Method for preparing low-aluminum high-grade iron ore concentrate for iron phosphate production by using pyrite cinder

Abstract

The invention discloses a method for preparing low-aluminum high-grade iron ore concentrate for iron phosphate production by using pyrite cinder, and belongs to the field of high-value utilization of solid waste resources and preparation of new energy materials. The method sequentially comprises the steps of screening, pre-magnetic separation, ore grinding, two-stage acid leaching, low-intensity magnetic separation and reverse flotation; according to the method, a two-stage acid leaching process is adopted, and deep chemical dissolution of aluminum impurities which are difficult to remove by a traditional physical method is realized through the synergistic complexing effect of inorganic acid and organic acid and assisted by a leaching aid; by combining magnetic separation pre-enrichment and mixed amine cation reverse flotation accurate separation, the pyrite cinder is converted into low-aluminum high-grade iron ore concentrate with the total iron grade larger than or equal to 69% and the aluminum grade smaller than or equal to 0.10%, the iron recovery rate is high, the harsh requirement of an iron phosphate precursor for an iron source is met, and an efficient solution is provided for high-value utilization of bulk solid waste.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization of solid waste resources and preparation of new energy materials, specifically a method for preparing low-alumina, high-grade iron concentrate for ferric phosphate production using sulfuric acid slag. Background Technology

[0002] Sulfuric acid slag (also known as sulfuric acid residue) is a major solid waste generated in the sulfuric acid industry after roasting pyrite. Its main component is iron oxide. When the furnace temperature is controlled at 850-950℃ and the oxygen potential is below 0.1 atm, Fe3O4 becomes a stable phase, forming a typical black slag (distinguishing it from the conventional red slag with the Fe2O3 phase). Simultaneously, sulfuric acid slag contains small amounts of residual non-ferrous metal elements and a certain amount of gangue minerals, such as SiO2, Al2O3, CaO, and MgO. With the widespread application of lithium iron phosphate (LiFePO4) as a cathode material for power batteries, the market demand for its precursor—iron phosphate (FePO4)—has surged. High-purity iron sources are one of the key raw materials for preparing high-quality iron phosphate.

[0003] Iron(III) oxide (Fe3O4) is an ideal iron source for preparing lithium iron phosphate due to its high iron content (theoretically 72.4%), good magnetic properties, and relatively stable chemical properties. In particular, "low-aluminum, high-grade iron concentrate" can effectively avoid introducing excessive Al impurities during subsequent lithium iron phosphate synthesis, thus affecting the electrochemical performance of the finished lithium iron phosphate product. Therefore, developing an economical and efficient technology for preparing low-aluminum, high-grade iron concentrate from iron-containing solid waste resources is of great significance for the high-value utilization of solid waste resources and the development of new energy cathode materials.

[0004] Sulfuric acid slag (black slag), as a secondary material rich in iron resources, has the advantages of wide availability and low cost, making it a potentially excellent raw material for preparing ferric oxide concentrate. However, directly utilizing sulfuric acid slag faces the following major technical challenges: 1. Aluminum impurities are difficult to remove effectively: Aluminum in sulfuric acid slag usually exists in the form of aluminosilicate minerals (such as kaolinite, illite, etc.) or alumina. These aluminum-containing minerals have relatively similar physicochemical properties (such as density, magnetism, and surface properties) to iron oxides, making it difficult for traditional single-method separation (such as magnetic separation or flotation) to achieve efficient and selective separation of aluminum. Conventional magnetic separation has limited effectiveness in removing weakly magnetic or non-magnetic aluminum-containing minerals; while single-method flotation may lose some iron minerals or introduce excessive beneficiation reagents while removing aluminum.

[0005] 2. The contradiction between iron grade improvement and impurity control: Improving iron grade usually requires the removal of all gangue minerals (including silicon, aluminum, calcium, magnesium, etc.) as much as possible. However, in sulfuric acid slag, iron oxides and gangue minerals are complexly interspersed, making it extremely difficult to efficiently remove all impurities, especially aluminum impurities. Due to their occurrence state and close symbiosis with iron minerals, aluminum impurities often become a key bottleneck restricting the improvement of concentrate grade and the achievement of aluminum content standards.

[0006] 3. Phase Control and Preservation of Magnetite (Fe3O4): Iron in sulfuric acid slag (black slag) mainly exists in the form of magnetite (Fe3O4), with some potentially containing hematite or pseudomorphic hematite (Fe2O3). The target product is magnetite concentrate, which often requires specific reduction or atmosphere control treatments before or during sorting to convert the non-magnetic or weakly magnetic Fe2O3 into the strongly magnetic Fe3O4. However, this conversion process requires precise control; otherwise, it may affect the mineral's beneficiability or result in unsuitable iron phases. Simultaneously, strong oxidizing conditions must be avoided in subsequent sorting processes to prevent the destruction of the magnetism of Fe3O4.

[0007] 4. Separation efficiency and cost issues: Existing technologies for processing sulfuric acid slag to prepare iron concentrate often employ single magnetic separation, single flotation, or simple series combinations thereof. A single method is insufficient to simultaneously achieve efficient aluminum removal and high-grade iron recovery; simple series combinations may result in high equipment investment, high energy consumption, high reagent consumption, and unsatisfactory separation efficiency (especially selectivity for aluminum), leading to an excessive Al grade in the final concentrate (>0.5% or higher), failing to meet the stringent requirements for iron source purity in the preparation of iron phosphate precursors (typically requiring an Al grade in the iron concentrate of <0.15%, or even <0.1%).

[0008] Application No. 202510019327.1, entitled "A Method for Recovering Iron from Sulfuric Acid Slag," also discloses a method for recovering iron from sulfuric acid slag. However, it still has some shortcomings. For example, the method requires reduction in a hydrogen atmosphere and the reduction temperature is relatively high, which poses a significant risk.

[0009] In summary, existing technologies have significant shortcomings in processing sulfuric acid slag to prepare iron concentrate suitable for the production of iron phosphate precursors, especially in achieving the core objective of efficiently and economically obtaining concentrates with low aluminum (Al grade less than 0.15%), high grade (TFe grade > 68%), and with iron tetroxide (Fe3O4) as the main phase. Summary of the Invention

[0010] To address the aforementioned technical problems, a novel separation method is being developed that synergistically enhances the removal of aluminum impurities and the efficient enrichment and recovery of iron tetroxide, taking into account the characteristics of sulfuric acid slag. This method has urgent market demand and significant application value. This invention aims to overcome the shortcomings of the existing technology and provide an efficient solution for preparing low-alumina, high-grade iron concentrate from sulfuric acid slag, as detailed below: A method for preparing low-alumina, high-grade iron concentrate using sulfuric acid slag, wherein the low-alumina, high-grade iron concentrate is used for the production of ferric phosphate, includes the following steps ( Figure 1 ): S1. Screening: The sulfuric acid slag is screened and classified to obtain fine-particle products; S2. Pre-magnetization: Pre-magnetic separation is performed on the fine-particle product to obtain a pre-magnetically separated product; S3. Grinding: Grinding the pre-magnetic separation product to obtain a ground product; S4. Acid leaching: After dehydration, the grinding product is subjected to acid leaching to obtain acid-leached solid product; The acid leaching treatment is a two-stage acid leaching process, including: First stage of acid leaching: acid leaching is carried out using sulfuric acid with a concentration of 20-50 g / L, a liquid-to-solid ratio of 4-5 mL / g, a temperature of 60-80℃, and a time of 60-90 min; Second stage acid leaching: Based on the first stage acid leaching, organic acid and leaching aid are added for a second stage acid leaching. The concentration of organic acid in the total system is 1%-2%, and the concentration of leaching aid in the total system is 0.2%-0.5%. The temperature is 60-80℃, and the time is 90-120min. S5. Weak magnetic separation: The acid-leached solid product is subjected to weak magnetic separation to obtain magnetic concentrate; S6. Flotation: The magnetic concentrate is subjected to reverse flotation to obtain the low-alumina, high-grade iron concentrate; The low-alumina, high-grade iron concentrate has a total iron grade of not less than 69% and an aluminum grade of not more than 0.10%, and is used as an iron source for the production of iron phosphate.

[0011] Preferably, in step S1, the sieve used for screening and grading is 80 mesh, and the fine-particle product is the product under-screened from the -80 mesh sieve.

[0012] Preferably, in step S2, the pre-magnetic separation uses an electromagnetic washing machine with a magnetic field strength of 200-250 Gs and a water pressure of 0.4-0.5 m. 3 / h.

[0013] Preferably, in step S3, the grinding is carried out using a vertical stirred ball mill with 5 mm zirconium balls as the grinding media; the pre-magnetic separation product is ground to a particle size of -0.023 mm or more, with a grinding concentration of 30%-50%.

[0014] Preferably, in step S4, the organic acid is one or more of citric acid, oxalic acid, and ethylenediaminetetraacetic acid.

[0015] Preferably, the impregnation aid is sodium fluoride.

[0016] Preferably, in step S5, the magnetic field strength used in the weak magnetic separation is 800-1200 Gs.

[0017] Preferably, in step S6, the reverse flotation is carried out in a flotation column, and the pulp concentration is 10%-15%; The inhibitors used in the reverse flotation are one or more of starch, dextrin, carboxymethyl cellulose, tannin, and sodium lignosulfonate. The collector used is a mixed amine cationic collector composed of quaternary ammonium salt, ether amine, and dodecylamine in a certain proportion.

[0018] On the other hand, the present invention develops a low-alumina, high-grade iron concentrate for the production of iron phosphate, which is prepared by the method described in the claims, with a total iron grade of not less than 69%, an aluminum grade of not more than 0.10%, and its main phase being iron(III) oxide.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses sulfuric acid slag industrial solid waste as raw material and adopts a two-stage acid leaching process. The first stage is sulfuric acid leaching to dissolve some soluble aluminum impurities, initially reducing the aluminum content. The second stage is synergistic acid leaching with organic acids and leaching aids: through the action of organic acids such as citric acid and oxalic acid and sodium fluoride leaching aids, the structure of aluminum-containing minerals is selectively destroyed, achieving deep removal of aluminum. The aluminum content of the prepared product is consistently below 0.10% (as low as 0.09%). The low aluminum content can avoid the negative impact of Al impurities on electrochemical performance in subsequent iron phosphate synthesis, meeting the stringent requirements for high-quality lithium iron phosphate precursors.

[0020] 2. This invention optimizes the enrichment efficiency of iron minerals through a process of pre-magnetic separation + grinding + weak magnetic separation + reverse flotation. The total iron grade (TFe) of the obtained product is consistently above 69% (up to 69.69%). The high total iron grade (>69%) can reduce the interference of impurities in the subsequent iron phosphate synthesis and improve the purity and performance of the product.

[0021] 3. The iron in sulfuric acid slag mainly exists in the form of Fe3O4, but some may contain Fe2O3. The technical solution of this invention avoids the conversion of Fe3O4 to Fe2O3, and at the same time maintains the magnetic and chemical stability of Fe3O4 through two-stage acid leaching and weak magnetic separation.

[0022] 4. While improving the grade of the concentrate, this invention also maintains a high iron recovery rate, with a TFe recovery rate between 59.11% and 63.48%. During the extraction of high-grade iron concentrate, there is less iron loss and high resource utilization efficiency.

[0023] 5. This invention utilizes the differences in particle size and magnetic properties between iron minerals (Fe3O4) and ores through screening and weak magnetic separation to initially enrich iron and remove some easily separable impurities. Subsequently, grinding is used to achieve mineral monomer dissociation, creating a prerequisite for subsequent deep separation. The joint adopts a two-stage acid leaching process. The first stage uses sulfuric acid leaching to dissolve some acid-soluble aluminum. The second stage utilizes the complexing effect of organic acids and the activation effect of fluorides to selectively dissolve stubborn aluminum-containing minerals that are closely associated with iron minerals and have similar physical properties, achieving deep dealuminization at the crystal lattice level. Finally, reverse flotation is used to suppress iron minerals with inhibitors and selectively collect residual aluminum-containing silicates with mixed amine cationic collectors. By utilizing the differences in surface properties between the two, the final precise separation is achieved, ultimately efficiently converting industrial solid waste into high-value-added battery material raw materials. Attached Figure Description

[0024] Figure 1 Flowchart for preparing low-alumina, high-grade iron concentrate from sulfuric acid slag. Detailed Implementation

[0025] Example 1 Using sulfuric acid slag from a sulfuric acid plant as raw material, with a TFe grade of 61.60% and an Al grade of 0.76%, the sulfuric acid slag was sorted according to the following steps: 1. Screening. The sulfuric acid slag (black slag) raw material is screened and graded using an 80-mesh sieve to obtain two grades: +80 mesh and -80 mesh. 2. Pre-magnetization. The raw material under -80 mesh sieve is placed in an electromagnetic washing machine with a magnetic field strength of 230 Gs for weak magnetic separation, and the water pressure is set to 0.4 m. 3 / h, to obtain pre-magnetic separation products; 3. Grinding. A vertical stirred ball mill (grinding media: 5 mm zirconium balls) is used to grind the pre-magnetic separation product to a density of -0.023 mm greater than 90%, with a ball mill slurry concentration of 30%, to obtain the ground product; 4. Acid Leaching. After dehydration of the ground ore, a two-stage acid leaching process is carried out. The first stage is sulfuric acid leaching, with a sulfuric acid concentration of 20 g / L, a liquid-to-solid ratio of 4 ml / g, an acid leaching temperature of 60℃, and an acid leaching time of 60 min. The second stage is enhanced acid leaching, mainly using a combination of inorganic and organic acids. The inorganic acid is the sulfuric acid from the first stage, and the organic acid is one or a combination of citric acid, oxalic acid, and ethylenediaminetetraacetic acid. The concentration of organic acid in the total system is 1%, and sodium fluoride is added at a concentration of 0.5% as a leaching aid. The acid leaching temperature is maintained at 60℃, and the acid leaching time is 120 min. After acid leaching, the solid product is separated by filtration. The solid product is washed with water until the pH of the filtrate is about 6, thus obtaining the acid-leached solid product. 5. Weak magnetic separation. The acid-leached solid product is placed in a drum-type wet weak magnetic separator with a magnetic field strength of 1000 Gs for weak magnetic separation to obtain the magnetically separated product; 6. Flotation. The magnetic separation product is placed in a flotation column for reverse flotation separation. The feed concentration is 12%. The depressant is one or a combination of starch, dextrin, carboxymethyl cellulose, tannin, and sodium lignosulfonate. The collector is a mixed amine cationic collector of quaternary ammonium salt, ether amine, and dodecylamine in a ratio of 1:1:1. The bottom product obtained is a low-alumina, high-grade iron concentrate with a TFe grade of 69.09%, an Al grade of 0.09%, and an iron concentrate purity of 97.02%.

[0026] Example 2 Using sulfuric acid slag from a sulfuric acid plant as raw material, with a TFe grade of 61.60% and an Al grade of 0.76%, the sulfuric acid slag was sorted according to the following steps: 1. Screening. The sulfuric acid slag is screened and classified to obtain two grades: +80 mesh and -80 mesh. 2. Pre-magnetization. The raw material under -80 mesh sieve is placed in an electromagnetic washing machine with a magnetic field strength of 230 Gs for weak magnetic separation, and the water pressure is set to 0.4 m. 3 / h, to obtain pre-magnetic separation products; 3. Grinding. A vertical stirred ball mill (grinding media: 5 mm zirconium balls) is used to grind the pre-magnetic separation product to a final thickness of -0.023 mm (100%), with a ball mill slurry concentration of 40%, to obtain the ground product. 4. Acid Leaching. After dehydration, the ground ore product undergoes a two-stage acid leaching process. The first stage is sulfuric acid leaching, with a sulfuric acid concentration of 50 g / L, a liquid-to-solid ratio of 4 ml / g, an acid leaching temperature of 60℃, and an acid leaching time of 60 min. The second stage is enhanced acid leaching, mainly using a combination of inorganic and organic acids. The inorganic acid is the sulfuric acid from the first stage, and the organic acid is one or a combination of citric acid, oxalic acid, and ethylenediaminetetraacetic acid, with the organic acid accounting for 1.5% of the total system concentration. Simultaneously, sodium fluoride is added at 0.2% of the system concentration as a leaching aid. The acid leaching temperature is maintained at 60℃, and the acid leaching time is 120 min. After acid leaching, the product is filtered for solid-liquid separation. The solid product is washed with water until the pH of the filtrate is approximately 6, yielding the acid-leached solid product. 5. Weak magnetic separation. The acid-leached solid product is placed in a drum-type wet weak magnetic separator with a magnetic field strength of 1000 Gs for weak magnetic separation to obtain the magnetically separated product; 6. Flotation. The magnetic separation product is placed in a flotation column for reverse flotation separation. The feed concentration is 10%. The depressant is one or a combination of starch, dextrin, carboxymethyl cellulose, tannin, and sodium lignosulfonate. The collector is a mixed amine cationic collector of quaternary ammonium salt, ether amine, and dodecylamine in a ratio of 1:1:1. The bottom product obtained is a low-alumina, high-grade iron concentrate with a TFe grade of 69.21%, an Al grade of 0.10%, and an iron concentrate purity of 97.21%.

[0027] Example 3 Using sulfuric acid slag from a sulfuric acid plant as raw material, with a TFe grade of 61.03% and an Al grade of 0.81%, the sulfuric acid slag was sorted according to the following steps: 1. Screening. The sulfuric acid slag is screened and classified to obtain two grades: +80 mesh and -80 mesh. 2. Pre-magnetization. The raw material passing through a -80 mesh sieve is placed in an electromagnetic washing machine with a magnetic field strength of 230 Gs for weak magnetic separation, and the water pressure is set to 0.5 m. 3 / h, to obtain pre-magnetic separation products; 3. Grinding. A vertical stirred ball mill (grinding media: 5 mm zirconium balls) is used to grind the pre-magnetic separation product to a concentration of -0.018 mm greater than 90%, with a ball mill slurry concentration of 40%, to obtain the ground product; 4. Acid Leaching. After dehydration, the ground ore product undergoes a two-stage acid leaching process. The first stage is sulfuric acid leaching, with a sulfuric acid concentration of 50 g / L, a liquid-to-solid ratio of 5 ml / g, an acid leaching temperature of 70℃, and an acid leaching time of 60 min. The second stage is enhanced acid leaching, mainly using a combination of inorganic and organic acids. The inorganic acid is the sulfuric acid from the first stage, and the organic acid is one or a combination of citric acid, oxalic acid, and ethylenediaminetetraacetic acid, with the organic acid accounting for 2% of the total system concentration. Simultaneously, sodium fluoride is added at 0.2% of the system concentration as a leaching aid. The acid leaching temperature is maintained at 70℃, and the acid leaching time is 120 min. After acid leaching, the product is filtered for solid-liquid separation. The solid product is washed with water until the pH of the filtrate is approximately 6, yielding the acid-leached solid product. 5. Weak magnetic separation. The acid-leached solid product is placed in a drum-type wet weak magnetic separator with a magnetic field strength of 1200 Gs for weak magnetic separation to obtain the magnetically separated product; 6. Flotation. The magnetic separation product is placed in a flotation column for reverse flotation separation. The feed concentration is 15%. The depressant is one or a combination of starch, dextrin, carboxymethyl cellulose, tannin, and sodium lignosulfonate. The collector is a mixed amine cationic collector of quaternary ammonium salt, ether amine, and dodecylamine in a ratio of 1:1:2. The bottom product obtained is a low-aluminum, high-grade iron concentrate with a TFe grade of 69.01%, an Al grade of 0.10%, and an iron concentrate purity of 96.92%.

[0028] Example 4 Using sulfuric acid slag from a sulfuric acid plant as raw material, with a TFe grade of 62.16% and an Al grade of 0.78%, the sulfuric acid slag was sorted according to the following steps: 1. Screening. The sulfuric acid slag is screened and classified to obtain two grades: +80 mesh and -80 mesh. 2. Pre-magnetization. The raw material under -80 mesh sieve is placed in an electromagnetic washing machine with a magnetic field strength of 230 Gs for weak magnetic separation, and the water pressure is set to 0.4 m. 3 / h, to obtain pre-magnetic separation products; 3. Grinding. A vertical stirred ball mill (grinding media: 5 mm zirconium balls) is used to grind the pre-magnetic separation product to a final concentration of -0.018 mm (100%), with a ball mill slurry concentration of 50%, to obtain the ground product. 4. Acid Leaching. After dehydration, the ground ore product undergoes a two-stage acid leaching process. The first stage is sulfuric acid leaching, with a sulfuric acid concentration of 30 g / L, a liquid-to-solid ratio of 5 ml / g, an acid leaching temperature of 80℃, and an acid leaching time of 90 min. The second stage is enhanced acid leaching, using a combination of inorganic and organic acids. The inorganic acid is the sulfuric acid from the first stage, and the organic acid is one or a combination of citric acid, oxalic acid, and ethylenediaminetetraacetic acid, with the organic acid accounting for 1.5% of the total system concentration. Simultaneously, sodium fluoride is added at 0.5% of the system concentration as a leaching aid. The acid leaching temperature is maintained at 80℃, and the acid leaching time is 90 min. After acid leaching, the product is filtered for solid-liquid separation. The solid product is washed with water until the pH of the filtrate reaches approximately 6, yielding the acid-leached solid product. 5. Weak magnetic separation. The acid-leached solid product is placed in a drum-type wet weak magnetic separator with a magnetic field strength of 800 Gs for weak magnetic separation to obtain the magnetically separated product; 6. Flotation. The magnetic separation product is placed in a flotation column for reverse flotation separation. The feed concentration is 13%. The depressant is one or a combination of starch, dextrin, carboxymethyl cellulose, tannin, and sodium lignosulfonate. The collector is a mixed amine cationic collector of quaternary ammonium salt, ether amine, and dodecylamine in a ratio of 1:1:3. The bottom product obtained is a low-alumina, high-grade iron concentrate with a TFe grade of 69.69%, an Al grade of 0.09%, and an iron concentrate purity of 97.87%.

[0029] Comparative Example 1 Using sulfuric acid slag from a sulfuric acid plant as raw material, with a TFe grade of 61.60% and an Al grade of 0.76%, the sulfuric acid slag was sorted according to the following steps: 1. Screening. The sulfuric acid slag is screened and classified to obtain two grades: +80 mesh and -80 mesh. 2. Pre-magnetization. The raw material under -80 mesh sieve is placed in an electromagnetic washing machine with a magnetic field strength of 230 Gs for weak magnetic separation, and the water pressure is set to 0.4 m. 3 / h, to obtain pre-magnetic separation products; 3. Grinding. A vertical stirred ball mill (grinding media: 5 mm zirconium balls) is used to grind the pre-magnetic separation product to a density of -0.023 mm greater than 90%, with a ball mill slurry concentration of 30%, to obtain the ground product; 4. Weak magnetic separation. The acid-leached solid product is placed in a drum-type wet weak magnetic separator with a magnetic field strength of 1000 Gs for weak magnetic separation to obtain the magnetically separated product; 5. Flotation. The magnetic separation product is placed in a flotation column for reverse flotation separation. The feed concentration is 12%. The depressant is one or a combination of starch, dextrin, carboxymethyl cellulose, tannin, and sodium lignosulfonate. The collector is a mixed amine cationic collector of quaternary ammonium salt, ether amine, and dodecylamine in a ratio of 1:1:1. The bottom product obtained is the iron concentrate product, with a TFe grade of 68.48%, an Al grade of 0.166%, and an iron concentrate purity of 96.18%.

[0030] Comparative Example 2 Using sulfuric acid slag from a sulfuric acid plant as raw material, with a TFe grade of 61.60% and an Al grade of 0.76%, the sulfuric acid slag was sorted according to the following steps: 1. Screening. The sulfuric acid slag is screened and classified to obtain two grades: +80 mesh and -80 mesh. 2. Pre-magnetization. The raw material under -80 mesh sieve is placed in an electromagnetic washing machine with a magnetic field strength of 230 Gs for weak magnetic separation, and the water pressure is set to 0.4 m. 3 / h, to obtain pre-magnetic separation products; 3. Grinding. A vertical stirred ball mill (grinding media: 5 mm zirconium balls) is used to grind the pre-magnetic separation product to a density of -0.023 mm greater than 90%, with a ball mill slurry concentration of 30%, to obtain the ground product; 4. Weak magnetic separation. The acid-leached solid product is placed in a drum-type wet weak magnetic separator with a magnetic field strength of 1000 Gs for weak magnetic separation. The magnetically separated product is the iron concentrate product, with a TFe grade of 67.02%, an Al grade of 0.283%, and an iron concentrate purity of 94.13%.

[0031] Comparative Example 3 Using sulfuric acid slag from a sulfuric acid plant as raw material, with a TFe grade of 61.60% and an Al grade of 0.76%, the sulfuric acid slag was sorted according to the following steps: 1. Screening. The sulfuric acid slag is screened and classified to obtain two grades: +80 mesh and -80 mesh. 2. Pre-magnetization. The raw material under -80 mesh sieve is placed in an electromagnetic washing machine with a magnetic field strength of 230 Gs for weak magnetic separation, and the water pressure is set to 0.4 m. 3 / h, to obtain pre-magnetic separation products; 3. Grinding. A vertical stirred ball mill (grinding media: 5 mm zirconium balls) is used to grind the pre-magnetic separation product to a density of -0.023 mm greater than 90%, with a ball mill slurry concentration of 30%, to obtain the ground product; 4. Flotation. The magnetic separation product is placed in a flotation column for reverse flotation separation. The feed concentration is 12%. The depressant is one or a combination of starch, dextrin, carboxymethyl cellulose, tannin, and sodium lignosulfonate. The collector is a mixed amine cationic collector of quaternary ammonium salt, ether amine, and dodecylamine in a ratio of 1:1:1. The bottom product obtained is the iron concentrate product, with a TFe grade of 65.57%, an Al grade of 0.351%, and an iron concentrate purity of 92.09%.

[0032] The key technical indicators (yield, grade, recovery rate) of the iron concentrate finally obtained by the above embodiments and comparative examples are shown in Table 1 below.

[0033] Table 1 Key Technical Indicators of Iron Concentrate

[0034] Note: The feed is sulfuric acid black slag; the concentrate is low-aluminum high-grade iron concentrate; the comprehensive tailings are all tailings generated from key process steps such as pre-magnetization, flotation and magnetic separation. Concentrate yield (%) = (concentrate weight / feed weight) × 100%.

[0035] As shown in the table above, the total iron grade in the concentrate from Examples 1 to 4 remained consistently above 69%, specifically 69.09%, 69.21%, 69.01%, and 69.69%. In contrast, the total iron grades in Comparative Examples 1 to 3 were lower, at 68.48%, 67.02%, and 65.57%, respectively. This indicates that the total iron grade of the concentrate was significantly improved using the preparation method of the present invention. The aluminum grade in Examples 1 to 4 decreased to below 0.10%, specifically 0.09%, 0.10%, 0.10%, and 0.09%. The aluminum grade in Comparative Example 1 was 0.166%, while the aluminum grades in Comparative Examples 2 and 3 were higher, at 0.283% and 0.351%, respectively, demonstrating the effectiveness of the present invention in deep dealuminization. The concentrate yield of the examples ranged from 52.72% to 56.58%, while the comparative examples, although having higher yields (e.g., Comparative Example 2 reached 78.37%, and its iron recovery rate was also as high as 85.27%), had significantly lower total iron grade and higher aluminum grade, indicating that their control over grade and impurities was not as good as that of the examples. The iron recovery rate (TFe recovery rate) of the examples ranged from 59.11% to 63.48%, indicating that while improving the concentrate grade, a high iron recovery rate was also maintained.

[0036] In addition, the tailings of the embodiment had a lower overall iron grade (50.82% to 53.76%) and a higher aluminum grade (1.52% to 1.71%), indicating that less iron was lost from the tailings and more impurities such as aluminum were separated into the tailings. The tailings of the comparative example had a relatively higher overall iron grade and a lower aluminum grade (e.g., the aluminum grade of the tailings of Comparative Example 1 was 1.43%), but overall it was not as efficient as the embodiment in separating iron and aluminum.

Claims

1. A method for preparing low-alumina, high-grade iron concentrate using sulfuric acid slag, wherein the low-alumina, high-grade iron concentrate is used in the production of ferric phosphate, characterized in that... Includes the following steps: S1. Screening: The sulfuric acid slag is screened and classified to obtain fine-particle products; S2. Pre-magnetization: Pre-magnetic separation is performed on the fine-particle product to obtain a pre-magnetically separated product; S3. Grinding: Grinding the pre-magnetic separation product to obtain a ground product; S4. Acid leaching: After dehydration, the grinding product is subjected to acid leaching to obtain acid-leached solid product; The acid leaching treatment is a two-stage acid leaching process, including: First stage of acid leaching: A first stage of acid leaching is carried out using sulfuric acid with a concentration of 20-50 g / L, a liquid-to-solid ratio of 4-5 mL / g, a temperature of 60-80℃, and a time of 60-90 min; Second stage acid leaching: Organic acid and leaching aid are added for second stage acid leaching to obtain acid-leached solid product; the concentration of organic acid in the total system is 1%-2%, the concentration of leaching aid in the total system is 0.2%-0.5%, the temperature is 60-80℃, and the time is 90-120min; S5. Weak magnetic separation: The acid-leached solid product is subjected to weak magnetic separation to obtain magnetic concentrate; S6. Flotation: The magnetic concentrate is subjected to reverse flotation to obtain the low-alumina, high-grade iron concentrate.

2. The preparation method according to claim 1, characterized in that, In step S1, the sieve used for screening and grading is 80 mesh, and the fine-particle product is the product under-screened from the -80 mesh sieve.

3. The preparation method according to claim 1, characterized in that, In step S2, the pre-magnetic separation uses an electromagnetic washing machine with a magnetic field strength of 200-250 Gs and a water pressure of 0.4-0.5 m. 3 / h.

4. The preparation method according to claim 1, characterized in that, In step S3, the grinding is carried out using a vertical stirred ball mill with 5 mm zirconium balls as the grinding media; the pre-magnetic separation product is ground to a particle size of -0.023 mm or more, with a grinding concentration of 30%-50%.

5. The preparation method according to claim 1, characterized in that, In step S4, the organic acid is one or more of citric acid, oxalic acid, and ethylenediaminetetraacetic acid.

6. The preparation method according to claim 1, characterized in that, The immersion aid is sodium fluoride.

7. The preparation method according to claim 1, characterized in that, In step S5, the magnetic field strength used in the weak magnetic separation is 800-1200 Gs.

8. The preparation method according to claim 1, characterized in that, In step S6, the reverse flotation is carried out in a flotation column with a pulp concentration of 10%-15%. The inhibitors used in the reverse flotation are one or more of starch, dextrin, carboxymethyl cellulose, tannin, and sodium lignosulfonate. The collector used is a mixed amine cationic collector composed of quaternary ammonium salt, ether amine, and dodecylamine in a certain proportion.

9. A low-alumina, high-grade iron concentrate for the production of ferric phosphate, characterized in that, Prepared by the method of any one of claims 1-9, the total iron content is not less than 69% and the aluminum content is not more than 0.10%.

Images