulfuric acid solution at a mass ratio of 1:3, dissolved and filtered to obtain a delithiated iron phosphate slag leachate with a trivalent iron molar concentration of 1 M and a pH of 1.53; the composition of the delithiated iron phosphate slag leachate was shown in Table 1 by ICP analysis.

[0157] 2) The leaching solution of the lithium-free phosphate slag is placed in the anode chamber of the first electrolytic cell as the anolyte, and ferric sulfate is placed in the cathode chamber of the first electrolytic cell as the cathode electrolyte, at a concentration of 0.06 A / cm. 2 Chloride ion electrolytic oxidation treatment was carried out under constant current conditions. After 6 h, a dechlorinated phosphorus iron slag solution with a chloride ion content of 9.26 ppm was obtained. At the same time, nitrogen gas was introduced into the anode chamber, and water was used to absorb the chlorine gas escaping from the anode chamber.

[0158] In the first electrolytic cell, the cathode in the cathode chamber is a stainless steel plate, and the anode in the anode chamber is a ruthenium-iridium coated titanium plate; the diaphragm separating the cathode chamber and the anode chamber is a perfluorosulfonic acid proton exchange membrane;

[0159] 3) The dechlorinated phosphorus slag solution from step 2) is introduced into the cathode chamber of the second electrolytic cell as the cathode electrolyte for the electrolytic reduction of ferric iron. The anolyte in the anode chamber of the second electrolytic cell is ferrous sulfate solution. When the molar concentration C2 of ferric iron in the cathode chamber is less than 0.001M, a reduction system is obtained.

[0160] In the second electrolytic cell, the cathode in the cathode chamber is a stainless steel plate, and the anode in the anode chamber is a ruthenium-iridium coated titanium plate; the diaphragm separating the cathode chamber and the anode chamber is a perfluorosulfonic acid proton exchange membrane.

[0161] 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;

[0162] 5) The solution of the divalent iron system in step 4) is introduced into the anode chamber of the third electrolytic cell as the anode electrolyte for divalent iron electrolytic oxidation treatment. The cathode electrolyte in the cathode chamber of the third electrolytic cell is dilute sulfuric acid. When the molar concentration of divalent iron C3 in the anode chamber is less than 0.001M, a trivalent iron system is obtained.

[0163] In the third electrolytic cell, the cathode in the cathode chamber is a stainless steel plate, and the anode in the anode chamber is a ruthenium-iridium coated titanium plate; the diaphragm separating the cathode chamber and the anode chamber is a perfluorosulfonic acid proton exchange membrane.

[0164] Example 9

[0165] The recycling method in this embodiment includes the following steps:

[0166] 1) The delithiated iron phosphate slag was mixed with sulfuric acid solution at a mass ratio of 1:3, dissolved and filtered to obtain a delithiated iron phosphate slag leachate with a trivalent iron molar concentration of 1 M and a pH of 1.53; the composition of the delithiated iron phosphate slag leachate was shown in Table 1 by ICP analysis.

[0167] 2) The leaching solution of delithiated iron phosphate slag was placed in the anode chamber of the first electrolytic cell as the anode electrolyte, and ferric sulfate was placed in the cathode chamber of the first electrolytic cell as the cathode electrolyte. A cell voltage of 6V was applied, and chloride ion electrolytic oxidation treatment was carried out under constant voltage. After 4 hours, a dechlorinated iron phosphate slag solution with a chloride ion content of 10.27ppm was obtained. At the same time, nitrogen gas was introduced into the anode chamber, and water was used to absorb the chlorine gas escaping from the anode chamber.

[0168] In the first electrolytic cell, the cathode in the cathode chamber is a stainless steel plate, and the anode in the anode chamber is a ruthenium-iridium coated titanium plate; the diaphragm separating the cathode chamber and the anode chamber is a perfluorosulfonic acid proton exchange membrane;

[0169] 3) The dechlorinated phosphorus iron slag solution from step 2) is introduced into the cathode chamber of the first electrolytic cell as the cathode electrolyte for the electrolytic reduction of ferric iron; the anolyte is the leaching solution of delithiated phosphorus iron slag, which is simultaneously oxidized and dechlorinated; when the molar concentration of ferric iron C2 in the cathode chamber is less than 0.001M, the reduction system is obtained.

[0170] 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;

[0171] 5) The solution of the divalent iron system in step 4) is introduced into the anode chamber of the second electrolytic cell as the anode electrolyte for divalent iron electrolytic oxidation treatment. The cathode electrolyte in the cathode chamber of the second electrolytic cell is dilute sulfuric acid. When the molar concentration of divalent iron C3 in the anode chamber is 0.001M, a trivalent iron system is obtained.

[0172] In the second electrolytic cell, the cathode in the cathode chamber is a stainless steel plate, and the anode in the anode chamber is a ruthenium-iridium coated titanium plate; the diaphragm separating the cathode chamber and the anode chamber is a perfluorosulfonic acid proton exchange membrane.

[0173] Example 10

[0174] The recycling method in this embodiment includes the following steps:

[0175] 1) The delithiated iron phosphate slag was mixed with sulfuric acid solution at a mass ratio of 1:3, dissolved and filtered to obtain a delithiated iron phosphate slag leachate with a trivalent iron molar concentration of 1 M and a pH of 1.53; the composition of the delithiated iron phosphate slag leachate was shown in Table 1 by ICP analysis.

[0176] 2) The leaching solution of the lithium-free phosphorus slag is placed in the anode chamber of the first electrolytic cell as the anolyte, and ferric sulfate is placed in the cathode chamber of the first electrolytic cell as the cathode electrolyte, at a concentration of 0.1 A / cm. 2 Chloride ion electrolytic oxidation treatment was carried out under constant current conditions. After 4 hours, a dechlorinated phosphorus iron slag solution with a chloride ion content of 7.82 ppm was obtained. At the same time, nitrogen gas was introduced into the anode chamber, and water was used to absorb the chlorine gas escaping from the anode chamber.

[0177] In the first electrolytic cell, the cathode in the cathode chamber is a stainless steel plate, and the anode in the anode chamber is a ruthenium-iridium coated titanium plate; the diaphragm separating the cathode chamber and the anode chamber is a perfluorosulfonic acid proton exchange membrane;

[0178] 3) The dechlorinated phosphorus slag solution from step 2) is introduced into the cathode chamber of the second electrolytic cell as the cathode electrolyte for the electrolytic reduction of ferric iron. The anolyte in the anode chamber of the second electrolytic cell is a ferrous sulfate solution. When the molar concentration C2 of ferric iron in the cathode chamber 3a is 0.001M, a reduction system is obtained.

[0179] In the second electrolytic cell, the cathode in the cathode chamber is a stainless steel plate, and the anode in the anode chamber is a ruthenium-iridium coated titanium plate; the diaphragm separating the cathode chamber and the anode chamber is a perfluorosulfonic acid proton exchange membrane.

[0180] 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;

[0181] 5) The solution of the divalent iron system in step 4) is introduced into the anode chamber of the second electrolytic cell as the anode electrolyte for divalent iron electrolytic oxidation treatment. The cathode liquid is dechlorinated ferric phosphorus leaching solution, and trivalent iron electrolytic reduction is carried out simultaneously. When the molar concentration of divalent iron C3 in the anode chamber is 0.001M, the trivalent iron system is obtained.

[0182] Example 11

[0183] The recycling method in this embodiment is basically the same as that in Example 1, except that the lithium iron phosphate residue in Table 3 is used to replace the delithiated iron phosphate residue. During acid leaching, 10% hydrogen peroxide is added to oxidize the ferrous iron in the lithium iron phosphate residue. Based on the same electrolysis time, current density and cell voltage as in step 2) of Example 1, a dechlorinated iron phosphate residue solution with a chloride ion content of 9.07 ppm is obtained.

[0184] Table 3

[0185]

[0186] Comparative Example 1

[0187] This comparative example is basically the same as Example 1, except that in step 2), under a water bath at 60°C, 30% hydrogen peroxide is used to dechlorinate the delithiated iron phosphate slag leachate. The volume ratio of the delithiated iron phosphate slag leachate to hydrogen peroxide is 1:1. After 6 hours, no bubbles are generated in the mixture, and a dechlorinated iron phosphate slag solution with a chloride ion content of 650.39 ppm is obtained.

[0188] Comparative Example 2

[0189] The difference between the recovery method in this comparative example and that in Example 1 is that the lithium-free phosphorus iron slag leachate from step 1) is directly used as the cathode electrolyte for trivalent iron reduction treatment, and the chloride ion electrolytic oxidation treatment in step 2) is omitted.

[0190] Test case

[0191] 1. The energy consumption (the sum of the energy consumption of chloride ion electrolytic oxidation treatment, ferric ion electrolytic reduction treatment, and ferrous ion electrolytic oxidation treatment) and recovery cost per unit mass of ferric iron were calculated for the examples and comparative examples. The results are shown in Table 4.

[0192] The electrical energy consumption E (kW·h· / ton) for recovering a unit mass of ferric iron refers to the electrical energy consumed to recover 1 ton of ferric iron. E is calculated according to Equation 1.

[0193] Formula 1

[0194] In Table 4, the power consumption in the examples refers to the sum of the power consumption of chloride ion electrolytic oxidation treatment for recovering a unit mass of trivalent iron, the power consumption of trivalent iron electrolytic reduction treatment for recovering a unit mass of trivalent iron, and the power consumption of divalent iron electrolytic oxidation treatment for recovering a unit mass of trivalent iron; the recovery cost in the examples refers to the cost of power consumption.

[0195] The energy consumption in the comparative examples refers to the sum of the energy consumption of the electrolytic reduction treatment of ferric iron and the energy consumption of the electrolytic oxidation treatment of ferrous iron per unit mass of ferric iron; the recovery cost in comparative example 1 refers to the sum of the cost of hydrogen peroxide and the cost of energy consumption for recovering ferric iron per unit mass; and the recovery cost in comparative example 2 refers to the cost of energy consumption.

[0196] In the cost of electricity consumption, electricity is calculated at 0.67 yuan / kWh; in the cost of hydrogen peroxide consumption, hydrogen peroxide is calculated at 850 yuan / ton.

[0197] 2. The iron content in the reduction system and the purified system solution in 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 5.

[0198] w (%) = Iron content in the solution of the purified system / Iron content in the reduced system

[0199] 3. Ferric iron recovered from each embodiment and comparative example was used as the iron source to prepare ferric phosphate. The impurity metals in the prepared ferric phosphate solid phase were analyzed by ICP, and their composition is shown in Table 5 below.

[0200] Table 4

[0201]

[0202] Table 5

[0203]

[0204] As shown in Tables 4 and 5, the recycling method of the present invention greatly improves the iron recovery rate of the phosphorus-iron system at a lower cost, and the amount of impurity elements in the recycled system is also lower.

[0205] 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 phosphorus-iron system was subjected to chloride ion electrolytic oxidation treatment to obtain a dechlorinated phosphorus-iron slag system; The dechlorinated phosphorus slag system was subjected to electrolytic reduction treatment with trivalent iron 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 removal process includes at least one of the following steps: titanium ion removal, aluminum ion removal, and copper ion removal.

3. The recycling method according to claim 1 or 2, 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.

4. The recycling method according to any one of claims 1-3, characterized in that, The chloride ion electrolytic oxidation treatment and the trivalent iron electrolytic reduction treatment are respectively the anodic side electrolytic oxidation reaction and the cathode side electrolytic reduction reaction of the first electrolytic treatment.

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

6. The recycling method according to any one of claims 1-5, characterized in that, At least 2n electrolytic circuits are connected in parallel under a single cell voltage, where n≥1; each pair of electrolytic circuits shares a cathode, wherein the cathode performs the electrolytic reduction treatment of ferric iron, and the two anodes perform the electrolytic oxidation treatment of chloride ions and the electrolytic oxidation treatment of ferrous iron, respectively.

7. The recycling method according to any one of claims 1-6, characterized in that, The chloride ion electrolytic oxidation treatment further includes: the step of introducing an inert gas into the phosphorus-iron system; or, the step of reducing the pressure of the phosphorus-iron slag system.

8. The recycling method according to any one of claims 1-7, characterized in that, It also includes the step of absorbing and treating the chlorine gas generated in the chloride ion electrolytic oxidation process using an absorbent.

9. The recycling method according to any one of claims 1-8, characterized in that, The recycling method further includes the step of using the trivalent iron system obtained from the oxidation treatment as an iron source to generate iron phosphate, lithium iron phosphate, or lithium manganese iron phosphate.

10. The recycling method according to claim 1, characterized in that, The phosphorus-iron slag is a delithiated phosphorus-iron slag leachate or a lithium iron phosphate slag leachate.

11. The recycling method according to claim 10, characterized in that, In the aforementioned phosphorus-iron system, the concentration of chloride ions does not exceed 10,000 ppm; and / or, In the dechlorinated phosphorus slag system, the chloride ion content is less than 30 ppm; and / or, The impurity content in the divalent iron system is less than 100 ppm.

12. The recycling method according to any one of claims 1-11, characterized in that, The chloride ion electrolytic oxidation treatment is a constant current electrolysis, with a voltage of 1~10V and a current density not exceeding 1A / cm. 2 ; and / or, The electrolytic oxidation treatment of ferrous iron is a constant current electrolysis, with a voltage of 1~10V and a current density not exceeding 1A / cm. 2 ; The electrolytic reduction of ferric iron is performed using constant current electrolysis with a voltage of 1~10V and a current density not exceeding 1 A / cm². 2 .

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

14. A recycling device, characterized in that, It includes a chloride ion electrolytic oxidation unit, a ferrous ion electrolytic oxidation unit, a ferric ion electrolytic reduction unit, and a purification unit; The outlet of the chloride ion electrolytic oxidation unit is connected to the inlet of the ferric ion electrolytic reduction unit, the outlet of the ferric ion electrolytic reduction unit is connected to the inlet of the impurity removal unit, and the outlet of the impurity removal unit is connected to the inlet of the ferrous ion electrolytic oxidation unit.

15. The recycling apparatus according to claim 14, characterized in that, Includes an electrolytic cell, which is separated into Q cathode chambers and N+M anode chambers by a diaphragm; The chloride ion electrolytic oxidation unit includes N chloride ion electrolytic oxidation sub-units, the ferrous iron electrolytic oxidation unit includes M ferrous iron electrolytic oxidation sub-units, and the ferric iron electrolytic reduction unit includes Q ferric iron electrolytic reduction units; N≥1, M≥1, Q≥1; Wherein, Q cathode chambers are Q ferric electrolytic reduction sub-units, and N+M anode chambers are N chloride ion electrolytic oxidation sub-units and M ferrous electrolytic oxidation sub-units, respectively; wherein, there is at least one ferric electrolytic reduction sub-unit between adjacent chloride ion electrolytic oxidation sub-units and ferrous electrolytic oxidation sub-units.

16. The recycling apparatus according to claim 15, characterized in that, The N anodes in the anode chambers and the Q cathodes in the cathode chambers form an electrolytic circuit, and the M anodes in the anode chambers and the Q cathodes in the cathode chambers form an electrolytic circuit.

17. The recycling apparatus according to claim 16, characterized in that, N+M anode chambers are electrically connected to the positive electrode of the electrolytic cell, and Q cathode chambers are electrically connected to the negative electrode of the electrolytic cell.

18. The recycling apparatus according to claim 17, characterized in that, N, M, and Q are all 1.

19. The recycling apparatus according to any one of claims 14-18, characterized in that, The impurity removal unit includes K impurity removal sub-units. The outlet of each of the trivalent iron electrolytic reduction sub-units is connected to the inlet of at least one of the impurity removal sub-units, and the outlet of each of the impurity removal sub-units is connected to at least one of the divalent iron electrolytic oxidation sub-units, where K ≥ 1.

20. The recycling apparatus according to any one of claims 14-19, characterized in that, It also includes an absorption unit, the inlet of which is connected to the chlorine outlet of the chloride ion electrolytic oxidation unit.

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