Method for synthesizing high value-added ternary hydrotalcite by utilizing coal gangue

Abstract

This invention discloses a method for synthesizing high-value-added ternary hydrotalcite from coal gangue through resource utilization, comprising the following steps: crushing and calcining coal gangue to obtain yellow-brown calcined coal gangue powder, mixing it with acid, continuously acidifying and stirring at 70-80℃ for 0.5-2.5 hours, centrifuging, and obtaining Al-containing... 3+ Fe 3+ With Mg 2+ The process involves preparing a metal salt solution, mixing it with magnesium salt, shaking, and adding alkali solution dropwise until the pH of the solution reaches 11-12. After crystallization at room temperature for 3 hours, the solution is washed and dried to obtain Mg-Al-Fe ternary hydrotalcite. This invention uses coal gangue, a major solid waste, as a substitute for high-purity chemical reagents as the aluminum, iron, and magnesium sources. Only magnesium salt is required, significantly reducing the cost of raw materials for hydrotalcite synthesis. This effectively avoids the bottleneck problem of high production costs and difficulty in large-scale industrial application of traditional hydrotalcite, while simultaneously realizing the high-value utilization of coal gangue resources.

Description

Technical Field

[0001] This invention relates to the resource utilization of solid waste, specifically to a method for synthesizing high-value-added ternary hydrotalcite from coal gangue. Background Technology

[0002] Coal gangue is a byproduct of coal mining and washing. Long-term stockpiling of coal gangue contains various heavy metals such as lead, mercury, and chromium, as well as acidic substances. Leaching by rainwater can seep into groundwater, causing serious pollution to water bodies and soil. Furthermore, coal gangue piles are prone to spontaneous combustion, releasing toxic and harmful gases such as sulfur dioxide and nitrogen oxides, severely impacting air quality and the health of residents in mining areas and surrounding regions. However, the resource utilization of coal gangue is mainly concentrated in power generation, production of low-end building materials, underground filling, and land reclamation. These approaches suffer from limitations such as limited utilization, low added value, and secondary environmental pollution. Against this backdrop, using coal gangue to extract valuable elements and transform them into high-value functional materials shows great potential. Currently, high-value utilization of coal gangue mainly focuses on the preparation of silica, molecular sieves, and water purification agents. However, reports on the synthesis of hydrotalcite using coal gangue as the main raw material are still relatively few. Given that coal gangue contains valuable metallic elements such as aluminum, iron, and magnesium, how to efficiently and with high added value utilize these components has become a research hotspot.

[0003] Layered double hydroxides (LDHs), also known as layered bimetallic hydroxides, are an important class of inorganic functional materials. Their general chemical formula can be represented as: Layered double hydroxides (LDHs) are composed of positively charged metal hydroxide layers and interlayer anions. This unique layered structure endows LDHs with excellent anion exchange capacity, surface alkalinity, and structural "memory effect," making them promising for applications in catalysis, adsorption, flame retardancy, biomedicine, and environmental remediation. Traditional LDH synthesis relies heavily on large quantities of high-purity chemical reagents, such as magnesium nitrate, aluminum nitrate, and ferric nitrate. This chemical-dependent synthesis route results in high production costs, limiting its large-scale industrial application. Furthermore, existing methods for synthesizing LDHs often employ hydrothermal or high-temperature aging methods, requiring high-temperature, high-pressure conditions and long reaction times, sometimes even necessitating the addition of seed crystals. These methods are not only demanding in terms of equipment, cost, and energy consumption, but also inefficient, hindering industrial production. For example, Chinese patent (CN120864542A) discloses a method for synthesizing aluminum-based LDHs using in-situ crystallization of coal gangue, utilizing only the metallic element aluminum from the coal gangue and adding seed crystals. This process still requires 100-150 kcal / kg of high-purity chemical reagents. o Crystallize at high temperature (C) for 12-72 hours.

[0004] In summary, there are few reports on the synthesis of hydrotalcite using coal gangue as the main raw material, and the synthesis technology has the following shortcomings: (1) The utilization rate of valuable metal elements in coal gangue is low, and most studies only utilize one or two of them; (2) It usually requires the use of a large amount of high-purity chemical reagents or added seed crystals, which increases the cost of raw materials, limits large-scale application, and may even introduce other impurities; (3) The process of synthesizing hydrotalcite requires long-term high-temperature treatment, which is energy-intensive, has a long cycle, and is complex. Therefore, developing a high-efficiency and low-energy-consumption new technology for effectively extracting valuable metal elements such as aluminum, iron, and magnesium from coal gangue and synthesizing high-purity Mg-Al-Fe ternary hydrotalcite at room temperature by adding an external magnesium source is of great practical significance for realizing the comprehensive resource utilization of coal gangue. Summary of the Invention

[0005] To overcome the problems of low utilization rate of valuable metal elements in coal gangue and high energy consumption, high cost and long cycle of traditional hydrotalcite synthesis technology, this invention provides a method for effectively extracting aluminum, iron and magnesium from coal gangue and synthesizing high-purity Mg-Al-Fe ternary hydrotalcite at room temperature by adding an external magnesium source.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for synthesizing high-value-added ternary hydrotalcite from coal gangue through resource utilization includes the following steps: S1. Use a pulverizer to pulverize the coal gangue to a particle size of less than 50µm, then calcine it to obtain yellow-brown calcined coal gangue powder. S2. The yellowish-brown roasted coal gangue powder is mixed with acid, and the mixture is continuously acidified and stirred at 70-80℃ for 0.5-2.5 hours. After centrifugation, an Al-containing product is obtained. 3+ Fe 3+ With Mg 2+ Metal salt solutions; S3, the Al-containing 3+ Fe 3+ With Mg 2+ The metal salt solution is mixed with the magnesium salt, shaken well, and then alkali solution is added dropwise until the pH of the solution is 11-12. S4. After crystallizing the solution obtained in step S3 at room temperature for 3 hours, wash and dry it to obtain Mg-Al-Fe ternary hydrotalcite.

[0007] In the preparation method provided by the present invention, in step S1, the calcination temperature is 500-700℃ and the calcination time is 1-5h.

[0008] In the preparation method provided by the present invention, in step S2, the acid is one of sulfuric acid, hydrochloric acid and nitric acid, and the concentration is 3-5 mol / L.

[0009] In the preparation method provided by the present invention, in step S3, the magnesium salt is 100-500 mg of magnesium nitrate hexahydrate.

[0010] In the preparation method provided by this invention, the added alkaline solution is a sodium hydroxide solution with a concentration of 3-5 mol / L.

[0011] The present invention has the following beneficial effects: 1. This invention uses coal gangue, a major solid waste, to replace high-purity chemical reagents as aluminum, iron, and magnesium sources. Only magnesium salts need to be added externally, which greatly reduces the cost of raw materials for the synthesis of hydrotalcite. It effectively avoids the bottleneck problem of high production cost and difficulty in large-scale industrial application of traditional hydrotalcite, while realizing the high-value resource utilization of coal gangue.

[0012] 2. This invention eliminates the high temperature and high pressure conditions required by the traditional hydrothermal synthesis method. Well-crystallized Mg-Al-Fe ternary hydrotalcite can be obtained in just 3 hours under normal temperature and pressure. This not only simplifies the process but also shortens the reaction cycle and reduces energy consumption.

[0013] 3. The prepared Mg-Al-Fe ternary hydrotalcite has a positive effect on the heavy metal copper (Cu). 2+ ) and nickel (Ni 2+ The maximum adsorption capacities of coal gangue can reach 201.8 mg / g and 246.7 mg / g respectively, so it can be widely used in functional materials fields such as the remediation of wastewater and soil polluted by multiple heavy metals. This realizes the transformation of coal gangue from an "ecological burden" to a "functional material" with high added value and has good environmental benefits.

[0014] 4. This invention is the first to achieve rapid room-temperature synthesis of coal gangue-based Mg-Al-Fe ternary hydrotalcite. Attached Figure Description

[0015] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is the XRD pattern of raw coal gangue.

[0016] Figure 2 The image shows the XRD pattern of the Mg-Al-Fe ternary hydrotalcite prepared in Example 1.

[0017] Figure 3 This is a SEM image of the Mg-Al-Fe ternary hydrotalcite prepared in Example 1.

[0018] Figure 4 The image shows the FTIR spectrum of the Mg-Al-Fe ternary hydrotalcite prepared in Example 1.

[0019] Figure 5The image shows the XPS diagram of the Mg-Al-Fe ternary hydrotalcite prepared in Example 1.

[0020] Figure 6 The Mg-Al-Fe ternary hydrotalcite prepared in Example 1 is used to counteract Cu. 2+ The trend of adsorption amount over time.

[0021] Figure 7 The Mg-Al-Fe ternary hydrotalcite prepared in Example 1 is used to counteract Ni 2+ The trend of adsorption amount over time.

[0022] Figure 8 The Mg-Al-Fe ternary hydrotalcite prepared in Example 1 is effective against the heavy metal Cu. 2+ with Ni 2+ Comparison of maximum adsorption capacity. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0024] The coal gangue used in the following specific embodiments was sourced from Shanxi Province and was crushed before use. The XRF elemental composition of the raw coal gangue was analyzed and tested, and the results are shown in Table 1.

[0025] Table 1. XRF elemental composition of raw coal gangue (mass percentage, %) <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[K2O]]> CaO <![CDATA[TiO2]]> MgO <![CDATA[Na2O]]> Other 53.73 16.95 15.99 5.65 2.33 1.86 1.73 0.79 0.97 Example 1

[0026] (1) Pass the crushed coal gangue through a 325-mesh sieve to make its particle size less than 50µm.

[0027] (2) The coal gangue processed in (1) is placed at 700 o After calcining at C for 3 hours, approximately 310 mg of yellowish-brown calcined coal gangue powder was obtained.

[0028] (3) The yellow-brown roasted coal gangue powder obtained in step (2) is mixed with 4 mol / L nitric acid and heated at 80°C. o After continuous acidification and stirring at C for 1 hour, centrifugation was performed to obtain a product containing Al. 3+ Fe 3+ With Mg 2+ Metal salt solutions.

[0029] (4) Take the Al-containing product obtained in step (3) 3+ Fe3+ With Mg 2+ The metal salt solution was mixed with 264.10 mg of magnesium nitrate, shaken well, and then 4 mol / L sodium hydroxide solution was added dropwise until the pH of the solution was 11-12. (5) Crystallize the solution obtained in step (4) at room temperature for 3 hours; after crystallization, wash and dry to obtain Mg-Al-Fe ternary hydrotalcite.

[0030] like Figure 2 The image shows the XRD pattern of the Mg-Al-Fe ternary hydrotalcite prepared in Example 1, revealing its crystal structure and interlayer spacing. Typical diffraction peaks appear at 2θ≈11.2, 22.8, and 34.7, corresponding to the (003), (006), and (009) crystal planes, respectively, indicating a highly ordered layered bimetallic hydroxide structure. The interlayer spacing is approximately 7.9 nm, formed by CO32-. 2- Anion intercalation maintenance; Fe 3+ The fact that doping did not disrupt long-range order and that the sharp peak shape indicates good crystallinity.

[0031] like Figure 3 The image shown is a SEM image of the Mg-Al-Fe ternary hydrotalcite prepared in Example 1. It reveals that the synthesized Mg-Al-Fe ternary hydrotalcite is formed by the random aggregation of a large number of two-dimensional nanosheets stacked together. The lateral size of these nanosheets is approximately 600-800 nm, and the surface of the aggregates is rough and uneven, exhibiting a porous and fluffy texture.

[0032] like Figure 4 The image shown is the FTIR spectrum of the Mg-Al-Fe ternary hydrotalcite prepared in Example 1. At approximately 3450 cm⁻¹... -1 The presence of characteristic vibrational peaks of -OH at this point indicates the presence of -OH in the host layered and interlayered water molecules. At depths less than 1000 cm⁻¹... -1 The origin is from the tensile vibration of the M-OH. At approximately 1370 cm⁻¹ -1 This part belongs to CO3 2- The asymmetric tensile vibrations indicate that the interlayer is affected by CO3. 2- Anion intercalation is maintained.

[0033] like Figure 6 As shown, this is the effect of the Mg-Al-Fe ternary hydrotalcite prepared in Example 1 on Cu. 2+ The trend of adsorption amount over time is shown in the figure. As can be seen from the figure, the Mg-Al-Fe ternary hydrotalcite adsorbs Cu... 2+ The adsorption rate is relatively fast, reaching a maximum adsorption capacity of 201.8 mg / g at 72 h, which is higher than the relevant performance of common adsorption materials.

[0034] like Figure 7As shown, the Mg-Al-Fe ternary hydrotalcite prepared in Example 1 is used to counteract Ni. 2+ The trend of adsorption amount over time is shown in the figure. As can be seen from the figure, the Mg-Al-Fe ternary hydrotalcite has a high adsorption capacity for Ni. 2+ The adsorption rate is relatively fast, reaching a maximum adsorption capacity of 246.7 mg / g at 34 h, which is higher than the relevant performance of common adsorption materials. Example 2

[0035] (1) Pass the crushed coal gangue through a 325-mesh sieve to make its particle size less than 50µm.

[0036] (2) The coal gangue processed in (1) is placed at 600 o After calcining at C for 3 hours, approximately 310 mg of yellowish-brown calcined coal gangue powder was obtained.

[0037] (3) The coal gangue treated in (2) is mixed with 4 mol / L nitric acid and heated at 80°C. o After continuous acidification and stirring at C for 1 hour, centrifugation was performed to obtain a product containing Al. 3+ Fe 3+ With Mg 2+ Metal salt solutions.

[0038] (4) Mix the metal salt solution treated in (3) with 117.18 mg of magnesium nitrate; after shaking, add 4 mol / L sodium hydroxide solution until the pH of the solution is 11-12; then crystallize at room temperature for 3 h; after crystallization, wash and dry to obtain Mg-Al-Fe ternary hydrotalcite. Example 3

[0039] (1) Pass the crushed coal gangue through a 325-mesh sieve to make its particle size less than 50µm.

[0040] (2) The coal gangue processed in (1) is placed at 700 o After calcining at C for 3 hours, approximately 310 mg of yellowish-brown calcined coal gangue powder was obtained.

[0041] (3) The coal gangue treated in (2) is mixed with 3 mol / L nitric acid and heated at 70 °C. o After continuous acidification and stirring at C for 1 hour, centrifugation was performed to obtain a product containing Al. 3+ Fe 3+ With Mg 2+ Metal salt solutions.

[0042] (4) Mix the metal salt solution treated in (3) with 239.23 mg of magnesium nitrate; after shaking, add 4 mol / L sodium hydroxide solution until the pH of the solution is 11-12; then crystallize at room temperature for 3 h; after crystallization, wash and dry to obtain Mg-Al-Fe ternary hydrotalcite.

[0043] Table 2. Al content in metal salt solutions obtained by centrifugation after acidification of coal gangue in Examples 1-3. 3+ Fe 3+ With Mg 2+ extraction rate sample Aluminum extraction rate (%) Magnesium extraction rate (%) Iron extraction rate (%) Example 1 53 87 20 Example 2 20 33 7 Example 3 33 50 12 As shown in Table 2, the roasting temperature of coal gangue and the concentration of nitric acid used during acidification are closely related. Example 1 shows a better extraction rate of valuable metal elements from coal gangue, significantly better than Examples 2 and 3. This indicates that increasing the roasting temperature and nitric acid concentration is more conducive to the extraction of valuable metal elements (Al) from coal gangue. 3+ Fe 3+ With Mg 2+ Leaching of ).

[0044] Table 3 shows the yields of the prepared Mg-Al-Fe ternary hydrotalcites in Examples 1-3. sample Example 1 Example 2 Example 3 Yield (mg) 100 50 75 Table 3 shows the yield of the prepared Mg-Al-Fe ternary hydrotalcite. As can be seen from the table, Example 1 has a better yield of Mg-Al-Fe ternary hydrotalcite, significantly better than Examples 2 and 3. Correspondingly, the increased calcination temperature and nitric acid concentration lead to a higher yield of valuable metal elements (Al2+, Al2+, and Al2+) in the coal gangue. 3+ Fe 3+ With Mg 2+ The increased leaching of Mg-Al-Fe ternary hydrotalcite led to an increase in its yield.

[0045] 50 mg of Mg-Al-Fe ternary hydrotalcite was added to 50 mL of copper nitrate solution and nickel nitrate solution, respectively (feed amount = 1.0 g / L, V = 50 mL, initial concentration of heavy metal ions C0 = 300 mg / L). The mixture was stirred continuously, and small amounts of solution were taken at different time points, filtered using a filter, and the filtrate was diluted a certain factor before the Cu content in the filtrate was determined. 2+ Ni 2+ concentration. Figure 6 The Mg-Al-Fe ternary hydrotalcite prepared in Example 1 is used to counteract Cu. 2+ The trend of adsorption amount over time. Figure 7 The Mg-Al-Fe ternary hydrotalcite prepared in Example 1 is used to counteract Ni 2+ The trend of adsorption amount over time. Figure 8The Mg-Al-Fe ternary hydrotalcite prepared in Example 1 is effective against the heavy metal Cu. 2+ with Ni 2+ Comparison of maximum adsorption capacity.

[0046] This invention constructs a green process system for the high-value utilization of coal gangue, with the core process divided into three main stages: 1. Coal gangue pretreatment and valuable metal extraction: First, the coal gangue is calcined and activated to change its mineral crystal structure at high temperature, disrupting the stable framework of aluminosilicates and transforming valuable metal elements such as aluminum, iron, and magnesium from a sparingly soluble state to a readily soluble state. Then, an acid leaching extraction process is used to dissolve the aluminum, iron, and magnesium elements in the activated coal gangue into the liquid phase using an acidic solution, achieving preliminary separation of valuable metals from impurities such as silicon and carbon. Finally, through precise pH control for impurity removal, the pH difference of different metal hydroxide precipitates is used to further remove residual silicon, carbon, and other impurities in the solution, resulting in a high-purity mixed metal solution of aluminum, iron, and magnesium.

[0047] 2. Room Temperature Coprecipitation Synthesis of Hydrotalcite: Using a mixed metal solution extracted from coal gangue as the main raw material, Mg-Al-Fe ternary hydrotalcite material is synthesized through a coprecipitation reaction at room temperature. This process does not require harsh reaction conditions such as high temperature and high pressure. By controlling parameters such as the pH value, reactant concentration, and stirring rate of the reaction system, magnesium, aluminum, and iron ions in the solution can spontaneously assemble into layered hydrotalcite crystals under the action of anions such as hydroxyl and carbonate ions.

[0048] 3. Product Post-processing and Performance Control: The hydrotalcite precursor obtained from the co-precipitation reaction undergoes post-processing operations such as filtration, washing, and drying to remove residual impurity ions and moisture, yielding a pure Mg-Al-Fe ternary hydrotalcite product. By adjusting the process parameters during synthesis, the properties of hydrotalcite, such as the types of interlayer anions, the proportion of metal elements in the layers, grain size, and specific surface area, can be precisely controlled to meet the needs of different application scenarios.

[0049] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for synthesizing high-value-added ternary hydrotalcite from coal gangue through resource utilization, characterized in that: Includes the following steps: S1. After crushing the coal gangue, roast it to obtain yellow-brown roasted coal gangue powder; S2. The yellowish-brown roasted coal gangue powder is mixed with acid, and the mixture is continuously acidified and stirred at 70-80℃ for 0.5-2.5 hours. After centrifugation, an Al-containing product is obtained. 3+ Fe 3+ With Mg 2+ Metal salt solutions; S3, the Al-containing 3+ Fe 3+ With Mg 2+ The metal salt solution is mixed with the magnesium salt, shaken well, and then alkali solution is added dropwise until the pH of the solution is 11-12. S4. After crystallizing the solution obtained in step S3 at room temperature for 3 hours, wash and dry it to obtain Mg-Al-Fe ternary hydrotalcite.

2. The method for synthesizing high-value-added ternary hydrotalcite from coal gangue as described in claim 1, characterized in that: In step S1, the calcination temperature is 500-700℃ and the calcination time is 1-5h.

3. The method for synthesizing high-value-added ternary hydrotalcite from coal gangue as described in claim 1, characterized in that: In step S2, the acid is one of sulfuric acid, hydrochloric acid, and nitric acid, with a concentration of 3-5 mol / L.

4. The method for synthesizing high-value-added ternary hydrotalcite from coal gangue as described in claim 1, characterized in that: In step S3, the magnesium salt is 100-500 mg of magnesium nitrate hexahydrate.

5. The method for synthesizing high-value-added ternary hydrotalcite from coal gangue as described in claim 1, characterized in that: In step S3, the added alkaline solution is a sodium hydroxide solution with a concentration of 3-5 mol / L.

Images