A cement chromium removal additive, its cement-based material and preparation method

Abstract

The present invention relates to the technical field of cement-based material preparation, and particularly relates to a chromium-removing additive for cement, a cement-based material thereof, and a preparation method. The chromium-removing agent includes a calcium polysulfide core, a first-level shell layer of Fe(II) and / or Sn(II) source coated on the surface of the core, and a second-level shell layer of nano-SiO2 coated on the surface of the first-level shell layer, that is, calcium polysulfide@Fe(II) / Sn(II)@SiO2. The present invention effectively overcomes the problems that calcium polysulfide is easily oxidized before reacting with Cr(VI) in the cement-based material and the removal rate is low due to the large solubility and dispersibility of Cr(VI) in the cement-based material by using calcium polysulfide@Fe(II) / Sn(II)@SiO2 with a special structure and composition, and realizes the precise removal of Cr(VI).

Description

Technical Field

[0001] The present invention relates to the technical field of cement-based material preparation, and particularly relates to a chromium-removing additive for cement, a cement-based material thereof, and a preparation method therefor. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and is not necessarily to be regarded as an admission or an implication in any form that this information has become the prior art known to those of ordinary skill in the art.

[0003] During the production process of cement clinker, Cr(VI) is mixed in it, including Cr(VI) introduced by iron-calibrating raw materials, industrial waste raw materials, chromium slag mineralizers, etc. in cement production, Cr(VI) introduced by chromium-containing grinding media during raw material crushing, raw meal and cement grinding, Cr(VI) introduced by chromium-containing refractory bricks in the cement rotary kiln, etc. These Cr(VI) will cause serious harm to buildings, the environment, and the human body, for example: (1) Due to the strong oxidizing property of Cr(VI), it will corrode the steel bars in the cement-based concrete structure, affecting the stability and safety of the building structure. (2) The presence of Cr(VI) will also reduce the bonding strength and compressive strength of the cement, thus affecting the building quality. (3) Since Cr(VI) is easily soluble in water, it can be transferred from cement buildings to groundwater or surface water through leaching, causing water pollution.

[0004] The chemical method is a commonly used method for removing Cr(VI) from cement-based materials. However, traditional reduction additives have various problems. Not only is the efficiency of removing Cr(VI) poor, but it may also cause secondary pollution. For example: Sodium sulfite (Na 2 SO 3 ), as a reducing agent, needs to be used under acidic conditions and is likely to corrode equipment. In addition, the reduction ability of sodium sulfite is limited, and a higher dosage is required to effectively reduce Cr(VI), which increases the treatment cost. Sodium metabisulfite (Na 2 S 2 O 5 ), as a reducing agent, is more economical and reasonable than sodium sulfite, but its stability is poor and it is easy to decompose, requiring additional stabilization measures. Barium sulfide (BaS) can also be used to precipitate chromium ions, but the generated precipitate needs to be further treated, otherwise it will cause secondary pollution. At the same time, the dosage of barium sulfide needs to be precisely controlled. Excessive dosage will cause the residue of barium ions and pollute the environment. Summary of the Invention

[0005] In view of the above problems, the present invention provides a cement chromium removal additive, its cement-based material and preparation method. This additive can effectively avoid the problem of reduced removal effect caused by oxidation before contacting with Cr(VI) in the cement-based material, and can also improve the mechanical properties of the cement-based material. Specifically, the present invention discloses the following technical solutions.

[0006] First of all, the present invention provides a cement chromium removal additive, which includes a calcium polysulfide core, a first-level shell layer of Fe(II) and / or Sn(II) source coated on the surface of the core, and a nano-SiO 2 second-level shell layer coated on the surface of the first-level shell layer, thereby forming the cement chromium removal additive with a calcium polysulfide@Fe(II) / Sn(II)@SiO 2 structure.

[0007] Furthermore, the Fe(II) source includes at least one of FeSO 4 , Fe(NO 3 ) 2 , FeCl 2 , etc.

[0008] Furthermore, the Sn(II) source includes at least one of SnSO 4 , SnCl 2 , etc.

[0009] Secondly, the present invention provides a cement-based material containing a chromium removal additive, and the dosage of this chromium removal additive is 0.1-0.3% of the mass of the cement-based material. Preferably, the cement-based material is a portland cement-based material, so as to utilize its hydration product calcium hydroxide to react with the chromium removal additive and avoid oxidation before the calcium polysulfide contacts with Cr(VI) in the cement-based material.

[0010] Thirdly, the present invention provides a preparation process of the cement chromium removal additive, which includes the following steps:

[0011] (1) Dissolve the Fe(II) source and / or Sn(II) source in supercritical water, and then add calcium polysulfide particles into it and disperse evenly to obtain a supercritical suspension mixture for standby.

[0012] (2) Pass the suspension mixture through the microporous plate in the throttler to quickly expand the suspension mixture into a protective atmosphere collection container, and then collect the solid product to obtain the first-level core-shell particles.

[0013] (3) Form nano-SiO on the surface of the first-level core-shell particles through magnetron sputtering technology 2The seed layer is then placed in an alcohol solution containing ammonia water and tetraethyl orthosilicate, heated and reacted under sealed conditions, followed by ultrasonic treatment. Then, the solid product in the reaction solution is collected and dried to obtain the chromium removal additive (calcium polysulfide @Fe(II) / Sn(II)@SiO 2 ).

[0014] Further, in step (1), the mass ratio of the Fe(II) source to the Sn(II) source is 0.41 - 1.27:1.

[0015] Further, in step (1), the ratio of the calcium polysulfide particles to supercritical water is 1 - 3 g: 30 - 100 ml. Optionally, the particle size of the calcium polysulfide particles is 10 - 25 μm.

[0016] Further, in step (1), the method for preparing the supercritical water includes: preheating water to 35 - 100 °C, then pressurizing it to a pressure of 22.1 MPa, and continuing to heat the water to 374 °C under this pressure to obtain supercritical water.

[0017] Further, in step (2), the pore diameter of the microplate in the throttler is 25 - 75 μm. Optionally, the protective atmosphere includes any one of nitrogen, argon, etc.

[0018] Further, in step (3), the method for forming the SiO 2 seed layer includes: dropping a mixed solution of the primary core - shell particles and a non - aqueous organic dispersant onto a cleaned silicon wafer, and then spin - coating to evenly distribute the primary core - shell particles on the surface of the silicon wafer. Then, the silicon wafer is heat - treated. After completion, SiO 2 is deposited on the surface of the primary core - shell particles on the silicon wafer to form the SiO 2 seed layer.

[0019] Further, the ratio of the primary core - shell particles to the non - aqueous organic dispersant is 1 g: 20 - 50 ml. Optionally, the non - aqueous organic dispersant includes at least one of absolute ethanol, ether, etc.

[0020] Further, in step (3), the ratio of ammonia water, tetraethyl orthosilicate, and the alcohol solution is 3 - 10 ml: 1 - 3 ml: 33 - 100 ml, and the concentration of the ammonia water is 1 - 5 mol / L. Optionally, the alcohol solution includes at least one of absolute methanol, absolute ethanol, n - propanol, n - butanol, etc.

[0021] Further, in step (3), the heating reaction temperature is 40 - 80 °C, and the reaction time is 1 - 3 h, so that the SiO 2 seed layer grows into a dense and evenly distributed coating layer.

[0022] Further, in step (3), the time of the ultrasonic treatment is 1 to 3 h, and the ultrasonic power is 300 to 500 W.

[0023] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0024] 1. Calcium polysulfide will be oxidized to Ca 2+ , SO 4 2- and S 0 under aerobic conditions. This is because calcium polysulfide has excellent reduction properties. Therefore, this characteristic of calcium polysulfate can be utilized to remove Cr(VI), reducing highly hazardous Cr(VI) to less hazardous Cr(III). During this process, not only will no substances that cause secondary pollution to the cement-based material be generated, but also the pH value of the system will not be changed, fully compensating for many shortcomings of traditional reduction additives. However, the present invention further discovers that when using calcium polysulfide to remove Cr(VI) from cement-based materials, the situation where calcium polysulfide is oxidized before contacting Cr(VI) will occur, resulting in a lower removal efficiency, causing calcium polysulfide to lose its reducibility and thus affecting the removal effect of Cr(VI). For this reason, the present invention proposes calcium polysulfide@Fe(II) / Sn(II)@SiO with a special structure and composition 2 which effectively overcomes the above problems and realizes the precise removal of Cr(VI). The reason is as follows:

[0025] First of all, the nano-SiO 2 layer is coated on the surface of the primary shell, which not only protects calcium polysulfide but also helps prevent the oxidation of Fe(II) and / or Sn(II) in the primary shell or their conversion to hydroxides in the alkaline environment provided by cement hydration, resulting in a decrease in the chromium removal effect. Thus: when the above chromium removal agent enters the cement, the nano-SiO 2 layer first reacts with calcium hydroxide provided by cement hydration to form the gel component C-S-H. On the one hand, it can increase the content of the gel component in the cement, contributing to the improvement of the mechanical strength of the cement. On the other hand, after the reaction of the nano-SiO 2 layer, the primary shell is exposed, and at this time, Fe(II) and / or Sn(II) therein react with Cr(VI) in an oxidation-reduction reaction. The Fe(II) will be oxidized to Fe(III), and these Fe(III) are further converted to Fe(OH) in the alkaline environment provided by the cement 3 , which can not only act as a catalyst to improve the electron transfer efficiency of removing Cr(VI) and increase the removal rate of Cr(VI). Moreover, the Fe(OH) 3Good adsorption performance can adsorb Cr(VI) to form stable coprecipitates to prevent its diffusion. At the same time, the Sn(II) is oxidized to Sn(IV), which forms [Sn(OH) 6 2- ions under the alkaline conditions of cement hydration. As a ligand, it forms stable insoluble complexes with Cr(VI), effectively reducing the mobility of Cr(VI). At the same time, Sn(IV) ions in the form of [Sn(OH) 6 2- ions are relatively stable in an alkaline environment and are not easily reduced to Sn(II) ions. Secondly, after the above reactions with Fe(II) and Sn(II), Cr(VI) is also converted to Cr(III), thus converting Cr(VI) into a more stable, less soluble and less mobile Cr(III) to prevent the leaching of chromium elements in cement-based materials. Finally, as the above reactions proceed, the calcium polysulfide is gradually released, which can react with the residual Cr(VI) in the cement paste and the Cr(VI) captured by the above Fe(OH) 3 and [Sn(OH) 6 2- ions to further carry out redox reactions, converting Cr(VI) to Cr(III), thereby more thoroughly removing Cr(VI), and making the removal of Cr(VI) more accurate and targeted, improving the removal efficiency. At the same time, the Ca 2+ formed by the calcium polysulfate combines with SO 4 2- to form CaSO 4 , which helps to increase the viscosity and hydration rate of the cement, thereby improving the early strength and durability of the cement.

[0026] 2. When preparing the calcium polysulfide@Fe(II) / Sn(II)@SiO 2 of the present invention, first, the coating materials Fe(II) and Sn(II) sources are dissolved in a supercritical fluid, and then the solubility of the supercritical fluid in the solute is rapidly reduced by throttling and depressurizing, so that the Fe(II) and Sn(II) sources precipitate due to supersaturation to form solid particles, which are deposited on the surface of the calcium polysulfide with the movement of the gas flow formed by the supercritical fluid to form a uniform thin film on the surface of the first shell layer, achieving the purpose of uniformly, comprehensively and densely coating and modifying the surface of the calcium polysulfide and providing good protection for the calcium polysulfide. Secondly, the present invention uses magnetron sputtering technology as an improvement means. Before forming the nano-SiO 2 layer on the surface of the first shell layer, a uniform nano-SiO 2 seed layer is first formed on the surface of the first shell layer, which can induce nano-SiO 2 ​​​The uniform development of the formation of grains enables the nano-SiO formed on the surface of the primary shell layer to be uniform and dense, effectively overcoming the disadvantages of the formed nano-SiO layer being uneven, having poor stability and poor dispersibility, improving the protection effect on the primary shell layer and the calcium polysulfide core, and avoiding the problem of reduced effectiveness or even failure before contacting with Cr(VI). 2 layer is uneven, with poor stability and poor dispersibility, improving the protection effect on the primary shell layer and the calcium polysulfide core, and avoiding the problem of reduced effectiveness or even failure before contacting with Cr(VI). 2 layer is uneven, with poor stability and poor dispersibility, improving the protection effect on the primary shell layer and the calcium polysulfide core, and avoiding the problem of reduced effectiveness or even failure before contacting with Cr(VI). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings forming a part of this invention are used to provide a further understanding of the invention. The schematic embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0028] Figure 1 It is a schematic structural diagram of a throttle used in the following embodiments.

[0029] Figure 2 It is a sample photo of a chromium-removing additive prepared in the following Example 1.

[0030] Figure 3 It is the SEM of the chromium-removing additive prepared in the following Example 1.

[0031] Figure 4 It is the XRD test result of the chromium-removing additive prepared in the following Example 1.

[0032] Figure 5 It is the SEM of the chromium-removing additive prepared in the following Example 2.

[0033] Figure 6 It is the XRD test result of the chromium-removing additive prepared in the following Example 2.

[0034] Figure 7 It is the SEM of the chromium-removing additive prepared in the following Example 3.

[0035] Figure 8 It is the XRD test result of the chromium-removing additive prepared in the following Example 3.

[0036] Figure 9 It is the SEM of the chromium-removing additive prepared in the following Example 4.

[0037] Figure 10 It is the XRD test result of the chromium-removing additive prepared in the following Example 4.

[0038] Figure 11 It is the XRD test result of the chromium-removing additive prepared in the following Example 5.

[0039] Figure 12 It is the SEM of the chromium-removing additive prepared in the following Example 6.

[0040] Figure 13 XRD test results of the chromium-removing additive prepared for Example 6 below.

[0041] Figure 14 SEM of the chromium-removing additive prepared for Example 7 below.

[0042] Figure 15 XRD test results of the chromium-removing additive prepared for Example 7 below.

[0043] Figure 16 SEM of the chromium-removing additive prepared for Example 8 below.

[0044] Figure 17 XRD test results of the chromium-removing additive prepared for Example 8 below.

[0045] Figure 18 SEM of the chromium-removing additive prepared for Example 9 below.

[0046] Figure 19 XRD test results of the chromium-removing additive prepared for Example 9 below. Detailed implementation manners

[0047] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally in accordance with conventional conditions or conditions recommended by the manufacturer.

[0048] Unless otherwise defined, all professional and scientific terms used in the present invention have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be obtained through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in accordance with the conventional methods in the art or in accordance with the product instructions. In addition, any methods and materials similar or equivalent to the described content can be applied to the method of the present invention. The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0049] Example 1

[0050] A preparation process of a cement chromium-removing additive includes the following steps:

[0051] (1) Place water in a reaction kettle, preheat it to 80 °C first, then pressurize it to 22.1 MPa, and then continue to heat the water to the supercritical state at 374 °C to obtain supercritical water. Then add FeSO 4 and SnSO 4Dissolve it in the supercritical water according to the mass ratio of 0.41:1, and then add calcium polysulfide particles with a particle size distribution between 10 and 25 μm according to the solid-liquid ratio of 1 g:30 ml, and mix evenly to obtain a supercritical suspension mixture for standby.

[0052] (2)Pass the suspension mixture through the microporous plate in the throttler (as Figure 1 shown, the inlet diameter is 11 mm, the outlet diameter is 7 mm, the pore diameter of the microporous plate is 25 μm, and the arrow indicates the flow direction of the suspension mixture, the same below), so that the suspension mixture expands rapidly and then cools down and reduces pressure into a collection container under a nitrogen protection atmosphere, and then collect the solid product to obtain primary core-shell particles for standby.

[0053] (3)Drop the mixture of the primary core-shell particles and absolute ethanol (the ratio of the two is 1 g:40 ml) on the cleaned silicon wafer, and then spin-coat it at a speed of 3000 r / min for 30 s to make the primary core-shell particles evenly distributed on the surface of the silicon wafer. Then place the silicon wafer in a vacuum oven at 60 °C and heat it for 5 min to make the primary core-shell particles firmly adhere to the silicon wafer.

[0054] (4)Use the silicon wafer finally obtained in step (3) as the substrate, and use nano-SiO 2 as the target target. Then place the substrate and the target target in the vacuum chamber of a high-vacuum magnetron sputtering instrument, evacuate to high vacuum and then introduce the inert gas argon into the vacuum chamber. Set the power to 300 W and start sputtering after setting the time to 120 s. The SiO 2 ejected from the target deposits on the substrate, so that the SiO 2 deposits on the surface of the primary core-shell particles to form a SiO 2 seed layer.

[0055] (5)Put the substrate finally obtained in step (4) into a container containing a mixed solution formed by ammonia water (concentration 1 mol / L), tetraethyl orthosilicate and absolute methanol according to the volume ratio of 3 ml:1 ml:33 ml. Seal the container and microwave heat it to 60 °C and keep it warm for 2 hours, and then perform ultrasonic treatment for 1 h with an ultrasonic power of 400 W to make the product attached to the silicon wafer react fully and detach into the solution. Finally, centrifuge the obtained reaction solution at a rate of 10000 rmp for 10 min, collect the solid product at the bottom, and dry it to constant weight under vacuum conditions at 60 °C to obtain a chromium removal additive, as Figure 2 shown, the SEM of this chromium removal additive is as Figure 3 shown, and the XRD test results are as Figure 4 shown.

[0056] Performance test: (1) Mix a commercially available 42.5 ordinary Portland cement in a certain city (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water in a mass ratio of 2:6:1, and add the chromium removal additive prepared in this example according to 0.2% of the mass of the cement, then stir for 20 min to obtain a cement paste. Then, use the diphenylcarbazide spectrophotometric method to measure the concentration of Cr(VI) in the cement paste and calculate the removal rate. The results are shown in Table 1 below. It can be seen that the chromium removal additive has excellent removal effect on Cr(VI) in cement, fully meeting the limit of water-soluble chromium(VI) in cement (not higher than 10 mg / kg) specified in the national standard GB 31893-2015 "Limit and Determination Method of Water-soluble Chromium(VI) in Cement". (2) Test the early strength of the specimens prepared from the cement paste according to GBT 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", and the results are shown in Table 1:

[0057] Table 1

[0058] 。

[0059] Example 2

[0060] A preparation process of a chromium removal additive for cement includes the following steps:

[0061] (1) Place water in a reaction kettle, preheat it to 35 °C first, then pressurize it to 22.1 MPa, and then continue to heat the water to the supercritical state of 374 °C to obtain supercritical water. Then dissolve Fe(NO 3 ) 2 and SnSO 4 in the supercritical water according to a mass ratio of 0.84:1, and then add polysulfide calcium particles with a particle size distribution between 10 and 25 μm according to a solid-liquid ratio of 2 g:70 ml, and mix evenly to obtain a supercritical suspension mixture for standby.

[0062] (2) Pass the suspension mixture through the microporous plate in the throttler (as Figure 1 shown, the inlet diameter is 11 mm, the outlet diameter is 7 mm, and the pore diameter of the microporous plate is 50 μm), so that the suspension mixture expands rapidly and then cools down and depressurizes into a collection container under a nitrogen protection atmosphere, and then collect the solid product, that is, the primary core-shell particles for standby.

[0063] (3) Drop the mixed solution of the primary core-shell particles and absolute ethanol (the ratio of the two is 1 g: 30 ml) onto the cleaned silicon wafer, and then spin-coat it at a speed of 3000 r / min for 30 s using a spin coater, so that the primary core-shell particles are evenly distributed on the surface of the silicon wafer. Then place the silicon wafer in a vacuum oven at 60 °C and heat it for 5 min to firmly attach the primary core-shell particles to the silicon wafer.

[0064] (4) Use the silicon wafer finally obtained in step (3) as the substrate, and use nano-SiO 2 as the target target. Then place the substrate and the target target in the vacuum chamber of a high-vacuum magnetron sputtering instrument, evacuate to high vacuum, and then introduce the inert gas argon into the vacuum chamber. Set the power to 300 W and start sputtering after setting the time to 120 s. The SiO 2 ejected from the target is deposited on the substrate, so that SiO 2 is deposited on the surface of the primary core-shell particles to form a SiO 2 seed layer.

[0065] (5) Put the substrate finally obtained in step (4) into a container containing a mixed solution formed by ammonia water (concentration 2.5 mol / L), tetraethyl orthosilicate and n-propanol in a volume ratio of 6 ml: 2 ml: 75 ml. Seal the container and microwave heat it to 80 °C and keep it warm for 1 hour, then perform ultrasonic treatment for 2 h, and the ultrasonic power is 500 W, so that the product attached to the silicon wafer reacts fully and detaches into the solution. Finally, centrifuge the obtained reaction solution at a rate of 10000 rmp for 10 min, collect the solid product at the bottom, and dry it to constant weight under vacuum conditions at 60 °C to obtain the chromium removal additive, and its SEM is as Figure 5 shown, and the XRD test results are as Figure 6 shown.

[0066] Performance test: (1) Mix a commercially available 42.5 ordinary Portland cement in a certain city (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water in a mass ratio of 2: 6: 1, and add the chromium removal additive prepared in this example according to 0.15% of the mass of the cement, and then stir for 20 min to obtain a cement paste. Then use the diphenylcarbazide spectrophotometric method to measure the concentration of Cr(VI) in the cement paste and calculate the removal rate. The results are shown in Table 2 below. It can be seen that the chromium removal additive has an excellent removal effect on Cr(VI) in cement, and fully meets the limit of water-soluble chromium(VI) in cement specified in the national standard GB 31893-2015 "Limit and Determination Method of Water-soluble Chromium(VI) in Cement". (2) Test the early strength of the specimens prepared from the cement paste according to GBT17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", and the results are shown in Table 2:

[0067] Table 2

[0068] 。

[0069] Example 3

[0070] A preparation process of a chromium-removing additive for cement, comprising the following steps:

[0071] (1) Place water in a reaction kettle, preheat it to 100 °C first, then pressurize it to 22.1 MPa, and then continue to heat the water to the supercritical state of 374 °C to obtain supercritical water. Then dissolve FeCl 2 and SnCl 2 in the supercritical water according to a mass ratio of 1.27:1, and then add polysulfide calcium particles with a particle size distribution between 10 and 25 μm according to a solid-liquid ratio of 3 g:100 ml and mix evenly to obtain a supercritical suspension mixture for standby.

[0072] (2) Pass the suspension mixture through the microporous plate in the throttler (as shown in Figure 1 , with an inlet diameter of 11 mm, an outlet diameter of 7 mm, and a pore diameter of the microporous plate of 75 μm), so that the suspension mixture expands rapidly and then cools down and reduces pressure into a collection container under an argon protection atmosphere, and then collect the solid product, namely the primary core-shell particles, for standby.

[0073] (3) Drop the mixture of the primary core-shell particles and ether (the ratio of the two is 1 g:50 ml) on the cleaned silicon wafer, and then spin-coat it at a speed of 3000 r / min for 30 s with a spin coater to make the primary core-shell particles evenly distributed on the surface of the silicon wafer. Then place the silicon wafer in a vacuum oven at 60 °C and heat it for 5 min to make the primary core-shell particles firmly adhere to the silicon wafer.

[0074] (4) Use the silicon wafer finally obtained in step (3) as a substrate and nano-SiO 2 as a target target. Then place the substrate and the target target in the vacuum chamber of a high-vacuum magnetron sputtering instrument, evacuate to high vacuum, and then introduce the inert gas argon into the vacuum chamber. Set the power to 400 W and the time to 110 s and then start sputtering. The SiO 2 ejected from the target deposits on the substrate, so that the SiO 2 deposits on the surface of the primary core-shell particles to form a SiO 2 seed layer.

[0075] (5) Place the substrate obtained in step (4) into a container filled with a mixed solution formed by ammonia water (concentration: 5 mol / L), tetraethyl orthosilicate, and absolute ethanol in a volume ratio of 10 ml: 3 ml: 100 ml. Seal the container and microwave heat it to 50 °C and keep it warm for reaction for 2 hours. Then, perform ultrasonic treatment for 2 h with an ultrasonic power of 300 W to fully react the product attached to the silicon wafer and detach it into the solution. Finally, centrifuge the obtained reaction solution at a rate of 10000 rmp for 10 min, collect the solid product at the bottom, and dry it to a constant weight under vacuum conditions at 60 °C to obtain the chromium removal additive. Its SEM is as shown in Figure 7 shown, and the XRD test results are as shown in Figure 8 shown.

[0076] Performance test: (1) Mix a commercially available 42.5 ordinary Portland cement (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water in a mass ratio of 2: 6: 1, and add the chromium removal additive prepared in this example according to 0.3% of the mass of the cement. Then stir for 20 min to obtain a cement paste. Then, use diphenylcarbazide spectrophotometry to measure the concentration of Cr(VI) in the cement paste and calculate the removal rate. The results are shown in Table 3 below. It can be seen that the chromium removal additive has an excellent removal effect on Cr(VI) in cement, fully meeting the limit of water-soluble chromium (VI) in cement specified in the national standard GB 31893-2015 "Limit and Determination Method of Water-soluble Chromium (VI) in Cement". (2) Test the early strength of the specimens prepared from the cement paste according to GBT17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", and the results are shown in Table 3:

[0077] Table 3

[0078] .

[0079] Example 4

[0080] A preparation process of a chromium removal additive for cement, comprising the following steps:

[0081] (1) Place water in a reaction kettle and preheat it to 50 °C first, then pressurize it to 22.1 MPa, and then continue to heat the water to the supercritical state of 374 °C to obtain supercritical water. Then dissolve SnSO 4 in the supercritical water to form a saturated solution, and then add calcium polysulfide particles with a particle size distribution between 10 and 25 μm according to a solid-liquid ratio of 2.5 g: 60 ml and mix evenly to obtain a supercritical suspension mixture for standby.

[0082] (2) Pass the suspension mixture through the microporous plate in the throttle (as shown in Figure 1As shown, with an inlet diameter of 11 mm, an outlet diameter of 7 mm, and a pore diameter of the microporous plate of 40 μm), the suspension mixture is rapidly expanded and then cooled and depressurized into a collection container under a nitrogen protection atmosphere, and then the solid product is collected to obtain primary core-shell particles for standby.

[0083] (3) Drop the mixture of the primary core-shell particles and diethyl ether (the ratio of the two is 1 g: 20 ml) onto the cleaned silicon wafer, and then spin-coat it at a speed of 3000 r / min for 30 s with a spin coater to make the primary core-shell particles evenly distributed on the surface of the silicon wafer. Then place the silicon wafer in a vacuum oven at 60 °C and heat it for 5 min to firmly attach the primary core-shell particles to the silicon wafer.

[0084] (4) Use the silicon wafer obtained finally in step (3) as the substrate, and 2 use nano-SiO 2 as the target target. Then place the substrate and the target target in the vacuum chamber of a high-vacuum magnetron sputtering instrument, evacuate to high vacuum, and then introduce the inert gas argon into the vacuum chamber. Set the power to 300 W and start sputtering after setting the time to 120 s. The SiO 2 ejected from the target is deposited on the substrate, so that SiO 2 is deposited on the surface of the primary core-shell particles to form a SiO

[0085] seed layer. Figure 9 As shown, the XRD test results are as Figure 10 shown.

[0086] Performance test: (1) Mix a commercially available 42.5 ordinary Portland cement in a certain city (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water according to a mass ratio of 2:6:1, and add the chromium removal additive prepared in this example according to 0.1% of the mass of the cement, and then stir for 20 min to obtain a cement paste. Then, use diphenylcarbazide spectrophotometry to measure the concentration of Cr(VI) in the cement paste and calculate the removal rate. The results are shown in Table 4 below. It can be seen that the chromium removal additive has an excellent removal effect on Cr(VI) in cement, fully meeting the limit of water-soluble chromium (VI) in cement specified in the national standard GB 31893-2015 "Limit and Determination Method of Water-soluble Chromium (VI) in Cement". (2) Test the early strength of the specimens prepared from the cement paste according to GBT17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", and the results are shown in Table 4:

[0087] Table 4

[0088] 。

[0089] Example 5

[0090] (1) Mix a commercially available 42.5 ordinary Portland cement in a certain city (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water according to a mass ratio of 2:6:1, and add a chromium removal additive (polysulfide calcium powder with a particle size distribution between 10 and 25 μm, and its XRD test results are as Figure 11 shown), and then stir for 20 min to obtain a cement paste. Then, use diphenylcarbazide spectrophotometry to measure the concentration of Cr(VI) in the cement paste and calculate the removal rate. The results are shown in Table 5 below. It can be seen that the chromium removal additive has insufficient removal effect on Cr(VI) in cement, resulting in the content of chromium (VI) in the cement paste not meeting the limit in the national standard GB 31893-2015 "Limit and Determination Method of Water-soluble Chromium (VI) in Cement". (2) Test the early strength of the specimens prepared from the cement paste according to GBT 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", and the results are shown in Table 5:

[0091] Table 5

[0092] 。

[0093] Example 6

[0094] A preparation process of a cement chromium removal additive is the same as that of Example 1 above, except that the supercritical suspension mixture in this example is prepared by the following method: Place water in a reaction kettle and preheat it to 80 °C first, then pressurize it to 22.1 MPa, and then continue to heat the water to the supercritical state of 374 °C to obtain supercritical water. Then, calcium polysulfide particles with a particle size distribution between 10 and 25 μm are added in a solid-liquid ratio of 1 g: 30 ml and mixed evenly to obtain a supercritical suspension mixture.

[0095] The SEM of the cement chromium removal additive prepared in this example is as Figure 12 shown, and the XRD test results are as Figure 13 shown.

[0096] Performance test: (1) Mix a commercially available 42.5 ordinary Portland cement (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water in a mass ratio of 2: 6: 1, and add the chromium removal additive prepared in this example in a proportion of 0.2% of the cement mass, and then stir for 20 min to obtain a cement paste. Then, the concentration of Cr(VI) in the cement paste is measured by the diphenylcarbazide spectrophotometric method, and the removal rate is calculated. The results are shown in Table 6 below. It can be seen that although the content of chromium (VI) in the cement paste meets the limit in the national standard GB 31893-2015 "Limit and Determination Method of Water-soluble Chromium (VI) in Cement", the removal effect of the chromium removal additive on Cr(VI) in cement has decreased significantly. (2) Test the early strength of the specimens prepared from the cement paste according to GBT17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", and the results are shown in Table 6:

[0097] Table 6

[0098] 。

[0099] Example 7

[0100] A preparation process of a cement chromium removal additive includes the following steps:

[0101] (1) Place water in a reaction kettle and preheat it to 35 °C first, then pressurize it to 22.1 MPa, and then continue to heat the water to the supercritical state of 374 °C to obtain supercritical water. Then dissolve Fe(NO 3 ) 2 and SnSO 4 in the supercritical water in a mass ratio of 0.84: 1, and then add calcium polysulfide particles with a particle size distribution between 10 and 25 μm in a solid-liquid ratio of 2 g: 70 ml and mix evenly to obtain a supercritical suspension mixture for standby.

[0102] (2) Pass the suspension mixture through the microporous plate in the throttler (as Figure 1 shown, the inlet diameter is 11 mm, the outlet diameter is 7 mm, and the pore diameter of the microporous plate is 50 μm), so that the suspension mixture rapidly expands and then cools down and reduces pressure into a collection container with a nitrogen protection atmosphere. Then collect the solid product, and use the obtained primary core-shell particles as a chromium removal additive. Its SEM is as Figure 14 shown, and the XRD test results are as Figure 15 shown.

[0103] Performance test: (1) Mix a commercially available 42.5 ordinary Portland cement in a certain city (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water in a mass ratio of 2:6:1, and add the chromium removal additive prepared in this example according to 0.15% of the mass of the cement. Then stir for 20 min to obtain a cement paste. Then use diphenylcarbazide spectrophotometry to measure the concentration of Cr(VI) in the cement paste and calculate the removal rate. The results are shown in Table 7 below. It can be seen that the chromium removal ability of the chromium removal additive prepared in this example for Cr(VI) in cement has decreased significantly. (2) According to GBT 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", test the early strength of the specimens prepared from the cement paste. The results are shown in Table 7:

[0104] Table 7

[0105] .

[0106] Example 8

[0107] A preparation process of a chromium removal additive for cement, comprising the following steps:

[0108] (1) Place water in a reaction kettle and preheat it to 100 °C first, then pressurize it to 22.1 MPa, and then continue to heat the water to the supercritical state of 374 °C to obtain supercritical water. Then dissolve FeCl 2 and SnCl 2 in the supercritical water according to a mass ratio of 1.27:1, and then add calcium polysulfide particles with a particle size distribution between 10 and 25 μm according to a solid-liquid ratio of 3 g:100 ml and mix evenly to obtain a supercritical suspension mixture for standby.

[0109] (2) Pass the suspension mixture through the microporous plate in the throttler (as Figure 1 shown, the inlet diameter is 11 mm, the outlet diameter is 7 mm, and the pore diameter of the microporous plate is 75 μm), so that the suspension mixture rapidly expands and then cools down and reduces pressure into a collection container with an argon protection atmosphere. Then collect the solid product, that is, obtain primary core-shell particles for standby.

[0110] (3) Drop the mixed solution of the primary core-shell particles and diethyl ether (the ratio of the two is 1 g: 50 ml) onto the cleaned silicon wafer, and then spin-coat it at a speed of 3000 r / min for 30 s using a spin coater to make the primary core-shell particles evenly distributed on the surface of the silicon wafer. Then place the silicon wafer in a vacuum oven at 60 °C and heat it for 5 min to firmly attach the primary core-shell particles to the silicon wafer.

[0111] (4) Put the silicon wafer obtained in the last step of step (3) into a container filled with a mixed solution formed by ammonia water (concentration 5 mol / L), tetraethyl orthosilicate and absolute ethanol in a volume ratio of 10 ml: 3 ml: 100 ml. Seal the container and microwave heat it to 50 °C and keep it warm for reaction for 2 hours, then perform ultrasonic treatment for 2 h with an ultrasonic power of 300 W to make the product attached to the silicon wafer fully react and detach into the solution. Finally, centrifuge the obtained reaction solution at a rate of 10000 rmp for 10 min, collect the solid product at the bottom, and dry it to constant weight under vacuum conditions at 60 °C to obtain the chromium removal additive, and its SEM is as Figure 16 shown, and the XRD test results are as Figure 17 shown.

[0112] Performance test: (1) Mix a commercially available 42.5 ordinary Portland cement (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water in a mass ratio of 2: 6: 1, and add the chromium removal additive prepared in this example according to 0.3% of the mass of the cement, then stir for 20 min to obtain a cement paste. Then use diphenylcarbazide spectrophotometry to measure the concentration of Cr(VI) in the cement paste and calculate the removal rate. The results are shown in Table 8 below. It can be seen that the chromium removal ability of the chromium removal additive prepared in this example for Cr(VI) in cement has decreased significantly. (2) Test the early strength of the specimens prepared from the cement paste according to GBT 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", and the results are shown in Table 8:

[0113] Table 8

[0114] .

[0115] Example 9

[0116] A preparation process of a cement chromium removal additive is the same as that of Example 2 above, except that the primary core-shell particles in this example are prepared by the following method:

[0117] (1) Mix Fe(NO 3 ) 2 and SnSO 4Dissolve it in water according to the mass ratio of 0.84:1, and then add calcium polysulfide particles with a particle size distribution between 10 and 25 μm according to the solid-liquid ratio of 2 g:70 ml and mix evenly to obtain a suspension mixture for standby.

[0118] (2) Dry the suspension mixture in a nitrogen protection atmosphere to remove moisture, and then collect the solid product, which is used as a chromium removal additive for cement. Its SEM is as Figure 18 shown, and the XRD test results are as Figure 19 shown.

[0119] Performance test: (1) Mix a commercially available 42.5 ordinary Portland cement in a certain city (the initial concentration of Cr(VI) measured is 18.2 mg / kg), standard sand, and mixing water according to the mass ratio of 2:6:1, and add the chromium removal additive prepared in this example according to 0.15% of the mass of the cement, and then stir for 20 min to obtain a cement paste. Then, use diphenylcarbazide spectrophotometry to measure the concentration of Cr(VI) in the cement paste and calculate the removal rate. The results are shown in Table 9 below. It can be seen that the chromium removal additive has insufficient removal effect on Cr(VI) in the cement, resulting in a significant decrease in the removal rate of chromium(VI) in the cement paste. (2) Test the early strength of the specimens prepared from the cement paste according to GBT 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", and the results are shown in Table 9:

[0120] Table 9

[0121] .

[0122] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for preparing a cement chromium removal additive, characterized in that: The steps include: (1) dissolving an Fe(II) source and / or a Sn(II) source into supercritical water, and then adding calcium polysulfide particles with a particle size of 10 to 25 μm and dispersing them evenly to obtain a supercritical suspension mixture for later use; (2) passing the suspension mixture through a microporous plate with a pore size of 25 to 75 μm in a restrictor to rapidly expand the suspension mixture into a protective atmosphere collection container, and then collecting the solid product to obtain primary core-shell particles; (3) forming a nano-SiO2 seed layer on the surface of the primary core-shell particles by magnetron sputtering technology, and then placing the particles in an alcohol solution containing ammonia water and tetraethyl orthosilicate, heating the reaction at 40-80°C for 1-3 hours under sealed conditions, and then performing ultrasonic treatment, and then collecting the solid product in the reaction solution, and obtaining the chromium removal additive after drying.

2. The preparation process of the cement chromium removal additive according to claim 1, characterized in that: In step (1), the Fe(II) source includes at least one of FeSO4, Fe(NO3)2, and FeCl2.

3. The preparation process of the cement chromium removal additive according to claim 1, characterized in that: In step (1), the Sn(II) source includes at least one of SnSO4 and SnCl2.

4. The preparation process of the cement chromium removal additive according to claim 1, characterized in that: In step (1), the mass ratio of the Fe(II) source to the Sn(II) source is 0.41-1.27:

1.

5. The preparation process of the cement chromium removal additive according to claim 1, characterized in that: In step (1), the ratio of the calcium polysulfide particles to supercritical water is 1-3 g: 30-100 ml.

6. The preparation process of the cement chromium removal additive according to claim 1, characterized in that: In step (2), the protective atmosphere includes any one of nitrogen and argon.

7. The preparation process of the cement chromium removal additive according to claim 1, characterized in that: In step (3), the method for forming a nano-SiO2 seed layer comprises: dropping a mixed solution of the primary core-shell particles and a non-aqueous organic dispersant onto a cleaned silicon wafer, and then spin coating the primary core-shell particles to evenly distribute the primary core-shell particles on the surface of the silicon wafer; then heating the silicon wafer; and after completion, using magnetron sputtering technology to deposit nano-SiO2 onto the surface of the primary core-shell particles on the silicon wafer, thereby forming a nano-SiO2 seed layer.

8. The preparation process of the cement chromium removal additive according to claim 7, characterized in that: The ratio of the primary core-shell particles to the non-aqueous organic dispersant is 1g:20-50ml.

9. The preparation process of the cement chromium removal additive according to claim 7, characterized in that: The non-aqueous organic dispersant includes at least one of anhydrous ethanol and ether.

10. The preparation process of the cement chromium removal additive according to any one of claims 1 to 9, characterized in that: In step (3), the ratio of ammonia water, tetraethyl orthosilicate and alcohol solution is 3-10 ml: 1-3 ml: 33-100 ml.

11. The preparation process of the cement chromium removal additive according to any one of claims 1 to 9, characterized in that: In step (3), the concentration of the ammonia water is 1-5 mol / L.

12. The preparation process of the cement chromium removal additive according to any one of claims 1 to 9, characterized in that: In step (3), the alcohol solution includes at least one of anhydrous methanol, anhydrous ethanol, n-propanol, and n-butanol.

13. The preparation process of the cement chromium removal additive according to any one of claims 1 to 9, characterized in that: In step (3), the ultrasonic treatment time is 1-3 hours, and the ultrasonic power is 300-500W.

14. A cement-based material containing a cement chromium removal additive obtained by the preparation process according to any one of claims 1 to 13, characterized in that: The dosage of the chromium removal additive is 0.1~0.3% of the mass of the cement-based material.

15. The cement-based material according to claim 14, characterized in that: The cement-based material is a silicate cement-based material.

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