Method for adsorbing and fixing heavy metal ions in water and geopolymer cementing material

Abstract

The application discloses a method for adsorbing and fixing heavy metal ions in water and a method for preparing a geopolymer cementing material, and belongs to the fields of environmental protection engineering and material engineering, and comprises the following steps: carbonized micro powder is used to adsorb heavy metal ions in water; the carbonized micro powder is obtained by carbonizing concrete micro powder in a carbon dioxide atmosphere; the carbonized micro powder after adsorbing heavy metal ions is mixed with one or more of granulated blast furnace slag, gypsum and steel slag to obtain a solid material; and the solid material is mixed with an alkali activator and then cured and shaped; the application can significantly improve the solidification amount of heavy metals, and the solidification efficiency can reach 99.99%; meanwhile, the prepared geopolymer has excellent mechanical properties, can be used as a low-cost green building material or in the field of solid waste landfill, and has remarkable environmental and economic benefits, and solves the problem of high-concentration heavy metal pollution treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental protection engineering and material engineering, and particularly relates to a method for adsorbing and fixing heavy metal ions in water and a geopolymer cementing material. BACKGROUND

[0002] In the past 30 years, the heavy metal industry has experienced rapid expansion, industrial manufacturing, mining, non-standard use and overuse of industrial wastewater, and a large amount of heavy metal waste has been discharged into the environment, which has seriously threatened human health and the living environment and has become a very challenging environmental problem.

[0003] Solidification / Stabilization (S / S) technology has been widely proven to be an efficient, fast and economical method for heavy metal treatment. Traditional Portland cement is a good solidification agent and binder, but the production of Portland cement will produce a large amount of carbon dioxide emissions and energy consumption, thereby exacerbating the greenhouse effect. Similar to Portland cement, geopolymer (geopolymer) also shows excellent heavy metal ion fixation capacity, and the production of geopolymer uses solid waste materials, which is more cost-effective and does not exacerbate the greenhouse effect. In Solidification / stabilization mechanism of Pb(II), Cd(II), Mn(II) and Cr(III) in fly ash based geopolymers (Construction and Building Materials, 2018, 160:818-827), Han Fenglan et al. prepared geopolymer using fly ash as raw material under alkaline activation conditions for solidification of heavy metals Pb 2+ , Cd 2+ , Mn 2+ and Cr 3+ , and the study showed that when the dosage of Pb 2+ , Cd 2+ , Mn 2+ and Cr 3+ was 1.5wt%, the solidification efficiency reached 99.92-99.98%, and the 28-day compressive strength of the sample reached a maximum of 49.34MPa; In Immobilization efficiency and mechanism of metal cations (Cd 2+ , Pb 2+ and Zn 2+ ) and anions (AsO4 3- and Cr2O7 2-)in wastes-based geopolymer》(Journal ofHazardous Materials,2020,384:121290) in which drinking water treatment residues (DWTR) and ground blast furnace slag (GBFS) were used as main raw materials to prepare geopolymers for immobilization of Cd 2+ , Pb 2+ and Zn 2+ under alkali activation conditions. The results showed that the immobilization efficiency reached 92.34%-100% when the content of Cd 2+ , Pb 2+ and Zn 2+ was below 4wt%, and the 7-day compressive strength of the samples reached a maximum of 16MPa. Existing research shows that alkali geopolymers have high efficiency in immobilizing heavy metal ions, but the maximum concentration of heavy metal ions that can be immobilized is generally low, usually limited to 0.5wt% to 4wt%. When the content of heavy metal ions is high, it will seriously hinder the progress of alkali activation reaction and cause poor fluidity, which limits its application in high-concentration heavy metal pollution control.

[0004] On the other hand, the resource utilization rate of construction waste in China is only 5%, and most of the construction waste is directly discarded or landfilled. Waste concrete, as the main component of construction waste, generates waste concrete powder with a particle size of less than 0.15mm during the recycling process, which is still mainly used for landfill or as a filler material and has not been effectively utilized. Waste concrete powder is rich in a large amount of hydration products such as hydrated calcium silicate, and these mineral components have high carbonation activity and can react with CO2 to reconstruct mineral components to generate calcium carbonate, amorphous silica gel and aluminum gel, etc. The carbonated micro-powder product can effectively adsorb and remove heavy metal ions in wastewater, and the carbonated micro-powder that has adsorbed heavy metals can be further solidified by alkali activation technology. SUMMARY

[0005] To solve the above problems, the present application uses the solidification / stabilization technology of geopolymer to provide a method for adsorbing and fixing heavy metal ions in water and a geopolymer cementing material, which can effectively adsorb and fix high-concentration heavy metal contaminated wastewater and at the same time produce a geopolymer cementing material with high compressive strength. The preparation cost is low, it is low-carbon and environmentally friendly, and it can be widely used in the field of solid waste landfill, etc.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A method for adsorbing and fixing heavy metal ions in water, comprising the following steps:

[0008] (1) absorbing heavy metal ions in water by carbonized micro powder, wherein the carbonized micro powder is obtained by carbonizing concrete micro powder in carbon dioxide atmosphere, and the concrete micro powder is obtained by grinding cement after hydration, such as grinding cement after natural curing into powder, grinding waste concrete into powder, or grinding waste concrete with coarse aggregate and / or fine aggregate into powder;

[0009] (2) mixing the carbonized micro powder after absorbing heavy metal ions with one or more of granulated blast furnace slag, gypsum, and steel slag to obtain a solid material;

[0010] (3) curing and forming the solid material after mixing with an alkali activator;

[0011] In some preferred embodiments, the heavy metal ions are one or more of lead ions, zinc ions, and copper ions.

[0012] In some preferred embodiments, the particle size of the concrete micro powder is less than 125 μm.

[0013] In some preferred embodiments, the content of CaO in the concrete micro powder is not less than 48.28% by weight, the content of SiO2 is not less than 15.27% by weight, and the content of Al2O3 is not less than 4.32% by weight.

[0014] In some preferred embodiments, the carbonization conditions are: humidity 70±3%, temperature 20±2℃, carbon dioxide concentration 20±3%, and carbonization time 7 days.

[0015] In some preferred embodiments, the granulated blast furnace slag is S95 grade slag, and the median particle size D50 is 12.06 μm.

[0016] In some preferred embodiments, the mass ratio of the carbonized micro powder after absorbing heavy metal ions in the solid material is 30-70%.

[0017] In some preferred embodiments, the alkali activator comprises a mixture of sodium hydroxide solution and water glass, the modulus of which is 1-2, and the content of Na2O is 3-6 wt%.

[0018] In some preferred embodiments, the water-cement ratio of the solid material to the alkali activator is 0.38-0.45.

[0019] In some preferred embodiments, the curing temperature in step (3) is 20±2℃, and the relative humidity is >95%.

[0020] Another object of the present application is to provide a geopolymer cementing material prepared by the aforementioned adsorption and fixation method.

[0021] The beneficial effects of the present application are:

[0022] The present application uses the huge adsorption capacity of carbonized concrete micro powder to first adsorb heavy metal ions in wastewater, and then uses its high alkali activation activity to react with slag and other precursors to generate a cementing material with a three-dimensional cross-linked structure, providing superior structural strength for geopolymer. In this process, a large amount of heavy metals are introduced into the geopolymer system, and heavy metal ions can form certain special phases in the matrix phase by forming certain chemical bonds with the aluminosilicate framework during the formation of the geopolymer structure; in addition, the gel network of geopolymer has good inclusion performance, which can stably embed heavy metals and their generated precipitates into its microstructure, thereby effectively limiting the migration ability of heavy metals and the possibility of secondary reaction, improving the environmental durability and safety of the material. The geopolymer solidified body after solidifying heavy metals has excellent mechanical properties, and can solidify a large amount of heavy metals, and the leaching concentration of each heavy metal is far below the limit value, reducing the environmental diffusion of heavy metals; the present application uses industrial by-products, effectively reducing the demand for expensive adsorption materials and waste treatment costs, while converting waste materials into valuable building materials, reducing the energy consumption and carbon emissions of new material production, meeting the standards of environmental protection and sustainable development, and improving environmental sustainability. BRIEF DESCRIPTION OF DRAWINGS

[0023] The present application is further illustrated by the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present application. For ordinary skilled persons in the art, other drawings can be obtained without creative labor on the basis of the following drawings.

[0024] Figure 1 is a flow chart of the heavy metal ion adsorption and solidification method in the wastewater described in the present application;

[0025] Figure 2 is the unconfined compressive strength result of the geopolymer cementing material test piece prepared in Example 1 of the present application;

[0026] Figure 3 is the unconfined compressive strength result of the geopolymer cementing material test piece prepared in Example 2 of the present application;

[0027] Figure 4 is the unconfined compressive strength result of the geopolymer cementing material test piece prepared in Example 3 of the present application;

[0028] Figure 5 is the toxicity leaching result of the geopolymer cementing material test piece prepared in Example 1 of the present application;

[0029] Figure 6 is the toxicity leaching result of the geopolymer cementing material test piece prepared in Example 2 of the present application;

[0030] Figure 7 Toxicity leaching results of geopolymer cementitious material test pieces prepared in Example 3 of the present application;

[0031] Figure 8 Toxicity leaching results of geopolymer cementitious material test pieces prepared in Comparative Example 1 of the present application;

[0032] Figure 9 Unconfined compressive strength results of geopolymer cementitious material test pieces prepared in Comparative Example 2 of the present application;

[0033] Figure 10 Toxicity leaching results of geopolymer cementitious material test pieces prepared in Comparative Example 2 of the present application;

[0034] Figure 11 Unconfined compressive strength results of geopolymer cementitious material test pieces prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0035] The present application is further described in conjunction with the following examples.

[0036] Example 1

[0037] This example relates to a method for adsorbing and solidifying heavy metal ions in wastewater, and also relates to a method for preparing a geopolymer cementitious material, comprising the following steps:

[0038] (1) grinding a cement naturally cured for 7 days in a ball mill to a particle size of less than 125 μm to obtain a concrete micro-powder, the concrete micro-powder having a CaO content of 48.28%, a SiO2 content of 15.27%, and an Al2O3 content of 4.32%, and then carbonating the concrete micro-powder under conditions of a humidity of 70±3%, a temperature of 20±2°C, and a carbon dioxide concentration of 20±3% for 7 days, the grayish white concrete micro-powder being converted into a carbonated concrete micro-powder that is pure gray after carbonation; adding the carbonated concrete micro-powder and lead-containing wastewater into a glass container in a ratio of 10 g:1 L, the concentration of lead ions in the wastewater being 1600 mg / L, and then shaking in a shaking bed at a speed of 200 revolutions per minute and a temperature of 25°C for 10 minutes, and then filtering with a 30 μm PP polypropylene filter membrane in a vacuum filtration device to obtain a powder and treated wastewater, and then drying the carbonated concrete micro-powder that has adsorbed the lead ions in a 60°C oven for 4 hours, and then testing the concentration of heavy metal ions in the treated wastewater;

[0039] (2) mixing water, NaOH and water glass to prepare an alkaline activator with a modulus of 1.2 and a Na2O content of 5%, and standing for 24 h for standby; mixing the carbonized concrete micro-powder after drying and adsorbing lead ions in step (1) and granulated blast furnace slag by weight (50%:50%, wherein the theoretical heavy metal accounts for about 7% of the mass of the ash body) in a cement paste mixer to obtain a solid material, then adding the alkaline activator at a water-cement ratio of 0.4 and stirring rapidly for 4 min, pouring the uniformly stirred slurry into a 20x20x20mm 3 hexagonal test mold, vibrating on a vibration table for 1 min, scraping the surface flat, standing and sealing with a preservative film for 1 day, then demolding and curing under the conditions of a temperature of 20±2°C and a relative humidity of >95% to the specified age;

[0040] The granulated blast furnace slag is S95 grade slag, and its main components are CaO (40.03%), SiO2 (33.58%), and Al2O3 (14.59%).

[0041] Example 2

[0042] This embodiment relates to a method for adsorbing and solidifying heavy metal ions in wastewater, and also relates to a preparation method of a geopolymer cementitious material, comprising the following steps:

[0043] (1) grinding cement naturally cured for 7 days in a ball mill to a particle size of less than 125 μm to obtain concrete micro-powder, wherein the CaO content of the concrete micro-powder is 48.28%, the SiO2 content is 15.27%, and the Al2O3 content is 4.32%; then carbonizing the concrete micro-powder under the conditions of a humidity of 70±3%, a temperature of 20±2°C, and a carbon dioxide concentration of 20±3% for 7 days, so that the grayish white concrete micro-powder is converted into pure gray carbonized concrete micro-powder; adding the carbonized concrete micro-powder and lead-containing wastewater into a glass container at a ratio of 10 g:1 L, wherein the concentration of lead ions in the wastewater is 2000 mg / L, and then shaking in a shaking bed at a speed of 200 rpm and a temperature of 25°C for 10 min, and then filtering with a 30 μm PP polypropylene filter membrane in a vacuum filtration device to obtain powder and treated wastewater, and drying the carbonized concrete micro-powder adsorbing lead ions obtained by filtration in an oven at 60°C for 4 h, and testing the concentration of heavy metal ions in the treated wastewater;

[0044] (2) mixing water, NaOH and water glass to prepare an alkaline activator with a modulus of 1.2 and a Na2O content of 4%, and standing for 24 h for standby; mixing the carbonized concrete micro-powder after drying and adsorbing lead ions in step (1) and granulated blast furnace slag by weight (50%:50%, wherein the theoretical heavy metal accounts for 8.5% of the mass of the ash body) in a cement paste mixer to obtain a solid material, then adding the alkaline activator at a water-cement ratio of 0.45 and stirring rapidly for 4 min, pouring the uniformly stirred slurry into a 20x20x20mm 3 hexagonal test mold, vibrating on a vibration table for 1 min, scraping the surface flat, standing and sealing with a preservative film for 1 day, then demolding and curing under the conditions of a temperature of 20±2°C and a relative humidity of >95% to the specified age;

[0045] The granulated blast furnace slag is S95 grade slag, and its main components are CaO (40.03%), SiO2 (33.58%), and Al2O3 (14.59%).

[0046] Example 3

[0047] This embodiment relates to a method for adsorbing and solidifying heavy metal ions in wastewater, and also relates to a preparation method of a geopolymer cementitious material, comprising the following steps:

[0048] (1) grinding cement naturally cured for 7 days in a ball mill to a particle size of less than 125 μm to obtain concrete micro-powder, the CaO content of the concrete micro-powder is 48.28%, the SiO2 content is 15.27%, and the Al2O3 content is 4.32%, then carbonizing the concrete micro-powder under the conditions of a humidity of 70±3%, a temperature of 20±2°C, and a carbon dioxide concentration of 20±3% for 7 days, the grayish white concrete micro-powder is changed into pure gray carbonized concrete micro-powder after carbonization; adding the carbonized concrete micro-powder and lead-containing wastewater into a glass container at a ratio of 10 g:1 L, the concentration of lead ions in the wastewater is 2000 mg / L, shaking in a shaker at a speed of 200 rpm and a temperature of 25°C for 10 min, then filtering with a 30 μm PP polypropylene filter membrane in a vacuum filtration device to obtain powder and treated wastewater, the carbonized concrete micro-powder adsorbing lead ions obtained by filtration is dried in a 60°C oven for 4 hours, and the treated wastewater is used for testing the concentration of heavy metal ions;

[0049] (2) Prepare an alkaline activator by mixing water, NaOH, and water glass, with a modulus of 1.2 and a Na2O content of 4%, and let it stand for 24 hours for later use; add the carbonized concrete micro powder with lead ions adsorbed in step (1) to a cement paste mixer at a mass ratio of 2:7:1 (theoretically, heavy metals account for about 3.33% of the ash mass) to obtain a solid material, and then add the alkaline activator at a water-cement ratio of 0.4 and stir quickly for 4 minutes. Pour the uniformly stirred paste into a 20×20×20mm... 3 In the six-unit trial mold, the surface was vibrated for 1 minute on the vibration table, the surface was scraped flat, it was left to stand and sealed with plastic wrap for 1 day, and then demolded and cured at a temperature of 20±2℃ and relative humidity of >95% until the specified age.

[0050] The granulated blast furnace slag is S95 grade slag, whose main components are CaO (40.03%), SiO2 (33.58%) and Al2O3 (14.59%).

[0051] The gypsum is phosphogypsum, whose main components are CaO (38.26%), SiO2 (7.52%) and SO3 (49.17%).

[0052] Performance testing

[0053] 1. Adsorption capacity

[0054] Pb(NO3)2 (160 mg / 200 mg) was added to 100 mL of deionized water to simulate heavy metal wastewater. The mixture was shaken in a shaker at 25 °C and 200 rpm for 10 minutes. The solution was then filtered through a 30 μm PP polypropylene membrane in a vacuum filtration device to obtain the powder and the treated wastewater. The Pb content in the treated wastewater was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). 2+ Concentration, adsorption capacity of heavy metal ions (Q) e The calculation formula is:

[0055]

[0056] In the formula, Q e Average adsorption capacity (mg / g); CO and C e The initial and equilibrium heavy metal ion concentrations are respectively (mg / L); V is the solution volume (L), and m is the mass of CRP (g).

[0057] The formula for calculating the adsorption rate Ae (%) is:

[0058]

[0059] In the formula, C0 and C eInitial and equilibrium heavy metal ion concentration (mg / L), respectively.

[0060] 2. Compressive strength

[0061] The geopolymer material test piece prepared in the examples and cured to the curing age under standard conditions was placed on the test bench of the constant loading cement flexural and compressive strength tester, the contact area was 400mm 2 , the loading rate was 0.1mm / min, until the solidified body was damaged, the compressive strength P (MPa) of the solidified body = F / A, wherein F was the peak load of damage, and A was the pressure area; the compressive strength experiment was determined in triplicate and the average value was taken.

[0062] 3. Toxicity leaching

[0063] After the test piece was cured for 3 days, 7 days and 28 days, it was crushed and sieved, the powder with a particle size less than 200μm was collected, 2g of the powder was taken, 40mL of acetic acid buffer leaching agent was added, and it was placed in a 100mL polyethylene bottle, the bottle opening was sealed, and it was placed in a constant temperature shaker, the speed was set to 120r / min, the temperature was 24±1℃, and the shaking was performed for 18 hours, then a needle filter was used to filter through a 0.45μm filter membrane, and the filtrate was collected in a test tube, after filtration, the filtrate was treated with concentrated nitric acid to reduce the pH value to below 2.0, and the concentration of heavy metals in the leachate was measured by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0064] The preparation method of the acetic acid buffer leaching agent is: 5.7mL of glacial acetic acid is added to deionized water, mixed uniformly, and then diluted to 1L, and the pH value of the solution is adjusted to 2.88±0.05.

[0065] Test results

[0066] (1) The adsorption amount and adsorption rate of the adsorption and solidification method described in examples 1-2 are shown in table 1.

[0067] Table 1 Adsorption amount and adsorption rate of examples 1-2

[0068]

[0069] (2) The compressive strength data of the test piece prepared by the adsorption and solidification method described in example 1-3 are shown in Figure 2 , Figure 3 , Figure 4 According to Figure 2 , Figure 3 and Figure 4 , it can be seen that the strength of the test piece gradually increases with the increase of the curing age, and after curing for 3 days, 7 days and 28 days, the strength can meet the requirements of construction (more than 10MPa).

[0070] (3) The leaching concentration is a key indicator for evaluating the solidification and stabilization effect of geopolymer. The lower the value, the stronger the solidification ability and stability of the geopolymer. The leaching concentration data of the test pieces prepared by the adsorption and solidification method described in Examples 1-3 are shown in Tables 1-3, respectively. Figure 5 、 Figure 6 、 Figure 7 as shown in Figure 5 、 Figure 6 、 Figure 7 As shown in 2+ When the adsorption amount of carbonized concrete micro powder to Pb 2+ reaches 200 mg / g, the leaching concentration of Pb 2+ does not exceed the limit value (Pb < 5 mg / L) specified in the Hazardous Waste Identification Standard-Leaching Toxicity Identification (GB5085.3-2007) within 3 days, 7 days or 28 days of curing period. The experimental results show that the solidification rate of Pb 2+ exceeds 99%, further verifying that the geopolymer material has excellent solidification ability and environmental stability to Pb 2+ In an alkaline environment, Pb - may form hydroxyl coordination ions with OH 2+ to generate stable heavy metal hydroxide precipitates and be sealed in the cementitious material of the geopolymer. In addition, Pb 2+ also ion-exchanges with Ca 2+ in the ettringite generated in the alkali-activated reaction of C-(A)-S-H and gypsum, and is incorporated into the silicate grid and adsorbed by ettringite. At the same time, the formation of hydration products refines the pore structure of the material, reducing the migration path of heavy metal ions. These factors work together to improve the adsorption and solidification ability of Pb

[0071] Comparative Example 1

[0072] A wastewater treatment method, which is also a preparation method of geopolymer cementitious material, is the same as Example 1, except that the solid raw material is obtained by mixing and stirring slag and carbonized micro powder, wherein the carbonized concrete micro powder accounts for 42%, the slag accounts for 50%, and the remaining 8% of lead nitrate is added in the form of a wastewater solution. The specific steps include:

[0073] (1) Grinding the cement naturally cured for 7 days in a ball mill to a particle size of less than 125 μm to obtain concrete micro powder, wherein the CaO content of the concrete micro powder is 48.28%, the SiO2 content is 15.27%, and the Al2O3 content is 4.32%. Then, carbonize the concrete micro powder under the conditions of humidity 70±3%, temperature 20±2℃, and carbon dioxide concentration 20±3% for 7 days. The grayish white concrete micro powder after carbonization turns into pure gray carbonized concrete micro powder;

[0074] (2) Prepare an alkaline activator by mixing water, NaOH and water glass, with a modulus of 1.2 and a Na2O content of 5%, and let it stand for 24 hours for later use; add the carbonized concrete powder obtained in step (1) and granulated blast furnace slag to a cement paste mixer at a ratio of 42%:50% to obtain a solid material, add lead-containing wastewater, and then add the remaining alkaline activator at a water-cement ratio of 0.4, stir quickly for 4 minutes, and pour the uniformly mixed paste into a 20×20×20mm container. 3 In the six-unit trial mold, the surface was vibrated for 1 minute on the vibration table, the surface was scraped flat, it was left to stand and sealed with plastic wrap for 1 day, and then demolded and cured at a temperature of 20±2℃ and relative humidity of >95% until the specified age.

[0075] The test methods for compressive strength and leaching concentration of the specimen in Comparative Example 1 were the same as those in Example 1.

[0076] Compared to Example 1, Comparative Example 1, where lead-containing wastewater was directly incorporated, showed no compressive strength at any age. This is because after directly adding Pb(NO3)2, the Pb dissolved from Pb(NO3)2... 2+ It reacts with sodium silicate and sodium hydroxide in the alkali activator to form flocculent products of lead silicate and lead hydroxide. After stirring, it eventually forms an insoluble precipitate, reducing the alkalinity of the solution. This severely hinders the alkali activation reaction process, resulting in poor flowability. It also hinders the dissolution of active Si and Al in the geopolymer precursor material, as well as [SiO4] and [AlO4]. - The aggregation of.

[0077] The leaching concentration of Comparative Example 1 is as follows Figure 8 As shown; according to Figure 8 It can be seen that the leaching concentration of Comparative Example 1 is much higher than that of Example 1, and the leaching concentration of Comparative Example 1 is higher than the limit after 3 days, and the leaching concentration after 28 days is also much higher than that of Example 1. This difference is mainly attributed to the partial direct dissolution of Pb. 2+ Hydroxide precipitates and complexes formed in alkaline environments readily redissolve under acidic conditions, thereby increasing Pb levels. 2+ The amount of leaching.

[0078] Comparative Example 2

[0079] A solid raw material is obtained by mixing and stirring slag and calcium carbide slag evenly, with slag accounting for 65% and calcium carbide slag accounting for 35%. Then, 1.5% lead nitrate is added in the form of a wastewater solution. The specific steps include:

[0080] An alkaline activator with a modulus of 1.2 and a Na₂O content of 5% was prepared by mixing water, NaOH, and water glass and allowing it to stand for 24 hours. Lead-containing wastewater was added, followed by the remaining alkaline activator at a water-cement ratio of 0.4. The mixture was stirred rapidly for 4 minutes, and the homogeneous slurry was poured into a 20×20×20mm container. 3 In the six-unit trial mold, the surface was vibrated for 1 minute on the vibration table, the surface was scraped flat, it was left to stand and sealed with plastic wrap for 1 day, and then demolded and cured at a temperature of 20±2℃ and relative humidity of >95% until the specified age.

[0081] The granulated blast furnace slag is S95 grade slag, whose main components are CaO (40.03%), SiO2 (33.58%) and Al2O3 (14.59%).

[0082] The main components of the carbide slag are CaO (89.5%), SiO2 (5.17%) and Al2O3 (2.99%).

[0083] The test methods for compressive strength and leaching concentration of the specimen in Comparative Example 2 were the same as those in Example 1.

[0084] The compressive strength data of the specimens prepared by the adsorption-curing method described in Comparative Example 2 are as follows: Figure 9 As shown, according to Figure 9 It can be seen that the strength of the specimens gradually increases with the increase of the curing age. However, after 3, 7, and 28 days of curing, the strength still fails to meet the construction requirements (greater than 10 MPa). This is mainly because the content of Al2O3 and SiO2 in the carbide slag is low, resulting in low alkali activation activity. Furthermore, after directly adding Pb(NO3)2, the Pb dissolved from Pb(NO3)2... 2+ It reacts with sodium silicate and sodium hydroxide in the alkali activator to form flocculent products of lead silicate and lead hydroxide. After stirring, it eventually forms an insoluble precipitate, reducing the alkalinity of the solution. This severely hinders the alkali activation reaction process, resulting in poor flowability. It also hinders the dissolution of active Si and Al in the geopolymer precursor material, as well as [SiO4] and [AlO4]. - Aggregation.

[0085] The leaching concentration of Comparative Example 2 is as follows Figure 10 As shown; according to Figure 10 It can be seen that the leaching concentrations of Comparative Example 2 at 3 and 7 days were much higher than the limits, and the leaching concentration after 28 days was also much higher than that of Example 1. This difference is mainly attributed to the partial direct dissolution of Pb. 2+ Hydroxide precipitates and complexes formed in alkaline environments readily redissolve under acidic conditions, thereby increasing Pb levels. 2+ The leaching amount is also related to the low compressive strength caused by the low activity of carbide slag.

[0086] Comparative Example 3

[0087] A geopolymer cementitious material, same as Example 1, except that the carbonated micro powder does not adsorb heavy metal ions:

[0088] (1) The concrete micro powder and its carbonation method are same as Example 1;

[0089] (2) Water, NaOH and water glass are mixed to prepare an alkaline activator with a modulus of 1.2 and a Na2O content of 5%, and are left to stand for 24 h for standby; the carbonated concrete micro powder prepared in step (1) is mixed with granulated blast furnace slag in equal weight (50%: 50%) and is added into a cement paste mixer to be stirred and mixed to obtain a solid material, then the alkaline activator is added at a water-cement ratio of 0.4 and is rapidly stirred for 4 min, the uniformly stirred paste is poured into a 20x20x20mm 3 six-unit test mold, is vibrated on a vibration table for 1 min, is scraped flat on the surface, is left to stand and is sealed with a preservative film for 1 day, then is demolded and is cured under the conditions of a temperature of 20±2℃ and a relative humidity of >95% to a specified age;

[0090] The granulated blast furnace slag is same as Example 1.

[0091] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for adsorbing and fixing heavy metal ions in water, characterized by, The method comprises the following steps: (1) adsorbing heavy metal ions in water by carbonized micro powder, wherein the carbonized micro powder is obtained by carbonizing concrete micro powder in a carbon dioxide atmosphere, and the concrete micro powder is obtained by grinding cement after hydration; the content of CaO in the concrete micro powder is not less than 48.28% by weight, the content of SiO2 is not less than 15.27% by weight, and the content of Al2O3 is not less than 4.32% by weight; (2) mixing the carbonized micro powder after adsorbing heavy metal ions with one or more of granulated blast furnace slag, gypsum and steel slag to obtain a solid material; (3) curing and forming the solid material after mixing with an alkali activator.

2. The method of claim 1, wherein the water is treated with the adsorbent to remove heavy metal ions from the water. The heavy metal ions are one or more of lead ions, zinc ions and copper ions.

3. The method of claim 1, wherein the method is characterized by: The particle size of the concrete micro powder is less than 125 μm.

4. The method of claim 1, wherein the water containing heavy metal ions is a waste water containing heavy metal ions. The carbonization conditions are as follows: humidity 70±3%, temperature 20±2 ℃, carbon dioxide concentration 20±3%, and carbonization time 7 days.

5. The method of claim 1, wherein the method is characterized by: The granulated blast furnace slag is S95 grade slag, and the median particle size D50 is 12.06 μm.

6. The method of claim 1, wherein the method is characterized by, The mass ratio of the carbonized micro powder after adsorbing heavy metal ions in the solid material is 30-70%.

7. The method of claim 1, wherein the method is characterized by: The alkali activator comprises a mixture of sodium hydroxide solution and water glass, the modulus of which is 1-2, and the content of Na2O is 3-6 wt%.

8. The method of claim 1, wherein the method is characterized by: The water-cement ratio of the solid material to the alkali activator is 0.38-0.

45.

9. A geopolymer cementitious material characterised in that, Prepared by the method of any one of claims 1-8.

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