A method for preparing ferric phosphate dihydrate using hot furnace rolling slag and its application

Abstract

This invention discloses a method for preparing ferric phosphate dihydrate from hot-rolled steel slag and its application, belonging to the field of solid waste recycling technology. Using hot-rolled steel slag as raw material, the iron element is leached out under the action of sulfuric acid. Then, iron powder is used to completely reduce the iron to ferrous iron (Fe2+). Ammonia water is used to adjust the pH and remove impurities. Then, under the action of an oxidant, the ferrous iron is oxidized to ferric iron (Fe3+), which reacts with ammonium dihydrogen phosphate to precipitate ferric phosphate, obtaining an intermediate ferric phosphate slurry. After solid-liquid separation, washing, and aging, followed by further solid-liquid separation, washing, and drying, battery-grade ferric phosphate dihydrate is finally obtained. The method provided by this invention realizes the resource utilization of hot-rolled steel slag, and the process is simple, convenient to operate, and has low production costs. The product has high purity, strong batch stability, and is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of solid waste recycling technology, and in particular to a method for preparing ferric phosphate dihydrate using hot furnace rolling slag and its application. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in passenger cars, buses, logistics vehicles, and low-speed electric vehicles due to their advantages such as good safety and low cost. Furthermore, LFP batteries possess a series of unique advantages, including high operating voltage, high energy density, long cycle life, low self-discharge rate, no memory effect, and environmental friendliness. They are suitable for large-scale energy storage and have promising applications in areas such as safe grid connection of renewable energy power plants, grid peak shaving, distributed power stations, UPS power supplies, and emergency power systems.

[0003] Currently, the preparation methods for lithium iron phosphate (LFP) batteries are mainly divided into solid-phase and liquid-phase methods, with the high-temperature solid-phase reaction method being the most commonly used. Common solid-phase methods include the ferrous oxalate process, the iron phosphate process, and the iron oxide red process. Among these, the ferrous oxalate process is the most mainstream production route, as it is simple but difficult to industrialize; however, controlling the morphology of ferrous oxalate raw materials is very difficult, resulting in poor processing performance of the finished LFP batteries. LFP batteries prepared via the iron phosphate process have better performance stability; however, iron phosphate accounts for more than 50% of the raw material cost in this process, resulting in a high price per ton, which is detrimental to enterprise development. Therefore, reducing the raw material cost of iron phosphate is crucial to ensuring that the superior electrical performance of batteries prepared via the iron phosphate process matches their market price.

[0004] Since most of the solid waste generated by metallurgical enterprises contains abundant iron (Fe) resources, the existing technology utilizes this Fe resource for regeneration and processing, using it as a raw material for synthesizing lithium iron phosphate. This not only solves the pressing solid waste treatment problem for steel companies but also significantly reduces the production cost of lithium iron phosphate at the source, resulting in significant social and economic benefits. For example, in patent application number CN202210835876.2, entitled "Method for Preparing Lithium Iron Phosphate, the Cathode Material for Lithium Batteries, from Iron-Rich Solid Waste in the Metallurgical Industry," iron-containing solid waste is regenerated to obtain ferrous oxalate. Ferrous oxalate is then used as a raw material to produce lithium iron phosphate batteries using the ferrous oxalate process route.

[0005] In the aforementioned patent, the solid waste resources undergoing recycling treatment contain Fe as Fe 3+ Fe 2+While elemental Fe exists, hot rolling processes generate a large amount of byproducts—hot furnace slag. Its main component is Fe3O4, and it also contains small amounts of impurities such as Al, Co, Cr, Cu, Mn, Ni, Ti, Zn, and Mg. Therefore, considering the raw material requirements for lithium iron phosphate batteries, how to achieve the resource utilization of hot furnace slag is a technical problem that needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing ferric phosphate dihydrate using hot furnace rolling slag and its application. This invention uses hot furnace rolling slag and ammonium dihydrogen phosphate solution as raw materials, and can ultimately prepare battery-grade ferric phosphate dihydrate, realizing the resource utilization of hot furnace rolling slag.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing ferric phosphate dihydrate using hot furnace rolling slag, comprising the following steps:

[0008] (1) Hot-rolled furnace slag is mixed with sulfuric acid solution, and after acid leaching for a preset time, solid-liquid separation is performed to obtain acid leaching solution;

[0009] (2) Mix the acid leaching solution from step (1) with a predetermined amount of iron powder to carry out a reduction reaction, and then separate the solid and liquid to obtain a reduced solution;

[0010] (3) Adjust the pH of the reducing solution in step (2) with alkaline solution to carry out the impurity removal reaction, and then separate the solid and liquid to obtain ferrous solution;

[0011] (4) Adjust the pH of the ferrous solution in step (3) with an acidic solution, then mix the adjusted ferrous solution, ammonium dihydrogen phosphate and hydrogen peroxide to carry out an oxidation reaction to obtain ferric phosphate intermediate slurry;

[0012] (5) The intermediate ferric phosphate slurry in step (4) is subjected to solid-liquid separation, and the resulting solid material is washed to obtain crude ferric phosphate.

[0013] (6) The crude iron phosphate, water and phosphoric acid from step (5) are mixed and aged to obtain aged slurry;

[0014] (7) The aged slurry in step (6) is subjected to solid-liquid separation, and the resulting solid material is washed and dried in sequence to obtain battery-grade iron phosphate dihydrate.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] This invention uses hot-rolled furnace steel slag as raw material and designs a method for recycling such solid waste based on the characteristics of the solid waste content in hot-rolled furnace steel slag, ensuring that the recycled iron phosphate dihydrate can meet the battery-grade usage standards.

[0017] This invention first uses sulfuric acid to leach iron, then uses a reducing agent to reduce all iron to ferrous iron (Fe2+), and removes impurities by adjusting the pH of the system. Then, under the action of an oxidizing agent, ferrous iron is oxidized to ferric iron (Fe3+), and ammonium dihydrogen phosphate is added to precipitate ferric phosphate, resulting in an intermediate ferric phosphate slurry. After solid-liquid separation, washing, aging, further solid-liquid separation, further washing, and drying, battery-grade ferric phosphate dihydrate is finally obtained.

[0018] The method provided by this invention realizes the resource utilization of hot-rolled furnace steel slag, and at the same time obtains structurally stable and inexpensive iron phosphate dihydrate product, thereby reducing the cost of preparing lithium iron phosphate batteries using the iron phosphate process route, which is conducive to the development of lithium iron phosphate battery preparation using the iron phosphate process route and improves the performance stability of lithium iron phosphate batteries.

[0019] Meanwhile, the process of this invention is simple, easy to operate, and has low production costs; the product has high purity, strong batch stability, and is suitable for large-scale production.

[0020] Furthermore, in step (1): the mass of sulfuric acid is 120% in excess relative to the mass of hot-rolled furnace slag;

[0021] The sulfuric acid solution has a mass fraction of 50%.

[0022] The acid leaching process requires heat preservation and stirring, with a stirring speed of 400 rpm, a temperature of 90℃, and a stirring time of 120 min.

[0023] The pH of the acid leaching solution is -0.20 to 0.00, and the mass content of iron is 2% to 3.2%.

[0024] Furthermore, in step (2):

[0025] During the reduction reaction, the mixture was kept at a constant temperature and stirred for 30 minutes at a stirring speed of 200 rpm and a temperature of 20-40℃.

[0026] The molar ratio of iron in the acid leaching solution to iron in the iron powder is 1:(0.2-0.3);

[0027] The pH of the reducing solution is 0.44-0.48.

[0028] Furthermore, in step (3):

[0029] During the impurity removal reaction, a heat preservation and stirring treatment is carried out, wherein the stirring speed is 200 rpm, the temperature is 20-40℃, and the time is 10-30 min;

[0030] The alkaline solution includes ammonia water with a molar concentration of 5-14 mol / L, which is used to adjust the pH of the reducing solution to 5.50.

[0031] Furthermore, in step (3):

[0032] The ferrous solution contains <80 ppm Al, <10 ppm Co, <10 ppm Cr, <10 ppm Cu, <80 ppm Mn, <10 ppm Ni, <80 ppm Ti, <20 ppm Zn, and <80 ppm Mg.

[0033] Furthermore, in step (4):

[0034] The oxidation reaction was subjected to a heat-keeping and stirring process, with a stirring speed of 200 rpm, a temperature of 60°C, and a time of 10 min.

[0035] When the adjusted ferrous solution, ammonium dihydrogen phosphate, and hydrogen peroxide are mixed:

[0036] Hydrogen peroxide and ammonium dihydrogen phosphate are added to the ferrous solution. The hydrogen peroxide is added at a time of 50-60 minutes, and the ammonium dihydrogen phosphate is added at a time of 20-30 minutes. The ammonium dihydrogen phosphate is added 50-60 minutes later than the hydrogen peroxide.

[0037] Furthermore, in step (4):

[0038] The acidic solution includes a dilute sulfuric acid solution, wherein the mass fraction of the dilute sulfuric acid solution is 5%-50%.

[0039] Adjust the pH of the ferrous solution to 2.00 using dilute sulfuric acid solution;

[0040] The molar ratio of iron to phosphorus in the adjusted ferrous solution was 1:(1.03-1.10), and the mass fraction of ammonium dihydrogen phosphate was 13.83%.

[0041] The molar ratio of hydrogen peroxide to iron in the adjusted ferrous solution is 1.5:1, and the mass fraction of hydrogen peroxide is 10-15%.

[0042] Furthermore, in step (6):

[0043] The mass fraction of phosphoric acid is 85%, and the amount of phosphoric acid added is such that the molar ratio of iron to phosphorus in the system obtained by mixing crude iron phosphate, water and phosphoric acid is 1:(1.00-1.15).

[0044] Furthermore, in step (7):

[0045] The drying temperature is 80-100℃, and the moisture content of battery-grade iron phosphate dihydrate is ≤10wt%.

[0046] On the other hand, the application of the iron phosphate dihydrate in the production process of lithium iron phosphate batteries is discussed in this application.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The iron phosphate dihydrate prepared in this application has the same spectrum as that in the standard PDF card (77-0094), exhibiting sharp diffraction peaks and distinct characteristic peaks. This indicates that the material has a definite crystal structure and can be used as a raw material to prepare lithium iron phosphate batteries using the iron phosphate process route, resulting in lithium iron phosphate batteries with better stability. Furthermore, since the iron phosphate dihydrate is prepared from recycled solid waste, the raw material cost of iron phosphate is reduced, promoting a better match between the superior electrical performance and market price of batteries prepared using the iron phosphate process route, thereby obtaining low-cost and more stable lithium iron phosphate batteries. Attached Figure Description

[0049] Figure 1 This is a SEM image of the battery-grade iron phosphate dihydrate prepared in Example 1 of the present invention;

[0050] Figure 2 The image shows the XRD pattern of the battery-grade iron phosphate dihydrate prepared in Example 1 of this invention. Detailed Implementation

[0051] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0052] The main component of the hot-rolled furnace slag in this application is Fe3O4, and it also contains impurities such as about 590 ppm Al, 50 ppm Co, 320 ppm Cr, 80 ppm Cu, 3800 ppm Mn, 900 ppm Ni, 180 ppm Ti, 80 ppm Zn, and 150 ppm Mg.

[0053] Based on the compositional characteristics of hot-rolled furnace slag described above, this invention provides a method for preparing ferric phosphate dihydrate using hot-rolled furnace slag, comprising the following steps:

[0054] (1) Hot-rolled furnace slag is mixed with sulfuric acid and acid leaching is performed, followed by solid-liquid separation to obtain acid leaching solution;

[0055] (2) The acid leaching solution is mixed with iron powder and reduced by a reduction reaction. Then the solid and liquid are separated to obtain a reduced solution.

[0056] (3) Adjust the pH of the reducing solution with alkaline solution to carry out the impurity removal reaction, and then separate the solid and liquid to obtain a ferrous solution;

[0057] (4) Adjust the pH of the ferrous solution with an acidic solution, then mix the adjusted ferrous solution, ammonium dihydrogen phosphate and hydrogen peroxide to carry out an oxidation reaction to obtain ferric phosphate slurry;

[0058] (5) The ferric phosphate intermediate slurry is subjected to solid-liquid separation, and the resulting solid material is washed to obtain crude ferric phosphate.

[0059] (6) The crude iron phosphate, water and phosphoric acid are mixed and aged to obtain aged slurry;

[0060] (7) The aged slurry is subjected to solid-liquid separation, and the resulting solid material is washed and dried in sequence to obtain battery-grade iron phosphate dihydrate.

[0061] Based on the compositional characteristics of hot-rolled furnace slag, this invention, through the method in step (1), first mixes the hot-rolled furnace slag with sulfuric acid for acid leaching, then performs solid-liquid separation to obtain an acid leaching solution. Specifically, the pH value of the acid leaching solution is preferably -0.20-0.00, and the iron content in the acid leaching solution is preferably 2%-3.2%. In this invention, the acid leaching process requires heat preservation and stirring treatment, with the temperature preferably at 90℃, the stirring speed preferably at 400 rpm, and the acid leaching time preferably at 120 min. In this invention, a mechanical stirrer is specifically used to provide the stirring conditions. The solid-liquid separation method in this invention specifically employs vacuum filtration.

[0062] After obtaining the acid leaching solution, the present invention uses the method in step (2) to mix the acid leaching solution with iron powder to carry out a reduction reaction, and then separates the solid and liquid to obtain a reduced solution. In the present invention, the molar ratio of iron element in the acid leaching solution to iron element in the iron powder is 1:(0.2-0.3).

[0063] In this invention, the reduction reaction temperature is preferably 20-40℃, and the reduction reaction time is preferably 30 minutes. In this invention, the reduction reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 200 rpm; in the embodiments of this invention, a mechanical stirrer is specifically used to provide the stirring conditions. The solid-liquid separation method in this invention specifically employs vacuum filtration.

[0064] After obtaining the reducing solution, the present invention removes impurities from the iron in the reducing solution using the method in step (3). For this purpose, the present invention first adjusts the pH value using an alkaline solution, preferably ammonia water, with a molar concentration of 5-14 mol / L. The present invention uses ammonia water to adjust the pH value of the reducing solution to carry out the impurity removal reaction, and then performs solid-liquid separation to obtain a ferrous solution.

[0065] In this invention, the mixing method of the reducing solution and ammonia water includes: pumping ammonia water into the reducing solution; before the pH of the reducing solution and ammonia water system reaches 3.00, the molar concentration of ammonia water is preferably 10-14 mol / L; after the pH of the reducing solution and ammonia water system reaches 3.00, the molar concentration of ammonia water is preferably 5-10 mol / L.

[0066] In this invention, the preferred temperature for the impurity removal reaction is 20-40°C; the preferred reaction time is 10-30 min; specifically, the reaction time refers to the reaction time after the pH of the reducing solution and ammonia system reaches 5.50. In this invention, the mixing of the reducing solution and ammonia, as well as the impurity removal reaction, are preferably carried out under stirring conditions, with the stirring speed preferably being 200 rpm; in embodiments of this invention, a mechanical stirrer is specifically used to provide the stirring conditions. The solid-liquid separation method in this invention specifically employs vacuum filtration.

[0067] After obtaining the ferrous solution, the present invention adjusts the pH value of the ferrous solution with an acidic solution using the method in step (4); specifically, the acidic solution is a dilute sulfuric acid solution, and the pH of the ferrous solution is preferably adjusted to 2.00. In the present invention, the mass fraction of the dilute sulfuric acid is preferably 5%-50%.

[0068] In this invention, the mixing method of the ferrous solution, ammonium dihydrogen phosphate, and hydrogen peroxide includes: adding hydrogen peroxide and ammonium dihydrogen phosphate to the ferrous solution, wherein the hydrogen peroxide is preferably added at a time of 50-60 minutes; the ammonium dihydrogen phosphate is preferably added at a time of 20-30 minutes; and the addition of ammonium dihydrogen phosphate is preferably started 50-60 minutes later than the addition of hydrogen peroxide. Specifically, ammonium dihydrogen phosphate is added only after the hydrogen peroxide has been added.

[0069] In this invention, the preferred temperature for the oxidation reaction is 60°C; the preferred reaction time is 10 minutes; specifically, the oxidation reaction time refers to the reaction time after hydrogen peroxide and ammonium dihydrogen phosphate are added. In this invention, the addition of hydrogen peroxide and ammonium dihydrogen phosphate, as well as the oxidation reaction, are preferably carried out under stirring conditions, with the stirring speed preferably being 200 rpm; in embodiments of this invention, a mechanical stirrer is specifically used to provide the stirring conditions. In this invention, the ferrous solution, ammonium dihydrogen phosphate, and hydrogen peroxide precipitate ferric phosphate to form an intermediate ferric phosphate slurry.

[0070] After obtaining the intermediate ferric phosphate slurry, the present invention will perform solid-liquid separation on the intermediate ferric phosphate slurry using the method in step (5), and wash the obtained solid material to obtain crude ferric phosphate. The solid-liquid separation method described in the present invention specifically adopts vacuum filtration.

[0071] In this invention, the washing is preferably a re-washing process; the re-washing is preferably performed three times, sequentially referred to as a first-stage re-wash, a second-stage re-wash, and a third-stage re-wash. Specifically, the ferric phosphate intermediate slurry is vacuum filtered to obtain filter residue and a first-stage mother liquor, wherein the moisture content of the filter residue is preferably ≤70%. The filter residue is then subjected to a first-stage re-wash, followed by a first vacuum filtration to obtain a first-stage washed filter residue and a first-stage washed liquid, wherein the moisture content of the first-stage washed filter residue is preferably ≤70%. The first-stage washed filter residue is then subjected to a second-stage re-wash, followed by a second vacuum filtration to obtain a second-stage washed filter residue and a second-stage washed liquid, wherein the moisture content of the second-stage washed filter residue is preferably ≤70%. The filter residue is then subjected to a third-stage re-wash, followed by a third vacuum filtration to obtain a third-stage washed filter residue and a third-stage washed liquid, wherein the moisture content of the third-stage washed filter residue is preferably ≤70%. The third-stage washed filter residue is the crude ferric phosphate product.

[0072] In this invention, the washing solution used in the first stage of re-sizing and washing, the second stage of re-sizing and washing, and the third stage of re-sizing is preferably water, more preferably deionized water; the mass ratio of water (or deionized water) to filter residue used in the first stage of re-sizing and washing, the second stage of re-sizing and washing, and the third stage of re-sizing is preferably (3.0-4.0):1.

[0073] After obtaining crude iron phosphate, the present invention will use the method in step (6) to mix the crude iron phosphate, water and phosphoric acid and then age it to obtain aged slurry.

[0074] In this invention, the mass fraction of phosphoric acid is preferably 85%, specifically, the phosphoric acid is industrial-grade phosphoric acid with a mass fraction of 85%, and the water is preferably deionized water. In this invention, the amount of phosphoric acid added is preferably such that the molar ratio of iron to phosphorus in the system obtained after mixing crude ferric phosphate, water, and phosphoric acid is 1:(1.00-1.15).

[0075] In this invention, the aging temperature is preferably 95°C; the aging time is preferably 4 hours; the aging is preferably carried out under stirring conditions, and the stirring speed is preferably 200 rpm. In embodiments of this invention, a mechanical stirrer is specifically used as the stirrer to provide the stirring conditions.

[0076] After obtaining the aged slurry, the present invention will use the method in step (6) to perform solid-liquid separation on the aged slurry, and wash and dry the obtained solid material in sequence to obtain battery-grade iron phosphate dihydrate.

[0077] The solid-liquid separation method described in this invention specifically employs vacuum filtration.

[0078] In this invention, the washing is preferably a re-washing process; the re-washing is preferably performed three times, sequentially referred to as two-stage re-washing-first-stage, two-stage re-washing-second-stage, and two-stage re-washing-third-stage. Specifically, the ferric phosphate intermediate slurry is vacuum filtered to obtain filter residue and a first-stage mother liquor, wherein the moisture content of the filter residue is preferably ≤70%; the filter residue is subjected to a two-stage re-washing-first-stage, followed by a first vacuum filtration to obtain a two-stage washing-first-stage filter residue and a two-stage washing-first-stage liquid, wherein the moisture content of the two-stage washing-first-stage filter residue is preferably ≤70%; the two-stage washing-first-stage filter residue is subjected to a two-stage re-washing-second-stage, followed by a second vacuum filtration to obtain a two-stage washing-second-stage filter residue and a two-stage washing-second-stage liquid, wherein the moisture content of the two-stage washing-second-stage filter residue is preferably ≤70%; the filter residue is subjected to a two-stage re-washing-third-stage, followed by a third vacuum filtration to obtain a two-stage washing-third-stage filter residue and a two-stage washing-third-stage liquid, wherein the moisture content of the two-stage washing-third-stage filter residue is preferably ≤70%, and the two-stage washing-third-stage filter residue is the crude ferric phosphate product.

[0079] In this invention, the washing solution used in the second stage resizing and washing, the second stage resizing and washing, and the third stage resizing is preferably water, more preferably deionized water; the mass ratio of water (or deionized water) to filter residue used in the second stage resizing and washing, the second stage resizing and washing, and the third stage resizing is preferably (3.0-4.0):1.

[0080] In this invention, the drying temperature is preferably 80-100℃; the drying time is preferably based on ensuring that the moisture content of the dried material is ≤10%, more preferably 2%-8%.

[0081] Example 1

[0082] A method for preparing ferric phosphate dihydrate using hot-rolled furnace slag, the specific steps of which are as follows:

[0083] (1) Take 16g of hot-rolled furnace slag, add 70.4g of sulfuric acid with a mass fraction of 50%, and perform acid leaching reaction for 120min under the conditions of stirring speed of 400rpm and temperature of 90℃. Then, vacuum filter to obtain acid leaching solution.

[0084] (2) The mass of the sulfuric acid is 120% excess relative to the mass of the hot-rolled furnace slag, the pH of the acid leaching solution is -0.06, and the iron content in the acid leaching solution is 3%.

[0085] (3) The acid leaching solution was mixed with 3.32g of iron powder, and the oxidation-reduction reaction was carried out for 30min under the conditions of stirring speed of 200rpm and temperature of 40℃. Then the solution was vacuum filtered to obtain the reduced solution.

[0086] (4) The pH of the reducing solution is 0.45;

[0087] (5) First, adjust the pH of the reducing solution to 3.30 with ammonia water with a molar concentration of 14 mol / L, and then adjust the pH of the reducing solution to 5.50 with ammonia water with a molar concentration of 7 mol / L. After the pH of the reducing solution reaches 5.50, react for 30 min at a stirring rate of 200 rpm and a temperature of 40 °C, and then filter under vacuum to obtain a ferrous solution.

[0088] (6) The pH of the ferrous solution is 5.35, the iron content in the ferrous solution is 5.5%, the Al content in the ferrous solution is 14.27 ppm, the Co content is 1.53 ppm, the Cr content is 6.64 ppm, the Cu content is 2.27 ppm, the Mn content is 63.23 ppm, the Ti content is 4.43 ppm, the Zn content is 12.30 ppm, and the Mg content is 3.20 ppm;

[0089] (7) Adjust the pH of the ferrous solution to 2.00 with 5% sulfuric acid by mass, and preheat the resulting ferrous solution to 60°C to obtain a preheated ferrous solution; add 60g of 11.82% hydrogen peroxide to the preheated ferrous solution at a uniform rate for 60min; after the hydrogen peroxide is added, add 127.2g of 13.83% ammonium dihydrogen phosphate solution to the resulting system at a uniform rate for 31.8min; after the hydrogen peroxide and ammonium dihydrogen phosphate solution are added, continue the reaction for 10min at 200rpm and 60°C to obtain an intermediate ferric phosphate slurry;

[0090] (8) The molar ratio of hydrogen peroxide to iron in the ferrous solution is 1.5:1; the molar ratio of iron in the ferrous solution to phosphorus in ammonium dihydrogen phosphate is 1:1.03.

[0091] (9) The intermediate ferric phosphate slurry is vacuum filtered to obtain a mother liquor and a filter cake with a water content of 70%; the first-washed filter cake is subjected to a second washing and a second vacuum filtration to obtain a second washing solution and a second-washed filter cake with a water content of 70%; the second-washed filter cake is subjected to a third washing and a third vacuum filtration to obtain a third washing solution and a third-washed filter cake with a water content of 70%; the third-washed filter cake is crude ferric phosphate.

[0092] (10) The mass ratio of deionized water to filter residue is 3.0:1 for the first stage of re-slurry washing, the second stage of re-slurry washing, and the third stage of re-slurry washing.

[0093] (11) The crude ferric phosphate product was mixed with 180g of deionized boiling water and 1.92g of phosphoric acid with a mass fraction of 85% by hand with a stirring paddle and then aged at 200rpm and 95℃ for 4h to obtain aged slurry.

[0094] (12) The molar ratio of iron to phosphorus in crude iron phosphate is 1:0.12;

[0095] (13) The aged slurry was vacuum filtered to obtain a second-stage mother liquor and an aged filter cake with a water content of 70%; the aged filter cake was subjected to a second-stage re-slurry and first-washing with 200g of deionized boiling water as washing liquid, and then vacuum filtered for the first time to obtain a second-stage first-washing liquid and a second-stage first-washing filter cake with a water content of 70%; the second-stage first-washing filter cake was subjected to a second-stage re-slurry and second-washing with 200g of deionized boiling water as washing liquid, and then vacuum filtered for the second time to obtain a second-stage second-washing liquid and a second-stage second-washing filter cake with a water content of 70%; the second-stage second-washing filter cake was subjected to a second-stage re-slurry and third-washing with 200g of deionized boiling water as washing liquid, and then vacuum filtered for the third time to obtain a second-stage third-washing liquid and a second-stage third-washing filter cake with a water content of 70%; the second-stage third-washing filter cake was dried at 80°C for 8 hours to obtain battery-grade iron phosphate dihydrate.

[0096] Testing revealed that the battery-grade iron phosphate dihydrate prepared in Example 1 contained 29.09% Fe and 16.62% by mass, with an iron-to-phosphorus ratio of 0.971. The iron-to-phosphorus ratio in the iron phosphate dihydrate is controllable, allowing it to meet the requirements for use as a raw material in the production process of lithium iron phosphate batteries.

[0097] Example 2

[0098] A method for preparing ferric phosphate dihydrate using hot-rolled furnace slag, the specific steps of which are as follows:

[0099] The specific steps for preparing battery-grade iron phosphate dihydrate are as follows:

[0100] (1) Take 16g of hot-rolled furnace slag, add 70.4g of sulfuric acid with a mass fraction of 50%, and perform acid leaching reaction for 120min under the conditions of stirring speed of 400rpm and temperature of 90℃. Then, vacuum filter to obtain acid leaching solution.

[0101] (2) The mass of the sulfuric acid is 120% excess relative to the mass of the hot-rolled furnace slag, the pH of the acid leaching solution is -0.07, and the iron content in the acid leaching solution is 3.2%;

[0102] (3) The acid leaching solution was mixed with 3.32g of iron powder, and the oxidation-reduction reaction was carried out for 30min under the conditions of stirring speed of 200rpm and temperature of 40℃. Then the solution was vacuum filtered to obtain the reduced solution.

[0103] (4) The pH of the reducing solution is 0.47;

[0104] (5) First, adjust the pH of the reducing solution to 3.30 with ammonia water with a molar concentration of 14 mol / L, and then adjust the pH of the reducing solution to 5.50 with ammonia water with a molar concentration of 7 mol / L. After the pH of the reducing solution reaches 5.50, react for 30 min at a stirring rate of 200 rpm and a temperature of 40 °C, and then filter under vacuum to obtain a ferrous solution.

[0105] (6) The pH of the ferrous solution is 5.39, the iron content in the ferrous solution is 5.5%, the Al content in the ferrous solution is 14.37 ppm, the Co content is 0.89 ppm, the Cr content is 7.58 ppm, the Cu content is 3.31 ppm, the Mn content is 53.48 ppm, the Ti content is 3.28 ppm, the Zn content is 14.58 ppm, and the Mg content is 3.28 ppm;

[0106] (7) Adjust the pH of the ferrous solution to 2.00 with 5% sulfuric acid by mass, and preheat the resulting ferrous solution to 60°C to obtain a preheated ferrous solution; add 60g of 11.82% hydrogen peroxide to the preheated ferrous solution at a uniform rate for 60min; after the hydrogen peroxide is added, add 133.5g of 13.83% ammonium dihydrogen phosphate solution to the resulting system at a uniform rate for 33.4min; after the hydrogen peroxide and ammonium dihydrogen phosphate solution are added, continue the reaction for 10min at 200rpm and 60°C to obtain an intermediate ferric phosphate slurry;

[0107] (8) The molar ratio of hydrogen peroxide to iron in the ferrous solution is 1.5:1; the molar ratio of iron in the ferrous solution to phosphorus in ammonium dihydrogen phosphate is 1:1.05;

[0108] (9) The intermediate ferric phosphate slurry is vacuum filtered to obtain a mother liquor and a filter cake with a water content of 70%; the first-washed filter cake is subjected to a second washing and a second vacuum filtration to obtain a second washing solution and a second-washed filter cake with a water content of 70%; the second-washed filter cake is subjected to a third washing and a third vacuum filtration to obtain a third washing solution and a third-washed filter cake with a water content of 70%; the third-washed filter cake is crude ferric phosphate.

[0109] (10) The mass ratio of deionized water to filter residue is 3.0:1 for the first stage of re-slurry washing, the second stage of re-slurry washing, and the third stage of re-slurry washing.

[0110] (11) The crude ferric phosphate product was mixed with 180g of deionized boiling water and 2.01g of phosphoric acid with a mass fraction of 85% by hand with a stirring paddle and then aged at 200rpm and 95℃ for 4h to obtain aged slurry.

[0111] (12) The molar ratio of iron to phosphorus in crude iron phosphate is 1:0.12;

[0112] (13) The aged slurry was vacuum filtered to obtain a second-stage mother liquor and an aged filter cake with a water content of 70%; the aged filter cake was subjected to a second-stage re-slurry and first-washing with 200g of deionized boiling water as washing liquid, and then vacuum filtered for the first time to obtain a second-stage first-washing liquid and a second-stage first-washing filter cake with a water content of 70%; the second-stage first-washing filter cake was subjected to a second-stage re-slurry and second-washing with 200g of deionized boiling water as washing liquid, and then vacuum filtered for the second time to obtain a second-stage second-washing liquid and a second-stage second-washing filter cake with a water content of 70%; the second-stage second-washing filter cake was subjected to a second-stage re-slurry and third-washing with 200g of deionized boiling water as washing liquid, and then vacuum filtered for the third time to obtain a second-stage third-washing liquid and a second-stage third-washing filter cake with a water content of 70%; the second-stage third-washing filter cake was dried at 80°C for 8 hours to obtain battery-grade iron phosphate dihydrate.

[0113] Testing revealed that the battery-grade iron phosphate dihydrate prepared in this embodiment contained 28.55% Fe by mass, 16.42% P by mass, and an iron-to-phosphorus ratio of 0.964.

[0114] To further verify the performance of the ferric phosphate dihydrate prepared in this application, chromatographic analysis was performed using the ferric phosphate dihydrate prepared in Example 1 as an example, and the results were obtained. Figure 1 , Figure 2 The results are shown.

[0115] Figure 1 This is a SEM image of the battery-grade iron phosphate dihydrate prepared in Example 1. Figure 1 It can be seen that the battery-grade iron phosphate dihydrate particles prepared in Example 1 are uniformly distributed, but some agglomeration occurs. Under a larger magnification, it can be seen that many small particles of hundreds of nanometers aggregate together to form agglomerates. The particle size distribution is uniform, and the surface is composed of small, plate-like particles stacked together to form large particles with a particle size of about 1-2 μm.

[0116] In the process of lithium iron phosphate battery manufacturing:

[0117] The uniform particle distribution of iron phosphate dihydrate allows for a more complete and stable reaction, which is conducive to the formation of lithium iron phosphate materials with better structure and performance. This improves the battery's charge and discharge efficiency, cycle life, and safety, allowing the battery to maintain good working condition and extend its service life under different environments.

[0118] The uniform particle distribution of ferric phosphate dihydrate avoids problems such as filtration and washing difficulties caused by particle agglomeration or uneven particle size, making solid-liquid separation and drying operations in the production process smoother, improving production efficiency, reducing production costs, shortening the production cycle, and increasing production capacity.

[0119] Meanwhile, the uniform particle distribution of ferric phosphate dihydrate ensures that the physical and chemical properties of each batch of products are similar, making the product quality more stable and uniform, meeting the stringent quality requirements of different application fields, improving product reliability and consistency, and facilitating large-scale production and application.

[0120] Furthermore, the uniformly distributed ferric phosphate dihydrate allows for better mixing with other substances during subsequent processing, such as mixing with other materials and molding. This improves the fluidity and formability of the mixture, making the processing smoother and resulting in higher quality finished products.

[0121] Figure 2 The image shows the XRD pattern of the battery-grade iron phosphate dihydrate prepared in Example 1. Figure 2 It can be seen that the battery-grade iron phosphate dihydrate prepared in Example 1 has the same spectrum as the standard PDF card (77-0094), both having sharp diffraction peaks and obvious characteristic peaks, indicating that the material has a definite crystal structure. This shows that the iron phosphate dihydrate prepared in this application has stable chemical and physical properties, meeting the raw material requirements in the production process of lithium iron phosphate batteries.

[0122] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing iron phosphate dihydrate using hot mill slag, characterized by: The method comprises the following steps: (1) mixing hot-rolled furnace slag with a sulfuric acid solution, performing acid leaching treatment for a preset time, and then performing solid-liquid separation to obtain an acid leaching solution; (2) mixing the acid leaching solution obtained in step (1) with a preset amount of iron powder, performing a reduction reaction, and then performing solid-liquid separation to obtain a reduction solution; (3) adjusting the pH value of the reduction solution in step (2) by using an alkali solution, performing an impurity removal reaction, and then performing solid-liquid separation to obtain a ferrous solution; (4) adjusting the pH value of the ferrous solution in step (3) by using an acidic solution, mixing the adjusted ferrous solution, ammonium dihydrogen phosphate and hydrogen peroxide, and performing an oxidation reaction to obtain an intermediate iron phosphate slurry; (5) performing solid-liquid separation on the intermediate iron phosphate slurry in step (4), and washing the obtained solid material to obtain a crude iron phosphate product; (6) mixing the crude iron phosphate product in step (5), water and phosphoric acid, and then performing aging to obtain an aged slurry; (7) performing solid-liquid separation on the aged slurry in step (6), and then sequentially performing washing and drying on the obtained solid material to obtain a battery-grade iron phosphate dihydrate. In step (2), in the reduction reaction, heat preservation stirring treatment is performed, wherein the stirring speed is 200 rpm, the temperature is 20-40 DEG C, and the time is 30 min; the molar ratio of iron elements in the acid leaching solution to iron elements in the iron powder is 1:(0.2-0.3); and the pH value of the reduction solution is 0.44-0.

48. In step (1), the mass of the sulfuric acid is 120% more than the mass of the hot-rolled furnace slag; the mass fraction of the sulfuric acid solution is 50%; the acid leaching treatment needs to be heat preservation stirring treatment, wherein the stirring speed is 400 rpm, the temperature is 90 DEG C, and the stirring time is 120 min; the pH value of the acid leaching solution is-0.20-0.00, and the mass content of iron elements is 2%-3.2%. In step (3), the temperature of the impurity removal reaction is 20-40 DEG C, and the pH value of the reduction solution is adjusted to 5.50 by using the alkali solution. In step (4), the pH value of the ferrous solution is adjusted to 2.00 by using the acidic solution; the oxidation reaction is heat preservation stirring treatment, wherein the stirring speed is 200 rpm, the temperature is 60 DEG C, and the time is 10 min; when the adjusted ferrous solution, ammonium dihydrogen phosphate and hydrogen peroxide are mixed, the hydrogen peroxide and the ammonium dihydrogen phosphate are added to the ferrous solution, the hydrogen peroxide is added for 50-60 min, the ammonium dihydrogen phosphate is added for 20-30 min, and the ammonium dihydrogen phosphate is added 50-60 min later than the hydrogen peroxide; In step (6), the mass fraction of the phosphoric acid is 85%, and the addition amount of the phosphoric acid is such that the molar ratio of iron elements to phosphorus elements in the system obtained after the crude iron phosphate product, water and the phosphoric acid are mixed is 1:(1.00-1.15).

2. The method for preparing iron phosphate dihydrate using hot mill slag according to claim 1, characterized in that: In step (3), in the impurity removal reaction, heat preservation stirring treatment is performed, wherein the stirring speed is 200 rpm, and the time is 10-30 min; the alkali solution comprises ammonia water, and the molar concentration of the ammonia water is 5-14 mol / L. In step (3), 3. The method of claim 1, wherein the method is characterized by: ​ The ferrous solution contains <80 ppm of Al, <10 ppm of Co, <10 ppm of Cr, <10 ppm of Cu, <80 ppm of Mn, <10 ppm of Ni, <80 ppm of Ti, <20 ppm of Zn, and <80 ppm of Mg.

4. The method for preparing iron phosphate dihydrate using hot mill slag according to claim 3, characterized in that: In step (4), the acid solution comprises a dilute sulfuric acid solution with a mass fraction of 5%-50%; the molar ratio of iron in the adjusted ferrous solution to phosphorus in ammonium dihydrogen phosphate is 1:(1.03-1.10), and the mass fraction of ammonium dihydrogen phosphate is 13.83%; the molar ratio of hydrogen peroxide to iron in the adjusted ferrous solution is 1.5:1, and the mass fraction of hydrogen peroxide is 10-15%.

5. The method of claim 1, wherein the method of preparing iron phosphate dihydrate using hot mill slag is characterized by: In step (7), the drying temperature is 80-100°C, and the moisture content of the battery-grade iron phosphate dihydrate is ≤10 wt%.

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