Solid waste-based filling material for improving heavy metal leaching rate and preparation method thereof

Abstract

This invention provides a solid waste-based backfill material for improving heavy metal leaching rate and its preparation method. The backfill material comprises the following raw materials in parts by weight: 40-60 parts Bayer red mud, 40-60 parts fly ash, 10-20 parts desulfurized gypsum, 5-8 parts nano-hydroxyapatite, 4-6 parts pumping agent, and 30-60 parts water. The pumping agent is a compound of organosilicon polycarboxylic acid water-reducing agent, polymaleic acid, and thiol-modified cellulose in a mass ratio of 4-6:3:10-12. The thiol-modified cellulose is prepared by a method including the following steps: dissolving carboxymethyl cellulose in water, adding aminothiol compounds, adjusting the pH, adding activators and activating aids, and reacting under controlled temperature. After the reaction, acetone is added until no precipitation occurs. The mixture is then filtered, washed, and dried to obtain thiol-modified cellulose. The heavy metal leaching performance of the backfill material is improved by introducing hydroxyapatite, which can both precipitate and adsorb heavy metals.

Description

Technical Field

[0001] This invention belongs to the field of filling material technology, specifically relating to a solid waste-based filling material for improving heavy metal leaching rate and its preparation method. Background Technology

[0002] With the ever-expanding demand for mineral resources, the large number of goaf areas generated by mining development are highly susceptible to engineering safety and ecological environmental problems. Currently, the main methods for managing goaf areas include backfilling, caving, closure, and regional relocation. Among these, backfilling uses filling materials to treat the goaf, effectively controlling ground pressure and preventing surface subsidence. The state encourages all regions to prioritize the use of backfilling for goaf treatment. Grouting backfilling is one of the most widely used backfilling methods due to its relatively simple construction process, lightweight and easy-to-operate equipment, strong adaptability to complex environments, immunity to weather and seasonal influences, and ability to complete backfilling operations in a relatively short time.

[0003] The materials used in grouting and backfilling mainly include red mud, fly ash, slag, cement, and other cementitious materials. Depending on the needs, some admixtures may also be included, such as water-reducing agents, setting regulators, and early-strength agents. Therefore, grouting and backfilling can not only dispose of solid waste from power plants, steel mills, and metal smelting plants, reducing the pressure of solid waste discharge, but also effectively reduce surface subsidence caused by mining, achieving coordinated development of mining resources and the environment.

[0004] The applicant's earlier patent application (application number 2024118343993) discloses a solid waste-based backfill material and its preparation method. Using Bayer red mud and fly ash as the main cementing materials, and with the aid of a pumping agent composed of an alkali activator, organosilicon polycarboxylate superplasticizer, polymaleic acid, and water-soluble cellulose in a mass ratio of 3-5:3-5:10, the backfill material exhibits excellent pumpability while simultaneously optimizing its mechanical properties. However, due to the lack of substances in the backfill material that can adsorb heavy metals, have a strong complexing ability for heavy metals, or otherwise form precipitates, the heavy metal leaching rate of the backfill material is relatively high. Although polymaleic acid, a component of the pumping agent, has a certain heavy metal complexing ability, the backfill material system contains a large number of competing ions such as calcium, aluminum, and iron ions. Furthermore, to improve pumpability, the surface of the red mud particles is coated with a thick, stable solvated water film, greatly reducing the possibility of heavy metal ions forming complexes or solidifying in the crystal lattice. Therefore, it is necessary to further improve it in order to reduce the leaching rate of heavy metal ions without diminishing its original performance. Summary of the Invention

[0005] To address the problem of high leaching rates of heavy metal ions, this invention improves the heavy metal leaching performance of the filling material by introducing hydroxyapatite, which can both precipitate and adsorb heavy metals.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] A solid waste-based backfill material for improving heavy metal leaching rate comprises the following raw materials in parts by weight: 40-60 parts Bayer red mud, 40-60 parts fly ash, 10-20 parts desulfurized gypsum, 5-8 parts nano-hydroxyapatite, 4-6 parts pumping agent, and 30-60 parts water. The pumping agent is a compound of organosilicon polycarboxylate superplasticizer, polymaleic acid, and thiol-modified cellulose in a mass ratio of 4-6:3:10-12. The thiol-modified cellulose is prepared by a method comprising the following steps: dissolving carboxymethyl cellulose in water, adding aminothiol compounds, adjusting the pH, adding an activator and an activating aid, controlling the temperature for reaction, adding acetone until no precipitate is formed after the reaction, filtering, washing, and drying to obtain thiol-modified cellulose.

[0008] The mass-to-volume ratio of carboxymethyl cellulose to water is 3-5 g: 100 mL. The aminothiol compound is selected from one or a combination of two or more of dithiobutylamine, β-mercaptoethylamine, 3-mercapto-1-propylamine, and 4-aminobutane-1-thiol; preferably dithiobutylamine. The degree of substitution of the carboxymethyl cellulose is 0.65-0.95, and the weight-average molecular weight is 50,000-100,000. The amount of the aminothiol compound used is 10-20 wt% of the carboxymethyl cellulose, preferably 15-20 wt%. The pH is adjusted to 4-6 using 3-5 mol / L hydrochloric acid. The temperature is controlled at 20-40℃. The reaction time is 2-10 h. The amount of the activator is 5-10 wt% of the carboxymethyl cellulose, and the amount of the activating aid is 2-6 wt% of the carboxymethyl cellulose. The activator is selected from one or a combination of two of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide (CMC). The activating aid is selected from one or a combination of two or more of N-hydroxysuccinimide, 1-hydroxybenzotriazole, 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-phenylpropanetriazine, 1-hydroxy-7-azabenzotriazole, and N-hydroxysulfonylsuccinimide. The washing is performed by alternating washing with acetone and water 1-3 times, and the drying is performed at 60-80°C to constant weight.

[0009] The nano-hydroxyapatite has an average particle size of 10-50 nm and a specific surface area of ​​30-100 m². 2 / g.

[0010] Nano-hydroxyapatite has a small particle size and a large specific surface area. The added nano-hydroxyapatite will compete with particles such as Bayer red mud and fly ash for adsorption of pumping agents, reducing the uniformity of pumping agent distribution on the surface of other particles and the effective adsorption amount, weakening its water reduction and dispersion effects, and resulting in reduced pumping performance. In order not to affect the pumping performance, the amount of pumping agent needs to be increased accordingly.

[0011] The relative molecular mass of the polymaleic acid is 600-1000.

[0012] The organosilicon polycarboxylate water-reducing agent is prepared by a method comprising the following steps:

[0013] The polymer was obtained by aqueous free radical polymerization under an inert atmosphere using unsaturated carboxylic acid monomers, polyethylene glycol monoallyl ether, and unsaturated silane monomers as polymerization monomers, initiated by an oxidation / reduction system initiator, and under the action of a chain transfer agent.

[0014] The mass ratio of the unsaturated carboxylic acid monomer, polyethylene glycol monoallyl ether, and unsaturated silane monomer is 1.5-2:2-4:0.8-1.

[0015] The unsaturated carboxylic acid monomer is selected from one or a combination of two or more of acrylic acid, methacrylic acid, fumaric acid, maleic anhydride, and itaconic acid.

[0016] The number-average molecular weight of the polyethylene glycol monoallyl ether is 1500-2400.

[0017] The unsaturated silane monomer is selected from one or a combination of two or more of triisopropyl acrylate, acryloyloxytrimethylsilane, and acryloyloxymethyltrimethylsilane.

[0018] The polymerization temperature is 30-60℃, and the polymerization reaction time is 1-3 hours. The polymerizable monomer has a mass fraction of 40-60 wt% in the aqueous solution. In the oxidation / reduction system, the amount of reducing agent is 0.5-1 wt% of the sum of the mass of the carboxylic acid monomer, polyethylene glycol monoallyl ether, and silane monomer, and the reducing agent is selected from one or more combinations of ascorbic acid, sodium sulfite, sodium hypophosphite, glucose, and sodium formaldehyde sulfoxylate. The amount of oxidizing agent is 0.5-1 wt% of the sum of the mass of the carboxylic acid monomer, polyethylene glycol monoallyl ether, and silane monomer, and is selected from one or more combinations of hydrogen peroxide, ammonium persulfate, and potassium persulfate. The amount of chain transfer agent is 0.3-0.5 wt% of the sum of the mass of the carboxylic acid monomer, polyethylene glycol monoallyl ether, and silane monomer, and is selected from one or more combinations of mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptoethanol.

[0019] The fly ash is selected from one or a combination of two of Grade I fly ash and Grade II fly ash.

[0020] The present invention also provides a method for preparing the above-mentioned solid waste-based backfill material with improved heavy metal leaching rate, comprising the following steps:

[0021] Mix Bayer red mud, fly ash, desulfurized gypsum, and nano hydroxyapatite evenly to obtain mixture 1. Mix pumping agent and water evenly to obtain mixture 2. Mix mixture 1 and mixture 2 evenly to obtain solid waste base filling material.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] This invention improves the heavy metal leaching performance of filling materials by introducing hydroxyapatite, which can both precipitate and adsorb heavy metals. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, but is not limited to the contents of the specification. Unless otherwise specified, all "parts" mentioned in the embodiments of the present invention are parts by weight. All reagents used are commercially available in the art.

[0025] Carboxymethyl cellulose, product number E012219, MW90000, degree of substitution DS=0.7, purchased from Anaiji Chemical.

[0026] The average particle size of nano-hydroxyapatite is 20 nm, and its specific surface area is 50 m². 2 / g, purchased from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd.

[0027] Polyethylene glycol monoallyl ether 2400 (number average molecular weight 2400) and polyethylene glycol monoallyl ether 1500 (number average molecular weight 1500) were both purchased from Haian Petrochemical Plant in Jiangsu Province.

[0028] Polymaleic acid with relative molecular masses of 600 and 1000 was purchased from Sinochem Chemicals.

[0029] Bayer red mud and Class I fly ash were purchased from Hebei Wenfeng New Materials Co., Ltd.; desulfurized gypsum was purchased from Shangqiu Tianyuan Desulfurized Gypsum Co., Ltd. The oxide composition of the above three raw materials is shown in Table 1:

[0030] Table 1 Composition of raw material oxides

[0031]

[0032]

[0033] Example 1

[0034] 1) Dissolve 50g of carboxymethyl cellulose E012219 in 1000mL of water, add 10g of dithiobutylamine, adjust the pH to 4 with 3mol / L hydrochloric acid, add 5g of activator 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1g of activating aid N-hydroxysuccinimide, and react at 20℃ for 7h. After the reaction is complete, add acetone until no precipitate is formed, filter, wash with acetone and water alternately 3 times, and dry at 80℃ to constant weight to obtain thiol-modified cellulose.

[0035] 2) Under a nitrogen atmosphere, 200g of acrylic acid, 200g of polyethylene glycol monoallyl ether 2400, 80g of triisopropyl silicone acrylate, and 1.4g of potassium persulfate were added to 720g of water. The mixture was heated to 60℃ and the monomer solution was mixed evenly. After 30 minutes, a solution consisting of 2.8g of ascorbic acid, 0.84g of mercaptoethanol, and 3.36g of water was added dropwise. The polymerization reaction was carried out for 3 hours. After the reaction was completed, the pH was adjusted to 7 with sodium hydroxide, and the water was removed by vacuum distillation to obtain an organosilicon polycarboxylate superplasticizer with a weight-average molecular weight of 124,000.

[0036] 3) Mix 60g Bayer red mud, 40g Grade I fly ash, 10g desulfurized gypsum, and 8g nano hydroxyapatite evenly to obtain mixture 1. Mix 6g of pumping agent composed of organosilicon polycarboxylate superplasticizer, polymaleic acid with a relative molecular mass of 1000, and thiol-modified cellulose in a mass ratio of 6:3:12, and 38g of water evenly to obtain mixture 2. Mix mixture 1 and mixture 2 evenly to obtain solid waste base filling material.

[0037] Example 2

[0038] The rest is the same as in Example 1, except that in step 1), 4-aminobutane-1-thiol is used instead of dithiobutylamine in equal mass.

[0039] Example 3

[0040] The rest is the same as in Example 1, except that in step 1), the amount of dithiobutylamine used is 5g.

[0041] Example 4

[0042] The rest is the same as in Example 1, except that in step 3), the amount of nano-hydroxyapatite used is 5g.

[0043] Example 5

[0044] The rest is the same as in Example 1, except that in step 3), the amount of pumping agent used is 4g.

[0045] Example 6

[0046] The rest is the same as in Example 1, except that in step 3), the pumping agent is a compound of organosilicon polycarboxylate superplasticizer, polymaleic acid with a relative molecular mass of 1000, and thiol-modified cellulose in a mass ratio of 6:3:10.

[0047] Example 7

[0048] 1) Dissolve 50g of carboxymethyl cellulose E012219 in 1000mL of water, add 10g of dithiobutylamine, adjust the pH to 4 with 3mol / L hydrochloric acid, add 5g of activator 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1g of activating aid N-hydroxysuccinimide, and react at 20℃ for 7h. After the reaction is complete, add acetone until no precipitate is formed, filter, wash with acetone and water alternately 3 times, and dry at 80℃ to constant weight to obtain thiol-modified cellulose.

[0049] 2) Under a nitrogen atmosphere, 200g of acrylic acid, 200g of polyethylene glycol monoallyl ether 1500, 80g of triisopropylsilyl acrylate, and 1.4g of potassium persulfate were added to 720g of water. The mixture was heated to 60℃ and the monomer solution was mixed evenly. After 30 minutes, a solution consisting of 2.8g of ascorbic acid, 0.84g of mercaptoethanol, and 3.36g of water was added dropwise. The polymerization reaction was carried out for 3 hours. After the reaction was completed, the pH was adjusted to 7 with sodium hydroxide, and the water was removed by vacuum distillation to obtain an organosilicon polycarboxylate superplasticizer with a weight-average molecular weight of 124,000.

[0050] 3) Mix 40g Bayer red mud, 60g Grade I fly ash, 10g desulfurized gypsum, and 8g nano hydroxyapatite evenly to obtain mixture 1. Mix 6g of pumping agent composed of organosilicon polycarboxylate superplasticizer, polymaleic acid with a relative molecular mass of 600, and mercapto-modified cellulose in a mass ratio of 4:3:12, and 38g of water evenly to obtain mixture 2. Mix mixture 1 and mixture 2 evenly to obtain solid waste base filling material.

[0051] Comparative Example 1

[0052] The rest is the same as in Example 1, except that nano-hydroxyapatite is not added in step 3).

[0053] Comparative Example 2

[0054] 1) Under a nitrogen atmosphere, 200g of acrylic acid, 200g of polyethylene glycol monoallyl ether 2400, 80g of triisopropyl silicone acrylate, and 1.4g of potassium persulfate were added to 720g of water. The mixture was heated to 60℃ and the monomer solution was mixed evenly. After 30 minutes, a solution consisting of 2.8g of ascorbic acid, 0.84g of mercaptoethanol, and 3.36g of water was added dropwise. The polymerization reaction was carried out for 3 hours. After the reaction was completed, the pH was adjusted to 7 with sodium hydroxide, and the water was removed by vacuum distillation to obtain an organosilicon polycarboxylate superplasticizer with a weight-average molecular weight of 124,000.

[0055] 2) Mix 60g Bayer red mud, 40g Grade I fly ash, 10g desulfurized gypsum, and 8g nano hydroxyapatite evenly to obtain mixture 1. Mix 6g of pumping agent composed of organosilicon polycarboxylate superplasticizer, polymaleic acid with a relative molecular mass of 1000, and carboxymethyl cellulose E012219 in a mass ratio of 6:3:12, and 38g of water evenly to obtain mixture 2. Mix mixture 1 and mixture 2 evenly to obtain solid waste base filling material.

[0056] Compared to Example 1, carboxymethyl cellulose E012219 was not modified with thiol groups.

[0057] Application examples

[0058] The filling materials prepared in the above embodiments and comparative examples were subjected to the following performance tests:

[0059] 1. Flowability: Refer to Appendix A.0.2 of the Technical Specification for Cement-based Grouting Materials GB / T 50448-2008 for flowability test. The initial spread is required to be ≥290mm and the 30min flowability retention value is required to be ≥260mm. Record the initial flowability and the 30min flowability retention value.

[0060] 2. Bleeding performance: The bleeding test shall be conducted in accordance with the bleeding test standard in GB / T 50080-2002 Standard for Test Methods of Performance of Concrete Mixtures.

[0061] 3. Compressive strength: Tested in accordance with standard GB / T 50081-2002 Practical Standard for Test Methods of Mechanical Properties of Ordinary Concrete.

[0062] 4. Environmental toxicity leaching risk test: The test was conducted in accordance with the methods and procedures of the national standard "Leaching Toxicity of Solid Waste - Horizontal Oscillation Method" (HJ557-2009), and the content of harmful ions in the leachate was determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0063] Table 2 Performance Test Results

[0064]

[0065] Table 3 Performance Test Results

[0066]

[0067] As can be seen from the performance test results in Tables 2 and 3, by adding hydroxyapatite, modifying carboxymethyl cellulose with mercapto groups, and appropriately adjusting the amount of pumping agent, the leaching rate of heavy metal ions can be reduced without diminishing the original performance of the filling material.

[0068] Examples 1-3, 6, and Comparative Example 2 clearly show that thiol-modified cellulose has a significant effect on the leaching of divalent heavy metals. The possible reason is that thiol-modified cellulose can form a transport channel for divalent heavy metal ions in the solubilized water film, accurately transporting divalent heavy metal ions to the active sites of cementitious materials such as red mud and fly ash for fixation.

[0069] Examples 1, 4, and Comparative Example 1 demonstrate that nano-hydroxyapatite exhibits excellent curing ability against heavy metals in the filling material. Examples 1, 1, and 2 show that nano-hydroxyapatite and the thiol-modified cellulose in the pumping agent have a synergistic effect in reducing the leaching rate of heavy metal ions.

[0070] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A solid waste-based backfill material for improving heavy metal leaching rate, characterized in that, The raw materials include the following parts by weight: 40-60 parts Bayer red mud, 40-60 parts fly ash, 10-20 parts desulfurized gypsum, 5-8 parts nano-hydroxyapatite, 4-6 parts pumping agent, and 30-60 parts water. The pumping agent is a compound of organosilicon polycarboxylate superplasticizer, polymaleic acid, and thiol-modified cellulose in a mass ratio of 4-6:3:10-12. The thiol-modified cellulose is prepared by a method including the following steps: dissolving carboxymethyl cellulose in water, adding aminothiol compounds, adjusting the pH, adding activators and activating aids, controlling the temperature for reaction, adding acetone after the reaction is completed until no precipitation is produced, filtering, washing, and drying to obtain thiol-modified cellulose.

2. The solid waste-based backfill material for improving heavy metal leaching rate according to claim 1, characterized in that, The aminothiol compound is selected from one or a combination of two or more of dithiobutylamine, β-mercaptoethylamine, 3-mercapto-1-propaneamine, and 4-aminobutane-1-thiol; the carboxymethyl cellulose has a degree of substitution of 0.65-0.95 and a weight-average molecular weight of 50,000-100,000.

3. The solid waste-based backfill material for improving heavy metal leaching rate according to claim 1, characterized in that, The amount of the aminothiol compound used is 10-20 wt% of carboxymethyl cellulose; the mass-volume ratio of carboxymethyl cellulose to water is 3-5 g: 100 mL.

4. The solid waste-based backfill material for improving heavy metal leaching rate according to claim 1, characterized in that, The activator is used in an amount of 5-10 wt% of carboxymethyl cellulose, and the activating aid is used in an amount of 2-6 wt% of carboxymethyl cellulose; the activator is selected from one or a combination of two of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide; the activating aid is selected from one or a combination of two or more of N-hydroxysuccinimide, 1-hydroxybenzotriazole, 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-phenylpropanetriazine, 1-hydroxy-7-azabenzotriazole, and N-hydroxysulfosuccinimide.

5. The solid waste-based backfill material for improving heavy metal leaching rate according to claim 1, characterized in that, The pH adjustment is achieved by using 3-5 mol / L hydrochloric acid to adjust the pH to 4-6; the temperature control is achieved by maintaining the temperature at 20-40℃; and the reaction time is 2-10 hours.

6. The solid waste-based backfill material for improving heavy metal leaching rate according to claim 1, characterized in that, The nano-hydroxyapatite has an average particle size of 10-50 nm and a specific surface area of ​​30-100 m². 2 / g.

7. The solid waste-based backfill material for improving heavy metal leaching rate according to claim 1, characterized in that, The relative molecular mass of the polymaleic acid is 600-1000.

8. The solid waste-based backfill material for improving heavy metal leaching rate according to claim 1, characterized in that, The organosilicon polycarboxylate water-reducing agent is prepared by a method comprising the following steps: The polymer was obtained by aqueous free radical polymerization under an inert atmosphere using unsaturated carboxylic acid monomers, polyethylene glycol monoallyl ether, and unsaturated silane monomers as polymerization monomers, initiated by an oxidation / reduction system initiator, and under the action of a chain transfer agent.

9. The solid waste-based backfill material for improving heavy metal leaching rate according to claim 8, characterized in that, The mass ratio of the unsaturated carboxylic acid monomer, polyethylene glycol monoallyl ether, and unsaturated silane monomer is 1.5-2:2-4:0.8-1; the unsaturated carboxylic acid monomer is selected from one or a combination of two or more of acrylic acid, methacrylic acid, fumaric acid, maleic anhydride, and itaconic acid; the number average molecular weight of the polyethylene glycol monoallyl ether is 1500-2400; the unsaturated silane monomer is selected from one or a combination of two or more of triisopropyl acrylate, acryloyloxytrimethylsilane, and acryloyloxymethyltrimethylsilane.

10. A method for preparing a solid waste-based backfill material for improving heavy metal leaching rate according to any one of claims 1-9, characterized in that, Includes the following steps: Mix Bayer red mud, fly ash, desulfurized gypsum, and nano hydroxyapatite evenly to obtain mixture 1. Mix pumping agent and water evenly to obtain mixture 2. Mix mixture 1 and mixture 2 evenly to obtain solid waste-based backfill material that improves heavy metal leaching rate.

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