Modified coal gangue adsorbent and preparation method thereof
By combining ferrous sulfate with citric acid, followed by nitrogen-protected calcination and ultrasonic treatment, the problems of unstable iron oxide crystal form and low functional group density in modified coal gangue were solved, resulting in a highly efficient modified coal gangue adsorbent suitable for the adsorption of heavy metal ions and industrial wastewater treatment.
Patent Information
- Application Number
- CN202511530633.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-24
- Publication Date
- 2026-02-10
AI Technical Summary
In existing coal gangue modification technologies, the crystal form of iron oxides is uncontrollable and the surface functional group density is low, resulting in unstable adsorption performance, making it difficult to meet environmental protection requirements. Furthermore, the modification methods suffer from ineffective oxidation and insufficient adsorption capacity.
Ferrous sulfate and citric acid were mixed in a 3:2 ratio as modifiers and calcined under nitrogen protection. The surface was then modified with thiol groups by ultrasonic treatment at 310W to prepare a modified coal gangue adsorbent with thiol functional groups grafted onto the surface.
It significantly improves the adsorption performance of coal gangue adsorbent for heavy metal ions, with an adsorption capacity of over 300 mg/g, reduces operating costs and the risk of secondary pollution, and has stable product performance, making it suitable for industrial wastewater treatment.
Smart Images
Figure CN121490734A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of coal gangue-related technologies, and in particular to a modified coal gangue adsorbent and its preparation method. Background Technology
[0002] Coal gangue, a solid waste generated during coal mining and washing, is emitted in enormous quantities. The stockpiling of large quantities of coal gangue not only occupies significant land resources but also generates harmful gases that pollute the atmosphere due to spontaneous combustion. Furthermore, heavy metals and other harmful substances from it seep into the ground after being washed away by rainwater, polluting soil and water bodies. Traditional methods of utilizing coal gangue, such as direct landfilling and use as roadbed filling, fail to fully exploit its potential value and pose environmental pollution risks.
[0003] In the field of adsorbents, the development of efficient and low-cost adsorption materials has always been a research hotspot. Coal gangue, due to its rich content of aluminosilicates and other components, possesses certain adsorption properties. However, natural coal gangue has a small specific surface area and limited adsorption sites, resulting in a low adsorption capacity for pollutants such as heavy metal ions, making it difficult to meet increasingly stringent environmental protection requirements. Currently, coal gangue generally suffers from problems such as uncontrollable iron oxide crystal forms and low surface functional group density, leading to unstable adsorption performance and limited improvement in adsorption capacity. Comparative studies show that without the staged addition of citric acid, the coating rate is only 68%, resulting in a 40% reduction in adsorption capacity. Some modification methods, due to the lack of effective gas protection during calcination, cause iron to oxidize and generate a large amount of ineffective adsorption materials. This reduces the adsorption activity for target pollutants; some surface modification processes, due to improper parameter control, cannot achieve efficient functional group grafting, thus limiting the selective adsorption capacity of adsorbents for specific pollutants. Therefore, developing a modification method that can effectively solve the above problems and significantly improve the adsorption performance of coal gangue is of great practical significance. Summary of the Invention
[0004] The purpose of this invention is to address the problems of uncontrollable iron oxide crystal form and low surface functional group density in existing coal gangue modification technologies. This invention preferably uses a mixture of ferrous sulfate and citric acid in a 3:2 ratio as a modifier, adding citric acid in stages at 200℃±10℃, and employing a calcination process at 450℃±5℃ under nitrogen protection (purity ≥99.99%). Simultaneously, surface thiol modification is performed using ultrasonic treatment with 310W±5W power. This preferred scheme effectively solves the problems of unstable iron oxide crystal form and low functional group grafting rate, significantly improving the adsorption performance of coal gangue adsorbents for heavy metal ions.
[0005] To achieve the above objectives, the present invention provides the following technical solution: a modified coal gangue adsorbent, the surface of which is grafted with thiol functional groups and contains... The crystalline phase was prepared from 100g of coal gangue, 12g of ferrous sulfate, 8g of citric acid, and 5g of mercaptosilane coupling agent; the S2p peak in the XPS spectrum of the adsorbent was 163.5±0.3eV, and XRD showed... The characteristic peak intensity is ≥9000 cps; the coal gangue is crushed to a particle size ≤5mm by a jaw crusher, then ground in a planetary ball mill at 280-320r / min for 30min, passed through a 200-mesh sieve, with a sieve residue ≤3%, and dried at 105℃ for 8h with a moisture content ≤0.5% and no visible coal powder or soil impurities; the ferrous sulfate is analytical grade. Content ≥99%, particle size ≤0.1mm; the citric acid is analytical grade. The content is ≥99.5%, and it is a white crystalline powder; the mercaptosilane coupling agent is 3-mercaptopropyltrimethoxysilane (KH590), with a purity ≥98%.
[0006] A method for preparing a modified coal gangue adsorbent includes the following steps:
[0007] Step 1: Coal gangue pretreatment. Take 100g of coal gangue with a particle size ≤5mm and place it in a 500mL beaker. Add 100mL of deionized water (conductivity ≤10μS / cm, pH 6.5-7.5) each time. Stir with a glass rod for 30s and let stand for 5min. Pour off the supernatant to remove the turbid liquid. Repeat the operation 3 times. Place the rinsed coal gangue in a forced-air drying oven and set the temperature to 105℃ and the wind speed to 1.5m / s. Dry for 8h until constant weight (mass change ≤0.1g over 2h). After removal, grind the gangue in a planetary ball mill at 280-320r / min for 30min. Pass the mixture through a 200-mesh standard sieve (stainless steel sieve material, wire diameter 0.071mm, mesh size 75μm) and collect the sieve material for later use.
[0008] Step 2: Composite Modification and Calcination. Place 100g of pretreated coal gangue and 12g of ferrous sulfate into a 500mL high-speed mixer. Set the speed to 200r / min, the impeller diameter to 8cm, and the gap between the impeller and the inner wall of the container to 1-2mm. Dry mix for 5min. When the muffle furnace reaches 200℃±10℃, pause the heating and add 8g of citric acid. At this point, the citric acid is in a molten state, with a coating rate of ≥95% for the coal gangue. After adding the materials, continue heating at 5℃ / min. Transfer the mixture to a 200mL corundum crucible (purity ≥95%, high temperature resistance ≥1600℃, with ventilation holes at the rim of the crucible having a total cross-sectional area ≥0.8cm² / kg of material, the cross-sectional area of which is calculated using the formula...). Calculations were performed, where Qgas is the gas production rate of citric acid decomposition (0.5 L / min·kg, v = 0.5 m / s), used to release CO produced by citric acid decomposition (to prevent pressure inside the crucible > 0.1 MPa). The material accumulation height inside the crucible was ≤ 5 cm. The crucible was placed in a muffle furnace and heated from room temperature at a rate of 5 °C / min, with nitrogen protection (purity ≥ 99.99%, oxygen content ≤ 0.001%, flow rate 1 L / min). After 89 min, the temperature was raised to 450 °C ± 5 °C and held for 3 h. This roasting step resulted in the product showing XRD patterns. Characteristic peak intensity ≥9000cps; After turning off the power and allowing it to cool naturally to room temperature for 2 hours, remove it and grind it in an agate mortar for 10 minutes, then pass it through a 200-mesh sieve, with a residue of ≤3%;
[0009] Step 3: Surface thiol modification. Measure 100 mL of anhydrous ethanol (analytical grade, volume fraction ≥99.7%) and pour it into a 250 mL three-necked flask. Add 5 g of thiol silane coupling agent, and turn on the magnetic stirrer (stirrer diameter 3 cm, speed 500 r / min) and stir for 5 min. Dissolve completely; weigh 50g of the product from step 2 and add it to a flask. Place the flask in an ultrasonic cleaner and set the temperature to 40℃±2℃, power to 310W±5W, and frequency to 40kHz±1kHz. Ultrasonically vibrate for 2 hours (ensuring no precipitation or stratification during this period, and the transmittance of the solution after ultrasonication is ≥90% (wavelength 600nm); filter under vacuum of -0.08MPa using a Buchner funnel and collect the solid product; transfer the product to a 250mL beaker, add 50mL of anhydrous ethanol, stir with a glass rod for 1 minute, and filter again. Repeat the washing process 3 times; place the washed product in a vacuum drying oven (shelf spacing 5cm), with the product spread to a thickness ≤1cm. Set the temperature to 60℃±2℃ and the vacuum to -0.09MPa±0.005MPa, and dry for 4 hours to obtain the modified coal gangue adsorbent, which has a specific surface area of 85-100m² / g and a specific surface area of ≥90% (wavelength 600nm). The adsorption capacity is ≥300mg / g, the S2p peak position in the XPS spectrum is 163.5±0.3eV, and the particle D50 after passing through a 200-mesh sieve is 12.0±0.5μm.
[0010] In step 1, the grinding media of the planetary ball mill is zirconia balls with a density ≥6.0g / cm³ and a ball-to-material ratio of 5:1, so that the sphericity of the particles after grinding is ≥0.85.
[0011] In step 2, the mixing time error of the high-speed mixer is controlled within ±10s.
[0012] In step 3, the ultrasonic time error of the ultrasonic cleaner does not exceed ±5 min, and there is a corresponding relationship between ultrasonic power and thiol grafting rate. When the ultrasonic power is 310W, the thiol grafting rate reaches 96%.
[0013] In step 3, the heating method of the vacuum drying oven is hot air circulation, and the wind speed is controlled at 0.8-1.2m / s.
[0014] Compared with the prior art, the beneficial effects of the present invention are:
[0015] This invention increases the coating rate of citric acid on coal gangue from 68% in the prior art to ≥95% by adding citric acid in stages (molten state at 200℃±10℃). Combined with nitrogen-protected roasting, it promotes the characteristic peak intensity of Fe3O4 to ≥9000cps, effectively avoiding ineffective treatment. The generation of 3, for The adsorption capacity reaches over 300 mg / g, which is more than 40% higher than the existing technology (≤220 mg / g).
[0016] Thiol group modification was performed using ultrasonic treatment with a power of 310W±5W, resulting in a thiol grafting rate of 96%. The S2p peak in the XPS spectrum was stabilized at 163.5±0.3eV, which significantly improved the selective adsorption capacity of the adsorbent for heavy metal ions.
[0017] The preparation process is compatible with laboratory, pilot-scale, and industrial production. It is suitable for both pilot-scale and industrial production lines, and the product performance is stable, with a specific surface area maintained at 85-100 m² / g. It is also suitable for use in actual industrial wastewater treatment. The removal rate is ≥98.5%, the treated wastewater meets the discharge standards, and the operating cost is reduced by 40% compared with traditional adsorbents, demonstrating significant economic feasibility.
[0018] After five regenerations (desorption by 0.1M HCl), the adsorbent retains ≥90% of its adsorption capacity, demonstrating excellent recyclability and reducing the risk of secondary pollution and operating costs.
[0019] The raw material is industrial solid waste coal gangue, which reduces land occupation and environmental pollution caused by coal gangue stockpiling.
[0020] The product has been tested and found that the leaching concentrations of heavy metals such as Pb / Cd / As are all <0.1mg / L, and the cytotoxic IC50 is >1000mg / L (belonging to the practically non-toxic level). There is no risk of secondary pollution during application, and the product is highly safe. Attached Figure Description
[0021] Figure 1 This is a schematic diagram of the preparation process of the modified coal gangue adsorbent of the present invention. Detailed Implementation
[0022] Example 1 (Laboratory Scale)
[0023] The preparation method according to claim 2 shall be followed.
[0024] Accurately weigh 100g of coal gangue with a particle size ≤5mm and pre-treat it.
[0025] The pretreated coal gangue has a moisture content of 0.4% and contains no visible coal dust or soil impurities.
[0026] Weigh out 12g of ferrous sulfate and 8g of citric acid, and carry out composite modification and calcination.
[0027] XRD analysis showed that the characteristic peak intensity of Fe3O4 in the calcined product was 9200 cps.
[0028] Take 100 mL of anhydrous ethanol, add 5 g of mercaptosilane coupling agent, and perform surface mercapto modification.
[0029] The final modified coal gangue adsorbent had a specific surface area of 93.7 m² / g, which is significant for... The adsorption capacity is 330 mg / g, the S2p peak position in the XPS spectrum is 163.4 eV, and the particle D50 after passing through a 200-mesh sieve is 12.0 ± 0.5 μm.
[0030] The leaching concentrations of Pb / Cd / As in the adsorbent were measured, and the results were all <0.1 mg / L.
[0031] An acid rain simulation experiment was conducted (pH=4.0±0.2), and the adsorption capacity decay rate was 3%.
[0032] The test showed that the COD removal rate in actual industrial wastewater was 45%.
[0033] After 5 regenerations (0.1M HCl desorption), the... The adsorption capacity retention rate was 92%.
[0034] Cytotoxicity tests were conducted, and the IC50 was >1000 mg / L (belonging to the practically non-toxic category).
[0035] Example 2 (Pilot-scale)
[0036] The same process parameters as in Example 1 were used to prepare the product on a pilot production line (capacity 50 kg / batch).
[0037] The pretreatment of coal gangue uses automated cleaning and drying equipment, and the moisture content after treatment is stabilized at 0.38%-0.42%.
[0038] The composite modified roasting was carried out in a continuous roasting furnace, with the nitrogen flow rate stably controlled at 1L / min, and the characteristic peak intensity of Fe3O4 was 9150-9250cps.
[0039] Surface thiol modification was performed using an industrial ultrasonic reactor with an ultrasonic power of 310W±5W. The final product had a specific surface area of 94.2 m² / g. The adsorption capacity is 328 mg / g, the S2p peak position in the XPS spectrum is 163.5 eV, and the particle D50 after passing through a 200-mesh sieve is 12.0 ± 0.5 μm.
[0040] The heavy metal leaching toxicity test results all met the standards, and the adsorption capacity decay rate in the acid rain simulation experiment was 3.1%.
[0041] A small-scale industrial wastewater treatment test was conducted on actual electroplating wastewater. The removal rate reached 98.5%, and the treated wastewater met the discharge standards.
[0042] After 5 regenerations, the adsorption capacity retention rate was 91%.
[0043] Example 3 (Industrial Application)
[0044] This preparation method was applied in an industrial production line with an annual output of 1,000 tons, using coal gangue from a large coal mine as raw material.
[0045] The pretreatment stage uses a drum washing machine and a belt dryer to control the moisture content of coal gangue at 0.4% ± 0.05%.
[0046] The roasting process uses a tunnel kiln, with strict control over the heating rate and nitrogen protection, and the characteristic peak intensity of Fe3O4 is ≥9000cps.
[0047] Surface modification is performed using large-scale ultrasonic mixing equipment, resulting in stable product performance with a specific surface area of 92-95 m² / g. Adsorption capacity: 325-332 mg / g.
[0048] The product was used to treat lead-containing wastewater from a chemical plant, with a treatment capacity of 500 m³ / d. The effluent... The concentration is kept stable below 0.1 mg / L, and the operating cost is reduced by 40% compared with traditional adsorbents.
[0049] After 5 regenerations, the adsorption capacity retention rate was 90%.
[0050] Comparative Example 1 (without nitrogen protection)
[0051] The operation is basically the same as in Example 1, except that nitrogen is not introduced during the composite modification calcination process, and it is carried out in an air atmosphere.
[0052] XRD analysis revealed that the characteristic peak intensity of Fe3O4 in the product was only 6000 cps, while a large amount of [unclear text - likely referring to a specific substance or component] was present. Characteristic peaks.
[0053] The final adsorbent had a specific surface area of 65.3 m² / g, which is beneficial for... The adsorption capacity was 200 mg / g, and the S2p peak in the XPS spectrum was not obvious, indicating a low thiol grafting rate.
[0054] Heavy metal leaching toxicity testing showed that the leaching concentration of some heavy metals was close to or exceeded the standard of 0.1 mg / L.
[0055] In acid rain simulation experiments, the adsorption capacity decay rate was as high as 15%.
[0056] Comparative Example 2 (Citrate added without staged addition)
[0057] The operation is basically the same as in Example 1, except that citric acid is mixed with coal gangue and ferrous sulfate in one step and then roasted.
[0058] The characteristic peak intensity of Fe3O4 in the calcined product was 7000 cps, and the pore structure of the product was not as uniform as that in Example 1.
[0059] The final adsorbent had a specific surface area of 70.5 m² / g, which is beneficial for... The adsorption capacity was 220 mg / g. Although the S2p peak could be detected in the XPS spectrum, the grafting rate was lower than that in Example 1.
[0060] Heavy metal leaching toxicity testing showed that some indicators were close to the critical value.
[0061] In the acid rain simulation experiment, the adsorption capacity decay rate was 12%.
[0062] Comparative Example 3 (Modification of Traditional Iron Salts)
[0063] The modification was performed using ferrous sulfate alone, without the addition of citric acid and mercaptosilane coupling agents. Other process parameters were the same as in Example 1.
[0064] The characteristic peak intensity of Fe3O4 in the calcined product was 6800 cps, and the specific surface area was 62.1 m² / g.
[0065] right The adsorption capacity of ⁺ is 185 mg / g, which is much lower than that of the product of this invention.
[0066] When used for industrial wastewater treatment, the amount of adsorbent required is 2.5 times that of the product of this invention, resulting in a significant increase in treatment costs.
[0067] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A modified coal gangue adsorbent, characterized in that, Its surface is grafted with thiol functional groups and contains The crystalline phase was prepared from 100g of coal gangue, 12g of ferrous sulfate, 8g of citric acid, and 5g of mercaptosilane coupling agent; the S2p peak in the XPS spectrum of the adsorbent was 163.5±0.3eV, and XRD showed... The characteristic peak intensity is ≥9000 cps; the coal gangue is crushed to a particle size ≤5mm by a jaw crusher, then ground in a planetary ball mill at 280-320r / min for 30min, passed through a 200-mesh sieve, with a sieve residue ≤3%, and dried at 105℃ for 8h with a moisture content ≤0.5% and no visible coal powder or soil impurities; the ferrous sulfate is analytical grade. Content ≥99%, particle size ≤0.1mm; the citric acid is analytical grade. The content is ≥99.5%, and it is a white crystalline powder; the mercaptosilane coupling agent is 3-mercaptopropyltrimethoxysilane (KH590), with a purity ≥98%.
2. A method for preparing a modified coal gangue adsorbent, as described in claim 1, characterized in that, Includes the following steps: Step 1: Coal gangue pretreatment. Take 100g of coal gangue with a particle size ≤5mm and place it in a 500mL beaker. Add 100mL of deionized water (conductivity ≤10μS / cm, pH 6.5-7.5) each time. Stir with a glass rod for 30s and let stand for 5min. Pour off the supernatant to remove the turbid liquid. Repeat the operation 3 times. Place the rinsed coal gangue in a forced-air drying oven and set the temperature to 105℃ and the wind speed to 1.5m / s. Dry for 8h until constant weight (mass change ≤0.1g over 2h). After removal, grind the gangue in a planetary ball mill at 280-320r / min for 30min. Pass the mixture through a 200-mesh standard sieve (stainless steel sieve material, wire diameter 0.071mm, mesh size 75μm) and collect the sieve material for later use. Step 2: Composite Modification and Calcination. Place 100g of pretreated coal gangue and 12g of ferrous sulfate into a 500mL high-speed mixer. Set the speed to 200r / min, the impeller diameter to 8cm, and the gap between the impeller and the inner wall of the container to 1-2mm. Dry mix for 5min. When the muffle furnace reaches 200℃±10℃, pause the heating and add 8g of citric acid. At this point, the citric acid is in a molten state, with a coating rate of ≥95% for the coal gangue. After adding the materials, continue heating at 5℃ / min. Transfer the mixture to a 200mL corundum crucible (purity ≥95%, high temperature resistance ≥1600℃, with ventilation holes at the rim of the crucible having a total cross-sectional area ≥0.8cm² / kg of material, the cross-sectional area of which is calculated using the formula...). Calculations were performed, where Qgas is the gas production rate of citric acid decomposition (0.5 L / min·kg, v = 0.5 m / s), used to release CO produced by citric acid decomposition (to prevent pressure inside the crucible > 0.1 MPa). The material accumulation height inside the crucible was ≤ 5 cm. The crucible was placed in a muffle furnace and heated from room temperature at a rate of 5 °C / min, with nitrogen protection (purity ≥ 99.99%, oxygen content ≤ 0.001%, flow rate 1 L / min). After 89 min, the temperature was raised to 450 °C ± 5 °C and held for 3 h. This roasting step resulted in the product showing XRD patterns. Characteristic peak intensity ≥9000cps; After turning off the power and allowing it to cool naturally to room temperature for 2 hours, remove it and grind it in an agate mortar for 10 minutes, then pass it through a 200-mesh sieve, with a residue of ≤3%; Step 3: Surface thiol modification. Measure 100 mL of anhydrous ethanol (analytical grade, volume fraction ≥99.7%) and pour it into a 250 mL three-necked flask. Add 5 g of thiol silane coupling agent and turn on a magnetic stirrer (3 cm diameter stir bar, 500 r / min) and stir for 5 min until completely dissolved. Weigh 50 g of the product from Step 2 and add it to the flask. Place the flask in an ultrasonic cleaner and set the temperature to 40℃±2℃, power to 310W±5W, and frequency to 40kHz±1kHz. Ultrasonically vibrate for 2 h (ensuring no precipitation or stratification during this period; the transmittance of the solution after ultrasonication should be ≥90% (wavelength 600 nm)). Use a Buchner funnel at -0.08 MPa. The product was collected by vacuum filtration. The product was transferred to a 250 mL beaker, and 50 mL of anhydrous ethanol was added. The mixture was stirred with a glass rod for 1 min and then filtered again. The washing process was repeated three times. The washed product was placed in a vacuum drying oven (shelf spacing 5 cm), with a product layer thickness ≤ 1 cm. The oven was set at 60℃±2℃ and a vacuum of -0.09MPa±0.005MPa for 4 h to obtain a modified coal gangue adsorbent with a specific surface area of 85-100 m² / g. The adsorption capacity is ≥300mg / g, the S2p peak position in the XPS spectrum is 163.5±0.3eV, and the particle D50 after passing through a 200-mesh sieve is 12.0±0.5μm.
3. The method for preparing a modified coal gangue adsorbent according to claim 2, characterized in that, In step 1, the grinding media of the planetary ball mill is zirconia balls with a density ≥6.0g / cm³ and a ball-to-material ratio of 5:1, so that the sphericity of the particles after grinding is ≥0.
85.
4. The method for preparing a modified coal gangue adsorbent according to claim 2, characterized in that, In step 2, the mixing time error of the high-speed mixer is controlled within ±10s.
5. The method for preparing a modified coal gangue adsorbent according to claim 2, characterized in that, In step 3, the ultrasonic time error of the ultrasonic cleaner does not exceed ±5 min, and there is a corresponding relationship between ultrasonic power and thiol grafting rate. When the ultrasonic power is 310W, the thiol grafting rate reaches 96%.
6. The method for preparing a modified coal gangue adsorbent according to claim 2, characterized in that, In step 3, the heating method of the vacuum drying oven is hot air circulation, and the wind speed is controlled at 0.8-1.2m / s.
7. The modified coal gangue adsorbent according to claim 1, characterized in that, The modified coal gangue adsorbent contains Applications in industrial wastewater treatment.