Method for recovering phosphoric acid and removing manganese

Abstract

The invention relates to a method for removing manganese by recovering phosphoric acid, which comprises the following steps: adding an oxidant capable of oxidizing divalent manganese into trivalent manganese into a recovered phosphoric acid solution, and after the reaction is completed, carrying out solid-liquid separation and separating to remove solid precipitate to obtain a manganese-removed recovered phosphoric acid solution, the phosphoric acid solution contains iron ions. The method is used for purifying phosphoric acid recovered in an iron phosphate preparation process and removing divalent manganese ions in the phosphoric acid.

Description

[0001] This application claims the priority of a prior application with application number 202311659615.0, filed with the State Intellectual Property Office on December 6, 2023, and invention name “A method for recovering phosphoric acid and removing manganese”, the full text of which is incorporated into this application. Technical Field

[0002] The invention belongs to the technical field of inorganic material and lithium battery material preparation, and specifically relates to a method for recovering phosphoric acid to remove manganese impurities, and specifically aims at recovering phosphoric acid mother liquor in the iron phosphate preparation process. Background Art

[0003] As a positive electrode material for lithium-ion batteries, lithium iron phosphate has high specific capacity, good safety, long cycle life, and good thermal stability. At the same time, the raw material source is wide and the price is cheap. It is a positive electrode material that can coexist with ternary materials for a long time. At present, most of the industrial production of lithium iron phosphate uses the precursor synthesis method, that is, first prepare iron phosphate (FePO 4 ), then iron phosphate is used as the iron source and phosphorus source, mixed with the lithium source and carbon source, and sintered at high temperature in an inert atmosphere to obtain lithium iron phosphate with a carbon layer on the surface. Iron phosphate is the precursor for preparing lithium iron phosphate, and the quality of the iron phosphate precursor has a great influence on the performance of lithium iron phosphate products.

[0004] At present, the synthesis methods of iron phosphate are mainly divided into the following categories: (1) Synthesis methods using iron salts and phosphates as iron sources and phosphorus sources, respectively. In this type of synthesis method, the iron source and phosphorus source introduce impurity anions and impurity cations, respectively, resulting in the need to use a large amount of deionized water to wash the precipitate after obtaining the iron phosphate precipitate, and the wastewater generated by washing the precipitate needs to be treated later to avoid polluting the environment. Therefore, the cost of iron phosphate synthesized by this method is high, and enterprises using this preparation method are difficult to survive in the current environment where the price of lithium iron phosphate has dropped sharply; (2) Synthesis methods using elemental iron powder and phosphoric acid as iron sources and phosphorus sources, respectively, produce ferrous phosphate, and then oxidize to prepare iron phosphate, such as CN111377426A or CN201510209131.5. In this type of synthesis method, the iron source and phosphorus source do not introduce impurity ions, and the washing of the precipitate and the subsequent wastewater treatment are relatively simple. However, the reaction between iron powder and phosphoric acid releases a large amount of heat and flammable and explosive hydrogen, and because of the added oxidation step, the process is complicated and difficult to control. In industrial production, the safety cost of using this method to synthesize iron phosphate in large quantities is high; (3) Using iron oxide to react with phosphoric acid to obtain iron phosphate. The above methods all involve the problem of recycling and reuse of phosphoric acid. The above phosphoric acid solution contains phosphoric acid and a large amount of iron ions. Given that most process routes for preparing iron phosphate use iron or iron oxide as the source of iron raw materials, and these industrial iron raw materials often contain manganese, after the recycled phosphoric acid is used for a period of time, manganese is enriched in the solution, affecting the purity of the iron phosphate product.

[0005] In the solution or wastewater produced by the chemical industry, in order to remove the manganese ions contained, it can be done by oxidation, that is, using a strong oxidant to convert Mn 2+ Oxidized to MnO with extremely low solubility 2 , and then the particles are separated and removed by physical methods. CN111018178A discloses a method for removing manganese from an acidic solution with a pH value of ≤ 3, in which ozone is added to form MnO 2 , to remove manganese. The patent application believes that adding a small amount of phosphoric acid as a hydroxyl radical inhibitor is beneficial to the reaction efficiency. DE578404C discloses a method for removing Mn from phosphoric acid, in which potassium ferrocyanide is added to phosphoric acid to remove manganese.

[0006] In the preparation process of iron phosphate, an important raw material for lithium iron phosphate, the raw materials are often sourced from industrial scrap iron, iron oxide (iron red) or ferroferric oxide (iron black). After separating the iron phosphate, the mother liquor contains a large amount of phosphoric acid, also known as recovered phosphoric acid. The recovered phosphoric acid contains a certain amount of iron ions (ferrous ions or trivalent iron ions). Part or all of the mother liquor will be recycled back to the iron phosphate preparation process, and the manganese element contained in the raw materials will be enriched in the recovered phosphoric acid. How to effectively remove manganese without introducing impurities that are detrimental to battery raw materials is a difficult problem in the industry.

[0007] The industry needs a method for purifying phosphoric acid recovered from the ferric phosphate preparation process, especially a method for removing manganese impurities therein. Summary of the invention

[0008] The recovered phosphoric acid described in the present invention is the recovered mother liquor of the ferric phosphate preparation process, specifically, the reaction solution from which the ferric phosphate precipitation is obtained, and the filtrate (mother liquor) is obtained after the ferric phosphate is separated by solid-liquid separation. The mother liquor still contains a large amount of phosphoric acid and ferric phosphate complex (or dissolved ferric phosphate). Compared with other methods for removing impurities such as ion exchange, the method of the present invention can remove manganese ions in a strong acid environment, while continuing to retain Fe ions in the phosphoric acid solution, so as to improve the yield of ferric phosphate and the conversion rate of iron-containing raw materials.

[0009] As an example of recovered phosphoric acid, the density of the recovered phosphoric acid is 1.395 g / ml (room temperature, 20° C.), corresponding to a phosphoric acid concentration of about 57%. The recovered phosphoric acid was subjected to an ICP test, and the test results showed that the Mn content was 4237 mg / L and the iron content was 19585 mg / L.

[0010] The invention discloses a method for recovering phosphoric acid and removing manganese. An oxidant capable of oxidizing divalent manganese into trivalent manganese is added to a recovered phosphoric acid solution. After the reaction is completed, solid-liquid separation is performed, and solid precipitation is separated and removed to obtain a recovered phosphoric acid solution from which manganese is removed. The phosphoric acid solution is a phosphoric acid solution recovered after preparing iron phosphate, and the phosphoric acid solution contains iron ions.

[0011] The inventors unexpectedly discovered that the solid precipitate removed by solid-liquid separation is ferromanganese phosphate.

[0012] The oxidant is selected from ozone, manganic acid, alkali metal salts of manganic acid, permanganic acid, alkali metal salts of permanganate, or ferric permanganate, ferric acid, alkali metal salts of ferric acid, preferably ozone, potassium permanganate, ferric permanganate, ferric acid, potassium ferrate. The alkali metal salt refers to potassium salt or sodium salt. The amount of oxidant is preferably equivalent. The so-called equivalent refers to the theoretical calculated amount of oxidant required to oxidize 100% of the reducing agent, which needs to be calculated based on the change in the valence of the oxidant and divalent manganese (reducing agent) in the redox reaction. In the present invention, if 1 mole of Mn is desired 2+ Removed, then the required equivalent molar amount of ozone oxidant is 0.5 mole, because the stoichiometric ratio during the reaction of ozone and divalent manganese ions is 1:2. And the required equivalent molar amount of potassium permanganate (oxidant) is 0.25 mole (the stoichiometric ratio of potassium permanganate to divalent manganese ions during the reaction is 1:4). But in the actual reaction process, the general oxidant needs to be excessive to ensure that the reducing agent is completely oxidized, and it is necessary to add more than an equivalent amount of oxidant. In the reaction of the present invention, considering the ozone fugitive, the amount of ozone introduced during actual use is usually 2-20 times the equivalent molar amount, considering that too much ozone will not remain too much in the solution, and potassium permanganate does not need to be added too much. The purpose of the present invention is to remove excess manganese ions, and the amount of oxidant added is not aimed at 100% removal of manganese ions. In most cases, it is sufficient to partially remove manganese to meet production needs, that is, it is not necessary to add an equivalent amount of oxidant. In fact, it may only be necessary to add 0.1 equivalent oxidant to partially remove manganese ions. Therefore, in the present invention, the amount of the oxidant added is calculated based on the molar amount of the divalent manganese ion, and the oxidant is 0.05-20 times the molar amount of the divalent manganese, preferably 0.2-5 times the molar amount of the divalent manganese.

[0013] The unreacted ozone gas in the reaction process is recycled back to the reaction system, which is beneficial to improving the utilization rate of ozone.

[0014] The phosphoric acid content in the recovered phosphoric acid should not be limited, and theoretically it only needs to contain enough phosphate ions to form ferromanganese phosphate precipitation. The embodiment of the present invention shows that when the phosphoric acid content is between 5wt% and 80wt%, ferromanganese phosphate precipitation can be formed, thereby achieving the purpose of removing manganese. The preferred phosphoric acid content is 10wt% to 70wt%.

[0015] The iron ion is a ferrous ion, a ferric ion, a ferrous complex ion or a ferric complex ion. When it is a ferrous ion or a ferrous complex ion, a supplementary oxidant can be added before or at the same time as the oxidant is added, preferably before the oxidant is added to reduce the consumption of the oxidant. The purpose of adding a supplementary oxidant in the present invention is to oxidize the ferrous ions into ferric ions to reduce the amount of the oxidant used to oxidize Mn. Considering that the oxidizing property of trivalent manganese ions is stronger than that of trivalent iron ions, the oxidizing property of the supplementary oxidant can be lower than or equal to that of the oxidant. The supplementary oxidant is selected from any oxidant that can oxidize ferrous ions into ferric ions in an acidic environment, such as an oxidant with a standard electrode potential exceeding +0.77, such as Ag ions (+0.80), Cl 2 (+1.36) etc. (see "General Chemistry Principles", Peking University Press, 4th edition, Table 10.1 on page 204), preferably selected from hydrogen peroxide, ozone, manganic acid, manganate, permanganic acid or permanganate, more preferably the supplementary oxidant is hydrogen peroxide. When the supplementary oxidant is the same as the oxidant, it indicates that more oxidant needs to be added to oxidize the manganese ions while oxidizing the iron ions. Preferably, the iron ions are trivalent iron ions, especially iron ions in the form of iron phosphate complexes.

[0016] The amount of supplementary oxidant added is calculated based on the molar amount (or content) of divalent iron ions, and it is best to add it in an equivalent amount (stoichiometric ratio). For example, if hydrogen peroxide is used as the supplementary oxidant, the stoichiometric ratio of hydrogen peroxide to divalent iron ions is 1:2, then the equivalent molar amount of hydrogen peroxide corresponding to 1 mole of divalent iron ions is 0.5 moles. The equivalent molar amounts of different supplementary oxidants are different. Considering the reaction efficiency, the supplementary oxidant is preferably 80%-120% equivalent molar amount. When the supplementary oxidant is added in an equivalent amount of 80%, more oxidant may be consumed. Supplementary oxidants exceeding 100% equivalent may result in waste.

[0017] The iron ion concentration is 1 g / L-200 g / L, preferably 3 g / L-150 g / L, calculated as elemental iron. The present invention demonstrates that when the iron content is as low as 3.8 g / L, manganese can still form a precipitate and be separated from the solution.

[0018] After the inventors added an oxidant, such as ozone, the manganese in the phosphoric acid was oxidized to trivalent manganese ions, and unexpectedly formed ferromanganese phosphate precipitation with the iron ions and phosphate ions in the phosphoric acid. The ferromanganese phosphate precipitation takes Mn out of the reaction system, thereby achieving the effect of removing manganese from the phosphoric acid solution. In addition, the usual practice is to remove a certain element, and the reagent of the element is usually avoided to avoid bringing in the element. The present invention is contrary to the usual practice. The present application uses potassium permanganate or other manganese-containing oxidants such as manganate and manganic acid, which are added to the recovered phosphoric acid, which can remove the manganese element.

[0019] The present invention also tests recovered phosphoric acid solutions with different concentrations, and also proves that the method of the present invention is effective for recovered phosphoric acid with different concentrations.

[0020] The recovered phosphoric acid of the present invention can be reused in the preparation process of ferric phosphate. A manganese removal process can also be added to the preparation process of ferric phosphate.

[0021] The present application further discloses a method for preparing iron phosphate, comprising:

[0022] S1: using phosphoric acid with a concentration of 35-85% to react with iron oxide at a reaction temperature between room temperature and 180°C, adding an oxidant during the reaction, filtering to remove insoluble matter, and collecting the first mother liquor;

[0023] S2: Control the temperature of the first mother liquor to be between room temperature and 180°C, add water to the first mother liquor, control the concentration of Fe ions to be between 0.1 mol / L and 2 mol / L, react for 1 min to 20 h, separate the solid and the liquid, and obtain solid iron phosphate dihydrate and the second mother liquor.

[0024] According to the present invention, the oxidant is selected from ozone, manganic acid, alkali metal salts of manganic acid, permanganic acid, alkali metal salts of permanganic acid, or ferric permanganate, ferric acid, alkali metal salts of ferric acid, preferably ozone, potassium permanganate, ferric permanganate, ferric acid, potassium ferrate. In one embodiment of the present invention, the oxidant is ozone or potassium permanganate.

[0025] According to the present invention, preferably, step S1 is performed at 60-140° C., and the phosphoric acid concentration is between 50-85%.

[0026] According to the present invention, preferably, step S2 is carried out at 60-160° C., and the reaction time is 10 min-6 h.

[0027] Optionally, step S2 may be performed under pressure, and the pressure is controlled within an absolute pressure range of 0.1-1 MPa, preferably 0.1-0.5 MPa. The water is pure water, and the pure water is selected from distilled water and deionized water (completely deionized).

[0028] In one embodiment of the present invention, the method further comprises step S3: according to the phosphoric acid concentration of the second mother liquor, phosphoric acid is not added or added to ensure that the phosphoric acid content in the second mother liquor meets the phosphoric acid concentration limit of step S1, and the second mother liquor is recycled back to step S1.

[0029] Preferably, the phosphorus to iron ratio in the first mother liquor is (2.5-10):1.

[0030] In step S1, an oxidant (e.g., ozone or potassium permanganate) is added to achieve oxidation of divalent manganese to trivalent manganese in this step, thereby forming ferromanganese phosphate precipitation, and then filtering to achieve the purpose of removing iron oxide impurities together with ferromanganese phosphate (removing excess manganese). This operation utilizes the aforementioned basic principle of removing manganese, and very cleverly places this operation in the preparation process of iron phosphate complex. Compared with the phosphoric acid recovery process after treatment and filtration, the method for preparing ferric phosphate can achieve the purpose of removing manganese in the reaction system without almost increasing the process flow or equipment.

[0031] Terminology explanation:

[0032] Ferric phosphate complex: Ferric phosphate-phosphate complex formed by iron phosphate and phosphoric acid, existing in the form of solution.

[0033] Iron phosphate dihydrate: also known as iron phosphate dihydrate or iron phosphate dihydrate, is iron phosphate containing two waters of crystallization. When iron phosphate precipitates from a solution, it often contains two waters of crystallization.

[0034] Phosphorus to iron ratio: In the present invention, the phosphorus to iron ratio (P:Fe) refers to the molar ratio (ratio of the amount of substance) of phosphorus element to iron element in the iron phosphate complex solution. Phosphorus refers to all phosphorus elements in the solution, and iron refers to all iron elements in the solution. For example, in the solution or product obtained by the reaction of 3 mol phosphoric acid with 1 mol ferric hydroxide, the phosphorus to iron ratio is 3:1, while the phosphorus to iron ratio of 6 mol phosphoric acid to 1 mol ferrosoferric oxide is 2:1. In the present invention, the phosphorus to iron ratio is described as 3:1 or 3, which have the same meaning, both indicating phosphorus: iron = 3:1.

[0035] Phosphorus-manganese ratio: In the present invention, it refers to the ratio of the amount of phosphorus to the amount of manganese, and is sometimes written as P:Mn.

[0036] Ferromanganese phosphate: The ferromanganese phosphate described in the present invention is a ferromanganese phosphate having Mn x Fe 1-x PO 4 A compound composed of wherein X is a positive number less than 1.

[0037] Manganese phosphate: The manganese phosphate described in the present invention is MnPO 4 , Mn is a trivalent ion. In the present invention, monohydrated manganese phosphate MnPO 4 ·H 2 The method for preparing manganese phosphate in the present invention often refers to the method for preparing manganese phosphate monohydrate or monohydrated manganese phosphate.

[0038] Iron ions: The iron ions described in the present invention include free iron ions or iron ions in the form of complex ions. The free iron ions include divalent iron ions (Fe 2+ ), ferric ion (Fe3+ ), complex ions include ferric complex ions and ferrous complex ions. Ferric ions tend to form ferric phosphate complex ions (belonging to ferric complex ions) in phosphoric acid solution, and ferrous ions tend to form ferrous phosphate complex ions (belonging to ferrous complex ions) in phosphoric acid solution. Since iron in ferrous complex ions and ferric complex ions still exists in the form of ferrous ions or ferric ions, thus, ferrous ions in the present invention tend to include ferric complex ions, and ferric ions also tend to include ferric complex ions. In addition, complex in the present invention also refers to complex ions, especially in solution state.

[0039] Equivalent, in the present invention, refers to the ratio of the amount of substances required for complete reaction between reactants according to the reaction equation (theoretical calculation), the equivalent molar amount is calculated by mole, and the equivalent mass number is calculated by mass. The amount of oxidant or supplementary oxidant used in the present invention is the equivalent mole number, which refers to the amount of the corresponding substance of the oxidant or supplementary oxidant calculated according to the stoichiometric ratio required to completely oxidize the reducing agent (set as 1 mole).

[0040] Supplementary oxidant: The supplementary oxidant of the present invention refers to an oxidant used to oxidize divalent iron ions, to be distinguished from the oxidant used to oxidize divalent manganese ions. In actual processes, the supplementary oxidant and the oxidant may be the same compound or substance. The supplementary oxidant may also be referred to as the second oxidant, while the corresponding oxidant used to oxidize divalent manganese ions is the first oxidant.

[0041] Room temperature: refers to the indoor temperature. In the present invention, the room temperature is between 15-25°C, a temperature that does not require heating.

[0042] Gauge pressure: refers to the amount by which the total absolute pressure exceeds the surrounding atmospheric pressure or the pressure at a certain point in the liquid that is higher than the atmospheric pressure. In the present invention, gauge pressure refers to the pressure value higher than the atmospheric pressure. When converted to absolute pressure, the atmospheric pressure value should be added. In the present invention, if not specifically indicated, the pressure is absolute pressure.

[0043] min: indicates minutes.

[0044] H: indicates hours

[0045] Beneficial Effects

[0046] 1. The present invention provides a new method for removing manganese from phosphoric acid, which can effectively remove manganese without introducing impurities or impurities that are harmful to the preparation process of iron phosphate;

[0047] 2. The present invention unexpectedly discovered that after the divalent manganese ions are oxidized to trivalent manganese ions, they will form manganese iron phosphate precipitates with iron phosphate. This phenomenon is discovered and disclosed for the first time. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the XRD pattern of the precipitate obtained in Example 1.

[0049] Figure 2 This is the XRD pattern of the precipitate obtained in Example 5.

[0050] Figure 3 This is the XRD pattern of the precipitate obtained in Example 6. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the examples. It should be noted that the examples cannot be used as a limitation on the protection scope of the present invention, and those skilled in the art understand that any improvements and changes made on the basis of the present invention are within the protection scope of the present invention.

[0052] The conventional reagents used in the following examples are all commercially available.

[0053] Undiluted recovered phosphoric acid: density is 1.395 g / ml, phosphoric acid concentration is 57%, of which the manganese content is 4237 mg / L and the iron content is 19585 mg / L.

[0054] The ICP detection method is as follows: For the supernatant measurement method, take 2 ml of the supernatant with a pipette into a 100 ml volumetric flask, add 2 ml of hydrochloric acid, dilute to 100 ml with water, and take 20 ml to measure ICP. For the solid precipitate measurement method, wash and dry the obtained cyan precipitate, take 0.2 g of the solid, add 20 ml (1:1) hydrochloric acid to digest and dilute to 100 ml, take 1 ml of the dilute solution to dilute to 100 ml, and take 20 ml to measure ICP).

[0055] The ozone generator used in the embodiment was purchased from Beijing Tonglin Technology Co., Ltd., model 3S-T10, gas production, air source ≤ 4.5 g / h, oxygen source ≤ 10 g / h. The air source is used in the present invention.

[0056] Example 1

[0057] Undiluted recycled phosphoric acid was used, wherein the manganese concentration was 4237 mg / L and the corresponding iron concentration was 19585 mg / L.

[0058] Experimental process:

[0059] (1) 150 ml of recovered phosphoric acid was placed in a three-necked flask and heated in a water bath, and ozone (0.3 L / min) was introduced into the solution. The temperature of the water bath was set to 90°C.

[0060] (2) During the heating process, it was found that the color of the diluted recovered phosphoric acid system gradually turned purple-red. When the temperature was raised to 90°C, a sample was taken for observation. At this time, the system was transparent purple-red.

[0061] (3) After the system was kept warm for 20 minutes, the system became turbid. Sampling, centrifugation and observation showed that the upper layer was a purple-red transparent liquid and the lower layer was a cyan-green precipitate. After 40 minutes, the system became more turbid. After the reaction was continued for 4 hours, the system was still turbid. The reaction was stopped and centrifuged. It was observed that the upper layer was a purple-red transparent liquid and the lower layer was a cyan-green precipitate.

[0062] (4) The supernatant was taken after 1 h, 2 h, 3 h, and 4 h of reaction, and the ICP of the supernatant was measured to obtain the manganese and iron content data. The green precipitate finally obtained was washed and dried, and XRD and ICP were measured.

[0063] Among them, the ICP data of the supernatant in Table 1 show that Mn was removed in large quantities. It should be pointed out that at 90°C, as ozone was introduced, the water in the solution system was continuously taken out, causing the volume of the reaction solution to change from 150 ml to 145 ml (2 h) and finally to 126 ml (4 h).

[0064] Table 1 Mn and Fe contents in supernatant at different time periods

[0065] Reaction time Mn concentration (mg / L) Fe concentration (mg / L) 0h 4237 19585 1h 2799 19195 2h 1166.5 17815 3h 466.75 18755 4h 375.5 22330

[0066] The XRD pattern of the separated turquoise precipitate is as follows: Figure 1 As shown, Figure 1 The precipitate was shown to be MnPO 4 ·H 2 O structure. The precipitate was measured by ICP, and the Mn content of the metal element was 0.768 and the Fe content was 0.232 (calculated based on the metal weight of 1). Combined with its ICP data, the chemical composition of the substance is Mn 0.768 Fe 0.232 PO 4 ·H 2 O.

[0067] Embodiment 2:

[0068] Take 100 ml of recovered phosphoric acid and add 50 ml of H 2 O. After dilution, its mass fraction is 42%. After dilution, the color of the recovered phosphoric acid is very light pink. The diluted recovered phosphoric acid is used as an example of the recovered phosphoric acid of this embodiment, wherein the manganese concentration is 2824.7 mg / L and the iron concentration is 13056.7 mg / L.

[0069] Experimental process:

[0070] (1) The diluted recovered phosphoric acid was placed in a three-necked flask and heated in a water bath, and ozone (0.3 L / min) was introduced into the solution. The temperature of the water bath was set to 90°C;

[0071] (2) During the heating process, it was found that the color of the diluted recovered phosphoric acid system gradually turned purple-red. When the temperature was raised to 90°C, a sample was taken for observation. At this time, the system was transparent purple-red.

[0072] (3) After the system was incubated for 20 minutes, the system became turbid. After sampling, centrifugation and observation, it was found that the upper layer was a purple-red transparent liquid and the lower layer was a turquoise precipitate. After 40 minutes, the system became more turbid. After the reaction was stopped 4 hours later, the system was still turbid. After centrifugation, it was observed that the upper layer was a light pink transparent liquid and the lower layer was a turquoise precipitate.

[0073] (4) Take the supernatant and measure ICP. Wash and dry the cyan precipitate, and measure XRD and ICP.

[0074] The Mn and Fe contents in the supernatant were measured, and the results showed that at the end of the 4-h reaction, the Mn content was 116.3 mg / L and the Fe content was 14000 mg / L. The volume reduction of the reaction system due to water evaporation also occurred.

[0075] The proportion of Mn in the turquoise precipitate sample is: 0.641, and the proportion of Fe is: 0.359, so the sample composition is: Mn 0.641 Fe 0.359 PO 4 ·H 2 O. The XRD of the precipitate of Example 2 is almost consistent with that of Example 1.

[0076] Example 3

[0077] Take 100 ml of recovered phosphoric acid and add 100 ml of H 2 O. After dilution, its mass fraction is 33%. After dilution, the color of the recovered phosphoric acid is very light pink. The recovered phosphoric acid after dilution is used as an example of recovered phosphoric acid in this embodiment, wherein the manganese concentration is 2118.50 mg / L and the iron concentration is 9792.5 mg / L.

[0078] Experimental process:

[0079] (1) The diluted recovered phosphoric acid was placed in a three-necked flask and heated in a water bath, and ozone (0.35 L / min) was introduced into the solution. The temperature of the water bath was set to 90°C;

[0080] (2) During the heating process, it was found that the color of the diluted recovered phosphoric acid system gradually turned purple-red. When the temperature was raised to 90°C, a sample was taken for observation. At this time, the system was transparent purple-red.

[0081] (3) After the system was kept warm for 20 minutes, the system became turbid. Sampling, centrifugation and observation showed that the upper layer was a purple-red transparent liquid and the lower layer was a cyan-green precipitate. After 40 minutes, the turbidity of the system deepened. After 4 hours, the reaction was stopped and the system was still turbid. Centrifugation was performed and it was observed that the upper layer was a very light pink transparent liquid and the lower layer was a cyan-green precipitate.

[0082] (4) Take the supernatant and measure ICP. Wash and dry the cyan precipitate, and measure XRD and ICP.

[0083] The Mn and Fe contents in the supernatant were measured, and the results showed that at the end of the 4-hour reaction, the Mn content was 35 mg / L and the Fe content was 10150 mg / L. The volume of the reaction system was reduced due to water evaporation.

[0084] The proportion of Mn in the turquoise precipitate sample is: 0.625, and the proportion of Fe is: 0.375, so the sample composition is: Mn 0.625 Fe 0.375 PO 4 ·H 2 O. The XRD of the precipitate of Example 3 is almost consistent with that of Example 1.

[0085] Example 4

[0086] Take 100 ml of recovered phosphoric acid and add 200 ml of H 2 The mass fraction of the recovered phosphoric acid after dilution is 24%. The color of the recovered phosphoric acid after dilution is very light pink. The recovered phosphoric acid after dilution is used as an example of the recovered phosphoric acid in this embodiment, wherein the manganese concentration is 1412 mg / L and the iron concentration is 6528 mg / L.

[0087] Experimental process:

[0088] (1) The diluted recovered phosphoric acid was placed in a three-necked flask and heated in a water bath, and ozone (0.35 L / min) was introduced into the solution. The temperature of the water bath was set to 90°C;

[0089] (2) During the heating process, it was found that the color of the diluted recovered phosphoric acid system gradually turned purple-red. When the temperature was raised to 90°C, a sample was taken for observation. At this time, the system was transparent purple-red.

[0090] (3) After the system was incubated for 20 minutes, the system became turbid. Sampling, centrifugation, and observation showed that the upper layer was a purple-red transparent liquid and the lower layer was a turquoise precipitate. After 40 minutes, the system became more turbid. After 4 hours, the reaction was stopped and the system was still turbid. Centrifugation was performed and it was observed that the upper layer was a very light pink transparent liquid and the lower layer was a turquoise precipitate.

[0091] (4) Take the supernatant and measure ICP. Wash and dry the cyan precipitate, and measure XRD and ICP.

[0092] The Mn and Fe contents in the supernatant were measured, and the results showed that at the end of the 4-h reaction, the Mn content was 11.6 mg / L and the Fe content was 9495 mg / L. The volume reduction of the reaction system due to water evaporation also occurred.

[0093] The proportion of Mn in the turquoise precipitate sample is: 0.523, and the proportion of Fe is: 0.477, so the sample composition is: Mn 0.523 Fe 0.477 PO 4 ·H 2 O. The XRD of the precipitate of Example 4 is almost consistent with that of Example 1.

[0094] Example 5

[0095] Take 100 ml of recovered phosphoric acid and add 300 ml of H 2 O. After dilution, its mass fraction is 18.5%. After dilution, the color of the recovered phosphoric acid is very light pink. The recovered phosphoric acid after dilution is used as an example of the recovered phosphoric acid in this embodiment, wherein the manganese concentration is 1059 mg / L and the iron concentration is 4896 mg / L.

[0096] Experimental process:

[0097] (1) The diluted recovered phosphoric acid was placed in a three-necked flask and heated in a water bath, and ozone (0.35 L / min) was introduced into the solution. The temperature of the water bath was set to 90°C;

[0098] (2) During the heating process, it was found that the color of the diluted recovered phosphoric acid system gradually changed to purple-red. When the temperature was raised to 90°C, sampling was performed and the system was transparent purple-red.

[0099] (3) After the system was incubated for 20 minutes, the system became turbid. Sampling, centrifugation, and observation showed that the upper layer was a purple-red transparent liquid and the lower layer was a cyan-green precipitate. After 40 minutes, the system became more turbid. After 4 hours, the reaction was stopped and the system was still turbid. Centrifugation was performed and it was observed that the upper layer was a nearly colorless transparent liquid and the lower layer was a cyan-green precipitate.

[0100] (4) Take the supernatant and measure ICP. Wash and dry the cyan precipitate, and measure XRD and ICP.

[0101] The Mn and Fe contents in the supernatant were measured, and the results showed that at the end of the 4-h reaction, the Mn content was 7 mg / L and the Fe content was 4327.5 mg / L. The volume of the reaction system was reduced due to water evaporation.

[0102] The proportion of Mn in the turquoise precipitate sample is: 0.581, and the proportion of Fe is: 0.419, so the sample composition is: Mn 0.581 Fe 0.419 PO 4 ·H 2 O. The XRD pattern of the precipitate of Example 5 is shown in Figure 2 .

[0103] Table 2 Mn and Fe contents in the supernatant at different time periods in Example 5

[0104] Reaction time Mn concentration (mg / L) Fe concentration (mg / L) 0h 1059.25 4896.25 1h 399.6 4492 2h 59.35 3829.5 3h 13.04 4245 4h 7.16 4327.5

[0105] Example 6

[0106] Recovered phosphoric acid: density is 1.395 g / ml, concentration is 57%, of which manganese impurity content is 4237 mg / L, and iron impurity content is 19585 mg / L.

[0107] Experimental process:

[0108] (1) Weigh 0.6094 g KMnO 4 Dissolve in 60 ml of water and connect to a peristaltic pump, setting the flow rate to 0.25 ml / min;

[0109] (2) Take 200 ml of recovered phosphoric acid, add 40 ml of water and place in a three-necked flask and heat in a water bath. Set the temperature of the water bath to 90°C. At this time, the solution is light pink;

[0110] (3) Raise the temperature to 90°C and pump KMnO into the solution. 4 (the addition rate is 15ml / h), the color of the system gradually turns purple-red; after the system is incubated for 20 minutes, the color of the system deepens, sampling, centrifugation, and observation show that no precipitation is produced; after 40 minutes, the color of the system deepens and becomes turbid; after 1h, the system is still in a turbid state, sampling, centrifugation, and observation show that the upper layer is a purple-red transparent liquid, and the lower layer is a dark green precipitate; after 2h, the system is still in a turbid state, the color turns dark red, sampling, centrifugation, and observation show that the upper layer is a purple-red transparent liquid, and the lower layer is a dark green precipitate; after 3h, the system is still in a turbid state, the color turns brown-green, sampling, centrifugation, and observation show that the upper layer is a purple-red transparent liquid, and the lower layer is a dark green precipitate; after 4h, the system is still in a turbid state, sampling, centrifugation, and observation show that the upper layer is a purple-red transparent liquid, and the lower layer is a dark green precipitate;

[0111] (4) Stop the reaction. Measure ICP of the supernatant obtained in the above four times. Centrifuge the solution after the reaction, wash and dry the obtained cyan precipitate, measure XRD and ICP.

[0112] Table 3 Mn and Fe contents in the supernatant at different time periods in Example 6

[0113] Reaction time Mn concentration (mg / L) Fe concentration (mg / L) 0h 3530.8* 16320* 1h 3195.5 14770 2h 1703 13640 3h 771 11680 4h 217.6 9565

[0114] *Potassium permanganate was added gradually at a rate of 15 ml / h, and 0 h was the Mn / Fe content after dilution of the original recovered phosphoric acid.

[0115] The green precipitate separated was measured by ICP, and the Mn content of the metal elements was 0.669 and the Fe content was 0.331. The chemical structure of the substance may be Mn 0.669 Fe 0.331 PO 4 ·H 2 O. The XRD pattern of the precipitate of Example 6 is shown in Figure 3 .

[0116] It should be noted that in Example 6, no gas was introduced or water vapor was taken out, and the volume change of the reaction system was not obvious. From this experiment, it can be seen that the Fe concentration is normally decreasing, indicating that Fe participates in and enters the precipitate.

[0117] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for recovering phosphoric acid and removing manganese, characterized in that: An oxidant capable of oxidizing divalent manganese into trivalent manganese is added to the recovered phosphoric acid solution. After the reaction is completed, the solid-liquid separation is performed, and the solid precipitate is separated and removed to obtain a recovered phosphoric acid solution from which manganese is removed. The recovered phosphoric acid solution is a phosphoric acid solution recovered after preparing iron phosphate, and the phosphoric acid solution contains iron ions.

2. The method according to claim 1, characterized in that The oxidant is selected from ozone, manganese acid, alkali metal salts of manganese acid, permanganate, alkali metal salts of permanganate, or ferric permanganate, ferric acid, alkali metal salts of ferric acid, preferably ozone, potassium permanganate, ferric permanganate, ferric acid, potassium ferrate.

3. The method according to claim 1, characterized in that The amount of the oxidant used is calculated based on the molar amount of the divalent manganese ion and is 0.05-20 times, preferably 0.2-10 times, the molar amount of manganese.

4. The method according to claim 1, characterized in that The recovered phosphoric acid has a phosphoric acid content of 5wt%-80wt%, and an iron ion concentration of 1g / L-200g / L in terms of elemental iron. Preferably, the phosphoric acid content is 10wt%-70wt%, and the iron ion concentration is 3g / L-150g / L in terms of elemental iron.

5. The method according to any one of claims 1 to 4, characterized in that: The iron ion is a divalent iron ion, a trivalent iron ion, a divalent iron complex ion or a trivalent iron complex ion.

6. The method according to any one of claims 1 to 5, characterized in that: When the iron ion is a divalent iron ion or a divalent iron complex ion, before or at the same time as the addition of the oxidant, a supplementary oxidant is added to oxidize the divalent iron into trivalent iron; the supplementary oxidant is selected from one or more combinations of hydrogen peroxide, ozone, manganic acid, manganate, permanganic acid, and permanganate; preferably, the supplementary oxidant is hydrogen peroxide.

7. The method according to claim 6, characterized in that The amount of the supplementary oxidant added is calculated based on the molar amount of the divalent iron ion or the divalent iron complex ion, and the equivalent molar amount is the best; preferably, the supplementary oxidant is 80%-120% of the equivalent molar amount.

8. The method according to claim 1, characterized in that The method is applied to the preparation process of ferric phosphate to process phosphoric acid recovered in the preparation process of ferric phosphate.

9. A method for preparing ferric phosphate, characterized in that: include: S1: using phosphoric acid with a concentration of 35-85% to react with iron oxide at a reaction temperature between room temperature and 180°C, adding an oxidant during the reaction, filtering to remove insoluble matter, and collecting the first mother liquor; S2: Control the temperature of the first mother liquor to be between room temperature and 180° C., add water to the first mother liquor, control the concentration of iron ions to be between 0.1 mol / L and 2 mol / L, react for 1 min to 20 h, separate the solid and the liquid, and obtain solid iron phosphate dihydrate and the second mother liquor; Preferably, the ratio of phosphorus to iron in the first mother liquor is (2.5-10):1; Preferably, the oxidant is selected from ozone, manganic acid, alkali metal salts of manganic acid, permanganic acid, alkali metal salts of permanganate, or ferric permanganate, ferric acid, alkali metal salts of ferric acid; more preferably, ozone, potassium permanganate, ferric permanganate, ferric acid, potassium ferrate; further preferably, the oxidant is ozone or potassium permanganate; Preferably, step S1 is carried out at 60-140° C., and the phosphoric acid concentration is between 50-85%; Preferably, step S2 is carried out at 60-160°C and the reaction time is 10min-6h; Preferably, step S2 is carried out under normal pressure or under pressure, and the pressure is controlled within an absolute pressure range of 0.1-1 MPa, preferably 0.1-0.5 MPa.

10. The method according to claim 9, characterized in that The method further comprises step S3: adding or not adding phosphoric acid according to the phosphoric acid concentration in the second mother liquor to ensure that the phosphoric acid content in the second mother liquor meets the phosphoric acid concentration limit in step S1, and recycling the second mother liquor back to step S1.

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