Recovery method and recovery device

Abstract

A recovery method and a recovery device. The recovery method comprises: a recovery process of phosphorus and iron elements in an iron phosphate system and a hydrochloric acid reuse process, wherein the recovery process of the phosphorus and iron elements comprises: an acid leaching step: subjecting the iron phosphate system to acid pickling by using an acid containing hydrochloric acid, so as to obtain an acid pickling solution; and the hydrochloric acid reuse process comprises: a chloride ion removal step: subjecting the acid pickling solution to electrolytic oxidation to remove chloride ions, so as to generate chlorine gas; a hydrochloric acid regeneration step: reacting the chlorine gas with hydrogen gas to generate hydrochloric acid; and a hydrochloric acid reuse step: reusing the hydrochloric acid in the acid pickling step.

Description

A recycling method and recycling apparatus

[0001] This application claims priority to Chinese Patent Application No. 2025100976731, filed on January 22, 2025, entitled "A Recycling Method and Recycling Apparatus", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery material recycling technology, and in particular to a recycling method and recycling apparatus. Background Technology

[0003] Lithium iron phosphate (LFP) batteries possess numerous advantages, including high specific capacity, stable structure, safe performance, and long service life, leading to their widespread application in the new energy field. However, over time, a large number of retired power batteries urgently require recycling. Since LFP batteries are rich in lithium and iron phosphate, achieving full-component recovery of lithium and iron phosphate from retired LFP batteries is crucial from the perspectives of resource recycling and environmental protection. Currently, there is no effective method for the full-component recovery of iron phosphate from retired LFP batteries; therefore, there is an urgent need to develop a low-cost, recyclable recycling method. Summary of the Invention

[0004] The purpose of this application is to provide a method and application for recovering iron phosphate, which simplifies the process and reduces recovery costs. The specific technical solution is as follows:

[0005] The first aspect of this application provides a recovery method, comprising: a recovery process of phosphorus and iron elements in an iron phosphate system and a hydrochloric acid reuse process, wherein the recovery process of phosphorus and iron elements includes:

[0006] Acid leaching step: The ferric phosphate system is acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution;

[0007] The hydrochloric acid reuse process includes:

[0008] Chloride ion removal step: The acid leaching solution is electrolytically oxidized to remove chloride ions and generate chlorine gas;

[0009] Hydrochloric acid regeneration step: The chlorine gas is reacted with hydrogen gas to generate hydrochloric acid;

[0010] Hydrochloric acid reuse step: The hydrochloric acid is reused in the acid leaching step.

[0011] The beneficial effects of this application are:

[0012] This application provides a recycling method and apparatus. The recycling method includes a process for recovering ferric phosphorus from a ferric phosphate system and a process for reusing hydrochloric acid. The ferric phosphorus recovery process includes: an acid leaching step: leaching the ferric phosphate system with an acid containing hydrochloric acid to obtain an acid leaching solution; the hydrochloric acid reuse process includes: a chloride ion removal step: electrolytically oxidizing the acid leaching solution to remove chloride ions and generate chlorine gas; a hydrochloric acid regeneration step: reacting the chlorine gas with hydrogen gas to generate hydrochloric acid; and a hydrochloric acid reuse step: reusing the hydrochloric acid in the acid leaching step. By using an acid containing hydrochloric acid to leach the ferric phosphate system to obtain an acid leaching solution rich in chloride ions, and using electrolytic oxidation to remove impurity chloride ions while generating chlorine gas, hydrochloric acid is resynthesized from hydrogen and chlorine gas and used in the initial acid leaching process. This recycling process achieves the recovery and reuse of industrial waste gas and hydrochloric acid, effectively reducing potential air pollution problems during the recycling process and significantly reducing recycling costs. Electrolytic oxidation is used to oxidize chloride ions into chlorine gas, which then escapes from the system, minimizing the impact on the acid leaching solution and simplifying subsequent processing. This application employs an electrochemical method that is simple, efficient, and cost-effective in recycling, reducing the amount of chemical reagents used. It also has minimal impact on the iron phosphate system, alleviating pressure on downstream impurity removal and iron phosphate regeneration processes. The resulting iron phosphate meets battery-grade iron phosphate standards and can therefore be used to prepare lithium iron phosphate batteries.

[0013] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0015] Figure 1 shows a method route for iron phosphate recovery according to one embodiment of this application;

[0016] Figure 2 illustrates the working principle of a cathode electrochemical reduction coupled to an anodic electrochemical oxidation according to one embodiment of this application. Detailed Implementation

[0017] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0018] Currently, the recovery process of ferric phosphate mainly includes four steps: acid leaching, impurity removal, oxidation, and regeneration. First, the ferric phosphate waste residue is treated with strong acid to dissolve phosphorus and iron elements in the leaching solution. Then, the leaching solution is purified to remove impurity ions such as titanium, aluminum, and copper. To achieve better impurity removal, iron ions can be reduced to divalent ferrous ions. Then, utilizing the difference in valence between ferrous ions and aluminum / titanium ions, as well as the difference in solubility of hydroxides, impurity ions are separated from the leaching solution through resin adsorption or pH adjustment. The inventors discovered that the acid leaching process mainly uses sulfuric acid, which can reduce waste gas generation in subsequent processes. However, sulfuric acid is difficult to recover and reuse throughout the process, and its large consumption leads to waste. The mainstream approach for the reduction process is chemical reduction, mainly by adding iron powder to reduce trivalent ferric ions in the leaching solution. However, this system is a strongly acidic environment. The added iron powder will not only be oxidized by iron ions but also by hydrogen ions in the system, leading to a series of problems in the production process, such as the generation of large amounts of hydrogen gas and premature hydrolysis and precipitation of ferric phosphate due to pH changes. Therefore, this scheme requires strict monitoring of the system's pH during implementation, and acid solution needs to be continuously added during the iron powder addition process to prevent hydrolysis. Furthermore, the added iron powder will cause changes in the phosphorus-iron element ratio in the system, requiring additional phosphorus source addition in subsequent processes, further increasing production costs. In view of this, this application provides the following technical solution:

[0019] The first aspect of this application provides a recovery method, comprising: a recovery process of phosphorus and iron elements in an iron phosphate system and a hydrochloric acid reuse process, wherein the recovery process of phosphorus and iron elements includes:

[0020] Acid leaching step: The ferric phosphate system is acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution;

[0021] The hydrochloric acid reuse process includes:

[0022] Chloride ion removal step: The acid leaching solution is electrolytically oxidized to remove chloride ions and generate chlorine gas;

[0023] Hydrochloric acid regeneration step: The chlorine gas is reacted with hydrogen gas to generate hydrochloric acid;

[0024] Hydrochloric acid reuse step: The hydrochloric acid is reused in the acid leaching step.

[0025] This application does not impose any particular limitation on the method of hydrogen production, as long as it achieves the purpose of this application.

[0026] Acid leaching of an iron phosphate system using hydrochloric acid yields an acid leaching solution rich in chloride ions. Impurities such as chloride ions are removed via electrolytic oxidation, simultaneously generating chlorine gas. Hydrochloric acid is then synthesized from hydrogen and chlorine gas and used in the initial acid leaching process. This recycling process achieves the recovery and reuse of industrial waste gas and hydrochloric acid, effectively reducing potential air pollution and significantly lowering recycling costs. The inventors discovered that electrolytic oxidation, which oxidizes chloride ions into chlorine gas and allows it to escape from the system, minimizes the impact on the acid leaching solution and simplifies subsequent treatment. The entire process utilizes an electrochemical method, reducing the amount of chemical reagents used and minimizing the impact on the iron phosphate system. This reduces the pressure on downstream impurity removal and iron phosphate regeneration processes, and the resulting iron phosphate meets battery-grade iron phosphate standards.

[0027] In one embodiment of this application, the iron phosphate system includes lithium iron phosphate slag or iron phosphate slag after lithium extraction from lithium iron phosphate slag. In this application, the lithium iron phosphate slag is not specifically limited and can be the lithium iron phosphate slag from waste lithium iron phosphate batteries; the iron phosphate slag after lithium extraction is not specifically limited and can be the iron phosphate slag after lithium extraction from waste lithium iron phosphate batteries or other iron phosphate slag (such as waste residue from iron phosphate production).

[0028] In this application, no particular limitation is made on the method for recovering hydrogen and chlorine, as long as it can achieve the purpose of this application. For example, an inert gas is introduced into a sealed electrolytic cell that generates hydrogen or chlorine to assist the hydrogen or chlorine to escape. After the hydrogen or chlorine is drawn out from the sealed electrolytic cell, it is dried by an acidic desiccant and then stored in a gas storage tank. The inert gas can be selected from at least one of nitrogen, argon and helium; the acidic desiccant can be selected from at least one of concentrated sulfuric acid, silica gel and phosphorus pentoxide.

[0029] In this application, the method for synthesizing hydrochloric acid after recovering hydrogen and chlorine is not particularly limited, as long as it achieves the purpose of this application. For example, hydrogen and chlorine are flowed into a sealed reactor isolated from air, water is added to the reactor, and the mixture is ignited to allow the gases to burn stably, producing hydrogen chloride gas which dissolves in the water to form hydrochloric acid. The reaction formula is: H2 + Cl2 = 2HCl. In this application, experimental conditions can be adjusted, such as adjusting electrolysis parameters, to ensure that the yields of hydrogen and chlorine are approximately the same, and all of it is used to produce hydrochloric acid, without releasing excess electrolysis waste gas to the outside.

[0030] In one embodiment of this application, the concentration of hydrochloric acid in the acid containing hydrochloric acid is 0.5–4 mol / L; and / or, the mass ratio of the ferric phosphate system to the hydrochloric acid is 1:1–5. For example, the concentration of hydrochloric acid in the acid containing hydrochloric acid can be 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, or any combination of two such values; the mass ratio of the ferric phosphate system to the hydrochloric acid can be 1:1, 1:2, 1:3, 1:4, 1:5, or any combination of two such values. The inventors have found that, during the acid leaching step, when the concentration of hydrochloric acid and the molar ratio of iron to chloride ions in the ferric phosphate system are within the above-mentioned ranges, the leaching rate of the elements can be better improved, thereby achieving greater recovery of phosphorus and iron components.

[0031] In one embodiment of this application, the acid leaching temperature is 40–80°C, and the time is 3–6 hours. For example, the acid leaching temperature can be 40°C, 50°C, 60°C, 70°C, 80°C, or a range of any two of these values, and the acid leaching time can be 3 hours, 4 hours, 5 hours, 6 hours, or a range of any two of these values. The inventors have discovered that using the above-mentioned acid leaching temperature and time in the acid leaching step can better improve the leaching rate of elements, thereby achieving greater recovery of phosphorus and iron components.

[0032] In one embodiment of this application, in the chloride ion removal step, the acid leaching solution is used as the anolyte, and the current density is 0.03–0.3 A / cm². 2 Electrolysis can be performed for 4 to 10 hours at a voltage of 4–7V. For example, the current density can be 0.03 A / cm². 2 0.1A / cm 2 0.2A / cm 2 0.3A / cm 2 The values ​​can be any two of these ranges; the voltage can be 4V, 5V, 6V, 7V, or any two of these ranges; the electrolysis time can be 4 hours, 6 hours, 8 hours, 10 hours, or any two of these ranges. Under these electrolytic oxidation conditions, the oxidation efficiency is higher.

[0033] The main reaction occurring on the anode side is: 2Cl - -2e - =Cl2↑

[0034] The side reaction occurring on the anode side is: 2H₂O - 4e⁻ - =O2↑+4H +

[0035] It should be noted that in the above electrolytic oxidation step, constant current electrolysis is used, and the current density is adjusted to 0.03–0.3 A / cm². 2 If constant voltage electrolysis is used, the regulating voltage is 4–7V. In this application, regulating current density refers to regulating the applied current density, and regulating voltage refers to regulating the applied voltage.

[0036] This application does not impose specific limitations on the cathode solution, cathode, anode, and diaphragm in the above-mentioned electrolytic oxidation steps, as long as they achieve the purpose of this application. For example, the cathode solution can be selected from, but is not limited to, solutions that can be electrolytically reduced, such as acid leaching solutions, water, dilute sulfuric acid, and ferric sulfate; the cathode can be selected from, but is not limited to, stainless steel, titanium, nickel metal, or carbon electrodes; the anode can be selected from, but is not limited to, plate or mesh electrodes made of metals such as ruthenium-titanium, ruthenium-iridium alloy, iridium-tantalum alloy, ruthenium-iridium-tantalum alloy, platinum, gold, and silver; the diaphragm can be selected from, but is not limited to, proton exchange membranes, such as perfluorosulfonic acid membranes (PFSA), sulfonated polyether ether ketone (SPEEK), polybenzimidazole (PBI), and polyphenylene ether (PPO). In some embodiments of this application, a diaphragm may not be provided between the cathode chamber and the anode chamber of the electrolytic cell, allowing chloride ions to spontaneously migrate to the anode under the action of an electric field and be oxidized to chlorine gas, while the cathode undergoes spontaneous hydrogen evolution or partial iron ion reduction reaction.

[0037] In one embodiment of this application, the recovery process of the phosphorus iron element includes: a trivalent iron electrolytic reduction step and an impurity removal step.

[0038] The inventors discovered that, compared to existing technologies that primarily rely on chemical reduction, electrolytic reduction offers a simpler and more efficient method, reducing recycling costs. Furthermore, the resulting iron phosphate meets battery-grade iron phosphate standards. The entire process utilizes an electrochemical method, minimizing the use of chemical reagents and reducing the impact on the iron phosphate system. This alleviates the pressure on downstream impurity removal and iron phosphate regeneration processes, ensuring the produced iron phosphate meets battery-grade iron phosphate standards.

[0039] In one embodiment of this application, in the electrolytic reduction step of ferric iron, the acid leaching solution is used as the cathode liquid, and the current density is 0.03–0.3 A / cm². 2 Electrolysis can be performed for 6 to 15 hours at a voltage of 3–6V. For example, the current density can be 0.03 A / cm². 2 0.1A / cm 2 0.2A / cm 2 0.3A / cm 2The values ​​can be any two of these ranges; the voltage can be 3V, 4V, 5V, 6V, or any two of these ranges; the electrolysis time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or any two of these ranges. Under these electrolytic reduction conditions, the reduction efficiency is higher.

[0040] The main reaction occurring on the cathode side is: Fe 3+ +e - =Fe 2+

[0041] The side reaction occurring on the cathode side is: 2H + +2e - =H2↑

[0042] It should be noted that in the above electrolytic reduction step, constant current electrolysis is used, and the controlled current density is 0.03–0.3 A / cm². 2 If constant voltage electrolysis is used, the regulating voltage is 3–6V. In this application, regulating current density refers to regulating the applied current density, and regulating voltage refers to regulating the applied voltage. For example, in the above electrolytic reduction step, if constant current electrolysis is used, the regulating applied current density is 0.03–0.3 A / cm². 2 If constant voltage electrolysis is used, the applied voltage should be adjusted to 3-6V.

[0043] This application does not impose any particular limitations on the anolyte, cathode, anode, and diaphragm in the above-mentioned electrolytic reduction step, as long as they can achieve the purpose of this application. For example, the anolyte can be selected from, but is not limited to, solutions that can be electrolyzed and oxidized, such as acid leaching solution, ferrous sulfate, water, or dilute sulfuric acid; the cathode can be selected from, but is not limited to, stainless steel, titanium metal plate or mesh electrodes; the anode can be selected from, but is not limited to, mesh or plate electrodes made of titanium metal or ruthenium-titanium metal; the diaphragm can be selected from, but is not limited to, proton exchange membranes, such as perfluorosulfonic acid membranes (PFSA), sulfonated polyether ether ketone (SPEEK), polybenzimidazole (PBI), polyphenylene ether (PPO), etc.

[0044] In this application, the specific operation of the impurity removal process is not limited, as long as it can achieve the separation of iron and phosphorus elements from impurities. The specific method depends on the differences between ferrous iron and impurity metal elements. For example, ferrous iron and other impurity metal elements can be separated by differences in valence or solubility.

[0045] In one embodiment of this application, the impurity removal step includes: removing metal impurity ions; the metal impurity ions are selected from at least one of titanium ions, aluminum ions, and copper ions.

[0046] In one embodiment of this application, the impurity removal step includes at least one of: impurity metal resin adsorption treatment, reduction treatment, and pH adjustment treatment.

[0047] In one embodiment of this application, the step of removing metal impurity ions includes: adjusting the pH to 1-3, stirring at 60-100°C for 1-3 hours, filtering, and then passing the solution through a cation exchange resin or chelating resin for adsorption. For example, the pH can be adjusted to 1-3, and the solution can be stirred at 60°C, 70°C, 80°C, 90°C, 100°C, or any two of these values ​​for 1 hour, 2 hours, 3 hours, or any two of these values, followed by filtration and then passing the solution through a cation exchange resin or chelating resin for adsorption. The inventors have found that adjusting the pH to 1-3 and stirring at 60-100°C for 1-3 hours can better remove impurity titanium ions; filtration followed by passing the solution through a cation exchange resin or chelating resin for adsorption can better remove impurity aluminum ions and a small amount of impurity titanium ions, without introducing new impurities or causing an increase in the solution pH, thus reducing the risk of hydrolysis.

[0048] This application does not specify a particular method for adjusting pH, as long as it achieves the purpose of this application. For example, an alkaline solution can be used to adjust the pH to 1-3, and the alkaline solution can be selected from at least one of sodium hydroxide and ammonia water. This application does not specify a particular type of cation exchange resin or chelating resin, as long as it achieves the purpose of this application. For example, the cation exchange resin can be selected from, but is not limited to, 001X4, 001X7, and... One of T-62MP, wherein the chelating resin may be selected from, but is not limited to, one of D401 and D402, and both the cation exchange resin and the chelating resin of this application can be obtained by purchase.

[0049] In one embodiment of this application, the recovery process of the phosphorus iron element further includes a ferrous iron oxidation step, wherein the ferrous iron oxidation step uses an oxidant to oxidize ferrous iron ions to ferric iron ions, or uses electrolytic oxidation to oxidize ferrous iron ions to ferric iron ions.

[0050] In one embodiment of this application, during the process of oxidizing ferrous ions to ferric ions with an oxidant, the oxidant is selected from at least one of hydrogen peroxide, ozone, oxygen, and sodium persulfate;

[0051] In the process of oxidizing ferrous ions to ferric ions by electrolytic oxidation, the solution of ferrous ions is used as the anolyte, and the current density is 0.03–0.3 A / cm². 2 Electrolysis can be performed for 6 to 15 hours at a voltage of 3–6V. For example, the current density can be 0.03 A / cm². 2 0.1A / cm 20.2A / cm 2 0.3A / cm 2 Or a range of any two of these values; the voltage can be 3V, 4V, 5V, 6V or a range of any two of these values; the electrolysis time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or a range of any two of these values.

[0052] It should be noted that in the above electrolytic oxidation step, constant current electrolysis is used, and the current density is adjusted to 0.03–0.3 A / cm². 2 If constant voltage electrolysis is used, the regulating voltage is 3-6V.

[0053] This application does not impose any particular limitations on the catholyte, cathode, anode, and diaphragm in the above-mentioned electrolytic oxidation steps, as long as they can achieve the purpose of this application. For example, the catholyte can be selected from, but is not limited to, solutions that can be electrolytically reduced, such as acid leaching solution, water, dilute sulfuric acid, and ferric sulfate; the cathode can be selected from, but is not limited to, stainless steel, titanium, nickel metal, or carbon electrodes; the anode can be selected from, but is not limited to, plate-shaped or mesh electrodes made of metals such as ruthenium-titanium, ruthenium-iridium alloy, iridium-tantalum alloy, ruthenium-iridium-tantalum alloy, platinum, gold, and silver; and the diaphragm can be selected from, but is not limited to, proton exchange membranes, such as perfluorosulfonic acid membranes (PFSA), sulfonated polyether ether ketone (SPEEK), polybenzimidazole (PBI), and polyphenylene ether (PPO).

[0054] This application does not impose any particular limitation on the specific steps of oxidation with oxidant, as long as the purpose of this application can be achieved. For example, an oxidant is added to the solution containing ferrous ions, and after mixing, it is stirred thoroughly. After the mixture is free of bubbles and the color changes from light green to light yellow, a sample is taken to detect the concentration of ferrous ions. According to the detection results, an appropriate amount of oxidant can be added. After the standard is met, a ferric phosphate solution is obtained.

[0055] In one embodiment of this application, the chloride ion removal step is performed before or simultaneously with the ferric electrolytic reduction step.

[0056] In one embodiment of this application, the chloride ion removal step and the trivalent iron electrolytic reduction step are performed on the anode side and cathode side of the same electrolytic cell or different electrolytic cells, respectively.

[0057] In one embodiment of this application, the ferrous iron oxidation step is carried out by electrolytic oxidation, and the chloride ion removal step and the ferrous iron oxidation step are carried out simultaneously on the anode side of the same electrolytic cell.

[0058] In one embodiment of this application, the hydrogen is generated on the cathode side of the electrolytic cell in the ferric electrolytic reduction step, and / or the hydrogen is generated on the cathode side of the electrolytic cell in the chloride ion removal step.

[0059] In one embodiment of this application, the ferrous iron oxidation step is carried out by electrolytic oxidation, and the hydrogen gas is generated on the cathode side of the electrolytic cell in the ferrous iron oxidation step.

[0060] In one embodiment of this application, the ferrous iron oxidation step is carried out by electrolytic oxidation, and the ferric iron electrolytic reduction step and the ferrous iron oxidation step are carried out on the cathode side and anode side of the same electrolytic cell, respectively.

[0061] In one embodiment of this application, the recycling method includes:

[0062] (A1) The ferric phosphate system is acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution;

[0063] (A2) The acid leaching solution is electrolyzed and oxidized to remove chloride ions to obtain the first solution A, while generating chlorine gas.

[0064] (A3) Electrolyze and reduce the first solution A to convert ferric ions into ferrous ions to obtain the second solution A, while generating hydrogen gas.

[0065] (A4) Remove the metal impurity ions from the second solution A to obtain the third solution A;

[0066] (A5) The third solution A is oxidized to convert ferrous ions into ferric ions to obtain ferric phosphate solution;

[0067] (A6) Hydrogen and chlorine are recovered to produce hydrochloric acid, which is then used for acid leaching.

[0068] The above method uses electrolytic reduction to convert ferric ions into ferrous ions and electrolytic oxidation to remove impurity chloride ions. The method is simple, has low recovery cost, reduces the amount of chemical reagents used, has little impact on the iron phosphate system, and reduces the pressure on the downstream impurity removal and iron phosphate regeneration process. The iron phosphate meets the battery-grade iron phosphate standard.

[0069] In one embodiment of this application, the recycling method includes:

[0070] (B1) The ferric phosphate system was acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution;

[0071] (B2) The acid leaching solution is electrolytically oxidized to remove chloride ions to obtain the first solution B, while generating chlorine gas.

[0072] (B3) Electrolyze the first solution B to reduce the ferric ions to ferrous ions, thereby obtaining the second solution B and generating hydrogen gas at the same time.

[0073] (B4) Remove the metal impurity ions from the second solution B to obtain the third solution B;

[0074] (B5) In the electrolytic cell, the anode electrolyzes and oxidizes the third solution B to convert ferrous ions into ferric ions to obtain ferric phosphate solution; the cathode couples the first solution B to electrolyze and reduce it to convert ferric ions into ferrous ions to obtain the second solution B (B3).

[0075] (B6) Hydrogen and chlorine are recovered to produce hydrochloric acid, which is then used for acid leaching.

[0076] The above method uses electrolytic reduction to convert ferric ions into ferrous ions and electrolytic oxidation to remove impurity chloride ions. At the same time, electrolytic oxidation is used to convert ferrous ions into ferric ions, which further optimizes the iron phosphate recovery method. In addition, in the step of electrolytic oxidation to convert ferrous ions into ferric ions, cathode-coupled electrolytic reduction converts ferric ions into ferrous ions, which further simplifies the reaction steps.

[0077] In one embodiment of this application, the recycling method includes:

[0078] (C1) The ferric phosphate system is acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution;

[0079] (C2) Electrolyze the acid leaching solution to convert ferric ions into ferrous ions, thereby obtaining the first solution C and generating hydrogen gas at the same time.

[0080] (C3) Remove the metal impurity ions from the first solution C to obtain the second solution C;

[0081] (C4) Electrolytically oxidize the second solution C to convert ferrous ions into ferric ions, while removing chloride ions to obtain ferric phosphate solution and generate chlorine gas.

[0082] (C5) Hydrogen and chlorine are recovered to produce hydrochloric acid, which is then used for acid leaching.

[0083] The above method uses electrolytic reduction to convert ferric ions into ferrous ions to remove impurities, followed by electrolytic oxidation to convert ferrous ions into ferric ions, while removing chloride ions, thus further optimizing the ferric phosphate recovery method, simplifying the reaction steps, and reducing recovery costs.

[0084] In one embodiment of this application, the recycling method includes:

[0085] (D1) The ferric phosphate system was acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution;

[0086] (D2) In the electrolytic cell, the anode electrolyzes and oxidizes the acid leaching solution to remove impurity chloride ions and obtains the first solution D, while generating chlorine gas; the cathode electrolyzes and reduces the first solution D to convert ferric ions into ferrous ions, obtaining the second solution D, while generating hydrogen gas.

[0087] (D3) Remove the metal impurity ions from the second solution D to obtain the third solution D;

[0088] (D4) The third solution D is oxidized to convert ferrous ions into ferric ions to obtain ferric phosphate solution;

[0089] (D5) Hydrogen and chlorine are recovered to produce hydrochloric acid, which is then used for acid leaching.

[0090] The above method uses electrolytic reduction to convert ferric ions into ferrous ions, coupled with electrolytic oxidation to remove impurity chloride ions, further optimizing the iron phosphate recovery method, simplifying the reaction steps, and reducing recovery costs.

[0091] In one embodiment of this application, the step of oxidizing the third solution D is carried out by electrolytic oxidation. The anode electrolytically oxidizes the third solution D, and the cathode electrolytically reduces the first solution D, so that the ferric ions are converted into ferrous ions to obtain the second solution D, while generating hydrogen gas.

[0092] The above method uses electrolytic reduction to convert ferric ions into ferrous ions, coupled with electrolytic oxidation to remove impurity chloride ions. Subsequent electrolytic oxidation converts ferrous ions into ferric ions, coupled with electrolytic reduction, further optimizes the iron phosphate recovery method, simplifies the reaction steps, and reduces recovery costs.

[0093] The method route for iron phosphate recovery according to one embodiment of this application is shown in Figure 1, and the working principle of the cathode electrochemical reduction coupled to the anode electrochemical oxidation according to one embodiment of this application is shown in Figure 2.

[0094] In one embodiment of this application, the recovery process of the ferric phosphorus element further includes: recovering ferric phosphate; the recovery of ferric phosphate includes: adjusting the pH of the ferric phosphate solution to 1-3 to form ferric phosphate precipitate, and washing, drying and heat-treating the ferric phosphate precipitate to obtain ferric phosphate.

[0095] In one embodiment of this application, the step of recovering ferric phosphate includes: adjusting the pH of the ferric phosphate solution to 1-3, reacting for 1-2 hours, filtering to obtain ferric phosphate precipitate, and washing, drying and heat-treating the ferric phosphate precipitate with water to obtain ferric phosphate.

[0096] This application does not impose any particular limitation on the method of adjusting the pH of the ferric phosphate solution, as long as it can achieve the purpose of this application. For example, the pH of the ferric phosphate solution can be adjusted to 1 to 3 using an alkaline solution, which can be selected from at least one of sodium hydroxide and ammonia water.

[0097] In one embodiment of this application, the drying temperature is 60–120°C; the heat treatment temperature is 400–1000°C, and the time is 1–10 hours. Through the above drying and heat treatment, a ferric phosphate product with low impurity content that meets the battery-grade ferric phosphate standard can be obtained.

[0098] The second aspect of this application provides a recycling apparatus for the recycling method described in the first aspect of this application, which includes a phosphorus iron element recovery unit and a hydrochloric acid recycling unit. The phosphorus iron element recovery unit includes an acid leaching unit; the hydrochloric acid recycling unit includes an electrolysis unit A, a chlorine gas storage unit, a hydrogen gas storage unit, and a hydrochloric acid regeneration unit.

[0099] The acid leaching unit is connected to the electrolysis unit A, the electrolysis unit A is connected to the chlorine gas storage unit, the chlorine gas storage unit and the hydrogen gas storage unit are respectively connected to the hydrochloric acid regeneration unit, and the hydrochloric acid regeneration unit is connected to the acid leaching unit.

[0100] In the above apparatus, the acid leaching unit is used to leach the ferric phosphate system to obtain an acid leaching solution. The obtained acid leaching solution enters the electrolysis unit A for electrolytic oxidation. The chlorine gas generated by electrolytic oxidation enters the chlorine gas storage unit. The chlorine gas in the chlorine gas storage unit enters the hydrochloric acid regeneration unit. The hydrogen gas in the hydrogen gas storage unit enters the hydrochloric acid regeneration unit. The chlorine gas and hydrogen gas are synthesized into hydrochloric acid in the hydrochloric acid regeneration unit. The hydrochloric acid regeneration unit is connected to the acid leaching unit and reuses the hydrochloric acid in the acid leaching unit.

[0101] In the following scheme, the hydrogen produced by electrolytic reduction enters the hydrogen storage unit, the chlorine produced by electrolytic oxidation enters the chlorine storage unit, and the chlorine and hydrogen are synthesized into hydrochloric acid in the hydrochloric acid regeneration unit. The hydrochloric acid regeneration unit is connected to the acid leaching unit, and the hydrochloric acid is reused in the acid leaching unit. This will not be described in detail.

[0102] In one embodiment of this application, the phosphorus and iron element recovery unit includes the electrolysis unit A and the impurity removal unit, wherein the electrolysis unit A is connected to the impurity removal unit.

[0103] It should be noted that the electrolysis unit A in the hydrochloric acid recycling unit can be shared with the ferric phosphorus recovery unit. For example, in one embodiment, the anode chamber of electrolysis unit A undergoes electrolytic oxidation to obtain a dechlorinated solution. The dechlorinated solution is then electrolytically reduced in the cathode chamber of electrolysis unit A to obtain a ferrous ion solution. The ferrous ion solution enters a purification unit to remove metal impurity ions, and then an oxidant is used to oxidize the ferrous ions to ferric ions, yielding a ferric phosphate solution. In another embodiment, the electrolysis unit A includes an anode chamber and a cathode chamber. The anode chamber of electrolysis unit A undergoes electrolytic oxidation to obtain a dechlorinated solution. The dechlorinated solution is then electrolytically reduced in the cathode chamber of electrolysis unit A to obtain a ferrous ion solution. The ferrous ion solution enters a purification unit to remove metal impurity ions. The solvent used to remove the metal impurity ions enters the anode chamber of electrolysis unit A for electrolytic oxidation, oxidizing the ferrous ions to ferric ions, yielding a ferric phosphate solution.

[0104] In one embodiment of this application, the phosphorus and iron element recovery unit includes the electrolysis unit A, and further includes a purification unit and an electrolysis unit B; the electrolysis unit A, the purification unit and the electrolysis unit B are connected in sequence.

[0105] It should be noted that electrolysis unit A in the hydrochloric acid recycling unit can be shared with the ferric phosphorus recovery unit. For example, in one embodiment, electrolytic oxidation is performed in the anode chamber of electrolysis unit A to obtain a dechlorinated solution. The dechlorinated solution is then electrolytically reduced in the cathode chamber of electrolysis unit A to obtain a ferrous ion solution. The ferrous ion solution enters a purification unit to remove metal impurity ions. The solution after removing metal impurity ions enters the anode chamber of electrolysis unit B for electrolytic oxidation, oxidizing the ferrous ions to ferric ions to obtain a ferric phosphate solution. In another embodiment, electrolytic reduction is performed in the cathode chamber of electrolysis unit B to obtain a ferrous ion solution. The ferrous ion solution enters a purification unit to remove metal impurity ions. The solvent after removing metal impurity ions enters the anode chamber of electrolysis unit A for electrolytic oxidation, oxidizing the ferrous ions to ferric ions and simultaneously removing chloride ions to obtain a ferric phosphate solution. In another implementation, the anode chamber of electrolysis unit A performs electrolytic oxidation to remove impurity chloride ions and generate chlorine gas, while the cathode chamber of electrolysis unit B performs electrolytic reduction to reduce ferric ions to ferrous ions. Then, the impurity removal unit removes metal impurity ions, and finally, an oxidant is used to oxidize the ferrous ions in the solution after removing metal impurity ions to ferric ions, thus obtaining a ferric phosphate solution.

[0106] In one embodiment of this application, the phosphorus and iron element recovery unit includes the electrolysis unit A, and further includes: a purification unit, an electrolysis unit B, and an electrolysis unit C, wherein the electrolysis unit A, the electrolysis unit B, the purification unit, and the electrolysis unit C are connected in sequence.

[0107] In the above-mentioned device, the anode chamber of the electrolysis unit A undergoes electrolytic oxidation to obtain a dechlorinated solution. The dechlorinated solution then enters the cathode chamber of the electrolysis unit B for electrolytic reduction to obtain a ferrous ion solution. The ferrous ion solution enters the impurity removal unit to remove metal impurity ions. The solvent used to remove the metal impurity ions then enters the anode chamber of the electrolysis unit C for electrolytic oxidation to obtain a ferric phosphate solution.

[0108] In one embodiment of this application, the recovery device further includes a material storage unit; the material storage unit is used to store various solutions synthesized during the recovery process.

[0109] Example

[0110] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0111] Test methods and equipment:

[0112] Composition testing of ferric phosphate system, composition testing of ferric phosphate acid leaching solution, and composition testing of ferric phosphate solution.

[0113] All measurements were performed using inductively coupled plasma spectroscopy (ICP), in accordance with the YS / T1263.1-2018 standard.

[0114] Iron yield calculation:

[0115] Phosphorus yield calculation:

[0116] Energy consumption calculation:

[0117] Example 1

[0118] The iron phosphate system used in this embodiment is the iron phosphate residue after lithium extraction from lithium iron phosphate residue of lithium iron phosphate recycling enterprises. The content of major elements in the iron phosphate residue was tested and found to be: Fe: 26.43wt%, P: 14.64wt%, Al: 0.62wt%, Ti: 0.43wt%, Cu: 0.41wt%.

[0119] (1) Mix ferric phosphate slag with hydrochloric acid, wherein the concentration of hydrochloric acid is 4 mol / L and the mass ratio of ferric phosphate slag to hydrochloric acid is 1:3; after mixing, acid leaching is carried out at a temperature of 60℃ and a stirring speed of 300 rpm for 3 hours; after acid leaching, vacuum filtration is used to obtain ferric phosphate leaching solution, the concentration of each major element in ferric phosphate leaching solution is detected, and the leaching rate of each major element is calculated, as shown in Table 1.

[0120] (2) Using the above-mentioned ferric phosphate leaching solution as the anolyte and dilute sulfuric acid (concentration of 1 mol / L) as the catholyte, the anode material is ruthenium-iridium titanium mesh, the cathode material is titanium metal mesh, and the diaphragm is PFSA membrane; constant voltage electrolysis is adopted, the voltage is 6V, and the time is 4 hours, and the first solution A is obtained in the anode area;

[0121] Nitrogen gas is introduced into the anode region to assist chlorine gas in escaping. The chlorine gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a chlorine gas storage tank. Nitrogen gas is introduced into the cathode region to assist hydrogen gas in escaping. The hydrogen gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a hydrogen gas storage tank.

[0122] (3) The first solution A is used as the cathode liquid, and ferrous sulfate solution is used as the anode liquid. The anode material is ruthenium-iridium titanium mesh, the cathode material is titanium mesh, and the diaphragm is PFSA membrane. Constant voltage electrolysis is performed at a voltage of 4V for 15 hours to obtain the second solution A in the cathode region.

[0123] Nitrogen gas is introduced into the cathode area to assist the escape of hydrogen gas. After being drawn out from the sealed electrolytic cell, the hydrogen gas is dried with concentrated sulfuric acid (98 wt%) and then stored in a hydrogen storage tank.

[0124] (4) The pH of the second solution A was adjusted to 2-3 with ammonia water, and the solution was stirred at 80°C for 2 hours to initially remove titanium ions. After titanium removal, the filtrate was passed through a cation exchange resin at a flow rate of 0.5 BV / h. T-62MP was used to remove aluminum ions and a small amount of titanium ions, resulting in a third solution A.

[0125] (5) Take 30 vol% hydrogen peroxide and the above-mentioned third solution A at a volume ratio of 1:5, mix them thoroughly, and stir until no more bubbles are produced and the color changes from light green to light yellow. Then, take a sample to test the ferrous ion concentration. Based on the test results, an appropriate amount of 30 vol% hydrogen peroxide can be added. If the ferrous ion concentration is below 1×10⁻⁶, the solution is suitable for further testing. -3 At a concentration of mol / L, an iron phosphate solution was obtained; the composition of the iron phosphate solution was analyzed, and the yields of iron and phosphorus were calculated, as shown in Table 2.

[0126] (6) Then, ammonia water is added to the above ferric phosphate solution to adjust the pH of the solution to 1-3. The reaction time is 2 hours. The ferric phosphate precipitate is obtained by filtration. The ferric phosphate precipitate is washed with water and dried at 80°C. Then, it is heat-treated at 400°C for 3 hours to obtain the ferric phosphate product.

[0127] (7) Draw chlorine and hydrogen gas from the chlorine gas storage tank and the hydrogen gas storage tank into a sealed reactor (isolated from air), add water into the reactor, ignite it, so that the gas burns stably and produces hydrogen chloride gas that dissolves in water to form hydrochloric acid, which is then used for acid leaching.

[0128] Example 2

[0129] The ferric phosphate slag used in this embodiment is the same as in Embodiment 1, and step (1) is the same as in Embodiment 1.

[0130] (2) Using the above-mentioned ferric phosphate leaching solution as the anolyte and dilute sulfuric acid (concentration of 1 mol / L) as the catholyte, the anode material is ruthenium-iridium titanium mesh, the cathode material is titanium metal mesh, and the diaphragm is PFSA membrane; constant voltage electrolysis is adopted, the voltage is 6V, and the time is 4 hours, and the first solution B is obtained in the anode area;

[0131] Nitrogen gas is introduced into the anode region to assist chlorine gas in escaping. The chlorine gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a chlorine gas storage tank. Nitrogen gas is introduced into the cathode region to assist hydrogen gas in escaping. The hydrogen gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a hydrogen gas storage tank.

[0132] (3) The first solution B is used as the cathode liquid, and ferrous sulfate solution is used as the anode liquid. The anode material is ruthenium-iridium titanium mesh, the cathode material is titanium mesh, and the diaphragm is PFSA membrane. Constant voltage electrolysis is performed at a voltage of 4V for 15 hours to obtain the second solution B in the cathode region.

[0133] Nitrogen gas is introduced into the cathode area to assist the escape of hydrogen gas. After being drawn out from the sealed electrolytic cell, the hydrogen gas is dried with concentrated sulfuric acid (98 wt%) and then stored in a hydrogen storage tank.

[0134] (4) The pH of the second solution B was adjusted to 2-3 with ammonia water, and the solution was stirred at 80°C for 2 hours to initially remove titanium ions. After titanium removal, the filtrate was passed through a cation exchange resin at a flow rate of 0.5 BV / h. T-62MP was used to remove aluminum ions and a small amount of titanium ions, resulting in a third solution B.

[0135] (5) Using the third solution B as the anolyte and the first solution B as the cathode, the anode material is a ruthenium-iridium titanium mesh, the cathode material is a titanium mesh, and the diaphragm is PFSA; constant voltage electrolysis is performed at a voltage of 4V for 6 hours. Iron phosphate solution is obtained in the anode region and second solution B is obtained in the cathode region; the composition of the iron phosphate solution is analyzed, and the yields of iron and phosphorus are calculated respectively, as shown in Table 2.

[0136] (6) Then, ammonia water is added to the above ferric phosphate solution to adjust the pH of the solution to 1-3. The reaction time is 2 hours. The ferric phosphate precipitate is obtained by filtration. The ferric phosphate precipitate is washed with water and dried at 80°C. Then, it is heat-treated at 400°C for 3 hours to obtain the ferric phosphate product.

[0137] (7) Draw chlorine and hydrogen gas from the chlorine gas storage tank and the hydrogen gas storage tank into a sealed reactor (isolated from air), add water into the reactor, ignite it, so that the gas burns stably and produces hydrogen chloride gas that dissolves in water to form hydrochloric acid, which is then used for acid leaching.

[0138] Example 3

[0139] The ferric phosphate slag used in this embodiment is the same as in Embodiment 1, and step (1) is the same as in Embodiment 1.

[0140] (2) The above ferric phosphate leaching solution was used as the cathode liquid and ferrous sulfate was used as the anode liquid. The anode material was ruthenium-iridium titanium mesh, the cathode material was titanium mesh, and the diaphragm was PFSA. Constant voltage electrolysis was performed at a voltage of 4V for 15 hours, and the first solution C was obtained in the cathode area.

[0141] Nitrogen gas is introduced into the cathode area to assist the escape of hydrogen gas. After being drawn out from the sealed electrolytic cell, the hydrogen gas is dried with concentrated sulfuric acid (98 wt%) and then stored in a hydrogen storage tank.

[0142] (3) The pH of the first solution C was adjusted to 2-3 with ammonia water, and the solution was stirred at 80°C for 2 hours to initially remove titanium ions; after titanium removal, the filtrate was passed through a cation exchange resin at a flow rate of 0.5 BV / h. T-62MP) was used to remove aluminum ions and a small amount of titanium ions to obtain a second solution C.

[0143] (4) Using the above-mentioned second solution C as the anolyte and dilute sulfuric acid (concentration of 1 mol / L) as the catholyte, the anode material is ruthenium-iridium titanium mesh, the cathode material is titanium mesh, and the diaphragm is PFSA; constant voltage electrolysis is adopted, the voltage is 6V, and the time is 6 hours, and iron phosphate solution is obtained in the anode region; the composition of the iron phosphate solution is analyzed, and the yields of iron and phosphorus are calculated respectively, as shown in Table 2.

[0144] Nitrogen gas is introduced into the anode region to assist chlorine gas in escaping. The chlorine gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a chlorine gas storage tank. Nitrogen gas is introduced into the cathode region to assist hydrogen gas in escaping. The hydrogen gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a hydrogen gas storage tank.

[0145] (5) Then, ammonia water is added to the above ferric phosphate solution to adjust the pH of the solution to 1-3. The reaction time is 2 hours. The ferric phosphate precipitate is obtained by filtration. The ferric phosphate precipitate is washed with water and dried at 80°C. Then, it is heat-treated at 400°C for 2 hours to obtain the ferric phosphate product.

[0146] (6) Chlorine and hydrogen gas are drawn from the chlorine and hydrogen gas storage tanks and flowed into a sealed reactor (isolated from air). Water is added to the reactor and ignited to make the gas burn stably, producing hydrogen chloride gas which dissolves in the water to form hydrochloric acid, which is then used for acid leaching.

[0147] Example 4

[0148] The ferric phosphate slag used in this embodiment is the same as in Embodiment 1, and step (1) is the same as in Embodiment 1.

[0149] (2) Using the above-mentioned ferric phosphate leaching solution as the anolyte and the ferric phosphate leaching solution as the catholyte, the anode material is a ruthenium-iridium titanium plate, the cathode material is a titanium plate, and the diaphragm is PFSA; constant voltage electrolysis is performed at a voltage of 7V for 4 hours, and the first solution D is obtained in the anode region; the above-mentioned first solution D is used to replace the ferric phosphate leaching solution as the catholyte for electrochemical reduction, and constant voltage electrolysis is performed at a voltage of 4V for 15 hours, and the second solution D is obtained in the cathode region;

[0150] Nitrogen gas is introduced into the anode region to assist chlorine gas in escaping. The chlorine gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a chlorine gas storage tank. Nitrogen gas is introduced into the cathode region to assist hydrogen gas in escaping. The hydrogen gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a hydrogen gas storage tank.

[0151] (3) The pH of the second solution D was adjusted to 2-3 using ammonia water, and the solution was stirred at 80°C for 2 hours to initially remove titanium ions. After titanium removal, the filtrate was passed through a cation exchange resin at a flow rate of 0.5 BV / h. T-62MP was used to remove aluminum ions and a small amount of titanium ions to obtain the third solution D.

[0152] (4) Using the third solution D as the anolyte and the first solution D as the cathode, the anode material is a ruthenium-iridium titanium mesh, the cathode material is a titanium mesh, and the diaphragm is PFSA; constant voltage electrolysis is used, with a voltage of 4V and a time of 6 hours. Iron phosphate solution is obtained in the anode region and the second solution D is obtained in the cathode region; the composition of the iron phosphate solution is analyzed, and the yields of iron and phosphorus are calculated respectively, as shown in Table 2.

[0153] (5) Then, ammonia water is added to the above ferric phosphate solution to adjust the pH of the solution to 1-2. The reaction time is 1 hour. The ferric phosphate precipitate is obtained by filtration. The ferric phosphate precipitate is washed with water and dried at 80°C. Then, it is heat-treated at 400°C for 4 hours to obtain the ferric phosphate product.

[0154] (6) Chlorine and hydrogen gas are drawn from the chlorine and hydrogen gas storage tanks and flowed into a sealed reactor (isolated from air). Water is added to the reactor and ignited to make the gas burn stably, producing hydrogen chloride gas which dissolves in the water to form hydrochloric acid, which is then used for acid leaching.

[0155] Example 5

[0156] The ferric phosphate slag used in this embodiment is the same as in Embodiment 1, and step (1) is the same as in Embodiment 1.

[0157] (2) Using the above-mentioned ferric phosphate leaching solution as the anolyte and the ferric phosphate leaching solution as the cathode, the anode material is a ruthenium-iridium titanium plate, the cathode material is a titanium plate, and the diaphragm is PFSA; constant current electrolysis is used, with a current density of 0.1 A / cm². 2 The reaction time was 6 hours, and the first solution D was obtained in the anolyte. This first solution D was then used to replace the ferric phosphate leaching solution as the catholyte for electrochemical reduction, employing constant current electrolysis at a current density of 0.1 A / cm². 2 The time was 15 hours, and the cathode region obtained the second solution D;

[0158] Nitrogen gas is introduced into the anode region to assist chlorine gas in escaping. The chlorine gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a chlorine gas storage tank. Nitrogen gas is introduced into the cathode region to assist hydrogen gas in escaping. The hydrogen gas is drawn out from the sealed electrolytic cell, dried with concentrated sulfuric acid (98 wt%), and then stored in a hydrogen gas storage tank.

[0159] (3) The pH of the second solution D was adjusted to 2-3 using ammonia water, and the solution was stirred at 80°C for 2 hours to initially remove titanium ions. After titanium removal, the filtrate was passed through a cation exchange resin at a flow rate of 0.5 BV / h. T-62MP was used to remove aluminum ions and a small amount of titanium ions to obtain the third solution D.

[0160] (4) Using the third solution D as the anolyte and the first solution D as the cathode, the anode material is a ruthenium-iridium titanium mesh, the cathode material is a titanium mesh, and the diaphragm is PFSA; constant current electrolysis is used, with a current density of 0.1 A / cm². 2 The reaction time was 10 hours. Iron phosphate solution was obtained in the anode region and a second solution D was obtained in the cathode region. The composition of the iron phosphate solution was analyzed and the yields of iron and phosphorus were calculated, as shown in Table 2.

[0161] (5) Then, ammonia water is added to the above ferric phosphate solution to adjust the pH of the solution to 1-2. The reaction time is 1 hour. The ferric phosphate precipitate is obtained by filtration. The ferric phosphate precipitate is washed with water and dried at 80°C. Then, it is heat-treated at 400°C for 4 hours to obtain the ferric phosphate product.

[0162] (6) Chlorine and hydrogen gas are drawn from the chlorine and hydrogen gas storage tanks and flowed into a sealed reactor (isolated from air). Water is added to the reactor and ignited to make the gas burn stably, producing hydrogen chloride gas which dissolves in the water to form hydrochloric acid, which is then used for acid leaching.

[0163] Example 6

[0164] Except for replacing "lithium iron phosphate residue after lithium extraction" with "lithium iron phosphate residue", the other steps are the same as in Example 4. The iron phosphate system used in this application is lithium iron phosphate residue. The content of major elements in the lithium iron phosphate residue was tested and found to be: Fe: 25.73 wt%, P: 14.19 wt%, Li: 3.18 wt%, Al: 0.57 wt%, Ti: 0.43 wt%, Cu: 0.45 wt%.

[0165] Comparative Example 1

[0166] Except replacing step (1) with “mixing ferric phosphate slag with oxalic acid, wherein the concentration of oxalic acid is 2 mol / L and the mass ratio of ferric phosphate slag to oxalic acid is 1:3; after mixing, acid leaching for 3 hours at a temperature of 60℃ and a stirring speed of 300 rpm”.

[0167] After acid leaching, vacuum filtration was performed to obtain a ferric phosphate leaching solution. The concentrations of the major ions in the ferric phosphate leaching solution were measured, and the leaching rates of the major ions were calculated. The results are shown in Table 1. Except for the above steps, the remaining steps are the same as in Example 1.

[0168] Table 1

[0169] In Table 1, " / " indicates that there is no relevant data.

[0170] Table 2

[0171] In Table 2, " / " indicates no relevant data, and "Power Consumption (kWh / t FePO4)" indicates the power consumption required to produce 1 ton of iron phosphate product.

[0172] As shown in Table 1, compared to the oxalic acid used in Comparative Example 1, the use of hydrochloric acid in Examples 1 and 6 of this application resulted in higher leaching rates of iron and phosphorus, thus enabling the recovery of more ferric phosphorus components. Furthermore, Example 6 also shows that the use of hydrochloric acid for leaching resulted in a higher lithium leaching rate. Simultaneously, the ferric phosphate system was leached with hydrochloric acid to obtain an acid leaching solution rich in chloride ions. Impurities in chloride ions were removed by electrochemical oxidation, generating chlorine gas. Ferric ions were converted from ferric to ferrous ions by electroreduction, obtaining a solution containing ferrous ions and generating hydrogen gas. Hydrochloric acid was then synthesized again using hydrogen and chlorine gas and used in the initial leaching process. In the ferric phosphate system recovery process, industrial waste gas was recovered and reused, and hydrochloric acid was reused, effectively reducing potential air pollution problems during ferric phosphorus recovery and significantly reducing the cost of ferric phosphorus recovery.

[0173] As shown in Table 2, the recovery method of this application achieves high phosphorus and iron recovery rates. Specifically, Example 3 uses electrochemical reduction to convert ferric ions to ferrous ions, removing impurities, followed by electrochemical oxidation to convert ferrous ions back to ferric ions, while simultaneously removing chloride ions. Although the recovery rate is relatively low, this method optimizes the iron phosphate recovery process, simplifies the reaction steps, and reduces recovery costs. Furthermore, in Example 6, the iron phosphate system is lithium iron phosphate slag, and as shown in Table 2, the recovery method of this application results in minimal lithium loss.

[0174] In summary, the recycling method of this application is simple and efficient to operate, has low recycling costs, reduces the amount of chemical reagents used, has little impact on the iron phosphate system, reduces the pressure on the downstream impurity removal and iron phosphate regeneration process, and the obtained iron phosphate meets the battery-grade iron phosphate standard, and can therefore be used to prepare lithium iron phosphate batteries.

[0175] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0176] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A recycling method, comprising: The process for recovering phosphorus and iron elements and the process for reusing hydrochloric acid in the ferric phosphate system, wherein the recovery process for phosphorus and iron elements includes: Acid leaching step: The ferric phosphate system is acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution; The hydrochloric acid reuse process includes: Chloride ion removal step: The acid leaching solution is electrolytically oxidized to remove chloride ions and generate chlorine gas; Hydrochloric acid regeneration step: The chlorine gas is reacted with hydrogen gas to generate hydrochloric acid; Hydrochloric acid reuse step: The hydrochloric acid is reused in the acid leaching step.

2. The recycling method according to claim 1, wherein, The iron phosphate system includes lithium iron phosphate slag or lithium iron phosphate slag after lithium extraction from lithium iron phosphate slag.

3. The recycling method according to claim 1, wherein, The concentration of hydrochloric acid in the acid containing hydrochloric acid is 0.5–4 mol / L; and / or, the mass ratio of the ferric phosphate system to the hydrochloric acid is 1:1–5.

4. The recycling method according to claim 1, wherein, In the chloride ion removal step, the acid leaching solution is used as the anolyte, and the current density is 0.03–0.3 A / cm². 2 Electrolysis can be performed for 4 to 10 hours under conditions of 4 to 7V.

5. The recycling method according to claim 1, wherein, The recovery process of phosphorus and iron includes: an electrolytic reduction step of ferric iron and a purification step.

6. The recycling method according to claim 5, wherein, In the electrolytic reduction step of ferric iron, the acid leaching solution is used as the cathode liquid, and the current density is 0.03–0.3 A / cm². 2 Electrolysis can be performed for 6 to 15 hours under conditions of 3 to 6V.

7. The recycling method according to claim 5, wherein, The impurity removal step includes: removing metal impurity ions; the metal impurity ions are selected from at least one of titanium ions, aluminum ions, and copper ions.

8. The recycling method according to claim 7, wherein, The impurity removal steps include at least one of the following: impurity metal resin adsorption treatment, reduction treatment, and pH adjustment treatment.

9. The recycling method according to any one of claims 5-8, wherein, The recovery process of phosphorus and iron elements also includes a ferrous oxidation step, in which ferrous ions are oxidized to ferric ions by an oxidant or by electrolytic oxidation.

10. The recycling method according to claim 9, wherein, In the process of oxidizing ferrous ions to ferric ions using an oxidizing agent, the oxidizing agent is selected from at least one of hydrogen peroxide, ozone, oxygen, and sodium persulfate; In the process of oxidizing ferrous ions to ferric ions by electrolytic oxidation, the solution of ferrous ions is used as the anolyte, and the current density is 0.03–0.3 A / cm². 2 Electrolysis can be performed for 6 to 15 hours under conditions of 3 to 6V.

11. The recycling method according to any one of claims 5-10, wherein, The chloride ion removal step is performed before or simultaneously with the ferric electrolytic reduction step.

12. The recycling method according to any one of claims 5-10, wherein, The chloride ion removal step and the trivalent iron electrolytic reduction step are performed on the anode side and cathode side of the same electrolytic cell or different electrolytic cells, respectively.

13. The recycling method according to any one of claims 9-10, wherein, The ferrous iron oxidation step is carried out by electrolytic oxidation, and the chloride ion removal step and the ferrous iron oxidation step are carried out simultaneously on the anode side of the same electrolytic cell.

14. The recycling method according to any one of claims 5-13, wherein, The hydrogen is generated on the cathode side of the electrolytic cell in the ferric electrolytic reduction step, and / or the hydrogen is generated on the cathode side of the electrolytic cell in the chloride ion removal step.

15. The recycling method according to any one of claims 9-13, wherein, The oxidation of ferrous iron is carried out by electrolytic oxidation, and the hydrogen gas is generated on the cathode side of the electrolytic cell in the oxidation of ferrous iron.

16. The recycling method according to any one of claims 9-13, wherein, The ferrous iron oxidation step is carried out by electrolytic oxidation, and the ferric iron electrolytic reduction step and the ferrous iron oxidation step are carried out on the cathode side and anode side of the same electrolytic cell, respectively.

17. The recycling method according to any one of claims 1-16, comprising: (A1) The ferric phosphate system is acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution; (A2) The acid leaching solution is electrolyzed and oxidized to remove chloride ions to obtain the first solution A, while generating chlorine gas. (A3) Electrolyze the first solution A to convert ferric ions into ferrous ions, thereby obtaining the second solution A and generating hydrogen gas at the same time. (A4) Remove the metal impurity ions from the second solution A to obtain the third solution A; (A5) The third solution A is oxidized to convert ferrous ions into ferric ions to obtain ferric phosphate solution; (A6) Hydrogen and chlorine are recovered to produce hydrochloric acid, which is then used for acid leaching.

18. The recycling method according to any one of claims 1-16, comprising: (B1) The ferric phosphate system was acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution; (B2) The acid leaching solution is electrolytically oxidized to remove chloride ions to obtain the first solution B, while generating chlorine gas. (B3) Electrolyze the first solution B to reduce the ferric ions to ferrous ions, thereby obtaining the second solution B and generating hydrogen gas at the same time. (B4) Remove the metal impurity ions from the second solution B to obtain the third solution B; (B5) In the electrolytic cell, the anode electrolyzes and oxidizes the third solution B, converting ferrous ions into ferric ions to obtain ferric phosphate solution; The first solution B is electrolytically reduced by cathode coupling to convert ferric ions into ferrous ions, thus obtaining the second solution B (B3). (B6) Hydrogen and chlorine are recovered to produce hydrochloric acid, which is then used for acid leaching.

19. The recycling method according to any one of claims 1-16, comprising: (C1) The ferric phosphate system is acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution; (C2) Electrolyze the acid leaching solution to convert ferric ions into ferrous ions, thereby obtaining the first solution C and generating hydrogen gas at the same time. (C3) Remove the metal impurity ions from the first solution C to obtain the second solution C; (C4) Electrolytically oxidize the second solution C to convert ferrous ions into ferric ions, while removing chloride ions to obtain ferric phosphate solution and generate chlorine gas. (C5) Hydrogen and chlorine are recovered to produce hydrochloric acid, which is then used for acid leaching.

20. The recycling method according to any one of claims 1-16, comprising: (D1) The ferric phosphate system was acid-leached with an acid containing hydrochloric acid to obtain an acid leaching solution; (D2) In the electrolytic cell, the anode electrolyzes and oxidizes the acid leaching solution to remove impurity chloride ions and obtains the first solution D, while generating chlorine gas; the cathode electrolyzes and reduces the first solution D to convert ferric ions into ferrous ions, obtaining the second solution D, while generating hydrogen gas. (D3) Remove the metal impurity ions from the second solution D to obtain the third solution D; (D4) The third solution D is oxidized to convert ferrous ions into ferric ions to obtain ferric phosphate solution; (D5) Hydrogen and chlorine are recovered to produce hydrochloric acid, which is then used for acid leaching.

21. The recycling method according to claim 20, wherein, The step of oxidizing the third solution D is carried out by electrolytic oxidation. The anode electrolytically oxidizes the third solution D, and the cathode electrolytically reduces the first solution D, so that the ferric ions are converted into ferrous ions to obtain the second solution D, and hydrogen gas is generated at the same time.

22. A recycling apparatus for the recycling method according to any one of claims 1-21, comprising a phosphorus iron element recovery unit and a hydrochloric acid recycling unit, wherein the phosphorus iron element recovery unit comprises an acid leaching unit; and the hydrochloric acid recycling unit comprises an electrolysis unit A, a chlorine gas storage unit, a hydrogen gas storage unit, and a hydrochloric acid regeneration unit. The acid leaching unit is connected to the electrolysis unit A, the electrolysis unit A is connected to the chlorine gas storage unit, the chlorine gas storage unit and the hydrogen gas storage unit are respectively connected to the hydrochloric acid regeneration unit, and the hydrochloric acid regeneration unit is connected to the acid leaching unit.

23. The recycling apparatus according to claim 22, wherein, The phosphorus and iron element recovery unit includes the electrolysis unit A and the impurity removal unit, and the electrolysis unit A is connected to the impurity removal unit.

24. The recycling apparatus according to claim 22, wherein, The phosphorus and iron element recovery unit includes the electrolysis unit A, and further includes a purification unit and an electrolysis unit B; the electrolysis unit A, the purification unit and the electrolysis unit B are connected in sequence.

25. The recycling apparatus according to claim 22, wherein, The phosphorus and iron element recovery unit includes the electrolysis unit A, and further includes a purification unit, an electrolysis unit B, and an electrolysis unit C, wherein the electrolysis unit A, electrolysis unit B, purification unit, and electrolysis unit C are connected in sequence.

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