Preparation and application of a soluble hexavalent chromium reducing agent in cement

Abstract

The invention relates to the technical field of cement production and solid waste utilization, and specifically discloses a preparation of a soluble hexavalent chromium reducing agent in cement, wherein the soluble hexavalent chromium reducing agent is mainly prepared from the following raw materials in weight percentage: 30%-70% industrial green vitriol, 20%-60% phosphogypsum, 1%-5% stabilizer, and 0%-5% setting regulator. The hexavalent chromium reducing agent prepared by the invention can make full use of two industrial solid wastes, industrial green vitriol and phosphogypsum, to reduce the soluble hexavalent chromium in cement, and has long time effect, little influence on cement performance, easy material feeding, and low preparation cost.

Description

Technical Field

[0001] The invention relates to the technical field of cement production and solid waste utilization, and in particular to the preparation and application of a soluble hexavalent chromium reducing agent used in cement. Background Art

[0002] With the official implementation of GB 31893-2015 "Limits and determination methods of water-soluble chromium (VI) in cement" in October 2016, a clear limit requirement for water-soluble chromium (VI) in cement was made (not exceeding 10 mg / kg), and cement companies have higher requirements for the chromium content of materials used in production. For example, some iron correction materials or industrial solid wastes such as steel slag and copper tailings with high chromium content used for clinker calcination are difficult to continue to use, and the cheaper iron material resources available to cement companies are even more scarce. In order to meet the water-soluble chromium (VI) limit requirements of cement in national standards, cement companies mainly choose raw materials with lower chromium content, but these materials are expensive or have other problems, such as the high price of iron content per unit of iron ore and the high chlorine content of steel plant pipelines, which affects the stable operation of cement kiln systems.

[0003] In view of the above situation, some cement enterprises in the prior art choose to add hexavalent chromium reducing agents in the cement production process. Commonly used reducing agents mainly include low-valent tin salts, antimony trioxide, sodium thiosulfate and other salts, as well as organic substances such as thioglycolic acid and mercaptopropionic acid. Among them, heavy metal salts are expensive and there is a risk of heavy metal hazards. Other inorganic salts such as sodium thiosulfate have problems such as high dosage and introduction of unfavorable elements such as alkali. Organic substances such as thioglycolic acid and mercaptopropionic acid are toxic, have poor thermal stability, and the reduction effect is greatly affected by conditions. In addition, there are some that use industrial solid waste green vitriol directly as a cement reducing agent. Although the price is relatively cheap, green vitriol is unstable and is easily oxidized in advance in air and cement grinding (high temperature), affecting the reduction effect and timeliness. At the same time, industrial green vitriol has a high degree of crystallization and crystal water content, is easy to agglomerate, and the material is not easy to flow. It is not suitable for unloading during cement production, and direct use will have a significant adverse effect on the consistency, setting time and strength of cement, thereby limiting its use. Some researchers have also tried to use other materials such as fly ash and solid sulfur ash to mix with industrial green vitriol to improve the material handling and usability of industrial green vitriol, but the improvement effect is not good and there are problems such as further reduction of the reduction effect of industrial green vitriol. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a preparation and application of a soluble hexavalent chromium reducing agent in cement. The hexavalent chromium reducing agent prepared by the invention can make full use of two industrial solid wastes, industrial green vitriol and phosphogypsum, to reduce the soluble hexavalent chromium in cement, and has a long time effect, little effect on cement performance, easy material discharge and low preparation cost.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is: a preparation of a soluble hexavalent chromium reducing agent in cement, characterized in that it is mainly prepared from the following raw materials in weight percentage: 30%-70% industrial green vitriol, 20%-60% phosphogypsum, 1%-5% stabilizer, and 0%-5% setting regulator.

[0006] The above industrial green vitriol is mainly derived from the main by-product of the production of titanium dioxide by sulfuric acid method. It is an industrial solid waste, and its main component is FeSO4•7H2O, which is the main component for the reduction of hexavalent chromium. Phosphogypsum is mainly produced by the main by-product of the phosphoric acid preparation process of phosphoric acid by phosphorus chemical industry. It is also an industrial solid waste, and its main component is CaSO4•2H2O. As a blending component, its main function is to improve the problems of poor material discharge of industrial green vitriol in the process of cement production and use, great impact on cement performance, and easy oxidation of green vitriol and failure of reduction effect.

[0007] Preferably, the pH of the phosphogypsum is 3 to 7. Under acidic conditions, divalent iron reacts with phosphate ions to generate diferrous phosphate, which stabilizes the divalent iron and prevents the divalent iron from being oxidized to trivalent iron, thereby causing the reduction property to fail.

[0008] Preferably, the stabilizer is one or two of ethylenediamine disuccinic acid (EDSS) and its salts, aminotri(methylenephosphonic acid) (ATMP) and its salts, which are mainly used as stabilizers for divalent iron in green vitriol to further improve the reducing effect of green vitriol and its stability under alkaline conditions of cement.

[0009] Preferably, the above-mentioned setting regulator is aluminum sulfate, mainly based on demand, to control the effect of the introduction of phosphogypsum and green vitriol in the reducing agent on the setting time and early strength of cement, which has the effect of improving the early strength of cement and shortening the setting time of cement.

[0010] Preferably, the specific process of preparing the above-mentioned soluble hexavalent chromium reducing agent for cement is to first put phosphogypsum, stabilizer and setting regulator into a stirring device in proportion and stir them, and then add industrial green vitriol in a corresponding proportion and continue to stir and mix.

[0011] The second technical solution adopted by the present invention is an application of a soluble hexavalent chromium reducing agent in cement in cement production, characterized in that it is specifically measured alone or compounded with admixtures and gypsum and added to a cement mill for grinding, wherein the gypsum includes one or more of phosphogypsum, desulfurized gypsum, natural gypsum, fluorinated gypsum, etc., and the admixture includes one or more of limestone powder, fly ash, coal gangue, coal-fired slag, steel slag, slag or mineral powder; the mass ratio of the reducing agent in cement is 1%-3%; and in the application process, according to the ratio of the hexavalent chromium reducing agent in cement, the dosage of gypsum and admixture in cement is appropriately reduced, wherein the dosage of gypsum in cement is reduced by 0.5-1 times the ratio of the hexavalent chromium reducing agent in cement, and the dosage of the admixture is reduced by 0-0.5 times the ratio of the hexavalent chromium reducing agent in cement.

[0012] The mechanism of action of the reducing agent of the present invention is: utilizing the strong reducing property of industrial green vitriol to reduce the soluble hexavalent chromium in cement. Since industrial green vitriol has the disadvantages of being unstable, easy to oxidize, having a high degree of crystallization and a high content of crystal water, and being difficult to feed, phosphogypsum is added to the formula. By adding phosphogypsum with a pH value below 7, on the one hand, under acidic conditions, the divalent iron of industrial green vitriol reacts with phosphate ions to generate diferrous phosphate, stabilizing the divalent iron ions and preventing the divalent iron ions in the industrial green vitriol from being oxidized to trivalent iron ions and thus rendering its reducing property ineffective; on the other hand, by wrapping the industrial green vitriol with phosphogypsum, the material properties of the industrial green vitriol are improved, and the problems of easy agglomeration, wall adhesion, and material clogging are improved, so that the reducing agent is easy to feed; and the addition of the stabilizer is to further stabilize the divalent iron ions in the industrial green vitriol and prevent them from being oxidized to trivalent iron ions and losing the function of reducing hexavalent chromium; the setting agent aluminum sulfate, on the one hand, reacts with the industrial green vitriol and phosphogypsum during the preparation of the reducing agent, and in the Al 3+ , Fe 2+ 、SO4 2- 、HPO4 2- and Ca 2+ In the presence of plasma, a small amount of ettringite seeds can be generated to provide nuclei and seeds for accelerating cement hydration and reduce soluble HPO4 which has a greater impact on cement setting time. 2- On the other hand, plasma can dissolve rapidly during cement hydration, providing Al for the formation of calcium sulfide. 3+ 、SO4 2- , effectively accelerating the formation of calcium aluminate during cement hydration, thereby improving early strength and shortening cement setting time.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. Make full use of industrial solid waste green vitriol and phosphogypsum to prepare hexavalent chromium reducing agent. The solid waste utilization rate in the product reaches more than 95%, which is beneficial to solid waste disposal and environmental protection. In addition, phosphogypsum is used to mix and wrap industrial green vitriol and protect the particles, solving the problems of green vitriol in cement production and application, such as poor material feeding, easy agglomeration and easy oxidation, which leads to the failure of reduction effect.

[0015] 2. Use one or two of ethylenediamine disuccinic acid (EDSS) and its salts, aminotrimethylphosphonic acid (ATMP) and its salts as stabilizers for divalent iron in green vitriol to further improve the reduction effect of green vitriol and its stability under alkaline conditions of cement;

[0016] 3. The prepared hexavalent chromium reducing agent is easy to use in cement production and application, has good stability and hexavalent chromium reduction effect, has a long reduction effect, does not contain other heavy metals or flammable and decomposable toxic organic matter, and is green and environmentally friendly;

[0017] 4. According to the ratio of hexavalent chromium reducing agent in cement, the amount of gypsum in cement is appropriately reduced. The amount of gypsum in cement is reduced by 0.5-1.0 times the ratio of hexavalent chromium reducing agent in cement, mainly to reduce the impact of the decrease in early strength of cement and the extension of setting time caused by the introduction of phosphogypsum and green vitriol in the reducing agent;

[0018] 5. Adding 0%-5% aluminum sulfate as a setting regulator into cement can shorten the setting time of cement and improve its early strength, and further control the influence of phosphogypsum and green vitriol in the reducing agent on the setting time and early strength of cement. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiment of the present application will be clearly and completely described below in conjunction with the appendix in the embodiment of the present application. Obviously, the described embodiment is only a part of the embodiment of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0020] And the parts not described in detail below should be carried out according to the existing technology.

[0021] Embodiment 1

[0022] Step 1), add phosphogypsum with pH=3, ethylenediamine disuccinic acid and aluminum sulfate in a mass ratio of 30%, 1% and 1% to a stirring container for mixing and stirring, and then add industrial green vitriol with a mass ratio of 68% and stir again;

[0023] Step 2), storing the hexavalent chromium reducing agent obtained by the above stirring for later use;

[0024] Step 3), the prepared hexavalent chromium reducing agent is ground with clinker, admixture and desulfurized gypsum to prepare cement, wherein the hexavalent chromium reducing agent is added to the cement at a ratio of 1%, and the desulfurized gypsum and admixture (i.e. limestone powder) are added to the cement at a ratio of 0.5% and 0.5% lower than that of blank sample 1 (cement ratio: 78% clinker, 5% desulfurized gypsum, 4% limestone powder, 5% coal gangue, 4% steel slag and 4% coal-fired slag), respectively. That is, the cement ratio in this embodiment is: 78% clinker, 4.5% desulfurized gypsum, 3.5% limestone powder, 5% coal gangue, 4% steel slag, 4% coal-fired slag, 1% of the hexavalent chromium reducing agent of the first embodiment, thereby completing the application of the hexavalent chromium reducing agent in cement production.

[0025] Table 1 shows the performance comparison of the cement prepared in Example 1, blank sample 1 and comparative examples 1-5.

[0026] The blank sample 1 does not use any hexavalent chromium reducing agent, and the rest is the same as Example 1. That is, the cement ratio of the blank sample 1 is: 78% clinker, 5% desulfurized gypsum, 4% limestone powder, 5% coal gangue, 4% steel slag and 4% coal-fired furnace slag;

[0027] Comparative Example 1 and Comparative Example 2 are the same as Example 1 except that only industrial green vitriol is added to the reducing agent, and the industrial green vitriol addition amount is 0.7% and 1% of the cement mass, respectively. That is, the cement ratio of Comparative Example 1 is: 78% clinker, 4.5% desulfurized gypsum, 3.8% limestone powder, 5% coal gangue, 4% steel slag, 4% coal-fired slag, 0.7% industrial green vitriol; the cement ratio of Comparative Example 2 is: 78% clinker, 4.5% desulfurized gypsum, 3.5% limestone powder, 5% coal gangue, 4% steel slag, 4% coal-fired slag, 1% industrial green vitriol;

[0028] Comparative Example 3 is a composite reducing agent 1 mixed with industrial green vitriol, phosphogypsum with a pH value of 3 and aluminum sulfate (compounding ratios are 69%, 30% and 1%), and the rest is the same as in Example 1. The mixing ratio of the composite reducing agent in Comparative Example 3 is 1% of the cement mass. That is, the cement ratio of Comparative Example 3 is: 78% clinker, 4.5% desulfurized gypsum, 3.5% limestone powder, 5% coal gangue, 4% steel slag, 4% coal-fired slag, and 1% composite reducing agent 1 (compounded from 69% industrial green vitriol, 30% phosphogypsum, and 1% aluminum sulfate);

[0029] Comparative Example 4 is a composite reducing agent 2 mixed with industrial green vitriol, phosphogypsum with a pH value of 3 and ethylenediamine disuccinic acid (the composite ratio is 69%, 30% and 1%), and the rest is the same as in Example 1. The composite reducing agent in Comparative Example 4 is mixed with 1% of the cement mass. That is, the cement ratio of Comparative Example 4 is: 78% clinker, 4.5% desulfurized gypsum, 3.5% limestone powder, 5% coal gangue, 4% steel slag, 4% coal-fired slag, and 1% composite reducing agent 2 (compounded with 69% industrial green vitriol, 30% phosphogypsum, and 1% ethylenediamine disuccinic acid);

[0030] The reducing agent in Comparative Example 5 is the same as that in Example 1, and the dosage is also 1%. The difference is that the dosage of desulfurized gypsum in cement is not reduced by 0.5%, but the limestone powder and coal gangue in the cement ratio are reduced by 0.5%. That is, the cement ratio of Comparative Example 5 is: 78% clinker, 5% desulfurized gypsum, 3.5% limestone powder, 4.5% coal gangue, 4% steel slag, 4% coal-fired slag and 1% hexavalent chromium reducing agent of Example 1.

[0031] Table 1 Comparison of cement properties prepared in Example 1 and Comparative Examples 1 to 5

[0032]

[0033] Note: 0d, 15d, 30d and 45d in the hexavalent chromium content respectively represent the soluble hexavalent chromium content of cement measured on the day when the cement sample is prepared, 15 days later, 30 days later and 45 days later.

[0034] From the data in the above table, it can be seen that after adding industrial green vitriol and its compounded hexavalent chromium reducing agent, the cement setting time, 3d compressive strength and hexavalent chromium content show different changes. The difference is that the comprehensive performance of Example 1 is better, among which the 3d compressive strength does not show a decline, the effect on cement consistency is smaller, and the hexavalent chromium content of cement is maintained at a low level after storage for different ages, and is still lower than the national standard 10mg / kg limit requirement after 45d. In Comparative Examples 1 and 2, the addition of industrial green vitriol alone has a significant adverse effect on the consistency and 3d compressive strength of cement, and the material is easy to agglomerate, the material is not smooth, it is not easy to use, the reduction effect has the worst timeliness, and the cement setting time is extended; in Comparative Example 3, the reducing agent does not contain a stabilizer, and only green vitriol is compounded with phosphogypsum and aluminum sulfate. Although the material is not easy to agglomerate, the hexavalent chromium reduction effect is improved compared with Comparative Examples 1 and 2, but the comprehensive effect is lower than that of Example 1. After 45 days, the hexavalent chromium content is close to exceeding the national standard 10 mg / kg limit requirement; in Comparative Example 4, there is no setting agent, and only green vitriol is compounded with phosphogypsum, aluminum sulfate and ethylenediamine disuccinic acid. Although the material is not easy to agglomerate and the hexavalent chromium reduction effect is good, it affects the early 3d strength of cement and prolongs the cement setting time; in Comparative Example 5, the same reducing agent as in Example 1 is used. Although the reduction effect is good, after the addition of the reducing agent, the amount of desulfurized gypsum in the cement is not properly adjusted, resulting in a more obvious extension of the cement setting time, and a greater impact on the early 3d compressive strength of cement.

[0035] Embodiment 2

[0036] Step 1), add phosphogypsum with pH=4.5, aminotri(methylenephosphonic acid) and aluminum sulfate in a mass ratio of 45%, 3% and 2% to a stirring container for mixing and stirring, and then add industrial green vitriol with a mass ratio of 50% and stir again;

[0037] Step 2), storing the hexavalent chromium reducing agent obtained by the above stirring for later use;

[0038] Step 3), the prepared hexavalent chromium reducing agent and gypsum are combined for cement grinding to prepare cement, the hexavalent chromium reducing agent is added to the cement at a ratio of 2%, and the natural gypsum is added at a ratio of 2% lower than that of blank sample 2 (cement ratio: 58% clinker, 5% natural gypsum, 22% limestone powder, 7% coal gangue and 8% coal slag), that is, the cement ratio in this embodiment is: 58% clinker, 3% natural gypsum, 22% limestone powder, 7% coal gangue, 8% coal slag, 2% hexavalent chromium reducing agent of the second embodiment, thereby completing the application of the hexavalent chromium reducing agent in cement production.

[0039] Table 2 shows the performance comparison of the cement prepared in Example 2, Blank Sample 2 and Comparative Examples 6-7.

[0040] Wherein, blank sample 2 does not use any hexavalent chromium reducing agent, and the rest is the same as Example 2;

[0041] Comparative Example 6 is a cement mixture in which only industrial green vitriol is added in an amount of 2% by mass of cement, and the rest is the same as in Example 2; that is, the cement ratio in Comparative Example 6 is: 58% clinker, 3% natural gypsum, 22% limestone powder, 7% coal gangue, 8% coal-fired slag, and 2% industrial green vitriol;

[0042] Comparative Example 7 is a composite reducing agent 3 in which industrial green vitriol and aminotri(methylene phosphonic acid) are added (the composite ratio is 97% and 3%), and the composite reducing agent 3 is added in a ratio of 2% of the mass of cement, and the rest is the same as Example 2; that is, the cement ratio in Comparative Example 7 is: 58% clinker, 3% natural gypsum, 22% limestone powder, 7% coal gangue, 8% coal-fired slag, and 2% composite reducing agent 3 (compounded from 97% industrial green vitriol and 3% aminotri(methylene phosphonic acid).

[0043] Table 2 Comparison of cement properties prepared in Example 2 and Comparative Examples 6-7

[0044]

[0045] From the data in the table above, it can be seen that after adding industrial green vitriol and its compound hexavalent chromium reducing agent, cement setting time, 3d compressive strength and hexavalent chromium content show different changes. The difference is that the comprehensive performance of Example 2 is better, among which the 3d compressive strength is basically close to that of blank sample 2, and the cement setting time is extended to the minimum, the effect on cement consistency is smaller, and the hexavalent chromium content of cement after storage at different ages is maintained at a low level, and after 45d, it is still lower than the national standard 10mg / kg limit requirement. Comparative Example 6 has a large adverse effect on cement consistency and 3d strength, and the material is easy to agglomerate, not easy to use, the reduction effect is the worst in timeliness, and the cement setting time is extended more obviously; only green vitriol is compounded with aminotrimethylphosphonic acid, and the hexavalent chromium reduction effect is improved, but the hexavalent chromium content still exceeds the national standard 10mg / kg limit requirement after 45d, and the material is easy to agglomerate, and the comprehensive effect of cement 3d strength and the effect on cement setting time extension is lower than Example 2.

[0046] Embodiment 3

[0047] Step 1), add phosphogypsum with pH=6.5, ethylenediamine disuccinic acid and aluminum sulfate in a mass ratio of 55%, 5% and 5% to a stirring container for mixing and stirring, and then add industrial green vitriol with a mass ratio of 35% and stir again;

[0048] Step 2), storing the hexavalent chromium reducing agent obtained by the above stirring for later use;

[0049] Step 3), the prepared hexavalent chromium reducing agent and gypsum are ground to prepare cement, the hexavalent chromium reducing agent is added to the cement at a ratio of 3%, and the addition ratio of desulfurized gypsum is reduced by 3% compared with blank sample 3 (cement ratio: 90% clinker, 6% desulfurized gypsum, 2% limestone powder and 2% coal-fired slag), that is, the cement ratio in Example 3 is: 90% clinker, 3% desulfurized gypsum, 2% limestone powder, 2% coal-fired slag, 3% hexavalent chromium reducing agent of Example 3, thereby completing the application of hexavalent chromium reducing agent in cement production.

[0050] Table 3 shows the performance comparison of the cement prepared in Example 3, blank sample 3 and comparative examples 8-10.

[0051] Wherein, blank sample 3 does not use any hexavalent chromium reducing agent, and the rest is the same as Example 3;

[0052] Comparative Example 8 is a cement mixture in which only industrial green vitriol is added in an amount of 3% by weight of cement, and the rest is the same as in Example 3; that is, the cement ratio in Comparative Example 8 is: 90% clinker, 3% desulfurized gypsum, 2% limestone powder, 2% coal-fired furnace slag, and 3% industrial green vitriol;

[0053] Comparative Example 9 is a composite reducing agent 4, the composite components are phosphogypsum, ethylenediamine disuccinic acid, aluminum sulfate and industrial green vitriol, and the composite ratio is the same as that of Example 3, except that the pH of the phosphogypsum is 9.5, and the proportion of the composite reducing agent in Comparative Example 9 is 3% of the mass of cement; that is, the cement ratio in Comparative Example 9 is: 90% clinker, 3% desulfurized gypsum, 2% limestone powder, 2% coal-fired furnace slag, 3% composite reducing agent 4 (55% phosphogypsum with pH=9.5, 5% ethylenediamine disuccinic acid, 5% aluminum sulfate, 35% industrial green vitriol);

[0054] Comparative Example 10 is a compound reducing agent 5. Compared with Example 3, the difference is that phosphogypsum is replaced with fly ash, and the compound reducing agent in Comparative Example 10 is added in an amount of 3% of the mass of cement; that is, the cement ratio in Comparative Example 10 is: 90% clinker, 3% desulfurized gypsum, 2% limestone powder, 2% coal-fired furnace slag, and 3% compound reducing agent 5 (55% fly ash, 5% ethylenediamine disuccinic acid, 5% aluminum sulfate, and 35% industrial green vitriol).

[0055] Table 3 Comparison of cement properties prepared in Example 3 and Comparative Examples 8-10

[0056]

[0057] From the data in the above table, it can be seen that after adding industrial green vitriol and its compound hexavalent chromium reducing agent, the cement setting time, 3d compressive strength and hexavalent chromium content show different changes. The difference is that the comprehensive performance of Example 3 is better, among which the 3d compressive strength decreases the least, and the effect on cement consistency and setting time is relatively small, and the hexavalent chromium content of cement is maintained at a low level after storage for different ages, and is still lower than the national standard 10mg / kg limit after 45d. Comparative Example 8, which only adds green vitriol, has a greater adverse effect on cement consistency, setting time and 3d strength, and the material is easy to agglomerate, not easy to use, and the reduction effect is the worst in terms of timeliness; Comparative Example 9 and Comparative Example 10 replace the phosphogypsum with pH=6.5 with phosphogypsum and fly ash with pH=9.5, and the reduction effect is significantly reduced, and the hexavalent chromium content will exceed the national standard 10mg / kg limit after 45d.

Claims

1. A soluble hexavalent chromium reducing agent in cement, characterized in that: The soluble hexavalent chromium reducing agent is mainly prepared from the following raw materials in weight percentage: 30%-70% industrial green vitriol, 20%-60% phosphogypsum, 1%-5% stabilizer, and 0%-5% setting regulator; the pH of the phosphogypsum is 3-7; the stabilizer is selected from one or two of ethylenediamine disuccinic acid and its salts, aminotri(methylenephosphonic acid) and its salts; the setting regulator is selected from aluminum sulfate.

2. A method for preparing a soluble hexavalent chromium reducing agent in cement according to claim 1, characterized in that: The specific process is to first put phosphogypsum, stabilizer and setting regulator into a stirring device in proportion and stir them, and then add industrial green vitriol in a corresponding proportion and continue to stir and mix.

3. Application of a cement-soluble hexavalent chromium reducing agent in cement production, characterized in that: Specifically, the soluble hexavalent chromium reducing agent as claimed in claim 1 is measured alone or compounded with admixtures and gypsum and then added to a cement mill for grinding; wherein the mass ratio of the soluble hexavalent chromium reducing agent in cement is 1%-3%, and in the application process, according to the ratio of the hexavalent chromium reducing agent in cement, the dosage of gypsum and admixtures in cement is reduced, wherein the dosage of gypsum in cement is reduced to 0.5-1 times the ratio of the hexavalent chromium reducing agent in cement, and the dosage of admixtures is reduced to 0-0.5 times the ratio of the hexavalent chromium reducing agent in cement.

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