Method for efficiently removing iron from bauxite through dry magnetic separator

Abstract

The invention provides a method for efficiently removing iron from bauxite through a dry magnetic separator. The method comprises the following steps that the bauxite is subjected to desliming and crushing, an oxidizing agent and an additive are added for ball milling, the bauxite is put into a tubular furnace for reduction roasting, the dry magnetic separator is adopted for segmented magnetic separation, and obtained non-magnetic products are aluminum concentrate and magnetic products are iron-containing tailings. Sulfur and carbon in the bauxite are effectively removed through desliming and crushing according to particle size screening, the impurity removal efficiency of the bauxite is improved through segmented magnetic separation of the dry magnetic separator, and the problem that inorganic carbon minerals are difficult to remove is solved. The method for removing iron from the bauxite is low in production cost, the recovery rate of aluminum in the bauxite is increased, the sulfur removal rate and the iron removal rate are increased, and the reuse value of iron is improved.

Description

Technical Field

[0001] The invention relates to the technical field of bauxite, in particular to a method for efficiently removing iron from bauxite using a dry magnetic separator. Background Art

[0002] With the rapid development of alumina and electrolytic aluminum industries, my country's consumption of bauxite resources has increased, the quality of domestic bauxite resources has been exposed, bauxite resources are in short supply, and my country's dependence on foreign bauxite has increased year by year. The issue of bauxite resources has become an important problem in the development of China's aluminum industry. The iron element in bauxite mainly exists in the form of pyrite and other forms. The mineral composition of high-iron bauxite is mainly aluminum and iron, and its impurities are mainly iron, which seriously affects the dissolution performance of bauxite and product quality. Therefore, before the industrial production of alumina, the iron content of bauxite needs to be reduced to a certain range. At present, there are mainly methods for removing iron from bauxite, such as flotation and roasting. The physical beneficiation method has low cost and simple process flow, but it is only suitable for high-iron bauxite that is easy to dissociate monomers. Flotation is a mature method currently used in industry. It mainly involves flotation after adding mineral processing agents. The iron is captured by the mineral processing agents, and then a frother is added to form foam that floats on the ore pulp. The foam is then separated by scraping. However, if the ore grade is low, the existing flotation method has the disadvantages of low efficiency, large reagent consumption, high equipment energy consumption, and increased energy consumption in the evaporation process due to the introduction of water.

[0003] The mineral phases of bauxite are mainly diaspore, hematite, goethite, kaolinite and anatase, with a dense structure. The aluminum-iron minerals are wrapped, which affects the dissolution activity. The dry magnetic separator can remove iron from bauxite efficiently. The main reactions are: 3FeO+H2O→Fe3O4+H2; Fe3O4+8NaOH+4Al2O3→Fe(OH)2+2Fe(OH)3+8NaAlO2. However, the dry magnetic separator has the following problems in removing iron from bauxite: First, magnetic force control. Too strong or too weak magnetic force will lead to uneven magnetic force distribution, affecting the magnetic separation effect. If the magnetic force is too strong, the minerals cannot fall off in time after being sucked up, thereby damaging the magnetic system. If the magnetic force is too weak, it will affect the iron removal effect. Secondly, effectively control the impurity content. High impurity content will affect the quality and value. Incomplete desludging and incomplete reduction roasting will have an important impact on the impurity content of bauxite. Summary of the invention

[0004] In view of this, the present invention provides a method for efficiently removing iron from bauxite using a dry magnetic separator to solve the above problems.

[0005] The technical solution of the present invention is achieved in this way: A method for efficiently removing iron from bauxite using a dry magnetic separator comprises the following steps: S1, desludging the bauxite, crushing the bauxite, adding an oxidant and an additive, ball milling to obtain a raw ore slurry, and drying the raw ore slurry to obtain powder ore; S2, adding water to the powder ore and mixing it, then putting it into a tubular furnace for reduction roasting, introducing N2 during heating, introducing H2 during heat preservation, and cooling it to room temperature to obtain roasted slag powder; S3. The roasted slag powder is subjected to segmented magnetic separation by a dry magnetic separator and dried. The obtained non-magnetic product is aluminum concentrate, and the magnetic product is iron-containing tailings.

[0006] Further, in step S1, the oxidant is hydrogen peroxide or hypochlorous acid with a mass fraction of 85%-95%, the added amount of the oxidant is 0.6%-1.2% of the dry weight of the bauxite, and the additive is one of calcium oxide, calcium hydroxide, magnesium oxide, and magnesium hydroxide, and the added mass of the additive is 5%-7% of the dry weight of the bauxite.

[0007] Furthermore, in step S1, after ball milling, 85-90% of the bauxite has a particle size below 800 μm.

[0008] Furthermore, in step S2, the mass volume kg / L ratio of the powder ore to water is 1:0.5-0.8.

[0009] Furthermore, in step S2, the heating temperature is 90-100°C, the heating time is 15-20 minutes, the insulation temperature is 95-100°C, and the insulation time is 40-45 minutes.

[0010] Further, in step S2, the purity of N2 is greater than 99%, the flow rate of N2 is 4-5 m / s, the purity of H2 is greater than 99%, and the flow rate of H2 is 3-3.5 m / s.

[0011] Furthermore, in step S3, the magnetic separation adopts a fully sealed spiral two-stage gradient magnetic separator for periodic magnetic separation. In the two-stage magnetic separation, the magnetic field strength of the first stage is 3000-5000 Gauss, the rotation speed is 45-50r / min, and the amplitude is 15-25mm.

[0012] Furthermore, the magnetic field strength of the second magnetic separation is 7000-9000, the rotation speed is 51-55r / min, and the amplitude is 26-30mm.

[0013] Furthermore, the chemical composition of the bauxite is Al2O3≥50%, Fe2O3≤25%, and the C content ranges from 0.5% to 8%.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention crushes and desluds the bauxite, then ball mills it, and performs segmented magnetic separation after reduction roasting. This method for removing iron from bauxite improves the recovery rate, sulfur removal rate and iron removal rate of aluminum in aluminum concentrate. By screening the bauxite according to a preset particle size, sulfur and carbon in the bauxite are effectively removed, and the interaction and magnetic agglomeration effect between fine-grained magnetite are overcome by introducing nitrogen and hydrogen. The use of a dry magnetic separator for segmented magnetic separation realizes the removal of impurities and quality improvement of the bauxite, and overcomes the problems of fine particle size of carbonaceous minerals in the bauxite, difficulty in removing inorganic carbon, and low efficiency of direct magnetic separation. The method for removing iron from bauxite of the present invention has low production costs, relatively stable production performance, increased aluminum recovery rate in bauxite, increased sulfur removal rate and iron removal rate, and improved the reuse value of iron. DETAILED DESCRIPTION

[0015] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0016] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods, and the reagents used in the examples are all available from commercial sources.

[0017] Example 1 A method for efficiently removing iron from bauxite by a dry magnetic separator comprises the following steps: Step (1): desludging the bauxite, wherein the chemical composition of the bauxite has an average Al2O3 content of 52%, an average Fe2O3 content of 17%, and an average C content of 6%. The bauxite is crushed, and an oxidant and an additive are added after crushing. The oxidant is 85% by mass hydrogen peroxide, and the amount of the oxidant added is 0.6% of the dry weight of the bauxite. The additive is calcium oxide, and the mass of the calcium oxide added is 5% of the dry weight of the bauxite. After adding calcium oxide and hydrogen peroxide to the bauxite, the mixture is evenly mixed and ball milled. After ball milling, 85% of the bauxite has a particle size of less than 800 μm. The raw ore slurry obtained after ball milling is dried to obtain bauxite powder; Step (2): adding water to the bauxite powder and mixing it, and then putting it into a tubular furnace for reduction roasting, the mass volume ratio of the powder to water is 1kg:0.5L, and then heating and roasting are performed after mixing. When the heating temperature is 90°C, N2 is introduced for 15 minutes, and the purity of N2 is 99.99%. The insulation temperature is 95°C, and H2 is introduced during the insulation, and the insulation time is 40 minutes. The purity of H2 is 99.99%, the flow rate of N2 is 4m / s, and the flow rate of H2 is 3m / s. The mixture is cooled to room temperature to obtain roasted slag powder; Step (3): The roasted slag powder is subjected to segmented magnetic separation using a dry magnetic separator, and the magnetic separation is performed using a fully sealed spiral two-stage gradient magnetic separator for periodic magnetic separation. The magnetic field strength of the first stage is 3000 Gauss, the rotation speed is 45 r / min, and the amplitude is 15 mm; the magnetic field strength of the second stage is 7000, the rotation speed is 51 r / min, and the amplitude is 26 mm. The product after magnetic separation is dried, and the non-magnetic product obtained is aluminum concentrate, and the magnetic product is iron-containing tailings.

[0018] Example 2 Step (1): desludging the bauxite, wherein the chemical composition of the bauxite has an average Al2O3 content of 52%, an average Fe2O3 content of 17%, and an average C content of 6%. The bauxite is crushed, and an oxidant and an additive are added after crushing, wherein the oxidant is hypochlorous acid with a mass fraction of 85%, and the added amount of the oxidant is 1.2% of the dry weight of the bauxite. The additive is magnesium oxide, and the added mass of magnesium oxide is 7% of the dry weight of the bauxite. After adding magnesium oxide and hypochlorous acid to the bauxite, the bauxite is ball-milled, and after ball-milling, 90% of the bauxite has a particle size of less than 800 μm, thereby obtaining a raw ore slurry, and the raw ore slurry is dried to obtain bauxite powder; Step (2): adding water to the bauxite powder and mixing it, then putting it into a tubular furnace for reduction roasting, wherein the mass volume ratio of the powder to water is 1:0.8. After mixing, the mixture is heated and roasted. When the heating temperature is 100°C, N2 is introduced for 20 minutes, and the purity of N2 is 99.99%. When the insulation temperature is 100°C, H2 is introduced for 45 minutes, and the purity of H2 is greater than 99.99%. The flow rate of N2 is 5 m / s, and the flow rate of H2 is 3.5 m / s. The mixture is cooled to room temperature to obtain roasted slag powder. Step (3): The roasted slag powder is subjected to segmented magnetic separation using a dry magnetic separator, and the magnetic separation is performed using a fully sealed spiral two-stage gradient magnetic separator for periodic magnetic separation. The magnetic field strength of the first stage is 5000 Gauss, the rotation speed is 50r / min, and the amplitude is 25mm; the magnetic field strength of the second stage is 9000, the rotation speed is 55r / min, and the amplitude is 30mm. The product after magnetic separation is dried, and the non-magnetic product obtained is aluminum concentrate, and the magnetic product is iron-containing tailings.

[0019] Example 3 Step (1): desludging the bauxite, wherein the chemical composition of the bauxite has an average Al2O3 content of 52%, an average Fe2O3 content of 17%, and an average C content of 6%. The bauxite is crushed, and an oxidant and an additive are added after crushing, wherein the oxidant is 90% by mass hydrogen peroxide, and the amount of hydrogen peroxide added is 1% of the dry weight of the bauxite; the additive is calcium hydroxide, and the amount of calcium hydroxide added is 6% of the dry weight of the bauxite. After adding and mixing evenly, ball milling is performed, and after ball milling, 90% of the bauxite has a particle size of less than 800 μm, thereby obtaining a raw ore slurry, and the raw ore slurry is dried to obtain bauxite powder; Step (2): adding water to the bauxite powder and mixing it, then putting it into a tubular furnace for reduction roasting, wherein the mass volume ratio of the powder to water is 1:0.7. After mixing, the mixture is heated and roasted. When the heating temperature is 100°C, N2 is introduced for 20 minutes, and the purity of N2 is 99.99%. When the insulation temperature is 100°C, H2 is introduced for 45 minutes, and the purity of H2 is 99.99%. The flow rate of N2 is 4.5 m / s, and the flow rate of H2 is 3 m / s. The mixture is cooled to room temperature to obtain roasted slag powder. Step (3): The roasted slag powder is subjected to segmented magnetic separation using a dry magnetic separator, and the magnetic separation is performed using a fully sealed spiral two-stage gradient magnetic separator for periodic magnetic separation. The magnetic field strength of the first stage is 4000 Gauss, the rotation speed is 50 r / min, and the amplitude is 20 mm; the magnetic field strength of the second stage is 8000, the rotation speed is 53 r / min, and the amplitude is 30 mm. The product after magnetic separation is dried, and the non-magnetic product obtained is aluminum concentrate, and the magnetic product is iron-containing tailings.

[0020] Comparative Example 1 The main differences between Comparative Example 1 and Example 3 are that in the bauxite desliming step (1), "the amount of hydrogen peroxide added is 1% of the dry weight of the bauxite" is replaced by "the amount of hydrogen peroxide added is 0.3% of the dry weight of the bauxite"; the "the mass of calcium hydroxide added is 6% of the dry weight of the bauxite" in step (1) is replaced by "the mass of calcium hydroxide added is 2% of the dry weight of the bauxite"; after ball milling, 50% of the bauxite has a particle size of less than 800 μm, and the remaining 50% of the bauxite has a particle size of greater than 800 μm.

[0021] Step (1): desludging the bauxite, wherein the chemical composition of the bauxite is 52% Al2O3, 17% Fe2O3 and 6% C. The bauxite is crushed, and an oxidant and an additive are added after crushing. The oxidant is 90% by mass hydrogen peroxide, and the amount of hydrogen peroxide added is 0.3% of the dry weight of the bauxite. The additive is calcium hydroxide, and the mass of calcium hydroxide added is 2% of the dry weight of the bauxite. After adding and mixing evenly, ball milling is performed. After ball milling, 50% of the bauxite has a particle size of less than 800 μm, thereby obtaining a raw ore slurry. The raw ore slurry is dried to obtain bauxite powder.

[0022] Comparative Example 2 The main difference between Comparative Example 2 and Example 3 is that the step of introducing N2 and H2 is omitted in step (2).

[0023] Step (2): adding water to the bauxite powder and mixing it, and then putting it into a tubular furnace for reduction roasting, wherein the mass volume ratio of the powder to water is 1:0.7. After mixing, the mixture is heated and roasted at a temperature of 100°C, and the temperature is kept for 45 minutes, and then cooled to room temperature to obtain roasted slag powder; Comparative Example 3 The main difference between Comparative Example 3 and Example 3 is that the segmented magnetic separation is removed in step (3) and replaced with a unified magnetic separation with a magnetic field strength of 4000 Gauss, a rotation speed of 50 r / min, and an amplitude of 20 mm; and the step of introducing H2 is removed in step (2).

[0024] test According to the method of Examples 1-3 and Comparative Examples 1-3, the bauxite was deironed, and the aluminum recovery rate, iron removal rate and sulfur removal rate were calculated. The chemical composition of the bauxite in this test was 52.0% Al2O3, 17.2% Fe2O3, 6.2% C, 20.3% SiO2, 2.7% TiO2, and a small amount of trace components such as CaO, MgO, SO3, Na2O, and K2O.

[0025] Iron removal rate (%) = iron content in iron-containing tailings / iron content in original bauxite * 100% Al2O3 recovery rate in aluminum concentrate (%) = aluminum content in aluminum concentrate / aluminum content in original bauxite * 100% Sulfur removal rate (%) = sulfur content in aluminum concentrate / sulfur content in original bauxite * 100% Table 1 The test results show that the method of removing iron from bauxite by adding oxidants and additives to the bauxite for crushing and desludging, ball milling and then placing it in a tubular furnace for reduction roasting, and adopting a dry magnetic separator for segmented magnetic separation improves the recovery rate, sulfur removal rate and iron removal rate of aluminum in aluminum concentrate. In Comparative Example 1, reducing the mass percentage of hydrogen peroxide and calcium hydroxide added and increasing the particle size after ball milling both reduce the recovery rate and iron removal rate of aluminum, and the recovery rate of aluminum is reduced by 13.9%. In Comparative Example 2, after removing the step of introducing N2 and H2 in step (2), the iron removal rate is reduced by 9.6%. In Comparative Example 3, the magnetic separation method is changed, and after the segmented magnetic separation is modified to a single magnetic separation, the recovery rate and iron removal rate of aluminum are also reduced. At the same time, the method of removing iron from bauxite of the present invention has low energy consumption and production cost, stable production performance, increased aluminum recovery rate, sulfur removal rate and iron removal rate, and improved the reuse value of iron.

[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for efficiently removing iron from bauxite using a dry magnetic separator, characterized in that: The following steps are involved: S1, desludging the bauxite, crushing the bauxite, adding an oxidant and an additive, ball milling to obtain a raw ore slurry, and drying the raw ore slurry to obtain powder ore; S2, adding water to the powder ore and mixing it, then putting it into a tubular furnace for reduction roasting, introducing N2 during heating, introducing H2 during heat preservation, and cooling it to room temperature to obtain roasted slag powder; S3. The roasted slag powder is subjected to segmented magnetic separation by a dry magnetic separator and dried. The obtained non-magnetic product is aluminum concentrate, and the magnetic product is iron-containing tailings.

2. The method for efficiently removing iron from bauxite by a dry magnetic separator according to claim 1, characterized in that: In step S1, the oxidant is hydrogen peroxide or hypochlorous acid with a mass fraction of 85%-95%, and the added amount of the oxidant is 0.6%-1.2% of the dry weight of the bauxite. The additive is one of calcium oxide, calcium hydroxide, magnesium oxide, and magnesium hydroxide, and the added mass of the additive is 5%-7% of the dry weight of the bauxite.

3. The method for efficiently removing iron from bauxite by a dry magnetic separator according to claim 1, characterized in that: Step S1, after ball milling, 85-90% of the bauxite has a particle size below 800 μm.

4. The method for efficiently removing iron from bauxite by a dry magnetic separator according to claim 1, characterized in that: In step S2, the mass volume kg / L ratio of the powder ore to water is 1:0.5-0.

8.

5. The method for efficiently removing iron from bauxite by a dry magnetic separator according to claim 1, characterized in that: Step S2, the heating temperature is 90-100°C, the heating time is 15-20min, the insulation temperature is 95-100°C, and the insulation time is 40-45min.

6. The method for efficiently removing iron from bauxite using a dry magnetic separator according to claim 1, characterized in that: In step S2, the purity of N2 is greater than 99%, and the flow rate of N2 is 4-5 m / s; the purity of H2 is greater than 99%, and the flow rate of H2 is 3-3.5 m / s.

7. The method for efficiently removing iron from bauxite using a dry magnetic separator according to claim 1, characterized in that: Step S3, the magnetic separation adopts a fully sealed spiral two-stage gradient magnetic separator for periodic magnetic separation. The two-stage magnetic separation, the magnetic field strength of the first stage is 3000-5000 Gauss, the rotation speed is 45-50r / min, and the amplitude is 15-25mm.

8. The method for efficiently removing iron from bauxite using a dry magnetic separator according to claim 7, characterized in that: The magnetic field strength of the second magnetic separation is 7000-9000, the rotation speed is 51-55r / min, and the amplitude is 26-30mm.

9. The method for efficiently removing iron from bauxite using a dry magnetic separator according to claim 1, characterized in that: The chemical composition of the bauxite is Al2O3≥50%, Fe2O3≤25%, and the C content ranges from 0.5% to 8%.

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