Preparation method of coal gangue solid waste synthetic material

Abstract

The invention discloses a preparation method of a coal gangue solid waste synthetic material, the preparation method comprises the steps of coal gangue pretreatment, coal gangue modification, ingredient stirring, molding maintenance and the like, through a dual modification process, firstly, thermal activation is used for destroying coal gangue crystal lattices, then a composite modifier is used for forming an organic-inorganic coating on the surface, and the activity and interfacial compatibility are synergistically improved; the geopolymer stimulates the activity of the coal gangue, the cement provides early strength, the zeolite powder adsorbs heavy metals and fills pores, and the geopolymer, the cement and the zeolite powder synergistically improve the strength and durability; the hazardous waste deep pretreatment comprises the steps of washing to remove soluble salt, leaching with acid to dissolve out heavy metal and adsorbing residues with zeolite powder, and harmlessness of the hazardous waste is achieved through cooperation of the three steps; high performance can be achieved without high temperature (20 + / -2 DEG C) maintenance, and the method is suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization and building materials, and particularly relates to a preparation method of a coal gangue solid waste synthetic material. BACKGROUND

[0002] Coal gangue is a byproduct of coal mining and washing, with an annual discharge of over 500 million tons and an accumulation of over 100,000 mu of land. The weathering and leaching of coal gangue lead to heavy metal leakage and dust pollution, which restricts the green development of the coal industry. The existing utilization methods of coal gangue have significant shortcomings:

[0003] 1. Low mixing amount: The mixing amount of coal gangue in traditional cement-based materials is only 20-40%, the solid waste disposal efficiency is low, and the mechanical properties decrease sharply (28-day compressive strength ≤ 35 MPa) under high mixing amount;

[0004] 2. Insufficient activity: The surface of coal gangue is dense and the crystal lattice is stable, and single alkali activation or coupling agent modification can only improve the activity by 10-15%, the interface compatibility with the cementitious matrix is poor, and cracks are easily generated;

[0005] 3. Defects in cementitious system: high carbon emission (85% higher than the present application) when relying on single cement, large amount of activator (≥ 15 parts) and high cost when relying on single geopolymer, and high temperature (≥ 60℃) is required for curing;

[0006] 4. Lack of hazardous waste disposal: hazardous waste such as smelting slag contains heavy metals such as Pb and Cd, and direct addition in the existing technology easily leads to leaching exceeding the standard, and single water washing can only remove 60% of soluble salts, and cannot achieve harmless and collaborative disposal;

[0007] 5. Poor comprehensive performance: the thermal conductivity of traditional materials is ≥ 0.048 W / (m·℃), and the impermeability grade is ≤ P8, which cannot meet the heat insulation and durability requirements of high-end buildings.

[0008] The existing technology only uses single thermal activation or coupling agent modification, does not construct a collaborative cementitious system, and has no deep pretreatment mechanism for hazardous waste, which makes it difficult to solve the above bottlenecks. Therefore, it is an urgent need in the industry to develop a "high mixing amount, high performance, low cost, and environmentally friendly" coal gangue synthetic material preparation technology. SUMMARY

[0009] In view of the deficiencies in the prior art, the present application provides a preparation method of a coal gangue solid waste synthetic material, which solves the problems of "low mixing amount, poor activity, poor interface, weak performance, difficult hazardous waste disposal, and high cost" in the prior art.

[0010] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a preparation method of a coal gangue solid waste synthetic material, comprising the following steps:

[0011] (1) Coal gangue pretreatment:

[0012] After the coal gangue is crushed, it is dried to a water content of ≤1%, and then sieved and activated at high temperature to obtain active coal gangue;

[0013] (2) Coal gangue modification:

[0014] A composite modifier solution of KH550 silane coupling agent, NaOH and deionized water is prepared in a mass ratio of 1.5-2.0:1.0-1.5:100;

[0015] The active coal gangue in step (1) is added to the composite modifier solution, and the liquid-solid ratio is controlled at 0.4-0.6:1. After sufficient stirring at a temperature of 70-90°C, filtration and drying to a constant weight, modified coal gangue is obtained;

[0016] (3) Mixing and stirring:

[0017] In parts by weight, 55-70 parts of modified coal gangue, 12-20 parts of Portland cement, 6-10 parts of geopolymer activator, 8-14 parts of river sand, 0.2-0.4 parts of polycarboxylate superplasticizer, 0.5-1.0 parts of zeolite powder, and 18-24 parts of tap water are mixed in step (2). Dry mixing is followed by wet mixing to obtain a uniform slurry;

[0018] (4) Molding and curing:

[0019] The slurry in step (4) is poured into a test mold and vibrated to compact it. After demolding and curing for 28 days, a synthetic material is obtained.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] 1. Breakthrough of the contradiction between high dosage and high performance: 55-70% high dosage of coal gangue is achieved while ensuring that the 28-day compressive strength is ≥48 MPa;

[0022] 2. Improve the activity and interfacial compatibility of coal gangue: through the "thermal activation-composite modification" double process, the activity is increased by more than 40%, and the interfacial bonding force is increased by more than 50%;

[0023] 3. Build a low-cost synergistic cementing system: optimize the ternary synergy of geopolymer-cement-zeolite powder, reduce the activator dosage to 6-10 parts, and reduce the cost by more than 35%;

[0024] 4. Realize the harmless disposal of hazardous waste: through the three-step pretreatment of "water washing-acid leaching-adsorption", the leaching concentration of heavy metals in smelting slag is reduced to less than 1 / 3 of the standard limit;

[0025] 5. Improve comprehensive performance: make the thermal conductivity of the material ≤0.038 W / (m·℃), the impermeability grade ≥P10, and meet the needs of high-end applications.

[0026] Further, in step (1), the coal gangue is crushed to a particle size of ≤5 mm; after drying, it is sieved through a 60 μm standard sieve, and high-temperature activation is performed;

[0027] The activation conditions are: heating rate 5-8℃ / min, final temperature 650-750℃, holding time 60-90min, and volume fraction 5-8% CO2 gas is introduced, and the active coal gangue is obtained after cooling to room temperature;

[0028] The coal gangue is washing / excavation coal gangue, with a loss on ignition of ≤8%, SiO2≥55%, and Al2O3≥15%.

[0029] Further, in step (3), the geopolymer activator is prepared as follows:

[0030] Sodium silicate: KOH=3-4:1, modulus 1.2-1.8;

[0031] River sand particle size 0.1-0.6mm, SiO2≥95%, 0.3-0.6mm particle size accounting for ≥65%, and clay content ≤0.8%.

[0032] Further, the geopolymer activator is prepared at a temperature of 30-40℃, stirred at 300-400r / min, and used after holding for 10min.

[0033] Further, in step (2), in the composite modifier solution, the effective ingredient of KH550 is ≥98%, the purity of NaOH is ≥96%, and the conductivity of deionized water is ≤10 μS / cm.

[0034] Further, in step (4), the impermeability grade of the synthetic material is ≥P10, and the sulfate resistance coefficient is ≥0.85.

[0035] Further, in step (3), part of the modified coal gangue is replaced with pretreated slag.

[0036] Further, the pretreated slag process is as follows:

[0037] According to the liquid-solid ratio of 3:1, after washing with water, the smelting slag is stirred and washed, and then according to the liquid-solid ratio of 0.8:1, it is treated by stirring and acid immersion with 1.5mol / L hydrochloric acid, then filtered, dried to a water content of ≤1%, and the pretreated slag is obtained.

[0038] Further, characterized in that 8-12 parts of pretreated slag are replaced in 55-70 parts of modified coal gangue. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application.

[0040] The present application provides a preparation method of coal gangue solid waste synthetic material, comprising the following steps:

[0041] (1) Coal gangue pretreatment:

[0042] After the coal gangue is crushed, it is dried to a water content of ≤1%, and then sieved and activated at high temperature to obtain active coal gangue;

[0043] (2) Coal gangue modification:

[0044] A composite modifier solution of KH550 silane coupling agent, NaOH and deionized water is prepared in a mass ratio of 1.5-2.0:1.0-1.5:100;

[0045] The active coal gangue in step (1) is added to the composite modifier solution, and the liquid-solid ratio is controlled at 0.4-0.6:1. After sufficient stirring at a temperature of 70-90℃, filtration and drying to a constant weight, modified coal gangue is obtained;

[0046] (3) Mixing and stirring:

[0047] In step (2), 55-70 parts of modified coal gangue, 12-20 parts of Portland cement, 6-10 parts of geopolymer activator, 8-14 parts of river sand, 0.2-0.4 parts of polycarboxylate superplasticizer, 0.5-1.0 parts of zeolite powder, and 18-24 parts of tap water are mixed in terms of weight; dry mixing is performed first, and then wet mixing is performed to obtain a uniform slurry;

[0048] (4) Molding and curing:

[0049] The slurry in step (4) is poured into a test mold and vibrated to compactness, then demolded and cured for 28 days to obtain a synthetic material.

[0050] Further, in step (1), the coal gangue is crushed to a particle size of ≤5mm; after drying, it is sieved through a 60μm standard sieve and activated at high temperature;

[0051] The activation conditions are as follows: the heating rate is 5-8℃ / min, the final temperature is 650-750℃, the holding time is 60-90min, CO2 gas with a volume fraction of 5-8% is introduced, and the temperature is cooled to room temperature to obtain active coal gangue;

[0052] The coal gangue is washed and selected / dug coal gangue, with a loss on ignition of ≤8%, SiO2≥55%, and Al2O3≥15%.

[0053] Further, in step (3), the geopolymer activator is prepared in the following ratio:

[0054] Water glass: KOH = 3-4:1, modulus 1.2-1.8;

[0055] River sand particle size 0.1-0.6mm, SiO2≥95%, 0.3-0.6mm particle size ratio ≥65%, silt content ≤0.8%.

[0056] Further, the geopolymer activator preparation temperature is 30-40℃, stirring 300-400r / min, and used after 10min of heat preservation.

[0057] Further, in step (2), the effective ingredient of KH550 in the composite modifier solution is ≥98%, the purity of NaOH is ≥96%, and the conductivity of deionized water is ≤10μS / cm.

[0058] Further, in step (4), the impermeability grade of the synthetic material is ≥P10, and the sulfate corrosion resistance coefficient is ≥0.85.

[0059] Further, in step (3), the modified coal gangue is partially replaced by pretreated waste residue.

[0060] Further, the pretreated waste residue process is as follows:

[0061] According to the liquid-solid ratio 3:1, after the water is used to wash the smelting waste residue by stirring, according to the liquid-solid ratio 0.8:1, after the acid treatment by stirring with 1.5mol / L hydrochloric acid, filtering, drying to the water content ≤1%, the pretreated waste residue is obtained.

[0062] Further, characterized in that 8-12 parts of pretreated waste residue are replaced in 55-70 parts of modified coal gangue.

[0063] In order to verify the effect of the present application, the present application is demonstrated by the following multiple examples and multiple comparative examples.

[0064] Example 1

[0065] A preparation method of a coal gangue solid waste synthetic material, comprising the following steps:

[0066] 1. Raw material pretreatment (precise control index):

[0067] ① Coal gangue pretreatment: select washed coal gangue (loss on ignition 6.5%, SiO2=58%, Al2O3=18%, Fe2O3=4.2%), crushed to particle size ≤5mm by PE-150×250 type jaw crusher (rotating speed 280r / min), sent to DHG-9070A type oven, dried at 110℃ for 3.5h, water content reduced to 0.9%; screened by 60μm standard screen (vibration frequency 50Hz), screen residue 1.8%; sent to Φ1.2×10m rotary kiln for heat activation, 0.8m3 / h, the temperature was raised to 700℃ at a rate of 6℃ / min, and kept for 75 min, and then cooled to room temperature to obtain the active coal gangue (pozzolanic activity index 78%).

[0068] The composite modifier was prepared by weighing 1.05 kg of silane coupling agent KH550 (effective ingredient 98.5%), 0.72 kg of NaOH (purity 96.3%) and 60 kg of deionized water (conductivity 8 μS / cm) according to a mass ratio of 1.8:1.2:100, and then pouring them into a 50LSF-50 type reaction kettle, and stirring at 30℃ and 300 r / min until the NaOH was completely dissolved to obtain a composite modifier solution.

[0069] The geopolymer activator was prepared by weighing 6.8 kg of water glass (modulus 1.5, solid content 38%) and 1.96 kg of KOH (purity 96.3%) according to a mass ratio of 3.5:1, and then pouring them into a JJ-5 type planetary mixer, and stirring at 35℃ and 350 r / min for 30 min, and then keeping for 10 min to obtain the activator (pH=13.2).

[0070] 2. Coal gangue modification: 30 kg of active coal gangue was added into the above-mentioned composite modifier solution, the liquid-solid ratio was controlled to be 0.5:1, the reaction kettle was heated to 80℃, and the stirring was carried out at 500 r / min for 45 min; after the reaction was completed, the filter cake was sent into a 110℃ oven for drying to constant weight through a plate and frame filter press (0.3 MPa pressure) to obtain modified coal gangue (water demand ratio 91.5%, specific surface area 320 m² / g).

[0071] 3. Dosing and stirring: 60 parts (30 kg) of modified coal gangue, 18 parts (9 kg) of P·O42.5 grade cement (3-day compressive strength 18.5 MPa, initial setting time 185 min), 8 parts (4 kg) of geopolymer activator, 11 parts (5.5 kg) of river sand (0.1-0.6 mm, SiO2=95.3%, mud content 0.7%, 0.3-0.6 mm particle size accounting for 68%), 0.3 parts (0.15 kg) of polycarboxylate superplasticizer (water-reducing rate 30%, air content 2.2%), and 21 parts (10.5 kg) of tap water (pH=7.2, total hardness 220 mg / L, CaCO3) were weighed according to weight parts; first, the solid raw materials were poured into a JJ-5 type planetary mixer, and dry stirring was carried out at 300 r / min for 2.5 min, then the superplasticizer and tap water were added, and wet stirring was carried out at 800 r / min for 5 min to obtain a uniform slurry with a slump of 120 mm and an air content of 2.1%.

[0072] 4. Molding and curing: Pour the slurry into a 40 mm x 40 mm x 160 mm cast iron test mold (inner wall coated with release agent), place it on a HZJ-1 type vibration table (frequency 50 Hz, amplitude 0.5 mm) and vibrate for 25 s to compact, then place it in a 20 ± 2℃, humidity 65% environment for 24 h to demold; send it to a YH-40B type curing box, 20℃, humidity 95% for 28 days.

[0073] 5. Test results: 28-day compressive strength 52.8 MPa, 28-day flexural strength 7.2 MPa, thermal conductivity 0.035 W / (m·℃), impermeability grade P14, sulfate attack resistance coefficient 0.92, production cost 850 yuan / ton.

[0074] Example 2

[0075] A preparation method of coal gangue solid waste synthetic material, comprising the following steps:

[0076] 1. Raw material pretreatment (adapt to high dosage requirements):

[0077] ① Coal gangue pretreatment: select washed coal gangue as in example 1, consistent with the parameters of crushing, drying and screening; when the rotary kiln is heat-activated, pass in 1.0 m³ / h, 99.2% pure CO2 gas, the heating rate is 6℃ / min, the final temperature is 720℃, and the holding time is 80 min, and the active coal gangue (pozzolanic activity index 81%) is obtained after cooling.

[0078] ② Compound modifier preparation: according to the mass ratio of 1.8:1.2:100, take 1.14 kg of KH550 silane coupling agent, 0.78 kg of NaOH and 60 kg of deionized water, and the preparation method is the same as in example 1 (modifier solution pH=12.8).

[0079] ③ Geopolymer activator preparation: the mass ratio of water glass to KOH is 3.5:1, take 7.56 kg of water glass and 2.16 kg of KOH, and the preparation parameters are the same as in example 1 (activator pH=13.3).

[0080] 2. Coal gangue modification: take 32.5 kg of active coal gangue, add the above-mentioned compound modifier solution (liquid-solid ratio 0.52:1), 80℃, 500 r / min stirring reaction for 45 min, filter and dry to obtain modified coal gangue (water requirement ratio 90.8%, specific surface area 335 m² / g).

[0081] 3. batching and mixing: modified coal gangue 65 parts (32.5 kg), P·O42.5 grade cement 15 parts (7.5 kg), geopolymer activator 9 parts (4.5 kg), river sand 10 parts (5 kg), polycarboxylate superplasticizer 0.35 parts (0.175 kg), tap water 22 parts (11 kg) by weight; dry mixing for 2.5 min (300 r / min), wet mixing for 5.5 min (800 r / min), to get a slurry with slump of 115 mm and air content of 2.3%.

[0082] 4. forming and curing: the pouring and vibrating parameters are the same as in example 1, and after demolding for 24 h, the specimen is cured in an environment of 20℃ and 95% humidity for 28 days.

[0083] 5. test results: 28-day compressive strength 50.5 MPa, 28-day flexural strength 6.9 MPa, thermal conductivity 0.036 W / (m·℃), impermeability grade P12, sulfate resistance coefficient 0.90, and production cost 820 yuan / ton (3.5% lower than example 1, and solid waste disposal capacity increased by 8.3%).

[0084] Example 3

[0085] A preparation method of a coal gangue solid waste synthetic material, comprising the following steps:

[0086] 1. raw material pretreatment (emphasis on controlling hazardous waste indicators):

[0087] ① smelting slag pretreatment: select lead and zinc smelting slag (initial Pb leaching 3.2 mg / L, Cd leaching 0.42 mg / L, soluble salt content 5.8%), send to XJ-100 type stirring tank, add tap water at liquid-solid ratio 3:1, stir at 200 r / min for 40 min, filter to remove soluble salt; then soak in 1.5 mol / L hydrochloric acid (purity 36%) at liquid-solid ratio 0.8:1, stir at room temperature for 20 min, filter; filter residue is sent to a 110℃ oven to dry to a moisture content of 0.8%, to get pretreated slag (soluble salt removal rate 92%, pH=7.2, Pb leaching 0.35 mg / L, Cd leaching 0.05 mg / L).

[0088] ② coal gangue pretreatment and modification: same as example 1, take 27.5 kg of active coal gangue, add composite modifier solution (modifier dosage 3.2%), and mix uniformly with 10 parts (5 kg) of pretreated slag and 0.8 parts (0.4 kg) of clinoptilolite powder (particle size 8 μm, specific surface area 320 m² / g, Pb²⁺ adsorption capacity 155 mg / g) to get a mixed aggregate.

[0089] ③ Geopolymer activator preparation: water glass and KOH mass ratio 3.5:1, water glass 5.46 kg, KOH 1.56 kg, preparation parameters same as example 1.

[0090] 2. batching and stirring: take mixed aggregate 65 parts (32.5 kg, of which modified coal gangue 55 parts, pretreated waste residue 10 parts, zeolite powder 0.8 parts), P·O42.5 grade cement 20 parts (10 kg), geopolymer activator 7 parts (3.5 kg), river sand 10 parts (5 kg), polycarboxylic acid type water reducer 0.3 parts (0.15 kg), tap water 23 parts (11.5 kg) by weight; dry mixing for 3 min (300 r / min), wet mixing for 5 min (800 r / min), and the slurry with a slump of 118 mm is obtained.

[0091] 3. molding and curing: same as example 1, demolding after pouring and vibrating for 24 h, curing at 20℃ and humidity 95% for 28 days.

[0092] 4. test results: 28-day compressive strength 49.2 MPa, 28-day flexural strength 6.7 MPa, thermal conductivity 0.037 W / (m·℃), impermeability grade P12, Pb leaching 0.09 mg / L, Cd leaching 0.013 mg / L (both far below the limit value of GB5085.3-2007), production cost 880 yuan / ton.

[0093] Example 4

[0094] A preparation method of coal gangue solid waste synthetic material, comprising the following steps:

[0095] 1. raw material pretreatment (strengthening hazardous waste adsorption):

[0096] ① smelting waste residue pretreatment: select the same batch of lead and zinc smelting waste residue as example 3, water washing and acid leaching parameters are consistent, the moisture content after drying is 0.9%, the removal rate of soluble salt is 91%, pH=7.1, Pb leaching is 0.38 mg / L, and Cd leaching is 0.06 mg / L.

[0097] ② coal gangue pretreatment and modification: same as example 1, take 29 kg of active coal gangue, the dosage of composite modifier is 3.5%, the reaction parameters are consistent, and the modified coal gangue is obtained; mix with 12 parts (6 kg) of pretreated waste residue and 1.0 parts (0.5 kg) of clinoptilolite powder to obtain mixed aggregate (loss on ignition 7.3%, SiO2=55.8%).

[0098] ③ Geopolymer activator preparation: same as example 1, take water glass 6.8 kg, KOH 1.96 kg, and the activator pH=13.2.

[0099] 2. Ingredients and mixing: the mixed aggregate 71 parts (35.5 kg, of which modified coal gangue 58 parts, pretreated waste residue 12 parts, zeolite powder 1.0 part), P·O42.5 grade cement 16 parts (8 kg), geopolymer activator 8 parts (4 kg), river sand 9 parts (4.5 kg), polycarboxylate superplasticizer 0.35 parts (0.175 kg), tap water 24 parts (12 kg) are weighed by weight parts; dry mixing for 3 min (300 r / min), wet mixing for 6 min (800 r / min), and the slurry with a slump of 112 mm is obtained.

[0100] 3. Molding and curing: same as example 1, demolding after pouring and vibrating for 24 h, curing at 20℃, humidity 95% for 28 days.

[0101] 4. Test results: 28-day compressive strength 48.3 MPa, 28-day flexural strength 6.5 MPa, thermal conductivity 0.038 W / (m·℃), impermeability grade P10, Pb leaching 0.13 mg / L, Cd leaching 0.016 mg / L (complying with national standard), production cost 900 yuan / ton (20% increase in hazardous waste disposal amount compared with example 3).

[0102] Comparative example 1

[0103] A preparation method of a coal gangue solid waste synthetic material, comprising the following steps:

[0104] 1. Raw materials and pretreatment (no innovative process):

[0105] ① Coal gangue: the same batch of coal gangue as in example 1 is selected, only crushed to 5 mm and dried at 110℃, without thermal activation and composite modification (activity index of active coal gangue volcanic ash 45%, water demand ratio 125%).

[0106] ② No geopolymer activator, only P·O42.5 grade cement (same as example 1) is used as cementitious material.

[0107] 2. Ingredients and mixing: unmodified coal gangue 40 parts (20 kg), cement 30 parts (15 kg), river sand 15 parts (7.5 kg), polycarboxylate superplasticizer 0.4 parts (0.2 kg), tap water 25 parts (12.5 kg) are weighed by weight parts; dry mixing for 2.5 min, wet mixing for 5 min, and the slurry with a slump of 105 mm (air content 3.0%) is obtained.

[0108] 3. Molding and curing: same as example 1, curing at 20℃, humidity 95% for 28 days.

[0109] 4. Test results: 28-day compressive strength 37.8 MPa (28.4% lower than Example 1), 28-day flexural strength 4.7 MPa (34.7% lower), thermal conductivity 0.052 W / (m·℃) (48.6% higher), impermeability grade P6, production cost 1300 yuan / ton (52.9% higher); due to no modification, the interface between the coal gangue and the cementitious matrix is poor, and fine cracks appear on the surface of the test block, and the compactness is insufficient.

[0110] Comparative Example 2

[0111] A preparation method of a coal gangue solid waste synthetic material, comprising the following steps:

[0112] 1. Raw materials and pretreatment (single modification):

[0113] ① Coal gangue: same as Example 1, after heat activation (consistent parameters), only treated with 2 mol / L NaOH solution (single modification), liquid-solid ratio 0.5:1, stirring at 80°C for 45 min, and then dried to obtain modified coal gangue (pozzolanic activity index 62%, water requirement ratio 108%).

[0114] ② No geopolymer activator, only P·O42.5 grade cement (same as Example 1) is used.

[0115] 2. Dosing and stirring: 60 parts (30 kg) of single modified coal gangue, 25 parts (12.5 kg) of cement, 10 parts (5 kg) of river sand, 0.3 parts (0.15 kg) of polycarboxylate superplasticizer, and 23 parts (11.5 kg) of tap water are weighed according to weight parts; dry mixing for 2.5 min and wet mixing for 5 min to obtain a slurry with a slump of 110 mm.

[0116] 3. Molding and curing: same as Example 1, 20°C, humidity 95%, curing for 28 days.

[0117] 4. Test results: 28-day compressive strength 42.3 MPa (20% lower than Example 1), 28-day flexural strength 5.3 MPa (26.4% lower), thermal conductivity 0.048 W / (m·℃) (37.1% higher), impermeability grade P8, production cost 1100 yuan / ton (29.4% higher); single NaOH modification can only slightly improve the activity, the interface compatibility is insufficient, and the strength of the cementitious system is limited.

[0118] Comparative Example 3

[0119] A preparation method of a coal gangue solid waste synthetic material, comprising the following steps:

[0120] 1. Raw materials and pretreatment (no environmental protection process):

[0121] ① Coal gangue: pretreatment and modification are the same as Example 1, and 27.5 kg (55 parts) of modified coal gangue is obtained.

[0122] ② Smelting waste residue: Untreated lead-zinc smelting waste residue (5kg, 10 portions) was directly selected without water washing or acid leaching. The initial Pb leaching was 3.2mg / L, Cd leaching was 0.42mg / L, and the soluble salt content was 5.8%.

[0123] ③ No zeolite powder was added; the geopolymer activator was prepared in the same way as in Example 3.

[0124] 2. Ingredients and mixing: Weigh 55 parts (27.5 kg) of modified coal gangue, 10 parts (5 kg) of untreated waste residue, 20 parts (10 kg) of cement, 7 parts (3.5 kg) of geopolymer activator, 10 parts (5 kg) of river sand, 0.3 parts (0.15 kg) of water-reducing agent, and 23 parts (11.5 kg) of tap water according to the following weight: dry mix for 3 minutes, wet mix for 5 minutes, and obtain a slurry with a slump of 115 mm.

[0125] 3. Molding and curing: Same as in Example 1, curing at 20℃ and 95% humidity for 28 days.

[0126] 4. Test results: 28-day compressive strength 39.5 MPa (19.7% lower than Example 3), 28-day flexural strength 4.9 MPa (26.9% lower), thermal conductivity 0.050 W / (m·℃) (35.1% higher), impermeability grade P6; Pb leaching 1.12 mg / L (2.7 times higher than the standard), Cd leaching 0.19 mg / L (2.8 times higher than the standard), production cost 950 yuan / ton (7.9% higher); heavy metals and soluble salts precipitated from the untreated waste residue, damaging the cementitious structure, and both strength and environmental protection standards were not met.

[0127] Comparative Example 4

[0128] A method for preparing synthetic materials from coal gangue solid waste includes the following steps:

[0129] 1. Raw materials and pretreatment (traditional process):

[0130] ① Coal gangue: The same batch of coal gangue as in Example 1 was selected, only crushed to 5mm and dried, without thermal activation or modification (volcanic ash activity index 45%).

[0131] ② Cementitious system: Only P·O42.5 grade cement (40 parts, 20kg) is used, with no geopolymers and no zeolite powder.

[0132] 2. Ingredients and mixing: Weigh out 30 parts (15kg) of unmodified coal gangue, 40 parts (20kg) of cement, 15 parts (7.5kg) of river sand, 0.4 parts (0.2kg) of water-reducing agent, and 26 parts (13kg) of tap water by weight; dry mix for 2.5 minutes and wet mix for 5 minutes to obtain a slump of 100mm (air content 3.2%).

[0133] 3. Molding and curing: Same as in Example 1, curing at 20℃ and 95% humidity for 28 days.

[0134] 4. Test results: 28-day compressive strength 35.6 MPa (32.6% lower than Example 1), 28-day flexural strength 4.3 MPa (40.3% lower), thermal conductivity 0.053 W / (m·℃) (51.4% higher), impermeability grade P4; production cost 1500 yuan / ton (76.5% higher), solid waste disposal rate only 30% (50% lower than Example 1); the traditional system relies on high cement consumption, resulting in high cost, low solid waste disposal rate, and poor overall performance.

[0135] The raw material requirements for Examples 1-4 and Comparative Examples 1-4 are as follows:

[0136] Coal gangue: Washed coal gangue, loss on ignition 6.5%, SiO2=58%, Al2O3=18%; Cement: P·O42.5 grade, 3-day compressive strength 18.5MPa; Geopolymer activator: Water glass (modulus 1.5):KOH=3.5:1; Composite modifier: KH550:NaOH:deionized water=1.8:1.2:100; River sand: 0.1-0.6mm, mud content 0.7%; Water-reducing agent: Polycarboxylate, water reduction rate 30%; Smelting waste: Lead-zinc smelting waste, initial Pb leaching 3.2mg / L, Cd leaching 0.42mg / L; Zeolite powder: Clinoptilolite, particle size 8μm, specific surface area 320m². 2 / g.

[0137] The parameter design comparison of the preparation process of Examples 1-4 and Comparative Examples 1-4 is shown in Table 1.

[0138] Table 1:

[0139] Group Core variable (only change here, the rest is the same as the benchmark) Key parameter correspondence (align with example 1) Example 1 (benchmark) Coal gangue 60 parts, no waste residue; double modification (CO2 thermal activation + KH550-NaOH); ternary cementing (containing geopolymer 8 parts) Modifier dosage 3.5%, CO2 flow 0.8 m3 / h, curing humidity 95%, water reducing agent 0.3 parts Example 2 (high dosage) Coal gangue 65 parts (5 parts are added), no waste residue; modifier dosage 3.8%, CO2 flow rate 1.0 m3 / h Cement 15 parts (benchmark 18 parts), activator 9 parts (benchmark 8 parts), the rest of the parameters are the same as example 1 Example 3 (hazardous waste synergy) Coal gangue 55 parts (decrease 5 parts), add 10 parts of pretreated waste residue; zeolite powder 0.8 parts; modifier dosage 3.2% Cement 20 parts (benchmark 18 parts), activator 7 parts (benchmark 8 parts), the rest of the parameters are the same as example 1 Example 4 (limit hazardous waste) Coal gangue 58 parts, add 12 parts of pretreated waste residue; zeolite powder 1.0 parts; wet mixing 6 min (benchmark 5 min) Cement 16 parts, activator 8 parts, the rest of the parameters are the same as example 1 Comparative example 1 (no modification + no synergy) Coal gangue 40 parts (unmodified, no thermal activation); no geopolymer; cement 30 parts (benchmark 18 parts) River sand 15 parts (benchmark 11 parts), water reducing agent 0.4 parts, the rest of the molding and curing parameters are the same as example 1 Comparative example 2 (single modification + no geopolymer) Coal gangue 60 parts (only NaOH single modification); no geopolymer; cement 25 parts (benchmark 18 parts) The rest of the raw material dosage and process parameters are the same as example 1 Comparative example 3 (no pretreatment + no zeolite powder) 10 parts of unpretreated waste residue; no zeolite powder; coal gangue 55 parts (modification is the same as the benchmark) Cement 20 parts, activator 7 parts, the rest of the parameters are the same as example 1 Comparative example 4 (traditional cementitious) Coal gangue 30 parts (unmodified); single cementitious (40 parts); no geopolymer, zeolite powder River sand 15 parts, water reducing agent 0.4 parts, the rest of the molding and curing parameters are the same as example 1

[0140] Note: “Baseline” in Table 1 refers to the relevant data in Example 1.

[0141] The synthetic materials prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance testing according to the following standards: compressive / flexural strength (GB / T17671-2021), thermal conductivity (GB / T10294-2008), impermeability grade (GB / T50082-2019), and heavy metal leaching (GB5085.3-2007). The results are shown in Table 2.

[0142] Table 2:

[0143] Group 28-day compressive strength (MPa) 28-day flexural strength (MPa) Thermal conductivity (W / (m·℃)) Permeability grade Pb leaching (mg / L) Cd leaching (mg / L) Cost (yuan / ton) Example 1 52.8 7.2 0.035 P14 - - 850 Example 2 50.5 6.9 0.036 P12 - - 820 Example 3 49.2 6.7 0.037 P12 0.09 0.013 880 Example 4 48.3 6.5 0.038 P10 0.13 0.016 900 Comparative example 1 37.8 4.7 0.052 P6 - - 1300 Comparative example 2 42.3 5.3 0.048 P8 - - 1100 Comparative example 3 39.5 4.9 0.050 P6 1.12 0.19 950 Comparative example 4 35.6 4.3 0.053 P4 - - 1500

[0144] The data in Table 2 shows that:

[0145] 1. The 28-day compressive strength (48.3-52.8 MPa) of Examples 1-4 is more than 30% higher than that of Comparative Examples 1-4 (35.6-42.3 MPa): ① Comparative Example 1 has poor interfacial bonding due to the lack of modification and geopolymer, resulting in a strength of only 37.8 MPa; ② Comparative Example 2 has insufficient activity improvement due to single modification, resulting in a strength of 42.3 MPa; ③ The Examples, through dual modification and ternary synergy, make the cementitious phase more compact and significantly improve the strength, thus resolving the contradiction between high dosage and high performance.

[0146] 2. The thermal conductivity of the embodiment (0.035-0.038 W / (m·℃)) is reduced by more than 25% compared with the comparative example (0.048-0.053 W / (m·℃)), and the impermeability grade (P10-P14) is increased by more than 50% compared with the comparative example (P4-P8): because the modified coal gangue has a tight interface with the matrix, and zeolite powder fills the pores to form a dense structure, improving the thermal insulation and impermeability performance, and solving the problem of poor comprehensive performance of traditional materials.

[0147] 3. The heavy metal leaching concentrations in Examples 3-4 were far below the standard limits, while the Pb leaching concentration in Comparative Example 3 (untreated waste residue) was 1.12 mg / L and the Cd leaching concentration was 0.19 mg / L, both exceeding the standard by more than 3 times. This indicates that the three-step pretreatment of "water washing-acid leaching-zeolite powder adsorption" can effectively seal heavy metals and solve the problem of difficult co-disposal of hazardous waste.

[0148] 4. The cost of the example (820-900 yuan / ton) is more than 35% lower than that of Comparative Example 1 (1300 yuan / ton) and Comparative Example 4 (1500 yuan / ton): Due to the high content of coal gangue replacing cement, the amount of geopolymer activator is reduced, and high-temperature curing is not required, which solves the problem of high cost of traditional technology.

[0149] Special note: In Example 4, the 28-day compressive strength is 48.3 MPa (slightly lower than in Example 1). This is mainly because 12 parts of high-proportion hazardous waste replaced coal gangue. Although the strength decreased slightly, it still met the invention index. Moreover, the amount of hazardous waste disposed of increased by 20%, resulting in better overall benefits.

[0150] In summary, the present invention has the following advantages:

[0151] 1. Dual modification process: thermal activation (CO2 atmosphere) destroys the crystal lattice of coal gangue, and the composite modifier (KH550-NaOH) forms an organic-inorganic coating on the surface, which synergistically improves activity and interfacial compatibility;

[0152] 2. Ternary Synergistic Cementation: Geopolymers activate the activity of coal gangue, cement provides early strength, and zeolite powder adsorbs heavy metals and fills pores. The three work synergistically to improve strength and durability.

[0153] 3. Deep pretreatment of hazardous waste: Water washing removes soluble salts, acid leaching dissolves heavy metals, and zeolite powder adsorbs residues. These three steps work together to achieve the harmless treatment of hazardous waste.

[0154] 4. Low-cost curing at room temperature: No high temperature is required; high performance can be achieved by curing at room temperature (20±2℃), making it suitable for large-scale production.

[0155] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing synthetic materials from coal gangue solid waste, characterized in that, Includes the following steps: (1) Coal gangue pretreatment: After being crushed, coal gangue is dried to a moisture content of ≤1%, sieved, and then activated at high temperature to obtain activated coal gangue. (2) Modification of coal gangue: Prepare a composite modifier solution of KH550 silane coupling agent, NaOH, and deionized water at a mass ratio of 1.5-2.0:1.0-1.5:

100. Add the active coal gangue from step (1) to the composite modifier solution, control the liquid-solid ratio to 0.4-0.6:1, stir thoroughly at a temperature between 70-90℃, filter and dry to constant weight to obtain modified coal gangue; (3) Ingredient mixing: By weight, mix 55-70 parts of modified coal gangue, 12-20 parts of silicate cement, 6-10 parts of geopolymer activator, 8-14 parts of river sand, 0.2-0.4 parts of polycarboxylate superplasticizer, 0.5-1.0 parts of zeolite powder, and 18-24 parts of tap water from step (2); first dry mix, then wet mix, to obtain a uniform slurry; (4) Molding and curing: The slurry from step (4) is poured into the test mold, vibrated to compact it, demolded, and cured for 28 days to obtain the synthetic material.

2. The method for preparing synthetic materials from coal gangue solid waste according to claim 1, characterized in that, In step (1), the coal gangue is crushed to a particle size ≤5mm; after drying, it is sieved through a 60μm standard sieve and then activated at high temperature. The activation conditions are: heating rate 5-8℃ / min, final temperature 650-750℃, holding temperature for 60-90min, introducing CO2 gas with a volume fraction of 5-8%, and cooling to room temperature to obtain activated coal gangue. The coal gangue is washed / mined coal gangue with a loss on ignition ≤8%, SiO2 ≥55%, and Al2O3 ≥15%.

3. The method for preparing synthetic materials from coal gangue solid waste according to claim 1, characterized in that, In step (3), the geopolymer activator formulation is as follows: Water glass:KOH = 3-4:1, modulus 1.2-1.8; River sand has a particle size of 0.1-0.6 mm, SiO2 ≥ 95%, a particle size of 0.3-0.6 mm ≥ 65%, and a mud content ≤ 0.8%.

4. The method for preparing synthetic materials from coal gangue solid waste according to claim 3, characterized in that, The geopolymer activator should be prepared at 30-40℃, stirred at 300-400r / min, and kept at that temperature for 10 minutes before use.

5. The method for preparing synthetic materials from coal gangue solid waste according to claim 1, characterized in that, In step (2), the KH550 effective component in the composite modifier solution is ≥98%, the NaOH purity is ≥96%, and the deionized water conductivity is ≤10μS / cm.

6. The method for preparing synthetic materials from coal gangue solid waste according to claim 1, characterized in that, In step (4), the impermeability grade of the synthetic material is ≥P10 and the sulfate erosion resistance coefficient is ≥0.

85.

7. The method for preparing synthetic materials from coal gangue solid waste according to any one of claims 1-6, characterized in that, In step (3), the modified coal gangue is partially replaced with pretreated waste residue.

8. The method for preparing synthetic materials from coal gangue solid waste according to claim 7, characterized in that, The pretreatment process for waste residue is as follows: After the smelting waste residue is washed with water at a liquid-to-solid ratio of 3:1, it is then treated with 1.5 mol / L hydrochloric acid at a liquid-to-solid ratio of 0.8:1, followed by filtration and drying until the moisture content is ≤1%, to obtain pretreated waste residue.

9. The method for preparing synthetic materials from coal gangue solid waste according to claim 7, characterized in that, 55-70 parts of modified coal gangue are replaced with 8-12 parts of pretreated waste residue.