High-valued utilization method of iron in high-phosphorus iron ore

Abstract

The invention discloses a method for high-valued utilization of iron in high-phosphorus iron ore, and belongs to the field of comprehensive utilization of high-phosphorus iron ore. The method comprises the following steps: mixing the high-phosphorus iron ore with inorganic acid to perform leaching reaction, and performing liquid-solid separation after the reaction is finished to obtain leached residues and filtrate; adding ferrocyanate into the filtrate to carry out precipitation reaction, and carrying out liquid-solid separation to obtain Prussian blue precipitate and phosphorus-containing filtrate; alkali liquor is added into the phosphorus-containing filtrate for a neutralization reaction, liquid-solid separation is conducted after the reaction is finished, sediment and water are obtained, and the sediment serves as a raw material of a fertilizer or a sodium-ion battery positive electrode material; the Prussian blue precipitate is washed and dried to serve as a raw material of the sodium ion battery positive electrode material, and the Prussian blue precipitate has excellent specific capacity and sodium storage performance. According to the method disclosed by the invention, excessive byproducts are avoided, the used acid liquor can be recycled, reagent consumption and environmental pollution are reduced, and a green and environment-friendly concept is embodied. The method has the technological characteristics of high iron separation efficiency, excellent product performance and environmental friendliness, and has a wide industrial application prospect in the aspects of comprehensive utilization of the high-phosphorus iron ore and development of new energy materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of comprehensive utilization of high-phosphorus iron ore, and particularly relates to a method for the high-value utilization of iron in high-phosphorus iron ore. Background Art

[0002] The main components of high-phosphorus iron ore are iron, phosphorus and other impurity elements, where the iron grade is 40% - 60% and the phosphorus grade is 0.5% - 2%. The iron element rich in high-phosphorus iron ore can be used as raw material for steel production. However, due to its complex composition and high phosphorus content, the steel produced is prone to "cold brittleness" phenomenon and is difficult to be directly utilized. Therefore, the control of phosphorus content has become one of the key factors in the development of steelmaking technology.

[0003] For high-phosphorus iron ore, the current main dephosphorization and iron extraction technologies include beneficiation method, chemical method, microbial method and high-temperature smelting method, etc. However, the beneficiation method and high-temperature smelting method have problems of low dephosphorization rate and excessive iron loss, and their applications are greatly limited. The chemical method and microbial method usually use inorganic acid or mineral acid to dissolve iron elements in the ore, but a large amount of wastewater will be generated during the refining process, which is not environmentally friendly.

[0004] In addition, with the enhancement of social environmental protection awareness and the increasingly strict environmental protection regulations in China, the problems existing in the above traditional high-phosphorus iron ore refining processes have received more and more attention. How to effectively remove phosphorus elements and reduce environmental pollution while realizing the high-value utilization of iron elements in high-phosphorus iron ore has become an urgent technical problem to be solved. Summary of the Invention

[0005] In order to overcome the above deficiencies, the present invention provides a method for the high-value utilization of iron in high-phosphorus iron ore. Through an innovative process flow, the present invention realizes the efficient co-recovery of iron and phosphorus, not only improves the recovery rate of iron and the utilization rate of phosphorus resources, but also reduces pollutant emissions during the production process, providing a new technical path for the comprehensive utilization of high-phosphorus iron ore. Therefore, the method of the present invention not only helps to alleviate the shortage of iron ore resources, but also provides new support for the development of the new energy industry.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for the high-value utilization of iron in high-phosphorus iron ore, including the following steps: mixing high-phosphorus iron ore with inorganic acid for leaching reaction, and after the reaction is completed, performing liquid-solid separation to obtain leaching residue and filtrate; adding ferrocyanate to the filtrate for dephosphorization and iron extraction, and after liquid-solid separation, obtaining Prussian blue precipitate and phosphorus-containing filtrate; adding alkali solution to the phosphorus-containing filtrate for neutralization reaction, and after the reaction is completed, performing liquid-solid separation to obtain precipitate and water, and the precipitate is used as fertilizer or raw material for the positive electrode material of sodium-ion battery; washing the Prussian blue precipitate and drying it to be used as raw material for the positive electrode material of sodium-ion battery.

[0008] Preferably, the method for the high-value utilization of iron in the high-phosphorus iron ore includes the following steps:

[0009] Step 1: Grind and crush the high-phosphorus iron ore and mix it fully with inorganic acid for acid leaching. After liquid-solid separation, leaching residue and filtrate are obtained. The filtrate is the leaching solution containing phosphorus and iron.

[0010] Step 2: Add ferrocyanate to the filtrate for reaction. After centrifugation and liquid-solid separation, Prussian blue precipitate and phosphorus-containing filtrate are obtained. Take a part of the phosphorus-containing filtrate for acidification treatment and it can be recycled.

[0011] Step 3: Fully neutralize the phosphorus-containing solution with alkali solution and then perform liquid-solid separation. The obtained precipitate can be used as a cathode material for a type of sodium-ion battery or fertilizer.

[0012] Step 4: Wash the obtained Prussian blue precipitate repeatedly with deionized water and absolute ethanol, and perform vacuum drying for dehydration to be used as the raw material for the cathode material of the sodium-ion battery.

[0013] The phosphorus-containing filtrate generated in Step 2 can be returned to Step 1 for use; after the phosphorus-containing filtrate subjected to acidification treatment in Step 2 is recycled multiple times (3 - 15 times), the content of phosphate ions in the solution accumulates to a relatively high level, which will affect the acid leaching effect. When the concentration of phosphate ions in the solution is above 30 wt.%, the recycling needs to be stopped. It can be used as the raw material solution for Step 3 or for producing agricultural fertilizers.

[0014] Preferably, in Step 1: the phosphorus content in the high-phosphorus iron ore is 0.5 - 2 wt.%.

[0015] The high-phosphorus iron ore needs to be crushed to 100-500 mesh before mixing with inorganic acid. The ore with a smaller particle size has a larger specific surface area, can contact with the acid more fully, improve the acid leaching efficiency, reduce the iron loss rate, and at the same time increase the phosphorus removal rate. While a larger particle size will reduce the reaction rate and dephosphorization effect. Over-crushing will increase the cost, so 100-500 mesh is selected as the optimal particle size range. In the present invention, the iron ore with a relatively high phosphorus content (i.e., high-phosphorus iron ore) in the smelting process is ground and broken into powder form, and fully mixed with inorganic acid. After liquid-solid separation, a leaching solution containing phosphorus and iron is obtained; then ferrocyanate is added to separate the iron in the solution in the form of Prussian blue precipitate, so as to achieve the purpose of dephosphorization and iron extraction. After the obtained filtrate is acidified to a certain extent, it can be returned to the acid leaching step for recycling to save production costs; when the number of cycles is relatively large (3-15 cycles) and the phosphorus element content in the solution is relatively high (the concentration of phosphate ions in the solution is above 30 wt.%), a strong alkali solution is added for harmless treatment. The treated solution can be directly discharged, and the obtained precipitate can be used as the raw material of the positive electrode material of sodium-ion battery or agricultural fertilizer (when the precipitate is high phosphate, it is used as the raw material of the positive electrode material of sodium-ion battery, and when the precipitate is orthophosphate, it is used as agricultural fertilizer). In addition, after the obtained Prussian blue precipitate is dried and dehydrated, it can also be used as the raw material of the positive electrode material of sodium-ion battery. The method of the present invention realizes the efficient co-recovery of iron and phosphorus through an innovative process flow, not only improves the recovery rate of iron and the utilization rate of phosphorus resources, but also reduces the pollutant emissions in the production process, providing a new technical path for the comprehensive utilization of high-phosphorus iron ore. Therefore, the method of the present invention not only helps to alleviate the problem of shortage of iron ore resources, but also provides new support for the development of the new energy industry.

[0016] Preferably, in step one: the concentration of the inorganic acid is 2-8 mol / L. The concentration of the inorganic acid directly affects the dissolution rate and removal rate of phosphorus and iron in the acid leaching process. When the acid concentration is too low, the phosphorus mineral cannot be effectively dissolved, resulting in a low phosphorus removal rate; while when the acid concentration is too high, it may increase the dissolution loss of iron;

[0017] and / or, the liquid-solid ratio of the inorganic acid to the high-phosphorus iron ore is (2-7) L∶1 g. The liquid-solid ratio determines the contact degree between the inorganic acid and the high-phosphorus iron ore. When the liquid-solid ratio is too low, the amount of acid is insufficient and phosphorus cannot be fully leached; when the liquid-solid ratio is too high, it will increase the acid consumption and cost;

[0018] And / or, after the high-phosphorus iron ore is mixed with an inorganic acid, it reacts for 1-5 h under the conditions of a temperature of 70-120 °C and a pH of 0.5-2. The reaction temperature has an important influence on the reaction rate and dephosphorization rate of the acid leaching process. As the temperature increases, the acid leaching reaction rate accelerates, and the removal rates of both phosphorus and iron will increase. At this temperature, the dissolution of iron increases, ensuring that the leaching rate of iron reaches the optimal level. The reaction time determines the degree of completion of the acid leaching process. If the time is too short, the leaching of phosphorus is incomplete; if the time is too long, it may lead to excessive dissolution of iron.

[0019] In step one of the method of the present invention, by adjusting the concentration of the inorganic acid, the liquid-solid ratio of the inorganic acid to the high-phosphorus iron ore (i.e., the pH of acid leaching), the temperature and time of acid leaching, the leaching rates of phosphorus and iron in the leaching solution containing phosphorus and iron can be increased. Within the above ranges of the present invention, it can be ensured that the leaching rate of iron in the leaching solution containing phosphorus and iron reaches more than 90%.

[0020] Exemplarily, the inorganic acid is hydrochloric acid, sulfuric acid or nitric acid, preferably sulfuric acid. Hydrochloric acid, sulfuric acid and nitric acid react with high-phosphorus iron ore to generate phosphoric acid and calcium chloride, phosphoric acid and calcium sulfate, phosphoric acid and calcium nitrate respectively, which can be used to prepare fertilizers.

[0021] Preferably, in step two: after adding ferrocyanate to the filtrate, adjust the pH to 0.1-1.5 and react at a temperature of 25-120 °C for 0.5-1.5 h. The acidic environment is conducive to the dissolution of iron ions and the reaction with ferrocyanate. For example, when using potassium ferrocyanide to react with ferric ions in an acidic solution, the control of the pH value can affect the formation efficiency and color depth of Prussian blue. Too low pH may lead to excessive dissolution of iron ions, while too high pH may cause Fe3 + to hydrolyze to form ferric hydroxide precipitate, reducing its effective concentration, thereby reducing the formation of Prussian blue and resulting in a lighter or uneven color of the product. The reaction temperature has an important influence on the formation and crystal structure of Prussian blue: at a lower temperature (such as 0 °C), the formed Prussian blue particles are smaller and evenly distributed, but the crystal structure is not complete enough; at a medium temperature (such as 25 °C), the crystal structure is relatively complete and the particle size is moderate; at a higher temperature (such as 60-80 °C), the crystal growth rate increases significantly and the particle size increases, but too high a temperature may lead to out-of-control crystal growth, introducing structural defects (such as lattice distortion) and affecting the performance. In the above reaction process of the present invention, the crystal growth rate and structural integrity can be balanced to obtain high-quality Prussian blue precipitate, ensuring that the iron recovery rate in the Prussian blue precipitate is higher than 95% and the phosphorus content is not higher than 0.02 wt.%.

[0022] Exemplarily, the ferrocyanide is sodium ferrocyanide, potassium ferrocyanide or calcium ferrocyanide.

[0023] Exemplarily, the alkaline solution is sodium hydroxide solution, potassium hydroxide solution or calcium hydroxide solution.

[0024] Preferably, in step three: the mass ratio of the alkaline solution to the phosphorus-containing filtrate is (1-3):1;

[0025] And / or, after adding the alkaline solution to the phosphorus-containing filtrate, the temperature of the neutralization reaction is 25°C to 100°C, and the reaction time is 0.5 to 1 h.

[0026] In step three of the method of the present invention, under the conditions of different mass ratios, reaction temperatures and times of the alkaline solution to the phosphorus-containing filtrate, high phosphates or orthophosphates with a purity of 45% to 65% can be obtained. The high phosphates can be used as raw materials for the positive electrode materials of sodium-ion batteries, and the orthophosphates can be used to prepare fertilizers.

[0027] Preferably, in step four: the drying temperature is 40 to 100°C, and the drying time is 24 to 72 h, reducing the occupancy of water molecules on the Prussian blue vacancies, improving its sodium storage capacity, and thus optimizing its performance as a positive electrode material for sodium-ion batteries.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] The present invention provides a method for the high-value utilization of iron in high-phosphorus iron ore, aiming to effectively separate iron from phosphorus, improve the recovery rate of iron and the utilization rate of phosphorus resources, while reducing production costs and environmental pollution. First, the iron ore with a relatively high phosphorus content is ground and crushed into a powder to fully release mineral particles and increase the contact area with the inorganic acid solution. Subsequently, the powdered iron ore is fully mixed with the inorganic acid solution, and through the leaching action of the acid, iron and phosphorus are dissolved out of the ore to form a leaching solution containing iron and phosphorus. In the prior art, the purpose of acid leaching high-phosphorus iron ore at low temperature (40 - 60°C) is usually to preliminarily separate iron and phosphorus, and make the structure of the ore powder loose, increasing the specific surface area of the ore powder, which facilitates the subsequent reduction and slag-iron separation processes. However, the present invention uses an inorganic acid (such as sulfuric acid, hydrochloric acid, nitric acid) with a concentration of 2 - 8 mol / L, and conducts acid leaching under the conditions of high temperature (70 - 120°C) and a pH value of 0.5 - 2 for 1 - 5 hours to achieve the efficient dissolution of iron and phosphorus, while avoiding iron loss caused by excessive acidification. Through liquid-solid separation technology, the solid residue is separated from the leaching solution to obtain a solution rich in iron and phosphorus. Ferrocyanate is added to the leaching solution, and the ferrocyanide ions in the ferrocyanate react with the iron ions in the solution to form Prussian blue precipitate. The formation of Prussian blue precipitate realizes the effective separation of iron from the solution, achieving the purpose of dephosphorization and iron extraction. The obtained filtrate is acidified and then returned to the acid leaching step for recycling, reducing the consumption of fresh acid, thereby saving production costs. As the number of recycling increases, the content of phosphorus element in the solution gradually accumulates. When the phosphorus content is higher than 30 wt.%, a strong base solution is added for harmless treatment. The strong base reacts with the phosphorus in the solution to form metaphosphate and orthophosphate, making the solution meet the environmental protection discharge standard and can be directly discharged. At the same time, the precipitate generated during the reaction is rich in phosphorus and can be used as a raw material for the positive electrode material of sodium-ion batteries or as a fertilizer, realizing the recycling of phosphorus resources. The obtained Prussian blue precipitate is dried and dehydrated to remove the moisture in it, obtaining a sodium-ion battery positive electrode material with low water content and high crystallinity. This material has good electrochemical performance and can be used as a raw material for the positive electrode material of sodium-ion batteries, not only expanding the application field of iron ore resources, but also providing new material options for the development of the new energy industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0031] Figure 1 It is a process flow chart of the method for the high-value utilization of iron in high-phosphorus iron ore of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation on the present invention, but rather as a more detailed description of certain aspects, features, and implementation manners of the present invention.

[0033] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0035] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0036] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0037] The embodiments of the present invention provide a method for the high-value utilization of iron in high-phosphorus iron ore. The process flow chart is shown in Figure 1 , and includes the following steps:

[0038] Step 1: Grind the high-phosphorus iron ore into powder and mix it fully with inorganic acid for acid leaching. After liquid-solid separation, leaching residue and filtrate are obtained. The filtrate is the leaching solution containing phosphorus and iron. The phosphorus content in the high-phosphorus iron ore is 0.5-2 wt.%. The high-phosphorus iron ore with a smaller particle size has a larger specific surface area, which can contact the acid fully, thus improving the rate and efficiency of the acid leaching reaction. A larger particle size may cause the acid to be difficult to penetrate into the interior of the ore, resulting in a decrease in the reaction rate and a poor dephosphorization effect. During the acid leaching process of the high-phosphorus iron ore with a smaller particle size, the phosphorus removal rate is higher and the iron loss rate is lower. The high-phosphorus iron ore with a larger particle size may lead to an increase in iron loss during the acid leaching process and a lower phosphorus removal rate. Excessive grinding will increase the cost, and the high-phosphorus iron ore with a larger particle size is not conducive to the leaching of iron and phosphorus. Therefore, it is preferably to crush the high-phosphorus iron ore to 100-500 mesh and then mix it with inorganic acid;

[0039] Step 2: Add ferrocyanate to the filtrate according to 1-2.5 times the theoretical dosage of ferrocyanate. After centrifugation and liquid-solid separation, Prussian blue precipitate and phosphorus-containing filtrate are obtained. Take a part of the phosphorus-containing filtrate for acidification treatment and then it can be recycled;

[0040] Step 3: After the phosphorus-containing solution and the alkali solution are fully neutralized and reacted, liquid-solid separation is carried out. The obtained precipitate can be used as a type of cathode material for sodium-ion batteries or fertilizer;

[0041] Step 4: Wash the obtained Prussian blue precipitate repeatedly with deionized water and absolute ethanol until it is neutral, and then carry out vacuum drying and dehydration. It is used as the raw material for the cathode material of sodium-ion batteries. The drying temperature is 40-100 °C, and the drying time is 24-72 h. This reduces the occupation of water molecules on the Prussian blue vacancies, improves its sodium storage capacity, and thus optimizes its performance as the cathode material of sodium-ion batteries.

[0042] The method of the present invention not only avoids the generation of unnecessary by-products, but also the acid solution used can be recycled, reducing reagent consumption and environmental pollution, which reflects the concept of green environmental protection. The method of the present invention has the technological characteristics of high iron separation efficiency, excellent product performance and environmental friendliness, and has broad industrial application prospects in the comprehensive utilization of high-phosphorus iron ore and the development of new energy materials.

[0043] The phosphorus-containing filtrate generated in Step 2 can be returned to Step 1 for use; after the phosphorus-containing filtrate subjected to acidification treatment in Step 2 is recycled for multiple times (3-15 times), the content of phosphate ions in the solution accumulates to a relatively high level, which will affect the acid leaching effect. When the concentration of phosphate ions in the solution is above 30 wt.%, the recycling needs to be stopped. It can be used as the raw material solution for Step 3 or for producing fertilizer.

[0044] In some embodiments of the present invention, in Step 1: the concentration of the inorganic acid is 2 - 8 mol / L. The concentration of the inorganic acid directly affects the dissolution rate and removal rate of phosphorus and iron during the acid leaching process. When the acid concentration is too low, phosphorus minerals cannot be effectively dissolved, resulting in a low dephosphorization rate; while when the acid concentration is too high, the dissolution loss of iron may increase.

[0045] The liquid-solid ratio of the inorganic acid to the high-phosphorus iron ore is (2 - 7) L∶1 g, and the reaction pH is 0.5 - 2. The liquid-solid ratio determines the contact degree between the inorganic acid and the high-phosphorus iron ore. When the liquid-solid ratio is too low, the amount of acid is insufficient and phosphorus cannot be fully leached; when the liquid-solid ratio is too high, the acid consumption and cost will increase.

[0046] After the high-phosphorus iron ore is mixed with the inorganic acid, the reaction is carried out at a temperature of 70 - 120 °C for 1 - 5 h. The reaction temperature has an important influence on the reaction rate and dephosphorization rate during the acid leaching process. As the temperature increases, the acid leaching reaction rate accelerates, and the removal rates of both phosphorus and iron will increase. At this temperature, the dissolution of iron increases, ensuring that the iron leaching rate reaches the optimal level. The reaction time determines the degree of completion of the acid leaching process. If the time is too short, the leaching of phosphorus is incomplete; if the time is too long, excessive dissolution of iron may occur.

[0047] By adjusting the concentration of the inorganic acid, the liquid-solid ratio of the inorganic acid to the high-phosphorus iron ore (i.e., the pH of the acid leaching), the temperature and time of the acid leaching, the leaching rates of phosphorus and iron in the leaching solution containing phosphorus and iron can be increased. Within the above ranges of the present invention, the iron leaching rate in the leaching solution containing phosphorus and iron can be ensured to reach more than 90%.

[0048] In some embodiments of the present invention, the inorganic acid is hydrochloric acid, sulfuric acid or nitric acid, preferably sulfuric acid. Hydrochloric acid, sulfuric acid and nitric acid react with the high-phosphorus iron ore to generate phosphoric acid and calcium chloride, phosphoric acid and calcium sulfate, phosphoric acid and calcium nitrate respectively, which can be used to prepare fertilizers.

[0049] In some embodiments of the present invention, in step two: after adding ferrocyanate to the filtrate, adjust the pH to 0.1 - 1.5, and react at a temperature of 25 - 120 °C for 0.5 - 1.5 h. An acidic environment is conducive to the dissolution of iron ions and the reaction with ferrocyanate. For example, when using potassium ferrocyanide to react with ferric ions in an acidic solution, the control of the pH value can affect the formation efficiency and color depth of Prussian blue. Too low a pH may cause excessive dissolution of iron ions, while too high a pH may inhibit the reaction, resulting in a lighter or uneven color of the product. The reaction temperature has an important influence on the formation and crystal structure of Prussian blue: at a lower temperature (such as 0 °C), the formed Prussian blue particles are smaller and evenly distributed, but the crystal structure is not complete enough; at a medium temperature (such as 25 °C), the crystal structure is relatively complete and the particle size is moderate; at a higher temperature (such as 60 °C - 80 °C), the crystal growth rate increases, the particle size increases, and the crystal structure is more complete. However, too high a temperature may lead to an increase in crystal structure defects and affect its performance. In the above reaction process of the present invention, the crystal growth rate and structural integrity can be balanced to obtain high-quality Prussian blue precipitate, ensuring that the iron recovery rate in the Prussian blue precipitate is higher than 95%, and the phosphorus content is not higher than 0.02 wt.%.

[0050] In some embodiments of the present invention, the ferrocyanide is sodium ferrocyanide, potassium ferrocyanide or calcium ferrocyanide.

[0051] In some embodiments of the present invention, the alkali solution is sodium hydroxide solution, potassium hydroxide solution or calcium hydroxide solution.

[0052] In some embodiments of the present invention, in step three: the mass ratio of the alkali solution to the phosphorus-containing filtrate is (1 - 3):1; after adding the alkali solution to the phosphorus-containing filtrate, the reaction temperature is 25 °C - 100 °C, and the reaction time is 0.5 - 1 h. Under different mass ratios, reaction temperatures and times of the alkali solution to the phosphorus-containing filtrate, high phosphates or orthophosphates with a purity of 45% - 65% can be obtained. The high phosphates can be used as raw materials for the positive electrode materials of sodium-ion batteries, and the orthophosphates can be used to prepare fertilizers.

[0053] In the following examples and comparative examples of the present invention, the acidification treatment can be: adding the corresponding inorganic acid to the filtered phosphorus-containing solution to the initial concentration, and then conducting a cyclic leaching experiment.

[0054] In the following examples and comparative examples of the present invention, the calculation methods of the iron leaching rate (ωiron, %), phosphorus leaching rate (ωphosphorus, %) and comprehensive iron recovery rate (ηiron, %) are as follows:

[0055] Iron leaching rate: Among them, ω 铁 is the iron leaching rate in the high-phosphorus iron ore, %; M 1(Iron) is the iron element content in the sample before leaching, g / L; M 2 (Iron) is the iron element content in the leaching residue, g / L;

[0056] Phosphorus leaching rate: Among them, ω 磷 is the leaching rate of phosphorus in high-phosphorus iron ore, %; M 1 (Phosphorus) is the phosphorus element content in the sample before leaching, g / L; M 2 (Phosphorus) is the phosphorus element content in the leaching residue, g / L;

[0057] Overall iron recovery rate:: Among them, η 铁 is the overall iron recovery rate, m 1 is the mass of high-phosphorus iron ore, kg; θ 1 is the iron content in high-phosphorus iron ore, %; m 2 is the mass of the obtained Prussian blue precipitate, kg; θ 2 is the iron content in the Prussian blue precipitate, %.

[0058] In the following examples and comparative examples of the present invention, the assembly method of the sodium-ion button battery mainly includes the following steps: First, the dried Prussian blue powder, Super P conductive agent, and PVDF binder are mixed into a slurry according to a mass ratio of 8:1:1, coated on the aluminum foil and dried; then cut into circular electrode sheets. Next, a gasket, a Celgard 2400 separator, and the positive electrode sheet are sequentially placed at the bottom of the battery case, and an appropriate amount of 1M NaPF 6 electrolyte (the solvent is ethylene carbonate (EC) and dimethyl carbonate (DMC), and the volume ratio of EC / DMC is 1:1) is dropped. Then, a sodium sheet is used as the negative electrode, and a gasket and a spring are placed on it. Finally, the battery case is buckled and sealed. After assembly, it is necessary to stand for more than 12 hours to complete the activation process of the battery, and then the electrochemical performance test can be carried out. The entire assembly process needs to be carried out in a dry and dust-free environment to ensure the battery performance and safety.

[0059] All raw materials and reagents used in the examples of the present invention are obtained by purchasing commercially.

[0060] It should be noted that the parts not described in detail in the present invention are all conventional operating means in the art and are not the focus of the present invention.

[0061] The technical solution of the present invention will be further described below through examples.

[0062] Example 1

[0063] Step 1: Grind and crush high-phosphorus iron ore (phosphorus content is 2 wt.%) to 100 mesh, and mix it thoroughly with hydrochloric acid solution with a concentration of 2 mol / L according to a liquid-solid ratio (L / g) of 2:1. Leach for 1 h under the conditions of 70 °C and a reaction pH of 2, and then perform solid-liquid separation to obtain a leachate containing phosphorus and iron and a leach residue.

[0064] Step 2: Mix the leachate containing phosphorus and iron with ferrocyanate thoroughly according to 1 times the theoretical dosage of ferrocyanate, adjust the pH to 1.5, and react at 25 °C for 0.5 h. After solid-liquid separation, a phosphoric acid solution and Prussian blue precipitate are obtained. Among them, the ferrocyanate is potassium ferrocyanide. Take a part of the phosphoric acid solution for acidification treatment and it can be recycled.

[0065] Step 3: After acid leaching is cycled 5 times, the phosphorus content in the solution is 30.21 wt.%. At this time, add potassium hydroxide solution (concentration is 30 wt.%) to the phosphoric acid solution according to a mass ratio of 3:1, and react at 25 °C for 0.5 h. After solid-liquid separation, orthophosphate can be obtained and used to prepare fertilizers.

[0066] Step 4: Dry and dehydrate the Prussian blue precipitate in a vacuum environment at 40 °C for 24 h as a raw material for preparing the cathode material of sodium-ion batteries.

[0067] Results of this example: The iron leaching rate is 91.25%, the phosphorus leaching rate is 89.53%, the comprehensive iron recovery rate is 98.23%, the number of cycles of the phosphoric acid solution is 5 times, and the purity of orthophosphate is 52.32%.

[0068] Example 2

[0069] Step 1: Grind and crush high-phosphorus iron ore (phosphorus content is 2 wt.%) to 300 mesh, and mix it thoroughly with nitric acid solution with a concentration of 5 mol / L according to a liquid-solid ratio (L / g) of 5:1. Leach for 3 h under the conditions of 100 °C and a reaction pH of 1.5, and then perform solid-liquid separation to obtain a leachate containing phosphorus and iron and a leach residue.

[0070] Step 2: Mix the leachate containing phosphorus and iron with ferrocyanate thoroughly according to 1.7 times the theoretical dosage of ferrocyanate, adjust the pH to 1, and react at 60 °C for 1 h. After solid-liquid separation, a phosphoric acid solution and Prussian blue precipitate are obtained. Among them, the ferrocyanate is calcium ferrocyanide. After taking a part of the phosphoric acid solution for acidification treatment, it is recycled.

[0071] Step 3: After acid leaching is cycled 8 times, the phosphorus content in the solution is 31.35 wt.%. At this time, add calcium hydroxide solution (concentration is 20 wt.%) to the phosphoric acid solution according to a mass ratio of 4:1, and react at 50 °C for 1 h. After solid-liquid separation, high phosphate can be obtained as a raw material for preparing the cathode material of sodium-ion batteries.

[0072] Step 4: Dry and dehydrate the Prussian blue precipitate in a vacuum environment at 60 °C for 48 h as the raw material for preparing the cathode material of the sodium-ion battery.

[0073] Results of this example: The iron leaching rate is 95.25%, the phosphorus leaching rate is 90.69%, the comprehensive iron recovery rate is 98.89%, the number of cycles of the phosphoric acid solution is 8 times, and the high phosphate purity is 62.33%.

[0074] Example 3

[0075] Step 1: Grind and crush the high-phosphorus iron ore (with a phosphorus content of 2 wt.%) to 500 mesh, and fully mix it with a sulfuric acid solution with a concentration of 7 mol / L according to a liquid-solid ratio (L / g) of 6:1. Leach for 4 h at 120 °C and a reaction pH of 0.8, and then perform solid-liquid separation to obtain a leachate containing phosphorus and iron and a leach residue.

[0076] Step 2: Fully mix the leachate containing phosphorus and iron with ferrocyanate according to 2 times the theoretical amount of ferrocyanate, adjust the pH to 0.5, and react at 100 °C for 1.5 h. Perform solid-liquid separation to obtain a phosphoric acid solution and a Prussian blue precipitate. Among them, the ferrocyanate is sodium ferrocyanide. Take a part of the phosphoric acid solution for acidification treatment and then recycle it.

[0077] Step 3: After 15 cycles of acid leaching, the phosphorus content in the solution is 34.63 wt.%. At this time, add sodium hydroxide solution (concentration of 20 wt.%) to the phosphoric acid solution according to a mass ratio of 5:1, and react at 80 °C for 1 h. Perform solid-liquid separation to obtain orthophosphate, which can be used to prepare fertilizers.

[0078] Step 4: Dry and dehydrate the Prussian blue precipitate in a vacuum environment at 100 °C for 72 h as the raw material for preparing the cathode material of the sodium-ion battery.

[0079] Results of this example: The iron leaching rate is 98.15%, the phosphorus leaching rate is 91.03%, the comprehensive iron recovery rate is 99.45%, the number of cycles of the phosphoric acid solution is 15 times, and the orthophosphate purity is 54.66%.

[0080] Comparative Example 1

[0081] Step 1: Use citric acid as the leaching agent and fully mix and react with the ground and crushed high-phosphorus iron ore (with a phosphorus content of 2 wt.%) powder (500 mesh). The parameters such as the concentration of the acid, the liquid-solid ratio, temperature, pH, and time of the reaction are the same as those in Example 3.

[0082] Step 2: According to 2 times the theoretical dosage of the iron precipitation agent, fully mix the leaching solution with ferrocyanate, adjust the pH to 0.5, react at 100 °C for 1.5 h, and perform solid-liquid separation to obtain phosphoric acid solution and Prussian blue precipitate. Among them, the ferrocyanate is sodium ferrocyanide. Take a part of the phosphoric acid solution for acidification treatment and then recycle it;

[0083] Step 3: After 3 cycles of acid leaching, the phosphorus content in the solution is 33.78 wt.%. At this time, add sodium hydroxide solution (concentration 20 wt.%) to the phosphoric acid solution according to a mass ratio of 5:1, and react at 80 °C for 1 h to obtain orthophosphate;

[0084] Step 4: Dry and dehydrate the obtained Prussian blue precipitate in a vacuum environment at 100 °C for 72 h, which can be used as a raw material for preparing the cathode material of sodium-ion batteries.

[0085] Results of this comparative example: The iron leaching rate is 75.56%, the phosphorus leaching rate is 69.33%, the comprehensive iron recovery rate is 77.78%, the number of cycles of the phosphoric acid solution is 3 times, and the purity of orthophosphate is 33.11%.

[0086] In Example 3 and Comparative Example 1, the significant difference in the leaching rates of iron and phosphorus mainly stems from the essential differences in acid strength, complexing ability, and stability between sulfuric acid and citric acid. As a strong acid, sulfuric acid is completely dissociated at pH = 0.5 and can efficiently dissolve iron (Fe 3+ ) and phosphorus (PO 4 3- ) in high-phosphorus iron ore to achieve high leaching rates. While citric acid, as a weak organic acid (pKa1 = 3.1), has a low degree of dissociation and weak leaching ability at the same pH. In addition, the stable complex formed by citric acid and Fe 3+ (such as [Fe(C 5 H 5 O 7 )]3 - ) will hinder the Prussian blue precipitation reaction because Fe 3+ needs to combine with ferrocyanate in the free state. At 120 °C high temperature, citric acid may decompose (such as decarboxylation to form acetic acid or CO 2 ), further reducing the leaching efficiency, while sulfuric acid remains stable and continuously provides H + to promote dissolution. In multiple cycles, Fe 3+It exists in a free state, can react completely with ferrocyanate to form Prussian blue, and has high sulfuric acid stability, continuously and effectively leaching iron and phosphorus. On the contrary, citric acid is prone to decomposition and inactivation after multiple cycles, resulting in a decrease in leaching efficiency. These factors lead to the iron leaching rate (75.56%) in Comparative Example 1 being much lower than that in Example 3 (98.15%), and the phosphorus leaching rate (69.33%) is also lower than that in Example 3 (91.03%). At the same time, the complex of citric acid and Fe 3+ still exists stably at pH = 0.5, resulting in insufficient free Fe 3+ , and ferrocyanate cannot fully react to form Prussian blue. In the sulfuric acid system, Fe 3+ is mainly in a free state and the reaction is more complete.

[0087] In addition, the comprehensive iron recovery rate in Comparative Example 1 is only 77.78%, much lower than 99.45% in Example 3, indicating that a large amount of iron remains in the solution or is not completely precipitated. Citric acid may not be completely removed during multiple cycles and competes with PO 4 3- to bind with NaOH, resulting in a decrease in the purity of orthophosphate (such as Na 3 PO 4 ). The decomposition products of citric acid (such as acetic acid) may introduce organic impurities and affect the crystallization process of orthophosphate. In terms of the purity of orthophosphate, that in Comparative Example 1 is 33.11%, significantly lower than 54.66% in Example 3, indicating serious impurity interference.

[0088] Comparative Example 2

[0089] Step 1: Using oxalic acid as the leaching agent, it is fully mixed and reacted with the powder (500 mesh) of high-phosphorus iron ore (phosphorus content is 2 wt.%), and the parameters such as the concentration of the acid, the liquid-solid ratio, temperature, pH, and time of the reaction solution are the same as those in Example 3;

[0090] Step 2: According to 2 times the theoretical dosage of the iron-precipitating agent, the leaching solution is fully mixed with ferrocyanate, and the pH is adjusted to 0.5, and the reaction is carried out at a temperature of 100 °C for 1.5 h. After solid-liquid separation, a phosphoric acid solution and Prussian blue precipitate are obtained. Among them, the ferrocyanate is sodium ferrocyanide. After acidifying a part of the phosphoric acid solution, it is recycled;

[0091] Step 3: After 5 cycles of acid leaching, the phosphorus content in the solution is 34.57 wt.%. At this time, a sodium hydroxide solution (concentration is 20 wt.%) is added to the phosphoric acid solution according to a mass ratio of 5:1, and the reaction is carried out at 80 °C for 1 h to obtain orthophosphate;

[0092] Step 4: The obtained Prussian blue precipitate is dried and dehydrated in a vacuum environment at 100 °C for 72 h, and can be used as a raw material for preparing the cathode material of a sodium-ion battery.

[0093] Results of this comparative example: the iron leaching rate was 80.65%, the phosphorus leaching rate was 75.36%, the comprehensive iron recovery rate was 86.66%, the number of cycles of the phosphoric acid solution was 5 times, and the purity of orthophosphate was 40.66%.

[0094] Oxalic acid, as a medium-strong organic acid, has pKa values of approximately 1.23 (first dissociation) and 4.19 (second dissociation). Under the condition of pH = 0.5, its degree of dissociation is higher than that of citric acid but lower than that of sulfuric acid. Therefore, although the leaching ability of oxalic acid is better than that of citric acid, it is still significantly lower than that of sulfuric acid. As a strong acid, sulfuric acid is completely dissociated at pH = 0.5 and can efficiently dissolve iron (Fe 3+ ) and phosphorus (PO 4 3- ) in high-phosphorus iron ore, thereby achieving a high leaching rate. In contrast, although oxalic acid has a higher degree of dissociation under the same pH condition, its leaching ability is still limited by its acid strength, resulting in a lower leaching efficiency than sulfuric acid. In addition, oxalic acid can form stable complexes with iron ions (Fe 3+ ), and the existence of these complexes will hinder the subsequent Prussian blue precipitation reaction because Fe 3+ needs to combine with ferrocyanate in the free state. Although the stability of the complexes formed by oxalic acid is lower than that of citric acid, it will still significantly reduce the iron recovery rate. In the sulfuric acid system, iron ions mainly exist in the free state and can react more completely with ferrocyanate to form Prussian blue. Oxalic acid is relatively stable at a high temperature of 120 °C, but partial decomposition may occur, generating carbon dioxide (CO 2 ) and water. This decomposition will reduce its leaching efficiency, but the degree of decomposition is usually less than that of citric acid. Sulfuric acid is very stable at high temperatures and can continuously provide H + , promoting the dissolution of minerals. During multiple cycles, oxalic acid may gradually decompose, resulting in a decrease in leaching efficiency. Although its stability is higher than that of citric acid, it is still not as good as sulfuric acid. Sulfuric acid maintains a high stability during multiple cycles and can continuously and effectively leach iron and phosphorus. These factors together lead to the fact that in Comparative Example 2, the iron leaching rate (80.65%) is much lower than that in Example 3 (98.15%), the phosphorus leaching rate (75.36%) is also lower than that in Example 3 (91.03%), the comprehensive iron recovery rate (86.66%) is lower than that in Example 3 (99.45%), the number of cycles of the phosphoric acid solution (5 times) is less than that in Example 3 (15 times), and the purity of orthophosphate (40.66%) is lower than that in Example 3 (54.66%).

[0095] Summarize the test results of Examples 1 - 3 and Comparative Examples 1 - 2, as shown in Table 1.

[0096] Table 1 Test results of Examples 1 - 3 and Comparative Examples 1 - 2

[0097] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Iron leaching rate 91.25％ 95.25％ 98.15％ 75.56％ 80.65％ Phosphorus leaching rate 89.53％ 90.69％ 91.03％ 69.33％ 75.36％ Overall iron recovery rate 98.23％ 98.89％ 99.45％ 77.78％ 86.66％ Circulation times of phosphoric acid solution 5 8 15 3 5 High / orthophosphate purity 52.23％ 62.33％ 54.66％ 33.11％ 40.66％

[0098] The dried Prussian blue of Examples 1-3 and Comparative Examples 1-2 was tested by inductively coupled plasma (ICP) to detect the proportion of sodium contained therein, and after being pressed into a film and assembled into a sodium-ion battery, a constant current charge-discharge test was carried out on a test bench. The results of its sodium content, initial discharge specific capacity, and capacity retention rate (the capacity retention rate is the data of cycling 50, 100, and 200 cycles under the condition of 1C) are shown in Table 2.

[0099] Table 2 Test results of sodium-ion capacity and cycling performance of Examples 1-3 and Comparative Examples 1-2

[0100]

[0101] As can be seen from Table 2, the sodium-ion battery prepared from the Prussian blue dried by the embodiment of the present invention has an initial discharge specific capacity of not less than 145 mAh / g, and after cycling and discharging 200 cycles under the condition of 1C, it can still be greater than 91%, having excellent electrochemical performance.

[0102] As can be seen from Table 1 and Table 2, the method of the present invention has the remarkable characteristics of high comprehensive iron recovery rate, high-value recovery and utilization of iron, and green and environmental protection of the process.

[0103] It can be seen from the above content that:

[0104] 1. The present invention uses inorganic acid as a leaching agent to be mixed with high-phosphorus iron ore powder for acid leaching, so that iron and phosphorus are fully dissolved in the leaching solution. After liquid-solid separation, other impurity elements are removed, and ferrocyanate is added to the leaching solution to precipitate and separate iron in the form of Prussian blue, with remarkable dephosphorization and iron extraction effects and a significant increase in the recovery rate of iron. At the same time, after the iron-removed solution is enriched, phosphoric acid can be converted into a cathode material for sodium-ion batteries or agricultural fertilizers, thus realizing the recycling of phosphorus resources, significantly improving the efficiency, and opening up a new path for the sustainable utilization of high-value resources.

[0105] 2. The Prussian blue obtained by the present invention can be used as a raw material for the cathode material of sodium-ion batteries, and the prepared cathode material for sodium-ion batteries has excellent electrochemical performance. This innovative application not only expands the application field of iron ore resources but also provides new material choices for the development of the new energy industry. As an emerging energy storage technology, sodium-ion batteries have the advantages of low cost, high safety, and environmental friendliness, and have broad application prospects in the fields of large-scale energy storage, smart grid, electric vehicles, etc. By combining iron ore resources with the new energy industry, the present invention significantly improves the added value of products, creates more economic benefits and market opportunities for enterprises, and promotes the integrated development of related industries.

[0106] 3. Technical indicators obtained by using the method of the present invention: the comprehensive iron recovery rate is greater than 98%, the leaching rate of phosphorus element is greater than 89%, and the purity of phosphate is greater than 50%, all of which meet the industry standards. After vacuum drying and dehydration of the obtained Prussian blue precipitate, it is pressed into a film and assembled into a sodium-ion battery sheet. After performance testing, the initial discharge specific capacity is not less than 145 mAh / g. Under the condition of 1C, it can still be greater than 90% after 200 cycles of cyclic discharge, showing excellent electrochemical performance.

[0107] The above is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for high-value utilization of iron in high-phosphorus iron ore, characterized in that: The following steps are involved: The high-phosphorus iron ore is mixed with an inorganic acid to carry out a leaching reaction, and after the reaction is completed, a leaching residue and a filtrate are obtained by liquid-solid separation; ferrocyanide is added to the filtrate to carry out a precipitation reaction, and after liquid-solid separation, a Prussian blue precipitate and a phosphorus-containing filtrate are obtained; an alkali solution is added to the phosphorus-containing filtrate to carry out a neutralization reaction, and after the reaction is completed, a liquid-solid separation is carried out to obtain a precipitate and water, and the precipitate is used as a raw material for fertilizer or a positive electrode material of a sodium ion battery; the Prussian blue precipitate is washed and dried to be used as a raw material for a positive electrode material of a sodium ion battery.

2. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The phosphorus content in the high-phosphorus iron ore is 0.5-2wt.%; And / or, before the high-phosphorus iron ore is mixed with the inorganic acid, the high-phosphorus iron ore is pulverized to 100-500 meshes.

3. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The inorganic acid is hydrochloric acid, sulfuric acid or nitric acid.

4. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The concentration of the inorganic acid is 2 to 8 mol / L; And / or, the liquid-to-solid ratio of the inorganic acid to the high-phosphorus iron ore is (2-7) L: 1 g.

5. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The conditions of the leaching reaction are: reaction temperature of 70-120° C., pH of 0.5-2, and reaction time of 1-5 hours.

6. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The conditions of the precipitation reaction are: pH 0.1-1.5, reaction temperature 25-120° C., and reaction time 0.5-1.5 h.

7. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The alkali solution is sodium hydroxide solution, potassium hydroxide solution or calcium hydroxide solution.

8. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The mass ratio of the alkali solution to the phosphorus-containing filtrate is (1-3):

1.

9. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The reaction temperature of the neutralization reaction is 25° C. to 100° C., and the reaction time is 0.5 to 1 h.

10. The method for high-value utilization of iron in high-phosphorus iron ore according to claim 1, characterized in that: The drying temperature is 40-100° C. and the drying time is 24-72 hours.

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