Method and system for preparing iron phosphate based on continuous acidolysis of phosphated iron powder

Abstract

The invention discloses a method and system for preparing iron phosphate based on continuous acidolysis of iron phosphide powder, and belongs to the technical field of wet metallurgy and battery material preparation. The method comprises the steps that a first oxidizing agent is added into reaction slurry containing a ferrous ion solution, acid and phosphating iron powder, so that Fe < 2 + > in the reaction slurry is oxidized into Fe < 3 + >, the Fe < 3 + > and iron phosphide are subjected to a redox reaction, and leachate rich in Fe < 2 + > and PO4 < 3-> is obtained; and at least part of the leachate reacts with a second oxidizing agent, so that Fe < 2 + > in the leachate is completely oxidized into Fe < 3 + >, and the Fe < 3 + > and PO4 < 3-> generate iron phosphate. According to the method, efficient and continuous dissolution of iron phosphide is achieved by constructing an ingenious iron ion internal circulation oxidation system, and the technical problem that in the prior art, direct acid dissolution of iron phosphide powder is difficult is solved; the method is short in process, low in cost and easy for industrial continuous production. The corresponding system is easy to set, simple in structure and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrometallurgy and battery material preparation, in particular to a method and system for preparing iron phosphate based on continuous acidolysis of iron phosphide powder. BACKGROUND

[0002] Iron phosphide is an important industrial intermediate or byproduct, which may also be derived from the recycling process of specific waste. Due to the stable crystal structure and high chemical inertness of iron phosphide, it is extremely difficult to dissolve in conventional acids (such as sulfuric acid and hydrochloric acid), which seriously restricts its use as an iron source and phosphorus source for high value-added products (such as battery-grade iron phosphate).

[0003] In the prior art, in order to deal with such insoluble materials, high temperature and high pressure enhanced leaching or the introduction of strong oxidizing agents (such as sodium chlorate and nitric acid) is usually used. However, high temperature and high pressure method has high requirements for equipment, high energy consumption and poor operation safety; while using liquid strong oxidizing agent has problems such as high cost, difficult to control, possible introduction of new anion impurities (such as Cl - , NO3 - ), and passivation or element loss of materials (such as phosphorus escaping in the form of PH3 gas) due to local over-concentration.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a method and system for preparing iron phosphate based on continuous acidolysis of iron phosphide powder, in order to solve or improve at least one of the above technical problems.

[0006] The present application can be realized as follows: In a first aspect, the present application provides a method for preparing iron phosphate based on continuous acidolysis of iron phosphide powder, comprising the following steps: adding a first oxidizing agent to a reaction slurry containing divalent iron ion solution, acid and iron phosphide powder, so as to oxidize Fe 2+ in the reaction slurry to Fe 3+ and make the generated Fe 3+ and iron phosphide undergo a redox reaction to obtain a leaching solution rich in Fe 2+ and PO4 3- ; reacting at least part of the leaching solution with a second oxidizing agent to oxidize all Fe 2+ in the leaching solution to Fe 3+ and generate iron phosphate with PO4 3- .

[0007] In an optional embodiment, the Fe 2+ and PO4 3-phosphide powder and acid is supplemented while continuously drawing out the Fe 2+ and PO4 3- rich leaching solution from the leaching reaction device to keep the system in the leaching reaction device in Fe 2+ state all the time.

[0008] In an optional embodiment, the molar ratio of Fe 2+ in the divalent iron ion solution to the phosphide powder is 9:2 to 9:5.

[0009] In an optional embodiment, the acid comprises at least one of sulfuric acid and phosphoric acid.

[0010] In an optional embodiment, the first oxidizing agent and the second oxidizing agent independently comprise at least one of oxygen, air, ozone and hydrogen peroxide.

[0011] In an optional embodiment, the first oxidizing agent and the second oxidizing agent independently comprise at least one of oxygen and air.

[0012] In an optional embodiment, the generated Fe 3+ and the phosphide powder undergoes redox reaction under the condition of pH value of 1.5 to 2 and temperature of 60°C to 95°C.

[0013] In an optional embodiment, the volume of the leaching solution used for reaction with the second oxidizing agent accounts for 30% to 40% of the total volume of the leaching solution in terms of volume percentage.

[0014] In an optional embodiment, the leaching solution not used for reaction with the second oxidizing agent is returned to the leaching reaction device of the Fe 2+ and PO4 3- rich leaching solution.

[0015] In an optional embodiment, it further comprises solid-liquid separation of the remaining leaching solution other than the one returned to the leaching reaction device, and the separated liquid is used for reaction with the second oxidizing agent.

[0016] In an optional embodiment, the pH value of at least part of the leaching solution for reaction with the second oxidizing agent is 1.5 to 3.0 and the temperature is 50°C to 90°C.

[0017] In an optional embodiment, the pH value of the reaction is adjusted by adding ammonia water.

[0018] In a second aspect, the present application provides a system for preparing iron phosphate based on continuous acidolysis of phosphide powder, comprising a leaching reaction device and a product synthesis device. The leaching reaction device is used for reaction of the reaction slurry formed by the divalent iron ion solution, the acid and the phosphide powder with the first oxidizing agent to obtain the Fe2+ and PO4 3- of the leaching solution; The product synthesis device is used for reacting at least part of the leaching solution with a second oxidizing agent to oxidize Fe 2+ in the leaching solution into Fe 3+ and generate phosphorus iron with PO4 3- .

[0019] In an optional embodiment, the leaching reaction device comprises a stirred tank reactor, a column reactor or a cascade reactor group.

[0020] In an optional embodiment, the system further comprises a solid-liquid separation device used for solid-liquid separation of the leaching solution reacted with the second oxidizing agent, and the separated liquid is used for reaction with the second oxidizing agent.

[0021] In an optional embodiment, the system further comprises a splitting and circulating device used for splitting the leaching solution rich in Fe 2+ and PO4 3- into a part returned to the leaching reaction device and a part used for entering the product synthesis device, and for circulating the part returned to the leaching reaction device to the leaching reaction device.

[0022] The beneficial effects of the present application include: The method for preparing phosphorus iron based on continuous acidolysis of ferrophosphorus powder provided by the present application is characterized in that a first oxidizing agent is added to a reaction slurry containing divalent iron ion solution, acid and ferrophosphorus powder, so as to oxidize Fe 2+ in the reaction slurry into Fe 3+ , and make the generated Fe 3+ undergo redox reaction with ferrophosphorus to obtain a leaching solution rich in Fe 2+ and PO4 3- ; at least part of the leaching solution is reacted with a second oxidizing agent to oxidize Fe 2+ in the leaching solution into Fe 3+ and generate phosphorus iron with PO4 3- .

[0023] The above method solves the technical bottleneck in the industry by introducing a divalent iron cycle system to convert ferrophosphorus which is difficult to be directly acid-dissolved into a form that can be efficiently and completely dissolved. Moreover, the method makes full use of the iron and phosphorus elements of ferrophosphorus powder itself, has a short process flow, consumes less reagent, has high raw material utilization rate and low comprehensive production cost. In addition, the method does not require high-temperature roasting or high-pressure intensified leaching, has low requirements for equipment, is easy to control in operation process, and has low energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0025] Figure 1 The process flow diagram of the method for preparing iron phosphate based on continuous acidolysis of ferrophosphorus powder provided by the present application. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions suggested by the manufacturers. The reagents or instruments not mentioned by the manufacturers are all conventional products that can be obtained by market purchase.

[0027] The method and system for preparing iron phosphate based on continuous acidolysis of ferrophosphorus powder provided by the present application will be described in detail as follows.

[0028] The present application provides a method for preparing iron phosphate based on continuous acidolysis of ferrophosphorus powder, as shown in Figure 1 , comprising the following steps: S1: adding a first oxidizing agent into a reaction slurry containing a divalent iron ion solution, an acid and ferrophosphorus powder, so as to oxidize Fe 2+ in the reaction slurry into Fe 3+ , and make the generated Fe 3+ have an oxidation-reduction reaction with the ferrophosphorus to obtain a leaching solution rich in Fe 2+ and PO4 3- .

[0029] In some optional embodiments, the initial divalent iron ion solution can be the leaching solution or ferrous sulfate solution of the system.

[0030] In some optional embodiments, the acid can exemplarily include at least one of sulfuric acid and phosphoric acid. When phosphoric acid is used, it can also play a role in adjusting the iron-phosphorus molar ratio in the final product iron phosphate.

[0031] In some optional embodiments, the first oxidizing agent can exemplarily include at least one of oxygen, air, ozone and hydrogen peroxide. In some preferable embodiments, the first oxidizing agent can include at least one of oxygen and air. The actual addition amount of the first oxidizing agent can be 1 times to 2 times of the theoretical addition amount, and the theoretical addition amount of the first oxidizing agent refers to the amount required to completely oxidize Fe 2+ into Fe 3+ .

[0032] In some alternative embodiments, the Fe 2+ The chemical reaction equation between Fe 3+ + 4H2O→ 11Fe 2+ + H2PO4 - + 6H + ; 2Fe 2+ + ½O2+ 2H + → 2Fe 3+ + H2O. According to the above chemical reaction equation, the Fe 2+ The chemical reaction stoichiometry between Fe 2+ The molar ratio between Fe 3+ is excessive, so as to ensure that the iron ions in the system after the reaction mainly exist in the form of Fe 2+ By controlling the amount of Fe 3+ , the reaction can be maintained stable and the premature hydrolysis of Fe

[0033] In some alternative embodiments, the Fe 3+ The redox reaction between Fe

[0034] In other words, the reaction in the S1 step is carried out at a pH value of 1.5-2 (10 g / L-30 g / L of residual acid) and a temperature of 60°C-95°C.

[0035] Preferably, the first oxidizing agent is continuously added so that the phosphorus powder in the reaction slurry is completely dissolved, and a leaching solution rich in Fe 2+ and PO4 3- is obtained.

[0036] In some alternative embodiments, the above S1 step can be continuously carried out in a single reactor or multiple reactors connected in series, and the acid, phosphorus powder and first oxidizing agent can be continuously or semi-continuously added, and the leaching solution can be continuously or semi-continuously discharged, so as to realize the continuous dissolution of the phosphorus powder. In some preferable embodiments, the Fe 2+and PO4 3- The iron phosphide powder and acid are added (supplemented) into the leaching reaction device, and the leaching solution rich in Fe 2+ and PO4 3- is continuously discharged (led out) from the leaching reaction device, so that the system in the leaching reaction device always maintains Fe 2+ state.

[0037] As mentioned above, the S1 step forms a reaction slurry mainly containing divalent iron by mixing the divalent iron ion solution with the acid and the iron phosphide powder; then the first oxidizing agent is introduced into the reaction slurry, which first oxidizes Fe 2+ in the reaction slurry to Fe 3+ ; the generated Fe 3+ immediately undergoes an oxidation-reduction reaction with the excess iron phosphide powder in the reaction slurry as a strong oxidizing agent, and Fe 2+ and PO4 3- in the iron phosphide powder are leached out, while Fe 3+ is reduced to Fe 2+ , achieving complete dissolution of the iron phosphide powder. The above "oxidation-leaching" process is cyclic, the first oxidizing agent continuously oxidizes Fe 2+ to Fe 3+ , and Fe 3+ continuously leaches the iron phosphide powder, until the theoretical double iron phosphide powder is completely dissolved, obtaining the leaching solution rich in Fe 2+ and PO4 3- .

[0038] S2: at least part of the leaching solution is reacted with the second oxidizing agent to oxidize all Fe 2+ in the leaching solution to Fe 3+ and PO4 3- to generate iron phosphate.

[0039] That is, part of the leaching solution obtained in the S1 step is used for subsequent oxidation synthesis of iron phosphate product, and the other part is returned to the S1 step as the source of Fe 2+ , mixed with the newly added acid and iron phosphide powder, to maintain the concentration of Fe 2+ in the leaching system, realize continuous leaching, and form a continuous and efficient closed-loop production process.

[0040] In some optional embodiments, the remaining leaching solution except for the one returned to the leaching reaction device is subjected to solid-liquid separation, and the separated liquid is used for reaction with the second oxidizing agent.

[0041] The leaching solution returned to the leaching reaction device as the circulating liquid continues to participate in the acidolysis process of the iron phosphide powder, and the remaining leaching solution is used for preparing the iron phosphate product in the S2 step after solid-liquid separation.

[0042] In some alternative embodiments, the volume of leaching solution used for reaction with the second oxidizing agent can account for 30% to 40% of the total volume of leaching solution, such as 30%, 32%, 35%, 38%, or 40%, or other values within the range of 30% to 40%. In addition, the ratio can be dynamically adjusted according to the concentration of Fe 2+ stability requirements and the product synthesis rate.

[0043] In some alternative embodiments, the second oxidizing agent can exemplarily include at least one of oxygen, air, ozone, and hydrogen peroxide. In some preferred embodiments, the second oxidizing agent can include at least one of oxygen and air. The actual amount of the second oxidizing agent added can be 1 to 1.5 times the theoretical amount, and the theoretical amount of the second oxidizing agent refers to the amount of the second oxidizing agent required to oxidize Fe 2+ to Fe 3+ .

[0044] In some alternative embodiments, the leaching solution not used for reaction with the second oxidizing agent is returned to the leaching reaction device of the Fe 2+ and PO4 3- rich leaching solution.

[0045] In some alternative embodiments, the pH value of at least part of the leaching solution reacting with the second oxidizing agent is 1.5 to 3.0 (such as 1.5, 1.8, 2.2, 2.5, 2.8, or 3), and the temperature is 50°C to 90°C (such as 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, or 90°C).

[0046] In some alternative embodiments, the pH value of the reaction can be adjusted by adding ammonia water.

[0047] As mentioned above, in the S2 step, the second oxidizing agent reacts with the corresponding leaching solution, so that Fe 2+ in the part of the leaching solution is oxidized to Fe 3+ , and Fe 3+ is combined with PO4 3- in the part of the leaching solution to generate iron phosphate.

[0048] Further, after the S2 step is completed, solid-liquid separation is performed, and the separated solid is washed and dried to obtain the battery-grade iron phosphate product.

[0049] In addition, the separated liquid can be recycled or discharged after treatment.

[0050] Based on the above, the application provides a method for preparing iron phosphate based on continuous acidolysis of ferrophosphorus powder, which realizes efficient and continuous dissolution reaction of ferrophosphorus by constructing a smart iron ion internal circulation oxidation system.

[0051] Correspondingly, the application also provides a system for preparing iron phosphate based on continuous acidolysis of ferrophosphorus powder, which comprises a dissolution reaction device and a product synthesis device.

[0052] The dissolution reaction device is used for reacting a reaction slurry containing a divalent iron ion solution, acid and ferrophosphorus powder with a first oxidizing agent to obtain a leaching solution rich in Fe 2+ and PO4 3- .

[0053] The dissolution reaction device at least comprises a reactor for acidolysis of ferrophosphorus powder, which is provided with a feeding port, an oxidizing agent inlet and a discharging port. The feeding port of the reactor is used for adding the divalent iron ion solution, acid and ferrophosphorus powder, the oxidizing agent inlet is used for adding the first oxidizing agent, and the discharging port is used for discharging the leaching solution rich in Fe 2+ and PO4 3- .

[0054] In some optional embodiments, the dissolution reaction device can comprise a stirred tank reactor, a tower reactor or a cascade reactor group.

[0055] The shunting and circulating device is used for dividing the leaching solution rich in Fe 2+ and PO4 3- into a part returned to the dissolution reaction device and a part used for entering the product synthesis device, and for circulating the part returned to the dissolution reaction device to the dissolution reaction device.

[0056] The solid-liquid separation device is used for performing solid-liquid separation on the leaching solution reacted with the second oxidizing agent, and the separated liquid is used for reacting with the second oxidizing agent. Specifically, the inlet of the shunting and circulating device is connected with the discharging port of the dissolution reaction device, and the shunting and circulating device separates the liquid into circulating liquid and product liquid. The outlet of the shunting and circulating device is divided into a circulating liquid outlet and a product liquid outlet. The circulating liquid outlet is connected with the feeding port of the dissolution reaction device to return the circulating liquid to the dissolution reaction device of the leaching solution rich in Fe 2+ and PO4 3- . The product liquid outlet is connected with the inlet of the solid-liquid separation device to perform solid-liquid separation on the product liquid, and the outlet of the solid-liquid separation device is connected with the inlet of the product synthesis device to transport the product liquid after solid-liquid separation to the product synthesis device to react with the second oxidizing agent.

[0057] The product synthesis device is used for reacting at least part of the leaching solution (i.e. the product liquid after the above-mentioned solid-liquid separation) with a second oxidizing agent, so as to oxidize Fe 2+ to Fe 3+ and PO4 3- to generate iron phosphate. The outlet of the product synthesis device is used for outputting the iron phosphate.

[0058] Further, the above-mentioned system can further be provided with a separation device, a washing device, a drying device, etc. according to needs, so as to prepare the iron phosphate product outputted by the product synthesis device into a battery-grade iron phosphate product.

[0059] The features and performances of the present application are further described in detail below in combination with embodiments.

[0060] The following embodiments all take industrial by-product ferrophosphorus powder Fe2P as raw materials.

[0061] Embodiment 1 The present embodiment provides a method for preparing iron phosphate based on continuous acidolysis of ferrophosphorus powder, comprising the following steps: S1: In a reaction kettle with heating and aeration device, pure water is added, ferrous sulfate (FeSO4·7H2O) is dissolved, and 10 L of divalent iron ion solution with a concentration of 0.8 mol / L is prepared. Concentrated sulfuric acid is added to the reaction kettle to adjust the acidity to 80 g / L, and the molar ratio of Fe 2+ to the ferrophosphorus powder is 9:4, and excess ferrophosphorus powder (Fe2P) is put in. Stirring is started, and air is simultaneously introduced at a flow rate of 3 L / min, and the reaction temperature is maintained at 95℃. The air oxidizes Fe 2+ to Fe 3+ , and Fe 3+ immediately undergoes redox reaction with the ferrophosphorus powder to dissolve the iron and phosphorus in the ferrophosphorus powder in the form of Fe 2+ and PO4 3- , and Fe 3+ is reduced to Fe 2+ itself, and the system always maintains Fe 2+ state. The ferrophosphorus powder and sulfuric acid are continuously supplemented to the reaction kettle, and the leaching solution rich in Fe 2+ and PO4 3- is continuously introduced from the bottom of the reaction kettle.

[0062] The leaching solution rich in Fe 2+ and PO4 3- is divided by a flow divider, about 70% of the flow is transported back to the reaction kettle as a circulating liquid to continue participating in the acidolysis process of the ferrophosphorus powder, and 30% of the flow is filtered, and the filtrate is transported to a synthesis kettle as a product liquid to prepare an iron phosphate product.

[0063] S2: In the synthesis reactor, the product liquid is heated to 80°C, excess air is introduced, and the pH is slowly adjusted and maintained at around 2.0 with ammonia. After 4 hours of reaction, a large amount of white precipitate (ferric phosphate) is generated.

[0064] The resulting white precipitate was filtered, washed, and dried to obtain the ferric phosphate product.

[0065] According to the test, the main components of the iron phosphate product, by mass percentage, are as follows: Fe 36.8%, P 20.56%, S 0.0034%, Ca 0.0025%, Mg 0.0024%, Si 0.002%, Na 0.006%. The main content of the product complies with the standard HG / T4701-2021 "Iron Phosphate for Batteries", and the content of key impurity elements (Ca, Mg and Na) is low.

[0066] Example 2 This embodiment provides a method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, including the following steps: S1: In a reactor equipped with heating and ventilation devices, add pure water to dissolve ferrous sulfate (FeSO4·7H2O) to prepare 10L of a 0.65mol / L ferrous ion solution. Add concentrated sulfuric acid to the reactor to adjust the acidity to 65g / L, and adjust the concentration of Fe in the ferrous ion solution according to the required concentration. 2+ An excess of iron phosphide powder (Fe₂P) was added at a molar ratio of 9:4 to the iron phosphide powder. Stirring was started, and air was simultaneously introduced at a flow rate of 2 L / min to maintain the reaction temperature at 80°C. The air carried the Fe... 2+ Oxidized to Fe 3+ Fe 3+ It immediately undergoes a redox reaction with iron phosphate powder, converting the iron and phosphorus in the iron phosphate powder into Fe. 2+ and PO4 3- Form dissolution, while Fe 3+ It was reduced to Fe 2+ The system always maintains Fe 2+ State. Iron phosphide powder and sulfuric acid are continuously added to the reactor, while Fe-rich water is continuously drawn from the bottom of the reactor. 2+ and PO4 3- The leachate.

[0067] rich in Fe 2+ and PO4 3- The leachate is diverted through a diversion valve, with about 60% of the flow being returned to the reactor as a circulating liquid to continue participating in the acidolysis process of iron phosphate powder, and 40% of the flow being filtered. The filtrate is then transported to the synthesis reactor as the product liquid to prepare iron phosphate products.

[0068] S2: In a synthesis kettle, the product liquid is heated to 75℃, excess air is introduced, and the pH is slowly adjusted and maintained at about 2.0 with ammonia water, after 4h of reaction, a large amount of white precipitate (iron phosphate) is generated.

[0069] The obtained white precipitate is filtered, washed, and dried to obtain the iron phosphate product.

[0070] Detection shows that, in terms of mass percentage, the main components in the iron phosphate product are as follows: Fe 35.6%, P 21.2%, S 0.004%, Ca 0.0021%, Mg 0.002%, Si 0.002%, and Na 0.001%. The main content of the product meets the standard, and the content of key impurity elements is low.

[0071] Example 3 The difference between this example and Example 1 is that, in S1, the molar ratio of Fe 2+ to phosphide powder is 9:2, and excess phosphide powder (Fe2P) is introduced.

[0072] Example 4 The difference between this example and Example 1 is that, in S1, the reaction is carried out at a pH of 1.5 and a temperature of 70℃.

[0073] Example 5 The difference between this example and Example 1 is that, in S2, the reaction is carried out at a pH of 1.5 and a temperature of 90℃.

[0074] Example 6 The difference between this example and Example 1 is that, in S2, the reaction is carried out at a pH of 3.0 and a temperature of 50℃.

[0075] Example 7 This example provides a system for preparing iron phosphate based on continuous acidolysis of phosphide powder, which includes a dissolution reaction device, a solid-liquid separation device, a shunt and circulation device, a product synthesis device, a separation device, a washing device, and a drying device.

[0076] The dissolution reaction device is used to react the reaction slurry formed by the divalent iron ion solution, the acid, and the phosphide powder with the first oxidizing agent to obtain the leaching solution rich in Fe 2+ and PO4 3- . The dissolution reaction device is a stirred kettle reactor, which is provided with a feed inlet, an oxidizing agent inlet, and a discharge outlet. The feed inlet is used to add the divalent iron ion solution, the acid, and the phosphide powder, the oxidizing agent inlet is used to add the first oxidizing agent, and the discharge outlet is used to discharge the leaching solution rich in Fe 2+ and PO4 3- .

[0077] The shunting and circulating device is used for dividing the leaching solution rich in Fe 2+ and PO4 3- into a part returning to the leaching reaction device and a part entering the product synthesis device, and for circulating the part returning to the leaching reaction device into the leaching reaction device. The solid-liquid separation device is used for performing solid-liquid separation on the leaching solution reacted with the second oxidant, and the separated liquid is used for reacting with the second oxidant.

[0078] The inlet of the shunting and circulating device is connected with the outlet of the leaching reaction device, and the liquid separated by the shunting and circulating device is divided into a circulating liquid and a product liquid. The outlet of the shunting and circulating device is divided into a circulating liquid outlet and a product liquid outlet. The circulating liquid outlet is connected with the inlet of the leaching reaction device to return the circulating liquid to the leaching reaction device of the leaching solution rich in Fe 2+ and PO4 3- ; and the product liquid outlet is connected with the inlet of the solid-liquid separation device to perform solid-liquid separation on the product liquid. The outlet of the solid-liquid separation device is connected with the inlet of the product synthesis device to deliver the product liquid after solid-liquid separation to the product synthesis device to react with the second oxidant.

[0079] The product synthesis device is used for reacting at least part of the leaching solution (i.e. the product liquid after solid-liquid separation) with the second oxidant, so as to oxidize Fe 2+ in the part of the leaching solution into Fe 3+ and generate phosphoric iron with PO4 3- . The outlet of the product synthesis device is used for outputting the phosphoric iron.

[0080] The inlet of the separation device is connected with the outlet of the product synthesis device to separate the product in the product synthesis device; the inlet of the washing device is connected with the outlet of the separation device to wash the solid separated by the separation device; and the inlet of the drying device is connected with the outlet of the washing device to dry the washed solid to obtain the battery-grade phosphoric iron product.

[0081] Comparative Example The present comparative example provides a method for preparing lithium iron phosphate by using phosphorus iron powder as raw material, which comprises the following steps: (1) Pretreatment and acid leaching of phosphorus iron powder: 100 g of phosphorus iron powder is placed in a muffle furnace and calcined at 650 ℃ for 4 h, so that phosphorus and iron in the phosphorus iron powder are oxidized into P2O5 and Fe2O3 respectively. The calcined product is cooled and ground into powder. Then the powder is transferred to a reaction kettle, 500 mL of 2 mol / L sulfuric acid solution is added, and leaching is performed at 90 ℃ for 2 h under stirring. In this process, most of Fe2O3 and P2O5 react with sulfuric acid to generate iron sulfate and phosphoric acid.

[0082] (2) Purification of the solution: the acid leaching slurry is filtered to obtain a leaching solution containing Fe 3+ , PO4 3- and various impurity ions (such as Al 3+ , Cu 2+ , etc.). Since Fe 3+ starts to hydrolyze and precipitate at a pH of about 2.5, the impurities cannot be removed by simply adjusting the pH. Therefore, the pH of the leaching solution is first adjusted to 4.0 using a NaOH solution, so that Fe 3+ and Al 3+ , etc. form hydroxide precipitates together, and phosphate ions form complex phosphate precipitates with some metal ions, resulting in loss of phosphorus. After filtration, an impure iron-rich residue and a phosphorus-containing filtrate (which needs to be treated to recover the phosphorus) are obtained.

[0083] The iron-rich residue is redissolved with dilute sulfuric acid, and then NaOH solution is slowly added to the solution while strictly controlling the pH at about 3.0, so that Fe 3+ hydrolyzes and precipitates, while Al 3+ remains in the solution. After filtration and washing, a preliminarily purified iron hydroxide precipitate is obtained. The precipitate is dissolved again with sulfuric acid to prepare a sulfuric iron solution with higher purity.

[0084] (3) Synthesis of iron phosphate: the purified sulfuric iron solution and the phosphorus-containing filtrate obtained in step (2) (after composition adjustment) are mixed at a molar ratio of iron to phosphorus of 1:1. The pH of the mixed solution is adjusted to 1.8 with ammonia water, and the solution is stirred and aged at 85°C for 2h to form an iron phosphate precipitate. After the reaction is completed, the precipitate is filtered, washed with deionized water multiple times, and dried at 110°C for 12h to obtain a precursor iron phosphate.

[0085] Test Examples The utilization rate and yield of P and Fe elements corresponding to the methods provided in Examples 1-6 and Comparative Examples are compared, and the results are shown in Table 1.

[0086] Table 1 results

[0087] As can be seen from Table 1, the methods provided in Examples 1-6 of the present application can all obtain high utilization rates and yields of P and Fe elements.

[0088] Compared with the embodiments, the method route provided by the comparative example is long, involves high-temperature calcination, multiple acid dissolution, multiple precipitation and filtration, the operation steps are complicated, the production cycle is long, leading to high energy consumption, large equipment investment, high labor cost, and the material yield of the whole process is reduced due to multiple transfers. In the purification and impurity removal process of step (2), iron and phosphorus are seriously lost. When the pH is adjusted to 4.0 for the first time, the phosphate and part of the metal impurities are co-precipitated, resulting in a low recovery rate of phosphorus. The multiple precipitation-dissolution process of iron also inevitably causes loss. Moreover, a large amount of sulfuric acid and NaOH are consumed for pH adjustment and precipitation in the preparation process of the comparative example, generating a large amount of wastewater containing high salt content, which has high subsequent treatment cost and heavy environmental burden.

[0089] Therefore, compared with the traditional method of the comparative example, the short process technology based on the divalent iron cycle provided by the present application has obvious advantages in production efficiency, raw material utilization rate, cost control and environmental friendliness, fully proving the progressiveness of the process of the present application.

[0090] In summary, the present application ingeniously utilizes the principle of trivalent iron oxidizing and dissolving phosphorus iron, and converts the phosphorus iron which is difficult to be directly acid-dissolved into a form which can be efficiently and completely dissolved by introducing a divalent iron cycle system, solving the technical bottleneck in the industry. The method builds an internal circulation divalent iron ion catalyst or oxygen carrier system by returning part of the leaching solution, so that acid, phosphorus iron powder and oxidizing agent can be continuously fed, and leaching solution can be continuously produced, greatly improving the production efficiency and being suitable for industrial large-scale production. Moreover, the whole reaction is carried out at normal pressure and medium temperature without high-temperature calcination; no strong oxidizing agent such as nitric acid is used in the whole process, and no toxic and harmful gas is generated, so the process is clean and environmentally friendly. In addition, the method provided by the present application fully utilizes the iron and phosphorus elements in the phosphorus iron powder itself, and has short process flow, less reagent consumption, high raw material utilization rate and low comprehensive production cost. Since the impurity elements (such as metal impurities) in the phosphorus iron powder are not easy to enter the solution or be separated in the subsequent synthesis under a certain redox potential, the iron phosphate product has high purity.

[0091] The above is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, characterized in that, Includes the following steps: A first oxidizing agent is added to a reaction slurry containing a solution of ferrous ions, an acid, and iron phosphide powder to oxidize the Fe in the reaction slurry. 2+ Oxidized to Fe 3+ and the generated Fe 3+ It undergoes a redox reaction with the iron phosphide to obtain a product rich in Fe. 2+ and PO4 3- The leachate; At least a portion of the leachate is reacted with a second oxidant to reduce the Fe in the leachate. 2+ All oxidized to Fe 3+ and PO4 3- Iron phosphate is produced.

2. The method according to claim 1, characterized in that, Continuous application to obtain Fe-rich 2+ and PO4 3- Iron phosphide powder and acid are added to the leaching reaction device of the leachate, while Fe-rich solutions are continuously drawn from the leaching reaction device. 2+ and PO4 3- The leaching solution is used to ensure that the system in the leaching reaction apparatus always maintains Fe... 2+ state.

3. The method according to claim 1, characterized in that, Fe in the divalent iron ion solution 2+ The molar ratio of the iron phosphate powder to the iron phosphate powder is 9:2 to 9:

5.

4. The method according to claim 1, characterized in that, The acid includes at least one of sulfuric acid and phosphoric acid.

5. The method according to claim 1, characterized in that, The first oxidant and the second oxidant independently include at least one of oxygen, air, ozone and hydrogen peroxide; Preferably, the first oxidant and the second oxidant independently comprise at least one of oxygen and air.

6. The method according to claim 1, characterized in that, The generated Fe 3+ The redox reaction with the iron phosphide is carried out under conditions of pH 1.5~2 and temperature 60℃~95℃.

7. The method according to claim 1, characterized in that, By volume percentage, the volume of leachate used to react with the second oxidant accounts for 30% to 40% of the total volume of leachate.

8. The method according to claim 7, characterized in that, Leachate not used for reaction with the second oxidant is returned to a Fe-rich state. 2+ and PO4 3- In the leaching reaction apparatus of the leachate; Preferably, the process further includes solid-liquid separation of the remaining leachate (excluding the leachate returned to the leaching reaction apparatus), with the separated liquid used to react with the second oxidant.

9. The method according to claim 1, characterized in that, The pH value of the at least part of the leachate reacting with the second oxidant is 1.5 to 3.0, and the temperature is 50°C to 90°C. Preferably, the pH value of the reaction is adjusted by adding ammonia.

10. A system for preparing ferric phosphate based on continuous acid hydrolysis of ferric phosphate powder, characterized in that, This includes a dissolution reaction apparatus and a product synthesis apparatus; The leaching reaction apparatus is used to react a reaction slurry containing a solution of ferrous ions, acid, and iron phosphide powder with a first oxidant to obtain a solution rich in Fe. 2+ and PO4 3- The leachate; The product synthesis apparatus is used to react at least a portion of the leachate with a second oxidant to reduce the Fe in the leachate. 2+ All oxidized to Fe 3+ and PO4 3- Iron phosphate is produced; Preferably, the dissolution reaction apparatus includes a stirred tank reactor, a tower reactor, or a cascade reactor group; Preferably, the system further includes a solid-liquid separation device for performing solid-liquid separation on the leachate reacting with the second oxidant, wherein the separated liquid is used to react with the second oxidant. Preferably, the system further includes a diversion and circulation device for diverting and circulating the Fe-rich water. 2+ and PO4 3- The leachate is divided into a portion that returns to the leaching reaction unit and a portion that is used to enter the product synthesis unit, and the portion that returns to the leaching reaction unit is recycled back to the leaching reaction unit.

Images