Method and system for separating and recovering phosphorus and iron in phosphorus-containing iron compound

Abstract

The invention discloses a method and a system for separating and recovering phosphorus and iron in a phosphorus-containing iron compound, and relates to the technical field of solid waste utilization. The method comprises the following steps: obtaining a crushed phosphorus-containing iron compound and a solid alkaline substance; the crushed ferrophosphorus-containing compound and the crushed solid alkaline substance are taken and placed in a reaction furnace, the ferrophosphorus-containing compound and the solid alkaline substance are fused and react to obtain a first mixed material, and the dosage of the solid alkaline substance is 1-1.2 times of the theoretical molar dosage; adding water into the first mixed material for leaching to obtain a first solid-liquid mixture, and performing solid-liquid separation on the first solid-liquid mixture to obtain a first filter cake and first filtrate; washing and drying the first filter cake to obtain a ferric oxide product; evaporating, concentrating, crystallizing and drying the first filtrate to obtain a phosphate finished product. The method provided by the invention has the advantages of environmental protection and high product quality.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste utilization, and particularly to a method and system for separating and recovering phosphorus and iron from phosphorus-containing iron compounds. Background Art

[0002] Lithium iron phosphate batteries (LiFePO4) are widely used in mobile electronic devices, new energy vehicles, and energy storage base stations due to their excellent electrochemical performance and high safety. To meet the high performance of the batteries, high purity of the raw materials for preparing lithium iron phosphate is required, usually reaching over 99%. The service life of power batteries for new energy vehicles is usually only 3 - 5 years, and there will surely be an explosive wave of scrapped lithium iron phosphate batteries in the future.

[0003] Before 2021, due to the high price of lithium, the recycling of lithium iron phosphate batteries mainly focused on the recovery rate of lithium, and rarely paid attention to the recovery quality of iron and phosphorus. For the recovered iron and phosphorus, they were usually used at a lower level, such as using phosphorus in the fields of chemical fertilizers, etc., with relatively low economic value. Traditional processes usually adopted wet methods to recycle lithium iron phosphate cathode materials. In this way, multiple processes such as acid leaching, solid-liquid separation, washing, and drying were required to separately recover phosphorus, iron, and lithium in lithium iron phosphate. After years of development, the lithium recovery process has been relatively mature.

[0004] However, by using wet methods to recycle lithium iron phosphate cathode materials, not only is the process route cumbersome, but also a large amount of acidic wastewater and solid waste are generated. The environmental protection problems and product quality problems during the recovery of lithium iron phosphate cathode materials have always been the pain points of the industry. Therefore, in recent years, for the recovery process of lithium iron phosphate cathode materials, more attention has been paid to the environmental protection problems and product quality during the recovery process.

[0005] Not limited to the battery material field, for phosphorus-containing iron materials such as phosphorus iron ore and iron phosphate generated during industrial production, there is a need to separate phosphorus and iron in the materials. In related technologies, wet processes are usually also used to separate and recover phosphorus and iron, and there are also environmental protection problems and product quality problems.

[0006] Therefore, providing a clean and high-quality recovery process for phosphorus and iron in phosphorus-containing iron compounds has become an urgent technical problem to be solved by those skilled in the art. Summary of the Invention

[0007] The present invention discloses a method and system for separating and recovering phosphorus and iron from phosphorus-containing iron compounds to solve the technical problems of generating a large amount of acidic wastewater and solid waste, and low product quality when using wet processes to recover phosphorus and iron in phosphorus-containing iron compounds in related technologies.

[0008] To solve the above problems, the present invention adopts the following technical solutions: The first aspect of the present invention discloses a method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds.

[0009] The method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds according to the present invention comprises the following steps: Obtain the crushed phosphorus-containing iron compound and solid alkaline substance; Put the crushed phosphorus-containing iron compound and the crushed solid alkaline substance into a reaction furnace, and the phosphorus-containing iron compound and the solid alkaline substance are melted and reacted to obtain a first mixed material, wherein the dosage of the solid alkaline substance is 1 to 1.2 times the theoretical molar dosage; Leach the first mixed material with water, and after leaching, obtain a first solid-liquid mixture. After solid-liquid separation of the first solid-liquid mixture, obtain a first filter cake and a first filtrate; Wash and dry the first filter cake to obtain a ferric oxide product; Evaporate, concentrate, crystallize and dry the first filtrate to obtain a finished phosphate product.

[0010] The second aspect of the present invention discloses a system for separating and recovering phosphorus and iron from phosphorus-containing iron compounds.

[0011] The system for separating and recovering phosphorus and iron from phosphorus-containing iron compounds according to the present invention is used for the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds described in any one of the technical solutions of the present invention, and the system comprises: A crushing device, which is used for crushing the phosphorus-containing iron compound and the solid alkaline substance; A reaction furnace, which is used for heating the crushed phosphorus-containing iron compound and the crushed solid alkaline substance, and melting and reacting the phosphorus-containing iron compound and the solid alkaline substance to obtain a first mixed material; A leaching device, which is used for leaching the first mixed material and obtaining a first solid-liquid mixture; A solid-liquid separation device, which is used for solid-liquid separation of the first solid-liquid mixture to obtain a first filter cake and a first filtrate; A drying device, which is used for drying the washed first filter cake and obtaining a ferric oxide product; A crystallization device, which is used for evaporating, concentrating, crystallizing and drying the first filtrate to obtain a finished phosphate product.

[0012] The technical solution adopted by the present invention can achieve the following beneficial effects: First aspect, the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in the present invention involves mixing the phosphorus-containing iron compounds with solid alkaline substances. The two are melted and reacted in a reaction furnace to form Na3PO4 and Fe2O3. Then, through the method of water leaching, Na3PO4 can be leached into the aqueous solution, while Fe2O3 is insoluble in water and remains in solid form. Through solid-liquid separation and subsequent steps such as washing and drying, Na3PO4 products and Fe2O3 products can be obtained respectively. It can be seen that in the recovery method of this application, the washing water and distillation mother liquor in the wet process stage can be reused for the water leaching step, and almost no wastewater and solid waste are generated in the remaining steps. That is: through the recovery process of pyrometallurgy combined with hydrometallurgy, compared with the pure pyrometallurgical process, the present invention can reduce energy consumption. Compared with the pure hydrometallurgical process, the solution of this application can greatly simplify the process flow and reduce the generation of wastewater and solid waste, and can solve the environmental protection problems in the recovery process of lithium iron phosphate cathode materials.

[0013] Second aspect, in the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in the present invention, when the phosphorus-containing iron compounds are mixed with solid alkaline substances, the dosage of the solid alkaline substance is 1 to 1.2 times the theoretical molar dosage, preferably the theoretical dosage. Compared with the prior art, the present application greatly reduces the dosage of the solid alkaline substance. When the phosphorus-containing iron compounds react with the solid alkaline substance, it can avoid the reaction of excessive solid alkaline substance with Fe2O3 to form sodium ferrate (NaFeO2), which is beneficial to improving the quality of Na3PO4 and Fe2O3.

[0014] Third aspect, in the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in the present invention, before the reaction, both the raw material phosphorus-containing iron compounds and the solid alkaline substances are crushed, which can enable the phosphorus-containing iron compounds and the solid alkaline substances to be fully mixed at high temperature, avoiding the formation of sodium ferrate (NaFeO2) due to excessive local solid alkaline substances, and thus is also beneficial to improving the quality of Na3PO4 and Fe2O3; before the reaction, both the raw material phosphorus-containing iron compounds and the solid alkaline substances are crushed, and the contact surface between the phosphorus-containing iron compounds and the solid alkaline substances is larger, which is beneficial to the full reaction of the phosphorus-containing iron compounds and the solid alkaline substances, so that even with a smaller dosage of the solid alkaline substance in this application, it can still ensure a high recovery rate of phosphorus and iron.

[0015] It can be seen that the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in the present invention also avoids the formation of sodium ferrate during the reaction process by controlling the dosage of the solid alkaline substance and the mixing uniformity of the phosphorus-containing iron compounds and the solid alkaline substances, which is beneficial to improving the quality of Na3PO4 and Fe2O3, and can solve the problem of product quality in the recovery process of lithium iron phosphate cathode materials. Description of the Drawings

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0017] Figure 1 is the process flow diagram of the method for separating and recovering phosphorus and iron in the phosphorus-containing iron compound in the embodiment of the present application; Figure 2 is the XRD pattern of the iron oxide obtained in Embodiment 1 of the present application; Figure 3 is the structural schematic diagram of the flash furnace in the embodiment of the present application; Figure 4 is the cross-sectional view of the flash furnace in the first embodiment of the present application; Figure 5 is the cross-sectional view of the flash furnace in the second embodiment of the present application.

[0018] In the figure: 100, furnace body; 110, main body; 120, cover body; 121, feed inlet; 122, exhaust gas pipeline; 200, crucible; 300, isolation protection layer; 300a, reaction chamber; 400, heat transfer transition layer; 500, induction coil; 600, spraying channel; 700, air supply channel; 800, air gap; 900, filter screen. Detailed Embodiments

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will describe the technical solutions of the present invention in detail. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0020] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, rather than to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of the same type, and the number of objects is not limited. For example, the first object can be one or multiple. In addition, "and / or" in the specification and claims means at least one of the connected objects, and the character " / " generally indicates an "or" relationship between the associated objects before and after.

[0021] The following will be combined with the attached Figures 1 to 5, the method and system for separating and recovering phosphorus and iron from phosphorus-containing iron compounds provided by the present application are described in detail through specific embodiments and their application scenarios.

[0022] Figure 1 The process flow diagram of the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in the embodiments of the present application is shown. As Figure 1 shown, the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in the present application includes the following steps: Step 100: Obtain the crushed phosphorus-containing iron compound and solid alkaline substance.

[0023] Exemplarily, the crushing of the phosphorus-containing iron compound and the solid alkaline substance can be directly crushing before use, or directly purchasing the already crushed phosphorus-containing iron compound and solid alkaline substance.

[0024] Exemplarily, the phosphorus-containing iron compound refers to a compound containing phosphorus element and iron element. The phosphorus-containing iron compound can be the lithium-extracted slag of lithium iron phosphate cathode material, or phosphorite, or phosphorus-containing iron waste residue. The main component of the phosphorus-containing iron compound can be FePO4, or FeP, Fe2P, Fe3P. The present application does not limit the type and specific source of the phosphorus-containing iron compound.

[0025] Exemplarily, for lithium iron phosphate battery waste, carbon and graphite in the waste can be removed by high-temperature calcination before use to avoid the reduction of the obtained iron oxide by carbon and graphite. Exemplarily, the calcination temperature is 500-600 °C.

[0026] Exemplarily, the method for crushing the phosphorus-containing iron compound and the solid alkaline substance can be ball milling or jet milling. Preferably jet milling. Compared with ball milling, the jet milling method can not only crush the phosphorus-containing iron compound and the solid alkaline substance to a smaller particle size, but more importantly, this method can avoid introducing metal impurities, which is of great significance for obtaining high-quality products.

[0027] Step 200: Place the crushed phosphorus-containing iron compound and the crushed solid alkaline substance in a reaction furnace, and the phosphorus-containing iron compound and the solid alkaline substance are melted and reacted to obtain a first mixed material. The dosage of the solid alkaline substance is 1-1.2 times the theoretical molar dosage. Preferably, the dosage of the solid alkaline substance is the theoretical dosage. Taking the main component of the phosphorus-containing iron compound as FePO4 and the solid alkaline substance as Na2CO3 as an example, the following reaction occurs between FePO4 and Na2CO3 in a high-temperature molten state: 2FePO4 + 3Na2CO3 = 2Na3PO4 + Fe2O3 + 3CO2↑ In theory, when the molar ratio of iron phosphate to sodium carbonate is 1:1.5, the two can react completely, enabling the separation of phosphorus and iron in the phosphorus-containing iron compound. In this application, the molar ratio of iron phosphate to sodium carbonate is 1:1.5 - 1.8.

[0028] Step 300: Add water to leach the first mixed material. After leaching, a first solid-liquid mixture is obtained. After performing solid-liquid separation on the first solid-liquid mixture, a first filter cake and a first filtrate are obtained. The first mixed material obtained by melting and reacting, including phosphate and iron(III) oxide, can be separated by water leaching using the difference in their solubility. Specifically, the phosphate dissolves in water to form an aqueous solution, while iron(III) oxide is insoluble in water and remains in the solid phase; subsequently, the separation of phosphate and iron(III) oxide can be achieved through solid-liquid separation.

[0029] Exemplarily, the method of solid-liquid separation can be common separation methods in existing technologies such as pressure filtration and filtration.

[0030] Exemplarily, before mixing the first mixed material with water, it further includes the step of crushing the first mixed material. For example, crushing the first mixed material to 100 - 500 mesh is beneficial to the leaching of phosphate.

[0031] Step 400: Wash and dry the first filter cake to obtain iron(III) oxide product.

[0032] Step 500: Evaporate, concentrate, crystallize, and dry the first filtrate to obtain phosphate finished product. The mother liquor generated during the crystallization process can also be recycled for use in the leaching process.

[0033] The method for separating and recovering phosphorus and iron in the phosphorus-containing iron compound in this application involves mixing the phosphorus-containing iron compound with a solid alkaline substance, melting and reacting the two in a reaction furnace to generate Na3PO4 and Fe2O3. Then, through water leaching, Na3PO4 can be leached into the aqueous solution, while Fe2O3 is insoluble in water and remains in solid form. Through solid-liquid separation and subsequent washing, drying and other steps, Na3PO4 product and Fe2O3 product can be obtained respectively. It can be seen that in the recovery method of this application, the washing water and distillation mother liquor in the wet stage can be reused for the water leaching step, and almost no wastewater and solid waste are generated in the other steps.

[0034] That is: Through the recovery process of combining pyrometallurgy and hydrometallurgy in this application, compared with a pure pyrometallurgical process, the energy consumption can be reduced. Compared with a pure hydrometallurgical process, the process flow of this application can be greatly simplified, and the generation of wastewater and solid waste can be reduced, which can solve the environmental protection problems in the recovery process of lithium iron phosphate cathode materials.

[0035] In the research, the inventor found that when a phosphorus-containing iron compound and a sodium salt are mixed and melted in the related art, in order to make the separation of phosphorus and iron in the phosphorus-containing iron compound more complete and improve the recovery rates of phosphorus and iron, generally, the addition amount of the sodium salt is relatively large, specifically 2 to 10 times that of the material to be treated. Such a large addition amount of the sodium salt not only increases the recovery cost, but more importantly, when the phosphorus-containing iron compound and the sodium salt are mixed and melted, Na3PO4 and Fe2O3 are generated, and the excessive sodium salt decomposes at high temperature to generate sodium oxide (Na2O). As a strong basic oxide, Na2O further reacts with Fe2O3 to generate sodium ferrate. The specific reaction formula is as follows: Na2CO3 = Na2O + 3CO2↑ Fe2O3 + Na2O = 2NaFeO2 In addition, the inventor also found that the excessive Na2CO3 reduces the melting point of the reaction system and promotes the combination of Fe2O3 and Na2O; in addition, sodium ferrate is more stable in a strong basic environment and a high sodium salt concentration, resulting in the reaction proceeding in the direction of generating sodium ferrate. The excessive sodium salt provides sufficient Na2O and basic conditions, further promoting the conversion of Fe2O3 into NaFeO2.

[0036] Furthermore, due to the presence of NaFeO2, the purity of both the product phosphate and iron trioxide will be affected. The specific analysis is as follows: due to the presence of sodium ferrate, in the subsequent hydrolysis process, although sodium ferrate can be hydrolyzed to generate iron hydroxide, and iron hydroxide can finally be dehydrated to obtain iron oxide. However, in this process, it is impossible to ensure the complete hydrolysis of sodium ferrate, and some unhydrolyzed sodium ferrate may be mixed in Fe2O3, resulting in a decrease in the purity of Fe2O3; in addition, even if sodium ferrate is completely hydrolyzed, the sodium salt generated during the hydrolysis process will be adsorbed on the surface of Fe(OH)3 in the form of Na + . After Fe(OH)3 is dehydrated, a small amount of sodium salt may still remain, resulting in an increase in the sodium content in Fe2O3 and a decrease in its purity. On the other hand, the sodium salt generated by the hydrolysis of sodium ferrate dissolves in the leaching solution, resulting in an increase in the sodium ion concentration in the leaching solution, which affects the purity of the phosphate after crystallization; under strong basic adjustment, Fe(OH)3 may also react with PO4 3﹣ to form a small amount of soluble Fe-PO4 complex, resulting in the presence of iron impurities in the phosphate product and affecting the purity of the phosphate product.

[0037] Exemplarily, if iron trioxide contains sodium ferrate impurities, when used in the field of lithium-ion batteries, due to the differences in the properties between sodium ferrate and iron trioxide, it will lead to a decrease in the capacity of the lithium-ion battery, a decline in the transmission performance, and structural instability.

[0038] The method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in this application. When the phosphorus-containing iron compound is mixed with the solid basic substance, the dosage of the solid basic substance is 1 to 1.2 times the theoretical molar dosage, preferably the theoretical dosage. Compared with the prior art, the dosage of the solid basic substance in this application is greatly reduced. When the phosphorus-containing iron compound reacts with the solid basic substance, the hidden danger of the excessive solid basic substance reacting with Fe2O3 to form sodium ferrate (NaFeO2) can be reduced, which is beneficial to improving the quality of Na3PO4 and Fe2O3.

[0039] On the other hand, for the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in this application, before the reaction, both the raw material phosphorus-containing iron compound and the solid basic substance are crushed, which can make the phosphorus-containing iron compound and the solid basic substance be fully mixed at high temperature, avoiding the formation of sodium ferrate (NaFeO2) caused by excessive local solid basic substance, and thus is also beneficial to improving the quality of Na3PO4 and Fe2O3; before the reaction, both the raw material phosphorus-containing iron compound and the solid basic substance are crushed, and the contact surface between the phosphorus-containing iron compound and the solid basic substance is larger, which is beneficial to the full reaction between the phosphorus-containing iron compound and the solid basic substance, so that in this application, even with a smaller dosage of the solid basic substance, a higher recovery rate of phosphorus and iron can still be ensured.

[0040] It can be seen that for the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in this application, the formation of sodium ferrate during the reaction is also avoided by controlling the dosage of the solid basic substance and the mixing uniformity of the phosphorus-containing iron compound and the solid basic substance, which is beneficial to improving the quality of Na3PO4 and Fe2O3, and can solve the problem of the product quality during the recovery process of the lithium iron phosphate cathode material.

[0041] According to an optional embodiment, the crushed phosphorus-containing iron compound has a first particle size, and the crushed solid basic substance has a second particle size. The crushed phosphorus-containing iron compound and the crushed solid basic substance are respectively added into the reaction furnace. Exemplarily, the first particle size is 300 to 500 mesh, and the second particle size is 300 to 500 mesh; or the first particle size is 300 to 500 mesh, and the second particle size is 500 to 800 mesh.

[0042] According to an optional embodiment, the phosphorus-containing iron compound and the solid basic substance are mixed in proportion to obtain a second mixed material, and the crushed second mixed material has a first preset particle size, and the crushed second mixed material is added into the reaction furnace. Exemplarily, the first preset particle size is 300 to 500 mesh.

[0043] According to an optional embodiment, after the phosphorus-containing iron compound is preliminarily crushed, the solid alkaline substance is dissolved in water to form a saturated solution, and the saturated solution is mixed with the crushed phosphorus-containing iron compound in a certain proportion to obtain a third mixed material. The third mixed material is dried and then crushed to a second preset particle size, and the crushed third mixed material is added into a reaction furnace. Exemplarily, the second preset particle size is 300-500 mesh.

[0044] For the method for separating and recovering phosphorus and iron from the phosphorus-containing iron compound in this application, any of the above methods can be used to crush the phosphorus-containing iron compound and the solid alkaline substance. By crushing the phosphorus-containing iron compound and the solid alkaline substance, not only can the phosphorus-containing iron compound and the solid alkaline substance be fully mixed at high temperature, avoiding the formation of sodium ferrite (NaFeO2) due to excessive local solid alkaline substance, but also the contact surface between the phosphorus-containing iron compound and the solid alkaline substance can be made larger, which is beneficial to the full reaction between the phosphorus-containing iron compound and the solid alkaline substance, so that in this application, even with a small amount of solid alkaline substance used, a high recovery rate of phosphorus and iron can still be ensured.

[0045] According to an optional embodiment, the solid alkaline substance is one or more of NaOH, Na2CO3, NaHCO3, Na2SO4, NaHSO4, Na2SO3, NaCl, Na2S, KOH, K2CO3, KHCO3, K2SO4, KHSO4, K2SO3, KCl, CaO, Ca(OH)2, (NH4)2SO4. Without limitation, it can also be other solid alkaline substances.

[0046] Preferably, the solid alkaline substance at least includes at least one of the alkaline substances that can decompose to produce acidic gases at high temperature. More preferably, the solid alkaline substance is two or more, and one of them is an alkaline substance that can decompose to produce acidic gases at high temperature. Exemplarily, the high temperature refers to the temperature when the phosphorus-containing iron compound reacts with the solid alkaline substance, such as 550 °C. Alkaline substances that can decompose to produce acidic gases at high temperature include Na2CO3, K2CO3, NaHCO3, KHCO3, etc. Exemplarily, the solid alkaline substance is a combination of NaOH and Na2CO3, or the solid alkaline substance is a combination of NaOH, Na2CO3 and NaHCO3, or the solid alkaline substance is a combination of Na2CO3 and NaHCO3, or the solid alkaline substance is a combination of KOH and K2CO3, or the solid alkaline substance is a combination of KOH, K2CO3 and KHCO3.

[0047] The method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in the present application selects at least two combinations of solid basic substances, which can reduce the melting point of the solid basic substances. The formation of liquid molten salts can significantly accelerate the diffusion rate of phosphorus-containing iron compounds and solid basic substances, promote the ion exchange and the mass transfer efficiency of solid-phase reactions, thereby reducing the reaction temperature or shortening the reaction time. In addition, the form of combining two salts can achieve the stepwise release of sodium ions and avoid the formation of NaFeO2 due to excessive local Na + concentration.

[0048] The method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in the present application includes at least one of the basic substances that can decompose at high temperatures to produce acidic gases, which is beneficial to inhibiting the formation of NaFeO2 and improving the product purity of phosphates and iron(III) oxide. Specifically, taking Na2CO3 as the solid basic substance as an example, the formation of NaFeO2 requires sufficiently active Na + to combine with Fe 3+ in an alkaline environment. Na2CO3 decomposes at high temperatures to produce Na2O and CO2, and the released CO2 can further react with the excessive Na2O. The CO2 consumes free Na + , thereby inhibiting the formation of NaFeO2; in addition, as a weak acidic gas, CO2 can partially reduce the alkalinity of the system and avoid the formation of Fe 3+ FeO2 ﹣ . Therefore, by selecting basic substances that can produce acidic gases in the present application, the formation of NaFeO2 can be inhibited from two aspects: reducing the Na + concentration and the alkalinity of the system.

[0049] According to an optional embodiment, the crushed phosphorus-containing iron compound and the crushed solid basic substance are placed in a muffle furnace or a rotary kiln for roasting. The roasting temperature is 550-1000 °C, and the roasting time is 2-6 h. Exemplarily, an appropriate amount of oxygen can be introduced into the muffle furnace or the rotary kiln during the roasting process to ensure that the iron salt can be completely converted into Fe2O3; not limited to this, an appropriate amount of inert gas can also be introduced into the muffle furnace or the rotary kiln so that the iron salt can form Fe3O4.

[0050] According to an optional embodiment, the crushed phosphorus-containing iron compound and the crushed solid basic substance are respectively sprayed into a flash furnace by a spraying method. The temperature in the flash furnace is 550-1000 °C, and the material reaction time is 10 s-20 min. Exemplarily, the phosphorus-containing iron compound and the solid basic substance are respectively sprayed into the flash furnace by a nozzle, and the particle sizes of the sprayed phosphorus-containing iron compound and the solid basic substance are both larger than 300 mesh.

[0051] According to an optional embodiment, the mixed material of the crushed phosphorus-containing iron compound and the solid alkaline substance is injected into the flash furnace by means of spraying. The temperature in the flash furnace is 550-1000°C, and the material reaction time is 10 s-20 min. Exemplarily, the mixed material of the phosphorus-containing iron compound and the solid alkaline substance is injected into the flash furnace by means of a nozzle, and the particle size of the ejected material is larger than 300 mesh.

[0052] Exemplarily, the spraying pressure is 0.6-0.7 MPa, and the nozzle aperture can be determined based on the size of the ejected particle size. Exemplarily, oxygen, air or inert gas can be used as the carrier gas to inject the material into the flash furnace.

[0053] Exemplarily, the heating method of the flash furnace is one or more of induction heating, microwave heating, fuel combustion heating, arc heating, plasma heating, and roasting heating.

[0054] Furthermore, the inventors also found in the research that in the phosphorus-containing iron compound, it is difficult to completely release the encapsulated phosphorus or phosphate radical by heating and melting. Generally, melting can reduce the encapsulation rate of phosphorus or phosphate radical from 30%-50% to about 5% (part of the phosphorus or phosphate radical is encapsulated in the unmolten particles with a higher melting temperature). Since part of the encapsulated phosphorus or phosphate radical is always difficult to release, there is a bottleneck in the phosphorus yield.

[0055] In the method for separating and recovering phosphorus and iron in the phosphorus-containing iron compound of the present application, the phosphorus-containing iron compound or the phosphorus-containing iron compound mixed with the solid alkaline substance is injected into the flash furnace by means of spraying. On the one hand, spraying can disperse the melt into fine droplets or particles, increase the specific surface area, make the encapsulated phosphorus or phosphate radical more easily exposed on the surface, and improve the reaction rate and the phosphorus yield; on the other hand, the shear force caused by high-speed spraying can break the phase boundary inside the phosphorus-containing iron compound, which is beneficial to the release of the encapsulated phosphorus or phosphate radical, thereby further improving the reaction rate and the phosphorus yield. Furthermore, in the present application, the phosphorus-containing iron compound is injected into the flash furnace by means of spraying, and the fluidity of spraying can also prevent the problem that when the melt is in a static state, phosphorus or phosphate radical is re-coated in the iron oxide to form a eutectic, thereby ensuring the phosphorus yield.

[0056] Furthermore, in the method for separating and recovering phosphorus and iron in the phosphorus-containing iron compound of the present application, the phosphorus-containing iron compound or the phosphorus-containing iron compound mixed with the solid alkaline substance is injected into the flash furnace by means of spraying, which can greatly increase the contact area between the phosphorus-containing iron compound and the solid alkaline substance, enable the raw materials to quickly melt and react, so that the recovery of phosphorus and iron can be realized by means of flashing, greatly reducing the reaction time, which is beneficial to reducing energy consumption.

[0057] In the related art, although a solution of spraying an alkaline substance onto the surface of the substance to be separated is provided, however, the spraying in the prior art cannot make the encapsulated phosphorus or phosphate radical more easily exposed on the surface, so as to achieve the purpose of improving the phosphorus recovery rate; in addition, in the present application, the phosphorus-containing iron compound or the solid alkaline substance enters the flash furnace by spraying at the same time, and an instantaneous contact field can be formed, which not only breaks through the diffusion limitation of the traditional solid-solid reaction, but also significantly increases the thermal shock rate.

[0058] According to an optional embodiment, when the phosphorus-containing iron compound and the solid alkaline substance are respectively sprayed into the flash furnace by spraying, the material is sprayed downward from the upper part of the flash furnace, and an included angle of 30° to 60° is formed between the discharging direction of the nozzle and the inner wall of the flash furnace. Alternatively, when the mixed material of the phosphorus-containing iron compound and the solid alkaline substance is sprayed into the flash furnace by using a nozzle, the material is sprayed downward from the upper part of the flash furnace, and an included angle of 30° to 60° is formed between the discharging direction of the nozzle and the inner wall of the flash furnace. Preferably, while spraying, air or inert gas is introduced upward from the bottom of the flash furnace.

[0059] In the method for separating and recovering phosphorus and iron in the phosphorus-containing iron compound of the present application, the material is sprayed into the flash furnace in an inclined downward manner, so that the material and the rising gas can form a spiral movement track, triggering forced turbulence, which can not only increase the falling path of the phosphorus-containing iron compound and the alkaline substance, extend the falling time of the two, so that the two can have sufficient reaction time; but also improve the uniformity of mixing of the phosphorus-containing iron compound and the alkaline substance, so that the phosphorus-containing iron compound and the alkaline substance can react fully, further ensuring that the phosphorus recovery rate can still be ensured while reducing the dosage of the alkaline substance. On the other hand, when the material is sprayed into the flash furnace in an inclined downward manner, the rising gas can generate a shearing force on the falling material, prompting the material to split into smaller particle sizes, which can further improve the recovery rates of phosphorus and iron.

[0060] According to an optional embodiment, when the first mixed material is leached with water, the leaching temperature is 40 to 80 °C, the leaching time is 30 to 180 min, and the leaching solid-liquid ratio is 100 to 200 g / L. Preferably, the pH during the leaching process is maintained at 8 to 9. Exemplarily, a commonly used existing pH regulator can be added to adjust the pH during the leaching process. The pH regulator is, for example, carbonic acid, phosphoric acid, etc.

[0061] In the method for separating and recovering phosphorus and iron in the phosphorus-containing iron compound of the present application, under heating conditions, it is beneficial to accelerate the dissolution of phosphate to effectively separate phosphate and iron trioxide. On the other hand, controlling the pH during the leaching process to be 8 to 9, at this pH, Fe(OH)3 precipitation can be promoted, which is beneficial to the complete hydrolysis of sodium ferrate, and then the reaction by-products can be converted into the target product iron trioxide, improving the recovery rate of iron trioxide; at the same time, it can also avoid incomplete hydrolysis of sodium ferrate, resulting in the purity of iron trioxide being affected.

[0062] According to an optional embodiment, water is added to wash the first filter cake obtained by solid-liquid separation 1 to 3 times, and the washing water is used to leaching the first mixed material. By washing the first filter cake with water, Na attached to the surface of ferric oxide can be effectively removed. + Impurities such as iron oxide can be removed, which is beneficial to improve the purity of ferric oxide.

[0063] According to an optional embodiment, carbon dioxide gas is blown into the first filtrate until the pH of the solution is 6-8 to obtain a second solid-liquid mixture, the second solid-liquid mixture is subjected to solid-liquid separation to obtain a second filter cake and a second filtrate, and the second filtrate is evaporated, concentrated, crystallized and dried to obtain a finished phosphate product.

[0064] As for phosphite, its composition is complex, and the obtained ferric oxide and phosphate impurities contain more. The present application discloses a method for separating and recovering phosphorus and iron in phosphorus-containing iron compounds. Carbon dioxide gas is blown into the first filtrate until the pH of the solution is 6-8. The pH value of the first filtrate is reduced, which can precipitate impurities such as aluminum and manganese in the first filtrate, and can greatly reduce the content of impurity aluminum in the obtained phosphate. Therefore, the phosphate can be directly used in the battery field without the need for impurity removal steps, which greatly improves the utilization value of phosphite slag. Specifically, the aluminum in the phosphate product is less than 10ppm, the manganese is less than 10ppm, and there is almost no silicon.

[0065] The system for separating and recovering phosphorus and iron in phosphorus-containing iron compounds of the present application is used for the method for separating and recovering phosphorus and iron in phosphorus-containing iron compounds of any technical solution in the present application.

[0066] The system for separating and recovering phosphorus and iron in phosphorus-containing iron compounds in the present application comprises: A crushing device is used to crush the phosphorus-containing iron compound and the solid alkaline substance. Exemplarily, the crushing device is a vertical jet mill or a jet pulverizer.

[0067] A reaction furnace, the reaction furnace is used to heat the crushed phosphorus-containing iron compound and the crushed solid alkaline substance, and melt the phosphorus-containing iron compound and the solid alkaline substance and react to obtain a first mixed material. Exemplarily, the reaction furnace is a muffle furnace or a rotary kiln. The structure of the muffle furnace or the rotary kiln is the same as that of the prior art, and will not be repeated here. Exemplarily, the reaction furnace is a flash furnace. The specific structure of the flash furnace is described in detail later.

[0068] The leaching device is used to leach the first mixed material and obtain the first solid-liquid mixture. Exemplarily, the leaching device is a leaching tank or a leaching tank.

[0069] A solid-liquid separation device is used to perform solid-liquid separation on a first solid-liquid mixture to obtain a first filter cake and a first filtrate. Exemplarily, the solid-liquid separation device is a filter, a plate-and-frame filter press, a screw extrusion type solid-liquid separator, etc.

[0070] A drying device is used to dry the washed first filter cake and obtain an iron oxide product. Exemplarily, the drying device is a dryer.

[0071] A crystallization device is used to evaporate, concentrate, crystallize, and dry the first filtrate to obtain a phosphate finished product. Exemplarily, the crystallization device is an evaporation crystallizer, etc.

[0072] The system for separating and recovering phosphorus and iron from a phosphorus-containing iron compound in the present application, through the above structure, can implement the method for separating and recovering phosphorus and iron from a phosphorus-containing iron compound in any one of the technical solutions in the present application, making the process of the present application have the advantages of environmental protection and high product quality.

[0073] According to an optional embodiment, the flash furnace includes a furnace body 100, a crucible 200, and an isolation protective layer 300, as Figure 3 and Figure 4 shown. Both the crucible 200 and the isolation protective layer 300 are arranged inside the furnace body 100, and the isolation protective layer 300 is arranged inside the crucible 200. A reaction chamber 300a is constructed inside the isolation protective layer 300, and the reaction chamber 300a is used to provide a reaction space for the phosphorus-containing iron compound and the solid alkaline substance, as Figure 4 shown. When the iron compound and the solid alkaline substance react inside the reaction chamber 300a, the crucible 200 can be separated from the reactants and products through the isolation protective layer 300.

[0074] Exemplarily, the furnace body 100, as a basic component of the reaction furnace, provides an installation space for the crucible 200, the isolation protective layer 300, etc., and also plays a protective role. The furnace body 100 is usually made of high-temperature resistant stainless steel.

[0075] Preferably, the isolation protective layer 300 is made of at least one of corundum, ceramic material, and quartz glass, and the crucible 200 is a graphite crucible or a silicon carbide crucible. Exemplarily, the ceramic material can be selected such as magnesium oxide (MgO), calcium oxide (CaO), beryllium oxide (BeO), etc. Exemplarily, the isolation protective layer 300 can also be made of at least a partial combination of corundum, quartz glass, ceramic material, etc. For example, corundum can be combined with other components (such as composite refractory materials) to make the isolation protective layer 300.

[0076] In the research, the inventor found that the product of the fusion of phosphorus-containing iron compound and sodium carbonate is sodium phosphate and iron oxide. At high temperature, there is a risk that the generated iron oxide is reduced by graphite carbon, which not only causes corrosion and damage to the graphite crucible, but also affects the purity of iron oxide.

[0077] In the flash furnace according to the embodiment of the present application, an isolation protective layer 300 is arranged in the crucible 200, and the isolation protective layer 300 is made of high-temperature resistant and stable materials such as corundum, ceramic materials and quartz glass. In this way, the reaction product can be separated from the graphite crucible, avoiding the risk of the product being reduced by graphite carbon, thereby avoiding the corrosion and damage of the graphite crucible and ensuring the purity of iron oxide.

[0078] According to an optional embodiment, the flash furnace further includes a heat transfer transition layer 400, and the heat transfer transition layer 400 is arranged between the crucible 200 and the isolation protective layer 300, as Figure 4 shown. The heat transfer transition layer 400 is closely attached to the crucible 200 and the isolation protective layer 300. Exemplarily, when the isolation protective layer 300 is a corundum layer and the crucible 200 is a graphite crucible, the heat transfer transition layer 400 is a mixed layer of graphite and corundum.

[0079] The crucible 200 is directly heated. During the process, the temperature of the crucible 200 will rise rapidly, and the isolation protective layer 300 obtains heat from the crucible 200 to achieve temperature rise, which will result in a large temperature difference between it and the crucible 200. This will generate a large thermal stress inside the two, easily causing device damage. Considering the material of the crucible 200, such as the graphite crucible 200, the risk of its cracking and damage will be greatly increased.

[0080] In response to this, in the flash furnace according to the embodiment of the present application, by arranging the heat transfer transition layer 400 between the crucible 200 and the isolation protective layer 300, the temperature rise performance of the heat transfer transition layer 400 is between that of the crucible 200 and the isolation protective layer 300. Therefore, during the process, the heat transfer transition layer 400 can obtain heat from the crucible 200 and achieve temperature rise relatively quickly. Its temperature rise efficiency is between that of the crucible 200 and the isolation protective layer 300. Compared with the case where the crucible 200 and the isolation protective layer 300 are in direct contact to form a large temperature difference between them, the temperature difference between the heat transfer transition layer 400 and the crucible 200 and the temperature difference between the heat transfer transition layer 400 and the isolation protective layer 300 in this example will be smaller. Therefore, the thermal stress inside the crucible 200 and the isolation protective layer 300 will be significantly reduced, thereby effectively preventing damage.

[0081] When the isolation protective layer 300 is a corundum layer and the crucible 200 is a graphite crucible 200, the heat transfer transition layer 400 is a mixed layer of graphite and corundum. With such a setting, in addition to achieving the function of buffering thermal stress, the relatively efficient heat conduction can be realized through the graphite in the heat transfer transition layer 400, thereby improving the heating uniformity.

[0082] Preferably, in the heat transfer transition layer 400, in the direction from the isolation protective layer 300 to the crucible 200, the proportion of the corundum component gradually decreases, and the proportion of the graphite component gradually increases. In the flash furnace according to the embodiment of the present application, the component gradient ratio method is adopted in the heat transfer transition layer 400. With such a setting, in the part of the heat transfer transition layer 400 close to the crucible 200 side, the proportion of its graphite component is higher, which is more conducive to heat conduction. The temperature of this part is closer to the temperature of the crucible 200 side, and its temperature tends to change gently, and the thermal stress can be effectively buffered. At the same time, in the part of the heat transfer transition layer 400 close to the isolation protective layer 300 side, the proportion of its corundum component is higher, its temperature is closer to the temperature of the isolation protective layer 300, and its temperature also tends to change gently, and the thermal stress can be effectively buffered. Compared with the method of making the heat transfer transition layer 400 of a homogeneous material, the heat conduction efficiency of this example is higher, and it has better thermal stress buffering performance.

[0083] According to an optional embodiment, the flash furnace further includes an induction coil 500. The induction coil 500 is arranged on the outer periphery of the crucible 200. The induction coil 500 is used to heat the phosphorus-containing iron compound and the solid alkaline substance in the reaction chamber 300a, such as Figure 4 shown. Specifically, the crucible 200 can be inductively heated through the induction coil 500 to realize the rapid heating of the crucible 200, and then the phosphorus-containing iron compound and the solid alkaline substance in the reaction chamber 300a can be radiatively heated through the crucible 200.

[0084] Preferably, there is an air gap 800 between the induction coil 500 and the crucible 200. In the flash furnace according to the embodiment of the present application, the short-circuit problem between the crucible 200 and the induction coil 500 can be prevented through the air gap 800, and it can ensure that the heating function of the two is realized reliably and stably.

[0085] According to an optional embodiment, the flash furnace further includes a spraying channel 600. The spraying channel 600 is located at the top or side of the furnace body 100. A nozzle is provided at the end of the spraying channel 600. An included angle of 30° to 60° is formed between the discharging direction of the nozzle and the inner wall of the isolation protective layer 300. Figure 4 The schematic diagram showing the spraying channel 600 located at the top of the furnace body 100 is shown. Preferably, the number of the spraying channels 600 is one or more.

[0086] Preferably, the flash furnace further includes an air supply channel 700 located at the bottom of the furnace body 100 for introducing gas into the reaction chamber 300a from the bottom, such as Figure 4 shown. The number of the air supply channels 700 is one or more.

[0087] Without limitation, the air supply channel 700 can also be used to supply air into the air gap 800 between the induction coil 500 and the crucible 200.

[0088] Injecting the material into the reaction chamber 300a in an inclined downward manner can make the material and the rising gas form a spiral movement trajectory, triggering forced turbulence, which not only allows sufficient reaction time between the two, but also ensures the phosphorus yield. On the other hand, injecting the material into the flash furnace in an inclined downward manner, the rising gas can generate a shear force on the falling material, prompting the material to split into smaller particle sizes, which can further improve the yields of phosphorus and iron.

[0089] According to an alternative embodiment, the furnace body 100 includes a main body 110 and a cover body 120, and the cover body 120 is movably arranged on the main body 110 so that the furnace body 100 has an open state and a closed state, such as Figure 3 and Figure 4 shown. Exemplarily, a seal, such as a graphite seal ring, can be provided at the joint of the cover body 120 and the main body 110 to achieve airtightness in a high-temperature reaction environment.

[0090] In some embodiments, the material is not limited to being injected into the reaction chamber 300a through the material injection channel 600, and can also be fed through the feed port 121 on the cover body 120, such as Figure 3 and Figure 4 shown.

[0091] In some embodiments, the flash furnace further includes an exhaust gas pipeline 122, such as Figure 3 and Figure 4 shown. A filter screen 900 is provided in the exhaust gas pipeline 122, such as Figure 4 shown. The filter screen 900 can intercept flue gas particles to prevent some reactant raw materials and / or products from escaping with the gas and causing losses, and the components on the filter screen 900 can be recycled subsequently. Among them, the filter screen 900 can be set as multiple layers. Further, the mesh numbers of different layers of the filter screen 900 can be set differently. Preferably, in the outlet direction of the exhaust gas pipeline 122, the mesh numbers of different layers of the filter screen 900 have a gradient from large to small.

[0092] In another embodiment, as Figure 5 shown, the inlet end of the exhaust gas pipeline 122 close to the reaction chamber 300a is open. It should be understood that the open end can increase the contact area between the inlet end of the exhaust gas pipeline 122 and the flue gas, so as to improve the adhesion effect on the component composition and thus improve the recovery effect.

[0093] Example 1 The method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds in this example includes the following steps: Step 100: Using the lithium extraction residue after carbon removal and graphite removal from lithium iron phosphate as the raw material, crush the lithium extraction residue to 300 mesh for use, and crush Na2CO3 to 300 mesh for use.

[0094] Step 200: Take the crushed lithium extraction residue and Na2CO3. The molar ratio of phosphorus in the lithium extraction residue to sodium ions in Na2CO3 is 1:3.2. After mixing the lithium extraction residue and Na2CO3, spray the mixed materials into the reaction chamber in a spraying manner. The particle size of the sprayed materials is 500 mesh, and an angle of 45° is formed between the spraying direction of the materials and the inner wall of the isolation protective layer. At the same time, introduce air into the reaction chamber from the bottom of the reaction chamber.

[0095] Control the temperature in the reaction chamber to 800 °C, and the reaction time of the materials in the reaction chamber is 15 min.

[0096] Step 300: After the reaction is completed, leach the molten slag with water. The solid-liquid ratio of leaching is 100 g / L, and the molten slag is leached at 70 °C for 60 min.

[0097] After the leaching is completed, perform solid-liquid separation to obtain the first filter cake and the first filtrate.

[0098] Step 400: Wash the first filter cake with water 2 times and then dry it to obtain the iron oxide product.

[0099] The washing water can be recycled and mixed with the molten slag to form the leaching solution.

[0100] Step 500: Evaporate, concentrate, crystallize, and dry the first filtrate to obtain the sodium phosphate finished product.

[0101] After testing, the recovery rate of phosphorus in this example is 98.56%, the purity of sodium phosphate is 99.43%, the recovery rate of iron is 99.21%, and the purity of iron oxide is 99.83%.

[0102] Perform XRD testing on the iron oxide product obtained in this example. The obtained spectrum is as Figure 2 shown. Comparing Figure 2 with Three the standard spectrum of iron oxide, it can be seen that there are no obvious impurity peaks in the iron oxide product, the peak shape is sharp, and the noise is low.

[0103] Example 2 The difference between this embodiment and Embodiment 1 is that in step 100, phospho-iron ore is used as the raw material. By performing elemental analysis on the phospho-iron ore, it can be known that the phospho-iron slag contains iron phosphate, calcium phosphate, etc., and also contains impurities such as manganese, silicon, and aluminum. The remaining steps are the same as those in Embodiment 1.

[0104] After testing, the phosphorus recovery rate in this embodiment is 96.29%, the purity of sodium phosphate is 94.52%, the iron recovery rate is 98.64%, and the purity of iron(III) oxide is 88.26%.

[0105] Embodiment 3 The difference between this embodiment and Embodiment 1 is that in step 100, the solid alkaline substance is a mixture of NaOH and Na2CO3, and the molar ratio of NaOH to Na2CO3 is 1:1. The remaining steps are the same as those in Embodiment 1.

[0106] After testing, the phosphorus recovery rate in this embodiment is 98.24%, the purity of sodium phosphate is 99.21%, the iron recovery rate is 99.13%, and the purity of iron(III) oxide is 99.38%.

[0107] Embodiment 4 The difference between this embodiment and Embodiment 1 is that in step 100, the solid alkaline substance is NaOH. The remaining steps are the same as those in Embodiment 1.

[0108] After testing, the phosphorus recovery rate in this embodiment is 98.29%, the purity of sodium phosphate is 99.08%, the iron recovery rate is 99.14%, and the purity of iron(III) oxide is 99.02%.

[0109] Embodiment 5 The difference between this embodiment and Embodiment 1 is that in step 100, the solid alkaline substance is K2CO3. The remaining steps are the same as those in Embodiment 1.

[0110] After testing, the phosphorus recovery rate in this embodiment is 97.97%, the purity of sodium phosphate is 99.45%, the iron recovery rate is 99.07%, and the purity of iron(III) oxide is 99.54%.

[0111] Embodiment 6 The difference between this embodiment and Embodiment 1 is that in step 200, the molar ratio of phosphorus in the lithium-extraction slag to sodium ions in Na2CO3 is 1:3. The remaining steps are the same as those in Embodiment 1.

[0112] After testing, the phosphorus recovery rate in this embodiment is 97.73%, the purity of sodium phosphate is 99.89%, the iron recovery rate is 99.19%, and the purity of iron(III) oxide is 99.94%.

[0113] Embodiment 7 The difference between this embodiment and Embodiment 1 is that in Step 200, the molar ratio of phosphorus in the lithium-extracted slag to sodium ions in Na2CO3 is 1∶3.6. The remaining steps are the same as those in Embodiment 1.

[0114] After testing, the recovery rate of phosphorus in this embodiment is 98.72%, the purity of sodium phosphate is 99.84%, the recovery rate of iron is 98.98%, and the purity of iron(III) oxide is 99.83%.

[0115] Embodiment 8 The difference between this embodiment and Embodiment 1 is that in Step 200, the temperature in the reaction chamber is controlled at 550 °C, and the reaction time of the materials in the reaction chamber is 20 min. The remaining steps are the same as those in Embodiment 1.

[0116] After testing, the recovery rate of phosphorus in this embodiment is 93.83%, the purity of sodium phosphate is 99.69%, the recovery rate of iron is 99.08%, and the purity of iron(III) oxide is 99.93%.

[0117] Embodiment 9 The difference between this embodiment and Embodiment 1 is that in Step 200, the temperature in the reaction chamber is controlled at 1000 °C, and the reaction time of the materials in the reaction chamber is 10 s. The remaining steps are the same as those in Embodiment 1.

[0118] After testing, the recovery rate of phosphorus in this embodiment is 98.87%, the purity of sodium phosphate is 99.28%, the recovery rate of iron is 98.65%, and the purity of iron(III) oxide is 99.34%.

[0119] Embodiment 10 The difference between this embodiment and Embodiment 1 is that in Step 200, the lithium-extracted slag and Na2CO3 are mixed and then put into a muffle furnace for roasting, and the roasting time is 2 h. The remaining steps are the same as those in Embodiment 1.

[0120] After testing, the recovery rate of phosphorus in this embodiment is 96.76%, the purity of sodium phosphate is 99.26%, the recovery rate of iron is 98.95%, and the purity of iron(III) oxide is 99.39%.

[0121] Embodiment 11 The difference between this embodiment and Embodiment 1 is that in Step 300, the leaching solid-liquid ratio is 150 g / L. The remaining steps are the same as those in Embodiment 1.

[0122] After testing, the recovery rate of phosphorus in this embodiment is 98.62%, the purity of sodium phosphate is 99.37%, the recovery rate of iron is 99.32%, and the purity of iron(III) oxide is 99.56%.

[0123] Embodiment 12 The difference between this embodiment and Embodiment 1 is that in step 300, the leaching solid-liquid ratio is 200 g / L. The remaining steps are the same as those in Embodiment 1.

[0124] After testing, the phosphorus recovery rate of this embodiment is 98.55%, the purity of sodium phosphate is 99.12%, the iron recovery rate is 99.15%, and the purity of iron(III) oxide is 99.52%.

[0125] Embodiment 13 The difference between this embodiment and Embodiment 1 is that in step 300, the molten slag is leached at 40 °C for 180 min. The remaining steps are the same as those in Embodiment 1.

[0126] After testing, the phosphorus recovery rate of this embodiment is 96.27%, the purity of sodium phosphate is 99.98%, the iron recovery rate is 98.35%, and the purity of iron(III) oxide is 99.87%.

[0127] Embodiment 14 The difference between this embodiment and Embodiment 1 is that in step 300, the molten slag is leached at 80 °C for 30 min. The remaining steps are the same as those in Embodiment 1.

[0128] After testing, the phosphorus recovery rate of this embodiment is 98.56%, the purity of sodium phosphate is 99.23%, the iron recovery rate is 99.18%, and the purity of iron(III) oxide is 99.63%.

[0129] Embodiment 15 The difference between this embodiment and Embodiment 2 is that in step 500, the following process is further included: carbon dioxide gas is bubbled into the first filtrate until the pH of the solution is 6 to obtain a second solid-liquid mixture. After the second solid-liquid mixture is subjected to solid-liquid separation, a second filter cake and a second filtrate are obtained. The second filtrate is evaporated, concentrated, crystallized, and dried to obtain the finished product of sodium phosphate. The remaining steps are the same as those in Embodiment 2.

[0130] After testing, the phosphorus recovery rate of this embodiment is 98.47%, the purity of sodium phosphate is 99.37%, the iron recovery rate is 98.29%, and the purity of iron(III) oxide is 99.49%.

[0131] Comparative Example 1 The difference between this comparative example and Embodiment 1 is that in step 200, the molar ratio of phosphorus in the lithium-extracted slag to sodium ions in Na2CO3 is 1:4. The remaining steps are the same as those in Embodiment 1.

[0132] After testing, the phosphorus recovery rate of this comparative example is 97.29%, the purity of sodium phosphate is 92.95%, the iron recovery rate is 98.77%, and the purity of iron(III) oxide is 94.24%.

[0133] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: in step 200, the molar ratio of phosphorus in the lithium-extracted slag to sodium ions in Na2CO3 is 1:8. The remaining steps are the same as those in Example 1.

[0134] It is detected that the recovery rate of phosphorus in this comparative example is 96.69%, the purity of sodium phosphate is 91.29%, the recovery rate of iron is 98.22%, and the purity of iron(III) oxide is 93.27%.

[0135] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: in step 200, the molar ratio of phosphorus in the lithium-extracted slag to sodium ions in Na2CO3 is 1:20. The remaining steps are the same as those in Example 1.

[0136] It is detected that the recovery rate in this comparative example is 96.14%, the purity of sodium phosphate is 90.38%, the recovery rate of iron is 98.25%, and the purity of iron(III) oxide is 91.39%.

[0137] Comparative Example 4 The difference between this comparative example and Example 1 is as follows: in step 200, the material is sprayed downward from the top of the reaction chamber, and the discharging direction is vertically downward. The remaining steps are the same as those in Example 1.

[0138] It is detected that the recovery rate of phosphorus in this comparative example is 92.32%, the purity of sodium phosphate is 99.13%, the recovery rate of iron is 93.41%, and the purity of iron(III) oxide is 99.45%. In the above examples and comparative examples, the iron content in the first filter cake is measured by the potassium dichromate titration method, and the recovery rate of iron is calculated based on the ratio of the obtained iron content to the iron content in the phosphorus-containing iron compound.

[0139] The phosphorus content in the filtrate is detected by the quinoline molybdate gravimetric method, and the recovery rate of phosphorus is calculated based on the ratio of the obtained phosphorus content to the phosphorus content in the phosphorus-containing iron compound.

[0140] The purity of iron(III) oxide is detected by atomic absorption spectrometry.

[0141] The purity of phosphate is detected by atomic absorption spectrometry.

[0142] From the analysis of Examples 1-15 and Comparative Examples 1-3 above, it can be seen that when the dosage of sodium carbonate is too large, the purity of sodium phosphate and iron(III) oxide will significantly decrease; in addition, from the analysis of Examples 1-15 and Comparative Example 4 above, it can be seen that by adopting the inclined downward feeding method, the recovery rates of phosphorus and iron can be significantly improved.

[0143] It should be noted that, in this document, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the existence of additional identical elements in the process, method, article or device comprising such element.

[0144] In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in a reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. Additionally, the features described with reference to certain examples may be combined in other examples.

[0145] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily conceive of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds, characterized in that, It includes the following steps: Obtain the crushed phosphorus-containing iron compound and solid alkaline substance; Put the crushed phosphorus-containing iron compound and the crushed solid alkaline substance into a reaction furnace, melt and react the phosphorus-containing iron compound and the solid alkaline substance to obtain a first mixed material, wherein the dosage of the solid alkaline substance is 1 to 1.2 times the theoretical molar dosage; Leach the first mixed material with water, obtain a first solid-liquid mixture after leaching, and perform solid-liquid separation on the first solid-liquid mixture to obtain a first filter cake and a first filtrate; Wash and dry the first filter cake to obtain a ferric oxide product; Evaporate, concentrate, crystallize and dry the first filtrate to obtain a phosphate finished product.

2. The method for separating and recovering phosphorus and iron from a phosphorus-containing iron compound according to claim 1, characterized in that, The crushed phosphorus-containing iron compound has a first particle size, and the crushed solid alkaline substance has a second particle size. Respectively add the crushed phosphorus-containing iron compound and the crushed solid alkaline substance into the reaction furnace; Or, mix the phosphorus-containing iron compound and the solid alkaline substance in proportion to obtain a second mixed material. The crushed second mixed material has a first preset particle size, and add the crushed second mixed material into the reaction furnace; Or, after the phosphorus-containing iron compound is preliminarily crushed, dissolve the solid alkaline substance in water to form a saturated solution, mix the saturated solution and the crushed phosphorus-containing iron compound in proportion to obtain a third mixed material, dry the third mixed material and crush it to a second preset particle size, and add the crushed third mixed material into the reaction furnace.

3. The method for separating and recovering phosphorus and iron from the phosphorus-containing iron compound according to claim 2, wherein The first particle size is 300 to 500 mesh, and the second particle size, the first preset particle size and the second preset particle size are the same as the first particle size; or the first particle size is 300 to 500 mesh, the second particle size is 500 to 800 mesh, and the first preset particle size and the second preset particle size are the same as the first particle size; And / or, crush the material by means of a jet mill.

4. The method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds according to claim 1, characterized in that, The solid alkaline substance is one or more of NaOH, Na2CO3, NaHCO3, Na2SO4, NaHSO4, Na2SO3, NaCl, Na2S, KOH, K2CO3, KHCO3, K2SO4, KHSO4, K2SO3, KCl, CaO, Ca(OH)2, (NH4)2SO4; And / or, the solid alkaline substance at least includes at least one of the alkaline substances that can decompose at high temperature to generate acidic gases.

5. The method for separating and recovering phosphorus and iron from a phosphorus-containing iron compound according to any one of claims 1 to 4, characterized in that, Roast the crushed phosphorus-containing iron compound and the crushed solid alkaline substance in a muffle furnace or a rotary kiln, the roasting temperature is 550 to 1000 °C, and the roasting time is 2 to 6 h; Or, spray the crushed phosphorus-containing iron compound and the crushed solid alkaline substance into a flash furnace by means of spraying respectively. The temperature in the flash furnace is 550 to 1000 °C, and the reaction time of the material is 10 s to 20 min; Or, spray the mixed material of the crushed phosphorus-containing iron compound and the solid alkaline substance into a flash furnace by means of spraying. The temperature in the flash furnace is 550 to 1000 °C, and the reaction time of the material is 10 s to 20 min.

6. The method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds according to claim 5, characterized in that, Use nozzles to spray the phosphorus-containing iron compound and the solid alkaline substance into the flash furnace respectively, and the particle sizes of the sprayed phosphorus-containing iron compound and the solid alkaline substance are both larger than 300 mesh; Alternatively, a nozzle is used to spray a mixed material of a phosphorus-containing iron compound and a solid alkaline substance into a flash furnace, and the particle size of the sprayed material is greater than 300 mesh.

7. The method for separating and recovering phosphorus and iron from a phosphorus-containing iron compound according to claim 6, characterized in that, When the phosphorus-containing iron compound and the solid alkaline substance are respectively sprayed into the flash furnace by means of jet injection, the materials are sprayed downward from the upper part of the flash furnace, and an angle of 30°-60° is formed between the discharging direction of the nozzle and the inner wall of the flash furnace; Alternatively, when a nozzle is used to spray a mixed material of a phosphorus-containing iron compound and a solid alkaline substance into the flash furnace, the materials are sprayed downward from the upper part of the flash furnace, and an angle of 30°-60° is formed between the discharging direction of the nozzle and the inner wall of the flash furnace; And / or, while jet injection is carried out, air or an inert gas is introduced upward from the bottom of the flash furnace.

8. The method for separating and recovering phosphorus and iron from a phosphorus-containing iron compound according to claim 1, wherein When the first mixed material is leached with water, the leaching temperature is 40-80 °C, the leaching time is 30-180 min, and the leaching solid-liquid ratio is 100-200 g / L; And / or, the first filter cake obtained by solid-liquid separation is washed with water 1-3 times, and the washing water is used for leaching the first mixed material; And / or, carbon dioxide gas is bubbled into the first filtrate until the pH of the solution is 6-8 to obtain a second solid-liquid mixture. After the second solid-liquid mixture is subjected to solid-liquid separation, a second filter cake and a second filtrate are obtained. The second filtrate is evaporated, concentrated, crystallized and dried to obtain a phosphate finished product.

9. A system for separating and recovering phosphorus and iron from phosphorus-containing iron compounds, which is used for the method for separating and recovering phosphorus and iron from phosphorus-containing iron compounds according to any one of claims 1 to 8, characterized in that, The system includes: A crushing device for crushing a phosphorus-containing iron compound and a solid alkaline substance; A reaction furnace for heating the crushed phosphorus-containing iron compound and the crushed solid alkaline substance, and melting and reacting the phosphorus-containing iron compound and the solid alkaline substance to obtain a first mixed material; A leaching device for leaching the first mixed material and obtaining a first solid-liquid mixture; A solid-liquid separation device for subjecting the first solid-liquid mixture to solid-liquid separation to obtain a first filter cake and a first filtrate; A drying device for drying the washed first filter cake to obtain an iron sesquioxide product; A crystallization device for evaporating, concentrating, crystallizing and drying the first filtrate to obtain a phosphate finished product.

10. The system for separating and recovering phosphorus and iron from a phosphorus-containing iron compound according to claim 9, characterized in that, The reaction furnace is a muffle furnace or a rotary kiln; or, The reaction furnace is a flash furnace, and the flash furnace includes a furnace body (100), a crucible (200) and an isolation protective layer (300). The crucible (200) and the isolation protective layer (300) are both arranged in the furnace body (100). The isolation protective layer (300) is arranged in the crucible (200). A reaction chamber (300a) is constructed in the isolation protective layer (300) for providing a reaction space for the phosphorus-containing iron compound and the solid alkaline substance. Wherein, the isolation protective layer (300) is made of at least one of corundum, ceramic material and quartz glass, and the crucible (200) is a graphite crucible or a silicon carbide crucible; And / or, the flash furnace further includes a heat transfer transition layer (400) disposed between the crucible (200) and the isolation protection layer (300). When the isolation protection layer (300) is a corundum layer and the crucible (200) is a graphite crucible, the heat transfer transition layer (400) is a mixed layer of graphite and corundum. And in the heat transfer transition layer (400), in the direction from the isolation protection layer (300) to the crucible (200), the proportion of the corundum component gradually decreases, and the proportion of the graphite component gradually increases; And / or, the flash furnace further includes an induction coil (500) disposed on the outer periphery of the crucible (200). There is an air gap (800) between the induction coil (500) and the crucible (200). The induction coil (500) is used to heat the phosphorus-containing iron compound and the solid alkaline substance in the reaction chamber (300a); And / or, the flash furnace further includes a material spraying channel (600) located at the top or side of the furnace body (100). A nozzle is provided at the end of the material spraying channel (600). An included angle of 30° - 60° is formed between the discharging direction of the nozzle and the inner wall of the isolation protection layer (300); And / or, the flash furnace further includes an air supply channel (700) located at the bottom of the furnace body (100). The air supply channel (700) is used to introduce gas into the reaction chamber (300a) from the bottom.

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