Method for gradually recovering and preparing MIL-88A (Fe) and autoclaved aerated concrete from red mud

Abstract

The invention discloses a method for gradually recovering and preparing MIL-88A (Fe) and autoclaved aerated concrete from red mud, which comprises the following steps of: extracting valuable metal elements in the red mud by using an inorganic strong acid leaching method to obtain a leaching solution and filter residues, adding organic acid into the leaching solution, uniformly mixing, performing hydrothermal reaction, cooling, centrifuging and drying a product to obtain MIL-88A (Fe) powder, and preparing the MIL-88A (Fe) powder into the autoclaved aerated concrete. The autoclaved aerated concrete is prepared from the filter residues, cement, steel slag, molecular sieve waste, gypsum and aluminum powder. According to the method, the leaching efficiency of Fe in the red mud can be fully guaranteed, the yield of the product MIL-88A (Fe) is increased, meanwhile, through selection of organic acid and use of a hydrothermal synthesis multi-parameter regulation and control system, on one hand, the crystallinity of the prepared MIL-88A (Fe) is guaranteed, on the other hand, the integrity of the microstructure of the MIL-88A (Fe) is achieved, and the method is suitable for industrial production. The autoclaved aerated concrete prepared from the leached filter residues meets the national strength standard.

Description

Technical Field

[0001] The invention belongs to the field of comprehensive utilization of solid waste red mud, and specifically relates to a method for gradually recovering and preparing MIL-88A (Fe) and autoclaved aerated concrete from red mud. Background Art

[0002] For many years, the Bayer process has been widely used in the refining of alumina from bauxite, but it has produced billions of tons of alkaline waste called red mud. Generally, about 1 to 1.5 tons of red mud are discharged for every ton of alumina produced. By 2023, the global stock of red mud has exceeded 5 billion tons, making red mud disposal sites extremely dangerous and toxic areas. Although countries have taken active measures to recycle red mud, its global utilization rate is still less than 5%, making the treatment of red mud an urgent environmental issue. The high alkalinity and heavy metal content of red mud have caused a series of major environmental problems such as land occupation and ecological pollution (water, soil and air pollution), and the treatment methods such as deep sea dumping, landfill and pond storage have caused significant damage to the natural environment. Red mud is rich in Fe and Al, and contains a certain amount of Si, Ti and Ca, as well as small amounts of elements such as Na, K, Mg, Mn and Zr, and trace amounts of rare earth elements such as Sc, La and Ce. The content of iron oxide (α-Fe2O3) can reach 30% to 60%, which is especially significant in high-iron red mud. Therefore, it is urgent to develop cost-effective and environmentally sustainable methods and technologies to realize the secondary resource utilization of red mud.

[0003] At present, the resource utilization of red mud mainly includes cement production, development of building materials, adsorption materials for pollutant removal, catalysts and synthesis of other functional products. In addition, red mud can also be used to recover valuable metals such as Fe, Ti, Al and rare earth elements. In particular, high-Fe red mud mainly exists in the form of compounds such as Fe2O3, FeOOH and FeTiO3, which makes it an important source of iron resource recovery. Therefore, the recovery of Fe from high-iron red mud has important research value and far-reaching practical significance.

[0004] Generally, the technical methods for extracting Fe from red mud can be divided into four categories: magnetic separation, pyrometallurgical reaction, hydrometallurgical reaction and the comprehensive application of these methods. Since red mud needs to be filtered or dried and dehydrated before the pyrometallurgical process, it is reasonable to regard hydrometallurgy as a promising method for recovering iron from red mud. Specifically, the hydrometallurgical process mainly relies on water chemical reactions for material separation, usually using acid leaching. Since red mud contains a variety of metal elements, most of which are soluble in acid, Fe is usually leached simultaneously with one or more other metal elements during the acid leaching process, resulting in an increase in metal impurities in the final Fe-containing terminal material. It is worth noting that Si-rich leaching residue can also be regarded as a secondary resource, however, the further utilization technology of this residue is still insufficient. Therefore, the comprehensive utilization of red mud, especially the technical development of leaching residue, urgently needs to be explored and developed in depth.

[0005] Autoclaved aerated concrete (AAC) is a new sustainable building material that has attracted widespread attention for its excellent thermal insulation and lightweight properties. It is suitable for a variety of modern construction applications, including private homes and commercial infrastructure. Compared with traditional heavy building materials, AAC is porous and lightweight, with a normal bulk density of 400-800 kg / m³, which is about 20% lower than that of ordinary concrete. The preparation of this material usually includes (1) siliceous materials (such as fly ash or quartzite), (2) calcareous materials (such as cement or lime), (3) admixtures (such as gypsum), and (4) aeration materials (such as aluminum powder). In recent years, many industrial solid wastes, such as coal gangue, steel slag, iron tailings, copper tailings, and spent zeolite-based catalysts, have also been used in the preparation of AAC to reduce costs and achieve waste recycling. Summary of the invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a comprehensive utilization technology of solid waste red mud in view of the shortcomings of the prior art. By converting solid waste red mud into MOF materials and autoclaved aerated concrete with economic value, its application potential in various processes is improved, thereby promoting the sustainability of future economic practices.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A method for gradually recovering and preparing MIL-88A (Fe) and autoclaved aerated concrete from red mud comprises the following steps: (1) Using an inorganic strong acid leaching method to extract valuable metal elements from red mud to obtain a leachate and a filter residue; (2) adding an organic acid to the above-mentioned leaching solution, mixing well, and then performing a hydrothermal reaction. The product is cooled, centrifuged, and then dried to obtain MIL-88A(Fe) powder; (3) Using the filter residue obtained in step (1), cement, steel slag, molecular sieve waste and gypsum as raw materials and aluminum powder as foaming material, autoclaved aerated concrete is prepared.

[0008] In the present invention, red mud can be regarded as a potential raw material for preparing metal organic framework materials (MOF) due to its rich chemical composition. The present invention uses red mud to synthesize MIL-88A (Fe), and uses the residue obtained after acid leaching in the preparation of autoclaved aerated concrete. The MIL-88A (Fe) prepared by the present invention is a functional MOF material, which is composed of metal ions (or clusters) and organic ligands, has an excellent coordination environment and a unique spatial geometric structure, so that it has been widely used in the imaging and drug delivery of biomedical carriers, lithium storage, carbon dioxide emission reduction, fuel cells, and degradation or adsorption of pollutants in environmental remediation. As an Fe-based MOF, MIL-88A (Fe) has an engineered pore structure with an adjustable surface and exhibits excellent application performance. In view of the fact that the red mud leaching residue is rich in silicon and has a low bulk density due to the dissolution of the Fe-containing matrix, the red mud leaching residue can be used as a supplementary siliceous material for autoclaved aerated concrete to expand its application prospects.

[0009] Preferably, in step (1), the inorganic strong acid comprises any one of hydrochloric acid, nitric acid and sulfuric acid, the mass concentration of the inorganic strong acid is 8-30%, and the liquid-to-solid ratio of the inorganic strong acid to red mud is 5-10:1 mL / g.

[0010] Preferably, in step (1), the leaching reaction temperature is 25-95°C, and the leaching reaction time is 15-120 min.

[0011] Preferably, in step (2), the organic acid comprises any one of terephthalic acid, trimesic acid and fumaric acid, the organic acid is solid, and the molar ratio of Fe to organic acid in the leachate is 0.6-1.3.

[0012] Preferably, in step (2), the temperature of the hydrothermal reaction is controlled at 90-200°C, the reaction pressure is controlled at 0.1-4 MPa, and the reaction time is 2-10 h.

[0013] Preferably, in step (3), the cement is PO cement with a grade higher than 42.5; and the molecular sieve waste is deactivated ZSM-5 waste.

[0014] Preferably, in step (3), cement accounts for 5-20% of the total mass of all raw materials, steel slag accounts for 20-50% of the total mass of all raw materials, molecular sieve waste accounts for 1-25% of the total mass of all raw materials, filter residue from red mud leaching accounts for 1-20% of the total mass of all raw materials, gypsum accounts for 1-6% of the total mass of all raw materials, and aluminum powder foaming material accounts for 0.05%-0.4% of the total mass of the above raw materials.

[0015] Specifically, in step (3), the filter residue extracted from red mud, cement, steel slag, molecular sieve waste and gypsum are first mixed with water and stirred evenly, and then aluminum powder is added. After sufficient stirring, the mixture is placed in a mold and sent to a curing box for curing and molding, and then demolded and cured by autoclaving and aeration.

[0016] Preferably, the water-to-solid ratio of all raw materials to water is 0.4-0.9.

[0017] Preferably, the steam temperature of the autoclave aeration curing is 160-260°C, the added steam pressure is 1.2-2.5 MPa, and the autoclave time is 4-12 h. Beneficial Effects

[0018] (1) The inorganic acid leaching, hydrothermal synthesis, and autoclaved aerated concrete multi-parameter control system provided by the present invention: First, the use of the leaching agent system can fully ensure the leaching efficiency of Fe in red mud and improve the yield of the product MIL-88A (Fe). When nitric acid is used as the leaching agent, the leaching rate of Fe at a leaching temperature of 70 ° C reaches 98.75%; at the same time, through the selection of organic acid and the use of the hydrothermal synthesis multi-parameter control system, on the one hand, the crystallinity of the prepared MIL-88A (Fe) is guaranteed, and on the other hand, the integrity of its microscopic morphology is achieved. And the raw material of the present invention is industrial solid waste-red mud. Compared with the existing MIL-88A (Fe) synthesis technology (ZL 202110541039.4), the present invention does not require chemically pure reagents containing Fe, and achieves the goal of green synthesis of MIL-88A (Fe) from iron-containing industrial solid waste.

[0019] (2) The present invention successfully prepared autoclaved aerated concrete that meets the national strength standard using the above-mentioned leached residue. The proportion of cement was 11%, the proportion of steel slag was 43%, the proportion of deactivated ZSM-5 waste was 22%, the proportion of red mud leached residue was 18%, the proportion of gypsum was 6%, and the proportion of aluminum powder was 0.2% of other raw materials. Under the conditions of autoclaving temperature of 180 °C, pressure of 1.5 MPa, and time of 6 h, the apparent density was 531 kg / m 3 , the compressive strength is 3.7 MPa, and finally all samples meet the national standard (GB / T 11968-2020). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0021] Figure 1 It is the XRD spectrum of MIL-88A(Fe) prepared by the present invention.

[0022] Figure 2 It is a SEM picture of MIL-88A(Fe) prepared by the present invention.

[0023] Figure 3 This is the XRD pattern of Fe MOF prepared by comparative experiment.

[0024] Figure 4 This is the SEM image of Fe MOF prepared by comparative experiment.

[0025] Figure 5 It is the XPS chart of MIL-88A(Fe) prepared by the present invention.

[0026] Figure 6 These are the XRD patterns of two types of autoclaved aerated concrete prepared with different amounts of red mud leaching residue.

[0027] Figure 7 is the SEM image of autoclaved aerated concrete sample 1.

[0028] Figure 8 is the SEM image of autoclaved aerated concrete sample 2.

[0029] Fig. 9 is the dry density of autoclaved aerated concrete sample 1 and sample 2.

[0030] Fig.10 is the compressive strength of autoclaved aerated concrete samples 1 and 2. DETAILED DESCRIPTION

[0031] The present invention can be better understood with reference to the following examples.

[0032] The invention utilizes nitric acid to extract Fe (and other impurity metal elements) in red mud by high temperature leaching, and utilizes the directional coordination of organic acid to synthesize MIL-88A (Fe); and then uses the leached residue as raw material, combined with PO 42.5 cement, steel slag, deactivated ZSM-5 waste, gypsum, aluminum powder and other raw materials to prepare autoclaved aerated concrete.

[0033] Add 6g of red mud sample to the beaker, take 48mL of 9 mol / L concentrated nitric acid and pour it into the beaker, stir magnetically at 300 r / min, heat in a water bath, and keep the water bath temperature at room temperature 75℃. After 100 minutes, filter and collect the residue and filtrate respectively, place the residue in a drying oven to dry, weigh 0.9836g, and collect the filtrate in a solution bottle. Take 30mL of the filtrate and place it in a beaker, then add 1.2g of fumaric acid to obtain a mixed solution, stir for 30 minutes, and then put the mixed solution into a 150mL high-pressure reactor. After setting the hydrothermal reaction temperature to 105℃ and the time to 7h, take it out and cool it at room temperature. Finally, centrifuge the obtained mixed solution and dry it at 70℃ for 18h with a blower dryer to obtain a MIL-88A(Fe) powder sample.

[0034] Then, the above-mentioned filter residue is used as raw material, and 11% cement, 43% steel slag, 22% deactivated ZSM-5 waste, 18% red mud leaching filter residue, and 6% gypsum are mixed, and 0.2% aluminum powder foaming agent of the total weight of the above raw materials is added (based on the total weight of other raw materials). According to the above proportion, the raw materials required for the experiment are put into the cement mortar mixer and mixed, and slowly stirred for 5 min to ensure that the raw materials are mixed evenly. Secondly, a certain amount of water is added to the above mixture, first slowly stirred for 2 min, and then quickly stirred for 4 min until the slurry is evenly mixed to obtain slurry 1. Then, aluminum powder is added to slurry 1 and stirred for 50 s to obtain slurry 2, which is poured into a 100´ 100 ´ 100 mm mold and placed in a 65 ℃ digital display constant temperature mixing circulating water tank for curing for 24 h. Finally, the autoclaved aerated concrete sample was obtained by autoclaving at 210 °C and 2 MPa for 10 h, and the sample was placed in a drying oven at 65 °C and dried to constant weight. The mechanical properties of autoclaved aerated concrete were tested using 100´ 100 ´100 mm cubic test blocks in accordance with the national standard GB / T 11969-2020.

[0035] First, the elemental analysis of red mud before and after nitric acid leaching at high temperature was carried out. The results are shown in Table 1. Through the elemental analysis of the filter residue, it is known that the leaching efficiency of Fe is high during the acid leaching process, and the leaching rate of Fe in this process is as high as 98.76%. In addition, since nitric acid leaching is not selective, the filtrate contains a certain amount of impurity metals, such as Al, Mg, Ca and Ti, as shown in Table 2.

[0036] Table 1 Elemental analysis of raw red mud, leaching residue, and raw materials for preparing autoclaved aerated concrete

[0037] Table 2 ICP analysis of main metal elements in the filtrate

[0038] Table 3 ICP analysis of main metal elements in hydrothermal synthesis solution

[0039] Figure 1 The XRD spectrum of MIL-88A(Fe) prepared in the present invention shows that although the filtrate contains a certain amount of other metals, the prepared MOF is MIL-88A(Fe) with high crystallinity. The characteristic peaks of (100) and (101) in MIL-88A(Fe) are near 2 theta of 10°, and there are no diffraction peaks of other MOFs. Moreover, the concentration of Fe in the filtrate after hydrothermal synthesis is greatly reduced, while the concentration of other metals remains basically unchanged, as shown in Table 3. This shows that fumaric acid can be directional combined with Fe in the leaching solution. Figure 2 The SEM image of the prepared MIL-88A(Fe) is shown in Figure 2. It is obvious that the product is in the shape of regular rods, which is highly similar to the MIL-88A(Fe) synthesized by pure chemical reagents containing Fe in the literature (ZL202110541039.4). If the hydrothermal conditions are adjusted to: temperature of 80 °C and time of 12 h, a comparative experiment is conducted. The XRD spectrum of the Fe MOF obtained in the experiment is shown in Figure 2. Figure 3 As shown, the product is a Fe MOF with low crystallinity and incomplete structure. Figure 4 The SEM surface shown in the figure shows that the product is an irregular rod-like structure. In addition, XPS analysis of the MIL-88A(Fe) prepared in the experiment shows that Figure 5 As shown, it was found that except for the signals of the three elements Fe, O and C, there were no signals of other impurities in the spectrum, indicating that the prepared Fe MOF has high purity and no other metal impurities. It also verified again that fumaric acid can bind to Fe in a directional manner.

[0040] Red mud leaching residue was then used to prepare autoclaved aerated concrete. Sample 1 was prepared according to the conditions in Example 1. The autoclaving curing parameters in the conditions were adjusted to autoclave at 110°C and a pressure of 1 MPa for 10 h, and other parameters remained unchanged to obtain Sample 2. Figure 6 The XRD patterns of two autoclaved aerated concrete samples show that sample 1 contains a certain amount of tobermorite, but sample 2 does not contain tobermorite. Tobermorite is a key product for improving the performance of autoclaved aerated concrete, indicating that autoclaved curing conditions play a key role in the formation of autoclaved aerated concrete. Figure 7 and Figure 8 These are the SEM images of two types of autoclaved aerated concrete. It can be seen that there are a large number of flaky tobermorite products in sample 1, which corresponds to the XRD analysis; while there is basically no such product in sample 2.

[0041] Finally, mechanical analysis was performed using two types of autoclaved aerated concrete, e.g. Fig. 9 and Fig.10 The results show that the dry density and compressive strength of sample 1 are higher than those of sample 2, indicating that the tobermorite in sample 1 enhances the dry density and compressive strength performance, while sample 2 does not have this product, so the macroscopic performance is poor, which also shows that the autoclave curing conditions play a decisive role in the performance of autoclaved aerated concrete.

[0042] The present invention provides a method and idea for gradually recovering and preparing MIL-88A (Fe) and autoclaved aerated concrete from red mud. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A method for gradually recovering and preparing MIL-88A (Fe) and autoclaved aerated concrete from red mud, characterized in that: The steps include: (1) Using an inorganic strong acid leaching method to extract valuable metal elements from red mud to obtain a leachate and a filter residue; (2) adding an organic acid to the above-mentioned leaching solution, mixing well, and then performing a hydrothermal reaction. The product is cooled, centrifuged, and then dried to obtain MIL-88A(Fe) powder; (3) Using the filter residue obtained in step (1), cement, steel slag, molecular sieve waste and gypsum as raw materials and aluminum powder as foaming material, autoclaved aerated concrete is prepared.

2. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 1, characterized in that: In step (1), the inorganic strong acid includes any one of hydrochloric acid, nitric acid and sulfuric acid, the mass concentration of the inorganic strong acid is 8-30%, and the liquid-to-solid ratio of the inorganic strong acid to the red mud is 5-10:1 mL / g.

3. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 1, characterized in that: In step (1), the leaching reaction temperature is 25-95°C, and the leaching reaction time is 15-120 min.

4. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 1, characterized in that: In step (2), the organic acid comprises any one of terephthalic acid, trimesic acid and fumaric acid, the organic acid is solid, and the molar ratio of Fe to organic acid in the leaching solution is 0.6-1.

3.

5. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 1, characterized in that: In step (2), the temperature of the hydrothermal reaction is controlled at 90-200°C, the pressure of the reaction is controlled at 0.1-4 MPa, and the reaction time is 2-10 h.

6. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 1, characterized in that: In step (3), the cement is PO cement with a grade higher than 42.5; and the molecular sieve waste is deactivated ZSM-5 waste.

7. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 1, characterized in that: In step (3), cement accounts for 5-20% of the total mass of all raw materials, steel slag accounts for 20-50% of the total mass of all raw materials, molecular sieve waste accounts for 1-25% of the total mass of all raw materials, filter residue from red mud leaching accounts for 1-20% of the total mass of all raw materials, gypsum accounts for 1-4% of the total mass of all raw materials, and aluminum powder foaming material accounts for 0.05%-0.4% of the total mass of the above raw materials.

8. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 1, characterized in that: In step (3), the filter residue extracted from red mud, cement, steel slag, molecular sieve waste and gypsum are first mixed with water and stirred evenly, and then aluminum powder is added. After sufficient stirring, the mixture is placed in a mold and sent to a curing box for curing and molding, and then demolded and autoclaved and aerated cured.

9. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 8, characterized in that: The water-to-solid ratio of all raw materials to water is 0.4-0.

9.

10. The method for gradually recovering MIL-88A(Fe) and autoclaved aerated concrete from red mud according to claim 8, characterized in that: The steam temperature of the autoclave aeration curing is 160-260°C, the steam pressure is 1.2-2.5 MPa, and the autoclave time is 4-12 h.

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