A composite cementitious material encapsulating chromium and a method of making the same

Abstract

The application discloses a kind of solid sealing chromium composite cementitious material and preparation method thereof, solid sealing chromium composite cementitious material includes the following mass percentage of substance: 65wt.%~75wt.% of clinker with heavy metal content, 20wt.%~34wt.% of poly-element auxiliary cementitious material, the rest is gypsum;Total chromium content in clinker with heavy metal content is greater than 150mg / kg;Poly-element auxiliary cementitious material includes the following mass percentage of substance: 30wt.%~50wt.% of microbial mineralization steel slag powder, 20wt.%~40wt.% of metakaolin, the rest is fly ash;Microbial mineralization steel slag powder is prepared by carbonic anhydrase producing bacteria and steel slag powder carbon fixation grinding.The application is based on the synergistic effect between clinker with heavy metal and the overall chemical composition of poly-element composite auxiliary cementitious material, and the pH value of solidified body is reduced by secondary hydration.

Description

Technical Field

[0001] This invention relates to composite cementitious materials and their preparation methods, specifically to a composite cementitious material for chromium sealing and its preparation method. Background Technology

[0002] Currently, waste materials rich in heavy metal ions, such as used batteries, used electrical appliances, and slag, are often mixed with municipal solid waste. Although cement kiln co-processing technology can effectively solidify these heavy metal ions and significantly reduce their leaching risk, once these ions enter the cement kiln system, they can still have a significant impact on the calcination process, mineral phase structure, and hydration activity of cement clinker, leading to potential ion leaching risks.

[0003] Because Cr(VI) compounds remain soluble in the strongly alkaline environment of cement hydration and readily dissolve upon contact with water or other liquids, how to solidify high-Cr(VI) content clinker produced through co-processing in cement kilns has become an urgent problem to be solved. However, most current techniques for solidifying Cr(VI) rely on physical adsorption. While this method is effective in liquid environments such as polluted water, when introduced into solid environments, such as cement concrete, the indiscriminate adsorption characteristics of the adsorbent significantly weaken its adsorption effect on heavy metal ions. Furthermore, it may adversely affect the cement hydration process and even pose a risk of desorption. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a composite cementitious material for sealing chromium with high strength. Another purpose of this invention is to provide a method for preparing a composite cementitious material for sealing chromium that has abundant raw material sources and low price.

[0005] Technical solution: The composite cementitious material for solidifying chromium described in this invention comprises the following substances by mass percentage: 65wt.% to 75wt.% clinker containing heavy metals, 20wt.% to 34wt.% multi-component auxiliary cementitious materials, and the remainder being gypsum; the total chromium content in the clinker containing heavy metals is greater than 150mg / kg;

[0006] The multi-component auxiliary cementitious material includes the following substances by mass percentage: 30 wt.% to 50 wt.% microbial mineralized steel slag powder, 20 wt.% to 40 wt.% metakaolin, and the balance being fly ash; the microbial mineralized steel slag powder is prepared by grinding carbon-fixing powder with carbon-fixing bacteria.

[0007] Furthermore, the carbon fixation rate of microbially mineralized steel slag powder is 8wt.%–10wt.%, and the specific surface area is ≥300m². 2 / kg, with satisfactory stability and an activity index ≥80% after 28 days.

[0008] To further reduce costs, metakaolin was replaced with aluminum waste residue. The aluminum waste residue is one or more of calcined coal gangue, lithium slag, and mineral slag.

[0009] Furthermore, the gypsum can be any one of desulfurized gypsum, phosphogypsum, or fluorogypsum.

[0010] Furthermore, the preparation method of microbial mineralized steel slag powder is as follows: Carbonic anhydrase-producing bacteria are activated and cultured for 24-48 hours, and then mixed with water at a mass ratio of 2%-6% to obtain a microbial additive. The microbial additive is then stirred with steel slag powder at a liquid-to-solid ratio of 0.10-0.40, and carbon is fixed at 10-70℃ for 60-70 minutes. The powder is then ground to a specific surface area of ​​300 μL. 2 / kg or more.

[0011] The preparation method of the above-mentioned composite cementitious material for chromium sealing includes the following steps:

[0012] Step 1: Weigh out the clinker, multi-component auxiliary cementitious materials, and gypsum containing the required amount of heavy metals, and mix them evenly.

[0013] Step 2: Weigh room temperature water according to a water-cement ratio of 0.35 to 0.45, slowly add the water to the mixture obtained in Step 1, stir slowly and then stir at high speed in a high-shear mode to form a plastic composite cementitious material slurry, pour it into a mold, and cure at room temperature.

[0014] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 28 to 35 days.

[0015] Furthermore, in step one, the stirring time is 1 to 3 minutes.

[0016] Furthermore, in step two, the slow stirring speed is 130 r / min to 150 r / min for 110 s to 130 s, and the high-speed stirring speed is 270 r / min to 290 r / min for 110 s to 130 s. The curing time at room temperature is 24 h to 30 h.

[0017] Preparation Principle: Compared to mineral calcium carbonate, bio-calcium carbonate in microbially mineralized steel slag powder has an unstable crystal form and smaller grain size, making it more prone to reaction. Furthermore, the reducing substances such as ferrous iron and sulfides in the steel slag powder have a reducing effect on heavy metal ions. Since low-valent chromium is easily oxidized to high-valent chromium in an alkaline environment, this invention proposes a five-element composite cementitious material system: clinker-calcareous binder-aluminous binder-silica binder-gypsum. This system lowers the pH value of the solidified body through secondary hydration (volcanic ash reaction). Aluminous binder (metakaolin) accelerates the formation of layered calcium aluminate carbonate from calcium carbonate, while high-silica binder (fly ash) synergistically reacts to generate a porous CASH gel, which can both stably seal heavy metal ions and maintain high strength even at a low clinker coefficient. To further reduce costs, the proportion of fly ash can be increased, and calcined coal gangue, lithium slag, and other aluminous waste residues can partially replace the more expensive metakaolin.

[0018] The composite cementitious material of this invention produces a novel solidified heavy metal ion system as its hydration product. Calcium aluminate carbide has a layered structure similar to graphene, consisting of a main layer and interlayered anions and water molecules forming layered bimetallic hydroxides (LDHs); its main layer contains positively charged Al... 3+ It can be replaced by heavy metal cations, such as Zn. 2+ Pb 2+ Cr 3 + Negatively charged CO3 in the interlayer 2- It can be replaced by heavy metal anion groups, such as CrO4. 2- (Cr(VI)) and AsO4 3- CASH gel is a three-dimensional network product composed of silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. Heavy metals can be chemically bound into this porous structure, exhibiting good heavy metal binding performance. Furthermore, this gel has excellent physical, mechanical, and durability properties.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0020] 1. Based on the synergistic effect between the overall chemical composition of heavy metal clinker and multi-component composite auxiliary cementitious materials, microbial mineralized steel slag powder containing bio-calcium carbonate and possessing reducing substances is introduced.

[0021] 2. Since low-valent chromium is easily oxidized to high-valent chromium in an alkaline environment, a five-element composite cementitious material system of "clinker-calcareous adhesive-aluminous adhesive-silica adhesive-gypsum" is proposed, which reduces the pH value of the solidified body through secondary hydration (volcanic ash reaction).

[0022] 3. Utilize aluminum-based adhesive (meta-kaolin) to accelerate the formation of calcium carbonate into stable calcium aluminate that seals heavy metal ions, while supplementing with silica-based adhesive (fly ash) to synergistically generate CASH gel that can chemically bind with heavy metals.

[0023] 4. While sealing heavy metal ions, the cementitious material has high strength under low clinker coefficient, which is conducive to promoting the application of microbial mineralized steel slag powder.

[0024] 5. This invention can also reduce costs while ensuring strength by increasing the proportion of fly ash and partially replacing the more expensive metakaolin with abundant and inexpensive aluminum waste (calcined coal gangue, zeolite, slag, etc.). Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the mechanism for solidifying heavy metal ions in this invention;

[0026] Figure 2 This is a SEM-EDS image of calcium aluminate-encapsulated Cr(VI) according to the present invention;

[0027] Figure 3 This is a SEM-EDS image of CASH gel-encapsulated Cr(VI) of the present invention;

[0028] Figure 4 This is the Cr(VI) leaching result of the solidified heavy metal specimen cured for 28 days according to the present invention;

[0029] Figure 5 This invention relates to the compressive strength of a solidified heavy metal specimen after 28 days of curing. Detailed Implementation

[0030] The experimental method described in the examples uses 52.5 grade silicate clinker with 3 wt.% potassium chromate (to provide Cr(VI)) to simulate clinker with high heavy metal content. The 52.5 grade silicate clinker used meets the requirements of GB 30760 "Technical Specification for Co-processing Solid Waste in Cement Kilns".

[0031] In the following embodiments, the Cr(VI) content provided by the clinker containing heavy metals through the external addition of 3wt.% potassium chromate (K2CrO4) is much higher than the requirements of GB 30760 "Technical Specification for Co-processing Solid Waste in Cement Kilns", approximately 53.6 times higher than the maximum value of "Limit of Heavy Metal Content in Cement Clinker" (150mg / kg).

[0032] The preparation method of microbial mineralized steel slag powder is as follows: Carbonic anhydrase-producing bacteria are activated and cultured for 24-48 hours, and then mixed with water at a mass ratio of 2%-6% to obtain a microbial additive. The microbial additive is then stirred with steel slag powder at a liquid-to-solid ratio of 0.15-0.16, and carbon is fixed at 30℃-40℃ for 60-70 minutes. The powder is then ground to a specific surface area of ​​300 μL. 2 / kg or more. Carbonic anhydrase-producing bacteria are known. The carbon fixation rate of microbially mineralized steel slag powder is 8wt.%~10wt.%, and the specific surface area is ≥300m². 2 / kg, with satisfactory stability and an activity index ≥80% after 28 days.

[0033] Example 1

[0034] A method for preparing a composite cementitious material for chromium sealing includes the following steps:

[0035] Step 1: Weigh out 65g of clinker containing heavy metals, 34g of multi-component auxiliary cementitious material, and 1g of gypsum. Stir for 1 minute to ensure they are evenly mixed. The gypsum is desulfurized gypsum. The 34g of multi-component auxiliary cementitious material includes 11.9g of microbial mineralized steel slag powder, 11.9g of metakaolin, and 10.2g of fly ash.

[0036] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, and slowly add the water to the mixture obtained in Step 1. Stir slowly at 145 r / min for 120 s in a mixer, and then stir at high speed at 285 r / min for 120 s in high shear mode to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 30 h.

[0037] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 33 days.

[0038] Example 2

[0039] A method for preparing a composite cementitious material for chromium sealing includes the following steps:

[0040] Step 1: Weigh out 65g of clinker containing heavy metals, 34g of multi-component auxiliary cementitious material, and 1g of gypsum. Stir for 1 minute to ensure they are evenly mixed. The gypsum is phosphogypsum. The 34g of multi-component auxiliary cementitious material includes 10g of microbially mineralized steel slag powder, 14g of metakaolin, and 10g of fly ash.

[0041] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, slowly add the water to the mixture obtained in Step 1, and slowly stir at 140 r / min for 120 s in a mixer. Then, use a high-shear mode to stir at 290 r / min for 120 s to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 30 h.

[0042] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 35 days.

[0043] Example 3

[0044] A method for preparing a composite cementitious material for chromium sealing includes the following steps:

[0045] Step 1: Weigh 70g of clinker containing heavy metals, 28.5g of multi-component auxiliary cementitious material, and 1.5g of gypsum. Stir for 1 minute to ensure they are evenly mixed. The gypsum is desulfurized gypsum. The 28.5g of multi-component auxiliary cementitious material includes 11.4g of microbial mineralized steel slag powder, 8.55g of metakaolin, and 8.55g of fly ash.

[0046] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, and slowly add the water to the mixture obtained in Step 1. Stir slowly at 135 r / min for 120 s in a mixer, and then stir at high speed at 270 r / min for 120 s in high shear mode to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 28 hours.

[0047] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 30 days.

[0048] Example 4

[0049] A method for preparing a composite cementitious material for chromium sealing includes the following steps:

[0050] Step 1: Weigh 70g of clinker containing heavy metals, 28.5g of multi-component auxiliary cementitious material, and 1.5g of gypsum. Stir for 1 minute to mix them evenly. The gypsum is fluorogypsum. The 28.5g of multi-component auxiliary cementitious material includes 9.5g of microbially mineralized steel slag powder, 9.5g of metakaolin, and 9.5g of fly ash.

[0051] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, slowly add the water to the mixture obtained in Step 1, and slowly stir at 130 r / min for 120 s in a mixer. Then, use a high-shear mode to stir at 275 r / min for 120 s to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 26 hours.

[0052] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 28 days.

[0053] Example 5

[0054] A method for preparing a composite cementitious material for chromium sealing includes the following steps:

[0055] Step 1: Weigh 75g of clinker containing heavy metals, 22.7g of multi-component auxiliary cementitious material, and 2.3g of gypsum, and stir for 1 minute to mix them evenly. The gypsum is phosphogypsum, and the 22.7g of multi-component auxiliary cementitious material includes 11.4g of microbially mineralized steel slag powder, 4.5g of metakaolin, and 6.8g of fly ash.

[0056] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, slowly add the water to the mixture obtained in Step 1, and slowly stir at 140 r / min for 120 s in a mixer. Then, use a high-shear mode to stir at 290 r / min for 120 s to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 25 h.

[0057] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 28 days.

[0058] Example 6

[0059] A method for preparing a composite cementitious material for chromium sealing includes the following steps:

[0060] Step 1: Weigh out 75g of clinker containing heavy metals, 22.7g of multi-component auxiliary cementitious material, and 2.3g of gypsum. Stir for 1 minute to mix them evenly. The gypsum is fluorogypsum. The 22.7g of multi-component auxiliary cementitious material includes 7.7g of microbial mineralized steel slag powder, 7g of metakaolin, and 8g of fly ash.

[0061] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, slowly add the water to the mixture obtained in Step 1, and slowly stir at 150 r / min for 120 s in a mixer. Then, use a high-shear mode to stir at 280 r / min for 120 s to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 24 hours.

[0062] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 29 days.

[0063] Example 7

[0064] A method for preparing a composite cementitious material for chromium sealing includes the following steps:

[0065] Step 1: Weigh 70g of clinker containing heavy metals, 28.5g of multi-component auxiliary cementitious material, and 1.5g of gypsum. Stir for 3 minutes to ensure they are evenly mixed. The gypsum is desulfurized gypsum. The 28.5g of multi-component auxiliary cementitious material includes 11.4g of microbial mineralized steel slag powder, 8.55g of lithium slag, and 8.55g of fly ash.

[0066] Step 2: Weigh room temperature water according to a water-cement ratio of 0.35, slowly add the water to the mixture obtained in Step 1, slowly stir at 130 r / min for 130 s in a mixer, and then use high shear mode to stir at 270 r / min for 130 s to form a plastic composite cementitious material slurry, pour it into a mold, and cure at room temperature for 24 hours.

[0067] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 28 days.

[0068] Example 8

[0069] A method for preparing a composite cementitious material for chromium sealing includes the following steps:

[0070] Step 1: Weigh 70g of clinker containing heavy metals, 28.5g of multi-component auxiliary cementitious material, and 1.5g of gypsum. Stir for 2 minutes to mix them evenly. The gypsum is phosphogypsum. The 28.5g of multi-component auxiliary cementitious material includes 9.5g of microbial mineralized steel slag powder, 9.5g of slag, and 9.5g of fly ash.

[0071] Step 2: Weigh room temperature water according to a water-cement ratio of 0.45, slowly add the water to the mixture obtained in Step 1, slowly stir at 150 r / min for 110 s in a mixer, and then use high shear mode to stir at 290 r / min for 110 s to form a plastic composite cementitious material slurry, pour it into a mold, and cure at room temperature for 30 h.

[0072] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 35 days.

[0073] Comparative Example 1

[0074] A method for preparing a composite cementitious material includes the following steps:

[0075] Step 1: Weigh 70g of clinker containing heavy metals, 28.5g of multi-component auxiliary cementitious material, and 1.5g of gypsum, and stir for 1 minute to mix them evenly. The gypsum is desulfurized gypsum, and the 28.5g of multi-component auxiliary cementitious material includes 28.5g of microbial mineralized steel slag powder.

[0076] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, and slowly add the water to the mixture obtained in Step 1. Stir slowly at 140 r / min for 120 s in a mixer, and then stir at high speed at 280 r / min for 120 s in high shear mode to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 26 h.

[0077] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 30 days.

[0078] Comparative Example 2

[0079] A method for preparing a composite cementitious material includes the following steps:

[0080] Step 1: Weigh 70g of clinker containing heavy metals, 28.5g of multi-component auxiliary cementitious material, and 1.5g of gypsum. Stir for 1 minute to mix them evenly. The gypsum is phosphogypsum, and the 28.5g of multi-component auxiliary cementitious material includes 28.5g of metakaolin.

[0081] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, slowly add the water to the mixture obtained in Step 1, and slowly stir at 130 r / min for 120 s in a mixer. Then, use a high-shear mode to stir at 290 r / min for 120 s to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 24 hours.

[0082] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 28 days.

[0083] Comparative Example 3

[0084] A method for preparing a composite cementitious material includes the following steps:

[0085] Step 1: Weigh 70g of clinker containing heavy metals, 28.5g of multi-component auxiliary cementitious material, and 1.5g of gypsum. Stir for 1 minute to ensure they are evenly mixed. The gypsum is desulfurized gypsum, and the 34g of multi-component auxiliary cementitious material includes 28.5g of fly ash.

[0086] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, and slowly add the water to the mixture obtained in Step 1. Stir slowly at 130 r / min for 120 s in a mixer, and then stir at high speed at 270 r / min for 120 s in high shear mode to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 27 h.

[0087] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 30 days.

[0088] Comparative Example 4

[0089] A method for preparing a composite cementitious material includes the following steps:

[0090] Step 1: Weigh out 95g of clinker containing heavy metals and 5g of gypsum, and stir for 1 minute to mix them evenly. The gypsum is phosphogypsum.

[0091] Step 2: Weigh room temperature water according to a water-cement ratio of 0.4, and slowly add the water to the mixture obtained in Step 1. Stir slowly at 140 r / min for 120 s in a mixer, and then stir at high speed at 280 r / min for 120 s in high shear mode to form a plastic composite cementitious material slurry. Pour the slurry into a mold and cure at room temperature for 24 hours.

[0092] Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 28 days.

[0093] Table 1. Composition ratios and related test results of each formulation in the examples and comparative examples (water-cement ratio 0.40)

[0094]

[0095] The cured solidified heavy metal composite cementitious material was subjected to compressive strength and leaching tests. The compressive strength test method followed GB / T 17671 "Test Method for Strength of Cement Mortar (ISO Method)"; the leaching test method followed HJ557 "Leaching Toxicity Method for Solid Waste - Horizontal Oscillation Method". The leaching agent was a simulated acid rain solution (pH 3.20±0.05, adjusted using a 2:1 mass ratio of concentrated sulfuric acid and concentrated nitric acid) prepared according to HJ / T 299 "Leaching Toxicity Method for Solid Waste - Sulfuric Acid and Nitric Acid Method". Due to the high content of potassium chromate, the leaching solution was diluted 10 times to facilitate result analysis using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0096] Table 1 shows that the synergistic effect of heavy metal clinker and multi-component auxiliary cementitious materials significantly reduces Cr(VI) leaching and improves compressive strength. Analysis of Examples 1 and 2 revealed that a clinker coefficient of 0.65 still ensures high compressive strength, and appropriately increasing the amount of microbially mineralized steel slag powder (Example 1) generates more calcium aluminate to stabilize and seal Cr(VI). Analysis of Examples 5 and 6 showed that a higher amount of metakaolin content slightly improves strength, as it generates more CASH gel to fill the voids and structure of the solidified body, thus increasing strength. Comparative Examples 1-3 showed that Comparative Example 1, with the addition of microbially mineralized steel slag powder, had the lowest leaching, possibly due to its presence of reducing substances and the reaction of a small amount of calcium carbonate to form calcium aluminate, but still higher than that without auxiliary cementitious materials (Comparative Example 4).

[0097] Of the above embodiments, the best embodiment is Embodiment 5, which has both a low Cr(VI) leaching amount and a high compressive strength.

[0098] It should also be noted that although both the examples and comparative examples simulated high-heavy-metal-content clinker by adding potassium chromate, the actual high-heavy-metal-content clinker produced has a significantly reduced risk of heavy metal ion leaching due to calcination and solidification, resulting in better solidification under the same content conditions.

Claims

1. A composite cementitious material for sealing chromium, characterized in that: The substance comprises the following mass percentages: clinker containing heavy metals at 65 wt.% to 75 wt.%, multi-component auxiliary cementitious materials at 20 wt.% to 34 wt.%, and the remainder being gypsum; the total chromium content in the clinker containing heavy metals is greater than 150 mg / kg; The multi-component auxiliary cementitious material comprises the following substances by mass percentage: 30 wt.% ~ 50 wt.% microbial mineralized steel slag powder, 20 wt.% ~ 40 wt.% metakaolin, and the balance being fly ash; the microbial mineralized steel slag powder is prepared by grinding carbon-fixing powder with carbon-fixing bacteria; The microbial mineralized steel slag powder has a carbon fixation rate of 8 wt.% ~ 10 wt.% and a specific surface area ≥ 300 m². 2 / kg, with satisfactory stability and an activity index ≥ 80% after 28 days; The preparation method of the microbial mineralized steel slag powder is as follows: Carbonic anhydrase-producing bacteria are activated and cultured for 24 h to 48 h, and then mixed with water at a mass ratio of 2% to 6% to obtain a microbial additive. The microbial additive is then stirred with steel slag powder at a liquid-to-solid ratio of 0.10 to 0.40, and carbon is fixed at 10 ℃ to 70 ℃ for 60 min to 70 min. The powder is then ground to a specific surface area of ​​300 m². 2 / kg or more.

2. The composite cementitious material for sealing chromium according to claim 1, characterized in that: The gypsum is any one of desulfurized gypsum, phosphogypsum, or fluorogypsum.

3. A method for preparing a composite cementitious material for sealing chromium according to any one of claims 1 to 2, characterized in that, Includes the following steps: Step 1: Weigh out the clinker, multi-component auxiliary cementitious materials, and gypsum containing the required amount of heavy metals, and mix them evenly. Step 2: Weigh room temperature water according to a water-cement ratio of 0.35 to 0.45, slowly add the water to the mixture obtained in Step 1, stir slowly and then stir at high speed in a high-shear mode to form a plastic composite cementitious material slurry, pour it into a mold, and cure at room temperature. Step 3: After removing the mold, the specimen is cured in an anhydrous environment with a humidity of not less than 90% for 28 to 35 days.

4. The method for preparing a composite cementitious material for chromium sealing according to claim 3, characterized in that: In step one, the stirring time is 1 to 3 minutes.

5. The method for preparing a composite cementitious material for chromium sealing according to claim 3, characterized in that: In step two, the slow stirring speed is 130 r / min ~ 150 r / min and the time is 110 s ~ 130 s, while the high-speed stirring speed is 270 r / min ~ 290 r / min and the time is 110 s ~ 130 s.

6. A method for preparing a composite cementitious material for chromium sealing according to claim 3, characterized in that: In step two, the curing time at room temperature is 24 h ~ 30 h.

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