A negative carbon slurry-like cement modifier, its preparation method and application

Abstract

This invention provides a carbon-negative slurry cement modifier, its preparation method, and its application. The method utilizes carbon-rich gas to carbonize the suspension of salt extraction residue from the bypass ash of a kiln to prepare a carbon-negative slurry cement modifier. This carbon-negative slurry cement modifier exhibits good dispersibility and significant reinforcing effect. Furthermore, the preparation method is simple, low-carbon, environmentally friendly, safe, and has high added value.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a negative carbon slurry cement modifier, its preparation method, and its application. Background Technology

[0002] Co-processing municipal solid waste in cement kilns is an efficient solution because cement kilns operate at temperatures as high as 1450℃, effectively avoiding pollution from incomplete combustion of municipal solid waste. Furthermore, municipal solid waste has a high calorific value, and co-processing in cement kilns can reduce coal consumption during cement clinker firing. However, municipal solid waste contains a large amount of chlor-alkali, which volatilizes during combustion, clogging the decomposer and preheater, damaging the rotary kiln system, and easily causing excessive alkali and chloride ion content in the cement clinker. To address these issues, bypass ventilation is typically used, utilizing kiln tail bypass ventilation technology to remove chlor-alkali from the rotary kiln system. The powdery waste generated from the gas extracted from the bypass of the firing system after cooling and dust collection is called bypass vent ash. The main components of co-processing kiln bypass vent ash are cement clinker minerals, CaO, sodium chloride, and potassium chloride, with a chloride ion content as high as 10%. Huaxin Cement Co., Ltd. currently has a mature technical solution (see CN217818202U and CN113233798A) for washing and salting the bypass ash from the co-processing kiln, and then reusing the residue after salting as raw material in the rotary kiln. This method can effectively alleviate the disposal problem of bypass kiln ash and produce high-value-added potassium chloride salt as a byproduct. However, since the resulting filter residue contains about 40% water, it will consume a lot of heat due to water evaporation when used as raw material. Furthermore, the filter residue generally still contains 1%-2% chloride ions, which will increase the risk of excessive chloride levels if it enters the cement kiln system or is used in other cement-based materials. A large part of the chloride ions remaining in these filter residues are due to the solidification effect of hydrated calcium silicate gel and hydrated calcium aluminate in the residue. By carbonizing the hydrated calcium silicate gel and hydrated calcium aluminate, these adsorbed or solidified chloride ions can be converted into free chloride and washed out. The carbonization products obtained in this process have a positive effect on improving the strength of cement-based materials. Therefore, carbonizing the residue from the washing and salt extraction of cement co-kiln bypass ash to further remove residual chloride ions that limit its application and its application in cement-based materials is of great research value. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a negative carbon slurry cement modifier, its preparation method and application, which addresses the shortcomings of the prior art. The method uses carbon-rich gas to carbonize the suspension of salt extraction residue from the bypass ash of the kiln to prepare a negative carbon slurry cement modifier. The negative carbon slurry cement modifier has good dispersibility and significant strengthening effect. Moreover, the preparation method is simple, low-carbon, environmentally friendly, safe and has high added value.

[0004] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0005] A method for preparing a carbon-negative slurry-like cement modifier includes the following steps:

[0006] (1) Add cement co-kiln bypass ash water washing and salt extraction residue and water into a mixing device to obtain a mixture, and then introduce carbon-rich gas into the mixture.

[0007] (2) When the pH value of the mixture obtained in step (1) drops to 7-8, the mixture is filtered to obtain filter residue;

[0008] (3) Wash the filter residue obtained in step (2) and control the moisture content of the washed filter residue to be 50%-70%;

[0009] (4) Add 0.01%-0.20% of the dry weight of the filter residue to the filter residue obtained in step (3) and stir it evenly in a stirring device to obtain the finished product of negative carbon slurry cement modifier.

[0010] In the above scheme, the composition requirements of the cement co-kiln bypass ash washing and salt extraction residue in step (1) are as follows: the sum of the mass content of hydrated calcium silicate, hydrated calcium aluminate and quicklime in its dry basis is not less than 65%, and the mass content of chloride ions is 1%-3%.

[0011] In the above scheme, the CO2 volume content in the carbon-rich gas in step (1) is not less than 10%; the carbon-rich gas is preferably the tail gas of cement plants, smelters and thermal power plants.

[0012] In the above scheme, the mass ratio of the cement co-kiln bypass ash water washing and salt extraction residue and the water in step (1) is 1:1-1:3.

[0013] In the above scheme, the washing described in step (3) is a 2-5 level washing.

[0014] In the above scheme, the stabilizer is used to maintain the suspension of particles in the slurry, and the stabilizer is one or more of water-based polyamide wax, organic polyol and methyl cellulose ether.

[0015] The negative carbon slurry cement modifier prepared by the above method and its application in cement-based materials, wherein the negative carbon slurry cement modifier replaces part of the cementitious materials at a dosage of 1.0%-3.0% of the solid content; and the water in the negative carbon slurry cement modifier replaces the mixing water by mass.

[0016] The principle involved in this invention is as follows:

[0017] When using existing technologies (CN202221836338A and CN113233798A) to wash and extract salt from bypass vent ash in a co-operating kiln, the 1%-3% chloride ions in the resulting filter residue cannot be completely removed by water washing. This is because the chemical composition of the bypass vent ash is similar to that of cement clinker. When it comes into contact with water, it generates a large amount of calcium hydroxide, hydrated calcium silicate gel (CaO·xSiO2·yH2O), and hydrated calcium aluminate (4CaO·Al2O3·nH2O). Among them, hydrated calcium aluminate and hydrated calcium silicate gel have strong chloride ion solidification capabilities. Their reaction with chloride ions can proceed according to the following formula:

[0018] CaO·xSiO2·yH2O+zCl - →CaO·xSiO2·(yz)H2O·zHCl+zOH - (1)

[0019] 4CaO·Al2O3·nH2O+2Cl - →3CaO·CaCl2·Al2O3·(n-1)H2O+2OH- (2)

[0020] Equations (1) and (2) are the chemical equations for the curing of chloride ions in hydrated calcium silicate gel and hydrated calcium aluminate, respectively. Literature indicates that silicate cement hydration products can cure 1.0%-3.0% of their own mass of chloride ions (see DOI: 10.1016 / j.cemconcomp.2020.103537; DOI: 10.1016 / J.CONBUILDMAT.2018.12.162). These chloride ions cannot be removed by simple water washing. Therefore, for the salt-extraction residue generated after washing the cement kiln bypass ash in the existing technical solutions, multiple water washing can only remove the free chloride in the water of the salt-extraction residue. To address the above problems, this invention performs carbonization treatment on the salt-extraction residue using carbon-rich gas, decomposing the formed chlorine-containing hydrated calcium silicate gel and chlorine-containing hydrated calcium aluminate to form nano-calcium carbonate, amorphous silica gel, and aluminum gel. During this process, a large amount of CO2 is consumed. The chemical reactions involved are as follows:

[0021] CaO·xSiO2·(yz)H2O·zHCl+CO2+zOH - →CaCO3+xSiO2+yH2O+zCl - (3)

[0022] 3CaO·CaCl2·Al2O3·(n-1)H2O+2OH - +4CO2→4CaCO3+Al2O3+yH2O+2Cl - (4)

[0023] Since the carbonation reaction takes place in a relatively dilute solution, the resulting calcium carbonate, amorphous silica gel, and alumina gel are nanoscale. When used as cement modifiers, nano-calcium carbonate can promote the hydration of clinker minerals and exert a good micro-aggregate effect. Amorphous silica gel and alumina gel can react with calcium hydroxide produced by cement hydration to reform hydrated calcium silicate and hydrated calcium aluminate. These effects will significantly optimize the microstructure of hardened cement-based materials, increase the amount of hydration products, and improve strength.

[0024] For the final carbon-negative slurry cement modifier, this technical solution maintains it in a slurry state because if it is made into powder, the following problems exist: (1) Drying the slurry rich in nanoparticles consumes a lot of energy; (2) When powdered nanomaterials are used in cement-based materials, they are difficult to disperse, which will significantly increase the water demand of cement-based materials and greatly weaken the beneficial effect. In order to maintain the uniformity of the carbon-negative slurry cement modifier, a polymeric dispersant is added so that the slurry can remain in a uniform and stable state for a long time, making it convenient to use.

[0025] Compared with existing technologies, the beneficial effects of this invention are:

[0026] (1) The negative carbon slurry cement modifier provided by the present invention has good dispersibility and significant strengthening effect; and the method is simple, low-carbon, environmentally friendly, safe and has high added value.

[0027] (2) The negative carbon slurry cement modifier provided by the present invention has a good reinforcing effect. Replacing cement with 1.0%-3.0% of the folded solid content can increase the 28-day strength of cement-based materials by more than 10%.

[0028] (3) The negative carbon slurry cement modifier prepared by the preparation method provided by the present invention is a negative carbon product. During its preparation process, CO2 accounting for 14%-40% of its dry basis mass is solidified, which is a typical application case of CCUS technology.

[0029] (4) All wastewater generated during the preparation process of the preparation method provided by the present invention can be recycled and reused, and zero wastewater discharge can be achieved.

[0030] (5) The preparation method provided by the present invention can release the chloride ions solidified in the residue after treating the salt extraction residue suspension of the bypass venting of the co-working kiln. The chloride ion content can be removed by water washing, and the chloride ion content is reduced to less than 0.5% (as a percentage of the dry basis mass of the modifier), which improves the safety of its use in cement-based materials. Detailed Implementation

[0031] The technical solution of the present invention will be described in detail below with reference to specific embodiments. However, the described embodiments are only some embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] A method for preparing a carbon-negative slurry-like cement modifier includes the following steps:

[0034] (1) Add cement co-kiln bypass ash water washing and salt extraction residue and water to a mixing device at a mass ratio of 1:2 to obtain a mixed liquid, and introduce carbon-rich gas into the mixed liquid.

[0035] (2) As stirring and carbonization proceed, the pH value of the mixture gradually decreases. When the pH value of the mixture drops to 7.2, the mixture is discharged, filtered, and filtrate and filter residue are formed.

[0036] (3) The filter residue is washed in two stages. After the final stage of washing, the moisture content of the filter residue is maintained at 57%.

[0037] (4) Add 0.05% of the dry weight of the filter residue to the filter residue produced by the last stage of washing, and stir evenly in the stirring device to make the solid particles in the filter residue uniformly and stably dispersed to obtain the finished product of negative carbon slurry cement modifier.

[0038] In step (1), the cement co-kiln bypass ash water washing and salt extraction residue is the bypass venting ash water washing and salt extraction residue generated by the technical solutions involved in CN217818202U and CN113233798A. The dry basis of the residue contains 77% hydrated calcium silicate, hydrated calcium aluminate and quicklime, and 1.9% chloride ion content. In step (1), the CO2 volume content of the carbon-rich gas is 22.5%, which is the tail flue gas of the cement kiln. In step (2), when the pH of the mixed liquid reaches 7.2, the amount of CO2 absorbed by the mixed liquid is 35% of the dry basis mass of the salt extraction residue. In step (4), the stabilizer is used to maintain the stability of the slurry modifier and is polyethylene glycol with a molecular weight of 2 million.

[0039] The main solid components of the obtained negative carbon slurry cement modifier are nano-calcium carbonate, nano-silica gel, and nano-aluminum colloid. After drying, the slurry modifier has a BET specific surface area of ​​33.7 m². 2 / g, the chloride ion content in the slurry is 0.3% by mass.

[0040] When the negative carbon slurry cement modifier is applied, it replaces cement in cement mortar at a ratio of 2.5% of its solid content. The water introduced is deducted from the mixing water. Finally, the 28-day strength of the cement mortar increases from 47.5 MPa to 54.7 MPa, an increase of 15.2%.

[0041] Example 2

[0042] A method for preparing a carbon-negative slurry-like cement modifier includes the following steps:

[0043] (1) Add cement co-kiln bypass ash water washing and salt extraction residue and water to a mixing device at a mass ratio of 1:3 to obtain a mixed liquid, and introduce carbon-rich gas into the mixed liquid.

[0044] (2) As stirring and carbonization proceed, the pH value of the mixture gradually decreases. When the pH value of the mixture drops to 7.7, the mixture is discharged, filtered, and filtrate and filter residue are formed.

[0045] (3) The filter residue is washed in four stages. After the last stage of washing, the moisture content of the filter residue is maintained at 68%.

[0046] (4) Add 0.10% of the dry weight of the filter residue to the filter residue produced by the last stage of washing, and stir evenly in the stirring device to make the solid particles in the filter residue uniformly and stably dispersed to obtain the finished product of negative carbon slurry cement modifier.

[0047] In step (1), the bypass ash water washing and salt extraction residue of the cement co-kiln is the bypass venting ash water washing and salt extraction residue produced by the technical solutions involved in CN217818202U and CN113233798A. The dry basis of the residue contains 71% hydrated calcium silicate, hydrated calcium aluminate and quicklime, and 2.8% chloride ion content. In step (1), the CO2 volume content of the carbon-rich gas is 13.7%, which is a mixture of CO2 and air. In step (2), when the pH of the mixture reaches 7.7, the amount of CO2 absorbed by the mixture is 27.5% of the dry basis mass of the salt extraction residue. In step (4), the stabilizer is used to maintain the stability of the slurry modifier and is hydroxypropyl methylcellulose ether with a molecular weight of 150,000.

[0048] The main solid components of the obtained negative carbon slurry cement modifier are nano-calcium carbonate, nano-silica gel, and nano-aluminum colloid. After drying, the slurry modifier has a BET specific surface area of ​​36.9 m². 2 / g, the chloride ion content in the slurry is 0.2% by mass.

[0049] When the negative carbon slurry cement modifier is applied, it replaces cement in concrete at 2.0% of its solid content. The introduced water is deducted from the mixing water. The final 28-day strength of the concrete increases from 44.5 MPa to 50.6 MPa, an increase of 13.7%.

[0050] Example 3

[0051] A method for preparing a carbon-negative slurry-like cement modifier includes the following steps:

[0052] (1) Add cement co-kiln bypass ash water washing and salt extraction residue and water to a mixing device at a mass ratio of 1:2 to obtain a mixed liquid, and introduce carbon-rich gas into the mixed liquid.

[0053] (2) As stirring and carbonization proceed, the pH value of the mixture gradually decreases. When the pH value of the mixture drops to 8.0, the mixture is discharged, filtered, and filtrate and filter residue are formed.

[0054] (3) The filter residue is washed in two stages. After the final stage of washing, the moisture content of the filter residue is maintained at 61%.

[0055] (4) Add 0.12% of the dry weight of the filter residue to the filter residue produced by the last stage of washing, and stir evenly in the stirring device to make the solid particles in the filter residue uniformly and stably dispersed to obtain the finished product of negative carbon slurry cement modifier.

[0056] In step (1), the bypass ash water washing and salt extraction residue of the cement co-kiln is the bypass venting ash water washing and salt extraction residue produced by the technical solutions involved in CN217818202U and CN113233798A. The total mass of hydrated calcium silicate, hydrated calcium aluminate and quicklime in its dry basis is 79%, and the chloride ion content is 2.2%. The CO2 volume content of the carbon-rich gas in step (1) is 24.3%, which is the tail gas of the cement kiln. In step (2), when the pH of the mixed liquid reaches 8.0, the amount of CO2 absorbed by the mixed liquid is 39.1% of the dry basis mass of the salt extraction residue. In step (4), the stabilizer is used to maintain the stability of the slurry modifier and is a water-based polyamide wax with a molecular weight of 200,000.

[0057] The main solid components of the obtained negative carbon slurry cement modifier are nano-calcium carbonate, nano-silica gel, and nano-aluminum colloid. After drying, the slurry modifier has a BET specific surface area of ​​31.9 m². 2 / g, the chloride ion content in the slurry is 0.3% by mass.

[0058] When the negative carbon slurry cement modifier is applied, it replaces cement in cement mortar at a ratio of 2.8% of its solid content. The water introduced is deducted from the mixing water. Finally, the 28-day strength of the cement mortar increases from 42.5 MPa to 50.9 MPa, an increase of 19.7%.

[0059] Comparative Example 1

[0060] The cement co-kiln bypass ash water washing and salt extraction residue from Example 1 was treated according to the steps in Example 1, as follows:

[0061] (1) Add cement co-kiln bypass ash water washing and salt extraction residue and water into a mixing device at a mass ratio of 1:2 to obtain a mixed liquid, but do not perform carbon-rich gas treatment.

[0062] (2) After stirring for the same time as in Example 1, the mixture is discharged, filtered, and filtrate and filter residue are formed;

[0063] (3) The filter residue is washed in two stages. After the final stage of washing, the moisture content of the filter residue is maintained at 57%.

[0064] (4) Add 0.05% of the dry weight of the filter residue to the filter residue produced by the last stage of washing, and stir evenly in a stirring device to make the solid particles in the filter residue uniformly and stably dispersed to obtain the cement-based material slurry modifier product.

[0065] In step (1), the cement co-kiln bypass ash water washing and salt extraction residue is the bypass venting ash water washing and salt extraction residue generated by the technical solutions involved in CN202221836338A and CN113233798A. The dry basis contains 77% hydrated calcium silicate, hydrated calcium aluminate and quicklime, and 1.9% chloride ion content. In step (4), the stabilizer is used to maintain the stability of the slurry modifier and is polyethylene glycol with a molecular weight of 2 million.

[0066] After drying, the obtained cement-based material slurry modifier has a BET specific surface area of ​​11.5 m². 2 / g, the chloride ion content in the slurry is 1.5% by mass.

[0067] When cement-based material paste modifiers are used to replace cement in cement mortar at a ratio of 2.5% of their admixture, the introduced water is deducted from the mixing water. As a result, the 28-day strength of the cement mortar decreases from 47.5 MPa to 46.3 MPa, with no improvement effect.

Claims

1. A method for preparing a carbon-negative slurry-like cement modifier, characterized in that, Includes the following steps: (1) Mix the cement co-kiln bypass ash water washing and salt extraction residue with water to obtain a mixed liquid, and then introduce carbon-rich gas into the mixed liquid; (2) When the pH value of the mixture obtained in step (1) drops to 7-8, the mixture is filtered to obtain filter residue; (3) Wash the filter residue obtained in step (2) and control the moisture content of the washed filter residue to be 50%-70%; (4) Add 0.01%-0.20% of the dry weight of the filter residue to the filter residue obtained in step (3) and stir evenly to obtain the finished product of negative carbon slurry cement modifier; The composition requirements of the cement co-kiln bypass ash washing and salt extraction residue in step (1) are as follows: the total mass content of hydrated calcium silicate, hydrated calcium aluminate and quicklime in its dry basis is not less than 65%, and the mass content of chloride ions is 1%-3%; the mass ratio of the cement co-kiln bypass ash washing and salt extraction residue to the water is 1:1-1:

3.

2. The method for preparing a carbon-negative slurry-like cement modifier according to claim 1, characterized in that, The CO2 volume content in the carbon-rich gas mentioned in step (1) is not less than 10%.

3. The method for preparing a carbon-negative slurry-like cement modifier according to claim 1, characterized in that, The washing described in step (3) is a 2-5 level washing.

4. The method for preparing a negative carbon slurry cement modifier according to claim 1, characterized in that, The stabilizer mentioned in step (4) is one or a mixture of waterborne polyamide wax, organic polyol and methyl cellulose ether.

5. A negative carbon slurry cement modifier prepared according to the preparation method of the negative carbon slurry cement modifier according to claim 1.

6. The application of the negative carbon slurry cement modifier according to claim 5 in cement-based materials, characterized in that, The negative carbon slurry cement modifier replaces part of the cementitious materials at a dosage of 1.0%-3.0% of the solid content.