Environment-friendly precoated sand and preparation method thereof

Abstract

The environment-friendly precoated sand is prepared from the following components in parts by mass: 80 parts of quartz sand, 15 to 20 parts of floating beads, 25 to 30 parts of red mud, 2 to 4 parts of phenolic resin, 3 to 5 parts of calcium carbonate micro powder, 0.6 to 0.9 part of urotropine solution, 0.1 to 0.3 part of calcium stearate and 0.1 to 0.2 part of water-soluble polyvinyl alcohol fiber. According to the precoated sand, effective and reasonable application of the floating bead and red mud industrial solid waste in the precoated sand is achieved, the unique porous structure of the precoated sand can adsorb harmful gas such as ammonia gas, the environment is protected, and the casting quality is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coated sand, in particular to an environment-friendly coated sand and a preparation method thereof. BACKGROUND

[0002] Red mud is an industrial solid waste discharged in the process of extracting alumina in the aluminum industry. It is called red mud because it contains a large amount of iron oxide and looks like red soil. Due to different ore grades, production methods and technical levels, about 1.0-1.8 tons of red mud are discharged for every ton of alumina produced. Red mud is an insoluble residue that can be divided into sintered red mud, Bayer red mud and combined red mud. The main components are SiO2, Al2O3, CaO, Fe2O3, etc. The sintered red mud contains less iron and more calcium oxide, so it is widely used as a raw material for cement and sintered bricks. The Bayer red mud contains more iron and less calcium oxide, so its application is more limited.

[0003] Fly ash is fine ash collected from flue gas after coal combustion and is the main solid waste produced in the furnace of a coal-fired power plant. Fly ash is a hollow ball that can float on water. It is grayish white, thin-walled and hollow, very light in weight, smooth on the surface, has a small thermal conductivity, and a fire resistance of ≥1610℃. It is mainly composed of silicon dioxide and aluminum oxide and is often used as a thermal insulation refractory material.

[0004] Coated sand is a type of sand that has a resin film pre-coated on the surface of the sand grains. It is widely used in the casting industry. The commonly used curing agent for coated sand is urotropine. During pouring, urotropine is easily decomposed into harmful gases such as NH3 and CN under heat, which is also an important factor for metal surface pores and pinhole defects. Patent CN 114346164 A discloses an environmentally friendly heat-resistant coated sand and its preparation method and application. By adding a certain amount of iron tailings during the production of coated sand, not only is the waste iron tailings effectively utilized, but the iron content in the iron tailings can effectively reduce the problem of subcutaneous pores and improve the quality of castings. However, the coated sand cannot effectively adsorb and solve the generated harmful gases such as ammonia, and the environmental performance needs to be further improved.

[0005] Patent CN109317598A discloses an environmentally friendly low-smoke wet coated sand and its preparation method. By adding zeolite powder to the coated sand, the zeolite powder's porous structure is used to adsorb the ammonia gas and formaldehyde generated by the thermal decomposition of urotropine, achieving the purpose of reducing the emission of toxic waste gas. However, the direct addition of zeolite powder with high specific surface area can adsorb resin or urotropine, leading to uneven resin coating and affecting the curing efficiency and strength of the sand mold.

[0006] How to effectively and reasonably apply red mud and other solid waste to coated sand is an important measure. SUMMARY

[0007] The present application aims to overcome the shortcomings of the prior art, and provides an environment-friendly coated sand and a preparation method thereof, so as to solve the problems that solid wastes such as fly ash and red mud cannot be effectively utilized and harmful gases such as ammonia are discharged in large quantities in the prior art.

[0008] The present application is achieved by the following technical scheme: an environment-friendly coated sand, by mass kg, comprises the following components: quartz sand 80 kg, floating beads 15-20 kg, red mud 25-30 kg, phenolic resin 2-4 kg, calcium carbonate powder 3-5 kg, urotropin solution 0.6-0.9 kg, calcium stearate 0.1-0.3 kg, and water-soluble polyvinyl alcohol fiber 0.1-0.2 kg.

[0009] Preferably, the particle size of the quartz sand and the floating beads is 60-80 mesh.

[0010] Preferably, the red mud comprises Fe2O3, Al2O3, SiO2, CaO, Na2O, TiO2, MgO and other components, wherein the mass ratio of Fe2O3, Al2O3, SiO2, CaO, Na2O, TiO2 and MgO is 20-48:15-25:5-20:5-14:2-20:2-15:0.5-2.

[0011] Preferably, the urotropin is a 42% mass fraction of hexamethylene tetramine aqueous solution.

[0012] Preferably, the length of the water-soluble polyvinyl alcohol fiber is 1-2 mm.

[0013] Preferably, the floating beads are pretreated, the surface of the floating beads is cleaned with alcohol to remove organic pollutants, the floating beads are filtered out and cleaned with purified water multiple times to remove alcohol, the floating beads are put into a nitric acid solution and stirred for 30 min for etching and opening holes, and the floating beads are filtered out and cleaned with purified water to neutral.

[0014] A preparation method of an environment-friendly coated sand, comprising the following steps, S1. The red mud is adjusted to neutral with an acid solution to prepare neutral red mud slurry; S2. The neutral red mud slurry is put into a vacuum stirring tank and heated to 80-90 DEG C; S3. The calcium carbonate powder is put into the neutral red mud slurry and stirred and mixed uniformly; S4. The opened floating beads are put into the mixed slurry, and stirred under reduced pressure for 1-1.5 h; S5. The floating beads are filtered out, placed in a calcining furnace and calcined at 850-900 DEG C for 3-4 h, and cooled to room temperature to obtain porous floating beads; S6. The quartz sand and the porous floating beads are put into a sand mixer and heated to 180 DEG C; S7. Put the phenolic resin into the sand mixer and mix for 2.5 minutes; S8. After cooling to 120℃, add urotropine and water-soluble polyvinyl alcohol fiber and mix for 5 minutes; S9. After cooling to 90℃, add calcium stearate and continue mixing until the mixture temperature is 85℃, then discharge, crush and sieve to obtain granular material; S10. Put the granular material into 70-80℃ water, stir for 20-30 minutes to dissolve the water-soluble polyvinyl alcohol fiber, filter and dry at low temperature to obtain coated sand.

[0015] Preferably, in step S1, the red mud slurry of the aluminum plant is pressure filtered to obtain dealkalized red mud, and the dealkalized red mud is dried to obtain dry powder red mud.

[0016] Preferably, the acid solution is hydrochloric acid.

[0017] The present application has the following advantages: 1. The hollow cavity of the floating bead, which is a waste of the coal-fired power plant, causes the structural strength to be lower than that of quartz sand. The present application introduces red mud into the interior of the floating bead and generates a porous structure in situ through calcination, which supports the shell of the floating bead from the inside, enhances the structural strength and quality of the floating bead as granular material, and enables the floating bead to replace quartz sand. The prepared porous structure has the advantage of large specific surface area, can adsorb the gas generated during pouring, and reduces the problem of subsurface porosity on the metal surface. The gas generated by the thermal decomposition of added calcium carbonate powder can not only optimize the porous structure of the red mud, but also the calcium chloride generated by the combination of residual calcium ions and chloride ions provided by hydrochloric acid is also an important component of complex ammonia gas, which further improves the adsorption capacity. The red mud selected is Bayer red mud, and the diiron trioxide contained in the red mud can increase the weight of the floating bead, making the mass of quartz sand and the floating bead close, reducing the separation problem during mixing and stirring, and the thermal conductivity of the coated sand can be significantly improved by balancing the heat insulation effect brought by the porous structure, accelerating the cooling process of the casting, reducing defects such as shrinkage and hot cracking, and the red mud also contains other trace elements, including but not limited to magnesium, titanium, nickel, copper, zinc, manganese and rare earth elements, which can form magnesium-based hydrogen storage alloy Mg2Ni and titanium-based hydrogen storage alloy TiFe at high temperature, absorb hydrogen generated during pouring, and avoid the problems of metal hydrogen embrittlement and white spot defects; 2. The present application applies the floating bead, a waste of the coal-fired power plant, and the red mud of the aluminum plant in the coated sand to replace part of the quartz sand, which not only maintains the original compressive and bending structural strength, but also the generated porous structure and carried trace elements can absorb various harmful gases such as ammonia and hydrogen, avoid releasing into the air to pollute the environment, and improve the quality of the metal casting during pouring; 3. The process of the present application realizes the comprehensive utilization of the floating bead and red mud industrial solid waste, which is in line with energy saving and emission reduction. DETAILED DESCRIPTION

[0018] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions will be clearly and completely described below in combination with the embodiments of the present application.

[0019] An environment-friendly coated sand is prepared by the following method, comprising the following steps, S1. The floating beads are screened through a 60-80 mesh screen; S2. The screened floating beads are pretreated, industrial alcohol is configured to have a mass concentration of 30-40%, the floating beads are put into the alcohol and stirred for 20 min to remove the surface ash impurities and organic pollutants, the floating beads are filtered out and cleaned with pure water multiple times to remove the alcohol, the floating beads are put into a concentrated nitric acid solution and stirred for 30 min for etching and opening holes, so as to facilitate the subsequent entry of the red mud into the internal cavity and avoid the collapse of the structure of the floating beads due to over time, the floating beads are filtered out and cleaned with pure water until neutral, and the cleaned floating beads are used without drying; S3. The red mud generated by the Bayer process in an aluminum plant is in a slurry state, after the alkaline filtrate is pressed out by using an alkaline filter press, the cost of subsequent acid adjustment is reduced, and the dealkalized red mud is obtained after natural air drying, and is put into a crusher to be crushed into powder; S4. According to the proportioning, each component is weighed, the dealkalized red mud dry powder is added into a configuration tank, concentrated hydrochloric acid is introduced and stirred, the red mud is adjusted from alkaline to neutral to prepare neutral red mud slurry, the concentrated hydrochloric acid can not only provide hydrogen ions, but also importantly provide chloride ions, the calcium chloride formed by the combination of the chloride ions and calcium ions can be complexed with ammonia gas to achieve the absorption of ammonia gas; S2. The neutral red mud slurry is added into a vacuum stirring tank and heated to 80-90°C to dissolve the red mud dry powder; S3. The calcium carbonate powder is put into the neutral red mud slurry and stirred to mix uniformly; S4. The opened floating beads are put into the mixed slurry, the vacuum pressure is 0.02-0.03 MPa, and the reduced pressure stirring is performed for 1-1.5 h to discharge the internal air, so that the red mud and the calcium carbonate enter the inside of the floating beads; S5. The floating beads are filtered out and placed in a calcining furnace for high-temperature firing at 850-900°C for 3-4 h, so that the calcium carbonate is decomposed to release carbon dioxide, and the red mud forms a porous structure in situ in the floating beads under the action of the carbon dioxide, and the porous floating beads are obtained after cooling to room temperature; S6. The quartz sand and the porous floating beads of the same particle size are put into a sand mixer and heated to 180°C; S7. The phenolic resin is put into the sand mixer and mixed and stirred for 2.5 min; S8. After cooling to 120°C, 42% urotropine solution and water-soluble polyvinyl alcohol fiber are added and mixed and stirred for 5 min, the water-soluble polyvinyl alcohol fiber is selected to be 1-2 mm, so as to facilitate cutting and not hinder the stirring and mixing. S9. Cooling to 90℃, adding calcium stearate to continue mixing sand to the mixture temperature of 85℃, discharging, crushing, and screening to get granular material; S10. Putting the granular material into 70-80℃ water, stirring for 20-30min to dissolve water-soluble polyvinyl alcohol fiber, the dissolved water-soluble polyvinyl alcohol fiber will form channels on the surface of the coated sand for gas exchange, filtering, and low-temperature drying at 60-75℃ to get porous coated sand.

[0020] The red mud used in the examples is waste discharged by a domestic aluminum plant, and the process is the Bayer process. The red mud includes Fe2O3, Al2O3, SiO2, CaO, Na2O, TiO2, MgO, and other trace elements. The component ratio is determined by multiple batches, and the mass ratio of Fe2O3, Al2O3, SiO2, CaO, Na2O, TiO2, and MgO is 20-48:15-25:5-20:5-14:2-20:2-15:0.5-2.

[0021] Example 1 An environmentally friendly coated sand, the mass of which is as follows: quartz sand 80kg, floating bead 15kg, red mud 30kg, phenolic resin 3.6kg, calcium carbonate powder 5kg, methenamine solution 0.6kg, calcium stearate 0.1kg, and water-soluble polyvinyl alcohol fiber 0.12kg.

[0022] The preparation process is as follows: dry powder of dealkalization red mud is adjusted to neutral by using concentrated hydrochloric acid to make a neutral red mud slurry, the neutral red mud slurry is put into a vacuum stirring tank and heated to 80℃, calcium carbonate powder is put into the neutral red mud slurry and stirred for 10min, the perforated floating bead is put into the mixed slurry, 0.02MPa reduced pressure stirring for 1h, the floating bead is filtered out, placed in a calcining furnace at 900℃ high temperature for 3h, and cooled to room temperature to get porous floating bead, the quartz sand and porous floating bead are put into a sand mixer and heated to 180℃, the phenolic resin is put into the sand mixer and mixed and stirred for 2.5min, after cooling to 120℃, methenamine and water-soluble polyvinyl alcohol fiber are added and mixed and stirred for 5min, calcium stearate is added at 90℃ to continue mixing sand, the mixture temperature is 85℃, discharging, crushing, and screening to get granular material, the granular material is put into 70℃ water, stirring for 30min to dissolve water-soluble polyvinyl alcohol fiber, filtering, and low-temperature drying at 70℃ to get coated sand.

[0023] Example 2 An environmentally friendly coated sand, the mass of which is as follows: quartz sand 80kg, floating bead 17kg, red mud 30kg, phenolic resin 2kg, calcium carbonate powder 4kg, methenamine solution 0.7kg, calcium stearate 0.2kg, and water-soluble polyvinyl alcohol fiber 0.1kg.

[0024] The preparation process is as follows: the dry powder of dealkalization red mud is adjusted to ph 6.9 by using concentrated hydrochloric acid to prepare neutral red mud slurry, the neutral red mud slurry is put into a vacuum stirring tank and heated to 88℃, the calcium carbonate powder is put into the neutral red mud slurry and stirred to mix uniformly, the opened porous beads are put into the mixed slurry, the pressure is reduced to 0.02MPa and stirred for 1.5h, the porous beads are filtered out, placed in a calcining furnace and calcined at 880℃ for 4h, cooled to room temperature to obtain porous beads, the quartz sand and the porous beads are put into a sand mixer and heated to 180℃, the phenolic resin is put into the sand mixer and stirred for 2.5min, after cooling to 120℃, the methenamine, water-soluble polyvinyl alcohol fiber are added and stirred for 5min, after cooling to 90℃, the calcium stearate is added and the sand is mixed until the temperature of the mixture is 85℃, then the mixture is discharged, crushed and sieved to obtain granular material, the granular material is put into 75℃ water and stirred for 30min to dissolve the water-soluble polyvinyl alcohol fiber, then the granular material is filtered and low-temperature dried to obtain coated sand.

[0025] Example 3 An environment-friendly coated sand, the mass of each component is as follows: 80kg of quartz sand, 19kg of beads, 25kg of red mud, 3kg of phenolic resin, 3kg of calcium carbonate powder, 0.8kg of methenamine solution, 0.3kg of calcium stearate and 0.2kg of water-soluble polyvinyl alcohol fiber.

[0026] The preparation process is as follows: the dry powder of dealkalization red mud is adjusted to ph 7.1 by using concentrated hydrochloric acid to prepare neutral red mud slurry, the neutral red mud slurry is put into a vacuum stirring tank and heated to 90℃, the calcium carbonate powder is put into the neutral red mud slurry and stirred to mix uniformly, the opened porous beads are put into the mixed slurry, the pressure is reduced to 0.025MPa and stirred for 1h, the porous beads are filtered out, placed in a calcining furnace and calcined at 850℃ for 4h, cooled to room temperature to obtain porous beads, the quartz sand and the porous beads are put into a sand mixer and heated to 180℃, the phenolic resin is put into the sand mixer and stirred for 2.5min, after cooling to 120℃, the methenamine, water-soluble polyvinyl alcohol fiber are added and stirred for 5min, after cooling to 90℃, the calcium stearate is added and the sand is mixed until the temperature of the mixture is 85℃, then the mixture is discharged, crushed and sieved to obtain granular material, the granular material is put into 80℃ water and stirred for 20min to dissolve the water-soluble polyvinyl alcohol fiber, then the granular material is filtered and low-temperature dried to obtain coated sand.

[0027] Example 4 An environment-friendly coated sand, the mass of each component is as follows: 80kg of quartz sand, 20kg of beads, 25kg of red mud, 2kg of phenolic resin, 5kg of calcium carbonate powder, 0.9kg of methenamine solution, 0.1kg of calcium stearate and 0.1kg of water-soluble polyvinyl alcohol fiber.

[0028] The preparation process is as follows: the dry powder of dealkalization red mud is adjusted to ph 7.2 by using concentrated hydrochloric acid to prepare neutral red mud slurry, the neutral red mud slurry is put into a vacuum stirring tank and heated to 80℃, the calcium carbonate powder is put into the neutral red mud slurry and stirred to mix uniformly, the opened porous float beads are put into the mixed slurry, 0.02MPa reduced pressure stirring for 1.5h, the float beads are filtered out, placed in a calcining furnace at 900℃ high temperature for 3h, cooled to room temperature to obtain porous float beads, the quartz sand and porous float beads are put into a sand mixer and heated to 180℃, the phenolic resin is put into the sand mixer and mixed and stirred for 2.5min, after cooling to 120℃, the methenamine, water-soluble polyvinyl alcohol fiber are added and mixed and stirred for 5min, after cooling to 90℃, the calcium stearate is added and the sand is continuously mixed until the temperature of the mixture is 85℃, the material is discharged, crushed and sieved to obtain granular material, the granular material is put into 80℃ water, stirred for 20min to dissolve the water-soluble polyvinyl alcohol fiber, filtered and low-temperature dried to obtain coated sand.

[0029] Example 5 An environment-friendly coated sand, the mass of each component is as follows: quartz sand 80kg, float beads 20kg, red mud 25kg, phenolic resin 2kg, calcium carbonate powder 3kg, methenamine solution 0.6kg, calcium stearate 0.1kg, water-soluble polyvinyl alcohol fiber 0.1kg.

[0030] The preparation process is as follows: the dry powder of dealkalization red mud is adjusted to ph 7.2 by using concentrated hydrochloric acid to prepare neutral red mud slurry, the neutral red mud slurry is put into a vacuum stirring tank and heated to 80℃, the calcium carbonate powder is put into the neutral red mud slurry and stirred to mix uniformly, the opened porous float beads are put into the mixed slurry, 0.02MPa reduced pressure stirring for 1.5h, the float beads are filtered out, placed in a calcining furnace at 900℃ high temperature for 3h, cooled to room temperature to obtain porous float beads, the quartz sand and porous float beads are put into a sand mixer and heated to 180℃, the phenolic resin is put into the sand mixer and mixed and stirred for 2.5min, after cooling to 120℃, the methenamine, water-soluble polyvinyl alcohol fiber are added and mixed and stirred for 5min, after cooling to 90℃, the calcium stearate is added and the sand is continuously mixed until the temperature of the mixture is 85℃, the material is discharged, crushed and sieved to obtain granular material, the granular material is put into 80℃ water, stirred for 20min to dissolve the water-soluble polyvinyl alcohol fiber, filtered and low-temperature dried to obtain coated sand.

[0031] Comparative Example 1 An environment-friendly coated sand, the mass of each component is as follows: quartz sand 80kg, float beads 20kg, phenolic resin 2kg, calcium carbonate powder 3kg, methenamine solution 0.6kg, calcium stearate 0.1kg.

[0032] The preparation process is: put the quartz sand and unopened pearl into the sand mixer and heat to 180℃, put the phenolic resin into the sand mixer and mix for 2.5min, after cooling to 120℃, add urotropin and mix for 5min, after cooling to 90℃, add calcium stearate and continue to mix until the temperature of the mixture is 85℃, then discharge, crush and sieve to get granular material.

[0033] Comparative example 2 An environmental type coated sand, the mass of which is as follows: quartz sand 80kg, pearl 20kg, red mud 25kg, phenolic resin 2kg, urotropin solution 0.6kg, calcium stearate 0.1kg, water-soluble polyvinyl alcohol fiber 0.1kg.

[0034] The preparation process is: use nitric acid solution to adjust the ph of the dealkalization red mud dry powder to 7.0 to make neutral red mud slurry, put the neutral red mud slurry into the vacuum stirring tank and heat to 90℃, put the opened pearl into the mixed slurry, reduce the pressure to 0.02MPa and stir for 1-1.5h, filter out the pearl, place it in the calcining furnace and heat at 400℃ for 3h, cool to room temperature to get porous pearl, put the quartz sand and porous pearl into the sand mixer and heat to 180℃, put the phenolic resin into the sand mixer and mix for 2.5min, after cooling to 120℃, add urotropin and water-soluble polyvinyl alcohol fiber and mix for 5min, after cooling to 90℃, add calcium stearate and continue to mix until the temperature of the mixture is 85℃, then discharge, crush and sieve to get granular material, put the granular material into 80℃ water, stir for 20min to dissolve the water-soluble polyvinyl alcohol fiber, filter and dry at low temperature to get the coated sand.

[0035] Comparative example 3 An environmental type coated sand, the mass of which is as follows: quartz sand 80kg, pearl 20kg, red mud 25kg, phenolic resin 2kg, calcium carbonate powder 3kg, urotropin solution 0.6kg, calcium stearate 0.1kg.

[0036] The preparation process is: use hydrochloric acid to adjust the ph of the dealkalization red mud dry powder to 7.0 to make neutral red mud slurry, put the neutral red mud slurry into the vacuum stirring tank and heat to 90℃, put the opened pearl into the mixed slurry, reduce the pressure to 0.02MPa and stir for 1-1.5h, filter out the pearl, place it in the calcining furnace and heat at 400℃ for 3h, cool to room temperature to get porous pearl, put the quartz sand and porous pearl into the sand mixer and heat to 180℃, put the phenolic resin into the sand mixer and mix for 2.5min, after cooling to 120℃, add urotropin and mix for 5min, after cooling to 90℃, add calcium stearate and continue to mix until the temperature of the mixture is 85℃, then discharge, crush and sieve to get the coated sand.

[0037] Comparative example 4 An environment-friendly coated sand, the mass of which is as follows: quartz sand 100 kg, phenolic resin 2 kg, methenamine solution 0.6 kg, calcium stearate 0.1 kg.

[0038] The preparation process is as follows: the quartz sand is put into a sand mixer and heated to 180℃, the phenolic resin is put into the sand mixer and mixed and stirred for 2.5 min, after cooling to 120℃, the methenamine is added and mixed and stirred for 5 min, after cooling to 90℃, the calcium stearate is added and the sand mixing is continued until the temperature of the mixture is 85℃, then the mixture is discharged, crushed and sieved to obtain the coated sand.

[0039] Performance test The coated sand prepared in Examples 1-5 and Comparative Examples 1-3 is subjected to performance test, and the test is carried out according to the standard of JB / T8583-2008, as shown in the following table.

[0040] No. Tensile strength at room temperature MPa Flexural strength at room temperature MPa Tensile strength at hot temperature MPa Gas evolution ml / g Ammonia release ppm / g Disintegration % (8-shaped 550°C for 7 minutes, 20 mesh sieve, 7 seconds vibration) Example 1 2.2 6.3 2.5 9.3 11 57.6 Example 2 2.2 6.4 2.4 9.1 12 56.8 Example 3 2.3 6.6 2.6 9.1 12 56.2 Example 4 2.2 6.3 2.3 8.8 10 56.9 Example 5 2.1 6.0 2.2 9.0 11 57.4 Comparative Example 1 1.6 5.3 1.7 18.6 32 59.7 Comparative Example 2 2.1 5.9 2.2 15.8 23 56.3 Comparative Example 3 2.1 5.9 2.3 14.3 56 56.4 Comparative Example 4 2.3 6.3 2.4 28.6 68 56.7 Analysis: from the results of Comparative Example 1 and Comparative Example 4, it can be seen that the addition of the unopened floating bead reduces the overall strength, which should be that the structural strength of the hollow floating bead is less than that of the solid coated sand, but the gas evolution amount is reduced, which is speculated to be that part of the floating bead is broken to form an adsorption structure during the production process; the tensile and bending strengths of Examples 1-5 and Comparative Examples 2-3 are improved compared with those of Comparative Example 1, which proves that the filling of the red mud inside the floating bead plays a role in stabilizing support and enhances the mechanical properties; from the results of the gas evolution amount and the ammonia gas release amount of Examples 1-5 and Comparative Example 2, it can be seen that the addition of calcium carbonate increases the gas adsorption amount and reduces the ammonia gas release amount, which is speculated to be that the decomposition of calcium carbonate further increases the specific surface area of the red mud, making its adsorption capacity stronger, and the calcium chloride generated by the combination of calcium ions and chloride ions can also adsorb the generated ammonia, which is also an important factor for the improvement of the adsorption capacity; from the results of Examples 1-5 and Comparative Example 3, it can be seen that the addition of water-soluble polyvinyl alcohol fiber can open the coating of the phenolic resin, which is beneficial to the entry of gas into the floating bead and the adsorption of the gas.

[0041] Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some of the technical features, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An environmentally friendly coated sand, characterized in that, The composition, by weight, includes the following components: 80 parts quartz sand, 15-20 parts cenospheres, 25-30 parts red mud, 2-4 parts phenolic resin, 3-5 parts calcium carbonate powder, 0.6-0.9 parts hexamethylenetetramine solution, 0.1-0.3 parts calcium stearate, and 0.1-0.2 parts water-soluble polyvinyl alcohol fiber.

2. The environmentally friendly coated sand according to claim 1, characterized in that: The particle size of both the quartz sand and the cenospheres is 60-80 mesh.

3. The environmentally friendly coated sand according to claim 1, characterized in that: The red mud includes Fe2O3, Al2O3, SiO2, CaO, Na2O, TiO2, MgO and other components, wherein the mass ratio of Fe2O3, Al2O3, SiO2, CaO, Na2O, TiO2 and MgO is 20-48:15-25:5-20:5-14:2-20:2-15:0.5-2.

4. The environmentally friendly coated sand according to claim 1, characterized in that: The hexamethylenetetramine is a 42% (w / w) aqueous solution of hexamethylenetetramine.

5. The environmentally friendly coated sand according to claim 1, characterized in that: The water-soluble polyvinyl alcohol fiber has a length of 1-2 mm.

6. The environmentally friendly coated sand according to claim 1, characterized in that, The cenospheres are pretreated by cleaning the surface of the cenospheres with alcohol to remove organic contaminants, filtering out the cenospheres and washing them repeatedly with purified water to remove the alcohol, then immersing the cenospheres in nitric acid solution and stirring for 30 minutes to etch and open pores, filtering out the cenospheres and washing them with purified water until neutral.

7. A method for preparing an environmentally friendly coated sand according to any one of claims 1-6, characterized in that, Includes the following steps, S1. Adjust the red mud to neutral using acid solution to prepare neutral red mud slurry; S2. Pour the neutral red mud slurry into a vacuum mixing tank and heat it to 80-90℃; S3. Add calcium carbonate powder to neutral red mud slurry and stir to mix evenly; S4. Add the perforated cenospheres into the mixed slurry and stir under reduced pressure for 1-1.5 hours; S5. Filter out the cenospheres, place them in a calcining furnace at 850-900℃ for 3-4 hours, and cool to room temperature to obtain porous cenospheres. S6. Add the quartz sand and porous cenospheres into the sand mixer and heat to 180°C; S7. Add phenolic resin into the sand mixer and mix for 2.5 minutes; S8. After cooling to 120℃, add hexamethylenetetramine and water-soluble polyvinyl alcohol fiber, mix and stir for 5 minutes; S9. Cool down to 90℃, add calcium stearate and continue mixing until the mixture temperature reaches 85℃, then discharge, crush and screen to obtain granular material; S10. Add the granular material to water at 70-80℃, stir for 20-30 minutes to dissolve the water-soluble polyvinyl alcohol fiber, filter, and dry at low temperature to obtain the coated sand.

8. The method for preparing an environmentally friendly coated sand according to claim 7, characterized in that: In step S1, the red mud slurry from the aluminum plant is filtered to obtain dealkalized red mud, and the dealkalized red mud is dried to produce dry powder red mud.

9. The method for preparing an environmentally friendly coated sand according to claim 7, characterized in that: The acid solution is hydrochloric acid.