New chromium reducing agents for use in cement.

Abstract

The present invention relates to a novel chromium reducer for use in cement. In particular, the present invention provides a chromium reducer composition, a method for reducing water-soluble hexavalent chromium in cement using the chromium reducer composition, and a cement-based composition containing the chromium reducer composition. The chromium reducer composition contains a chelating agent, preferably in an amount of 30 to 60 wt %, preferably 35 to 55 wt %, and preferably 40 to 50 wt %, based on the total weight of the chromium reducer composition, and optionally a stabilizer, preferably in an amount of 0.1 to 1 wt %, preferably 0.3 to 0.7 wt %, and preferably 0.4 to 0.6 wt %, based on the total weight of the chromium reducer composition. The chromium reducer composition has a significant chromium reduction effect, excellent high-temperature resistance, durability, and storage stability, and is inexpensive.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a chromium reducer composition, preferably for use in cement. [Background technology]

[0002] Water-soluble hexavalent chromium in cement is harmful to humans and the environment. Due to the complexity and variety of raw materials used in cement production, hexavalent chromium can be introduced into cement from raw materials, high-temperature refractories in cement rotary kilns, and crushing and grinding equipment. Many cement plants face this problem, and if the water-soluble hexavalent chromium in cement does not meet the standard requirements, it is not permitted to be sold or used. Therefore, many cement plants must use chromium reducers to meet the standard requirements. The present invention is aimed at cement plants and grinding departments, and if the water-soluble hexavalent chromium exceeds the national standard, a chromium reducer must be used.

[0003] Currently, most cement manufacturers use reducing agents as chromium reducers. Water-soluble hexavalent chromium in cement is reduced to harmless trivalent chromium by the reducing agent, achieving the goal of chromium reduction. Ferrous sulfate is a commonly used reducing agent and is widely used as a chromium reducer due to its low price and strong reducing properties. However, due to its strong reducing properties, ferrous sulfate's chromium reduction effect decreases due to its own oxidation when stored in air. In addition, cement is exposed to high temperatures during the manufacturing process, and ferrous sulfate oxidizes at an accelerated rate at high temperatures, reducing its chromium reduction effect. This results in a deterioration of ferrous sulfate's high-temperature resistance. Tin salts and antimony salts can also be used as chromium reducers. Although these salts have excellent chromium reduction effects and high-temperature resistance, they are too expensive to be put to practical use.

[0004] In consideration of the above problems, a new idea of ​​using a chelating agent has been devised. Hexavalent chromium in cement is chelated and captured by using a chelating agent having various chelating groups. By using this method, the reduction effect of water-soluble hexavalent chromium is remarkable, and this effect is not affected by high temperatures. In other words, the chelating agent has excellent high-temperature resistance.

[0005] CN101282917A provides a novel method and composition for maintaining the effectiveness of a chromium reducing agent in cement over a period of time. Before the chromium reducing agent is added to hydratable cement, a chromium(VI) reducing agent, such as tin sulfate (tin II), is mixed with a non-lignosulfonate-based complexing agent, such as sodium gluconate, to form a molecular association or coordination compound, thereby stabilizing the chromium(VI) reducing agent in the hydratable cement during storage, so that when the cement is eventually mixed with water and hydration occurs, the chromium(VI) reducing agent maintains its activity in reducing water-soluble chromium VI to chromium III.

[0006] WO2009073026A1 discloses a composition for reducing the level of hexavalent chromium, the composition comprising (A) at least one transition metal carbonyl compound or derivative thereof, and (B) at least one other additive including (i) a cement additive, (ii) an antioxidant, (iii) at least one other chromium reducing agent (e.g., ferrous sulfate, stannous sulfate), (iv) a chelating agent, or (v) a mixture thereof.

[0007] JP 2002-029805 A discloses a method for preparing cement mortar, which comprises kneading cement with water, a reducing agent, a dithiocarbamic acid-based chelating agent, and an optional water-reducing agent. The reducing agent is preferably an iron compound, particularly ferrous sulfate, ferrous nitrate, and ferrous chloride. The dithiocarbamic acid-based chelating agent includes, in particular, dimethyldithiocarbamic acid and its salts, and diethyldithiocarbamic acid and its salts.

[0008] JP 2003-306365 A discloses a cement additive containing a metal salt of a chelating agent, and a reduced metal is incorporated into at least a portion of the functional groups having metal coordinating ability, the reduced metal being iron(II). Examples of the chelating agent include, in particular, compounds having a dithiocarbamic acid group.

[0009] JP 2002-060751 A discloses a hexavalent chromium elution reducer containing a chelating compound and a hexavalent chromium elution reducer containing a chelating compound and a sulfate. The chelating compound is selected from one or more of thiourea compounds, thiazole compounds, dithiocarbamate compounds, triazine compounds, and chelating resins having sulfur atoms and nitrogen atoms. The sulfate is selected from one or more of ferrous sulfate, sodium sulfite, sodium bicarbonate, potassium sulfite, and potassium bicarbonate.

[0010] Most of the chelating / complexing agents reported in the prior art are used in combination with reducing agents, mainly to enhance the stability of the reducing agent. JP2002-060751A discloses the use of a chelating agent alone as a chromium reducing agent, but does not investigate the durability of the chromium reducing agent.

[0011] Therefore, there remains a need for a chromium reducing agent for use in cement that can overcome the shortcomings of the prior art chromium reducing agents, and that has significant chromium reducing effect, excellent high temperature resistance, durability and storage stability, and is inexpensive. Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a novel chromium reducing agent for use in cement, which has a remarkable effect of reducing water-soluble hexavalent chromium in cement, and which is not affected by high temperatures and does not lose this effect over a long period of time, i.e., which has excellent high-temperature resistance and durability, and which itself has storage stability and is inexpensive. [Means for solving the problem]

[0013] Surprisingly, it has been found that this objective can be achieved by a chromium reducer composition as defined in claim 1, which comprises a chelating agent and, optionally, a stabilizer. Unlike the prior art, which primarily uses strong reducing agents to reduce hexavalent chromium to trivalent chromium, the present invention uses a chelating agent having various chelating groups as the main component for chromium reduction. This chelating agent has strong chelating ability and can form a chelate with water-soluble hexavalent chromium in cement to capture it, thereby achieving a significant chromium reduction effect. The chromium reducer composition of the present invention has excellent high-temperature resistance, and its chromium reduction effect is not affected by high temperatures. The chromium reducer composition of the present invention is stable in air and does not need to be concerned about oxidation, resulting in excellent storage stability. In particular, the introduction of a stabilizer can prevent the gradual oxidation of the chromium reducer in cement, thereby extending the durability of the product.

[0014] Further aspects of the invention are the subject of further independent claims. Preferred embodiments of the invention are the subject of the dependent claims.

[0015] In a first aspect, the present invention provides a chromium reducer composition, preferably for use in cement, the chromium reducer composition comprising a chelating agent, preferably in an amount of 30 to 60 wt %, preferably 35 to 55 wt %, preferably 40 to 50 wt %, based on the total weight of the chromium reducer composition, and optionally a stabilizer, preferably in an amount of 0.1 to 1 wt %, preferably 0.3 to 0.7 wt %, preferably 0.4 to 0.6 wt %, based on the total weight of the chromium reducer composition.

[0016] In a second aspect, the present invention provides a method for reducing water-soluble hexavalent chromium in cement, the method comprising adding a chromium reducer composition described herein, preferably in liquid form, to a cementitious binder, preferably in an amount such that the proportion of chelating agent is 0.01 to 0.5 wt. %, preferably 0.03 to 0.125 wt. %, preferably 0.05 to 0.1 wt. %, based on the cement on a dry weight basis.

[0017] In a third aspect, the present invention provides a cementitious composition comprising at least one cementitious binder and a chromium reducer composition as described herein, preferably wherein the chromium reducer composition is present in an amount such that the proportion of chelating agent is 0.01 to 0.5 wt. %, preferably 0.03 to 0.125 wt. %, preferably 0.05 to 0.1 wt. %, based on the cementitious binder on a dry weight basis. DETAILED DESCRIPTION OF THE INVENTION

[0018] definition The term "hydraulic binder" refers, in particular, to a substance that hardens by a hydration chemical reaction, producing a hydrate that is not water-soluble. In particular, the hydration chemical reaction of a hydraulic binder occurs essentially independently of the water content. This means that a hydraulic binder can harden and retain its strength even when exposed to water, for example, under water or under humid conditions. In contrast, "non-hydraulic binders" (e.g., weathered hydrated lime or gypsum) are at least partially water-soluble and must be kept dry to retain their strength. In particular, in this context, a "hydraulic binder" can harden directly when mixed with water without requiring additional activation.

[0019] The hydraulic binder comprises or consists of cement. Preferably, the cement is Portland cement, and / or alumina cement, and / or sulfoaluminate cement, and / or a three-component adhesive. It may be a mixture of Portland cement and alumina cement. The three-component adhesive may comprise or consist of alumina cement, calcium sulfate, and optionally Portland cement.

[0020] Preferred Portland cements comply with the EN 197 standard, in particular type CEM I. The term "aluminous cement" in particular denotes cements having an aluminum content, measured as Al2O3, of at least 30% by weight, in particular at least 35% by weight, in particular 35-58% by weight. Preferably, the aluminous cement is an aluminous cement complying with the EN 14647 standard. Preferably, the sulfoaluminate cement is a calcium sulfoaluminate cement.

[0021] The term "gypsum" refers to any known form of gypsum, in particular anhydrous calcium sulfate, calcium sulfate alpha-hemihydrate, calcium sulfate beta-hemihydrate, calcium sulfate anhydrous or mixtures thereof.

[0022] The term "latent hydraulic and / or pozzolanic binder material" refers in particular to a type II concrete additive having latent hydraulic and / or pozzolanic properties according to EN 206-1. In particular, the latent hydraulic or pozzolanic binder material comprises or consists of slag, fly ash, silica fume, and / or natural pozzolans. In particular, "latent hydraulic and / or pozzolanic binder materials" cannot harden directly when mixed with water. These materials usually require additional activation.

[0023] The term "slag" has its usual meaning and refers in particular to a by-product of iron and steel production that is commonly used for blending cement in accordance with EN 15167. Preferably, the slag is ground granulated slag, in particular ground granulated blast furnace slag. In this context, preferred slags have a particle size of 3000-5000 cm 2 / g. Blaine fineness is 5000cm 2 Although slag exceeding 1 / g can be used in principle, the production cost increases.

[0024] "Fly ash" refers to the residue produced during coal combustion, consisting primarily of silicon dioxide, aluminum oxide, and calcium oxide. Preferred fly ash conforms to the EN450-1 standard.

[0025] "Silica fume" is a by-product of silicon manufacturing and consists primarily of amorphous silicon dioxide. The preferred silica fume conforms to the EN 13263-1 standard.

[0026] In a first aspect, the present invention provides a chromium reducer composition. The chromium reducer composition of the present invention comprises a chelating agent as the main chromium-reducing component, preferably the only chromium-reducing component. This means that the chromium reducer composition of the present invention is distinct from the prior art redox mechanism and captures water-soluble hexavalent chromium solely through the chelating effect of the chelating agent.

[0027] In one embodiment, the chromium reducer composition according to the present invention preferably comprises a chelating agent in an amount of 30 to 60 wt %, preferably 35 to 55 wt %, preferably 40 to 50 wt %, based on the total weight of the chromium reducer composition.

[0028] A chelating agent is a compound having a chelating group containing a metal coordinating atom such as oxygen, nitrogen, or sulfur, capable of forming a metal complex compound with a metal cation, and the chelating agent forms a bidentate or multidentate ligand when protonated at one or more positions. Examples of chelating groups include, but are not limited to, dithiocarbamic acid groups, phosphate groups, carboxylic acid groups, aminocarboxylic acid groups, dithiocarboxylic acid groups, phosphoramidic acid groups, and thiol groups.

[0029] In one embodiment, the chelating agent used in the chromium reducing agent composition of the present invention is preferably an organic sulfur chelating agent. The organic sulfur chelating agent generally refers to a chelating agent containing sulfur as a coordinating group, and examples thereof include dithiocarbamate-based chelating agents, xanthogenate-based chelating agents, trimercapto-s-triazine (TMT)-based chelating agents, and trithiocarbonate (STC)-based chelating agents.

[0030] Preferably, the organic sulfur chelating agent used in the chromium reducer composition of the present invention is a dithiocarbamate chelating agent, which is typically prepared by the reaction of a primary or secondary amine with carbon disulfide.

[0031] Preferably, the dithiocarbamate chelating agent used in the chromium reducer composition according to the present invention is selected from dimethyldithiocarbamic acid or a salt thereof, diethyldithiocarbamic acid or a salt thereof, and / or dibutyldithiocarbamic acid or a salt thereof, preferably dimethyldithiocarbamate, diethyldithiocarbamate, and / or dibutyldithiocarbamate, and most preferably dimethyldithiocarbamate.

[0032] In one embodiment, the dimethyldithiocarbamate used in the chromium reducer composition according to the present invention is selected from sodium dimethyldithiocarbamate, potassium dimethyldithiocarbamate, magnesium dimethyldithiocarbamate, calcium dimethyldithiocarbamate, barium dimethyldithiocarbamate and / or zinc dimethyldithiocarbamate, preferably sodium dimethyldithiocarbamate and / or potassium dimethyldithiocarbamate, and most preferably sodium dimethyldithiocarbamate.

[0033] Commercially available dithiocarbamate chelating agents include SDD from Shandong Boshan Dongfang Chemical Engineering Co., Ltd., heavy metal scavenger from Zhonglong Environmental Protection Technology Co., Ltd., and sodium dimethyldithiocarbamate from Hunan Fortune Environmental Protection Technology Co., Ltd.

[0034] As mentioned above, in the chromium reducing agent composition of the present invention, a chelating agent is the primary chromium reducing component. Because the chelating agent is metal sensitive, in order to maintain the chromium reducing ability of the chelating agent, it is necessary to prevent the introduction of metal ions during the manufacture, storage, transportation, and use of the chromium reducing agent composition.

[0035] In one embodiment, the chromium reducer composition according to the present invention is metal ion-free. The term "metal ion-free" means that the chromium reducer composition contains less than 1 wt. %, preferably less than 0.5 wt. %, more preferably less than 0.1 wt. %, and most preferably 0 wt. % of metal ions by weight, based on the total weight of the chromium reducer composition.

[0036] The present inventors have surprisingly found that the introduction of a stabilizer can mitigate the slow oxidation of the chromium reducing agent in the cement, thereby extending the durability of the product.

[0037] In one embodiment, the chromium reducer according to the present invention further comprises a stabilizer, preferably in an amount of 0.1 to 1 wt %, preferably 0.3 to 0.7 wt %, preferably 0.4 to 0.6 wt %, based on the total weight of the chromium reducer composition.

[0038] In one embodiment, the stabilizer is a cellulose ether. Cellulose ethers are derivatives of cellulose. Specifically, in cellulose ethers, the hydrogen atoms of the hydroxyl groups are typically partially or completely substituted with alkyl groups, hydroxyalkyl groups, carboxy groups, and / or carboxyalkyl groups. In particular, the alkyl groups include methyl groups, ethyl groups, and / or propyl groups.

[0039] In particular, the cellulose ether is a water-soluble cellulose ether.

[0040] In one embodiment, the cellulose ether is selected from hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, hydroxymethylcellulose, hydroxyethyl cellulose and / or carboxymethylcellulose, preferably hydroxypropyl methylcellulose and / or hydroxyethyl methylcellulose, most preferably hydroxypropyl methylcellulose.

[0041] An example of a commercially available cellulose ether is 60HD20 from Taian Ruite New Material Co., Ltd.

[0042] The chromium reducing agent composition of the present invention is preferably prepared and used in a liquid form. Therefore, in order to maintain the fluidity of the chromium reducing agent composition during use, the content of the stabilizer, if any, must not be too high; otherwise, the viscosity of the system will become too high to be applicable. The inventors of the present invention have found that the viscosity of the chromium reducing agent composition of the present invention becomes too high if the content of the cellulose ether exceeds 1 wt %, so the upper limit of the content is 1 wt %.

[0043] The present inventors have surprisingly found that the incorporation of additional molasses, for example, the simultaneous incorporation of the stabilizer and molasses described above, can prevent the slow oxidation of the chromium reducing agent in the cement and significantly extend the durability of the product.

[0044] In one embodiment, the chromium reducer composition according to the present invention further comprises molasses, preferably in an amount of 10 to 40 wt %, preferably 15 to 35 wt %, preferably 18 to 30 wt %, based on the total weight of the chromium reducer composition.

[0045] Molasses is a sucrose-containing composition produced in large quantities as a by-product of the sugar manufacturing process and is available cheaply worldwide. In addition to the main component sucrose, molasses contains, among other things, dextrin, lactic acid, nitrogenous compounds, and inorganic salts. Molasses mainly includes beet molasses, sugarcane molasses, glucose molasses, corn molasses, as well as inverted molasses and refined molasses. WO 2005110941 A1 discloses the use of chemically modified molasses as a plasticizer for cementitious compositions. CN 103732556 A discloses the use of proteolytically converted molasses as a dispersant for inorganic binders. There are no reports in the prior art on the use of molasses, especially in combination with cellulose ethers, to improve the durability of chromium-reducing agent compositions.

[0046] Without being bound by theory, it is believed that in the chromium reducing agent composition of the present invention, blackstrap molasses functions primarily as an antioxidant, and therefore, in cooperation with, for example, the cellulose ether as a stabilizer, it is possible to retard oxidation of the chromium reducing agent composition in cement and significantly improve the durability of the chromium reducing agent composition. In addition, in the chromium reducing agent composition of the present invention, blackstrap molasses can also function as a pH adjuster, so that its use can eliminate the need for a pH adjuster.

[0047] As with cellulose ethers, too much molasses can make the chromium reducing agent composition too viscous to be usable in liquid form. Therefore, if used, the molasses content in the chromium reducing agent composition of the present invention is preferably less than 40% by weight, preferably less than 35% by weight.

[0048] Commercially available molasses include molasses from Changshu Huadong Chemical Auxiliary Sales Co. Ltd. and molasses from Shanghai Kangbaizhi Technology Co. Ltd.

[0049] Chelating agents have requirements regarding the pH of the medium in order to exert their chelating ability. Dimethyldithiocarbamate salts, which are preferred chelating agents according to the present invention, require an alkaline medium, particularly an alkaline medium with a pH of about 10. Therefore, in order to meet the pH requirements of the chelating agent, it may be necessary to add a pH adjuster to the chromium reducer composition.

[0050] In one embodiment, the chromium reducer composition according to the present invention further comprises a pH adjuster, preferably in an amount of 1 to 10 wt %, preferably 1.5 to 5 wt %, preferably 2 to 3 wt %, based on the total weight of the chromium reducer composition.

[0051] In one embodiment, the pH adjuster is selected from a polymer polyol and / or sodium lignosulfonate.

[0052] Commercially available pH adjusters include polymer polyol from Nanjing Changjiang Jiangyu Energy Technology Co. Ltd. and sodium lignosulfonate from Foshan Junda Import and Export Co. Ltd.

[0053] In one embodiment, the chromium reducer composition according to the present invention further comprises a solvent, preferably water, preferably in an amount of 10 to 58 wt %, preferably 15 to 48 wt %, preferably 20 to 39 wt %, based on the total weight of the chromium reducer composition.

[0054] In a preferred embodiment, the chromium reducer composition according to the present invention comprises: - a chelating agent, preferably in an amount of 30-60 wt. %, preferably 35-55 wt. %, preferably 40-50 wt. %, based on the total weight of the chromium reducer composition; - optionally a stabilizer, preferably in an amount of 0.1 to 1 wt. %, preferably 0.3 to 0.7 wt. %, preferably 0.4 to 0.6 wt. %, based on the total weight of the chromium reducer composition; - optionally molasses, preferably in an amount of 10-40 wt. %, preferably 15-35 wt. %, preferably 18-30 wt. %, based on the total weight of the chromium reducer composition; - optionally a pH adjuster, preferably in an amount of 1 to 10 wt. %, preferably 1.5 to 5 wt. %, preferably 2 to 3 wt. %, based on the total weight of the chromium reducer composition; a solvent, preferably water, in an amount of 10 to 58% by weight, preferably 15 to 48% by weight, preferably 20 to 39% by weight, based on the total weight of the chromium reducer composition; The sum of the aforementioned components is 100% by weight.

[0055] In a second aspect, the present invention provides a method for reducing water-soluble hexavalent chromium in cement, comprising adding a chromium reducer composition described herein, preferably in liquid form, to a cementitious binder, preferably wherein the chromium reducer composition is added in an amount such that the proportion of chelating agent is 0.01 to 0.5 wt. %, preferably 0.03 to 0.125 wt. %, preferably 0.05 to 0.1 wt. %, based on the cement on a dry weight basis.

[0056] The chromium reducing agent may be added to the chromium reducing agent composition in powder form or liquid form. When added in powder form, additional addition equipment is required, which increases additional costs. In contrast, addition in liquid form can reduce costs by utilizing existing equipment. Therefore, the chromium reducing agent composition according to the present invention is preferably added to cement in liquid form.

[0057] The chromium reducer composition according to the present invention may be added to the cementitious binder before, during or after hydration caused by adding water to the cementitious binder.

[0058] In a third aspect, the present invention provides a cementitious composition comprising at least one cementitious binder and a chromium reducer composition as described herein, preferably wherein the chromium reducer composition is present in an amount such that the proportion of chelating agent is 0.01 to 0.5 wt. %, preferably 0.03 to 0.125 wt. %, preferably 0.05 to 0.1 wt. %, based on the cementitious binder on a dry weight basis.

[0059] The chromium reducer composition of the present invention is suitable for almost all cements.

[0060] In one embodiment, in the above methods and cementitious compositions, the cementitious binder comprises a hydraulic binder, a non-hydraulic binder and / or a latent hydraulic binder, preferably Portland cement, aluminous cement, sulfoaluminate cement, gypsum, lime, slag, fly ash, silica fume and / or natural pozzolan.

[0061] The chromium reducer composition according to the present invention has the following advantages: 1. The chromium reducing agent composition of the present invention has a significant effect of reducing water-soluble hexavalent chromium and has excellent high-temperature resistance, i.e., the chromium reducing effect is not affected by high temperatures. 2. The chromium reducing agent composition of the present invention is stable in air and is not susceptible to oxidation, and therefore has excellent storage stability. 3. The incorporation of a stabilizer, particularly the incorporation of molasses and a stabilizer, can prevent the slow oxidation of the chromium reducing agent composition of the present invention in cement, thereby achieving excellent durability. 4. The chelating agent is used in a low content to achieve a significant chromium reduction effect, so that the chromium reducer composition according to the present invention has a commercially acceptable low price.

[0062] The present invention is further illustrated by the following examples, which are not intended to limit the invention. [Example]

[0063] The raw materials used in the examples are shown in Table 1 below.

[0064] [Table 1]

[0065] Example 1. Chromium reduction effect test in a high temperature environment To simulate a high-temperature process, 0.1% by weight of ferrous sulfate, 0.05% by weight of a chelating agent (powder), and 0.1% by weight of a chelating agent (powder) were added to the cement. The mixture was placed in a 130°C oven and dried for 5 hours. After the mixture was cooled, the hexavalent chromium content was tested. Similarly, cement without the chromium reducing agent was placed in a 130°C oven and dried for 5 hours. After the cement was cooled, the hexavalent chromium content was tested. The chromium content test was conducted in accordance with GB31893-2015. The results are shown in Table 2 below.

[0066] [Table 2]

[0067] As shown in the results in Table 2, the addition of 0.1 wt% ferrous sulfate reduces the amount of water-soluble hexavalent chromium to 7.5 ppm. On the other hand, the addition of only 0.05 wt% chelating agent reduces the amount of water-soluble hexavalent chromium to 1.6 ppm. The addition of 0.1 wt% chelating agent reduces the amount of water-soluble hexavalent chromium to 0 ppm. The above results indicate that the chromium reduction effect of the chelating agent is more pronounced than that of ferrous sulfate in high-temperature environments.

[0068] Example 2. Chromium reduction effect test in a grinding environment To simulate the grinding process, a mixture of clinker and gypsum (95% clinker by weight, 5% gypsum by weight) was added with 0.05% powder chelating agent and 0.125% liquid chelating agent (40% by weight) based on the total weight of the clinker and gypsum (95% clinker by weight, 5% gypsum by weight). The mixture was then placed in a laboratory ball mill and ground for 20 minutes. The water-soluble hexavalent chromium content was then tested. Similarly, cement without added chelating agent was placed in a laboratory ball mill and ground for 20 minutes. The water-soluble hexavalent chromium content was tested. The chromium content test was conducted in accordance with GB 31893-2015. The results are shown in Table 3 below.

[0069] [Table 3]

[0070] As shown by the results in Table 3, adding 0.05 wt% of the chelating agent to the powder reduces the amount of water-soluble hexavalent chromium to 0.3 ppm. Adding 0.125 wt% of the chelating agent to the liquid (also 0.05 wt% of the chelating agent compound) reduces the amount of water-soluble hexavalent chromium to 1.3 ppm. These results demonstrate that the chelating agent, whether in powder or liquid form, exerts a significant chromium reduction effect in a grinding environment.

[0071] Example 3. Durability test To investigate the durability of the chromium reducer compositions, chromium reducer compositions A, B, and C were prepared according to the compositions shown in Table 4 below. The preparation method was as follows: the weighed and prepared chelating agent was added to molasses and stirred until completely uniform. Then, water was added and stirring was continued until completely uniform. HPMC was then added and stirring was continued until completely dissolved. Finally, a pH adjuster was added, if necessary, and stirring was continued until completely uniform. Chromium reducer compositions A, B, and C were each added to cement in an amount of 0.05% by weight of chelating agent relative to the cement. The mixture was then placed in a laboratory ball mill and ground. The water-soluble hexavalent chromium content (ppm) was tested over the grinding time. Similarly, cement without the added chromium reducer was placed in a laboratory ball mill and ground. The water-soluble hexavalent chromium content (ppm) was tested over the grinding time. The chromium content test was conducted in accordance with GB31893-2015. The results are shown in Table 5 below.

[0072] [Table 4]

[0073] [Table 5]

[0074] As shown in Table 5, all three chromium-reducing compositions achieved significant chromium reduction effects at the start of the test. However, the chromium-reducing effect of chromium-reducing composition A (containing only a pH adjuster and no HPMC or molasses) gradually decreased over time, as evidenced by the increase in hexavalent chromium content. This is believed to be the result of the slow oxidation of the chelating agent in the cement. On the other hand, when chromium-reducing composition B containing HPMC was used, the hexavalent chromium content increased slowly over time. This suggests that the addition of HPMC can mitigate the slow oxidation of the chromium-reducing composition in the cement and extend the durability of the product. When chromium-reducing composition C containing both HPMC and molasses was used, the increase in hexavalent chromium content over time was even slower. This suggests that the simultaneous addition of HPMC and molasses can essentially prevent the slow oxidation of the chromium-reducing composition in the cement and significantly extend the durability of the product.

Claims

1. 1. A chromium reducer composition, the chromium reducer composition being preferably used in cement, the chromium reducer composition comprising: a chelating agent, preferably in an amount of 30 to 60 wt. %, preferably 35 to 55 wt. %, preferably 40 to 50 wt. %, based on the total weight of the chromium reducer composition; Optionally, a stabilizer, preferably in an amount of 0.1 to 1 wt. %, preferably 0.3 to 0.7 wt. %, preferably 0.4 to 0.6 wt. %, based on the total weight of the chromium reducer composition.

1. A chromium reducer composition comprising:

2. 2. The chromium reducer composition of claim 1, wherein the chelating agent is an organic sulfur chelating agent, preferably a dithiocarbamate-based chelating agent, preferably selected from dimethyldithiocarbamic acid or a salt thereof, diethyldithiocarbamic acid or a salt thereof, and / or dibutyldithiocarbamic acid or a salt thereof, preferably dimethyldithiocarbamate, diethyldithiocarbamate, and / or dibutyldithiocarbamate, and most preferably dimethyldithiocarbamate.

3. 3. The chromium reducer composition of claim 2, wherein the dimethyldithiocarbamate is selected from sodium dimethyldithiocarbamate, potassium dimethyldithiocarbamate, magnesium dimethyldithiocarbamate, calcium dimethyldithiocarbamate, barium dimethyldithiocarbamate and / or zinc dimethyldithiocarbamate, preferably sodium dimethyldithiocarbamate and / or potassium dimethyldithiocarbamate, most preferably sodium dimethyldithiocarbamate.

4. 4. The chromium reducer composition according to claim 1, wherein the stabilizer is a cellulose ether, preferably selected from hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, hydroxymethyl cellulose, hydroxyethyl cellulose and / or carboxymethyl cellulose, preferably hydroxypropyl methylcellulose and / or hydroxyethyl methylcellulose, most preferably hydroxypropyl methylcellulose.

5. 5. The chromium reducer composition of any one of claims 1 to 4, further comprising molasses, preferably in an amount of 10 to 40 wt%, preferably 15 to 35 wt%, preferably 18 to 30 wt%, based on the total weight of the chromium reducer composition.

6. 6. The chromium reducer composition of any one of claims 1 to 5, further comprising a pH adjuster, preferably in an amount of 1 to 10 wt %, preferably 1.5 to 5 wt %, preferably 2 to 3 wt %, based on the total weight of the chromium reducer composition.

7. 7. The chromium reducer composition of claim 6, wherein the pH adjuster is selected from polymer polyols and / or sodium lignosulfonates.

8. 8. The chromium reducer composition of any one of claims 1 to 7, further comprising a solvent, preferably water, preferably in an amount of 10 to 58 wt%, preferably 15 to 48 wt%, preferably 20 to 39 wt%, based on the total weight of the chromium reducer composition.

9. 10. A method for reducing water-soluble hexavalent chromium in cement, said method comprising adding the chromium reducer composition according to any one of claims 1 to 8, preferably in liquid form, to a cementitious binder, preferably in an amount such that the proportion of the chelating agent is 0.01 to 0.5 wt. %, preferably 0.03 to 0.125 wt. %, preferably 0.05 to 0.1 wt. %, based on the cement on a dry weight basis.

10. A cementitious composition, comprising: at least one cementitious binder; The chromium reducer composition according to any one of claims 1 to 8. wherein preferably the chromium reducer composition is present in an amount such that the proportion of the chelating agent is 0.01 to 0.5 wt. %, preferably 0.03 to 0.125 wt. %, preferably 0.05 to 0.1 wt. %, based on the cementitious binder on a dry weight basis.

11. 11. The method of claim 9 or the cementitious composition of claim 10, wherein the cementitious binder comprises a hydraulic binder, a non-hydraulic binder and / or a latent hydraulic binder, preferably Portland cement, aluminous cement, sulfoaluminate cement, gypsum, lime, slag, fly ash, silica fume and / or natural pozzolan.

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