CN114573034B - A method for preparing layered iron-aluminum double metal hydroxide using Bayer red mud - Google Patents

Abstract

The invention discloses a method for preparing iron-aluminum bimetallic hydroxide using red mud, which includes the following steps: 1) eluting the red mud with water to remove alkali to neutrality, and then mixing it with inorganic acid to obtain a mixed slurry; 2) The obtained mixed slurry is heated and leached under stirring conditions, and the obtained leached product is subjected to solid-liquid separation to obtain a supernatant liquid and residue; 3) Mix the obtained supernatant liquid with urea, and then perform a hydrothermal reaction to The obtained solid product is centrifuged, washed and dried to obtain layered iron-aluminum double metal hydroxide powder. The method of the invention adopts simple dealkalization, separation and hydrothermal processes, and uses bulk industrial solid waste red mud to prepare high value-added iron-aluminum bimetallic hydroxide; the synthesized iron-aluminum bimetallic hydroxide can be used as nanocatalysis Materials suitable for wastewater treatment and other fields.

Description

A method for preparing layered iron-aluminum double metal hydroxide using Bayer red mud

Technical field

The invention belongs to the technical field of resource utilization of bulk industrial solid waste, and specifically relates to a method for preparing layered iron-aluminum bimetallic hydroxide by using Bayer red mud.

Background technique

Red mud is a strongly alkaline waste residue produced when the aluminum industry extracts alumina. It is reddish-red because it is rich in Fe ₂ O ₃ . In my country, more than 90% of alumina and aluminum hydroxide products are produced by the Bayer process. On average, 1 to 1.4 tons of red mud will be produced for every ton of alumina produced. However, red mud has strong alkalinity and complex composition, and its comprehensive utilization rate is less than 4%. At present, in our country and even the world, the main treatment method of red mud is storage and disposal. Red mud storage not only occupies a large amount of land and increases maintenance costs, but also the strong alkaline substances and heavy metal ions in the red mud enter the soil and groundwater, causing soil alkalization, groundwater pollution and other environmental problems. At the same time, there are safety issues such as dam collapse in the red mud yard problems and will cause significant harm to the local surrounding environment and society. How to properly dispose and utilize red mud is a difficult problem that must be solved for the sustainable development of the alumina industry, which is of great significance to humans and the ecological environment. At this stage, the comprehensive utilization of red mud is mainly concentrated in the fields of building materials, roadbed, valuable metal recovery, catalyst preparation and other fields. The efficiency of the preparation process is not high, the cost remains high, and the added value of the products is generally not high, so the utilization rate of red mud is very low.

Layered double metal hydroxides (LDHs) have a large specific surface area, many active sites, and good conductivity. Based on their unique layered structure and excellent anion exchange properties, they are widely used in ion exchange, water treatment, and catalysts. , adsorbents, flame retardant materials, etc. have been widely used. With in-depth research on LDHs materials, LDHs has played an important role in pesticides, medicines, synthetic materials, biological materials and other fields. Among many LDHs, due to the presence of reducing Fe ²⁺ ions, FeAl-LDHs exhibits special adsorption-coupled reduction capabilities and has been widely reported for use in treating wastewater containing heavy metals and organic matter. Chitrakar et al. used ferrous sulfate and aluminum sulfate as raw materials, first used co-precipitation method under nitrogen protection to obtain precipitation, and then used hydrothermal method to prepare FeAl-LDHs (Sep. Purif. Technol, 2011, 80, 652.). Zhong et al. used ultrasonic-assisted co-precipitation method to prepare FeAl-LDHs using ferrous sulfate and aluminum sulfate as raw materials under nitrogen protection (J. Hazard. Mater., 2013, 250-251, 345.). On the other hand, although there have been some studies on the comprehensive utilization of red mud, due to its complex composition and large changes in content depending on the origin and production process, the existing comprehensive utilization methods usually have problems such as insufficient universality. Difficult to promote.

Contents of the invention

The main purpose of the present invention is to provide a method for preparing iron-aluminum bimetallic hydroxide using Bayer red mud. This method can effectively increase the added value of red mud resource products and improve the comprehensive utilization rate of red mud; and the acid involved It has the advantages of simple means and processes such as immersion, separation and hydrothermal treatment, strong universality, low cost and environmental friendliness, and does not require the use of complex processes and equipment.

In order to achieve the above objects, the technical solutions adopted by the present invention are:

A method for preparing iron-aluminum bimetallic hydroxide using Bayer red mud, including the following steps:

1) Elute the alkali from the red mud with water until it becomes neutral, and then mix it with inorganic acid after drying to obtain a mixed slurry;

2) The mixed slurry is heated and leached under stirring conditions, and the resulting leached product is subjected to solid-liquid separation to obtain the supernatant liquid and residue;

3) Mix the obtained supernatant liquid with urea, then perform a hydrothermal reaction, and centrifuge, wash and dry the obtained solid product to obtain layered iron-aluminum double metal hydroxide powder.

In the above solution, the main components and their mass percentages in the red mud include: Fe ₂ O ₃ 5 to 15%, Al ₂ O ₃ 5 to 20%, SiO ₂ 10 to 25%, TiO ₂ 2 to 10%, Na ₂ O 2～8%, CaO 15～40%.

In the above solution, the inorganic acid solution is one or more of hydrochloric acid, sulfuric acid, nitric acid solution, etc.

In the above scheme, the mass concentration of the inorganic acid solution is 15-40%.

In the above solution, the dosage ratio of the inorganic acid to red mud is 7-14 mL:1g.

In the above scheme, the leaching reaction temperature is 60-100°C and the time is 5-24 hours.

In the above scheme, the mass ratio of red mud to urea is 1: (2-5).

In the above solution, the hydrothermal reaction temperature is 80-180°C; the time is 5-20 hours.

The layered iron-aluminum double metal hydroxide prepared according to the above scheme has a size of 0.2 to 1 μm and a specific surface area of 40 to 100 m ² /g.

The invention first uses an acid leaching method to dissociate the iron and aluminum elements in the red mud into the liquid phase, and then introduces urea and corresponding hydrothermal conditions to provide weak alkaline conditions and simultaneously reduce iron ions to ferrous ions. Finally, The reaction forms layered FeAl-LDHs (Fe(II)-Al(III)-LDHs).

Compared with the prior art, the beneficial effects of the present invention are:

1) The technical solution described in the present invention can successfully achieve the purpose of preparing layered iron-aluminum bimetallic hydroxide using Bayer red mud, and can significantly improve the added value of red mud resource utilization products;

2) Non-toxic and cheap urea is used to reduce iron ions in red mud into ferrous ions to form FeAl-LDHs, which can effectively replace the synthesis conditions that require the addition of ferrous salts and aluminum salt raw materials in the traditional preparation process, and make full use of red mud. Effective elements such as iron and aluminum in the mud; in the reaction system, the decomposition of urea is also used to regulate alkalinity and control the growth rate;

3) The two-dimensional flake iron-aluminum double metal hydroxide prepared by the present invention has a uniform morphology, a large specific surface area, and a wide range of size control.

Description of drawings

Figure 1 is an XRD pattern of the product obtained in Example 1 of the present invention;

Figure 2 is an SEM image of the product obtained in Example 2 of the present invention;

Figure 3 is an XRD pattern of the product prepared in Example 4 of the present invention;

Figure 4 is an XRD pattern of the product prepared in Example 5 of the present invention;

Figure 5 is an XRD pattern of the product prepared in Comparative Example 1 of the present invention;

Figure 6 is a graph showing the degradation performance of the phenol-containing wastewater of the product prepared in Example 1 of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with examples. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

There are no specific instructions in the following examples, and all reagents used are commercially available chemical reagents or industrial products.

In the following examples, the red mud used was provided by Chalco Shandong Branch. Its chemical composition and content include: Fe ₂ O ₃ 12.5%, Al ₂ O ₃ 9.2%, SiO ₂ 18.9%, TiO ₂ 2.5%, Na ₂ O 3.9%, CaO 34.6%.

Example 1

A method for preparing layered iron-aluminum bimetallic hydroxide using red mud, including the following steps:

Weigh 2g of original Bayer red mud, wash it with distilled water until neutral and then dry it; disperse the obtained dealkalized red mud in 6mL of deionized water, stir evenly, add 20mL of concentrated hydrochloric acid (12mol/L), and then place it at a constant temperature of 80°C. Stir for 24 hours, use a vacuum pump to perform suction filtration to obtain the supernatant liquid; weigh 4.0g of urea and dissolve it in the above solution, stir for 30 minutes; transfer the resulting mixed liquid to a polytetrafluoroethylene-lined stainless steel reactor, and heat to 120°C for dehydration Thermal reaction was carried out for 12 hours; the obtained product was cooled to room temperature, centrifuged and washed with ethanol and deionized water, and dried for 12 hours to obtain the final product.

The product obtained in this example was subjected to X-ray diffraction analysis. The results are shown in Figure 1. The characteristic peaks of the product obtained in the figure are consistent with the FeAl-LDHs (Ye et al. J. Hazard. Mater. 2020, 388, 122120) spectrum in the literature. It shows that the obtained product is a layered iron-aluminum double metal hydroxide; after testing, the specific surface area of the obtained product is 53.2m ² /g.

Example 2

A method for preparing layered iron-aluminum bimetallic hydroxide using red mud, including the following steps:

Weigh 2g of original Bayer red mud, wash it with distilled water until neutral and then dry it; disperse the obtained dealkalized red mud in 6mL of deionized water, stir evenly, add 20mL of concentrated hydrochloric acid (12mol/L), and then place it at a constant temperature of 80°C. Stir for 24 hours, use a vacuum pump to perform suction filtration to obtain the supernatant liquid; weigh 5.0g of urea and dissolve it in the above solution, stir for 30 minutes; transfer the resulting mixture to a polytetrafluoroethylene-lined stainless steel reactor, and heat it to 120°C for dehydration. Thermal reaction was carried out for 12 hours; the obtained product was cooled to room temperature, centrifuged and washed with ethanol and deionized water, and dried for 12 hours to obtain the final product.

Figure 2 is an SEM image of the layered iron-aluminum double metal hydroxide obtained in this embodiment. It can be seen from the figure that the morphology of the obtained product is flake-like with a size of 0.2 to 1 μm.

Example 3

A method for preparing layered iron-aluminum bimetallic hydroxide using red mud, including the following steps:

Weigh 2g of original Bayer red mud, wash it with distilled water until neutral and then dry it; disperse the obtained dealkalized red mud in 6mL of deionized water, stir evenly, add 20mL of concentrated hydrochloric acid (12mol/L), and then place it at a constant temperature of 80°C. Stir for 24 hours, use a vacuum pump to perform suction filtration to obtain the supernatant liquid; weigh 10.0g of urea and dissolve it in the above solution, stir for 30 minutes; transfer the resulting mixed liquid to a polytetrafluoroethylene-lined stainless steel reactor, and heat to 120°C for dehydration Thermal reaction was carried out for 12 hours; the obtained product was cooled to room temperature, centrifuged and washed with ethanol and deionized water, and dried for 12 hours to obtain the final product.

Example 4

A method for preparing layered iron-aluminum bimetallic hydroxide using red mud, including the following steps:

Weigh 2g of original Bayer red mud, wash it with distilled water until neutral and then dry it; disperse the obtained dealkalized red mud in 6mL of deionized water, stir evenly, add 20mL of concentrated hydrochloric acid (12mol/L), and then place it at a constant temperature of 80°C. Stir for 24 hours, use a vacuum pump to perform suction filtration to obtain the supernatant liquid; weigh 4.0g of urea and dissolve it in the above solution, stir for 30 minutes; transfer the resulting mixed liquid to a polytetrafluoroethylene-lined stainless steel reactor, and heat to 120°C for dehydration The thermal reaction was carried out for 20 hours; the obtained product was cooled to room temperature, centrifuged and washed with ethanol and deionized water, and dried for 12 hours to obtain the final product.

Figure 3 is an XRD pattern of the layered iron-aluminum double metal hydroxide obtained in this example.

Compared with Example 1, it can be found that as the hydrothermal reaction time becomes longer, the crystallinity of the FeAl-LDHs layered material obtained becomes higher and the crystal grain size becomes larger. This result is consistent with the growth mechanism of inorganic material particles under hydrothermal conditions.

Example 5

A method for preparing layered iron-aluminum bimetallic hydroxide using red mud, including the following steps:

Weigh 2g of original Bayer red mud, wash it with distilled water until neutral and then dry it; disperse the obtained dealkalized red mud in 6mL of deionized water, stir evenly, add 20mL of concentrated hydrochloric acid (12mol/L), and then place it at a constant temperature of 80°C. Stir for 24 hours, use a vacuum pump to perform suction filtration to obtain the supernatant liquid; weigh 5.0g of urea and dissolve it in the above solution, and stir for 30 minutes; transfer the resulting mixture to a polytetrafluoroethylene-lined stainless steel reactor, and heat to 180°C for dehydration Thermal reaction was carried out for 12 hours; the obtained product was cooled to room temperature, centrifuged and washed with ethanol and deionized water, and dried for 12 hours to obtain the final product.

Figure 4 is an XRD pattern of the layered iron-aluminum double metal hydroxide obtained in this example.

Compared with Example 2, in addition to the two characteristic peaks at 11.5° and 23.2°, more obvious characteristic peaks attributed to layered double metal hydroxide can be observed at 35.1°, 46.6°, and 61.1°, indicating that The higher the hydrothermal reaction temperature, the more conducive it is to the growth of LDHs particles, thereby forming more complete crystal particles.

Example 6

A method for preparing layered iron-aluminum bimetallic hydroxide using red mud, including the following steps:

Weigh 2g of original Bayer red mud, wash it with distilled water until neutral and then dry it; disperse the obtained dealkalized red mud in 6mL of deionized water, stir evenly, add 14mL of concentrated hydrochloric acid (12mol/L), and then place it at a constant temperature of 80°C Stir for 24 hours, use a vacuum pump to perform suction filtration to obtain the supernatant liquid; weigh 5.0g of urea and dissolve it in the above solution, stir for 30 minutes; transfer the resulting mixture to a polytetrafluoroethylene-lined stainless steel reactor, and heat it to 120°C for dehydration. Thermal reaction was carried out for 12 hours; the obtained product was cooled to room temperature, centrifuged and washed with ethanol and deionized water, and dried for 12 hours to obtain the final product.

Comparative ratio

A method for preparing iron-aluminum mixed oxide using red mud, including the following steps:

Weigh 2g of original Bayer red mud, wash it with distilled water until neutral and then dry it; disperse the obtained dealkalized red mud in 6mL of deionized water, stir evenly, add 20mL of concentrated hydrochloric acid (12mol/L), and then place it at a constant temperature of 80°C. Stir for 24 hours, use a vacuum pump to perform suction filtration to obtain the supernatant liquid; transfer the obtained supernatant liquid to a polytetrafluoroethylene-lined stainless steel reactor, heat to 120°C for hydrothermal reaction for 12 hours; cool the obtained product to room temperature before use Centrifuge and wash with ethanol and deionized water, and dry for 12 hours to obtain the final product.

Figure 5 is the XRD pattern of the product obtained in this comparative example. It can be seen from the figure that without adding urea, the prepared sample has no specific crystal structure and is an amorphous iron-aluminum metal oxide. This result proves the important role of urea in the formation of FeAl-LDHs layered crystal structure; it reduces iron ions to ferrous ions, and forms layered iron-aluminum double metal hydroxide through hydrothermal reaction under weakly alkaline conditions.

Application examples

The layered iron-aluminum bimetallic hydroxide nanomaterial obtained in Example 1 was used to perform a phenol-containing wastewater degradation experiment, which specifically included the following steps:

Weigh 50 mg of the FeAl-LDHs nanomaterial obtained in this example and disperse it in 100 mL of wastewater solution (containing 10 mg/L nitrophenol), place it in a quartz reactor and perform magnetic stirring in the dark, and adsorb for 30 minutes in the dark to achieve adsorption. balance. Then, according to different reaction systems, PMS was added and UV light irradiation was applied. Samples were collected at different times and nitrophenol concentrations were measured.

Figure 6 is a comparison chart of the nitrophenol degradation performance of the FeAl-LDHs nanomaterials prepared in Example 1 under different conditions. It can be seen that FeAl-LDHs nanomaterials can be successfully prepared using red mud using a simple process, and can effectively degrade phenol-containing wastewater. Demonstrate high processing efficiency. In the presence of monopersulfate, the degradation rate of nitrophenol by FeAl-LDHs can reach 99.4% in 180 minutes, which is 4 times higher than that under the condition of single FeAl-LDHs.

The above results show that the preparation process of the present invention is simple and environmentally friendly, and the prepared FeAl-LDHs nanomaterials can be used to treat phenol-containing wastewater.

The above-mentioned embodiments are only examples for clear explanation and are not intended to limit the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made based on the above description. It is not necessary and impossible to exhaustively enumerate all the implementation methods. Therefore, the obvious changes or changes are derived. are still within the protection scope of the present invention.

Claims (6)

1. A method for preparing iron-aluminum bimetallic hydroxide using red mud, which is characterized in that it includes the following steps: 1) Elute the red mud with water to remove alkali to neutrality, dry it and mix it with inorganic acid to obtain a mixed slurry; 2) The mixed slurry is heated and leached under stirring conditions, and the resulting leached product is subjected to solid-liquid separation to obtain the supernatant liquid and residue; 3) Mix the obtained supernatant liquid with urea, then perform a hydrothermal reaction, and centrifuge, wash and dry the obtained solid product to obtain layered iron-aluminum double metal hydroxide powder; The main components and their mass percentages in the red mud include: Fe ₂ O ₃ 5 to 12.5%, Al ₂ O ₃ 5 to 9.2%, SiO ₂ 10 to 25%, TiO ₂ 2 to 10%, Na ₂ O 2～8%, CaO 15～40%; The mass ratio of red mud to urea is 1: (2-5). 2. The method according to claim 1, characterized in that the inorganic acid is one or more of hydrochloric acid, sulfuric acid and nitric acid. 3. The method according to claim 1, characterized in that the mass concentration of the inorganic acid is 15-40%. 4. The method according to claim 1, characterized in that the dosage ratio of the inorganic acid to red mud is 7-14 mL: 1 g. 5. The method according to claim 1, characterized in that the leaching reaction temperature is 60-100°C and the time is 5-24 hours. 6. The method according to claim 1, characterized in that the hydrothermal reaction temperature is 80-180°C and the time is 5-20 hours.