Composite-based biochar material for treating acid tail water of mine and preparation method of composite-based biochar material

Abstract

The invention discloses a composite-based biochar material for mine acid tail water treatment and a preparation method thereof.The composite-based biochar material is based on bamboo reed-based activated carbon high in ash content and is combined with ammonium hydrogen phosphate, magnesium oxide, calcium hydroxide, carboxymethyl cellulose and other components to form a slow-release composite-based material; the composite material realizes rapid adjustment of the pH value of the acidic mine tail water, efficient adsorption of heavy metals and improvement of the long-term stability of the treatment effect through a multi-component synergistic effect.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and specifically to a composite-based biochar material for treating acidic mine tail water and a preparation method thereof. Background Art

[0002] Long-term large-scale mining activities have led to serious problems of acidic mine tail water pollution. Such pollution mainly comes from the oxidation process of sulfur-containing minerals (such as pyrite, marcasite, etc.) under the combined action of air, water and microorganisms, generating sulfuric acid and releasing heavy metal ions. It seriously pollutes surface water and groundwater.

[0003] Traditional treatment methods such as the alkali neutralization process require continuous input of a large amount of chemical agents, and will generate a large amount of sludge that needs subsequent treatment, resulting in high operating costs. Moreover, the initial investment in related equipment is large, and many regions currently do not have much funds for continuous investment. Currently, there are also chemical base materials used for treatment, but their costs are relatively high, mainly relying on chemical reactions to maintain the effect, with poor compatibility with plants, etc., and there are problems such as non-persistent treatment effect and incomplete heavy metal removal. Summary of the Invention

[0004] The present invention provides a composite-based biochar material for treating acidic mine tail water and a preparation method thereof, so as to at least solve one of the many defects existing in the prior art.

[0005] In view of this, the solution of the present invention is as follows: In the first aspect of the present invention, a composite-based biochar material for treating acidic mine tail water is proposed, and its composition by weight percentage is as follows: 55-65% of Arundo donax-based activated carbon, 10-15% of ammonium hydrogen phosphate, 8-12% of magnesium oxide, 12-18% of calcium hydroxide, and 2-5% of carboxymethyl cellulose.

[0006] Further, the composition of the composite-based biochar material by weight percentage is as follows: 60% of Arundo donax-based activated carbon, 12% of ammonium hydrogen phosphate, 10% of magnesium oxide, 15% of calcium hydroxide, and 3% of carboxymethyl cellulose.

[0007] In the second aspect of the present invention, a preparation method of the composite-based biochar material is proposed, and the steps include: S1. After making ammonium hydrogen phosphate into an aqueous solution, mix it with Arundo donax-based activated carbon and keep it moist and ripe. S2. Take magnesium oxide and calcium hydroxide and premix them, then add them to the ripe material obtained in step S1 and stir to mix. S3. After pre-making carboxymethyl cellulose into a colloid, slowly add it to the material obtained in step S2 and stir until it forms a mass. S4. Use a screw extrusion granulator for extrusion and granulation, and introduce hot steam containing glutaraldehyde for curing, followed by drying to obtain the composite-based biochar material.

[0008] Further, in step S1, the aging time is 12 - 30 h.

[0009] Further, in step S2, water is sprayed during the stirring and mixing process, and the amount of water used is 25 - 30% of the total mass of the magnesium oxide and calcium hydroxide premix; and / or, the time of the stirring and mixing process is 40 - 60 min.

[0010] Further, in step S3, the water content of the lumpy product is 35 - 40%.

[0011] Further, in step S4, the extrusion pressure is 2 - 5 MPa; and / or, the glutaraldehyde content in the hot steam containing glutaraldehyde is 2 - 5%, the relative humidity is 75 - 85%, and the temperature is 45 - 55 °C; the curing process time is 0.5 - 2 h.

[0012] Further, in step S4, the drying process uses gradient heating to dry until the moisture content is less than 5%.

[0013] The third aspect of the present invention lies in proposing the application of the composite-based biochar material described in the first aspect above or the composite-based biochar material prepared by the preparation method described in the second aspect in the treatment of acidic mine tail water.

[0014] Further, the pH value of the acidic mine tail water after treatment is 6.0 - 7.5.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The composite-based biochar material provided by the present invention is based on Arundo donax-based activated carbon with a relatively high ash content, and combines components such as ammonium hydrogen phosphate, magnesium oxide, calcium hydroxide, and carboxymethyl cellulose to form a slow-release composite-based material. Through the synergistic effect of multiple components, the composite material can rapidly adjust the pH value of acidic mine tail water, efficiently adsorb heavy metals, and improve the long-term stability of the treatment effect.

[0016] The preparation method of the composite-based biochar material of the present invention has a simple process, easily available raw materials, and the product is granular with high abrasion resistance and compressive strength; and it can be prepared into products with different particle sizes to suit different application scenarios, which is suitable for industrial promotion. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the composite-based biochar material particles prepared by the preparation method of the present invention. Detailed Embodiments

[0018] The technical solutions of the present invention will be clearly and completely described below in conjunction with preferred embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] In one embodiment, a composite-based biochar material for treating acidic mine tail water is proposed. Its composition by weight percentage is as follows: Arundo donax-based activated carbon 55-65%, ammonium hydrogen phosphate 10-15%, magnesium oxide 8-12%, calcium hydroxide 12-18%, and carboxymethyl cellulose 2-5%. The composite-based biochar material is based on Arundo donax-based activated carbon with a relatively high ash content, and combines components such as ammonium hydrogen phosphate, magnesium oxide, calcium hydroxide, and carboxymethyl cellulose to obtain a production plan for a slow-release composite-based material, which is specifically used for treating acidic mine tail water. Through the synergistic effect of multiple components, this composite material can achieve pH adjustment, heavy metal adsorption, and long-term stable treatment of acidic mine tail water.

[0020] In the above embodiment, the composite-based biochar material uses high-ash Arundo donax-based activated carbon as a matrix carrier, and through the introduction of various functional components, realizes the comprehensive treatment of acidic mine tail water. The specific principle is as follows: Arundo donax-based activated carbon, as the main framework structure of the material, has dual functions: on the one hand, its developed pore structure (specific surface area can reach 1674 m 2 / g) provides abundant adsorption sites for heavy metal ions; on the other hand, the alkaline minerals contained in the relatively high ash content (usually about 15%) can participate in the neutralization reaction. Research shows that the removal rate of heavy metals such as Pb 2+ and Cd 2+ by Arundo donax-based activated carbon can reach more than 90%, and its surface is rich in functional groups such as hydroxyl and carboxyl groups, which can fix heavy metal ions through ion exchange and surface complexation.

[0021] Ammonium hydrogen phosphate (NH4H2PO4) plays multiple roles in this material: as a pH buffer, it can maintain a neutral environment in the solution for a long time; the decomposed NH4 + and PO4 - ions can form stable phosphate precipitates with heavy metals; in addition, ammonium hydrogen phosphate can also interact with the oxygen-containing functional groups on the surface of activated carbon to enhance the stability of the material.

[0022] Magnesium oxide (MgO) and calcium hydroxide (Ca(OH)2) constitute the alkaline components of the material, providing the main alkalinity required to neutralize acidic wastewater. Magnesium oxide has the characteristic of slow dissolution, which can extend the effective action time of the material; calcium hydroxide provides immediate neutralization ability, and the two cooperate to achieve the spatio-temporal gradient control of acid-base adjustment. In addition, Mg2+ and Ca 2+ can react with SO4 2- to form insoluble compounds, reducing the mobility of sulfate ions.

[0023] Carboxymethyl cellulose (CMC) is used as a binder and slow-release regulator. The carboxyl groups on its molecular chain can form coordination bonds with metal ions, further enhancing the fixation effect of heavy metals. The hydration of CMC can form a gel network, controlling the release rate of functional components, while improving the mechanical strength and water resistance of the material.

[0024] The structural design of the composite-based biochar material adopts the "core-shell" concept: the inner core consists of Arundo donax-based activated carbon and ammonium hydrogen phosphate, providing adsorption and buffering functions; the outer shell is mainly composed of magnesium oxide, calcium hydroxide, and CMC, responsible for initial neutralization and structural protection. This structure can be achieved by adjusting the preparation process to ensure that the material can achieve the best effect in different pH environments. When the material contacts acidic wastewater, the outer components react first, and over time, the inner components are gradually released, forming a long-term treatment mechanism.

[0025] The composite-based biochar material is specifically designed for the characteristics of acidic mine tailings water, and can simultaneously solve core problems such as low pH value, high heavy metal content, and high sulfate concentration. Compared with single-component treatment materials, this composite material has significant advantages such as a long action time (up to several months), strong adaptability (effective in the range of 1.5 - 4.0 for the pH value of tailings water), and a high heavy metal removal rate (>90%). Moreover, the raw materials are easily available and the cost is controllable, making it suitable for large-scale mine environmental governance applications.

[0026] In a preferred embodiment, the composite-based biochar material is composed by weight percentage as follows: 60% Arundo donax-based activated carbon, 12% ammonium hydrogen phosphate, 10% magnesium oxide, 15% calcium hydroxide, and 3% carboxymethyl cellulose. The composite-based biochar material with this composition has better treatment performance.

[0027] In another embodiment, a preparation method of the above composite-based biochar material is proposed, including the following steps: 1) Material pretreatment Treatment of Arundo donax L.-based activated carbon: Crush the Arundo donax L.-based activated carbon to 100-200 mesh (about 75-150 μm) to increase the specific surface area and reaction activity; Magnesium oxide (MgO): Select light magnesium oxide (particle size <50 μm); Calcium hydroxide (Ca(OH)2): Select high-purity slaked lime (purity >95%), pass through a 200-mesh sieve; Treatment of ammonium hydrogen phosphate (NH4H2PO4): Crush the analytical reagent grade ammonium hydrogen phosphate and pass through a 100-mesh sieve to prevent caking and affecting dispersibility; Activation of carboxymethyl cellulose (CMC): Dissolve the CMC powder in deionized water (concentration 3-5%), stir at 50 °C for 2 hours to form a uniform colloidal solution, select medium-viscosity CMC with a degree of substitution of 0.7-1.2 (molecular weight about 250,000) to balance the bonding performance and solubility; 2) Preparation of materials

[0028] Adopt a three-stage mixing process to ensure the uniform dispersion of each component and form an ideal structural gradient. The process flow is as follows: The first stage: Preparation of activated carbon-ammonium hydrogen phosphate matrix Mix the pretreated Arundo donax L.-based activated carbon with the ammonium hydrogen phosphate solution in proportion, fully soak the Arundo donax L.-based activated carbon, mix at a speed of 30-50 rpm for 30 minutes to partially dissolve the ammonium hydrogen phosphate and soak the pores of the activated carbon. The mixture is moisturized and aged at room temperature for 12-30 hours to promote the interaction between components.

[0029] The second stage: Composite of alkaline components

[0030] Premix magnesium oxide and calcium hydroxide evenly in proportion (mix at low speed for 10 minutes). Gradually add the alkaline mixture to the matrix prepared in the first stage, and control the feeding speed to prevent local overheating. Spray an appropriate amount of atomized water during the mixing process (the total water volume is controlled at 25-30% of the dry material) to promote the bonding between particles. The mixing time is 40-60 minutes until the material shows a uniform grayish black.

[0031] The third stage: CMC bonding and forming

[0032] Slowly add the pre-prepared CMC colloidal solution to the above mixture while stirring. Adjust the stirring speed to 20-30 rpm to avoid high-speed shear from destroying the formed structure. Mix until the material forms a plastic mass (about 30 minutes), and the water content is about 35-40% at this time.

[0033] The fourth stage: Forming, curing, and drying

[0034] a. Extrusion granulation: Using a screw extrusion granulator, the extrusion pressure is controlled at 2 - 5 MPa to ensure the particle density while avoiding excessive compression that may damage the pores. The extruded strip is cut into cylindrical particles of a certain length by a rotating blade. The wet particles after granulation are evenly spread on a breathable tray with a thickness not exceeding 3 cm. The pre-dried particles are placed in a curing chamber and treated with hot and humid air (relative humidity 80%, temperature 50°C) containing 2 - 5% glutaraldehyde vapor for 1 hour.

[0035] b. Final drying: Dry at 80°C until the water content is <5% (about 4 - 6 hours). The stepwise heating method (60°C for 1 h → 80°C for 2 h → 100°C for 1 h) is adopted to reduce the cracks caused by drying stress.

[0036] c. Screening and grading: The particles are graded by particle size (1 - 3 cm, 3 - 5 cm, 5 - 8 cm) through a vibrating screen, and products of different particle sizes are suitable for different application scenarios. The morphology of the prepared composite-based biochar material particles is as Figure 1 shown.

[0037] The following are the preferred implementation examples of the present invention. Unless otherwise specified, the raw material reagents involved are commercially available standard products, and the experimental or testing methods are common known methods for those skilled in the art.

[0038] Example 1

[0039] The preparation method of the composite-based biochar material comprises the following steps: 1) Material pretreatment: The Arundo donax-based activated carbon is crushed to 100 - 200 meshes, the light magnesium oxide and high-purity slaked lime are respectively sieved through 300-mesh and 200-mesh sieves; the ammonium hydrogen phosphate is crushed and sieved through 100-mesh sieve; take the following formula: 60% of Arundo donax-based activated carbon, 12% of ammonium hydrogen phosphate, 10% of light magnesium oxide, 15% of high-purity slaked lime, and 3% of medium-viscosity carboxymethyl cellulose. The ammonium hydrogen phosphate is made into a 10% solution, and the carboxymethyl cellulose is prepared into a 5% colloidal solution for standby; 2) The pretreated Arundo donax-based activated carbon and the ammonium hydrogen phosphate solution are added to a V-type mixer to fully soak the Arundo donax-based activated carbon, and mixed at a speed of 30 - 50 rpm for 30 minutes to dissolve the ammonium hydrogen phosphate and soak the pores of the activated carbon. The mixture is moisturized and aged at room temperature for 24 hours; 3) The magnesium oxide and calcium hydroxide are mixed at a low speed for 10 minutes, and gradually added to the matrix prepared in step 2), controlling the feeding speed to prevent local overheating. During the mixing process, an appropriate amount of atomized water is sprayed (the total water volume is controlled at 30% of the dry material), and mixed for 60 minutes until the material shows a uniform grayish-black color; 4) The pre-prepared CMC colloidal solution is slowly added to the above mixture while stirring. Adjust the stirring speed to 20 - 30 rpm and mix for 30 minutes until the material forms a plastic mass; 5) Use a screw extrusion granulator to control the extrusion pressure at 2 - 5 MPa. The extruded strip is cut into cylindrical particles of a certain length by a rotary blade. The wet particles after granulation are evenly spread on a breathable tray with a thickness not exceeding 3 cm. Place the pre-dried particles in a curing chamber and treat them with humid hot air containing 3% glutaraldehyde vapor (relative humidity 80%, temperature 50°C) for 1 hour. Then use the gradient heating method (60°C for 1 h → 80°C for 2 h → 100°C for 1 h) to dry and obtain the composite-based biochar material particles.

[0040] Example 2

[0041] The formula of the composite-based biochar material is: 65% Arundo donax-based activated carbon, 13% ammonium hydrogen phosphate, 8% light magnesium oxide, 12% high-purity slaked lime, and 2% medium-viscosity carboxymethyl cellulose. Its preparation method is the same as that of Example 1.

[0042] Example 3

[0043] The formula of the composite-based biochar material is: 55% Arundo donax-based activated carbon, 10% ammonium hydrogen phosphate, 12% light magnesium oxide, 18% high-purity slaked lime, and 5% medium-viscosity carboxymethyl cellulose. Its preparation method is the same as that of Example 1.

[0044] Comparative Example 1

[0045] Directly use Arundo donax-based activated carbon as the finished material.

[0046] Comparative Example 2

[0047] The difference in the formula from Example 1 is that ammonium hydrogen phosphate is not added, and magnesium oxide and calcium hydroxide are directly added to the Arundo donax-based activated carbon for mixing during the preparation process. Other steps are the same as those in Example 1.

[0048] Comparative Example 3

[0049] The difference in the formula from Example 1 is that light magnesium oxide is not added, and the addition amount of high-purity slaked lime is 20%; the preparation steps are the same as those in Example 1.

[0050] Comparative Example 4

[0051] The difference in the formula from Example 1 is that high-purity slaked lime is not added, and the addition amount of light magnesium oxide is 20%; the preparation steps are the same as those in Example 1.

[0052] Comparative Example 5

[0053] The difference in the formula from Example 1 is that carboxymethyl cellulose is not added, and the material obtained in step 3) is directly subjected to step 5) extrusion granulation, curing, and drying, which is the same as that in Example 1.

[0054] Comparative Example 6

[0055] The difference between the formulation and Example 1 is that the pre-drying particle curing step is not included in step 5), and the other steps are the same as in Example 1.

[0056] Test Example

[0057] The following performance tests were carried out on the materials prepared in the above examples and comparative examples.

[0058] 1. Physical property test: The bulk density, compressive strength and abrasion resistance were measured, and the results are shown in Table 1.

[0059] The specific test methods or standards are as follows: The test method for bulk density is: GB / T 12496.6-2015, vibration table method; The test standard for compressive strength is: GB / T 30202.3-2013, crushing method; The test standard for abrasion resistance is: GB / T 30202.3-2013, using an activated carbon strength tester.

[0060] Table 1:

[0061] The following is the on-site sampling of the tail water of the abandoned pyrite mine in Qijiagou, Wuduhe Town, Yichang City, and the verification of the reagent effect. The pH value of the tail water of this pyrite mine is 2.2, the average daily water inflow is nearly 800 cubic meters, and the iron content is 579 mg / L, exceeding (the "Groundwater Quality Standard" (GB / T-14848-2017)).

[0062] 2. Test the pH adjustment ability and iron adsorption efficiency

[0063] 10 kg of the materials of the examples and comparative examples were respectively added to 100 L of the liquid to be treated with a pH value of 2.2 collected from the above abandoned mine. The pH value of the treated liquid was detected after 24 hours and 72 hours (usually the hydraulic retention time of the water treatment method is less than 3 days), and the iron adsorption rate after 72 hours; the adsorption rate = (1 - iron content in the treated liquid after adsorption / iron content in the original treated liquid) × 100%, and the results are shown in Table 2.

[0064] Table 2:

[0065] 3. Test the heavy metal adsorption ability

[0066] Prepare corresponding solutions for other heavy metals to verify the adsorption effect of the material for 72 hours. Manganese is 7.5 mg / L, copper is 7.5 mg / L, lead is 0.5 mg / L, and the relevant contents are all 5 times that of the "Groundwater Environmental Quality Standard" (GB / T - 14848 - 2017). Cadmium is 0.05 mg / L, and the content is 5 times that of the Class V water standard of the "Surface Water Environmental Quality Standard" (GB 3838 - 2002). Detect the adsorption efficiency, and the results are shown in Table 3.

[0067] Table 3:

[0068] It is not difficult to see from the results of Table 1 - Table 3 above: The bulk density of the composite - based biochar material prepared in this application meets 0.6 - 0.8 g / cm 2 , has high compressive strength and wear resistance, fast pH - adjustment response, good stability, good adsorption effect on harmful elements, and fast adsorption speed. It is an ideal material for treating pyrite tailings.

[0069] Compared with Example 1, when directly using Arundo donax - based activated carbon as the treatment material in Comparative Example 1, the bulk density is small, the compressive resistance is poor, and the wear rate is high. Its performance in aspects such as pH adjustment and heavy - metal adsorption is significantly worse, and it cannot be used as an ideal material for treating pyrite tailings; in Comparative Examples 2 to 5, one component is reduced respectively, and in Comparative Example 6, without curing with humid hot air containing 3% glutaraldehyde vapor, the pH - adjustment ability and heavy - metal adsorption performance show different degrees of decline. The above - mentioned comparative examples fully illustrate the synergism existing between the components of the composite - based biochar material and the methods.

[0070] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite-based biochar material for treating acidic mine tail water, characterized in that, The composition by weight percentage is: 55 - 65% of Arundo donax - based activated carbon, 10 - 15% of ammonium hydrogen phosphate, 8 - 12% of magnesium oxide, 12 - 18% of calcium hydroxide, and 2 - 5% of carboxymethyl cellulose.

2. The composite-based biochar material according to claim 1, wherein The composition by weight percentage is: 60% of Arundo donax - based activated carbon, 12% of ammonium hydrogen phosphate, 10% of magnesium oxide, 15% of calcium hydroxide, and 3% of carboxymethyl cellulose.

3. The preparation method of the composite-based biochar material according to claim 1, characterized in that the steps It includes: S1. After making ammonium hydrogen phosphate into an aqueous solution, mix it with Arundo donax - based activated carbon and keep it moist and cured. S2. Take magnesium oxide and calcium hydroxide and premix them, then add them to the cured material obtained in step S1 and stir - mix. S3. After pre - making carboxymethyl cellulose into a colloid, slowly add it to the material obtained in step S2 and stir until it forms a mass. S4. Use a screw - extrusion granulator to extrude and granulate, and pass hot steam containing glutaraldehyde for curing, and then dry to obtain the composite - based biochar material.

4. The preparation method according to claim 3, wherein, In step S1, the curing time is 12 - 30 h.

5. The preparation method according to claim 3, characterized in that, In step S2, water is sprayed during the stirring - mixing process, and the water consumption is 25 - 30% of the total mass of the premixed magnesium oxide and calcium hydroxide. And / or, the stirring - mixing process time is 40 - 60 min.

6. The preparation method according to claim 3, characterized in that, In step S3, the water content of the mass - like product is 35 - 40%.

7. The preparation method according to claim 3, wherein In step S4, the extrusion pressure is 2 - 5 MPa. And / or, the glutaraldehyde content in the hot steam containing glutaraldehyde is 2 - 5%, the relative humidity is 75 - 85%, and the temperature is 45 - 55 °C; the curing process time is 0.5 - 2 h.

8. The preparation method according to claim 3, characterized in that, In step S4, the drying process uses gradient heating to dry until the water content is less than 5%.

9. The application of the composite - based biochar material according to claim 1 or 2, or the composite - based biochar material prepared by the preparation method according to any one of claims 3 - 8 in the treatment of acidic mine tail water.

10. The application according to claim 9, characterized in that, After treatment, the pH value of the acidic mine tail water is 6.0 - 7.5.

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