Method for purifying iron oxide for soft magnetic ferrite from red mud and application

Abstract

The invention belongs to the technical field of iron oxide preparation, and discloses a method for purifying iron oxide for soft magnetic ferrite from red mud and application of the method. The red mud is subjected to crushing and wet grinding, and red mud slurry is obtained; the red mud slurry is subjected to magnetic separation, drying and grinding into powder, and a magnetic product containing ferric oxide is obtained; the magnetic product is subjected to acid leaching and suction filtration with hydrochloric acid, and first filtrate is obtained; carrying out alkaline leaching treatment on the first filtrate by adopting sodium hydroxide, filtering and drying to obtain a red brown dry material; grinding the red brown dry material into powder, washing with deionized water, carrying out suction filtration, and drying to obtain a first dry material; and grinding the first dry material to a powder state, and carrying out aerobic sintering to obtain the reddish brown solid iron oxide. The iron oxide extracted through the method can replace existing high-purity commercial iron oxide and can be applied to preparation and development of soft magnetic materials, and various properties of the soft magnetic materials are indifferent or even higher.

Description

Technical Field

[0001] The invention belongs to the technical field of iron oxide preparation, and particularly relates to a method for purifying iron oxide for soft ferrite from red mud and application thereof. Background Art

[0002] Magnetite (Fe₃O₄) was the first iron-based magnetic material discovered. Its properties were exploited to develop permanent magnets and related mechanical devices. Subsequently, the discovery of the unique property of iron oxide (Fe₂O₃) exhibiting weak magnetism in its normal state led to the development of soft ferrite materials. By the 21st century, humans had developed sophisticated technology for producing high-performance iron oxide, significantly improving the performance of soft magnetic material powders and their corresponding devices.

[0003] Currently, the production of high-purity iron oxide (purity above 99.92%) is expensive, and therefore the cost of producing the corresponding soft magnetic materials is relatively high. The production of alumina also generates a significant amount of waste—red mud. Because red mud contains large amounts of iron oxide and other hazardous substances (such as aluminum oxide, calcium oxide, sodium oxide, silicon oxide, and titanium oxide), these substances pose a significant threat to the ecological environment and the socioeconomic environment. Dried red mud is classified as Class II general industrial solid waste according to the National List of Hazardous Wastes. Therefore, based on the principles of harmlessness, resource utilization, and economic efficiency, the effective utilization of iron oxide in red mud for the development and preparation of soft magnetic materials will not only save costs and resources but also bring significant economic benefits. Summary of the Invention

[0004] To solve the above problems, the present invention provides a method and application of purifying iron oxide for soft magnetic ferrite from red mud. The iron oxide extracted by the present invention can replace the existing high-purity iron oxide and can be used in the preparation and development of soft magnetic materials, and can make the various properties of soft magnetic materials the same or even higher.

[0005] The technical solution adopted in the present invention is as follows: A method for purifying iron oxide for soft ferrite from red mud comprises the following steps: Crushing and wet-grinding the red mud to obtain red mud slurry; The red mud slurry is subjected to magnetic separation, drying, and grinding into powder to obtain a magnetic product containing iron oxide; The magnetic product is acid-leached with hydrochloric acid and filtered to obtain a first filtrate; The first filtrate is subjected to alkaline leaching treatment with sodium hydroxide, filtered, and dried to obtain a reddish-brown dry material; Grinding the reddish-brown dry material into a powder state, washing with deionized water, filtering, and drying to obtain a first dry material; The first dry material is ground into a powder state and then subjected to oxygen sintering to obtain reddish-brown solid iron oxide.

[0006] Preferably, the red mud is crushed and wet-ground to obtain the red mud slurry, and the particle size of the crushed red mud particles reaches the millimeter level; during wet grinding, the particle size of the red mud particles is controlled to be at the micron level; during the wet grinding process, deionized water is used to adjust the slurry, and the mass concentration of the obtained red mud slurry is controlled to be 34%-36%.

[0007] Preferably, the red mud slurry is subjected to step-by-step multi-stage circulating magnetic separation, and then dried and ground into powder. The obtained magnetic product containing iron oxide contains, by mass percentage, 78% to 88% iron oxide, 5% to 10% aluminum oxide, 2% to 4% calcium oxide, 1% to 2% silicon oxide, and less than 1% titanium oxide, with the remainder being impurities.

[0008] Preferably, when the magnetic product is acid-leached with hydrochloric acid, the mass ratio of iron oxide to hydrochloric acid in the magnetic product is controlled to be 1:(1.0-2.5), the mass concentration of the hydrochloric acid is 36%-38%, the acid leaching temperature is 50-85°C, the acid leaching time is 5-8h, and the stirring rate is 160-200r / min.

[0009] Preferably, when the first filtrate is subjected to alkali leaching treatment with sodium hydroxide, sodium hydroxide is added to the first filtrate, and the mass ratio of ferric chloride in the first filtrate to the added sodium hydroxide is controlled to be 1:(1.5-3.5), the alkali leaching temperature is 50-90°C, the alkali leaching time is 6-10 hours, and the stirring rate is 160-200 r / min.

[0010] Preferably, the reddish-brown dry material is ground into a powder state, then washed with deionized water, filtered, and dried to obtain the first dry material: During water washing, the water washing temperature is controlled at 50-55°C and the washing time is 1-2h; after filtration, the mixture is transferred to a rotary flash dryer for drying, and during drying, the air inlet temperature is controlled at 195-205°C and the air outlet temperature is controlled at 115-125°C.

[0011] Preferably, after the first dry material is ground into a powder state, oxygen sintering is performed in a muffle furnace; During oxygen sintering, the roasting temperature is controlled to be 400~650℃, the holding time is 1-5-2.5h, and the furnace is cooled after the holding is completed to obtain reddish-brown solid iron oxide with a moisture content of less than 0.3%.

[0012] Preferably, the red mud comprises, by mass percentage, 35% to 50% iron oxide, 15% to 25% aluminum oxide, 8% to 13% calcium oxide, 6% to 10% sodium oxide, 0.5% to 2% silicon oxide, 0% to 1% titanium oxide, and the remainder is impurities. The reddish-brown solid iron oxide comprises, by mass percentage, iron oxide ≥ 99.25%, aluminum oxide ≤ 0.08%, calcium oxide ≤ 0.01%, silicon oxide ≤ 0.08%, titanium oxide ≤ 0.005%, sodium oxide ≤ 0.015%, and the remainder is impurities.

[0013] The present invention also provides the use of the above-mentioned method for purifying iron oxide for soft ferrite from red mud. Specifically, the obtained reddish-brown solid iron oxide is used for the preparation of soft ferrite materials.

[0014] Preferably, the reddish-brown solid iron oxide is made into powder and used as a raw material for preparing a nickel-zinc-based soft ferrite material with a magnetic permeability of 3000@100MHz; The preparation process of the nickel-zinc-based soft ferrite material is as follows: Fe2O3 powder, ZnO powder and NiO powder were wet-milled in a mass ratio of 7:1.8:1.2 to obtain a mixture A. During the wet-milling, the weight ratio of zirconium balls: ultrapure water: powder was 6:(1.4-1.6):1, the ball milling speed was 100-300 r / min, and the wet-milling time was 3-6 h. Mixture A is dried, and then pre-calcined and dried to obtain material B, wherein the pre-calcination temperature is controlled at 900-940° C., the pre-calcination time is 90-150 minutes, and the pre-calcination atmosphere is air; Doping components are added to material B, ball milling is performed to mix the mixture, and then drying is performed to obtain a mixture C; wherein the ball milling time is controlled at 5.5-6.5 hours; the doping components include MoO3, CaCO3, V2O5 and Nb2O5, the MoO3 content is 0.06%-0.10% of the mass of material B, the CaCO3 content is 0.01%-0.04% of the mass of material B, the V2O5 content is 0.03%-0.07% of the mass of material B; and the Nb2O5 content is 0.02%-0.07% of the mass of material B; The mixture C is granulated and pressed to obtain a sample ring blank, specifically comprising: adding polyvinyl alcohol glue to the mixture C for granulation, wherein the mass of the polyvinyl alcohol glue is 8% to 12% of the mass of the mixture C, and the granulation particle size is 120 to 250 μm; during the pressing, 0.14% of zinc stearate by weight of the mixture C is added to the mixture C as a release agent, and the molding method adopts bidirectional pressurized cold pressing molding, and the molding pressure is 10 MPa; The sample ring blank is sintered using a gradient heating process, specifically including: first heating to 450°C at a heating rate of 1.3~1.7°C / min, keeping warm for 2h, then heating to 900°C at a heating rate of 2.8~3.5°C / min, and then heating to 1100~1170°C at a heating rate of 1.8~2.2°C / min, keeping warm for 2h, and then naturally cooling in the furnace to obtain the ferrite magnetic ring.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention is achieved through the following technical solutions: The process of the present invention is a new process combining magnetic separation-acid leaching-alkali leaching-roasting-water washing to purify iron oxide. The process is simple, green and pollution-free, with a high purification rate. The equipment is easy to operate and economical, with fewer types of reagents and low prices. Among them, the magnetic separation process is extremely critical. The use of multi-stage step-by-step magnetic separation can remove a large number of wrapped and embedded impurities, so that the iron oxide is basically dissociated from other oxides, greatly improving the purity of the iron oxide and making sufficient preparations for the subsequent acid leaching and alkali leaching treatments. The process route of the present invention allows the high-value-added iron oxide in red mud to be recycled, achieving the purpose of harmless resource utilization, thereby turning waste into treasure; more importantly, the purity of the obtained iron oxide is high, reaching the new standard for iron oxide used in the soft magnetic industry, and is used to replace the existing high-purity iron oxide powder for sale. It is used in the preparation of nickel-zinc-based ferrite magnetic powder and has excellent performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of graded magnetic separation for purifying iron oxide for soft ferrite from red mud in an embodiment of the present invention; Figure 2 The present invention is a flowchart of a method for purifying iron oxide for soft magnetic ferrite from red mud in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The present invention will be described clearly and completely below with reference to the accompanying drawings and embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, not all embodiments.

[0018] The present invention can purify high-performance iron oxide for soft magnetic ferrite from solid waste - red mud. The purified iron oxide is mainly used in the preparation of nickel-zinc-based soft ferrite materials.

[0019] The method for purifying iron oxide for soft ferrite from red mud of the present invention comprises the following steps: First, the red mud is pretreated. The red mud raw material is placed in a crusher and crushed, and then wet-ground to a certain particle size to obtain red mud slurry; after slurry adjustment, it is placed in a magnetic separator for magnetic separation to obtain the magnetic product iron oxide, which is then dried and ground for later use.

[0020] The magnetic product iron oxide obtained by magnetic separation is subjected to acid-base, alkaline leaching, roasting, water washing and drying treatment to obtain the target product iron oxide, whose purity reaches more than 99.25%. The content of other impurities is: aluminum oxide ≤0.08%, calcium oxide ≤0.01%, silicon oxide ≤0.08%, titanium oxide ≤0.005%, sodium oxide ≤0.015%, meeting the new standard for iron oxide used in the soft magnetic industry.

[0021] The purified iron oxide is used as the raw material of nickel-zinc-based soft magnetic ferrite material. After the processes of primary ball milling, pre-sintering, secondary ball milling, granulation, molding, sintering and the like, a nickel-zinc-based magnetic ring is obtained, and its magnetic permeability is measured.

[0022] More specifically, see Figure 1 and Figure 2 The method for purifying soft ferrite iron oxide from red mud of the present invention comprises the following steps: Step (1), magnetic separation: first, pre-treat the red mud, that is, place the red mud raw material in a crusher, crush it, and then wet-grind it to a certain particle size to obtain red mud slurry; after slurry adjustment, place it in a magnetic separator for magnetic separation to obtain fine iron ore - magnetic iron oxide (i.e., a magnetic product containing iron oxide), dry it and grind it for later use. The red mud contains, by mass percentage, 35% to 50% iron oxide, 15% to 25% aluminum oxide, 8% to 13% calcium oxide, 6% to 10% sodium oxide, 0.5% to 2% silicon oxide, 0 to 1% titanium oxide, and the remainder is impurities.

[0023] During magnetic separation, the crusher crushing time is 8 seconds, so that the particle size of the red mud particles reaches the millimeter level, which facilitates the better exposure of the iron oxide. During wet grinding, the red mud particle size is controlled to the micron level to maximize the monomer dissociation of the iron oxide and other minerals. During slurry adjustment, the mass concentration of the slurry is controlled to be 35% ± 1% (wherein ± 1% is the error in operation. In the following embodiments of the present invention, the slurry is adjusted at a nominal value of 35%, and the actual mass concentration is between 34% and 36%). The magnetic separation process adopts step-by-step multi-stage circulation magnetic separation. For details, see Figure 1 Magnetic separation is divided into three steps for cyclic magnetic separation. The first step: after the first-level magnetic separation, the first-level impurities and the first-level crude iron ore are obtained; the second step, the first-level crude iron ore is subjected to the second-level magnetic separation to obtain the second-level impurities and the second-level crude iron ore; the second-level crude iron ore is subjected to the third-level magnetic separation to obtain the third-level impurities and fine iron ore, and the fine iron ore is used as the magnetic product after magnetic separation; the content of each substance in the iron oxide of the magnetic product obtained after magnetic separation is: iron oxide 78%~88%, aluminum oxide 5%~10%, calcium oxide 2%~4%, silicon oxide 1%~2%, titanium oxide <1%, and the rest is impurities.

[0024] Step (2), acid leaching: the magnetic product containing iron oxide obtained in step (1) is mixed with hydrochloric acid in a certain proportion, and then placed in an oil bath pot-three-necked flask for acid leaching. The acid leaching temperature and time are appropriately controlled, and a ferric chloride solution is obtained after filtration. The mass ratio of iron oxide to hydrochloric acid in the magnetic product is controlled to be 1: (1.0-2.5), the mass concentration of the hydrochloric acid is 36%-38%, the acid leaching temperature is 50-85°C, the acid leaching time is 5-8h, and the stirring rate is 160-200r / min.

[0025] Step (3), alkali leaching: The ferric chloride solution obtained by acid leaching in step (2) and sodium hydroxide are mixed in a certain proportion and placed in a three-necked flask for alkali leaching. The alkali leaching temperature and time are appropriately controlled to obtain ferric hydroxide precipitate and sodium chloride solution; after filtration and drying, a reddish-brown ferric hydroxide dry material is obtained. The mass ratio of ferric chloride to added sodium hydroxide in the first filtrate is controlled to be 1:(1.5-3.5), the alkali leaching temperature is 50-90°C, the alkali leaching time is 6-10 hours, and the stirring rate is 160 r / min.

[0026] Step (4), water washing: In order to remove soluble impurities such as sodium hydroxide and sodium aluminate remaining in the ferric hydroxide, the obtained reddish-brown ferric hydroxide dry material is ground into a powder state, and then deionized water is added to a three-necked flask and washed for a certain period of time, wherein the water washing temperature is controlled to be 50-55°C and the water washing time is 1-2h; then, after filtration, it is transferred to a rotary flash dryer for drying, and the air inlet temperature is controlled to be 200±5°C and the air outlet temperature is controlled to be 120±5°C to obtain pure ferric hydroxide dry material for use.

[0027] Step (5), calcination: After the washed purified ferric hydroxide is ground into a powder, it is placed in a muffle furnace for oxygen sintering to obtain the target product, reddish-brown solid ferric oxide. When calcining in the muffle furnace, the calcination temperature is controlled to be 400-650°C, and the temperature is kept for 1-5-2.5 hours to obtain the target product, ferric oxide, while the moisture content is reduced to ensure that the moisture content is less than 0.3%. After the temperature is kept, the product is cooled in the furnace.

[0028] The purity of iron oxide purified by the combined process of magnetic separation-acid leaching-alkaline leaching-roasting-water washing is ≥99.25%, among which aluminum oxide ≤0.08%, calcium oxide ≤0.01%, silicon oxide ≤0.08%, titanium oxide ≤0.005%, and sodium oxide ≤0.015%, meeting the new standard for iron oxide used in the soft magnetic industry.

[0029] The iron oxide prepared by the above method of the present invention can be applied to the development and research of soft magnetic ferrite materials and related materials. The present invention is particularly applicable to the preparation of nickel-zinc-based soft magnetic ferrite materials.

[0030] The purified iron oxide is used as the raw material of nickel-zinc-based soft ferrite material. After the processes of primary ball milling, pre-sintering, secondary ball milling, granulation, molding and sintering, nickel-zinc-based magnetic ring is obtained. The detailed preparation process is as follows: Fe2O3 powder, ZnO powder and NiO powder were wet-milled in a mass ratio of 7:1.8:1.2 to obtain a mixture A. During the wet-milling, the weight ratio of zirconium balls: ultrapure water: powder was 6:(1.4-1.6):1, the ball milling speed was 100-300 r / min, and the wet-milling time was 3-6 h. Mixture A is dried, and then pre-calcined and dried to obtain material B, wherein the pre-calcination temperature is controlled at 900-940° C., the pre-calcination time is 90-150 minutes, and the pre-calcination atmosphere is air; Doping components are added to material B, ball milling is performed to mix the mixture, and then drying is performed to obtain a mixture C; wherein the ball milling time is controlled at 5.5-6.5 hours; the doping components include MoO3, CaCO3, V2O5 and Nb2O5, the MoO3 content is 0.06%-0.10% of the mass of material B, the CaCO3 content is 0.01%-0.04% of the mass of material B, the V2O5 content is 0.03%-0.07% of the mass of material B; and the Nb2O5 content is 0.02%-0.07% of the mass of material B; The mixture C is granulated and pressed to obtain a sample ring blank, specifically comprising: adding polyvinyl alcohol glue to the mixture C for granulation, wherein the mass of the polyvinyl alcohol glue is 8% to 12% of the mass of the mixture C, and the granulation particle size is 120 to 250 μm; during the pressing, 0.14% of zinc stearate by weight of the mixture C is added to the mixture C as a release agent, and the molding method adopts bidirectional pressurized cold pressing molding, and the molding pressure is 10 MPa; The sample ring blank is sintered using a gradient heating process, specifically including: first heating to 450°C at a heating rate of 1.3~1.7°C / min, keeping warm for 2h, then heating to 900°C at a heating rate of 2.8~3.5°C / min, and then heating to 1100~1170°C at a heating rate of 1.8~2.2°C / min, keeping warm for 2h, and then naturally cooling in the furnace to obtain the ferrite magnetic ring.

[0031] In the following embodiments of the present invention, the process for preparing the nickel-zinc-based magnetic ring is the same as the above process, and the specific process and parameters are as follows: Fe2O3 powder, ZnO powder and NiO powder were wet-milled in a mass ratio of 7:1.8:1.2 to obtain a mixture A. During the wet-milling, the weight ratio of zirconium balls: ultrapure water: powder was 6:1:1, the ball milling speed was 240 r / min, and the wet-milling time was 5 h. Mixture A is dried, and then pre-calcined and dried to obtain material B, wherein the pre-calcination temperature is controlled at 925° C., the pre-calcination time is 110 minutes, and the pre-calcination atmosphere is air; Doping components (including MoO3, CaCO3, V2O5 and Nb2O5) were added to material B, wherein the content of MoO3 was 0.06% by weight of material B, the content of CaCO3 was 0.02% by weight of material B, the content of V2O5 was 0.03% by weight of material B, and the content of Nb2O5 was 0.02% by weight of material B, and then ball milling was performed to mix the mixture, followed by drying to obtain a mixture C, wherein the ball milling time was controlled within 5.5 h; The mixture C is granulated and pressed to obtain a sample ring blank, specifically comprising: adding polyvinyl alcohol glue to the mixture C for granulation, wherein the mass of the polyvinyl alcohol glue is 12% of the mass of the mixture C, and the granulation particle size is 130 μm; during the pressing, 0.14% of zinc stearate by weight of the mixture C is added to the mixture C as a release agent, and the molding method adopts bidirectional pressurized cold pressing molding, and the molding pressure is 10 MPa; The sample ring blank is sintered using a gradient heating process, specifically including: first heating to 450°C at a heating rate of 1.3°C / min, keeping warm for 2 hours, then heating to 900°C at a heating rate of 2.8°C / min, and then heating to 1140°C at a heating rate of 2°C / min, keeping warm for 2 hours, and then naturally cooling in the furnace to obtain the ferrite magnetic ring.

[0032] In the following embodiments of the present invention, the red mud used includes, by mass percentage, 45% iron oxide, 26% aluminum oxide, 13% calcium oxide, 10% sodium oxide, 2% silicon oxide, 1% titanium oxide, and the remainder is unavoidable impurities.

[0033] Example 1: The method for purifying iron oxide for soft ferrite from red mud in this embodiment comprises the following steps: Step 1: Magnetic separation (1) Crushing: The red mud raw material is placed in a crusher and crushed for 8 seconds to make the particle size of the red mud particles reach the millimeter level. Then, it is wet-milled and slurried with deionized water to control the red mud particle size to the micron level. The mass concentration of the obtained red mud slurry is 35%; (2) Magnetic separation: see Figure 1 The red mud slurry is subjected to graded magnetic separation, which is divided into three steps of cyclic magnetic separation to convert the red mud slurry from coarse iron ore into fine iron ore, dry the moisture and grind it for later use.

[0034] Step 2: Acid leaching An oil bath-three-necked flask-circulating condenser apparatus was constructed; the mass ratio of iron oxide to hydrochloric acid (mass concentration of 36%) in the magnetic product containing iron oxide obtained in step (1) was controlled to be 1:1, the acid leaching temperature was 50°C, the acid leaching time was 5 h, and the stirring rate was 160 r / min; after filtration, the filtrate (containing ferric chloride) was retained for later use.

[0035] Step 3: Alkali Soaking An oil bath-three-necked flask-circulating condenser apparatus was constructed, and the mass ratio of ferric chloride to added sodium hydroxide in the filtrate obtained in step 2 was controlled to be 1:1.5, the alkali leaching temperature was 50°C, the alkali leaching time was 6 h, and the stirring rate was 160 r / min; after filtration, the filter cake (ferric hydroxide) was retained and dried for later use.

[0036] Step 4: Wash Build an oil bath pot-three-necked flask apparatus; in order to remove soluble impurities such as sodium hydroxide, sodium chloride, and sodium aluminate remaining in the filter cake (containing ferric hydroxide) obtained in step 3, grind the filter cake obtained in step 3 into a powder state, add deionized water and wash it in a three-necked flask for a certain period of time; during washing, control the washing temperature to 50±5°C, the washing time to 1.5h, and after filtration, transfer it to a rotary flash dryer for drying, control the inlet air temperature to 200±5°C, and the outlet air temperature to 120±5°C, to obtain pure ferric hydroxide dry material for use.

[0037] Step 5: Firing The ferric hydroxide dry material obtained in step 4 is ground into a powder state and placed in a muffle furnace for aerobic sintering. During aerobic sintering, the roasting temperature is controlled to 400°C. After keeping warm for 2 hours, iron oxide is obtained, and the moisture content is reduced to ensure that the moisture content is less than 0.3%; the target product, iron oxide, is then obtained by grinding it into a powder state.

[0038] The purity and impurity content of the target product iron oxide obtained in this example can be tested as shown in Table 1.

[0039] The purified iron oxide powder was used to prepare a nickel-zinc-based soft ferrite material with a magnetic permeability of 3000@100MHz. A nickel-zinc-based standard magnetic ring was obtained, and its magnetic permeability and Curie temperature were measured. The results are shown in Table 2.

[0040] Example 2: The method for purifying iron oxide for soft ferrite from red mud in this embodiment comprises the following steps: Step 1: Magnetic separation (1) Crushing: The red mud raw material is placed in a crusher and crushed for 8 seconds until the particle size of the red mud particles reaches the millimeter level. It is then wet-milled and slurried with deionized water to control the slurry concentration to 35%; (2) Magnetic separation: see Figure 1The red mud slurry is subjected to graded magnetic separation, which is divided into three steps of cyclic magnetic separation to convert the red mud slurry from coarse iron ore into fine iron ore, dry the moisture and grind it for later use.

[0041] Step 2: Acid leaching An oil bath-three-necked flask-circulating condenser apparatus was constructed; the mass ratio of iron oxide to hydrochloric acid (mass concentration of 36%) in the magnetic product containing iron oxide obtained in step (1) was controlled to be 1:1.55, the acid leaching temperature was 70°C, the acid leaching time was 6.5 h, and the stirring rate was 160 r / min; after filtration, the filtrate (containing ferric chloride) was retained for later use.

[0042] Step 3: Alkali Soaking An oil bath-three-necked flask-circulating condenser apparatus was constructed, and the mass ratio of ferric chloride to added sodium hydroxide in the filtrate obtained in step 2 was controlled to be 1:2.5, the alkali leaching temperature was 75°C, the alkali leaching time was 8 h, and the stirring rate was 160 r / min; after filtration, the filter cake (ferric hydroxide) was retained and dried for later use.

[0043] Step 4: Wash An oil bath-three-necked flask apparatus was constructed; in order to remove soluble impurities such as sodium hydroxide, sodium chloride, and sodium aluminate remaining in the filter cake (containing ferric hydroxide) obtained in step three, the filter cake obtained in step three was ground into a powder state, and then deionized water was added to a three-necked flask and washed for a certain period of time; during washing, the washing temperature was controlled at 50°C, the washing time was 1.5h, and after filtration, the mixture was transferred to a rotary flash dryer for drying, and the inlet air temperature was controlled at 200±5°C and the outlet air temperature was controlled at 120±5°C to obtain pure ferric hydroxide dry material for use.

[0044] Step 5: Firing The ferric hydroxide dry material obtained in step 4 is ground into a powder state and placed in a muffle furnace for aerobic sintering. During aerobic sintering, the roasting temperature is controlled to 500°C. After keeping warm for 2 hours, iron oxide is obtained, and the moisture content is reduced to ensure that the moisture content is less than 0.3%; the target product, iron oxide, is then obtained by grinding it into a powder state.

[0045] The purity and impurity content of the target product iron oxide obtained in this example can be tested as shown in Table 1.

[0046] The purified iron oxide powder was used to prepare a nickel-zinc-based soft ferrite material with a magnetic permeability of 3000@100MHz. A nickel-zinc-based standard magnetic ring was obtained, and its magnetic permeability and Curie temperature were measured. The results are shown in Table 2.

[0047] Example 3: The method for purifying iron oxide for soft ferrite from red mud in this embodiment comprises the following steps: Step 1: Magnetic separation (1) Crushing: The red mud raw material is placed in a crusher and crushed for 8 seconds until the particle size of the red mud particles reaches the millimeter level. It is then wet-milled and slurried with deionized water to control the slurry concentration to 35%; (2) Magnetic separation: see Figure 1 The red mud slurry is subjected to graded magnetic separation, which is divided into three steps of cyclic magnetic separation to convert the red mud slurry from coarse iron ore into fine iron ore, dry the moisture and grind it for later use.

[0048] Step 2: Acid leaching An oil bath-three-necked flask-circulating condenser apparatus was constructed; the mass ratio of iron oxide to hydrochloric acid (mass concentration of 36%) in the magnetic product containing iron oxide obtained in step (1) was controlled to be 1:2, the acid leaching temperature was 80°C, the acid leaching time was 8 h, and the stirring rate was 160 r / min; after filtration, the filtrate (containing ferric chloride) was retained for later use.

[0049] Step 3: Alkali Soaking An oil bath-three-necked flask-circulating condenser apparatus was constructed, and the mass ratio of ferric chloride to added sodium hydroxide in the filtrate obtained in step 2 was controlled to be 1:3, the alkali leaching temperature was 80°C, the alkali leaching time was 9 h, and the stirring rate was 160 r / min; after filtration, the filter cake (ferric hydroxide) was retained and dried for later use.

[0050] Step 4: Wash Build an oil bath pot-three-necked flask apparatus; in order to remove soluble impurities such as sodium hydroxide, sodium chloride, and sodium aluminate remaining in the filter cake (containing ferric hydroxide) obtained in step 3, grind the filter cake obtained in step 3 into a powder state, add deionized water and wash it in a three-necked flask for a certain period of time; during washing, control the washing temperature to 50±5°C, the washing time to 1.5h, and after filtration, transfer it to a rotary flash dryer for drying, control the inlet air temperature to 200±5°C, and the outlet air temperature to 120±5°C, to obtain pure ferric hydroxide dry material for use.

[0051] Step 5: Firing The iron hydroxide obtained in step 4 is placed in a muffle furnace for aerobic sintering. During aerobic sintering, the calcination temperature is controlled to 600°C. After keeping warm for 2 hours, iron oxide is obtained. At the same time, the moisture content is reduced to ensure that the moisture content is less than 0.3%; and then the target product, iron oxide, is obtained by grinding it into a powder state.

[0052] The purity and impurity content of the target product iron oxide obtained in this example can be tested as shown in Table 1.

[0053] The purified iron oxide powder was ground into powder and used to prepare a nickel-zinc-based soft ferrite material with a magnetic permeability of 3000@100MHz. A nickel-zinc-based standard magnetic ring was obtained, and its magnetic permeability and Curie temperature were measured. The results are shown in Table 2.

[0054] Example 4: The method for purifying iron oxide for soft ferrite from red mud in this embodiment comprises the following steps: Step 1: Magnetic separation (1) Crushing: Place the red mud raw material in a crusher and crush it for 8 seconds, then add deionized water to adjust the slurry so that the particle size of the red mud particles reaches the millimeter level, and then wet grind it and control the slurry mass concentration to 35%; (2) Magnetic separation: see Figure 1 The red mud slurry is subjected to graded magnetic separation, which is divided into three steps of cyclic magnetic separation to convert the red mud slurry from coarse iron ore into fine iron ore, dry the moisture and grind it for later use.

[0055] Step 2: Acid leaching An oil bath-three-necked flask-circulating condenser apparatus was constructed; the mass ratio of iron oxide to hydrochloric acid (mass concentration of 36%) in the magnetic product containing iron oxide obtained in step (1) was controlled to be 1:2.5, the acid leaching temperature was 85°C, the acid leaching time was 8 hours, and the stirring rate was 160 r / min; after filtering, the filtrate (containing ferric chloride) was retained for later use.

[0056] Step 3: Alkali Soaking An oil bath-three-necked flask-circulating condenser apparatus was constructed, and the mass ratio of ferric chloride to added sodium hydroxide in the filtrate obtained in step 2 was controlled to be 1:3.5, the alkali leaching temperature was 90°C, the alkali leaching time was 10 h, and the stirring rate was 160 r / min; after filtration, the filter cake (ferric hydroxide) was retained and dried for later use.

[0057] Step 4: Wash Build an oil bath pot-three-necked flask apparatus; in order to remove soluble impurities such as sodium hydroxide, sodium chloride, and sodium aluminate remaining in the filter cake (containing ferric hydroxide) obtained in step 3, grind the filter cake obtained in step 3 into a powder state, add deionized water and wash it in a three-necked flask for a certain period of time; during washing, control the washing temperature to 50±5°C, the washing time to 1.5h, and after filtration, transfer it to a rotary flash dryer for drying, control the inlet air temperature to 200±5°C, and the outlet air temperature to 120±5°C, to obtain pure ferric hydroxide dry material for use.

[0058] Step 5: Firing The ferric hydroxide dry material obtained in step 4 is ground into a powder state and placed in a muffle furnace for aerobic sintering. During aerobic sintering, the roasting temperature is controlled to 600°C. After keeping warm for 2 hours, iron oxide is obtained, and the moisture content is reduced to ensure that the moisture content is less than 0.3%; the target product, iron oxide, is then obtained by grinding it into a powder state.

[0059] The purity and impurity content of the target product iron oxide obtained in this example can be tested as shown in Table 1.

[0060] The purified iron oxide powder was used to prepare a nickel-zinc-based soft ferrite material with a magnetic permeability of 3000@100MHz. A nickel-zinc-based standard magnetic ring was obtained, and its magnetic permeability and Curie temperature were measured. The results are shown in Table 2.

[0061] Comparative Example: Commercial iron oxide (SRP, brand name: Changzhou Licai Chemical Co., Ltd.) was used as the raw material to prepare a nickel-zinc-based soft ferrite material with a magnetic permeability of 3000@100MHz. A nickel-zinc-based standard magnetic ring was obtained. Its magnetic permeability and Curie temperature were measured. The results are shown in Table 2.

[0062] The purity and impurity content of the iron oxide in each embodiment can be tested as shown in Table 1: Table 1

[0063] The performance test results of the application of iron oxide in soft magnetic materials in various embodiments and comparative examples are shown in Table 2: Table 2

[0064] As can be seen from Table 1, the purity and impurities of the iron oxide purified in Examples 1 to 4 all meet the standard requirements, and the purity of Example 2 is as high as 99.33%, with the best purification effect. At the same time, when applied to nickel-zinc-based ferrite materials with a magnetic permeability of 3000, the iron oxides of the four groups of experiments can achieve the same properties as commercial iron oxides. However, as can be seen from Table 2, the soft magnetic material prepared from the iron oxide obtained in Example 2 has the highest magnetic permeability and Curie temperature, with a magnetic permeability of 3200@100MHz and a Curie temperature of T C The temperature is 102℃, which can reach the same level as commercial iron oxide or even higher.

[0065] It can be seen from the above experimental results that the technical solution of the present invention has the following characteristics: (1) The present invention uses a new process of magnetic separation-acid leaching-alkali leaching-roasting-water washing to obtain iron oxide with a purity of ≥99.25%. The contents of other impurities are: aluminum oxide ≤0.08%, calcium oxide ≤0.01%, silicon oxide ≤0.08%, titanium oxide ≤0.005%, and sodium oxide ≤0.015%, reaching the new standard for iron oxide used in the soft magnetic industry.

[0066] (2) The iron oxide described in the present invention is used as a raw material for the development of a nickel-zinc-based soft magnetic ferrite material with a magnetic permeability of 3000@100MHz. The maximum magnetic permeability is measured to be 3200@100MHz, and the maximum Curie temperature is 102°C. The performance is stable and has been improved to a certain extent.

[0067] (3) Taking a certain small and medium-sized soft magnetic material enterprise as a reference, the average annual production of various soft magnetic materials requires about 220 tons of iron oxide. Calculated at RMB 3,500 per ton, the high-purity iron oxide purified from red mud can replace commercial iron oxide, which can save RMB 770,000 per year. At the same time, it also improves the utilization rate of red mud and protects the ecological environment. It achieves three goals at one stroke and realizes a win-win situation for the economy and ecology.

[0068] The foregoing is merely a preferred embodiment of the present invention. It should be noted that improvements and modifications may be made without departing from the present invention, and such improvements and modifications shall also fall within the scope of patent protection of the present invention. Any changes within the meaning and scope equivalent to the claims of the present invention shall be deemed included within the scope of the claims.

Claims

1. A method for purifying iron oxide for soft ferrite from red mud, characterized in that: The process includes the following: Crushing and wet-grinding the red mud to obtain red mud slurry; The red mud slurry is subjected to magnetic separation, drying, and grinding into powder to obtain a magnetic product containing iron oxide; The magnetic product is acid-leached with hydrochloric acid and filtered to obtain a first filtrate; The first filtrate is subjected to alkaline leaching treatment with sodium hydroxide, filtered, and dried to obtain a reddish-brown dry material; Grinding the reddish-brown dry material into a powder state, washing with deionized water, filtering, and drying to obtain a first dry material; The first dry material is ground into a powder state and then subjected to oxygen sintering to obtain reddish-brown solid iron oxide.

2. The method for purifying iron oxide for soft ferrite from red mud according to claim 1, characterized in that: The red mud is crushed and wet-ground to obtain red mud slurry, and the particle size of the crushed red mud particles reaches the millimeter level; during wet grinding, the particle size of the red mud particles is controlled to be at the micron level; during the wet grinding process, deionized water is used to adjust the slurry, and the mass concentration of the obtained red mud slurry is controlled at 34%-36%.

3. The method for purifying iron oxide for soft ferrite from red mud according to claim 1, characterized in that: The red mud slurry is subjected to step-by-step multi-stage circulating magnetic separation, and then dried and ground into powder. The resulting magnetic product containing iron oxide contains, by mass percentage, 78% to 88% iron oxide, 5% to 10% aluminum oxide, 2% to 4% calcium oxide, 1% to 2% silicon oxide, less than 1% titanium oxide, and the remainder is impurities.

4. The method for purifying iron oxide for soft ferrite from red mud according to claim 1, characterized in that: When the magnetic product is acid-leached with hydrochloric acid, the mass ratio of iron oxide to hydrochloric acid in the magnetic product is controlled to be 1:(1.0-2.5), the mass concentration of the hydrochloric acid is 36%-38%, the acid leaching temperature is 50-85°C, the acid leaching time is 5-8h, and the stirring rate is 160-200r / min.

5. The method for purifying iron oxide for soft ferrite from red mud according to claim 1, characterized in that: When the first filtrate is subjected to alkali leaching treatment with sodium hydroxide, sodium hydroxide is added to the first filtrate, and the mass ratio of ferric chloride in the first filtrate to the added sodium hydroxide is controlled to be 1:(1.5-3.5), the alkali leaching temperature is 50-90° C., the alkali leaching time is 6-10 hours, and the stirring rate is 160-200 r / min.

6. The method for purifying iron oxide for soft ferrite from red mud according to claim 1, characterized in that: The reddish-brown dry material is ground into powder, washed with deionized water, filtered, and dried to obtain the first dry material: During water washing, the water washing temperature is controlled at 50-55°C and the washing time is 1-2h; after filtration, the mixture is transferred to a rotary flash dryer for drying, and during drying, the air inlet temperature is controlled at 195-205°C and the air outlet temperature is controlled at 115-125°C.

7. The method for purifying iron oxide for soft ferrite from red mud according to claim 1, characterized in that: After the first dry material is ground into a powder state, oxygen sintering is performed in a muffle furnace; During oxygen sintering, the roasting temperature is controlled to be 400~650℃, the holding time is 1-5-2.5h, and the furnace is cooled after the holding is completed to obtain reddish-brown solid iron oxide with a moisture content of less than 0.3%.

8. The method for purifying iron oxide for soft ferrite from red mud according to claim 1, wherein: The red mud comprises, by mass percentage, 35% to 50% iron oxide, 15% to 25% aluminum oxide, 8% to 13% calcium oxide, 6% to 10% sodium oxide, 0.5% to 2% silicon oxide, 0% to 1% titanium oxide, and the remainder being impurities; The reddish-brown solid iron oxide comprises, by mass percentage, iron oxide ≥ 99.25%, aluminum oxide ≤ 0.08%, calcium oxide ≤ 0.01%, silicon oxide ≤ 0.08%, titanium oxide ≤ 0.005%, sodium oxide ≤ 0.015%, and the remainder is impurities.

9. The use of iron oxide for purifying soft magnetic ferrite from red mud according to claims 1-8, characterized in that: The obtained reddish-brown solid iron oxide is used to prepare soft magnetic ferrite materials.

10. The use according to claim 9, characterized in that The reddish-brown solid iron oxide is made into powder and used as raw material for preparing nickel-zinc-based soft magnetic ferrite material with a magnetic permeability of 3000@100MHz; The preparation process of the nickel-zinc-based soft ferrite material is as follows: Fe2O3 powder, ZnO powder and NiO powder were wet-milled in a mass ratio of 7:1.8:1.2 to obtain a mixture A. During the wet-milling, the weight ratio of zirconium balls: ultrapure water: powder was 6:(1.4-1.6):1, the ball milling speed was 100-300 r / min, and the wet-milling time was 3-6 h. Mixture A is dried, and then pre-calcined and dried to obtain material B, wherein the pre-calcination temperature is controlled at 900-940° C., the pre-calcination time is 90-150 minutes, and the pre-calcination atmosphere is air; Doping components are added to material B, ball milling is performed to mix the mixture, and then drying is performed to obtain a mixture C; wherein the ball milling time is controlled at 5.5-6.5 hours; the doping components include MoO3, CaCO3, V2O5 and Nb2O5, the MoO3 content is 0.06%-0.10% of the mass of material B, the CaCO3 content is 0.01%-0.04% of the mass of material B, the V2O5 content is 0.03%-0.07% of the mass of material B; and the Nb2O5 content is 0.02%-0.07% of the mass of material B; The mixture C is granulated and pressed to obtain a sample ring blank, specifically comprising: adding polyvinyl alcohol glue to the mixture C for granulation, wherein the mass of the polyvinyl alcohol glue is 8% to 12% of the mass of the mixture C, and the granulation particle size is 120 to 250 μm; during the pressing, 0.14% of zinc stearate by weight of the mixture C is added to the mixture C as a release agent, and the molding method adopts bidirectional pressurized cold pressing molding, and the molding pressure is 10 MPa; The sample ring blank is sintered using a gradient heating process, specifically including: first heating to 450°C at a heating rate of 1.3~1.7°C / min, keeping warm for 2h, then heating to 900°C at a heating rate of 2.8~3.5°C / min, and then heating to 1100~1170°C at a heating rate of 1.8~2.2°C / min, keeping warm for 2h, and then naturally cooling in the furnace to obtain the ferrite magnetic ring.

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