CN113860278A - Method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as iron source - Google Patents
Method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as iron source Download PDFInfo
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Abstract
The invention provides a method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as an iron source, which comprises the following steps: carrying out acid leaching reaction on the red mud and sulfuric acid, and then carrying out solid-liquid separation to obtain a first solid and a first liquid; the adding amount of the sulfuric acid and the red mud is (3-6) by weight: 1; adding a heavy metal capture agent into the first liquid, and then carrying out solid-liquid separation to obtain a liquid without heavy metals; adding an oxidant into the liquid without the heavy metals for oxidation reaction to obtain a mixed solution, then adjusting the pH value to 3.5-5.5, and carrying out solid-liquid separation to obtain a second solid and a second liquid; adjusting the pH value of the second solid to 12 +/-0.5 after size mixing, and carrying out solid-liquid separation to obtain an iron hydroxide filter cake; adding water after washing and uniformly mixing to obtain slurry; adding phosphoric acid into the slurry to react, then performing filter pressing to obtain a ferric phosphate filter cake, and washing, drying and sintering to obtain the battery-grade nano anhydrous ferric phosphate. The method realizes resource utilization of the red mud.
Description
Technical Field
The invention relates to the technical field of preparation of battery-grade iron phosphate, and particularly relates to a method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as an iron source.
Background
The red mud is polluting waste residue discharged when aluminum oxide is extracted in the aluminum industry, and generally 1.0-2.0 tons of red mud are additionally generated when 1 ton of aluminum oxide is produced on average. China, as the 4 th alumina producing country in the world, discharges up to millions of tons of red mud every year. At present, the comprehensive utilization of red mud still belongs to a worldwide problem, and the conventional comprehensive utilization of red mud mainly comprises the steps of extracting valuable metals from red mud, preparing materials to produce cement, building bricks, mine cemented filling cementing materials, roadbed consolidation materials, high-performance concrete admixtures, Chemical Bonding Ceramics (CBC) composite materials, heat-insulating refractory materials, environment-friendly materials and the like. However, these studies are still in the laboratory stage and have not yet been industrialized. At present, with the rapid increase of the loading amount of lithium iron phosphate batteries, the demand of iron phosphate also increases explosively, and the demand of upstream iron resources also increases day by day. Because the red mud contains high-content iron resources, if the red mud can be processed to be used as an iron source of iron phosphate, the iron source path of the iron phosphate is enriched, and meanwhile, the high-value utilization of the red mud can be realized.
In the prior art, no report related to the preparation of battery-grade iron phosphate by taking the red mud of the high-iron Bayer process as an iron source exists, and how to develop a method for preparing battery-grade iron phosphate by taking the red mud of the high-iron Bayer process as the iron source provides a new way for high-value utilization of the huge stockpiling amount of solid wastes, and becomes a technical problem to be solved urgently.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a method for preparing battery-grade iron phosphate by using high-iron Bayer process red mud as an iron source, so that high-value resource utilization of the high-iron Bayer process red mud is realized, and the superfine nano iron phosphate is prepared and can be used for preparing a high-rate lithium iron phosphate cathode material.
The invention adopts the following technical scheme:
the invention provides a method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as an iron source, which comprises the following steps:
sulfuric acid and red mud are subjected to acid leaching reaction, and then solid-liquid separation is carried out to obtain a first solid and a first liquid; wherein the adding amount of the sulfuric acid and the red mud is (3-6) by weight: 1, the mass fraction of the sulfuric acid is 60-80%;
adding a heavy metal capture agent into the first liquid, and then carrying out solid-liquid separation to obtain a liquid without heavy metals; wherein, the addition amount of the heavy metal catching agent is added according to the total volume of the solution (0.02-0.04) g/L;
adding an oxidant into the liquid without the heavy metals for oxidation reaction to obtain a mixed solution;
adding a pH regulator into the mixed solution to regulate the pH of the mixed solution to 3.5-5.5, and then carrying out solid-liquid separation to obtain a second solid and a second liquid;
adding alkali liquor into the second solid to adjust the pH value to 12 +/-0.5, and then carrying out solid-liquid separation to obtain an iron hydroxide filter cake and a sodium metaaluminate filtrate;
washing the ferric hydroxide filter cake by adopting alkali liquor with the pH value of 12 +/-0.5 to obtain a washed ferric hydroxide filter cake;
adding water into the washed ferric hydroxide filter cake, and uniformly mixing to obtain slurry with the solid content of 10-15%;
adding the slurry into industrial-grade or battery-grade phosphoric acid for reaction, wherein the addition amount of the phosphoric acid is 15-20% of the stoichiometric excess; and then carrying out filter pressing, washing, drying and sintering to obtain the battery-grade nano anhydrous iron phosphate.
In the technical scheme, the adding amount of the sulfuric acid and the red mud is (3-6) by weight: 1; preferably, the adding amount of the sulfuric acid and the red mud is (4-5) by weight: 1, the mass fraction of the sulfuric acid is 65-75%.
And adjusting the pH value of the solution to 3.5-5.5 to enable iron ions and aluminum ions to have precipitation reaction to generate ferric hydroxide and aluminum hydroxide, wherein if the pH value is less than 3.5, the complete precipitation reaction of the iron ions and the aluminum ions is not facilitated, and if the pH value is more than 5.5, the waste of the pH regulator is caused.
Adjusting the pH value to 12 +/-0.5, fully stirring to dissolve aluminum hydroxide to generate a sodium metaaluminate solution, if the pH value is less than 11.5, the conversion of the aluminum hydroxide is incomplete, and if the pH value is more than 12.5, alkali liquor waste is caused;
the solid content of the slurry is the weight of solid phase/total weight of the slurry.
As an optional technical scheme, the temperature of the acid leaching reaction is 20-30 ℃, and the time of the acid leaching reaction is 50-80 min.
In the technical scheme, the temperature of the acid leaching reaction is normal temperature, the time of the acid leaching reaction is 50-80min, the leaching rate of iron is favorably improved and is as high as 90-93%, if the time of the acid leaching is too short, the leaching rate of the iron is not favorably improved, and if the time of the acid leaching is too long, the production efficiency is reduced;
in the technical scheme, the addition amount of the heavy metal capture agent is added according to the total volume (0.02-0.04) g/L of the solution, the heavy metal capture agent is continuously stirred and reacts for 15-30min after the addition, and the heavy metal capture agent comprises at least one of sodium sulfide, ammonium sulfide and potassium sulfide.
As an optional technical scheme, the temperature of the oxidation reaction is 20-30 ℃, and the oxidant at least comprises H2O2And Na2O2In the oxidation reaction, the mass fraction of the oxidant is 22-28%, and the oxidant is added in an excess amount of 12-15% according to the reaction stoichiometric ratio of ferrous iron and hydrogen peroxide.
In the technical scheme, the oxidation reaction is carried out at normal temperature, and the oxidizing agent is added according to the reaction stoichiometric excess of 12-15% so as to completely oxidize ferrous iron in the first liquid into ferric iron; wherein, the excess of 12-15% specifically refers to mole percentage.
Preferably, the pH regulator comprises at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia water, ammonium carbonate and ammonium bicarbonate, and the mass fraction of the pH regulator is 25-35%.
Preferably, the second liquid contains sodium sulfate/ammonium sulfate, and can be used for preparing byproduct mirabilite or ammonium sulfate fertilizer.
Preferably, the industrial grade or battery grade phosphoric acid diluted by pure water is added into the slurry for reaction, and the reaction comprises the following steps:
adding industrial grade or battery grade phosphoric acid diluted by pure water into the slurry at the temperature of 20-30 ℃ under the stirring condition (the content of P in the diluted phosphoric acid is (5.0 +/-0.2)%), wherein the adding amount of the phosphoric acid is 15-20% according to the stoichiometric ratio, the dripping time of the phosphoric acid is 30-50min, stirring and reacting are continuously carried out for 30-60min after the dripping of the phosphoric acid is finished, then, the stirring is stopped, the temperature is raised to 88-94 ℃, and the temperature is continuously kept for 1.5-3h after the color of the slurry is observed to be changed from yellow to white or slightly pink. Wherein the excess of 15-20% is specifically the mole percentage.
In the technical scheme, white precipitate cannot be generated when carbon dioxide is introduced into washing water in the washing process.
The solid content in the present invention refers to the ratio of the mass of the solid phase in the slurry to the total mass.
In the invention, the red mud comprises the following components in percentage by mass: fe2O3：25-60％，Al2O3：10-30％，SiO2：5-25％，CaO：2-10％，Na2O：5-10％，TiO2: 2-6%, MgO: 0.5-2%, FeO: 2-5%, and < 1% (CuO + ZnO).
Compared with the prior art, the invention has the beneficial effects that:
1. according to the method for preparing battery-grade iron phosphate by using the high-iron Bayer process red mud as an iron source, the leaching rate of iron is improved by controlling the acid leaching reaction condition; completely oxidizing ferrous iron into ferric iron through an oxidation reaction; precipitating iron ions and aluminum ions by adjusting the pH value of the solution to 3.5-5.5 to generate a precipitation reaction, generating mixed precipitates of ferric hydroxide and aluminum hydroxide, pulping the mixed precipitates, adjusting the pH value to 12 +/-0.5, fully stirring to convert precipitated aluminum into soluble meta-aluminate ions so as to separate iron and aluminum, washing the ferric hydroxide for pulping, adding phosphoric acid for reaction, and preparing the battery-grade nano anhydrous ferric phosphate; thereby realizing the resource utilization of the red mud of the high-iron Bayer process.
2. The utilization rate of iron in the method reaches more than 90 percent, and the iron resources in the red mud can be effectively utilized to prepare the battery-grade iron phosphate product with high added value; meanwhile, because the ferric hydroxide colloid particles are smaller, the superfine nano ferric phosphate is easy to prepare, and the battery-grade nano anhydrous ferric phosphate obtained by the method has uniform particle size distribution and good dispersibility; can be used for preparing a high-rate lithium iron phosphate anode material.
Drawings
Fig. 1 is a flowchart of a method for preparing battery-grade iron phosphate by using a high-iron bayer process red mud as an iron source according to an embodiment of the present invention;
FIG. 2 is an electron microscope image of the battery grade iron phosphate obtained in example 1 of the present invention at a size of 200 nm;
fig. 3 is an electron micrograph of the battery grade iron phosphate obtained in example 1 of the present invention at a 1 μm scale.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the embodiments of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that the present embodiments and examples are illustrative of the present invention and are not to be construed as limiting the present invention.
In order to solve the technical problems, the embodiment of the invention provides the following general ideas:
the method comprises the steps of firstly, carrying out acid leaching on red mud, and carrying out solid-liquid separation, wherein a first liquid mainly contains aluminum sulfate, ferric sulfate, ferrous sulfate, magnesium sulfate and sodium sulfate, and a first solid mainly contains calcium sulfate, silicon dioxide and titanium dioxide; the leaching rate of the iron is 90-93%;
adding a heavy metal capture agent into the first liquid, and then carrying out solid-liquid separation to obtain a liquid without heavy metals; this step is to remove heavy metals;
then, oxidizing all ferrous iron in the first liquid into ferric iron through an oxidation reaction to obtain a mixed solution containing the ferric iron;
and then adding a pH regulator to the mixed solution to adjust the pH to 3.5-5.5 to extract iron and aluminum. Adjusting the pH value of the solution to 3.5-5.5 to enable iron ions and aluminum ions to have precipitation reaction to generate ferric hydroxide and aluminum hydroxide, wherein a second solid obtained by solid-liquid separation mainly comprises the aluminum hydroxide and the ferric hydroxide, and a second liquid mainly comprises sodium sulfate/ammonium sulfate;
adding alkali liquor into the second solid to adjust the pH value to 12 +/-0.5, fully stirring to dissolve aluminum hydroxide to generate a sodium metaaluminate solution, and then carrying out solid-liquid separation on the sodium metaaluminate filtrate and the ferric hydroxide filter cake; sodium metaaluminate solution can be used for extracting aluminum;
washing the ferric hydroxide filter cake by adopting alkali liquor with the pH value of 12 +/-0.5 to remove residual sodium metaaluminate, adding water and uniformly mixing to obtain slurry with the solid content of 10-15%;
adding the slurry into industrial grade or battery grade phosphoric acid diluted by pure water for reaction, then performing filter pressing to obtain a ferric phosphate filter cake, and washing, drying and sintering to obtain the battery grade nano anhydrous ferric phosphate.
The method for preparing battery grade iron phosphate by using the high-iron Bayer process red mud as an iron source is described in detail below by combining examples, comparative examples and experimental data.
The following examples are provided only for illustrating the present invention and are not intended to limit the scope of the present invention. All other embodiments obtained by a person skilled in the art based on the specific embodiments of the present invention without any inventive step are within the scope of the present invention.
In the examples of the present invention, all the raw material components are commercially available products well known to those skilled in the art, unless otherwise specified; in the examples of the present invention, unless otherwise specified, all technical means used are conventional means well known to those skilled in the art. In the examples of the present invention, the raw materials used were all conventional commercially available products.
Example 1
The embodiment of the invention provides a method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as an iron source, which comprises the following steps of:
and step S1, acid leaching. Carrying out acid leaching reaction on the high-iron Bayer process red mud and sulfuric acid, wherein the adding amount of the sulfuric acid and the red mud is as follows by weight ratio of 5: 1, the concentration of sulfuric acid is 70%, the reaction time is 60min, and the reaction temperature is normal temperature; filtering to obtain filtrate and residue; the filtrate mainly contains aluminum sulfate, ferric sulfate, ferrous sulfate, magnesium sulfate, sodium sulfate and a small amount of copper sulfate and zinc sulfate, and the filter residue mainly contains calcium sulfate, silicon dioxide and titanium dioxide; the leaching rate of the iron is 90-93%.
Step S2, heavy metal removal: adding ammonium sulfide into the first liquid, and then carrying out solid-liquid separation to obtain a liquid without heavy metals; wherein the addition amount of the heavy metal catching agent is 0.03g/L of the total volume of the solution;
and step S3, oxidizing. Detecting the content of the ferrous iron in the filtrate obtained in the step S1, adding an oxidant according to the reaction stoichiometric ratio excess of 12-15%, and completely oxidizing the ferrous iron in the solution into ferric iron at normal temperature;
and step S4, extracting iron and aluminum. Adding a pH regulator into the solution obtained in the step S2, regulating the pH of the solution to 5.2, carrying out precipitation reaction on iron ions and aluminum ions to generate ferric hydroxide and aluminum hydroxide, filtering to obtain a filter cake and a filtrate, wherein the filter cake mainly comprises the aluminum hydroxide and the ferric hydroxide, and the filtrate mainly comprises sodium sulfate/ammonium sulfate (which can be used for preparing a byproduct mirabilite or an ammonium sulfate fertilizer);
and step S5, extracting iron. Adding liquid caustic soda into the filter residue obtained in the step S3, adjusting the pH value to 12, fully stirring to dissolve aluminum hydroxide to generate a sodium metaaluminate solution, and filtering to obtain a sodium metaaluminate filtrate and an iron hydroxide filter cake; sodium metaaluminate solution can be used for extracting aluminum;
and step S6, washing. And (3) washing the ferric hydroxide filter cake by using a sodium hydroxide solution with the pH value of 12 to remove residual sodium metaaluminate in the filter cake, and washing until no white precipitate is generated when carbon dioxide is introduced into washing water.
And step S7, preparing iron phosphate. And (4) adding pure water into the iron hydroxide filter cake washed in the step S5 for pulping, wherein the solid content of the slurry is 12%, fully stirring and uniformly mixing, and sampling to test the iron content. Adding industrial or battery grade phosphoric acid (the content of P in diluted dilute phosphoric acid is 5.0 +/-0.2 percent) at normal temperature), wherein the adding amount of the phosphoric acid is 15-20 percent according to the stoichiometric ratio, the dropping time of the phosphoric acid is 35min, continuously stirring and reacting for 30min after the dropping is finished, then heating to 90 ℃, continuously keeping the temperature for 2h after the color of the slurry is observed to be changed from yellow to white or slightly pink, then carrying out filter pressing to obtain an iron phosphate filter cake, washing, drying and sintering to obtain the battery grade nano anhydrous iron phosphate.
Example 2
The embodiment of the invention provides a method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as an iron source, which comprises the following steps:
and step S1, acid leaching. Carrying out acid leaching reaction on the high-iron Bayer process red mud and sulfuric acid, wherein the adding amount of the sulfuric acid and the red mud is as follows by weight ratio of 3: 1, the concentration of sulfuric acid is 60%, the reaction time is 50min, and the reaction temperature is normal temperature; filtering to obtain filtrate and residue; the filtrate mainly contains aluminum sulfate, ferric sulfate, ferrous sulfate, magnesium sulfate and sodium sulfate, and the filter residue mainly contains calcium sulfate, silicon dioxide and titanium dioxide; the leaching rate of the iron is 90-93%.
Step S2, heavy metal removal: adding ammonium sulfide into the first liquid, and then carrying out solid-liquid separation to obtain a liquid without heavy metals; wherein the addition amount of the heavy metal catching agent is 0.02g/L of the total volume of the solution;
and step S3, oxidizing. Detecting the content of the ferrous iron in the filtrate obtained in the step S1, adding an oxidant according to the reaction stoichiometric ratio excess of 12-15%, and completely oxidizing the ferrous iron in the solution into ferric iron at normal temperature;
and step S4, extracting iron and aluminum. Adding a pH regulator into the solution obtained in the step S2, regulating the pH of the solution to 3.5, carrying out precipitation reaction on iron ions and aluminum ions to generate ferric hydroxide and aluminum hydroxide, filtering to obtain a filter cake and a filtrate, wherein the filter cake mainly comprises the aluminum hydroxide and the ferric hydroxide, and the filtrate mainly comprises sodium sulfate/ammonium sulfate (which can be used for preparing a byproduct mirabilite or an ammonium sulfate fertilizer);
and step S5, extracting iron. Adding liquid caustic soda into the filter residue obtained in the step S3, adjusting the pH value to 11.5, fully stirring to dissolve aluminum hydroxide to generate a sodium metaaluminate solution, and filtering to obtain a sodium metaaluminate filtrate and an iron hydroxide filter cake; sodium metaaluminate solution can be used for extracting aluminum;
and step S6, washing. And (3) washing the ferric hydroxide filter cake by using a sodium hydroxide solution with the pH value of 11.5 to remove residual sodium metaaluminate in the filter cake, and washing until no white precipitate is generated when carbon dioxide is introduced into washing water.
And step S7, preparing iron phosphate. And (4) adding pure water into the iron hydroxide filter cake washed in the step S5 for pulping, wherein the solid content of the slurry is 10%, and sampling to test the iron content after fully and uniformly stirring. Adding industrial or battery grade phosphoric acid (the content of P in diluted dilute phosphoric acid is 5.0 +/-0.2 percent) at normal temperature), wherein the adding amount of the phosphoric acid is 15-20 percent according to the stoichiometric ratio, the dropping time of the phosphoric acid is 35min, continuously stirring and reacting for 30min after the dropping is finished, then heating to 90 ℃, continuously keeping the temperature for 2h after the color of the slurry is observed to be changed from yellow to white or slightly pink, then carrying out filter pressing to obtain an iron phosphate filter cake, washing, drying and sintering to obtain the battery grade nano anhydrous iron phosphate.
Example 3
The embodiment of the invention provides a method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as an iron source, which comprises the following steps:
and step S1, acid leaching. Carrying out acid leaching reaction on the high-iron Bayer process red mud and sulfuric acid, wherein the adding amount of the sulfuric acid and the red mud is as follows by weight ratio of 6: 1, the concentration of sulfuric acid is 80%, the reaction time is 80min, and the reaction temperature is normal temperature; filtering to obtain filtrate and residue; the filtrate mainly contains aluminum sulfate, ferric sulfate, ferrous sulfate, magnesium sulfate and sodium sulfate, and the filter residue mainly contains calcium sulfate, silicon dioxide and titanium dioxide; the leaching rate of the iron is 90-93%.
Step S2, heavy metal removal: adding ammonium sulfide into the first liquid, and then carrying out solid-liquid separation to obtain a liquid without heavy metals; wherein the addition amount of the heavy metal catching agent is 0.04g/L of the total volume of the solution;
and step S3, oxidizing. Detecting the content of the ferrous iron in the filtrate obtained in the step S1, adding an oxidant according to the reaction stoichiometric ratio excess of 12-15%, and completely oxidizing the ferrous iron in the solution into ferric iron at normal temperature;
and step S4, extracting iron and aluminum. Adding a pH regulator into the solution obtained in the step S2, regulating the pH of the solution to 5.5, carrying out precipitation reaction on iron ions and aluminum ions to generate ferric hydroxide and aluminum hydroxide, filtering to obtain a filter cake and a filtrate, wherein the filter cake mainly comprises the aluminum hydroxide and the ferric hydroxide, and the filtrate mainly comprises sodium sulfate/ammonium sulfate (which can be used for preparing a byproduct mirabilite or an ammonium sulfate fertilizer);
and step S5, extracting iron. Adding liquid caustic soda into the filter residue obtained in the step S3, adjusting the pH value to 12.5, fully stirring to dissolve aluminum hydroxide to generate a sodium metaaluminate solution, and filtering to obtain a sodium metaaluminate filtrate and an iron hydroxide filter cake; sodium metaaluminate solution can be used for extracting aluminum;
and step S6, washing. And (3) washing the ferric hydroxide filter cake by using a sodium hydroxide solution with the pH value of 12.5 to remove residual sodium metaaluminate in the filter cake, and washing until no white precipitate is generated when carbon dioxide is introduced into washing water.
And step S7, preparing iron phosphate. And (4) adding pure water into the iron hydroxide filter cake washed in the step S5 for pulping, wherein the solid content of the slurry is 10%, and sampling to test the iron content after fully and uniformly stirring. Adding industrial or battery grade phosphoric acid (the content of P in diluted dilute phosphoric acid is 5.0 +/-0.2 percent) at normal temperature), wherein the adding amount of the phosphoric acid is 15-20 percent according to the stoichiometric ratio, the dropping time of the phosphoric acid is 35min, continuously stirring and reacting for 30min after the dropping is finished, then heating to 90 ℃, continuously keeping the temperature for 2h after the color of the slurry is observed to be changed from yellow to white or slightly pink, then carrying out filter pressing to obtain an iron phosphate filter cake, washing, drying and sintering to obtain the battery grade nano anhydrous iron phosphate.
Comparative example 1
In the comparative example, in the acid leaching reaction, the addition amount of the sulfuric acid and the red mud is 2: 1; the other steps were the same as in example 1.
Comparative example 2
In this comparative example, in the step of extracting iron and aluminum, the pH was adjusted to 3.0; the other steps were the same as in example 1.
Comparative example 3
In this comparative example, in the iron extraction step, the pH was adjusted to 11.0; the other steps were the same as in example 1.
Comparative example 4
In this comparative example, phosphoric acid was added in stoichiometric ratio, i.e., without excess; the other steps were the same as in example 1.
Experimental example 1
1. The iron utilization (i.e., recovery) statistics for each example and each comparative example are shown in table 1.
TABLE 1
| Group of | Utilization ratio of iron% | Whether the iron and the aluminum are completely separated |
| Example 1 | 92.03 | Is that |
| Example 2 | 91.95 | Is that |
| Example 3 | 92.27 | Is that |
| Comparative example 1 | 82.56 | Is that |
| Comparative example 2 | 85.79 | Is that |
| Comparative example 3 | 91.99 | Whether or not |
| Comparative example 4 | 88.75 | Is that |
From the data in table 1, it can be seen that:
in the comparative example 1, the dosage of sulfuric acid in the leaching process is low, so that the leaching rate of iron in red mud is low, and the utilization rate of iron is low;
in the comparative example 2, in the process of extracting iron and aluminum, the pH value of the solution is low, so that iron ions are not completely precipitated, and the utilization rate is low;
in the comparative example 3, in the processes of extracting iron and separating aluminum, the pH value of the solution is low, aluminum hydroxide precipitate is not completely converted into sodium metaaluminate, the residual aluminum hydroxide precipitate reacts with phosphoric acid to generate aluminum phosphate precipitate, and the aluminum phosphate precipitate coexists with the product, so that the aluminum content of the product exceeds the standard;
in comparative example 4, since phosphoric acid was not excessive, iron reaction was incomplete during the reaction, resulting in low iron utilization and low iron phosphate yield;
in examples 1 to 3, the utilization rate of iron was 90% or more.
2. The iron phosphate of each example and comparative example was examined, and the examination results of the iron phosphate are shown in tables 2 to 3;
TABLE 2
TABLE 3
As can be seen from the data in tables 1, 2 and 3, under different reaction conditions, although the utilization rates of iron are different, each index of the iron phosphate finally prepared by using red mud as an iron source is relatively stable, which indicates that the process is relatively stable and reliable.
The comparison with commercially available battery-grade iron phosphate purchased from outsourcing shows that the iron phosphate obtained in examples 1 to 3 has a slightly larger specific surface area result than that of a commercial material, and other indexes reach the same or higher level, so that the requirement of the battery-grade iron phosphate can be met. The reason for the slightly larger BET is that the iron phosphate with smaller primary particles is easily prepared by adopting the ferric hydroxide colloid with smaller particle size as an iron source, so that the specific surface area is slightly increased.
It should be noted that the above examples are only for further illustration and description of the technical solution of the present invention, and are not intended to further limit the technical solution of the present invention, and the method of the present invention is only a preferred embodiment, and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A method for preparing battery-grade iron phosphate by taking high-iron Bayer process red mud as an iron source is characterized by comprising the following steps:
sulfuric acid and red mud are subjected to acid leaching reaction, and then solid-liquid separation is carried out to obtain a first solid and a first liquid; wherein the adding amount of the sulfuric acid and the red mud is (3-6) by weight: 1, the mass fraction of the sulfuric acid is 60-80%;
adding a heavy metal capture agent into the first liquid, and then carrying out solid-liquid separation to obtain a liquid without heavy metals; wherein, the addition amount of the heavy metal catching agent is added according to the total volume of the solution (0.02-0.04) g/L;
adding an oxidant into the liquid without the heavy metals for oxidation reaction to obtain a mixed solution;
adding a pH regulator into the mixed solution to regulate the pH of the mixed solution to 3.5-5.5, and then carrying out solid-liquid separation to obtain a second solid and a second liquid;
adding alkali liquor into the second solid to adjust the pH value to 12 +/-0.5, and then carrying out solid-liquid separation to obtain an iron hydroxide filter cake and a sodium metaaluminate filtrate;
washing the ferric hydroxide filter cake by adopting alkali liquor with the pH value of 12 +/-0.5 to obtain a washed ferric hydroxide filter cake;
adding water into the washed ferric hydroxide filter cake, and uniformly mixing to obtain slurry with the solid content of 10-15%;
adding the slurry into industrial-grade or battery-grade phosphoric acid for reaction, wherein the addition amount of the phosphoric acid is 15-20% of the stoichiometric excess; and then carrying out filter pressing, washing, drying and sintering to obtain the battery-grade nano anhydrous iron phosphate.
2. The method for preparing battery-grade iron phosphate by using high-iron Bayer process red mud as an iron source according to claim 1, wherein the temperature of the acid leaching reaction is 20-30 ℃, and the time of the acid leaching reaction is 50-80 min.
3. The method for preparing battery-grade iron phosphate by using high-iron Bayer process red mud as an iron source according to claim 1, wherein the temperature of the oxidation reaction is 20-30 ℃, and the oxidant at least comprises H2O2And Na2O2In the oxidation reaction, the mass fraction of the oxidant is 22-28%, and the oxidant is added in an excess amount of 12-15% according to the reaction stoichiometric ratio of ferrous iron and hydrogen peroxide.
4. The method for preparing battery-grade iron phosphate by using high-iron Bayer process red mud as an iron source according to claim 1, wherein the pH regulator comprises one of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonia water, ammonium carbonate and ammonium bicarbonate, and the mass fraction of the pH regulator is 25-35%.
5. The method for preparing battery-grade iron phosphate by using high-iron Bayer process red mud as an iron source according to claim 1, wherein the second liquid contains sodium sulfate/ammonium sulfate for preparing a byproduct mirabilite or ammonium sulfate fertilizer.
6. The method for preparing battery-grade iron phosphate by using the high-iron Bayer process red mud as an iron source according to claim 1, wherein white precipitates are not generated until carbon dioxide is introduced into washing water during washing.
7. The method for preparing battery-grade iron phosphate by using high-iron Bayer process red mud as an iron source according to claim 1, wherein the step of adding the slurry into industrial-grade or battery-grade phosphoric acid for reaction comprises the following steps:
adding the slurry into industrial grade or battery grade phosphoric acid at the temperature of 20-30 ℃ under the stirring condition, wherein the adding amount of the phosphoric acid is 15-20% of the stoichiometric excess, the dropping time of the phosphoric acid is 30-50min, stirring is stopped after stirring reaction is continued for 30-60min after the dropping of the phosphoric acid is finished, then the temperature is raised to 88-94 ℃, and the temperature is continuously kept for 1.5-3h after the color of the slurry is observed to be changed from yellow to white or slightly pink.
8. The method for preparing battery-grade iron phosphate by using high-iron Bayer process red mud as an iron source according to claim 1, wherein the addition amount of the sulfuric acid to the red mud is (4-5) by weight: 1, the mass fraction of the sulfuric acid is 65-75%.
9. The method for preparing battery grade iron phosphate by using high-iron Bayer process red mud as an iron source according to claim 1, wherein the red mud comprises the following components in percentage by mass: fe2O3：25-60％，Al2O3：10-30％，SiO2：5-25％，CaO：2-10％，Na2O：5-10％，TiO2: 2-6%, MgO: 0.5-2%, FeO: 2-5%, and < 1% (CuO + ZnO).
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