Method for recovering aluminum, iron and sodium from high-iron Bayer process red mud and realizing harmlessness of tailings based on one-step low-calcium reduction sintering, water leaching and magnetic separation processes

Abstract

According to the method, sodium carbonate, limestone and coke are used as sintering aids and are uniformly mixed with the high-iron Bayer process red mud, the mixed material is sintered by adopting a one-step low-calcium reduction sintering process, and the sintered clinker is subjected to water leaching and dissolution to obtain a sodium aluminate crude solution and filter residues. And returning the sodium aluminate crude liquid to an aluminum oxide industrial production line to prepare aluminum oxide, and carrying out a hydrolysis alkali recovery process on filter residues to obtain industrial sodium carbonate. The hydrolysis residues are subjected to magnetic separation and recovery to obtain fine iron powder, and the remaining tailings are completely harmless and can be used as raw materials of building materials or used for soil backfilling. The process is characterized in that the one-step low-calcium reduction sintering temperature is 200-300 DEG C lower than the sintering temperature of a sintering method, and the energy consumption is low; na2CaSiO4 is a sintering target product, Ca2SiO4 generally generated by a traditional sintering method is not generated, the situation that Ca2SiO4 is hydrolyzed in the water leaching process to inhibit dissolution of aluminum oxide is avoided, and the recycling rate of aluminum oxide is increased while the using amount of limestone is greatly reduced. The technological process is simple, efficient, energy-saving and free of three-waste emission, and the method is a novel method capable of treating the high-iron red mud in a large-scale and reduction mode.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically to a method for recovering aluminum, iron, and sodium from high-iron Bayer process red mud based on a one-step low-calcium reduction sintering, water leaching, and magnetic separation process, and for achieving harmless treatment of tailings. Background Technology

[0002] Red mud is a solid waste discharged after alumina extraction from bauxite, and it is a highly alkaline waste residue. It not only causes numerous social and environmental problems, but also poses a significant threat to the future development of China's alumina industry. Driven by national policies, the harmless treatment and large-scale utilization of red mud have become crucial for the sustainable development of the alumina industry, with the extraction of valuable metals being the core driver. Representative technologies for the comprehensive utilization of red mud that demonstrate outstanding benefits are all driven by the extraction of valuable metal elements, maximizing resource value by constructing efficient separation and high-value utilization pathways for metals such as iron, aluminum, and sodium.

[0003] Red mud has a complex composition, making large-scale utilization difficult. Furthermore, the high levels of sodium oxide and iron oxide in red mud limit its applications. Existing research focuses primarily on extracting single valuable components from red mud, with fewer studies on the synergistic extraction of multiple valuable components due to the complexity and high cost of the process. Red mud has a small particle size and complex mineral composition; iron-bearing minerals are often interbedded and intergrown with other minerals. During magnetic separation, Al, Ca, and Ti minerals are easily separated together and enter the concentrate, affecting the Fe grade and Fe recovery rate of the concentrate.

[0004] The experimental raw material for this invention, red mud, came from a company in Shandong Province. The main mineral components of the red mud are goethite, rutile, nepheline, diaspore, α-quartz, and calcite. The red mud raw material has a very high Fe2O3 content, at 41.46%, making it a typical high-iron red mud.

[0005] Based on the above problems, this invention proposes a method for recovering aluminum, iron, and sodium from high-iron Bayer process red mud using a one-step low-calcium reduction sintering, water leaching, and magnetic separation process, and achieving harmless treatment of tailings. This is a new method that can dispose of high-iron red mud on a large scale and in reduced volume, generating good economic, social, and environmental benefits. Summary of the Invention

[0006] In view of this, the purpose of this invention is to recover aluminum, iron and sodium from high-iron Bayer process red mud based on a one-step low-calcium reduction sintering, water leaching and magnetic separation process, and to achieve the harmless treatment of tailings.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for recovering aluminum, iron, and sodium from high-iron Bayer process red mud based on a one-step low-calcium reduction sintering, water leaching, and magnetic separation process, and for achieving harmless treatment of tailings, comprising the following steps:

[0009] S1 involves the low-calcium reduction sintering of Bayer red mud raw materials. Bayer red mud is uniformly mixed with soda ash, limestone, coke, and abrasives, and sintered in an oxygen-deficient atmosphere in a muffle furnace under certain conditions. The resulting sintered clinker is then pulverized to obtain clinker powder.

[0010] S2 dissolves alumina from the sintered clinker, heats and stirs the sintered clinker powder in a water bath, and obtains crude sodium aluminate liquid and filter residue by vacuum filtration.

[0011] S3 recovers alkali from the filter residue. The filter residue will undergo a hydrolysis reaction under hydrothermal conditions. After washing and filtration, sodium hydroxide solution and hydrolysis residue are obtained.

[0012] S4 separates the hydrolysis residue by magnetic separation. After wet magnetic separation, the magnetite concentrate can be separated from the hydrolysis residue, and the remaining solid phase is harmless tailings.

[0013] In a preferred embodiment, in step S1, the calcium-silicon molar ratio in the ingredients is fixed at 1.0.

[0014] In a preferred embodiment, in step S1, the molar ratio of alkali-aluminum in the ingredients is 1.00-1.10.

[0015] In a preferred embodiment, in step S1, the mass ratio of Bayer red mud to coke in the ingredients is 5%-12%.

[0016] In a preferred embodiment, in step S1, the low-calcium reduction sintering time is 0.5h-2h.

[0017] In a preferred embodiment, in step S1, the low-calcium reduction sintering temperature is 950℃-1050℃.

[0018] In a preferred embodiment, in step S2, the liquid-to-solid mass ratio of the dissolved material is 3-15.

[0019] In a preferred embodiment, in step S2, the dissolution temperature of the clinker is 25°C-65°C.

[0020] In a preferred embodiment, in step S2, the dissolution time of the clinker is 5 min to 20 min.

[0021] In a preferred embodiment, in step S3, the reaction temperature for recovering alkali from the filter residue is 100℃-150℃.

[0022] In a preferred embodiment, in step S3, the reaction time for recovering alkali from the filter residue is 1-2 hours.

[0023] In a preferred embodiment, in step S3, the required NaOH concentration for alkali recovery from the filter residue is 1 mol / L to 2 mol / L.

[0024] In a preferred embodiment, in step S4, the magnetic field strength for the magnetic separation of the hydrolysis residue is 0.05-0.2T.

[0025] This invention provides a method for recovering aluminum and iron from high-speed rail Bayer red mud based on one-step low-calcium reduction sintering, comprising the following steps: Bayer red mud raw material is subjected to low-calcium reduction sintering; Bayer red mud is uniformly mixed with soda ash, limestone, and coke, and ground into a grinding powder; sintering is carried out in an oxygen-deficient atmosphere in a muffle furnace; the resulting sintered clinker is pulverized to obtain clinker powder; alumina is dissolved from the sintered clinker; the sintered clinker powder is heated and stirred in a water bath; and after vacuum filtration, sodium aluminate crude liquid and filter residue are obtained; the Al2O3 dissolution rate in the clinker is... The alkali recovery rate of the filter residue is 80.24%. The filter residue undergoes hydrolysis under hydrothermal conditions. After washing and filtration, sodium hydroxide solution and hydrolysis residue are obtained. The Na2O leaching rate in the filter residue is 88.35%, and the Na2O recovery rate of the whole process is 73.91%. The hydrolysis residue is separated by magnetic separation. After wet magnetic separation, magnetite concentrate can be separated from the hydrolysis residue. The remaining solid phase is harmless tailings. The iron grade in the iron concentrate is 62.21%, and the iron recovery rate is 80.96%.

[0026] The reaction equation involved in this invention is:

[0027] 12FeOOH+C=4Fe3O4+3H2O↑+CO2↑

[0028] 2AlOOH+Na2CO3=2NaAlO2+CO2↑+H2O↑

[0029] SiO2+Na2CO3+CaCO3=Na2CaSiO4+2CO2↑

[0030] TiO2 + CaCO3 = CaTiO3 + CO2↑

[0031] NaAlSiO4+Na2CO3+CaCO3=Na2CaSiO4+NaAlO2+2CO2↑

[0032] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0033] This invention draws upon existing low-calcium sintering methods for processing aluminum-containing resources and incorporates a series of improvements. The low-calcium reduction sintering method has lower requirements for the grade of aluminum and iron-containing raw materials, achieves alkali recovery and utilization within the process, reduces industrial production costs, and decreases alkali consumption. During the low-calcium reduction sintering process, precise control of reaction parameters such as temperature and time allows calcium to participate more effectively in key reactions, improving calcium utilization efficiency. The low-calcium reduction sintering method alters the mineral transformation pathways in Bayer process red mud, enabling some reactions that previously required large amounts of calcium to proceed via new pathways with lower calcium consumption. By adjusting the raw material ratio, the low-calcium reduction sintering method fully utilizes the components of Bayer process red mud, reducing dependence on calcium. Furthermore, based on a one-step low-calcium reduction sintering method, multiple reactions are integrated into a single step, avoiding energy losses in intermediate processes and significantly reducing overall energy consumption.

[0034] Furthermore, this invention designs novel product phases Na2CaSiO4, NaAlO2, and CaTiO3. This invention does not generate Ca2SiO4, reducing the encapsulation and loss of aluminum in aluminosilicate materials, thereby improving the dissolution rate of Al. In traditional sintering processes, the generated Ca2SiO4 is decomposed by NaOH during clinker dissolution to generate Ca(OH)2 and Na2SiO3. This decomposition product reacts with NaAlO2 to form hydrated sodium aluminosilicate, resulting in the loss of Al2O3. Simultaneously, the generated NaAlO2 is a water-soluble aluminate that rapidly dissolves into the solution during dissolution, existing as sodium aluminate, thus achieving efficient aluminum dissolution. The newly designed product phases Na2CaSiO4 and CaTiO3 alter the mineral phase composition and reaction pathway of the system, shifting the reaction towards a direction more favorable to the formation of NaAlO2 and suppressing other side reactions detrimental to aluminum dissolution.

[0035] This invention further improves the recovery rate of subsequent alkali. By designing the generation of phases such as Na2CaSiO4, NaAlO2, and CaTiO3, this invention avoids the formation of alkali-consuming minerals such as calcium silicate, reducing the ineffective consumption of alkali from the source and allowing more alkali to be recovered and reused during the leaching process. At the same time, the generated NaAlO2 is easily soluble in water and quickly dissolves into the solution during the leaching process, existing in the form of sodium aluminate. Since no other side reactions that consume alkali occur, the alkali concentration in the solution is relatively high, which is conducive to maintaining the dissolved state of NaAlO2 and avoiding hydrolysis and precipitation due to excessively low alkali concentration. Therefore, when the leaching solution is treated to recover alkali, more alkali can be effectively recovered.

[0036] Therefore, the technical solution provided by this invention shows broad application prospects in the fields of building materials, environment, and valuable metal recycling. Attached Figure Description

[0037] Figure 1 This is an experimental flow chart of a method for recovering aluminum, iron, and sodium from high-iron Bayer process red mud based on a one-step low-calcium reduction sintering, water leaching, and magnetic separation process, and achieving harmless treatment of tailings. Specific implementation methods

[0038] This invention provides a method for recovering aluminum, iron, and sodium from high-iron Bayer process red mud based on a one-step low-calcium reduction sintering, water leaching, and magnetic separation process, and for achieving harmless treatment of tailings, comprising the following steps:

[0039] S1 involves the low-calcium reduction sintering of Bayer red mud raw materials. Bayer red mud is uniformly mixed with soda ash, limestone, coke, and abrasives, and sintered in a muffle furnace under certain conditions. The resulting sintered clinker is then pulverized to obtain clinker powder.

[0040] S2 dissolves alumina from the sintered clinker, heats and stirs the sintered clinker powder in a water bath, and obtains crude sodium aluminate liquid and filter residue by vacuum filtration.

[0041] S3 recovers alkali from the filter residue. The filter residue will undergo a hydrolysis reaction under hydrothermal conditions. After washing and filtration, sodium hydroxide solution and hydrolysis residue are obtained.

[0042] S4 separates the hydrolysis residue by magnetic separation. After wet magnetic separation, the magnetite concentrate can be separated from the hydrolysis residue, and the remaining solid phase is harmless tailings.

[0043] This invention involves uniformly mixing Bayer red mud with soda ash, limestone, coke, and abrasive, and then sintering the mixture in an oxygen-deficient atmosphere in a muffle furnace to obtain sintered clinker.

[0044] In this invention, the red mud raw material has a high Fe2O3 content of 41.46%, and this raw material is a typical high-iron red mud.

[0045] In this invention, unlike the traditional soda lime sintering method, the low-calcium reduction sintering method uses soda ash, limestone and coke as sintering aids. The Al2O3 component in the Bayer process red mud reacts to generate NaAlO2 and KAlO2, the SiO2 component reacts to generate Na2CaSiO4, the TiO2 component reacts to generate CaTiO3, and the Fe2O3 component reacts to generate Fe3O4.

[0046] In this invention, the generated Na2CaSiO4 is insoluble in aqueous solution and dilute alkaline solution at room temperature, but it is easily hydrolyzed under hydrothermal conditions, reacting to generate CaO·SiO2·nH2O and NaOH, thereby recovering the Na2O component and achieving recycling.

[0047] In this invention, the generated Fe3O4 has a strong specific magnetization coefficient and is insoluble in aqueous solution and dilute alkali solution. Therefore, magnetite can be recovered from hydrolysis residue by wet magnetic separation process. At the same time, the generation of Fe3O4 also increases the added value of sintering reaction products.

[0048] In this invention, compared with the traditional soda lime sintering method, the low-calcium reduction sintering method uses Na2CO3 to replace part of CaCO3. The generation of Na2O·CaO·SiO2 during the sintering process reduces the consumption of CaCO3 resources and lowers energy consumption.

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] A method for recovering aluminum, iron, and sodium from high-iron Bayer process red mud based on a one-step low-calcium reduction sintering, water leaching, and magnetic separation process, and achieving harmless treatment of tailings, is as follows:

[0052] 25g of Bayer process red mud raw material was used for batching, with the alkali-alumina ratio controlled at 1.10, the calcium-silicon ratio at 1.0, and the carbon ratio at 8%. A low-calcium reduction sintering experiment was conducted under experimental conditions of a sintering reaction temperature of 1050℃ and a reaction time of 2h. The resulting sintered clinker was crushed and ball-milled to obtain clinker powder. The main sintering reaction products were sodium aluminate, magnetite, perovskite, and disodium calcium silicate.

[0053] 8g of sintered clinker was weighed, the clinker dissolution temperature was selected as 65℃, distilled water was used as the dissolution medium, and a liquid-solid ratio of 3 was selected for the dissolution experiment. The reaction was carried out in a water bath for 15 minutes, and vacuum filtration was performed using a circulating water vacuum pump. The filter cake was washed with hot water, and the analysis showed that the dissolution rate of Al2O3 in the sintered clinker was 80.24%.

[0054] 10g of iron-silicon-calcium-alkali residue was weighed and placed in the inner liner of a polytetrafluoroethylene reactor. A 2mol / L NaOH solution was added, and the residue was hydrolyzed at 150℃ for 2 hours. At this time, the dissolution rate of Na2O in the residue was 88.35%. The main phase of the hydrolyzed residue was magnetite.

[0055] During the magnetic separation experiment of hydrolysis slag, the magnetic field strength was set to 0.18T. The hydrolysis slag slurry was introduced from the top of the magnetic separator. After separation, filtration and drying, magnetite concentrate was obtained. The iron grade in the iron concentrate reached 62.21%, and the iron recovery rate reached 80.96%.

[0056] Although the above embodiments have provided a detailed description of the present invention, they are merely some, not all, embodiments of the present invention. Other embodiments can be obtained based on these embodiments without inventive step, and all such embodiments fall within the scope of protection of the present invention. The purpose of selecting and describing exemplary embodiments is to explain the specific principles of the present invention and its practical application, thereby enabling those skilled in the art to implement and utilize various exemplary embodiments of the present invention, as well as various choices and modifications. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for recovering aluminum, iron, and sodium from high-iron Bayer process red mud based on a one-step low-calcium reduction sintering, water leaching, and magnetic separation process, and achieving harmless treatment of tailings, characterized in that... Includes the following steps: S1 involves the low-calcium reduction sintering of Bayer red mud raw materials. Bayer red mud is uniformly mixed with soda ash, limestone, coke, and abrasives, and sintered in a muffle furnace under certain conditions. The resulting sintered clinker is then pulverized to obtain clinker powder. S2 dissolves alumina from the sintered clinker, heats and stirs the sintered clinker powder in a water bath, and obtains crude sodium aluminate liquid and filter residue by vacuum filtration. S3 recovers alkali from the filter residue. The filter residue will undergo a hydrolysis reaction under hydrothermal conditions. After washing and filtration, sodium hydroxide solution and hydrolysis residue are obtained. S4 separates the hydrolysis residue by magnetic separation. After wet magnetic separation, the magnetite concentrate can be separated from the hydrolysis residue, and the remaining solid phase is harmless tailings.

2. The method as described in claim 1, characterized in that, The calcium-silicon molar ratio in the fixed ingredients is 1.

0. Where RCa=[CaO] / [SiO2+TiO2+3P2O5].

3. The method as described in claim 1, characterized in that, The alkali-aluminum molar ratio in the ingredients is 1.00-1.

10. Wherein RNa=[Na2O+K2O] / [SiO2+Al2O3].

4. The method as described in claim 1, characterized in that, The mass ratio of Bayer red mud to coke in the ingredients is 5%-12%. Wherein RC = coke / red mud.

5. The method as described in claim 1, characterized in that, The low-calcium reduction sintering time is 0.5h-2h.

6. The method as described in claim 1, characterized in that, The low-calcium reduction sintering temperature is 950℃-1050℃.

7. The method as described in claim 1, characterized in that, The liquid-to-solid mass ratio of the dissolved material is 3-15.

8. The method as described in claim 1, characterized in that, The dissolution temperature of the clinker is 25℃-65℃.

9. The method as described in claim 1, characterized in that, The dissolution time of the clinker is 5 min to 20 min.

10. The method as described in claim 1, characterized in that, The reaction temperature for recovering alkali from the filter residue is 100℃-150℃.

11. The method as described in claim 1, characterized in that, The reaction time for recovering alkali from the filter residue is 1-2 hours.

12. The method as described in claim 1, characterized in that, The required NaOH concentration for alkali recovery from the filter residue is 1 mol / L-2 mol / L.

13. The method as described in claim 1, characterized in that, The magnetic field strength for the magnetic separation of the hydrolysis residue is 0.05-0.2T.

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