Building waste recycling method

Abstract

The invention relates to the technical field of building materials, in particular to a building waste recycling method. The method comprises the following steps: removing impurities from the building waste, crushing, and treating with an acid solution and carbonate in sequence to obtain a first precipitate containing silicon dioxide, calcium sulfate and alpha-ferric oxide, a second precipitate containing calcium carbonate, magnesium carbonate and aluminum hydroxide, and a second solution containing sodium salt and potassium salt; coating the first precipitate with polysiloxane to obtain a coating, crystallizing and dehydrating the second solution to obtain a solid, and ball-milling and mixing the solid and the coating to obtain a first mixture; heating and hydrating the second precipitate to a second mixture; and mixing the first mixture with the second mixture to obtain the flame-retardant material. According to the invention, calcium carbonate, magnesium hydroxide, aluminum hydroxide and polysiloxane are synergistically flame-retardant in parallel at 200-1000 DEG C, and silicon dioxide, carbonate, calcium sulfate and ferric oxide coated with polysiloxane form a composite silicate glass phase at 1000 DEG C or above for further flame retardance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, and particularly relates to a method for recycling building waste. BACKGROUND

[0002] The building waste refers to the residual mud, residual slag, mud and other waste generated in the process of construction, demolition, repair and decoration of residents by construction and construction units or individuals. At present, most of the building waste is directly transported to the suburbs or rural areas by the construction units without any treatment, and is open-air stacked or landfilled, which consumes a large amount of construction funds such as land acquisition fee, garbage cleaning fee and the like. Meanwhile, the problems such as scattering and dust, flying ash and sand and the like in the process of cleaning and stacking cause serious environmental pollution. Therefore, the pollution prevention and treatment of the building waste is imminent, and the resource treatment of the building waste is the first choice.

[0003] The resource treatment of the building waste refers to the management and technical measures for recycling useful substances and energy from the building waste. The main chemical components of the building waste are mainly oxides of silicon, calcium, aluminum and iron, but the content fluctuates greatly, and the specific composition is highly dependent on the source and classification degree of the waste. Clay bricks and concrete are the two most common building waste materials in construction waste and old city reconstruction. If the main components in the two kinds of building waste can be effectively recycled, the land occupation of the building waste can be greatly reduced, which meets the current economic interests and long-term social interests. The mineral composition of the clay brick generally includes quartz SiO2, kaolinite Al2O3·2SiO2·2H2O, albite NaAlSi3O8, anorthite CaAl2Si2O8, hematite Fe2O3, potassium feldspar KAlSi3O8, calcite CaCO3 and the like. The mineral composition of the concrete generally includes quartz SiO2, ettringite 3CaO·Al2O3·3CaSO4·32H2O, hydrated calcium silicate Ca3Si2O7·2H2O, calcium oxide CaO, calcium hydroxide Ca(OH)2, magnesium oxide MgO, muscovite KAl2(AlSi3O 10 )(OH)2 and the like.

[0004] Currently, there are mainly two ways to utilize waste clay bricks and concrete construction waste: one is to utilize some physical and chemical properties of construction waste, such as using waste clay bricks and waste concrete for paving roads, land backfilling, etc. This kind of direct use in construction engineering, foundation engineering and agriculture, although the consumption of construction waste is large, but does not fully play the value of construction waste as a secondary resource. The second is to treat construction waste as a valuable renewable resource, according to the specific characteristics of waste clay bricks and waste concrete, to extract or prepare new products from them according to a certain process, such as using waste clay bricks, concrete to prepare recycled concrete, cement, recycled wall materials, cementitious materials, refractory materials, etc. For example, the patent document with the publication number CN117142868A discloses a production process of a refractory material, which contains 60-120 parts of construction waste, 20-40 parts of wood fiber, 10-20 parts of composite flame retardant, 30-60 parts of nano calcium silicate, 40-80 parts of lime. However, the prior art still needs to add a large amount of composite flame retardant, nano calcium carbonate, lime and other materials, and does not effectively utilize the components in the construction waste to achieve fire resistance. SUMMARY

[0005] The present application solves the above problems, and provides a construction waste recycling method which fully utilizes the components in the construction waste and recycles the construction waste into a flame-retardant material.

[0006] The technical solution of the present application is to provide a construction waste recycling method, comprising the following steps: S1. Selecting construction waste, the construction waste comprising clay bricks and concrete; after removing light impurities in the construction waste by air separation, crushing the construction waste into particulate matter; S2. Adding the particulate matter into an acid solution to react, obtaining a first precipitate and a first solution; the first precipitate comprising silicon dioxide, calcium sulfate and alpha-iron oxide, and the first solution comprising calcium salt, aluminum salt, sodium salt, magnesium salt and potassium salt; S3. Adding carbonate to the first solution to obtain a second precipitate and a second solution; the second precipitate comprising calcium carbonate, magnesium carbonate and aluminum hydroxide, and the second solution comprising sodium salt and potassium salt; S4. Coating the first precipitate with polysiloxane to obtain a coated material, crystallizing and dehydrating the second solution to obtain a solid material, and ball-milling the solid material and the coated material to obtain a first mixture; S5. Heating the second precipitate to 350-450℃, then hydrating and drying to obtain a second mixture; S6. Mixing the first mixture and the second mixture to obtain a flame-retardant material.

[0007] In the present application, the construction waste is divided into a first precipitate containing silicon dioxide, calcium sulfate and alpha-iron oxide, a second mixture containing calcium carbonate, magnesium hydroxide and aluminum hydroxide, and a solid containing at least sodium carbonate and potassium carbonate through several steps, and then is combined with polysiloxane to obtain a material with good flame retardation in a wide temperature range.

[0008] Specifically, the flame-retardant material comprises a first mixture and a second mixture, the first mixture is a coating of polysiloxane on silicon dioxide, calcium sulfate and alpha-iron oxide, and a structure of sodium carbonate and potassium carbonate coated by ball milling, and the second mixture is a mixture of calcium carbonate, magnesium hydroxide and aluminum hydroxide. Overall, calcium carbonate, magnesium hydroxide, aluminum hydroxide and polysiloxane are mixed in parallel: below 300℃, flame retardation by the decomposition and dehydration of aluminum hydroxide; at 300-500℃, flame retardation by the decomposition and dehydration of magnesium hydroxide and oxygen isolation by magnesium oxide product; at 400-800℃, heat and oxygen isolation by the formation of a silicon-carbon coating layer of polysiloxane; at 800-1000℃, oxygen isolation and combustion assistance by the decomposition of calcium carbonate to produce carbon dioxide and calcium oxide. Meanwhile, the polysiloxane is further coated with silicon dioxide, calcium sulfate, alpha-iron oxide and sodium carbonate, potassium carbonate, and at temperatures above 1000℃, calcium sulfate decomposes into calcium oxide, molten sodium carbonate or / and potassium carbonate reacts with silicon dioxide to form sodium silicate or / and potassium silicate, and further forms a composite silicate glass phase with iron oxide and calcium oxide, which can flow and wrap unreacted particles, improving the density of the silicon-carbon coating layer and further flame retardation.

[0009] It can be understood that although calcium sulfate produces sulfur dioxide, first, its concentration is very low (almost none in discarded clay bricks, and the mass fraction of SO3 in discarded concrete is not more than 1wt%); second, it needs to penetrate the polysiloxane silicon-carbon coating layer to overflow, and the silicon-carbon coating layer has a certain microporous adsorption property to adsorb and fix sulfur dioxide; third, there is also iron oxide, which may oxidize sulfur dioxide to sulfate at high temperatures. Therefore, no significant harmful gas is produced during the flame retardation process.

[0010] Based on this, the technical solution of the present application is completed, in which, in addition to polysiloxane, no other substances are added, and the compound characteristics of the construction waste itself are fully utilized, improving the utilization rate of construction waste.

[0011] In step S1The building waste includes clay bricks and concrete. The main chemical components of both are SiO2, Al2O3 (as aluminum oxide structural units in mineral lattices, with high activity), CaO, and a relatively small amount of Fe2O3 (mainly in the form of α, with low activity), MgO, Na2O, K2O, and SO3. The proportions of SiO2, Al2O3, and CaO are more than 80 wt%.

[0012] Air separation is used to remove light impurities such as plastic and wood from the building waste.

[0013] In some preferred embodiments, a magnetic separation operation is further included to remove iron from the recycled building waste.

[0014] When the building waste is crushed into granular material, the smaller the particle size of the granular material, the more favorable it is for subsequent reactions. In some preferred embodiments, the particle size of the granular material is not more than 50 mm. Preferably, it is not more than 10 mm.

[0015] To achieve the crushing of the building waste, a multi-step crushing method can be adopted. For example, the crushing process includes a first crushing step, a second crushing step, and a screening step. A crusher is used to crush the building waste into granular material. Then, a roller mill is used to further crush the granular material. Finally, a screening step is performed to separate the granular material with a particle size of not more than 50 mm, and the granular material with a particle size of more than 50 mm is returned to the second crushing step for further crushing.

[0016] In step S2 The acid solution used can be any acid except hydrofluoric acid. However, some acids such as sulfuric acid, hydrochloric acid, and nitric acid will introduce sulfur, chlorine, and nitrogen elements into the system, which are not desired in the flame retardant material. Therefore, in some preferred embodiments, the acid solution is acetic acid. Based on this, the calcium salt, aluminum salt, sodium salt, magnesium salt, and potassium salt in the first solution are all acetate salts.

[0017] In some preferred embodiments, to ensure the dissolution effect of acetic acid on the above-mentioned ores, the acid solution is acetic acid with a mass concentration of not less than 30%, and the reaction temperature of step S2 is not less than 60°C. Further preferably, the acid solution is acetic acid with a mass concentration of 30% to 50%, and the reaction temperature of step S2 is 60°C to 80°C. For example, the mass concentration of acetic acid can be 30%, 35%, 40%, 45%, or 50%, and the reaction temperature can be 60°C, 65°C, 70°C, 75°C, or 80°C.

[0018] The amount of acid solution used is not limited, and the acid solution can just cover the granular material.

[0019] In some preferred embodiments, in order to facilitate subsequent reactions, the obtained first precipitate is dried and then further ground and sieved to a particle size of no more than 1 mm. Preferably, the further grinding and sieving is to a particle size of no more than 0.5 mm.

[0020] In step S2, both calcium sulfate precipitate and calcium salt can be obtained, because the sulfate ions in the system only come from ettringite, and the content is low, and most of the calcium ions form soluble substances with acetate ions. In addition, the first precipitate can also contain a small amount of aluminum oxide.

[0021] In step S3 The carbonates used for reaction with the first solution can be carbon dioxide, carbonic acid, any soluble carbonate or / and bicarbonate containing carbonate ions, or a mixture of any two or more of these compounds. For example, the carbonate ions come from at least one of carbon dioxide, carbonic acid, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate.

[0022] Preferably, the carbonate ions come from sodium carbonate and / or potassium carbonate, which have better performance in terms of cost and stability, and increase the content of sodium ions and / or potassium ions in the system, thereby increasing the amount of silicate generated during the fire-retardant process at high temperature, thereby improving the fire-retardant effect.

[0023] Further preferably, the carbonate ions come from sodium carbonate and potassium carbonate, which increase the amount of sodium silicate and potassium silicate generated during the fire-retardant process at high temperature, and the sodium silicate promotes the formation of carbonized layer, and the potassium silicate has higher thermal stability, thereby improving the fire-retardant performance. The amount ratio of sodium carbonate to potassium carbonate is not limited. For example, the mass ratio of sodium carbonate to potassium carbonate is (1~10):1, such as 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0024] The amount ratio of the first solution to the carbonate is not limited. For example, the carbonate raw material is added to the first solution while stirring until no new precipitate is produced or no bubbles are produced.

[0025] In some preferred embodiments, in order to facilitate subsequent use, the obtained second precipitate is dried and then further ground and sieved to a particle size of no more than 1 mm. Preferably, the further grinding and sieving is to a particle size of no more than 0.5 mm.

[0026] In step S3, the second precipitate can also contain part of magnesium hydroxide, which comes from the hydrolysis of part of magnesium carbonate.

[0027] In step S4The purpose of coating the first precipitate with polysiloxane is to introduce polysiloxane to compensate for the fire-retardant performance of the system in the range of 400-800°C, to guide the migration and coverage of silica and other materials on the surface of the material to promote the formation of a dense layer and improve the fire-retardant effect, and to isolate calcium sulfate and prevent the escape of a small amount of sulfur dioxide during the fire-retardant process.

[0028] The coating method is not limited, and in some preferred embodiments, the coating includes the following steps: dispersing the first precipitate in an aqueous ethanol solution, hydrolyzing under alkaline conditions after adding a polysiloxane precursor to obtain a coated material.

[0029] In some preferred embodiments, the polysiloxane precursor includes methyltrimethoxysilane and polyethylene glycol modified siloxane. Methyltrimethoxysilane as the main precursor provides high cross-linking density, and polyethylene glycol modified siloxane as the auxiliary precursor improves the compatibility of calcium sulfate and inhibits the agglomeration of iron oxide. Preferably, the mass ratio of methyltrimethoxysilane to polyethylene glycol modified siloxane is 1:(0.1-0.5), and for example, it can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, or 1:0.5.

[0030] In some preferred embodiments, the mass ratio of the polysiloxane precursor to the first precipitate is 1:(4-8). For example, it can be 1:4, 1:5, 1:6, 1:7, or 1:8.

[0031] In addition, preferably, the mass concentration of anhydrous ethanol in the aqueous ethanol solution is 50%-70%, and for example, it can be 50%, 55%, 60%, 65%, or 70%. The amount ratio of the first precipitate to the aqueous ethanol solution is 1 kg:(3-5) L, and for example, it can be 1:3, 1:3.5, 1:4, 1:4.5, or 1:5. After adding the first precipitate to the aqueous ethanol solution, a dispersant polyvinylpyrrolidone is added to promote dispersion stability.

[0032] The method for crystallizing and dehydrating the second solution is not limited, and for example, when the acid solution uses acetic acid, the second solution is heated to 90-105°C, and then solid-liquid separation is performed to obtain a solid containing sodium carbonate and a first liquid; the first liquid is slowly cooled to 20°C, and then solid-liquid separation is performed to obtain a solid containing sodium acetate and a second liquid; the second liquid is further cooled to 5-10°C, and then solid-liquid separation is performed to obtain a solid containing potassium acetate and potassium carbonate; sodium carbonate and sodium acetate are vacuum dried at 100-120°C to complete dehydration; potassium acetate and potassium carbonate are vacuum dried at 50-60°C to complete dehydration; and finally, the solid is obtained by mixing.

[0033] The purpose of ball milling the solid and the coating is to make the polysiloxane physically coat the sodium salt or / and potassium salt, and increase the probability of the sodium salt or / and potassium salt generating silicate with silica at high temperature, and continuing to compound with calcium oxide and iron oxide.

[0034] To achieve the purpose of physical coating, in some preferred embodiments, the solid and the coating are ball milled in a water-free environment at 200-400 rpm, a ball-to-material ratio of 10-20:1 for 2-6 h. For example, the rotation speed can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm; the ball-to-material ratio can be 10:1, 12:1, 14:1, 16:1, 18:1, 20:1; and the ball milling time can be 2 h, 3 h, 4 h, 5 h, 6 h.

[0035] In step S5 The purpose of heating and hydrating the second precipitate is to convert magnesium oxide into magnesium hydroxide. 350-450℃ is a range in which magnesium carbonate decomposes but calcium carbonate does not decompose, for example, the heating temperature can be 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃. It can be understood that at 350-450℃, although aluminum hydroxide will also dehydrate, it will not completely dehydrate, and it needs to be heated to above 1000℃ to completely dehydrate; the amorphous aluminum oxide obtained at 350-450℃ can be hydrated into aluminum hydroxide again in the subsequent hydration process.

[0036] To improve the hydration effect, in some preferred embodiments, the hydration includes the following steps: stirring in hot water at 60-80℃ for 1-2 h. For example, the temperature can be 60℃, 65℃, 70℃, 75℃, 80℃; and the stirring time can be 1 h, 1.5 h, 2 h.

[0037] In step S6 The mixing method is not limited, and in some preferred embodiments, the first mixture is added to the second mixture in batches under continuous stirring.

[0038] The beneficial effects of the present application are: The present application provides a method for recycling construction waste, which divides the construction waste into a first precipitate containing silicon dioxide, calcium sulfate and α-iron oxide, a second mixture containing calcium carbonate, magnesium hydroxide and aluminum hydroxide, and a solid containing at least sodium carbonate and potassium carbonate, and then cooperates with polysiloxane to obtain a material with good flame retardation in a wide temperature range. Without adding other flame retardants, the compound characteristics of the construction waste are fully utilized, and the utilization rate of the construction waste is improved. DETAILED DESCRIPTION

[0039] The following is a specific embodiment of the present application, and the technical solutions of the present application are further described, but the present application is not limited to these embodiments. Example 1

[0040] A building waste recycling method, comprising the following steps: S1. Selecting building waste, the building waste including clay bricks and concrete; after removing light impurities in the building waste by air separation, the building waste is crushed, ground and sieved in sequence into particulate matter with a particle size of not more than 50 mm (denoted as K).

[0041] For subsequent comparison, only part of the particulate matter K is taken to continue the following steps.

[0042] S2. Adding an acetic acid solution with a mass concentration of 30% to the particulate matter K until the acetic acid solution completely covers the particulate matter K. The system is heated to 60°C and continuously stirred until no new precipitate is generated. Solid-liquid separation is performed to obtain a first precipitate (denoted as K-C1) and a first solution (denoted as K-R1), and the first precipitate K-C1 is dried and then crushed, ground and sieved to a particle size of not more than 1 mm. The first precipitate K-C1 includes silicon dioxide, calcium sulfate and α-iron oxide, mainly silicon dioxide. The first solution K-R1 includes calcium acetate, aluminum acetate, sodium acetate, magnesium acetate and potassium acetate, mainly calcium acetate and aluminum acetate.

[0043] For subsequent comparison, only part of the first precipitate K-C1 and part of the first solution K-R1 are taken to continue the following steps.

[0044] S3. While stirring, a mixture of sodium carbonate and potassium carbonate with a mass ratio of 5:1 is added to the first solution K-R1 until no new precipitate is generated. Solid-liquid separation is performed to obtain a second precipitate (denoted as K-R1-C2) and a second solution (denoted as K-R1-R2), and the second precipitate K-R1-C2 is dried and then crushed, ground and sieved to a particle size of not more than 1 mm. The second precipitate K-R1-C2 includes calcium carbonate, magnesium carbonate and aluminum hydroxide, and the second solution K-R1-R2 includes sodium carbonate, sodium acetate, potassium carbonate and potassium acetate.

[0045] For subsequent comparison, only part of the second precipitate K-R1-C2 is taken to continue the following steps.

[0046] S4. After drying the first precipitate K-C1 at 110°C, the first precipitate K-C1 and polyvinylpyrrolidone were dispersed in a mixture of anhydrous ethanol and water (mass ratio of anhydrous ethanol to water was 2:1) at a mass ratio of 1 kg:0.01 kg:4 L, ultrasonic dispersion was performed, and ammonia water was added to adjust the pH of the system to about 10. Then, 20% of the mass of the first precipitate K-C1 of methyltrimethoxysilane and a polyethylene glycol modified siloxane mixture (mass ratio of methyltrimethoxysilane to polyethylene glycol modified siloxane was 1:0.3) was added to the system under high-speed stirring, and the system was stirred at 60°C for 6 h. Solid-liquid separation was performed to obtain a coated material (denoted as K-C1-B).

[0047] For subsequent comparison, only part of the coated material K-C1-B was taken to continue the following steps.

[0048] The second solution K-R1-R2 was heated to 105°C, and then solid-liquid separation was performed to obtain a solid containing sodium carbonate and a first liquid. The first liquid was slowly cooled to 20°C, and then solid-liquid separation was performed to obtain a solid containing sodium acetate and a second liquid. The second liquid was further cooled to 5°C, and then solid-liquid separation was performed to obtain a solid containing potassium acetate and potassium carbonate. The solid containing sodium carbonate and sodium acetate was vacuum dried at 110°C to complete dehydration. The solid containing potassium acetate and potassium carbonate was vacuum dried at 50°C to complete dehydration. Finally, a solid material (denoted as K-R1-R2-G) was obtained by mixing.

[0049] For subsequent comparison, only part of the solid material K-R1-R2-G was taken to continue the following steps.

[0050] The coated material K-C1-B and the solid material K-R1-R2-G were added to a ball mill, and ball milling was performed in an anhydrous environment at a ball-to-material ratio of 15:1 and a speed of 300 rpm for 4 h to obtain a first mixture (denoted as H1).

[0051] S5. The second precipitate K-R1-C2 was heated to 400°C in air and maintained for 30 min. Then, hot water at 70°C was added to the heated second precipitate K-R1-C2, and the system temperature was maintained at 70°C. After stirring for 2 h, solid-liquid separation was performed, and the solid was dried at 80°C to obtain a second mixture (denoted as H2).

[0052] S6. The first mixture and the second mixture were mixed to obtain a flame-retardant material. Example 2

[0053] This example is basically the same as Example 1, except that the sodium carbonate was reacted with the first solution K-R1.

[0054] Specifically, the first solution K-R1 obtained in step S2 of Example 1 and the coating K-C1-B obtained in step S4 are subjected to the following steps.

[0055] S3. Sodium carbonate is added to the first solution K-R1 under stirring until no new precipitate is formed. Solid-liquid separation is performed to obtain a second precipitate (denoted as K-R1-C2') and a second solution (denoted as K-R1-R2'), and the second precipitate K-R1-C2' is dried, crushed, ground and sieved to a particle size of not more than 1 mm.

[0056] S4. The second solution K-R1-R2' obtained in this example is heated to 105°C, and then solid-liquid separation is performed to obtain a solid containing sodium carbonate and a first liquid; the first liquid is slowly cooled to 20°C, and then solid-liquid separation is performed to obtain a solid containing sodium acetate and a second liquid; the second liquid is further cooled to 5°C, and then solid-liquid separation is performed to obtain a solid containing potassium acetate and potassium carbonate; the solid containing sodium carbonate and sodium acetate is vacuum dried at 110°C to complete dehydration; the solid containing potassium acetate and potassium carbonate is vacuum dried at 50°C to complete dehydration; and finally, a solid product (denoted as K-R1-R2'-G') is obtained by mixing.

[0057] The coating K-C1-B in Example 1 and the solid product K-R1-R2'-G' obtained in this example are added to a ball mill, and ball milling is performed in a water-free environment at 300 rpm and a ball-to-material ratio of 15:1 for 4 h to obtain a first mixture.

[0058] S5. The second precipitate K-R1-C2' obtained in this example is heated to 400°C in air and maintained for 30 min. Then, hot water at 70°C is added to the heated second precipitate K-R1-C2', and the system temperature is maintained at 70°C. After stirring for 2 h, solid-liquid separation is performed, and the solid is dried at 80°C to obtain a second mixture.

[0059] S6. The first mixture and the second mixture are mixed to obtain a flame-retardant material. Example 3

[0060] This example is basically the same as Example 1, except that the precursor of polysiloxane is only methyltrimethoxysilane.

[0061] Specifically, the first precipitate K-C1 obtained in step S2 of Example 1, the solid product K-R1-R2-G obtained in step S4, and the second mixture H2 obtained in step S5 are subjected to the following steps.

[0062] S4. After drying the first precipitate K-C1 at 110°C, the first precipitate and polyvinylpyrrolidone are dispersed in a mixture of anhydrous ethanol and water (mass ratio of anhydrous ethanol to water is 2:1) according to a mass ratio of 1 kg:0.01 kg:4 L, ultrasonic dispersion is performed, and ammonia water is added to adjust the pH of the system to about 10. Then, under high-speed stirring, methyltrimethoxysilane with a mass of 20% of the mass of the first precipitate K-C1 is added to the system, and after stirring at 60°C for 6 h, solid-liquid separation is performed to obtain a coated material (denoted as K-C1-B’).

[0063] The coated material K-C1-B’ obtained in this example and the solid material K-R1-R2-G in Example 1 are added to a ball mill, and ball milling is performed in an anhydrous environment at 300 rpm and a ball-to-material ratio of 15:1 for 4 h to obtain a first mixture.

[0064] S5. The second mixture H2 obtained in step S5 of Example 1 is taken.

[0065] S6. The first mixture obtained in this example is mixed with the second mixture H2 in Example 1 to obtain a flame-retardant material.

[0066] Blank Example

[0067] The building waste particle material K obtained in step S1 of Example 1 is further crushed, rolled, and sieved to a particle size of not more than 1 mm, serving as a blank example. Comparative Example 1

[0068] This comparative example is basically the same as Example 1, except that the coating of polysiloxane and ball milling are not performed.

[0069] Specifically, the first precipitate K-C1 obtained in step S2 of Example 1, the solid material K-R1-R2-G obtained in step S4, and the second mixture H2 obtained in step S5 are further subjected to the following steps.

[0070] S4. After drying the first precipitate K-C1 at 110°C, the first precipitate and polyvinylpyrrolidone are dispersed in a mixture of anhydrous ethanol and water (mass ratio of anhydrous ethanol to water is 2:1) according to a mass ratio of 1 kg:0.01 kg:4 L, ultrasonic dispersion is performed, and ammonia water is added to adjust the pH of the system to about 10. Then, under high-speed stirring, methyltrimethoxysilane with a mass of 20% of the mass of the first precipitate K-C1 is added to the system, and after stirring at 60°C for 6 h, solid-liquid separation is performed to obtain a coated material (denoted as K-C1-B’).

[0071] The mixture obtained in this comparative example is uniformly mixed with the solid material K-R1-R2-G in Example 1 to obtain a first mixture.

[0072] S5. The second mixture H2 obtained in step S5 of Example 1 is taken.

[0073] S6. The first mixture obtained in this example is mixed with the second mixture H2 in Example 1 to obtain a flame-retardant material. Comparative Example 2

[0074] The comparative example is basically the same as example 1, the difference is only that the heated hydration is not carried out.

[0075] Specifically, the first mixture H1 obtained in step S4 of example 1 and the second precipitate K-R1-C2 obtained in step S3 are continued to the following steps.

[0076] S5. Take the second precipitate as the second mixture.

[0077] S6. Mix the second mixture obtained in the comparative example with the first mixture H1 in example 1 to obtain a flame-retardant material. Flame-retardant performance detection

[0078] The flame-retardant material obtained in the example, the blank example and the comparative example is respectively co-extruded with wood powder and HDPE to obtain a wood-plastic composite board (according to mass parts, 50 parts of wood powder, 40 parts of HDPE and 10 parts of the flame-retardant material).

[0079] According to GB / T 5464-2010 Building Materials Non-combustibility Test Method, the combustion performance of the obtained wood-plastic composite board is tested respectively, and the results are shown in the following table 1.

[0080] Table 1.

[0081] As shown in table 1, the building waste is treated in the present application, and a material with good flame-retardant performance can be obtained.

[0082] Specifically: in the blank example, directly using the particles of construction waste, because there are more impurities, affecting its compatibility and dispersibility in wood powder and HDPE, at the same time, most of its components are oxides as crystal lattices, do not have the effect of forming a protective layer at high temperature, and lack of polysiloxane to form a silicon-carbon coating layer, so the flame retardant performance is poor; at the same time, some oxides have the problem of exothermic reaction with water, causing a significant temperature rise. In Comparative Example 1, the direct mixing of the first precipitate, the crystalline dehydrated solid of the second solution, polysiloxane and the second mixture, compared with the blank example, reduces impurities, increases polysiloxane, and obtains carbonates and hydroxides with better flame retardant performance, and the flame retardant performance is improved; but compared with Example 1, the flame retardant performance is still insufficient, which may be due to the lack of polysiloxane coating, poor compatibility and dispersibility of silicon dioxide in wood powder and HDPE, and the lack of polysiloxane aggregation with silicon dioxide and sodium carbonate, potassium carbonate and sodium silicate, potassium silicate with good flame retardant performance. In Comparative Example 2, the second precipitate is not heated and hydrated, and the main difference from Example 1 is magnesium carbonate and magnesium hydroxide, and magnesium hydroxide has better synergistic effect than magnesium carbonate and magnesium hydroxide in flame retardant, which may be due to the overlapping of the decomposition temperature of magnesium hydroxide and the main chain decomposition temperature of polysiloxane, the endothermic effect of magnesium hydroxide decomposition to release water vapor to delay the decomposition of polysiloxane, and polysiloxane strengthens the magnesium oxide barrier generated by magnesium hydroxide; while the decomposition temperature range of magnesium carbonate is wider, and the high temperature decomposition zone of polysiloxane is weaker, and the endothermic effect of calcium carbonate decomposition to release carbon dioxide to delay the decomposition of polysiloxane is not as good as magnesium hydroxide, and the synergistic effect of the two is limited.

[0083] The specific embodiments described herein merely exemplify the spirit of the present application. Those skilled in the art of the present application can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, without deviating from the spirit of the present application or exceeding the scope defined by the appended claims.

Claims

1. A method of recycling construction waste, characterized by: The method comprises the following steps: S1. selecting construction waste, the construction waste comprising clay bricks and concrete; the construction waste is crushed into granular materials after light impurities in the construction waste are removed by air separation; S2. the granular materials are added into an acid solution to obtain a first precipitate and a first solution; the first precipitate comprises silicon dioxide, calcium sulfate and alpha-iron oxide, and the first solution comprises calcium salt, aluminum salt, sodium salt, magnesium salt and potassium salt; S3. carbonates are added into the first solution to obtain a second precipitate and a second solution; the second precipitate comprises calcium carbonate, magnesium carbonate and aluminum hydroxide, and the second solution comprises sodium salt and potassium salt; S4. the first precipitate is coated with polysiloxane to obtain coated materials, the second solution is crystallized and dehydrated to obtain solid materials, and the solid materials are mixed with the coated materials by ball milling to obtain a first mixture; S5. the second precipitate is heated to 350-450 DEG C, then hydrated and dried to obtain a second mixture; S6. the first mixture is mixed with the second mixture to obtain a flame-retardant material.

2. The method for recycling construction waste according to claim 1, wherein: In step S2, the acid solution is acetic acid with a mass concentration of not less than 30%, and the reaction temperature in step S2 is not less than 60 DEG C.

3. The method for recycling construction waste according to claim 1, wherein: In step S3, the carbonates are at least one of carbon dioxide, carbonic acid, sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate.

4. The method for recycling construction waste according to claim 1, wherein: In step S4, the coating comprises the following steps: the first precipitate is dispersed in an ethanol aqueous solution, a polysiloxane precursor is added, and then hydrolysis is performed under alkaline conditions to obtain coated materials.

5. The method of recycling construction waste according to claim 4, wherein: The mass ratio of the polysiloxane precursor to the first precipitate is 1:(4-8).

6. The method for recycling construction waste according to claim 4, wherein: The polysiloxane precursor comprises methyltrimethoxysilane and polyethylene glycol modified siloxane.

7. The method for recycling construction waste according to claim 1, wherein: In step S4, the solid materials and the coated materials are ball milled in a water-free environment at 200-400 rpm and a ball-material ratio of (10-20):1 for 2-6 h.

8. The method of claim 1, wherein: In step S5, the hydration comprises the following steps: stirring in hot water at 60-80 DEG C for 1-2 h.

9. The method for recycling construction waste according to claim 1, wherein: In step S1, the particle size of the granular materials is not more than 50 mm.

10. The method for recycling construction waste according to claim 1, wherein: When the first precipitate or the second precipitate is obtained, a crushing treatment is performed until the particle size is not more than 1 mm.

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