A method for preparing a silica gel

Abstract

The application relates to a preparation method of silica gel, which extracts siliceous elements from waste concrete rich in SiO2, Al2O3 and other components to prepare inorganic silica gel, and comprises the following steps: crushing, calcining, peeling, ball milling, preparation of a silicon-containing mixture, sol-gel, centrifugation, drying and the like; the application rationally utilizes the component characteristics of the waste concrete block, and prepares inorganic silica gel by taking the separated old hardened cement stone as a silicon source, has the advantages of simple process, low synthesis temperature, low energy consumption, green environmental protection, and the prepared inorganic silica gel has the advantages of large specific surface area and uniform pore structure; the method saves the production cost, effectively improves the economic added value and utilization rate of the waste concrete and the old hardened cement stone, avoids land resource occupation and environmental pollution, and has important environmental protection significance and application value.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of waste concrete, and particularly to a method for preparing silica gel. Background Technology

[0002] A large amount of waste concrete, accounting for approximately 30% of total construction waste, is generated during the demolition of buildings upon reaching the end of their service life, damage from natural disasters, or the construction of new buildings. This severely restricts urban development and the improvement of the living environment, bringing significant environmental risks and a huge waste of land resources, and also creating certain safety hazards. Currently, using waste concrete after crushing, washing, and grading to prepare recycled concrete aggregates, recycled cement, and recycled mortar is an important technical approach for the resource utilization of waste concrete. This technology can effectively solve the problems of resource utilization of waste concrete and the shortage of natural sand and gravel aggregates, but many problems still exist.

[0003] First, when hardened cement stone is peeled off the surface of recycled aggregate under mechanical impact or thermal stress, numerous microcracks are generated in the interfacial transition zone, reducing the bonding strength in this area and easily causing a large amount of hardened cement stone to detach from the surface of the recycled aggregate. Second, because the peeled old cement stone has high porosity, high standard viscosity water requirement, and low activity index, there are limits to its admixture during use, resulting in poor workability and mechanical properties of building materials made from it. Third, because the peeled old cement stone contains a certain amount of inert silica, it also brings difficulties to the grinding of cement raw materials and the calcination of clinker, increasing the f-CaO content in clinker, reducing clinker quality, and increasing production costs. Therefore, old cement stone faces significant obstacles in the preparation of recycled building materials, and there is an urgent need to develop new application areas. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an inorganic silica gel and its preparation method. The inorganic silica gel is prepared by extracting siliceous elements from waste concrete rich in SiO2, Al2O3, and other components. This method can reduce raw material costs and enable the recycling of old cement stone, thus having significant environmental protection significance and application value.

[0005] The technical solution adopted in this invention is: a method for preparing silicone, comprising the following steps:

[0006] (1) Crushing: The collected waste concrete blocks are fed into a jaw crusher through a vibrating feeder and crushed to a particle size of 5-40mm.

[0007] (2) Calcination: The crushed waste concrete blocks are sent into a muffle furnace for heat treatment. The difference in thermal expansion coefficient between old cement stone and sand and gravel aggregate reduces the strength of the interface transition zone and causes cracking of the bonding surface.

[0008] (3) Peeling: The calcined waste concrete blocks are fed into an electromagnetic vibration crusher and vibrated for 1 to 15 seconds to cause the old hardened cement stone to fall off the surface of the recycled aggregate.

[0009] (4) Ball milling: The old cement stone fine powder is separated from the waste concrete after vibration and sent to the ball mill for ball milling. The output particle size is 100-500 mesh.

[0010] (5) Preparation of silicon-containing mixture: Weigh the finely ground old cement stone powder and place it in a dry distillation flask. Add ammonium chloride solid and mix evenly to obtain a silicon-containing mixture.

[0011] (6) Sol-gel: Place the silicon-containing mixture in a clean beaker and add hydrochloric acid dropwise along the mouth of the beaker. Stir until the sample is fully dissolved and centrifuge the remaining insoluble SiO2 in the solution. Heat and stir the obtained filtrate, adding dilute NaOH solution during the stirring process. After the reaction is completed, let it stand for 24 to 72 hours.

[0012] (7) Centrifugation: After standing, centrifuge to separate the precipitate from the filtrate, and wash the precipitate repeatedly with deionized water until the concentration of the deionized water used for washing remains unchanged.

[0013] (8) Drying: The cleaned precipitate is vacuum dried to obtain inorganic silica gel.

[0014] As a preferred option, in step (2), the calcination temperature is 300-1200℃.

[0015] As a preferred embodiment, in step (5), the mass ratio of ammonium chloride to finely ground old cement stone powder is 1 to 10.

[0016] As a preferred embodiment, in step (6), the mass ratio of the silicon-containing mixture to hydrochloric acid is 1:1 to 1:10, and the mass concentration of hydrochloric acid is 1% to 10%.

[0017] As a preferred embodiment, in step (6), the pH of the filtrate is 3 to 4, the heating and stirring temperature is 40 to 200°C, and the reaction time is 10 to 40 min.

[0018] As a preferred option, in step (8), the vacuum drying temperature is 40-80℃.

[0019] As a preferred embodiment, the inorganic silica gel has a specific surface area of ​​660–670 m². 2 / g, with an average pore size of 7-8 nm.

[0020] The beneficial effects of this invention are:

[0021] (1) The old cement stone separated from waste concrete is rich in SiO2, Al2O3 and other components. This invention extracts silicon elements from large-scale industrial old cement stone to prepare inorganic silica gel, which not only saves production costs, but also effectively improves the economic added value and utilization rate of waste concrete and old hardened cement stone, and avoids occupying land resources and polluting the environment.

[0022] (2) Traditional organosilicon raw materials used for synthesizing silica gel are mainly water glass, tetrachlorosilane, tetraethyl orthosilicate, etc. The by-products of the preparation process are highly toxic, which directly restricts their large-scale application in silica gel preparation. Compared with traditional preparation methods and raw materials, the preparation method of this invention makes reasonable use of the component characteristics of waste concrete blocks and uses the separated old hardened cement stone as a silicon source to prepare inorganic silica gel. It has the advantages of simple process, low synthesis temperature, low energy consumption, and green environmental protection. The inorganic silica gel obtained has a large specific surface area and uniform pore structure. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions will be clearly and completely described below in conjunction with the embodiments of the present invention. The solutions of the present invention will be described in detail below with reference to specific embodiments:

[0024] Example 1

[0025] Inorganic silica gel is a highly active adsorbent material. Due to its insolubility in water and any solvent, non-toxicity, odorlessness, and chemical stability, it has wide applications in industrial catalysis, chemical coatings, environmental remediation, drug purification, food processing, and high-precision electronics. Old cement stone separated from waste concrete is rich in components such as SiO2 and Al2O3. Based on these characteristics, this invention provides a method for preparing silica gel by extracting silicon elements from bulk industrial old cement stone to prepare inorganic silica gel. This method saves production costs, effectively improves the economic added value and utilization rate of waste concrete and old hardened cement stone, and avoids occupying land resources and polluting the environment. Specifically, it includes the following steps:

[0026] (1) Crushing: The collected waste concrete blocks are fed into a jaw crusher through a vibrating feeder and crushed to a particle size of 5-15mm. During the crushing process, a large number of microcracks are generated in the interface transition zone between the recycled aggregate and the hardened cement stone adhering to its surface under the action of mechanical impact force, which reduces the bonding force in this area and is conducive to the peeling off of old cement stone.

[0027] (2) Calcination: The crushed waste concrete blocks are sent into a muffle furnace for heat treatment at a temperature of 300℃. The purpose of this step is: on the one hand, to take advantage of the difference in thermal expansion coefficients between old cement stone and sand and gravel aggregate, so that the strength of the interface transition zone between the two is reduced and the bonding surface cracks; on the other hand, calcination can dehydrate and activate the calcium silicate hydrate in the old cement stone, thus creating a prerequisite for the subsequent preparation of silica gel from the old cement stone.

[0028] (3) Peeling: The calcined waste concrete blocks are fed into an electromagnetic vibration crusher and vibrated for 1 to 15 seconds to cause the old hardened cement stone to fall off the surface of the recycled aggregate.

[0029] (4) Ball milling: The old cement stone fine powder is separated from the waste concrete after vibration and sent to the ball mill for ball milling. The output particle size is 100-200 mesh.

[0030] (5) Preparation of silicon-containing mixture: Weigh the finely ground old cement stone powder and place it in a dry distillation flask. Add ammonium chloride solid and mix evenly to obtain a silicon-containing mixture. The mass ratio of ammonium chloride to finely ground old cement stone powder is 1.

[0031] (6) Sol-gel: Place the silicon-containing mixture in a clean beaker and add hydrochloric acid dropwise along the mouth of the beaker. The mass ratio of the silicon-containing mixture to hydrochloric acid is 1:1 and the mass concentration of hydrochloric acid is 1%. Stir until the sample is fully dissolved and centrifuge the insoluble SiO2 remaining in the solution. The pH of the filtrate is 3. Heat and stir the obtained filtrate. Add dilute NaOH solution during the stirring process. The heating and stirring temperature is 40℃ and the reaction time is 10 min. After the reaction is completed, let it stand for 24 h.

[0032] (7) Centrifugation: After standing, centrifuge to separate the precipitate from the filtrate, and wash the precipitate repeatedly with deionized water until the concentration of the deionized water used for washing remains unchanged.

[0033] (8) Drying: The cleaned precipitate is vacuum dried at 40℃ to obtain inorganic silica gel with a specific surface area of ​​660 m². 2 / g, with an average pore size of 7nm.

[0034] Compared with traditional preparation methods and raw materials, the preparation method of this invention makes reasonable use of the component characteristics of waste concrete blocks and uses the separated old hardened cement stone as a silicon source to prepare inorganic silica gel. It has the advantages of simple process, low synthesis temperature, low energy consumption, and green environmental protection. The inorganic silica gel obtained has a large specific surface area and uniform pore structure.

[0035] Example 2

[0036] A method for preparing silicone includes the following steps:

[0037] (1) Crushing: The collected waste concrete blocks are fed into a jaw crusher through a vibrating feeder and crushed to a particle size of 15-25mm. During the crushing process, a large number of microcracks are generated in the interface transition zone between the recycled aggregate and the hardened cement stone adhering to its surface under the action of mechanical impact force, which reduces the bonding force in this area and is conducive to the peeling off of old cement stone.

[0038] (2) Calcination: The crushed waste concrete blocks are sent into a muffle furnace for heat treatment at a temperature of 600℃. The purpose of this step is: on the one hand, to take advantage of the difference in thermal expansion coefficients between old cement stone and sand and gravel aggregate, so that the strength of the interface transition zone between the two is reduced and the bonding surface cracks; on the other hand, calcination can dehydrate and activate the calcium silicate hydrate in the old cement stone, thus creating a prerequisite for the subsequent preparation of silica gel from the old cement stone.

[0039] (3) Peeling: The calcined waste concrete blocks are fed into an electromagnetic vibration crusher and vibrated for 1 to 15 seconds to cause the old hardened cement stone to fall off the surface of the recycled aggregate.

[0040] (4) Ball milling: The old cement stone fine powder is separated from the waste concrete after vibration and sent to the ball mill for ball milling. The output particle size is 200-300 mesh.

[0041] (5) Preparation of silicon-containing mixture: Weigh the finely ground old cement stone powder and place it in a dry distillation flask. Add ammonium chloride solid and mix evenly to obtain a silicon-containing mixture. The mass ratio of ammonium chloride to finely ground old cement stone powder is 5.

[0042] (6) Sol-gel: Place the silicon-containing mixture in a clean beaker and add hydrochloric acid dropwise along the mouth of the beaker. The mass ratio of the silicon-containing mixture to hydrochloric acid is 1:5 and the mass concentration of hydrochloric acid is 5%. Stir until the sample is fully dissolved and centrifuge the remaining insoluble SiO2 in the solution. The pH of the filtrate is 4. Heat and stir the obtained filtrate. Add dilute NaOH solution during the stirring process. The heating and stirring temperature is 120℃ and the reaction time is 25 min. After the reaction is completed, let it stand for 36 h.

[0043] (7) Centrifugation: After standing, centrifuge to separate the precipitate from the filtrate, and wash the precipitate repeatedly with deionized water until the concentration of the deionized water used for washing remains unchanged.

[0044] (8) Drying: The cleaned precipitate is vacuum dried at 60℃ to obtain inorganic silica gel with a specific surface area of ​​665 m². 2 / g, with an average pore size of 7.5nm.

[0045] Example 3

[0046] A method for preparing silicone includes the following steps:

[0047] (1) Crushing: The collected waste concrete blocks are fed into a jaw crusher through a vibrating feeder and crushed to a particle size of 25-40mm. During the crushing process, a large number of microcracks are generated in the interface transition zone between the recycled aggregate and the hardened cement stone adhering to its surface under the action of mechanical impact force, which reduces the bonding force in this area and is conducive to the peeling off of old cement stone.

[0048] (2) Calcination: The crushed waste concrete blocks are sent into a muffle furnace for heat treatment at a temperature of 1200℃. The purpose of this step is: on the one hand, to take advantage of the difference in thermal expansion coefficients between old cement stone and sand and gravel aggregate, so that the strength of the interface transition zone between the two is reduced and the bonding surface cracks; on the other hand, calcination can dehydrate and activate the calcium silicate hydrate in the old cement stone, thus creating a prerequisite for the subsequent preparation of silica gel from the old cement stone.

[0049] (3) Peeling: The calcined waste concrete blocks are fed into an electromagnetic vibration crusher and vibrated for 1 to 15 seconds to cause the old hardened cement stone to fall off the surface of the recycled aggregate.

[0050] (4) Ball milling: The old cement stone fine powder is separated from the waste concrete after vibration and sent to the ball mill for ball milling. The output particle size is 400-500 mesh.

[0051] (5) Preparation of silicon-containing mixture: Weigh the finely ground old cement stone powder and place it in a dry distillation flask. Add ammonium chloride solid and mix evenly to obtain a silicon-containing mixture. The mass ratio of ammonium chloride to finely ground old cement stone powder is 10.

[0052] (6) Sol-gel: Place the silicon-containing mixture in a clean beaker and add hydrochloric acid dropwise along the mouth of the beaker. The mass ratio of the silicon-containing mixture to hydrochloric acid is 1:10 and the mass concentration of hydrochloric acid is 10%. Stir until the sample is fully dissolved and centrifuge the insoluble SiO2 remaining in the solution. The pH of the filtrate is 4. Heat and stir the obtained filtrate. Add dilute NaOH solution during the stirring process. The heating and stirring temperature is 200℃ and the reaction time is 40 min. After the reaction is completed, let it stand for 72 h.

[0053] (7) Centrifugation: After standing, centrifuge to separate the precipitate from the filtrate, and wash the precipitate repeatedly with deionized water until the concentration of the deionized water used for washing remains unchanged.

[0054] (8) Drying: The cleaned precipitate is vacuum dried at 80℃ to obtain inorganic silica gel with a specific surface area of ​​670 m². 2 / g, with an average pore size of 8nm.

[0055] In addition, the foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing silicone, characterized in that, Includes the following steps: (1) Crushing: The collected waste concrete blocks are fed into a jaw crusher through a vibrating feeder and crushed to a particle size of 5-40mm. (2) Calcination: The crushed waste concrete blocks are sent into a muffle furnace for heat treatment. The difference in thermal expansion coefficient between old cement stone and sand and gravel aggregate reduces the strength of the interface transition zone and causes cracking of the bonding surface. (3) Peeling: The calcined waste concrete blocks are fed into an electromagnetic vibration crusher and vibrated for 1 to 15 seconds to cause the old hardened cement stone to fall off the surface of the recycled aggregate. (4) Ball milling: The old cement stone fine powder is separated from the waste concrete after vibration and sent to the ball mill for ball milling. The output particle size is 100-500 mesh. (5) Preparation of silicon-containing mixture: Weigh the finely ground old cement stone powder and place it in a dry distillation flask. Add ammonium chloride solid and mix evenly to obtain a silicon-containing mixture. (6) Sol-gel: Place the silicon-containing mixture in a clean beaker and add hydrochloric acid dropwise along the mouth of the beaker. Stir until the sample is fully dissolved and centrifuge the remaining insoluble SiO2 in the solution. Heat and stir the obtained filtrate, adding dilute NaOH solution during the stirring process. After the reaction is completed, let it stand for 24 to 72 hours. (7) Centrifugation: After standing, centrifuge to separate the precipitate from the filtrate, and wash the precipitate repeatedly with deionized water until the concentration of the deionized water used for washing remains unchanged. (8) Drying: The cleaned precipitate is vacuum dried to obtain inorganic silica gel.

2. The method for preparing silicone according to claim 1, characterized in that, In step (2), the calcination temperature is 300-1200℃.

3. The method for preparing silicone according to claim 1, characterized in that, In step (5), the mass ratio of ammonium chloride to finely ground old cement stone powder is 1 to 10.

4. The method for preparing silicone according to claim 1, characterized in that, In step (6), the mass ratio of the silicon-containing mixture to hydrochloric acid is 1:1 to 1:10, and the mass concentration of hydrochloric acid is 1% to 10%.

5. The method for preparing silicone according to claim 1, characterized in that, In step (6), the pH of the filtrate is 3 to 4, the heating and stirring temperature is 40 to 200°C, and the reaction time is 10 to 40 minutes.

6. The method for preparing silicone according to claim 1, characterized in that, In step (8), the vacuum drying temperature is 40-80℃.

7. The method for preparing silicone according to claim 1, characterized in that, The inorganic silica gel has a specific surface area of ​​660–670 m². 2 / g, with an average pore size of 7-8 nm.