Method for manufacturing iron phosphate and method for manufacturing lithium iron phosphate

Abstract

The present invention provides a method for manufacturing iron phosphate and a method for manufacturing lithium iron phosphate. The method for manufacturing iron phosphate comprises the steps of: uniformly mixing sulfuric acid slag and sulfite with water to obtain a first mixture; adding phosphoric acid and a buffer to the first mixture to perform a leaching reaction; performing a first solid-liquid separation on the slurry obtained from the leaching reaction to obtain a first filtrate and a first filtrate residue; introducing air into the first filtrate to perform a first stirring reaction; performing a second solid-liquid separation on the slurry obtained from the first stirring reaction to obtain a second filtrate and a second filtrate residue; and calcining the second filtrate residue, wherein the pressure of the leaching reaction is 0.25 to 0.5 MPa and the time is 1 to 2 hours; the pH of the reaction system of the leaching reaction is 1.5 to 3; and the buffer comprises sodium dihydrogen phosphate and / or disodium hydrogen phosphate. The above method for manufacturing iron phosphate can utilize the iron within sulfuric acid slag, thereby reducing the manufacturing cost of iron phosphate, and is simple and easy to operate.

Description

Technology Field

[0001] This application claims priority to a Chinese patent application filed on March 30, 2022, with application number 202210328818.0 and titled "Method for manufacturing iron phosphate and method for manufacturing lithium iron phosphate," all of which are by reference.

[0002] Technology field

[0003] The present invention belongs to the field of battery technology and, in particular, relates to a method for manufacturing iron phosphate and a method for manufacturing lithium iron phosphate. Background Technology

[0004] Sulfuric acid slag has been used as a raw material for ironmaking and other industries for over 100 years. The amount of sulfuric acid slag discharged annually exceeds 3 million tons, but only about 1 million tons are rationally utilized, with the remainder being released into the environment. When accumulated, it encroaches upon agricultural land and pollutes the soil, and when discharged into rivers, it pollutes water bodies.

[0005] Currently, there are various methods for the comprehensive utilization of sulfuric acid slag, but most adopt the "method of manufacturing bricks from the residue after iron concentrate separation." As a raw material for ironmaking, sulfuric acid slag with an iron content of 25% or higher has a certain economic value in the separation of iron concentrate; the separation process does not differ significantly from the general iron ore separation process and can be performed using gravity separation or magnetic separation, respectively, depending on the comparison of the magnetization susceptibility of the iron minerals within the slag. The economic analysis is as follows. Assuming that the annual selection volume of sulfuric acid slag is 20,000 tons, and that iron-grade concentrate with an iron grade of 60 (iron concentrate with a grade of 60 or higher can be used directly for ironmaking) is separated from slag with an iron grade of 30, 8,000 tons of iron concentrate can be produced annually based on a yield of 40%. The selling price of iron-grade concentrate with an iron grade of 60 (sulfur content ≤ 0.5) is 110 yuan per ton, and the production cost is 70 yuan per ton, resulting in a profit of 40 yuan per ton and an annual profit of 320,000 yuan. The total investment required to construct one iron sorting plant is approximately 500,000 yuan, and the investment can be fully recovered in less than two years of production. After separating the iron concentrate, 12,000 tons of residue remain, which can be used to manufacture bricks. Although sulfuric acid slag itself has no binding ability, it contains active substances such as SiO2 and Al2O3.

[0006] Sulfuric acid slag can be used as a raw material for sintered ore, and the production costs of sintering raw materials are reduced primarily by utilizing the iron-containing components within the slag. However, it has poor spheroidization characteristics and a high water absorption rate, which affects sintering productivity. Additionally, it has a relatively high sulfur content and contains harmful elements such as Cu, Pb, and Zn, which affects the quality of the sintered ore. The amount of sulfuric acid slag incorporated into the sintering material is generally 10% or less. Sulfuric acid slag can be treated to increase fineness, increase iron content, and decrease sulfur content so that it can be used as a raw material for pellet ore. Some conventional technologies chlorine the metals contained in the slag using a high-temperature chlorination process, and then use a wet metallurgy method to leach precious metals such as gold and silver and remove harmful metals from the slag.

[0007] With the advancement of lithium iron phosphate, low-cost iron sources are gaining attention. The price of ferrous sulfate crystals, a byproduct of titanium white powder, has continued to rise, currently reaching 350 yuan per ton. Transportation costs amount to approximately 70 to 90 yuan per ton, and as lithium iron production capacity expands, the price of ferrous sulfate crystals continues to increase, making it difficult to purchase. Therefore, it is urgent to develop new iron sources that are affordable and easily available. A large amount of sulfuric acid slag, amounting to millions of tons annually, is generated, yet its recycling efficiency is low.

[0008] In this regard, the present invention is proposed.

[0009] With this in mind, the present invention aims to provide a method for manufacturing iron phosphate and a method for manufacturing lithium iron phosphate that can recover cobalt, copper, gold, silver, and sodium sulfate from sulfuric acid slag in a simple and low-cost manner, in order to significantly increase the added value of sulfuric acid slag and improve the resource utilization rate of sulfuric acid slag.

[0010] The method for producing iron phosphate according to the present invention is,

[0011] The method comprises the steps of: obtaining a first mixture by uniformly mixing sulfuric acid slag and sulfite with water; performing a leaching reaction by adding phosphoric acid and a buffer to the first mixture; performing a first solid-liquid separation on the slurry obtained from the leaching reaction to obtain a first filtrate and a first filtrate residue; introducing air into the first filtrate to perform a first stirring reaction; performing a second solid-liquid separation on the slurry obtained from the first stirring reaction to obtain a second filtrate and a second filtrate residue; and calcining the second filtrate residue to obtain iron phosphate, wherein

[0012] Here, the pressure of the leaching reaction is 0.25 to 0.5 MPa; and the time of the leaching reaction is 1 to 2 hours;

[0013] The pH of the reaction system for the above leaching reaction is 1.5 to 3;

[0014] The above buffer comprises sodium dihydrogen phosphate and / or disodium hydrogen phosphate.

[0015] Preferably, the particle size of the sulfuric acid slag is 80 to 120 mesh;

[0016] Preferably, the molar ratio of the iron element in the sulfuric acid slag to the sulfite, the phosphoric acid, and the buffer is 1:(0.35~0.4):(0.25~0.3):(1.7~1.75);

[0017] Preferably, the phosphoric acid and the buffer are added to the first mixture within 15 to 30 minutes;

[0018] Preferably, the ratio of the amount of air input per hour to the first filtrate to the amount of ferrous ions in the first filtrate is (8 to 12) m 3 :(28~32)mol.

[0019] Preferably, the temperature of the leaching reaction is 130 to 170°C;

[0020] Preferably, the leaching reaction is carried out under stirring conditions.

[0021] Before introducing air into the first filtrate, the first filtrate is heated to 40~60℃ under stirring conditions;

[0022] Preferably, the first stirring reaction is specifically,

[0023] It includes stirring the first filtered liquid into which air has been introduced until the iron element content of the supernatant becomes 0.5 g / L or less, heating the first filtered liquid to 90 to 95°C, and then continuing to stir for 30 to 60 minutes.

[0024] Before calcining the second filtration residue, the above includes additional washing and drying steps;

[0025] Preferably, the temperature of the washing water for the washing is 40 to 50°C;

[0026] Preferably, the washing is performed until the pH of the washing solution exceeds 4.5;

[0027] Preferably, the moisture content of the second filtration residue after drying is less than 0.5%. The second filtration residue is calcined at a temperature of 650 to 680°C;

[0028] Preferably, the second filtration residue is calcined for 60 to 90 minutes.

[0029] The above-described method for manufacturing iron phosphate is,

[0030] After the above leaching reaction is completed, the method further includes the step of introducing the gas generated by the leaching reaction into a sodium hydroxide solution to obtain sodium sulfite.

[0031] The above-described method for manufacturing iron phosphate is,

[0032] The method further comprises the steps of: cooling and performing a third solid-liquid separation on the second filtrate to obtain sodium sulfate crystals and a mother liquor; adding sodium sulfide to the mother liquor to obtain a third filtrate and a third filtrate residue; adjusting the pH of the third filtrate to 9-10 and performing a fourth solid-liquid separation to obtain a fourth filtrate and a fourth filtrate residue; calcining the third filtrate residue and dissolving the calcined third filtrate residue in sulfuric acid to obtain a second mixed system; and extracting, concentrating, and crystallizing the second mixed system to obtain crude copper sulfate and crude cobalt sulfate, wherein

[0033] Preferably, the second filtrate has a temperature of 5 to 10°C after cooling;

[0034] Preferably, the third filtration residue is calcined at a temperature of 500 to 700°C;

[0035] Preferably, the third filtration residue is calcined for 2 to 4 hours.

[0036] The above-described method for manufacturing iron phosphate is,

[0037] The method further comprises the steps of: adding aqua regia to the first filtration residue obtained by flotation separation and concentration to obtain a third mixture; performing a fifth solid-liquid separation on the third mixture to obtain a fifth filtrate; adding sodium chloride to the fifth filtrate and then performing a sixth solid-liquid separation to obtain silver chloride and a sixth filtrate; and adding iron powder to the sixth filtrate to obtain crude gold powder.

[0038] The present invention provides a method for manufacturing lithium iron phosphate comprising a method for manufacturing iron phosphate according to the technical method described above.

[0039] The above method for manufacturing lithium iron phosphate is simple and inexpensive.

[0040] Compared to conventional technology, the present invention has the following beneficial effects.

[0041] (1) The method for producing iron phosphate provided in the present invention utilizes high-pressure reduction leaching to dissolve triiron tetroxide and ferric oxide, which are difficult to dissolve in acid, and also uses a mixed solution of phosphoric acid and sodium dihydrogen phosphate to leach the reduced iron salt to obtain a ferrous phosphate (Fe(H2PO4)2) solution. Additionally, by preventing some aluminum, calcium, magnesium, etc. from dissolving at a relatively high pH, ​​the leaching rate of iron can be significantly improved, and the leached iron is used to produce iron phosphate.

[0042] (2) The method for producing iron phosphate provided in the present invention can also recover cobalt, copper, gold, silver, and sodium sulfate from sulfuric acid slag, thereby greatly increasing the added value of sulfuric acid slag and improving the resource utilization rate of sulfuric acid slag.

[0043] (3) The method for manufacturing lithium iron phosphate provided in the present invention is simple and inexpensive. Brief explanation of the drawing

[0044] To more clearly explain specific embodiments of the present invention or technical methods of the prior art, the drawings used in the description of specific embodiments or prior art are briefly described. The drawings in the following description are merely specific embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative work. Figure 1 is a diagram showing the results of observing iron phosphate according to an embodiment of the present invention using a scanning electron microscope. Figure 2 is a diagram showing the results of observing iron phosphate according to another embodiment of the present invention using a scanning electron microscope. Figure 3 is a diagram showing the particle size distribution results of iron phosphate according to an embodiment of the present invention. Specific details for implementing the invention

[0045] The technical means of the present invention will be described more clearly and comprehensively below with reference to the attached drawings and specific embodiments. However, those skilled in the art will understand that the described embodiments are merely partial embodiments and not all embodiments of the present invention, and that they are provided only to explain the present invention and should not be interpreted as limiting the scope of the present invention. All other embodiments obtained without creative effort by those skilled in the art based on the embodiments of the present invention will fall within the scope of protection of the present invention. In the following embodiments, where specific conditions are not mentioned, ordinary conditions or conditions recommended by the manufacturer shall apply. Unless the manufacturer is specified, the reagents or equipment used are all ordinary products available on the market.

[0046] A method for producing iron phosphate according to one aspect of the present invention is,

[0047] The method comprises the steps of: obtaining a first mixture by uniformly mixing sulfuric acid slag and sulfite with water; performing a leaching reaction by adding phosphoric acid and a buffer to the first mixture; performing a first solid-liquid separation on the slurry obtained from the leaching reaction to obtain a first filtrate and a first filtrate residue; introducing air into the first filtrate to perform a first stirring reaction; performing a second solid-liquid separation on the slurry obtained from the first stirring reaction to obtain a second filtrate and a second filtrate residue; and calcining the second filtrate residue.

[0048] Here, the pressure of the leaching reaction is 0.25~0.5MPa;

[0049] The pH of the reaction system for the above leaching reaction is 1.5 to 3;

[0050] The above buffer comprises sodium dihydrogen phosphate and / or disodium hydrogen phosphate.

[0051] In some specific embodiments, the pressure of the leaching reaction may be, for example, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, or 0.5 MPa, but is not limited thereto.

[0052] In some specific embodiments, the pH of the reaction system of the leaching reaction may be, for example, 1.5, 2, 2.5, or 3, but is not limited thereto.

[0053] Sulfuric acid slag refers to the residue generated during the process of manufacturing sulfuric acid from pyrite, and is also known as dry pyrite slag or combustion slag. It is a type of chemical waste. Since the slag contains iron, it can be used as a raw material for steel metallurgy. In sulfuric acid slag, the content of iron oxides (Fe2O3, Fe3O4, FeO) is about 20–50%, the content of silicon dioxide is about 15–65%, the content of aluminum oxide is about 10%, the content of calcium oxide is about 5%, the content of magnesium oxide is 5% or less, and the content of sulfur is about 1–2%; generally, copper, cobalt, lead, zinc, gold, and silver are also included. Here, triiron tetroxide forms dense triiron tetroxide due to the passivation effect of sulfuric acid.

[0054] The method for producing iron phosphate provided in the present invention utilizes high-pressure reduction leaching to dissolve triiron tetroxide and ferric oxide, which are difficult to dissolve in acid, and also uses a mixed solution of phosphoric acid and sodium dihydrogen phosphate to leach the reduced iron salt to obtain a ferrous phosphate (Fe(H2PO4)2) solution, and also controls the pH of the reaction system of the leaching reaction to 1.5 to 3 to prevent the dissolution of some aluminum, calcium, magnesium, etc., thereby improving the leaching rate of iron.

[0055] Phosphoric acid can provide hydrogen ions, and sodium dihydrogen phosphate and disodium hydrogen phosphate act as buffer solutions to replenish hydrogen ions after the hydrogen ions from the phosphoric acid are consumed, while simultaneously preventing other impurities from leaching out due to the solution's pH becoming too low.

[0056] Since the leaching reaction of the present invention proceeds under specific leaching conditions, the leaching rate is significantly improved. Furthermore, by adding sulfites, it can exhibit reducing properties in an acidic environment, thereby reducing ferric ions to ferrous ions, which further enhances the leaching rate and ultimately yields a ferrous dihydrogen phosphate solution. Simultaneously, a ferrous dihydrogen phosphate solution is produced in a weakly acidic environment and in an environment where a large amount of dihydrogen phosphate is present.

[0057] Preferably, the sulfite comprises sodium sulfite and / or potassium sulfite.

[0058] Preferably, the particle size of the sulfuric acid slag is 80 to 120 mesh.

[0059] In some specific embodiments, the particle size of the sulfuric acid slag may be, for example, 80 mesh, 90 mesh, 100 mesh, 110 mesh, or 120 mesh, but is not limited thereto.

[0060] Preferably, the molar ratio of the iron element in the sulfuric acid slag to the sulfite, the phosphoric acid, and the buffer is 1:(0.35~0.4):(0.25~0.3):(1.7~1.75).

[0061] In some specific embodiments, the molar ratio of the iron element in the sulfuric acid slag to the sulfite, the phosphoric acid, and the buffer may be, for example, 1:0.35:0.25:1.7, 1:0.37:0.28:1.173, or 1:0.4:0.3:1.75, but is not limited thereto.

[0062] Preferably, the phosphoric acid and the buffer are added to the first mixture system within 15 to 30 minutes (e.g., 15 minutes, 20 minutes, 25 minutes, or 30 minutes).

[0063] Preferably, the ratio of the amount of air input per hour to the first filtrate to the amount of ferrous ions in the first filtrate is (8 to 12) m 3 :(28~32)mol.

[0064] In some specific embodiments, the ratio of the amount of air input per hour to the first filtrate to the ferrous ions of the first filtrate may be, for example, 8:28, 10:30, or 12:32, but is not limited thereto.

[0065] Preferably, the temperature of the leaching reaction is 130 to 170°C.

[0066] In some specific embodiments, the temperature of the leaching reaction may be, for example, 130°C, 140°C, 150°C, 160°C, or 170°C, but is not limited thereto.

[0067] Preferably, the time of the leaching reaction is 1 to 2 hours.

[0068] In some specific embodiments, the time of the leaching reaction may be, for example, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, or 2 h, but is not limited thereto.

[0069] Preferably, the leaching reaction is carried out under stirring conditions.

[0070] Preferably, before introducing air into the first filtrate, the first filtrate is heated to 40 to 60°C (e.g., 40°C, 45°C, 50°C, 55°C, or 60°C) under stirring conditions.

[0071] Preferably, the first stirring reaction is specifically,

[0072] The method includes stirring the first filtered liquid into which air has been introduced until the iron element content of the supernatant becomes 0.5 g / L or less, heating the first filtered liquid to 90 to 95°C (e.g., 90°C, 91°C, 92°C, 93°C, 94°C, or 95°C), and then continuing to stir for 30 to 60 minutes (e.g., 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, or 60 minutes).

[0073] Preferably, the washing and drying steps are further included before calcining the second filtration residue.

[0074] Preferably, the temperature of the washing is 40 to 50°C (e.g., 40°C, 42°C, 44°C, 46°C, 48°C, or 50°C).

[0075] Preferably, the washing is performed until the pH of the washing solution exceeds 4.5 (e.g., 4.5, 4.8, 5, 5.5, 6, or 6.5).

[0076] Preferably, the moisture content of the second filter residue after drying is less than 0.5% (e.g., 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%).

[0077] Preferably, the second filtration residue is calcined at a temperature of 650 to 680°C (e.g., 650°C, 655°C, 660°C, 665°C, 670°C, 675°C, or 680°C).

[0078] Preferably, the second filtration residue is calcined for 60 to 90 minutes (e.g., 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, or 90 minutes).

[0079] Preferably, the second filtration residue is calcined, and then subjected to cooling, grinding, screening, iron removal, and vacuum packaging to obtain anhydrous iron phosphate.

[0080] Preferably, the above method for manufacturing iron phosphate is,

[0081] After the above leaching reaction is completed, the method further includes the step of introducing the gas generated by the leaching reaction into a sodium hydroxide solution to obtain sodium sulfite, and recovering and using it.

[0082] Preferably, the above method for manufacturing iron phosphate is,

[0083] The method further comprises the steps of: cooling and performing a third solid-liquid separation on the second filtrate to obtain sodium sulfate crystals and a mother liquor; adding sodium sulfide to the mother liquor to obtain a third filtrate and a third filtrate residue; adjusting the pH of the third filtrate to 9-10 and performing a fourth solid-liquid separation to obtain a fourth filtrate and a fourth filtrate residue; calcining the third filtrate residue and dissolving the calcined third filtrate residue in sulfuric acid to obtain a second mixed system; and extracting and concentrating the second mixed system to crystallize crude copper sulfate and crude cobalt sulfate.

[0084] Preferably, the temperature of the second filtrate after cooling is 5 to 10°C (e.g., 5°C, 7°C, 8°C, 9°C, or 10°C).

[0085] After mixing sulfites into the second filtrate, sodium dihydrogen phosphate is further mixed and leached into sulfuric acid slag to return it. The second filtrate, which has been recycled three times, is concentrated to a Baume degree of 45 to 50, then cooled to a temperature of 5 to 10°C and centrifugally dried to obtain sodium sulfate crystals.

[0086] After adding phosphoric acid and sodium dihydrogen phosphate to the fourth filtrate, it is leached back into sulfuric acid slag and returned.

[0087] Preferably, the third filtration residue is calcined at a temperature of 500 to 700°C (e.g., 530°C, 560°C, 590°C, 620°C, 650°C, 680°C, or 700°C).

[0088] Preferably, the third filtration residue is calcined for 2 to 4 hours (e.g., 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours).

[0089] The waste gas generated by calcining the third filtration residue is absorbed by a sodium hydroxide solution and leached out as sulfuric acid slag for return.

[0090] Preferably, the above method for manufacturing iron phosphate is,

[0091] The method further comprises the steps of: adding aqua regia to the first filtration residue obtained by flotation separation and concentration to obtain a third mixture; performing a fifth solid-liquid separation on the third mixture to obtain a fifth filtrate; adding sodium chloride to the fifth filtrate and then performing a sixth solid-liquid separation to obtain silver chloride and a sixth filtrate; and adding iron powder to the sixth filtrate to obtain crude gold powder.

[0092] The present invention can produce iron phosphate using iron contained in sulfuric acid slag, and at the same time concentrate copper and cobalt contained in sulfuric acid slag into crude copper sulfate and crude cobalt sulfate, and concentrate silver and gold contained in sulfuric acid slag.

[0093] A method for manufacturing lithium iron phosphate according to another aspect of the present invention comprises the above-described method for manufacturing iron phosphate.

[0094] The method for manufacturing lithium iron phosphate is as follows.

[0095] After adding the above anhydrous iron phosphate to a lithium source, a carbon source, and a dopant, purified water is added to form a slurry, nano-grinding is performed, spray drying is carried out, the obtained spray-dried material is calcined in an inert atmosphere, and the obtained calcined material is subjected to grinding, screening, iron removal, and vacuum packaging to obtain lithium iron phosphate.

[0096] The mass ratio of the anhydrous iron phosphate, lithium source, carbon source, and dopant is 1:(0.2~0.25):(0.1~0.2):(0.0005~0.005), the lithium source is lithium carbonate or lithium hydroxide, and the carbon source is at least one of glucose, sucrose, soluble starch, PEG, citric acid, ascorbic acid, and benzoic acid. The dopant is at least one of titanium compound, vanadium compound, magnesium compound, and manganese compound.

[0097] Nano-polishing is performed until the slurry particle size becomes 100 to 600 nm, the inert atmosphere is nitrogen, the calcination temperature is 600 to 900°C, and the calcination time is 5 to 40 h.

[0098] The above method for manufacturing lithium iron phosphate is simple and inexpensive.

[0099] Hereinafter, in order to explain the present invention more specifically, the method for manufacturing iron phosphate and the method for manufacturing lithium iron phosphate according to the present invention will be described in detail with reference to examples, but the present invention should not be interpreted as being limited thereto.

[0100] The method for manufacturing iron phosphate provided in Example 1 includes the following steps.

[0101] (1) Sulfuric acid slag was ground with a ball mill and passed through a 100-mesh sieve, and the inspection data of the sampled sulfuric acid slag is shown in Table 1.

[0102]

[0103] (2) Sulfuric acid slag was placed in an autoclave and a sodium sulfite solution was added and mixed and stirred; a mixed solution of phosphoric acid and sodium dihydrogen phosphate was added to the autoclave using a high-pressure pump while raising the temperature to 150°C so that the pressure inside the autoclave became 0.42 MPa, and the time for adding the mixed solution of phosphoric acid and sodium dihydrogen phosphate was 20 minutes, and the reaction was stirred and reacted for 1.5 hours at such temperature and pressure; the reaction-completed slurry was filtered to obtain a first filtrate and a first filtrate residue; the first filtrate residue was sampled to obtain inspection data as shown in Table 2.

[0104]

[0105] The leaching rate of iron exceeds 95%, and elements such as gold and silver are concentrated.

[0106] (3) The first filtrate was heated to 50°C under stirring, air was introduced, and the reaction was stirred under these conditions until the iron element content of the supernatant was 0.35 g / L, and the temperature was raised to 95°C; the reaction was stirred for 40 minutes at this temperature and filtered to obtain the second filtrate and the second filtrate residue; the second filtrate residue was washed, dried, and calcined. The calcination was performed using a rotary kiln, with a calcination temperature of 670°C and a calcination time of 80 minutes. The calcined material was then cooled, ground, screened, iron removed, and vacuum-packed to obtain anhydrous iron phosphate. The measurement data of the anhydrous iron phosphate is shown in Table 3, the results of observing the iron phosphate with a scanning electron microscope are shown in Figures 1 and 2, and the particle size distribution of the iron phosphate is shown in Figure 3.

[0107]

[0108] (4) The second filtrate is mixed with sodium dihydrogen phosphate and leached back into the sulfuric acid slag to return it; the second filtrate, which has been recycled three times, is concentrated to a Baume degree of 48, then the temperature of the solution is cooled to 8°C and centrifugally dried to obtain sodium sulfate crystals, and a sodium sulfide solution is added to the mother liquor after crystallization and filtered to obtain a third filtrate and a third filtrate residue; a sodium hydroxide solution is added to the third filtrate to adjust the pH to 9.5 and filtered to obtain a fourth filtrate and a fourth filtrate residue, and the fourth filtrate is combined with a new phosphoric acid and sodium dihydrogen phosphate solution and used; the purity of the obtained sodium sulfate crystals is 98.5% or higher.

[0109] The molar ratio of iron element in the sulfuric acid slag to sodium sulfite, phosphoric acid, and sodium dihydrogen phosphate is 1:0.37:0.3:1.7, the concentration of the sodium sulfite solution is 2.5 mol / L, and the sum of the molar concentrations of the mixed solution of phosphoric acid and sodium dihydrogen phosphate is 2 mol / L.

[0110] (5) The third filtration residue is calcined in a rotary kiln at a calcination temperature of 600°C and a calcination time of 3 hours, and the waste gas generated from the calcination is absorbed by a sodium hydroxide solution and leached into sulfuric acid slag and returned; after calcining the third filtration residue, sulfuric acid is added to dissolve it, and cobalt and copper are extracted and separated using a P2O4 extraction solvent; the obtained cobalt-copper solution is concentrated and crystallized to obtain crude copper sulfate with a purity of 95.6% and crude cobalt sulfate with a purity of 91.5%.

[0111] (6) After flotation of the first filtration residue, the gold and silver are further concentrated, and aqua regia is added to dissolve them. Then, sodium chloride is added to the filtrate obtained by filtration to precipitate the silver, thereby obtaining silver chloride. Iron powder is added to the remaining filtrate to replace the gold, thereby obtaining crude gold powder.

[0112] (7) The gas inside the autoclave is introduced into a 2 mol / L sodium hydroxide solution, and at the same time, nitrogen is introduced into the autoclave so that all sulfur dioxide gas is discharged and absorbed into the sodium hydroxide solution, and finally, the sodium hydroxide concentration of the absorption solution is less than 0.2 mol / L, and the obtained absorption solution is reused as sodium sulfite; the flow rate of air introduced per hour (m 3 The ratio between ) and the total number of moles (mol) of ferrous ions in the solution is 20.

[0113] The method for manufacturing lithium iron phosphate is as follows.

[0114] After adding the above anhydrous iron phosphate to a lithium source, a carbon source, and a dopant, purified water is added to form a slurry, nano-grinding is performed, spray drying is carried out, the obtained spray-dried material is calcined in an inert atmosphere, and the obtained calcined material is subjected to grinding, screening, iron removal, and vacuum packaging to obtain lithium iron phosphate.

[0115] The mass ratio of anhydrous iron phosphate, a lithium source, a carbon source, and a dopant is 1:0.23:0.13:0.0015, the lithium source is lithium carbonate, and the carbon source is glucose. The dopant is titanium dioxide.

[0116] Nano-polishing is performed until the slurry particle size becomes 320 nm, the inert atmosphere is nitrogen, the calcination temperature is 780°C, and the calcination time is 12 h.

[0117] The final inspection data for lithium iron phosphate is as follows.

[0118]

[0119] Powder resistivity is measured using the four-probe method, and the pressure is 10 MPa.

[0120] The pressure used for compaction density is 3T.

[0121] [Example 2]

[0122] The method for manufacturing iron phosphate provided in this embodiment includes the following steps.

[0123] (1) Same as Example 1.

[0124] (2) Sulfuric acid slag is placed in an autoclave and a potassium sulfite solution is added and mixed and stirred; a mixed solution of phosphoric acid and sodium dihydrogen phosphate is added to the autoclave using a high-pressure pump while raising the temperature to 130°C so that the pressure inside the autoclave becomes 0.5 MPa, and the time for adding the mixed solution of phosphoric acid and sodium dihydrogen phosphate is 15 minutes, and the reaction is stirred and reacted for 2 hours at this temperature and pressure; the reaction is completed by filtering the slurry to obtain a first filtrate and a first filtrate residue.

[0125] (3) The first filtrate is heated to 40°C under stirring, air is introduced, and the reaction is stirred under these conditions until the iron element content of the supernatant becomes 0.1 g / L, and the temperature is raised to 95°C; the reaction is stirred for 30 minutes at this temperature and filtered to obtain the second filtrate and the second filtrate residue; the second filtrate residue is washed, dried, and calcined, and the calcination is performed using a rotary kiln calcination with a calcination temperature of 680°C and a calcination time of 60 minutes, and the calcined material is cooled, crushed, screened, iron removed, and vacuum packaged to obtain anhydrous iron phosphate.

[0126] (4) The second filtrate is mixed with sodium dihydrogen phosphate and leached back into the sulfuric acid slag to return it; the second filtrate, which has been recycled three times, is concentrated to a Baume degree of 48, then the temperature of the solution is cooled to 8°C and centrifugally dried to obtain sodium sulfate crystals, and a sodium sulfide solution is added to the mother liquor after crystallization and filtered to obtain the third filtrate and the third filtrate residue; a sodium hydroxide solution is added to the third filtrate to adjust the pH to 9 and filtered to obtain the fourth filtrate and the fourth filtrate residue, and the fourth filtrate is combined with a new phosphoric acid and sodium dihydrogen phosphate solution and used.

[0127] The molar ratio of iron element in the sulfuric acid slag to potassium sulfite, phosphoric acid, and sodium dihydrogen phosphate is 1:0.35:0.25:1.7, the concentration of the potassium sulfite solution is 2.5 mol / L, and the sum of the molar concentrations of the mixed solution of phosphoric acid and sodium dihydrogen phosphate is 2 mol / L.

[0128] (5) The third filtration residue is calcined in a rotary kiln at a calcination temperature of 500°C and a calcination time of 4 hours, and the waste gas generated from the calcination is absorbed by a sodium hydroxide solution and leached back into sulfuric acid slag; after calcining the third filtration residue, sulfuric acid is added to dissolve it, and cobalt and copper are extracted and separated using a P204 extraction solvent; the obtained cobalt-copper solution is concentrated and crystallized to obtain crude copper sulfate and crude cobalt sulfate.

[0129] (6)~(7) are identical to Example 1.

[0130] [Example 3]

[0131] The method for manufacturing iron phosphate provided in this embodiment includes the following steps.

[0132] (1) Same as Example 1.

[0133] (2) Sulfuric acid slag is placed in an autoclave and a sodium sulfite solution is added and mixed and stirred; a mixed solution of phosphoric acid and sodium dihydrogen phosphate is added to the autoclave using a high-pressure pump while raising the temperature to 170°C so that the pressure inside the autoclave becomes 0.25 MPa, and the time for adding the mixed solution of phosphoric acid and sodium dihydrogen phosphate is 30 minutes, and the reaction is stirred and reacted for 1 hour at this temperature and pressure; the reaction is completed by filtering the slurry to obtain a first filtrate and a first filtrate residue.

[0134] (3) The first filtrate is heated to 60°C under stirring, air is introduced, and the reaction is stirred under these conditions until the iron element content of the supernatant becomes 0.5 g / L, and the temperature is raised to 90°C; the reaction is stirred for 60 minutes at this temperature and filtered to obtain the second filtrate and the second filtrate residue; the second filtrate residue is washed, dried, and calcined, and the calcination is performed using a rotary kiln calcination, with a calcination temperature of 650°C and a calcination time of 90 minutes, and the calcined material is cooled, crushed, screened, iron removed, and vacuum packaged to obtain anhydrous iron phosphate.

[0135] (4) The second filtrate is mixed with sodium dihydrogen phosphate and leached back into the sulfuric acid slag to return it; the second filtrate, which has been recycled three times, is concentrated to a Baume degree of 48, then the temperature of the solution is cooled to 8°C and centrifugally dried to obtain sodium sulfate crystals, and a sodium sulfide solution is added to the mother liquor after crystallization and filtered to obtain the third filtrate and the third filtrate residue; a sodium hydroxide solution is added to the third filtrate to adjust the pH to 10 and filtered to obtain the fourth filtrate and the fourth filtrate residue, and the fourth filtrate is combined with a new phosphoric acid and sodium dihydrogen phosphate solution and used.

[0136] The molar ratio of iron element in the sulfuric acid slag to sodium sulfite, phosphoric acid, and sodium dihydrogen phosphate is 1:0.4:0.3:1.75, the concentration of the sodium sulfite solution is 2.5 mol / L, and the sum of the molar concentrations of the mixed solution of phosphoric acid and sodium dihydrogen phosphate is 2 mol / L.

[0137] (5) The third filtration residue is calcined in a rotary kiln at a calcination temperature of 700°C and a calcination time of 2 hours, and the waste gas generated from the calcination is absorbed by a sodium hydroxide solution and leached back into sulfuric acid slag; after calcining the third filtration residue, sulfuric acid is added to dissolve it, and cobalt and copper are extracted and separated using a P204 extraction solvent; the obtained cobalt-copper solution is concentrated and crystallized to obtain crude copper sulfate and crude cobalt sulfate.

[0138] (6)~(7) are identical to Example 1.

[0139] [Comparative Example 1]

[0140] In the method for producing iron phosphate provided in this comparative example, the only difference compared to Example 1 is that the pressure of the leaching reaction is 0.1 MPa and the leaching rate of iron is 83%.

[0141] [Comparative Example 2]

[0142] In the method for producing iron phosphate provided in this comparative example, the only difference compared with Example 1 is that the pH of the reaction system of the leaching reaction is 1, and detailed information on the obtained first filter residue is shown in Table 4.

[0143]

[0144] [Comparative Example 3]

[0145] In the method for producing iron phosphate provided in this comparative example, the only difference compared to Example 1 is that the leaching reaction time is 0.5h and the iron leaching rate is 81%.

[0146] As can be seen from Example 1, Comparative Example 1, and Comparative Example 3, in order to secure the leaching effect of iron, the pressure and time of the leaching reaction must be within a certain range.

[0147] As can be seen from Example 1 and Comparative Example 2, the leaching rate of other impurities increases significantly at low pH, so many impurities are introduced into the iron solution and affect the leaching effect of iron; therefore, in order to ensure the leaching purity of iron, the pH must be within a certain range.

[0148] Although the present invention has been described in detail above through specific embodiments, it should be noted that each of the above embodiments is intended to explain the technical means of the present invention and is not intended to limit the present invention. Those skilled in the art may modify the technical means described in the above embodiments or equivalently substitute some or all of the technical features without departing from the spirit of the present invention. Since the technical means resulting from such modification or substitution do not essentially depart from the technical scope of the various embodiments of the present invention, it is obvious that all such modifications or substitutions that do not depart from the spirit of the present invention are included within the claims of the present invention.

[0149] The above description is merely a preferred embodiment of the present invention, and those skilled in the art may make various modifications and variations without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention.

Claims

Claim 1 A method for producing iron phosphate, comprising: a step of obtaining a first mixture by uniformly mixing sulfuric acid slag and sulfite with water; a step of performing a leaching reaction by adding phosphoric acid and a buffer to the first mixture; a step of obtaining a first filtrate and a first filtrate residue by performing a first solid-liquid separation on the slurry obtained from the leaching reaction; a step of performing a first stirring reaction by introducing air into the first filtrate; a step of obtaining a second filtrate and a second filtrate residue by performing a second solid-liquid separation on the slurry obtained from the first stirring reaction; and a step of obtaining iron phosphate by calcining the second filtrate residue, wherein the pressure of the leaching reaction is 0.25 to 0.5 MPa; the time of the leaching reaction is 1 to 2 hours; the pH of the reaction system of the leaching reaction is 1.5 to 3; and the buffer comprises one or more of sodium dihydrogen phosphate and disodium hydrogen phosphate. Claim 2 In claim 1, the condition that the particle size of the sulfuric acid slag is 80 to 120 mesh; the condition that the molar ratio of the iron element in the sulfuric acid slag to the sulfite, the phosphoric acid, and the buffer is 1:(0.35~0.4):(0.25~0.3):(1.7~1.75); the condition that the phosphoric acid and the buffer are added to the first mixing system within 15 to 30 minutes; and the ratio of the hourly air input to the first filtrate to the ferrous ions in the first filtrate is (8~12) m 3 A method for producing iron phosphate characterized by satisfying at least one of the conditions of (28~32) mol. Claim 3 A method for producing iron phosphate according to claim 1, characterized in that at least one of the following conditions is satisfied: the temperature of the leaching reaction is 130 to 170°C; and the leaching reaction is performed under stirring conditions. Claim 4 A method for producing iron phosphate according to claim 1, characterized by satisfying at least one of the following conditions: a condition of heating the first filtrate to 40 to 60°C under stirring conditions before introducing air into the first filtrate; and a condition in which the first stirring reaction includes stirring the first filtrate into which air has been introduced until the iron element content of the supernatant becomes 0.5 g / L or less, and then continuing to stir for 30 to 60 minutes after heating the first filtrate to 90 to 95°C. Claim 5 A method for producing iron phosphate according to claim 1, further comprising a washing and drying step before calcining the second filtration residue, wherein at least one of the following conditions is satisfied: a condition in which the washing water temperature of the washing is 40 to 50°C; a condition in which the washing is performed until the pH of the washing solution exceeds 4.5; and a condition in which the moisture content of the second filtration residue after drying is less than 0.5%. Claim 6 A method for producing iron phosphate according to claim 1, characterized by satisfying at least one of the conditions of calcining the second filtration residue at a temperature of 650 to 680°C and calcining the second filtration residue for 60 to 90 minutes. Claim 7 A method for producing iron phosphate according to claim 1, further comprising the step of introducing the gas generated by the leaching reaction into a sodium hydroxide solution to obtain sodium sulfite after the leaching reaction is completed. Claim 8 A method for manufacturing iron phosphate according to claim 1, further comprising the steps of: cooling and performing a third solid-liquid separation on the second filtrate to obtain sodium sulfate crystals and a mother liquor; adding sodium sulfide to the mother liquor to obtain a third filtrate and a third filtrate residue; adjusting the pH of the third filtrate to 9-10 and performing a fourth solid-liquid separation to obtain a fourth filtrate and a fourth filtrate residue; calcining the third filtrate residue and dissolving the calcined third filtrate residue with sulfuric acid to obtain a second mixed system; and extracting, concentrating, and crystallizing the second mixed system to obtain crude copper sulfate and crude cobalt sulfate, wherein at least one of the following conditions is satisfied: a condition in which the temperature of the second filtrate after cooling is 5-10°C; a condition in which the third filtrate residue is calcined at a temperature of 500-700°C; and a condition in which the third filtrate residue is calcined for 2-4 hours. Claim 9 A method for manufacturing iron phosphate according to claim 1, further comprising the steps of: adding aqua regia to the first filter residue obtained by flotation separation and concentration to obtain a third mixture; performing a fifth solid-liquid separation on the third mixture to obtain a fifth filtrate; adding sodium chloride to the fifth filtrate and then performing a sixth solid-liquid separation to obtain silver chloride and a sixth filtrate; and adding iron powder to the sixth filtrate to obtain crude gold powder. Claim 10 A method for manufacturing lithium iron phosphate, characterized by comprising: a step of adding iron phosphate produced by a method for manufacturing iron phosphate according to any one of claims 1 to 9 to a lithium source, a carbon source, and a dopant, then adding purified water to form a slurry, and then spray-drying to obtain a spray-dried product; and a step of calcining the spray-dried product in an inert atmosphere to obtain lithium iron phosphate.

Images