CN116161908B

CN116161908B - Preparation method of magnesium slag carbon-fixing water permeable brick

Info

Publication number: CN116161908B
Application number: CN202211598113.7A
Authority: CN
Inventors: 王瑞兴; 滕航; 卞思源; 徐正祥; 白晶; 王胜青; 范付军; 徐旭
Original assignee: Baowu Magnesium Industry Technology Co ltd; Southeast University Suzhou Medical Device Research Institute
Current assignee: Baowu Magnesium Industry Technology Co ltd; Southeast University Suzhou Medical Device Research Institute
Priority date: 2022-12-12
Filing date: 2022-12-12
Publication date: 2024-09-13
Anticipated expiration: 2042-12-12
Also published as: CN116161908A

Abstract

The invention belongs to the technical field of recycling of solid wastes, and particularly discloses a preparation method of a magnesium slag carbon-fixing water permeable brick. According to the preparation method, a large amount of magnesium reducing slag serving as an industrial byproduct is used as a raw material, the application problem of low hydration activity of the magnesium slag is overcome by carbonization maintenance, and the production period of the maintenance type water permeable brick is greatly shortened based on the acceleration of carbonization of microorganisms. In addition, the water permeable brick product with the performance meeting the requirement of 'sponge city' pavement construction is prepared by combining the inherent component properties of magnesium reducing slag and through a reasonable carbonization process, and has the advantages of simple process, short production period, high magnesium slag utilization rate, environmental friendliness and the like, and has good economic and social benefits.

Description

Preparation method of magnesium slag carbon-fixing water permeable brick

Technical Field

The invention belongs to the technical field of recycling of solid waste, and particularly relates to a preparation method of a magnesium slag carbon-fixing water permeable brick based on microorganism accelerated carbonization.

Background

The magnesium reducing slag is solid waste discharged when the original magnesium is refined by an industrial Pidgeon method, has high water absorption and is accumulated in a large amount, thus not only occupying the land, but also easily causing salinization and hardening of the soil and polluting the environment; meanwhile, because magnesium slag particles are tiny, about 60 percent of the magnesium slag particles are in dust shape and are easy to suspend in the air, thereby causing human respiratory diseases. China is a large country for producing original magnesium, and the annual production of the original magnesium accounts for 80-90% of the total world original magnesium yield. The yield of raw magnesium in 2021 is 94.88 ten thousand tons in the whole year, and about 8 tons of magnesium slag can be produced per 1 ton of raw magnesium smelted. The problems of high annual emission and low comprehensive utilization rate of magnesium slag are not solved effectively. On the other hand, as the energy consumption and cement production in China, the industrial development in the present stage of China mainly depends on the traditional fossil energy, and the aim of emission reduction of 'carbon peak and carbon neutralization' still faces great pressure. In recent years, the development of microorganism mineralization technology is mature, and carbonic anhydrase is used as an environment-friendly microorganism, so that the carbonization reaction process can be accelerated, and the production period of carbonized bricks is greatly shortened. Along with the continuous acceleration of the urban process, urban surface multipurpose waterproof materials such as cement, asphalt and the like are paved, so that the ground water level is easy to drop to cause ground settlement, and the waterlogging drainage pressure is increased to cause urban waterlogging. A large number of researches show that the water permeable brick has the advantages of reducing water accumulation on the road surface, reducing the heat island effect, improving the soil environment and the like, and is an important part indispensable for promoting construction of sponge cities.

The existing water permeable bricks are mainly divided into maintenance type water permeable bricks and firing type water permeable bricks, and the energy consumption of the firing type water permeable bricks is large and additional carbon emission can be generated. Compared with the prior art, the maintenance type water permeable brick has low energy consumption, but most of researches on the water permeable brick have the defects of longer production period, higher time cost and the like. In addition, the problems of low magnesium slag utilization rate, low hydration activity, poor cost and environmental benefit of the water permeable brick and the like are also commonly existed in the prior art.

Therefore, how to simply, efficiently and cleanly prepare the water permeable brick by utilizing a large amount of solid waste magnesium reducing slag is still required to be continuously researched and technically improved.

Disclosure of Invention

Aiming at a plurality of problems existing in the prior art when magnesium slag is used for preparing the water permeable brick, the inventor of the invention provides a preparation method of the water permeable brick which is based on the microorganism acceleration carbonization and takes magnesium slag as a raw material for carbon fixation on the basis of long-term study on the microorganism mineralization technology. The method adopts natural coarse aggregate and reduced magnesium slag micropowder as main components, accelerates carbonization by mineralization of microorganisms, and prepares the water permeable brick by reasonable carbonization process, and has the advantages of simple process, short production period, high magnesium slag utilization rate, environmental friendliness and the like.

The invention adopts the following technical scheme:

The preparation method of the magnesium slag carbon-fixing water permeable brick comprises the following steps:

S1, uniformly mixing natural coarse aggregate with acetic acid solution;

S2, adding magnesium slag micro powder and microbial powder into the mixture obtained in the step S1, stirring until the slurry is uniformly coated on the surface of the aggregate, and molding in a mold to obtain a sample;

s3, naturally curing the sample at the temperature of 25+/-2 ℃ and the humidity of 40% -60% for 8-12 h to obtain a primary curing sample;

s4, carrying out CO ₂ pre-curing on the primary curing sample for 0.5-1 h to obtain a shaping sample;

s5, after the shaping sample is demoulded, CO ₂ is carried out for pressurized maintenance for 4-6 hours, and the magnesium slag carbon-fixing water permeable brick is obtained.

In the steps, the grain size of the natural coarse aggregate is 2.35 mm-4.75 mm, and coarse aggregates such as sand, stone and the like which meet the grain size requirements can be selected from concrete materials. The magnesium slag micropowder is powder with the grain diameter smaller than 0.075mm, which is obtained by ball milling of industrial magnesium smelting reducing slag, the mixing amount is controlled to be 25% -40% of natural coarse aggregate, and the preferable mixing amount is about 1/3. The acetic acid solution is diluted acetic acid with the concentration of 0.1 mol/L to 1mol/L, the mixing amount is 20 percent to 30 percent of the mass of the magnesium slag micro powder, and the preferable mixing amount is about 1/4; the microbial powder is the microbial powder for producing carbonic anhydrase, and the mixing amount is about 1% of the mass of the magnesium slag micro powder.

Alternatively, the microbial powder may be Bacillus mucilaginosus.

According to the preparation method, on one hand, the acetic acid solution is adopted to dissolve out the calcium source in the magnesium slag micro powder to participate in carbonization, so that the carbonization degree is improved, the bonding performance between the slurry and the aggregate is improved, and the product is initially formed; on the other hand, the coarse crystal morphology of gamma-C ₂ S in the magnesium slag micro powder can be destroyed, so that a compact carbonized product layer is not easy to form on the surface of the product, CO ₂ is easier to permeate into and react with the inside, and the strength of the prepared water permeable brick is improved.

The low-pressure carbonization is used in the pre-curing stage because the excessively high concentration of CO ₂ can quickly generate compact calcium carbonate on the surface of the product, so that the pores on the surface of the product are easily closed, gas is difficult to permeate inwards, and the subsequent carbonization degree inside is affected. The reason for adopting pressurized carbonization after demolding is that the CO ₂ gas is promoted to diffuse into the product by using pressure, so that the carbonization degree is improved, and the working performance of the product is improved.

In the preparation method, after the microbial powder is added, carbonic anhydrase secreted in the recovery process can increase the rate of CO ₂ dissolved in water to generate CO ₃ ^2-, and CO ₃ ^2- permeates into the product along with moisture from pores and reacts with Ca ²⁺, so that the process of carbonization reaction can be accelerated, and the production period is shortened. Meanwhile, under the influence of carbonic anhydrase, calcium carbonate generated at the initial stage is mainly in the vaterite type, and the calcium carbonate is loose in structure and cannot seal pores on the surface of a product, so that gas can enter the product, and the carbonization degree is improved. The vaterite is unstable in morphology, and gradually converts to a calcite phase with stable structure in the later carbonization stage, so that the strength of the product is not influenced.

Generally, the curing of CO ₂ in steps S4 and S5 is performed in a carbonization autoclave, that is, the carbonization autoclave is evacuated in advance, and then CO ₂ is filled to perform carbonization curing.

In the step S4, the concentration of CO ₂ used for the pre-curing is at least 99%, and the pressure of the carbonization reaction pressure kettle is controlled to be not more than 0.02MPa for low-pressure curing; in the step S5, the CO ₂ concentration used for the pressurized curing is at least 99%, but the pressure of the carbonization reaction autoclave is controlled to be 0.10 MPa-0.15 MPa for the pressurized curing.

Meanwhile, the pre-curing time is not too long, otherwise, the demolding is difficult easily, and the bottom of the molded sample is also carbonized unevenly.

The reason that the preparation method adopts the two-step CO ₂ maintenance of low pressure and then pressurization is that the main reaction mineral phase in the magnesium slag micro powder is gamma-C ₂S,γ-C₂ S and has almost no hydration activity (namely the capability of reacting with water to generate a gel substance), but the carbonization activity (namely the capability of reacting with CO ₂ to generate calcium carbonate) is very high; therefore, the demoulding is realized by low-pressure pre-carbonization maintenance so as to ensure that a gel substance is generated between the natural coarse aggregate and the magnesium slag micro powder, and the natural coarse aggregate is prevented from being scattered due to the cementing effect of the gel substance in the demoulding process; in other words, the main purpose of the first-step pre-carbonization is to give the magnesium slag carbon-fixing water permeable brick the brick demoulding strength, not the brick strength development. After the brick is demolded (namely the obtained shaping sample), pressurizing and carbonizing and curing the brick, so that CO ₂ is caused to break through the pore blocking effect of calcium carbonate formed on the surface of the brick during pre-curing, and the calcium carbonate is not continuously generated on the surface of the brick, but is permeated into the brick for continuous reaction; and the higher carbonization pressure can also promote the reaction speed, shorten the carbonization time and ensure the completeness of the carbonization inside the brick.

The present invention is directed to the above-described two-step CO ₂ curing of magnesium slag, low pressure-then pressurized, which is quite different from the carbonization treatment of steel slag in the prior art. This is because the main reaction mineral phase in the steel slag is beta-C ₂S,β-C₂ S which has both hydration activity and carbonization activity, i.e. the steel slag can have a certain molding and demolding strength without carbonization (because the strength is provided by the hydration product C-S-H gel). In short, the steel slag is generally treated, the steel slag product meeting the mechanical requirements can be obtained through one-step carbonization treatment of the steel slag, and the magnesium slag cannot be treated by adopting the same process, so that the magnesium slag can be subjected to preliminary demoulding strength only after calcium carbonate and silica gel are generated through preliminary carbonization.

In addition, the reaction pressure in the pressurizing and curing step is not required to be adjusted to be large, so that the development of the brick strength can be realized, which is different from the treatment of part of steel slag pellets in the prior research. When the general steel slag forms steel slag pellets, the aim of ensuring the balling rate by means of low pressure is to prevent the mother balls with smaller grain diameters from cracking under high pressure in the initial stage; and only after forming the mother balls with qualified particle size, the carbonization can be continued under pressure, and obviously, the low-pressure-pressurizing two-step carbonization aims at the strength development of the steel slag balls.

Therefore, the water permeability coefficient of the magnesium slag carbon-fixing water permeable brick obtained by the preparation method is kept to be 0.15 cm/s-0.25 cm/s, and the magnesium slag carbon-fixing water permeable brick meets the A-level water permeability grade (not lower than 2.0X10 ^-2 cm/s) specified in GBT 25993-2010 water permeable pavement bricks and water permeable pavement boards.

The invention has the beneficial effects that:

The invention is an advanced technology for comprehensively utilizing the solid waste of the industrial magnesium smelting reduction slag and the CO ₂ gas waste in a recycling way, and solves the application problem of low hydration activity of the magnesium slag by carbonization maintenance; the carbonization process is accelerated by utilizing the enzyme catalysis of microorganisms, so that the production period of the maintenance type water permeable brick is greatly shortened. The technology not only realizes the recycling of double wastes, but also prepares the water permeable brick product with the performance meeting the requirement of 'sponge city' pavement construction, and has good economic and social benefits. In particular, the method comprises the steps of,

1. The invention uses the reducing slag generated in the industrial magnesium smelting as the main raw material to prepare the water permeable brick, and utilizes the carbonization technology to overcome the problems of low hydration activity of magnesium slag, slow hydration reaction and difficult direct realization of application.

2. The main components of the invention are only magnesium slag micropowder and natural aggregate, no other active excitation substances are required to be doped, compression molding and long-term maintenance are not required, the cost is low, and the energy consumption is low.

3. The microbial enzyme catalysis technology adopted in the invention has a specific accelerated carbonization function in the preparation process of the magnesium slag carbon-fixing water permeable brick, and is not involved in the existing magnesium slag brick preparation technology.

4. The gradient carbonization process of 'pre-curing-pressurizing curing' adopted in the invention can effectively improve the pore structure of carbonized products and improve the carbonization degree, thereby improving the strength of the water permeable bricks.

Drawings

FIG. 1 is an XRD pattern of the magnesium slag micropowder raw materials used in examples 1 to 4 and comparative examples 1 to 6, the magnesium slag carbon-fixing water permeable brick of example 3, and the third comparative water permeable brick of comparative example 3 according to the present invention;

FIG. 2 is an SEM image of the microstructure of the magnesium slag micropowder raw materials used in examples 1 to 4 and comparative examples 1 to 6 according to the present invention;

FIGS. 3 and 4 are SEM images of the inner and outer structures of the water permeable bricks under gradient carbonization maintenance according to the acetic acid concentration of 1mol/L in example 3 of the present invention;

FIG. 5 is an SEM image of the internal structure of a water permeable brick under the CO ₂ carbonization pressure of 0.02MPa in comparative example 5 according to the present invention;

FIG. 6 is an SEM image of the surface structure of a water permeable brick at a CO ₂ carbonization pressure of 0.10MPa to 0.15MPa in comparative example 6 according to the present invention.

Detailed Description

The following description of the technical solution in the embodiments of the present invention is clear and complete. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The XRD patterns of the magnesium slag micropowder raw materials used in the following examples and comparative examples are shown in FIG. 1. As can be seen from FIG. 1, the main mineral phases in the magnesium slag micropowder include beta-C ₂ S and gamma-C ₂ S, but gamma-C ₂ S is a predominant number, and beta-C ₂ S is very small.

SEM characterization of the magnesium slag micropowder raw material is shown in fig. 2. As can be seen from fig. 2, the magnesium slag micropowder has coarse grains and poor self-compaction, and is therefore not easily consolidated without external force. The bar shape is one of the characteristic crystal forms of gamma-C ₂ S, which shows that the bar shape is the main component of the magnesium slag micropowder.

Through the above component analysis and microscopic characterization of the magnesium slag micropowder, the process requirements of the magnesium slag micropowder and steel slag can be also verified.

Example 1

The method for preparing the magnesium slag carbon-fixing water permeable brick by utilizing the microorganism acceleration carbonization provided by the embodiment comprises the following steps:

(1) Natural coarse aggregate with the grain diameter of 2.35 mm-4.75 mm is sieved, magnesium slag is ball ground into micro powder with the grain diameter of less than 0.075mm, dilute acetic acid with the concentration of 0.1mol/L is prepared, and materials are prepared according to the component amount in the following table 1.

Table 1 raw material usage of magnesium slag carbon-fixing water permeable brick

(2) Pouring 1500g of natural coarse aggregate into a stirring pot, adding 125g of dilute acetic acid solution, stirring until the mixture is uniformly mixed, adding 500g of magnesium slag micro powder and 5g of microbial powder, continuously stirring until slurry is uniformly coated on the surface of the aggregate, and pouring into a mould for forming.

(3) And (3) standing the sample at the temperature of 25+/-2 ℃ and the relative humidity of 40% -60%, naturally curing for 8-12 h, and then placing the sample and the mould into a carbonization reaction pressure kettle.

(4) Firstly, vacuumizing the carbonization reaction pressure kettle, and then introducing CO ₂ with the concentration of 99% to the carbonization pressure of 0.02MPa to perform pre-curing for 1 hour.

(5) And after the pre-curing is finished, taking out the sample, demolding, putting into a carbonization reaction pressure kettle, vacuumizing, introducing CO ₂ with the concentration of 99% to carbonization pressure of 0.10-0.15 MPa, and carbonizing and curing for 6 hours to obtain the magnesium slag carbon-fixing water permeable brick.

In the pressure curing step, the valve and the vent hole are normally closed after the pressure is inflated to 0.15MPa in the carbonization reaction autoclave to prevent gas leakage, and the pressure gradually decreases to not lower than 0.10MPa as the carbonization reaction proceeds, that is, the valve is opened again to inflate to not higher than 0.15MPa, and the above steps are repeated until the total carbonization curing time is reached. Therefore, the whole pressure curing process is carried out in the pressure change process of 0.10-0.15 MPa, and a fixed reaction pressure is not always maintained.

According to GB/T28635-2012 'concrete pavement brick' and GB/T25993-2010 'permeable pavement brick and permeable pavement slab', the compressive strength is measured to be 7.92MPa, and the permeability coefficient is measured to be 0.223cm/s.

Example 2

The same points as those of embodiment 1 are not described here, and only the differences from embodiment 1 are described. This example differs from example 1 in that a dilute acetic acid solution of 0.5mol/L was used; the rest is shown in reference example 1, and the magnesium slag carbon-fixing water permeable brick is obtained.

And performing performance test on the obtained magnesium slag carbon-fixing water permeable brick, wherein the compressive strength is 9.48MPa, and the water permeability coefficient is 0.218cm/s.

Example 3

The same points as those of embodiment 1 are not described here, and only the differences from embodiment 1 are described. This example differs from example 1 in that a 1mol/L dilute acetic acid solution is used; the rest is shown in reference example 1, and the magnesium slag carbon-fixing water permeable brick is obtained.

And performing performance test on the obtained magnesium slag carbon-fixing water permeable brick, wherein the compressive strength is 12.04MPa, and the water permeability coefficient is 0.245cm/s.

XRD test was performed on the magnesium slag carbon-fixing water permeable brick prepared in this example, as indicated by carbonization of the fungus powder in FIG. 1. Comparing the magnesium slag micropowder raw material with the component analysis of the magnesium slag carbon-fixing water permeable brick in fig. 1, it can be seen that the diffraction peaks of the main mineral phases beta-C ₂ S and gamma-C ₂ S in the magnesium slag micropowder are obviously changed before and after carbonization, which indicates that the magnesium slag micropowder participates in the reaction and generates calcium carbonate; moreover, under the condition of the microbial powder, the generated vaterite has stronger and wider diffraction peak, which indicates that the participation of microorganisms changes the crystal form of the carbonized product calcium carbonate, and the vaterite has loose structure and is not easy to close pores, so that the subsequent carbonization process is not hindered.

Scanning electron microscope pictures of the inner and outer structures of the magnesium slag carbon-fixing water permeable bricks prepared and obtained by the embodiment are respectively shown in fig. 3 and fig. 4. As can be clearly seen from fig. 3 and 4 when comparing the morphology of the magnesium slag micropowder raw material diagram shown in fig. 2, the crystal form of the magnesium slag micropowder particles is obviously changed, the magnesium slag micropowder particles participate in the reaction to be carbonized, and the carbonized product CaCO ₃ forms cementation on the surface of the brick, and takes aggregate as a core in the inside to play a role of cladding and bonding, so that the strength development of the brick is supported together.

The mechanical strength of the magnesium slag carbon-fixing water permeable bricks obtained in the examples 1 to 3 is compared, and it can be seen that under the same carbonization condition, as the concentration of the acetic acid solution is increased, the dissolution of the calcium source in the magnesium slag micro powder is increased, the magnesium slag micro powder fully participates in carbonization, the carbonization degree is improved, and the mechanical property is also greatly increased.

Example 4

The same points as those of embodiment 3 are not described here, and only the differences from embodiment 3 are described. This example is different from example 3 in that the press carbonization curing is performed for 4 hours after the completion of the pre-curing for 0.5 hours; the rest is shown in reference example 3, and the magnesium slag carbon-fixing water permeable brick is obtained.

And performing performance test on the obtained magnesium slag carbon-fixing water permeable brick, wherein the compressive strength is 11.74MPa, and the water permeability coefficient is 0.212cm/s.

As can be seen from comparative examples 3 and 4, the magnesium slag carbon-fixing water permeable bricks obtained after 4 hours of pressure carbonization have almost no difference from the magnesium slag carbon-fixing water permeable bricks obtained after 6 hours of carbonization, so that it can be considered that 4 hours have been enough for strength development of the product, and the purpose of pressure carbonization is to ensure complete carbonization of the product.

In order to show the importance of each treatment condition in the above preparation method, the following comparative experiment was performed.

Comparative example 1

In this comparative example 1, the same points as those of example 1 are not described here again, and only the differences from example 1 are described. This comparative example differs from example 1 in that an equivalent amount of deionized water was used instead of the dilute acetic acid solution therein; the remainder was as described with reference to example 1, a first comparative water permeable brick was obtained.

In the first comparison water permeable brick, as the magnesium slag micro powder cannot react with water, the magnesium slag micro powder has no certain cohesiveness, a large amount of aggregate can fall off around a product during molding, and the appearance of the product is incomplete.

And performing performance test on the obtained first comparison water permeable brick, wherein the compressive strength is only 2.38MPa, and the water permeability coefficient is only 0.018cm/s.

The great reduction of the compressive strength and the water permeability coefficient is caused by the fact that gamma-C ₂ S crystal forms in the magnesium slag micro powder are too coarse, products are gathered on the surface of the product to form a compact calcium carbonate layer, so that the carbonization degree and the strength are low, and the water permeability is poor.

Comparative example 2

In this comparative example 2, the same points as those of example 1 are not described here again, and only the differences from example 1 are described. This comparative example is different from example 1 in that the concentration of acetic acid solution was adjusted to 3mol/L; a second comparative water permeable brick was obtained as described with reference to example 1.

And performing performance test on the obtained second comparative water permeable brick, wherein the compressive strength is 5.66MPa, and the water permeability coefficient is 0.315cm/s.

This is because a large amount of heat is released when the acetic acid solution with too high concentration reacts with the magnesium slag micropowder, so that the water loss in the product is accelerated, the medium converted into CO ₃ ^2- is lost by CO ₂, and the carbonization degree and the product strength are adversely affected to some extent.

Comparative example 3

In this comparative example 3, the same points as those of example 1 are not described here again, and only the differences from example 1 are described. This comparative example differs from example 1 in that no microbial powder was added; a third comparative water permeable brick was obtained as described with reference to example 1.

And performing performance test on the third comparative water permeable brick, wherein the compressive strength is 6.94MPa, and the water permeability coefficient is 0.215cm/s.

As can be seen from the comparison of the compressive strength of the magnesium slag carbon-fixing water permeable bricks obtained in the example 1, the compressive strength of the obtained products is obviously reduced when the same carbonization conditions (mainly referred to as carbonization time) are adopted in the absence of microbial powder. Therefore, the microbial powder is also important to shorten carbonization time and improve carbonization efficiency.

XRD tests were performed on the third comparative water permeable bricks prepared in this comparative example, as indicated by the hollow white carbonization in fig. 1. Comparing the products of this comparative example with those of example 3, it was found that carbonization of this comparative example in the absence of microbial powder produced similar product types to those of example 1, but as seen from the characteristic peaks of calcite and vaterite, the presence of microbial powder induced changes in the crystalline form and crystallinity of the two major products; that is, the addition of the microbial powder in example 1 has a certain influence on the carbonized product under the same curing conditions, mainly because the calcium carbonate crystal form generated based on the action of the microorganism is more prone to vaterite, and vaterite is the most active calcium carbonate crystal form, and is converted into a stable and high-strength calcite crystal form after carbonization and neutralization, which is one of the greatest actions of the microorganism.

Comparative example 4

In this comparative example 4, the same points as those of example 3 are not described here again, and only the differences from example 1 are described. This comparative example differs from example 3 in that no microbial powder was added; a fourth comparative water permeable brick was obtained as described with reference to example 1.

And performing performance test on the fourth comparative water permeable brick, wherein the compressive strength is 8.97MPa, and the water permeability coefficient is 0.220cm/s.

In order to observe the increase in mechanical strength of the comparative water permeable bricks in comparative example 3 and comparative example 4, the pressure carbonization was continuously performed. It was found that the compression carbonization time was prolonged to 24 hours or more, and the obtained water permeable bricks could be ensured to have the equivalent compressive strength as in example 1 and example 3, respectively.

Therefore, no matter the acetic acid solution with lower concentration or higher concentration is adopted to dissolve out the calcium source in the magnesium slag micro powder, only the microbial powder exists, carbonic anhydrase secreted in the recovery process can improve the rate of CO ₂ dissolved in water to generate CO ₃ ^2-, and CO ₃ ^2- permeates into the product along with moisture from pores and reacts with Ca ²⁺, so that the carbonization reaction process can be greatly accelerated, and the production period is shortened.

Comparative example 5

In this comparative example 5, the same points as those of example 3 are not described here again, and only the differences from example 3 are described. This comparative example is different from example 3 in that only one-step carbonization maintenance was employed and the carbonization pressure of 0.02MPa was always maintained; a fifth comparative water permeable brick was obtained as described with reference to example 3.

And performing performance test on the obtained fifth comparative water permeable brick, wherein the compressive strength is 10.76MPa, and the water permeability coefficient is 0.232cm/s.

SEM tests were performed on the inside of the fifth comparative water permeable brick, and the SEM image thereof is shown in fig. 5. As can be clearly seen from fig. 5, the morphology of the magnesium slag micropowder raw material diagram shown in fig. 2 is that the strip shape is gamma-C ₂ S still remained, and the unreacted magnesium slag appears, which is a remarkable incomplete carbonization phenomenon, because the pressure in the whole carbonization process is too low, and thus the mechanical strength is inevitably deteriorated.

Comparative example 6

In this comparative example 6, the same points as those of example 3 are not described here again, and only the differences from example 3 are described. This comparative example is different from example 3 in that only one-step carbonization maintenance is adopted and carbonization pressure of 0.10MPa to 0.15MPa is always maintained; a sixth comparative water permeable brick was obtained as described with reference to example 3.

And performing performance test on the obtained sixth comparative water permeable brick, wherein the compressive strength is 6.42MPa, and the water permeability coefficient is 0.153cm/s.

SEM tests were performed on the inside of the sixth comparative water permeable brick, and the SEM image thereof is shown in fig. 6. As can be seen from fig. 6, the product is concentrated on the surface of the water permeable brick, because the pressure of the whole carbonization process is too high, and a hoop sealing effect is formed, so that the carbonization degree is low, and the mechanical strength is further deteriorated.

As can be seen from comparative examples 5 and 6, if the one-step carbonization method is adopted, the carbonization is performed under low pressure or pressurized conditions, which causes the disadvantage of low carbonization degree; the low-pressure pre-carbonization-pressurized re-carbonization two-step carbonization method is very critical to the water permeable bricks capable of obtaining the product performance.

Claims

1. The preparation method of the magnesium slag carbon-fixing water permeable brick is characterized by comprising the following steps of:

S1, uniformly mixing natural coarse aggregate with acetic acid solution; the natural coarse aggregate is coarse aggregate in concrete materials with the particle size of 2.35-4.75 mm;

S2, adding magnesium slag micro powder and microbial powder into the mixture obtained in the step S1, stirring until the slurry is uniformly coated on the surface of the aggregate, and molding in a mold to obtain a sample; the magnesium slag micro powder is powder with the grain diameter smaller than 0.075mm, which is obtained by ball milling treatment of industrial magnesium smelting reducing slag;

S3, naturally curing the sample at the temperature of 25+/-2 ℃ and the humidity of 40% -60% for 8-12 hours to obtain a primary curing sample;

S4, carrying out CO ₂ pre-curing on the primary curing sample for 0.5-1 h to obtain a shaping sample; the pre-curing pressure is not more than 0.02MPa; wherein, the concentration of CO ₂ used for curing is at least 99%;

S5, after the shaping sample is demoulded, carrying out CO ₂ pressurizing maintenance for 4-6 hours to obtain the magnesium slag carbon-fixing water permeable brick; the pressure maintenance pressure is 0.10MPa to 0.15MPa; wherein, the concentration of CO ₂ used for curing is at least 99%;

wherein the mixing amount of the acetic acid solution is 20-30% of the mass of the magnesium slag micro powder, and the mixing amount of the magnesium slag micro powder is 25-40% of the natural coarse aggregate.

2. The method according to claim 1, wherein the microbial powder is a carbonic anhydrase-producing microbial powder.

3. The method according to claim 2, wherein the microbial powder is bacillus mucilaginosus.

4. The method according to claim 1, wherein in the step S1, the acetic acid solution is diluted acetic acid of 0.1mol/L to 1 mol/L.