Method for recovering iron, aluminum and sodium in red mud

Abstract

The invention discloses a method for recovering iron, aluminum and sodium in red mud, which comprises the following steps: mixing the red mud and an alkaline solution, and introducing hydrogen into high-temperature and high-pressure equipment to react; carrying out solid-liquid separation on the slurry after reaction, and carrying out magnetic separation after solid-phase grinding to obtain concentrate and tailings; and adding a calcium-containing additive aqueous solution into the tailings for dealkalization reaction to obtain dealkalized residues and dilute alkali liquor. Red mud, an alkaline solution and hydrogen are stirred and reacted in high-temperature and high-pressure reaction equipment, (aluminum) hematite and (aluminum) goethite in the red mud are completely converted into ferroferric oxide, the purpose of extracting aluminum in the red mud is achieved, solid-liquid separation is conducted on slurry after the reaction, ferroferric oxide in a solid phase is separated through magnetic separation, and the iron content in concentrate is high; the method can cooperate with large-scale absorption in the iron and steel industry, and also considers recovery of iron minerals; comprehensive recovery of iron, aluminum and sodium in the red mud is realized, and the method has the advantage of environmental friendliness.

Description

Technical Field

[0001] The invention belongs to the technical field of red mud treatment, and particularly relates to a method for recovering sodium iron, aluminum and sodium from red mud. Background Art

[0002] Guinea, Australia, and Indonesia are major importers of bauxite from China. These regions primarily produce gibbsite-type bauxite, which is commonly found in certain amounts of goethite, boehmite, and diaspore. Red mud is the industrial solid waste discharged after alumina extraction from bauxite. Generally, 1.0 to 2.0 tons of red mud are generated for every ton of alumina produced. Furthermore, the presence of large amounts of goethite significantly impacts the red mud settling and separation process, reducing the efficiency of iron separation from the mud.

[0003] The comprehensive utilization methods of red mud can be divided into the following five categories: (1) Functional utilization of red mud: mainly including construction materials, wastewater treatment, waste gas adsorbent and soil remediation, but most functional utilization is used in a mixed manner, with a relatively small treatment volume. According to statistics, the utilization rate is less than 5%. (2) Acid leaching: Generally, hydrochloric acid, sulfuric acid, oxalic acid or nitric acid are used to treat red mud to obtain an acidic aqueous solution of salts of various elements (iron, aluminum, titanium, rare earth, etc.), and then the target elements are extracted from the solution through chemical precipitation, extraction and ion exchange. However, during the acid treatment process, most of the elements in the red mud will be leached into the liquid phase, making the recovery of the target elements complicated and costly. To solve the problem of impurity leaching, researchers proposed the sulfate roasting method. This method involves first sulfating and roasting red mud at low temperature to convert the metal elements in it into corresponding sulfates. Then, it is roasted at a controlled higher temperature (500-600°C) to convert the sulfates of impurities (such as iron, titanium, and aluminum) into oxides, while rare earth elements still exist in the form of sulfates. Water is then added for leaching to achieve the separation of rare earth elements from impurity elements. However, this method ignores the extraction of other major valuable elements such as iron, titanium, and aluminum. (3) High-pressure hydrochemical method: Red mud is mixed with sodium hydroxide and water and reacted at 180-400°C. After liquid-solid separation, sodium aluminate solution is obtained for the preparation of aluminum hydroxide. Li et al. used 45% sodium hydroxide solution to leach red mud at 170-200°C for 2-3 hours, and the aluminum oxide recovery rate reached 87%. However, the low alkali circulation efficiency and the difficulty of solid-liquid separation limited the implementation of this scheme. (4) Reduction smelting method: Red mud is mixed with reducing agents (coke, graphite, CO, H2) at 1400℃~1500℃ and smelted at high temperature in an electric furnace / blast furnace / rotary kiln. At the same time, molten iron is obtained and slag containing mainly aluminum, titanium and rare earths is prepared. After the slag is separated, the metals are recovered through a hydrometallurgical process. This type of technology is represented by the Pedersen method, but this process has not been widely used due to its high energy consumption, long process, and difficulty in separating slag and iron. (5) Reduction roasting method: In the range of 700~1200℃, the iron minerals in the red mud are converted into magnetite / metallic iron by controlling the reducing atmosphere (adding reducing agents) and then enriching the iron through magnetic separation. The tailings can be used as a raw material for extracting alumina. However, during the reduction process, fayalite and iron spinel are easily formed. Furthermore, micron-sized sodium silicate slag easily adheres to magnetite and coarse iron particles, resulting in suboptimal separation products after magnetic roasting and magnetic separation. Iron grade (based on Fe₃O₄) and iron recovery are approximately 50% and 80%, respectively. Therefore, researchers have proposed adding fluxes (sodium carbonate, sodium hydroxide, and sodium sulfate) to the reduction roasting process to form water-soluble sodium silicates and aluminates to remove aluminum, silicon, and sodium. This improves the efficiency of iron reduction and magnetic separation, achieving iron grade (based on Fe₃O₄) and iron recovery of approximately 90% and 88%, respectively. However, this process requires the addition of a reducing agent, resulting in high reaction temperatures and high production costs. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a method for recovering iron, aluminum and sodium from red mud, which improves the recovery rate of iron, aluminum and sodium in red mud, and fully utilizes the recovered components, which is conducive to the full utilization of the iron in the red mud.

[0005] The present invention is achieved through the following technical solutions: A method for recovering sodium iron, aluminum and sodium from red mud, characterized by comprising the following steps: (1) Red mud and alkaline solution are mixed, hydrogen is introduced and reacted in a high-temperature and high-pressure device; (2) After the reaction, the slurry is subjected to solid-liquid separation, and the solid phase is ground and then subjected to magnetic separation to obtain concentrate and tailings; (3) Adding a calcium-containing additive aqueous solution to the tailings to carry out a dealkalization reaction to obtain dealkalized slag and dilute alkali solution.

[0006] Furthermore, the red mud in step (1) has TFe≥35 wt%, Al2O3≥5 wt%, and Na2O≥2 wt%, wherein the content of aluminum hematite and aluminum goethite is ≥10 wt%.

[0007] Furthermore, the alkaline solution in step (1) is a sodium hydroxide solution or a sodium aluminate solution with a concentration of 100-400 g / L, and a solid content of 100-400 g / L after mixing.

[0008] Furthermore, the reaction temperature in step (1) is 100-300°C, the partial pressure of hydrogen after the introduction of hydrogen is ≥1 MPa, and the reaction time is 0.5h-24h; preferably, the partial pressure of hydrogen after the introduction of hydrogen is 1-3 MPa.

[0009] Furthermore, the magnetic separation intensity of the reaction in step (2) is 0.05~1T.

[0010] Furthermore, the calcium-containing additive in step (3) is one or more of calcium oxide, calcium hydroxide and tricalcium aluminate hexahydrate.

[0011] Furthermore, the temperature of the dealkalization reaction in step (3) is 25-100° C., the time is 0.5 h-10 h, the mass concentration of the aqueous solution containing the calcium additive is 1-10%, and the solid content of the tailings after addition is 50-500 g / L.

[0012] Furthermore, the concentrate in step (2) is directly used in the steel industry.

[0013] Furthermore, the dealkalized slag in step (3) is used in the brick and cement industries.

[0014] Beneficial effects The present invention involves stirring red mud, an alkaline solution, and hydrogen in a high-temperature, high-pressure reactor to completely convert the (aluminum) hematite and (aluminum) goethite in the red mud into ferroferric oxide, thereby extracting the aluminum. After the reaction, the slurry undergoes solid-liquid separation, and the ferroferric oxide is separated from the solid phase through magnetic separation. The resulting concentrate, with a high iron content, can be used for large-scale consumption by the steel industry, while also maximizing iron mineral recovery. The tailings are then dealkalized by adding a calcium-containing additive to recover the sodium oxide, and the dealkalized residue can be used in the brick and cement industries. Therefore, the present invention achieves comprehensive recovery of iron, aluminum, and sodium from red mud, offering environmentally friendly advantages. DETAILED DESCRIPTION

[0015] The above contents of the present invention are further described in detail below through examples, but this should not be understood as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0016] The red mud in the embodiments of the present invention and the comparative example contains (calculated as oxides) 11 wt% Al2O3, 42 wt% Fe2O3, 1.5 wt% Na2O, 3 wt% SiO2, and the remainder is other components, of which the content of aluminum hematite and aluminum goethite is 40%.

[0017] Example 1 (1) Red mud and 300 g / L sodium hydroxide solution were mixed to a solid content of 200 g / L. The mixture was placed in a high-temperature and high-pressure reactor, and hydrogen was introduced to a hydrogen partial pressure of 3 MPa. The mixture was reacted at 270 °C for 2 h. (2) After the reaction, the slurry is subjected to solid-liquid separation, and the solid phase is ground and then subjected to magnetic separation with a magnetic field strength of 0.1T to obtain concentrate and tailings; (3) Add 5wt% calcium hydroxide solution to the tailings in an amount that makes the solid content 200g / L for dealkalization reaction. The reaction time is 6h to obtain dealkalized slag and dilute alkali solution to recover sodium oxide. The dealkalized slag can be used in the brick and cement industries.

[0018] In this embodiment, the recovery rate of iron is 98%, the recovery rate of aluminum is 92%, the recovery rate of sodium is 87%, the total iron content in the concentrate is 60%, the sodium oxide content is 0.8%, and the alkali recovery rate is 92%.

[0019] Example 2 (1) Red mud and 200 g / L sodium hydroxide solution were mixed to a solid content of 150 g / L. The mixture was placed in a high-temperature and high-pressure reactor, and hydrogen was introduced to a hydrogen partial pressure of 2 MPa. The mixture was reacted at 300 °C for 4 h. (2) After the reaction, the slurry is subjected to solid-liquid separation, and the solid phase is ground and then subjected to magnetic separation with a magnetic field strength of 0.5 T to obtain concentrate and tailings; (3) Add 10 wt% calcium hydroxide solution to the tailings in an amount that makes the solid content 350 g / L for dealkalization reaction. The reaction time is 12 h to obtain dealkalized slag and dilute alkali solution to recover the sodium oxide. The dealkalized slag can be used in the brick and cement industries.

[0020] In this embodiment, the recovery rate of iron is 98%, the recovery rate of aluminum is 90%, the recovery rate of sodium is 85%, the total iron content in the concentrate is 62%, the sodium oxide content is 0.8%, and the alkali recovery rate is 92%.

[0021] Example 3 (1) Red mud and 300 g / L sodium hydroxide solution were mixed to a solid content of 200 g / L. The mixture was placed in a high-temperature and high-pressure reactor, and hydrogen was introduced to a hydrogen partial pressure of 2 MPa. The mixture was reacted at 250 °C for 6 h. (2) After the reaction, the slurry is subjected to solid-liquid separation, and after solid phase grinding, magnetic separation is performed with a magnetic field strength of 0.8T to obtain concentrate and tailings; (3) Add 5wt% calcium hydroxide solution to the tailings in an amount that makes the solid content 200g / L for dealkalization reaction. The reaction time is 12h to obtain dealkalized slag and dilute alkali solution to recover sodium oxide. The dealkalized slag can be used in the brick and cement industries.

[0022] In this embodiment, the recovery rate of iron is 97%, the recovery rate of aluminum is 90%, the recovery rate of sodium is 91%, the total iron content in the concentrate is 59%, the sodium oxide content is 1.1%, and the alkali recovery rate is 94%.

[0023] Example 4 (1) Red mud and 300 g / L sodium hydroxide solution were mixed to a solid content of 200 g / L. The mixture was placed in a high-temperature and high-pressure reactor, and hydrogen was introduced to a hydrogen partial pressure of 1 MPa. The mixture was reacted at 200 °C for 4 h. (2) After the reaction, the slurry is subjected to solid-liquid separation, and the solid phase is ground and then subjected to magnetic separation with a magnetic field strength of 0.5 T to obtain concentrate and tailings; (3) Add 5wt% calcium hydroxide solution to the tailings in an amount that makes the solid content 200g / L for dealkalization reaction. The reaction time is 6h to obtain dealkalized slag and dilute alkali solution to recover sodium oxide. The dealkalized slag can be used in the brick and cement industries.

[0024] In this embodiment, the recovery rate of iron is 96%, the recovery rate of aluminum is 89%, the recovery rate of sodium is 84%, the total iron content in the concentrate is 58%, the sodium oxide content is 0.5%, and the alkali recovery rate is 88%.

[0025] Comparative Example 1 Compared with Example 1, the hydrogen partial pressure after the hydrogen was introduced in step (1) of Comparative Example 1 was 5 MPa, and the other conditions were the same as those of Example 1. In Comparative Example 1, the iron recovery rate was 86%, the aluminum recovery rate was 90%, and the sodium recovery rate was 88%. The total iron content in the concentrate was 55%, and the sodium oxide content was 0.9%.

[0026] Comparative Example 2 Compared with Example 1, the hydrogen partial pressure after the hydrogen was introduced in step (1) of Comparative Example 2 was 0.5 MPa, and the other conditions were the same as those of Example 1. In Comparative Example 1, the iron recovery rate was 84%, the aluminum recovery rate was 81%, the sodium recovery rate was 78%, the total iron content in the concentrate was 52%, and the sodium oxide content was 0.7%.

Claims

1. A method for recovering sodium iron, aluminum and sodium from red mud, characterized in that: The following steps are involved: (1) Red mud and alkaline solution are mixed, hydrogen is introduced and reacted in a high-temperature and high-pressure device; (2) After the reaction, the slurry is subjected to solid-liquid separation, and the solid phase is ground and then subjected to magnetic separation to obtain concentrate and tailings; (3) Adding a calcium-containing additive aqueous solution to the tailings to carry out a dealkalization reaction to obtain dealkalized slag and dilute alkali solution.

2. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 1, wherein: The red mud in step (1) has TFe≥35 wt%, Al2O3≥5 wt%, and Na2O≥2 wt%, wherein the content of aluminum hematite and aluminum goethite is ≥10 wt%.

3. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 1, wherein: The alkaline solution in step (1) is a sodium hydroxide solution or a sodium aluminate solution with a concentration of 100-400 g / L, and the solid content after mixing is 100-400 g / L.

4. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 1, wherein: The reaction temperature in step (1) is 100-300°C, the partial pressure of hydrogen after the introduction of hydrogen is ≥1 MPa, and the reaction time is 0.5h-24h.

5. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 4, wherein: After hydrogen is introduced in step (1), the partial pressure of hydrogen is 1-3 MPa.

6. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 1, wherein: The magnetic separation intensity of the reaction in step (2) is 0.05~1T.

7. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 1, wherein: The calcium-containing additive in step (3) is one or more of calcium oxide, calcium hydroxide and tricalcium aluminate hexahydrate.

8. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 1, wherein: The temperature of the dealkalization reaction in step (3) is 25-100° C., the time is 0.5 h-10 h, the mass concentration of the aqueous solution containing the calcium additive is 1-10%, and the solid content of the tailings after addition is 50-500 g / L.

9. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 1, wherein: The concentrate in step (2) is directly used in the steel industry.

10. The method for recovering sodium iron, aluminum and sodium from red mud according to claim 1, wherein: The dealkalized slag in step (3) is used in the brick and cement industries.