Preparation method of yak dung-based materials and their application in selective adsorption of heavy metals

Abstract

This invention relates to the field of environmental protection technology, and discloses a yak dung-based material, its preparation method, and its application in the selective adsorption of heavy metals. Yak dung, a common agricultural and pastoral waste in the cold climate zone of Tibet, is used as the raw material, and is formulated with Fe-containing... 3+ and Mn 7+ A mixed solution is modified, and the modified mixture is then pyrolyzed under oxygen-limited conditions to obtain an acidic groundwater treatment adsorbent material with selective adsorption capacity and good permeability. The process is simple. The acidic groundwater treatment selective adsorbent material prepared by the method of this invention can effectively adsorb cadmium, iron, lead, and copper ions, while the removal rate of magnesium ions, sulfate ions, and silicate ions is less than 5%, and the permeability coefficient is greater than 10. ‑3 cm / s, it is particularly suitable for the treatment of complex heavy metal pollution in acidic groundwater in mines, and has excellent pollution removal performance and economic applicability.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, and discloses a method for preparing yak dung-based materials and their application in the selective adsorption of heavy metals. Background Technology

[0002] Mineral resource development generates large amounts of wastewater containing acids, alkalis, suspended solids, heavy metal ions, and various residual flotation reagents, causing serious pollution to the mine and its surrounding soil and groundwater environment. Currently, the main measures for treating acidic groundwater in non-ferrous metal mines include source control technology and end-of-pipe treatment technology. However, source control technology is limited by numerous factors in preventing the generation and pollution of acidic groundwater, making end-of-pipe treatment a necessary step to prevent its pollution of the surrounding environment. Traditional groundwater treatment adsorbents suffer from poor selectivity and small particle size (around 200 mesh). Poor selectivity leads to premature saturation, resulting in poor long-term effectiveness, while small particle size leads to poor permeability. Therefore, it is necessary to develop new groundwater adsorbents to address these problems.

[0003] Compared to mineral-based adsorbents, biomass-based materials offer advantages such as larger specific surface area, abundant pores, and numerous surface adsorption sites, and have been widely used in the treatment of heavy metal-containing wastewater. However, reported biomass-based adsorbents readily adsorb magnesium ions, sulfate ions, and silicate ions coexisting in acidic groundwater from mines, occupying the active adsorption sites and resulting in poor long-term effectiveness. Furthermore, their extremely fine particle size leads to poor permeability and easy clogging of the adsorbent packing. Therefore, it is necessary to develop novel large-particle biomass-based adsorbents suitable for the selective adsorption of characteristic heavy metals under acidic conditions to achieve efficient removal of complex heavy metal pollution from acidic groundwater in mines. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a method for preparing large-particle yak dung-based materials suitable for the selective removal of complex heavy metal pollution in acidic groundwater from mines. This method, by controlling the particle size of the yak dung to be large, and modifying and pyrolyzing it under large-particle conditions, achieves selective adsorption of characteristic heavy metals copper, lead, cadmium, and iron ions in acidic groundwater systems with high sulfate, magnesium, and silicate ion concentrations. Furthermore, it exhibits good permeability; that is, the adsorbent material efficiently adsorbs only the characteristic heavy metals copper, lead, cadmium, and iron ions, while the removal rate of coexisting magnesium, sulfate, and silicate ions is less than 5%, and the permeability coefficient is greater than 10. -3 The speed of cm / s breaks through the technical bottleneck of traditional biomass-based adsorption materials in acidic mine groundwater, which have poor selectivity and permeability for adsorption of characteristic heavy metals.

[0005] Therefore, the first technical solution of this application discloses a method for preparing yak dung-based materials, comprising the following steps:

[0006] S1. Add yak dung pellets containing Fe 3+ and Mn 7+ In the mixed solution, a solid-liquid reaction system is dispersed.

[0007] S2. The solid-liquid reaction system is dried in a constant-temperature water bath to obtain preliminary material;

[0008] S3. The preliminary material is subjected to oxygen-limited pyrolysis to obtain yak dung-based material.

[0009] Furthermore, the yak dung particles mentioned in S1 are obtained by crushing yak dung, and the particle size of the crushed yak dung particles is 30-60 mesh.

[0010] Furthermore, the Fe mentioned in S1 3+ The concentration is 0.025 mol / L, Mn 7+ The concentration is 0.050-0.075 mol / L, Fe 3+ and Mn 7+ The concentration ratio is 1:(2-3)(n:n).

[0011] Furthermore, the yak dung pellets described in S1 and Fe 3+ and Mn 7+ The solid-liquid ratio of the mixed solution is (150-175):1000 (m / v).

[0012] Furthermore, the dispersion described in S1 specifically involves mixing yak dung particles with Fe... 3+ and Mn 7+ After the mixed solution is mixed, it is first stirred at a low speed, and then ultrasonically dispersed. The low-speed stirring speed is 200-250 rpm, the stirring time is 60-90 minutes, and the ultrasonic dispersion time is 90-120 minutes.

[0013] Furthermore, the constant temperature water bath described in S2 is 90-95℃, and the time is 90-120 minutes.

[0014] Furthermore, the oxygen-limited pyrolysis described in S3 is as follows: after heating to 400-450℃ at a heating rate of 10℃ / min, nitrogen gas is introduced to carry out oxygen-limited pyrolysis under anaerobic conditions.

[0015] And the yak dung-based material prepared according to the above preparation method.

[0016] The second technical solution of this application discloses the application of the above-mentioned yak dung-based material as an adsorbent for the selective adsorption of complex heavy metals in mine groundwater.

[0017] Preferably, the groundwater in the mine is acidic and contains high concentrations of sulfate, magnesium, and silicate ions, and the complex heavy metals include copper, cadmium, lead, and iron ions.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention uses yak dung, a common agricultural and pastoral waste in the cold climate zone of Tibet, as raw material, and modifies it with FeCl3 and KMnO4. The modified mixture is then pyrolyzed under limited oxygen conditions to obtain an acidic groundwater treatment adsorbent material with selective adsorption capacity and good permeability. The process is simple. The acidic groundwater treatment selective adsorbent material prepared by the method of this invention can effectively adsorb cadmium, iron, lead, and copper ions, while the removal rate of magnesium ions, sulfate ions, and silicate ions is less than 5%, and the permeability coefficient is greater than 10. -3 cm / s, it is particularly suitable for the treatment of complex heavy metal pollution in acidic groundwater in mines, and has excellent pollution removal performance and economic applicability. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments. This embodiment is implemented based on the technology of the present invention, and detailed implementation methods and specific operating procedures are given to illustrate the inventiveness of the present invention. However, the scope of protection of the present invention is not limited to the following embodiments.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0022] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0023] The embodiments of this application disclose a method for preparing yak dung-based materials, comprising the following steps:

[0024] S1. Add yak dung pellets to Fe 3+ and Mn 7+ In the mixed solution, a solid-liquid reaction system is dispersed.

[0025] S2. The solid-liquid reaction system is dried in a constant-temperature water bath to obtain preliminary material;

[0026] S3. After the initial material is subjected to a first pyrolysis, it is heated and subjected to oxygen-limited pyrolysis to obtain yak dung-based material.

[0027] It is understood that the yak dung particles are obtained by crushing yak dung. The yak dung in this application is taken from Tibet, which is an agricultural and pastoral waste from a high-altitude and cold climate. It is crushed to a particle size of 30-60 mesh.

[0028] In this embodiment, crushed yak dung particles are added to a mixture containing Fe. 3+ and Mn7+ The purpose of the FeCl3 and KMnO4 mixed solution is to modify yak dung by controlling the surface potential of the yak dung particles through the valence state transition between variable-valence metals iron and manganese. This allows for selective adsorption of heavy metals in complex environments, thereby increasing adsorption capacity. Yak dung particles without surface potential modulation are less capable of selectively removing heavy metals from complex systems and have low adsorption capacity. In a specific embodiment, FeCl3 and KMnO4 are used to modify the surface potential of yak dung particles. 3+ and Mn 7+ The mixed solution can be improved by adding Fe 3+ and Mn 7+ Salts are achieved, for example, by preferably adding FeCl3 and KMnO. 4。

[0029] In a specific embodiment, the Fe 3+ The concentration is 0.025 mol / L, Mn 7+ The concentration is 0.050-0.075 mol / L, Fe 3+ and Mn 7+ The concentration ratio is 1:(2-3)(n:n); the yak dung particles and Fe 3+ and Mn 7+ The solid-liquid ratio of the mixed solution is (150-175):1000 (m / v); the dispersion specifically involves mixing yak dung particles with Fe... 3+ and Mn 7+ After the mixed solution is mixed, it is first stirred at a low speed, and then ultrasonically dispersed. The low-speed stirring speed is 200-250 rpm, the stirring time is 60-90 minutes, and the ultrasonic dispersion time is 90-120 minutes.

[0030] In this embodiment, the modified yak dung solid-liquid reaction system is subjected to constant temperature water bath treatment. The purpose of this step is to allow the Fe... 3+ and Mn 7+ It reacts fully with yak dung pellets to ensure that iron and manganese elements are evenly attached to the surface of the yak dung pellets.

[0031] In a specific embodiment, the constant temperature water bath temperature is 90-95℃ and the time is 90-120min. It is understood that the material needs to be dried after the reaction, and the drying temperature is preferably 80℃.

[0032] In this embodiment, the preliminary material after constant temperature water bath treatment is subjected to oxygen-limited treatment. The purpose of this step is to convert the cellulose and hemicellulose components inside the yak dung particles into active groups with selective heavy metal adsorption properties, thereby increasing the selective adsorption performance of yak dung-based materials for heavy metals in complex systems.

[0033] Furthermore, the oxygen-limited pyrolysis described in S3 is as follows: after heating to 400-450℃ at a heating rate of 10℃ / min, nitrogen gas is introduced to carry out oxygen-limited pyrolysis under anaerobic conditions.

[0034] In this embodiment, the heating rate is 10℃ / min. The purpose of this step is to allow cellulose and hemicellulose to gradually pyrolyze into biochar-based materials at a heating rate of 10℃ / min. The oxygen-limited pyrolysis temperature is 400-450℃. The purpose of this step is to allow cellulose and hemicellulose to pyrolyze to the maximum extent under this temperature condition, resulting in the maximum yield of yak dung-based materials.

[0035] The second embodiment of this application discloses the application of yak dung-based material prepared by the above preparation method as an adsorbent for selectively compounding heavy metals in mine groundwater.

[0036] It should be noted that groundwater in mines is wastewater generated during the mineral resource development process. This wastewater contains acids, alkalis, suspended solids, heavy metal ions, and various residual flotation reagents, and is generally acidic. Existing biomass-based adsorbents, while adsorbing heavy metal ions, also readily adsorb magnesium ions, sulfate ions, silicate ions, etc., which coexist in groundwater. These ions occupy the active sites of the material, resulting in poor long-term effectiveness of the adsorbent.

[0037] The yak-based material prepared by the above method, when used as an adsorbent to adsorb heavy metal ions in mine groundwater, can selectively adsorb heavy metal ions, including but not limited to copper, cadmium, lead, and iron ions, even when magnesium, sulfate, and silicate ions coexist. The removal rate for magnesium, sulfate, and silicate ions is less than 5%, and the permeability coefficient is greater than 10. -3 With a flow rate of cm / s, it is particularly suitable for the treatment of complex heavy metal pollution in acidic groundwater of copper mines, and has excellent pollution removal performance and economic applicability.

[0038] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0039] The following examples contain Fe 3+ The solution was obtained by adding FeCl3 and contained Mn. 7+ The solution was obtained by adding KMnO4. Through previous experimental studies, the optimal modification concentrations were determined to be 0.025 mol / L FeCl3 and 0.075 mol / L KMnO4. Therefore, the examples are described in detail by changing the solid-liquid ratio of yak dung particles to the modification solution.

[0040] Example 1: Preparation of yak dung-based materials

[0041] S1. Place 6.76g FeCl3·6H2O and 11.85g KMnO4 in a beaker, add 1000mL of water to prepare a mixed solution of FeCl3·6H2O and KMnO4. Add 165g of yak dung granules (30-60 mesh) to the aforementioned 1000mL mixed solution, stir at 200rpm for 60 minutes at room temperature (25℃), and then place in an ultrasonic cleaner (25℃) for ultrasonic dispersion for 120 minutes to obtain a solid-liquid reaction system.

[0042] S2. The solid-liquid reaction system was placed in a water bath and heated at a constant temperature (95℃) for 2 hours, then filtered and dried at 80℃ to obtain the preliminary material.

[0043] S3. The preliminary material is pyrolyzed in a tube furnace and heated to 450°C at a heating rate of 10°C / min. Nitrogen gas is introduced and oxygen-limited pyrolysis is carried out under anaerobic conditions for 2 hours. After natural cooling in a sealed environment, yak dung-based material is obtained.

[0044] Example 2: Preparation of yak dung-based materials

[0045] S1. Place 6.76g FeCl3·6H2O and 11.85g KMnO4 in a beaker, and add 1000mL of water to prepare a mixed solution of FeCl3 and KMnO4. Add 175g of yak dung granules (30-60 mesh) to the aforementioned 1000mL mixed solution, stir at 200rpm for 60 minutes at room temperature (25℃), and then place it in an ultrasonic cleaner (25℃) for ultrasonic dispersion for 90 minutes to obtain a solid-liquid reaction system.

[0046] S2. The solid-liquid reaction system is placed in a water bath and heated at a constant temperature (90°C) for 1.5 hours, then filtered and dried at 80°C to obtain the preliminary material.

[0047] S3. The preliminary material is pyrolyzed in a tube furnace and heated to 400°C at a heating rate of 10°C / min under limited oxygen conditions for 2 hours. After natural cooling in a sealed environment, yak dung-based material is obtained.

[0048] Example 3: Preparation of yak dung-based materials

[0049] S1. Place 6.76g FeCl3·6H2O and 11.85g KMnO4 in a beaker, add 1000mL of water to prepare a mixed solution of FeCl3·6H2O and KMnO4. Add 150g of yak dung granules (30-60 mesh) to the aforementioned 1000mL mixed solution, stir at 200rpm for 60 minutes at room temperature (25℃), and then place in an ultrasonic cleaner (25℃) for ultrasonic dispersion for 120 minutes to obtain a solid-liquid reaction system.

[0050] S2. The solid-liquid reaction system was placed in a water bath and heated at a constant temperature (92℃) for 2 hours, then filtered and dried at 80℃ to obtain the preliminary material.

[0051] S3. The preliminary material is pyrolyzed in a tube furnace and heated to 420°C at a heating rate of 10°C / min. Nitrogen gas is introduced and oxygen-limited pyrolysis is carried out under anaerobic conditions for 2 hours. After natural cooling in a sealed environment, yak dung-based material is obtained.

[0052] Comparative Example 1: Preparation of Yak Dung-Based Materials

[0053] The preparation method is the same as in Example 1, except that in Comparative Example 1, water is used instead of the FeCl3·6H2O and KMnO4 mixed solution for dispersion treatment.

[0054] Comparative Example 2: Preparation of Yak Dung-Based Materials

[0055] The preparation method is the same as in Example 1, except that Comparative Example 2 does not undergo the constant temperature water bath treatment described in S2.

[0056] Comparative Example 3: Preparation of Yak Dung-Based Materials

[0057] The preparation method is the same as in Example 1, except that Comparative Example 3 does not undergo the oxygen-limited pyrolysis reaction described in S3.

[0058] Experimental Example 1: Selective Adsorption Experiment of Yak Dung-Based Materials

[0059] Experimental method: Weigh 0.8g of the yak dung-based material prepared in Examples 1-3 and Comparative Examples 1-3 into a 1000mL beaker, add 800mL of a mixed solution with pH=5.0, copper ion concentration of 2mg / L, cadmium ion concentration of 0.02mg / L, lead ion concentration of 0.40mg / L, magnesium ion concentration of 10mg / L, sulfate ion concentration of 1000mg / L, and silicate ion concentration of 25mg / L. Perform rapid adsorption at room temperature for 2.0 hours, then filter and test the heavy metal concentration in the filtrate using ICP-OES.

[0060] Experimental results: see Table 1.

[0061] Table 1 Results of selective adsorption experiments on yak dung-based materials

[0062]

[0063] Results Analysis: Table 1 shows that the yak dung-based materials prepared in Examples 1-3 exhibited the highest adsorption rates for copper ions (87.9%), cadmium ions (88.3%), and lead ions (99.4%). However, their adsorption rates for magnesium ions, sulfate ions, and silicate ions were relatively weak, all below 5%. Furthermore, the permeability coefficient of the prepared yak dung materials was 0.007 cm / s, while the permeability coefficient of the main water-bearing rock strata in mines is generally around 7.64 × 10⁻⁶ cm / s. -7 cm / s. This indicates that the material prepared in this application has strong adsorption selectivity and good permeability, thereby extending the material's service life (improving its long-term effectiveness) and solving the clogging problem caused by the extremely fine particle size of previously reported biomass-based adsorbent materials, which is beneficial for industrial applications. The method of this invention achieves the purpose of preparing selective large-particle adsorbent materials for acidic groundwater treatment by controlling the particle size of yak dung, modification conditions, and oxygen-limited calcination conditions.

[0064] Comparative Examples 1-3 demonstrate that only yak dung-based materials prepared under the modification conditions, constant temperature water bath, and oxygen-limited calcination conditions specified in this application can achieve the goal of preparing selective large-particle adsorbent materials for acidic groundwater treatment.

[0065] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing yak dung-based materials for selectively adsorbing complex heavy metals in mine groundwater, characterized in that, Includes the following steps: S1. Add yak dung pellets containing Fe 3+ and Mn 7+ In a mixed solution, a solid-liquid reaction system is dispersed; S2. The solid-liquid reaction system is dried in a constant-temperature water bath to obtain preliminary material; S3. The preliminary material is subjected to oxygen-limited pyrolysis to obtain yak dung-based material; in, The Fe in S1 3+ The concentration is 0.025 mol / L, Mn 7+ The concentration is 0.050-0.075 mol / L; S1 yak dung pellets and Fe 3+ and Mn 7+ The solid-liquid ratio of the mixed solution is (150-175) g: 1000 mL; The constant temperature water bath described in S2 is 90-95℃, and the time is 90-120min; The oxygen-limited pyrolysis described in S3 is as follows: after heating to 400-450℃ at a heating rate of 10℃ / min, nitrogen gas is introduced, and oxygen-limited pyrolysis is carried out under anaerobic conditions.

2. The preparation method according to claim 1, characterized in that, The yak dung pellets mentioned in S1 are obtained by crushing yak dung, and the particle size of the crushed yak dung pellets is 30-60 mesh.

3. The preparation method according to claim 1, characterized in that, The dispersion described in S1 specifically involves mixing yak dung particles with Fe... 3+ and Mn 7+ After the mixed solution is mixed, it is first stirred at a low speed, and then ultrasonically dispersed. The low-speed stirring speed is 200-250 rpm, the stirring time is 60-90 minutes, and the ultrasonic dispersion time is 90-120 minutes.

4. A yak dung-based material prepared by any one of the preparation methods according to claims 1-3.

5. The application of the yak dung-based material according to claim 4 as an adsorbent for the selective adsorption of complex heavy metals in mine groundwater.

6. The application according to claim 5, characterized in that, The groundwater in the mine is acidic and contains high concentrations of sulfate, magnesium, and silicate ions. The complex heavy metals include copper, cadmium, and lead ions.

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