Preparation process and application of cement chromium removal mineral admixture

Abstract

The invention discloses a preparation process and application of a cement chromium removal mineral admixture, and the process comprises the following steps: (1) leaching siliceous phosphate tailing powder in an acid solution, carrying out solid-liquid separation to obtain a solid product and a leaching solution, washing the solid product, uniformly mixing with a dihydric phosphate solution, and drying to obtain active siliceous phosphate tailing powder; and (2) calcining coal gangue powder in a protective atmosphere to carbonize organic matters in the coal gangue powder, mixing a calcined product with the leaching solution, adding alkali for neutralization, drying, and performing thermal decomposition to obtain pretreated coal gangue powder. And (3) uniformly mixing the pretreated coal gangue powder with a calcium nitrite solution, drying or performing vacuum drying in a protective atmosphere, and uniformly mixing the obtained powder with the active siliceous phosphate tailing powder to obtain the cement chromium removal mineral admixture. The admixture disclosed by the invention not only can be used as an auxiliary cementing material to replace part of cement clinker and promote the utilization of solid wastes, but also can reduce the content of water-soluble chromium (VI) in the cement clinker.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mineral admixtures, in particular to a preparation process of cement chromium-removing mineral admixtures and application thereof. BACKGROUND

[0002] Cement is widely used in various construction projects as an important component of building materials. In the production process of cement, raw materials, crushing and grinding of raw materials, clinker and other links may introduce chromium elements, for example, limestone and iron correction raw materials as raw materials, the chromium content in limestone in some areas reaches 50 mg / kg, and even in some high-chromium mining areas, the chromium content in limestone exceeds 200 mg / kg. These chromium elements are oxidized to chromium (VI) in the process of high-temperature firing of raw materials to form cement clinker. The wear and tear of equipment metal parts during the grinding and crushing process of raw materials and cement clinker also introduces chromium elements. Therefore, it is difficult to avoid the introduction of chromium (VI) in cement clinker. However, chromium (VI) has high biological toxicity, and especially water-soluble chromium (VI) may eventually enter the biological chain through soil and water, endangering the environment and human health. Therefore, how to reduce the content of water-soluble chromium (VI) in cement clinker is an important problem faced by the cement industry. SUMMARY

[0003] In view of the above problems, the present application provides a preparation process of cement chromium-removing mineral admixtures and application thereof. After being mixed into cement, it not only can replace part of the cement clinker as an auxiliary cementitious material, promote the utilization of solid waste, but also can reduce the content of water-soluble chromium (VI) in cement clinker. In order to achieve the above purpose, the present application discloses the following technical scheme.

[0004] In the first aspect, the present application discloses a preparation process of cement chromium-removing mineral admixtures, comprising the following steps: (1) Put siliceous phosphorus tailings powder into acid solution for acid leaching treatment, and after completion, solid-liquid separation is performed to obtain solid product and leaching solution. After washing the solid product, mix it with dihydrogen phosphate solution, and dry to obtain active siliceous phosphorus tailings powder.

[0005] (2) Calcine coal gangue powder in a protective atmosphere to carbonize the organic matter therein, then mix the obtained calcined product with the leaching solution and stand still, add alkali liquor for neutralization after completion, dry the mixture, and then heat and decompose in a protective atmosphere to obtain pretreated coal gangue powder.

[0006] (3) Mix the pretreated coal gangue powder with calcium nitrite solution, and then dry or vacuum dry in a protective atmosphere, then mix the obtained powder with the active siliceous phosphorus tailings powder, and the cement chromium-removing mineral admixtures are obtained.

[0007] Further, in step (1), the ratio of the siliceous phosphate tailings powder to the acid solution is 1g:10-35ml. Optionally, the acid solution comprises at least one of hydrochloric acid, sulfuric acid, nitric acid, etc. The concentration of the acid solution is 3-5mol / L.

[0008] Further, in step (1), the acid leaching time is 11-14 hours, and the temperature is 40-80℃.

[0009] Further, in step (1), the solid product is mixed with a dihydrogen phosphate solution according to a ratio of 3-4:1 of the magnesium content in the leaching solution to the dihydrogen phosphate mass, wherein the magnesium content is calculated based on magnesium oxide. Optionally, the dihydrogen phosphate comprises at least one of potassium dihydrogen phosphate, ammonium dihydrogen phosphate, etc.

[0010] Further, in step (1), the specific surface area of the active siliceous phosphate tailings powder is not less than 380m 2 / kg.

[0011] Further, in step (2), the calcination temperature is 500-650℃, and the time is 1-2 hours. Optionally, the protective atmosphere comprises at least one of nitrogen, argon, etc.

[0012] Further, in step (2), the ratio of the calcined product to the leaching solution is 1g:0.8-1.5ml. Optionally, the standing time is not less than 20min, so that the calcined product can fully absorb the leaching solution.

[0013] Further, in step (2), the alkali solution comprises at least one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, ammonia, etc.

[0014] Further, in step (2), the decomposition treatment temperature is 450-520℃, and the time is 45-60min.

[0015] Further, in step (3), the calcium nitrite is 7-12% of the mass of the pre-treated coal gangue powder.

[0016] Further, in step (3), the mass ratio of the powder to the active siliceous phosphate tailings powder is 1:1-1.35. Optionally, the specific surface area of the powder is not less than 380m 2 / kg.

[0017] In a second aspect, the application discloses application of the cement chromium-removing mineral admixture in Portland cement clinker. Optionally, the admixture is 15-25% of the mass of the cement clinker.

[0018] Compared with the prior art, the application has at least the following beneficial technical effects: The present application prepares active mineral admixtures from siliceous phosphorus tailings and coal gangue, which can not only replace part of cement clinker as cementitious materials to realize the resource utilization of solid waste, but also use the composition characteristics of the siliceous phosphorus tailings and coal gangue to prepare a chromium removal agent that can reduce the water-soluble chromium(VI) in cement clinker. To this end, the magnesium element in the siliceous phosphorus tailings is separated out by acid leaching, and at the same time, the acid liquor is used to activate the siliceous phosphorus tailings, so that the siliceous and aluminous mineral phases are depolymerized to form active SiO4 and AlO4 groups, thereby making the obtained siliceous phosphorus tailings powder have better cementitious activity. These active groups can further react with the calcium hydroxide, a hydration product of cement, to form cementitious products such as calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), thereby increasing the content of cementitious products in cement-based materials and improving the strength of cement-based materials. Further, the siliceous phosphorus tailings powder is further treated with a dihydrogen phosphate solution, which not only further activates the siliceous phosphorus tailings using the acidity of the dihydrogen phosphate, but also loads dihydrogen phosphate on the siliceous phosphorus tailings. Secondly, the coal gangue is first carbonized and then mixed with the leaching liquor. On the one hand, the organic matter in the coal gangue is converted into porous carbon, which can adsorb magnesium ions in the leaching liquor and store them inside the coal gangue. After neutralization with an alkali solution, the magnesium ions are converted into magnesium hydroxide, which is further decomposed into magnesium oxide. On the other hand, the carbonization and the acidity of the leaching liquor achieve secondary activation of the coal gangue, improving its cementitious activity. Finally, the coal gangue treated in the above manner is further modified with calcium nitrite, and is compounded with the active siliceous phosphorus tailings powder to form a cement chromium removal mineral admixture. After adding the admixture to cement, the porous coal gangue uses the good adsorption capacity of the carbon to adsorb the water-soluble chromium(VI) in the cement and store it inside the coal gangue particles. At the same time, the nitrite released by the calcium nitrite can reduce the chromium(VI) to chromium(III), reducing the content of chromium(VI). The magnesium oxide in the coal gangue reacts with the dihydrogen phosphate released by the siliceous phosphorus tailings to form struvite, which can solidify the chromium(VI) and chromium(III) and fix them inside the coal gangue, reducing leaching. At the same time, the formation of struvite can also improve the mechanical strength of the cement material. After the nitrite is oxidized to nitrate by chromium(VI), the calcium nitrate formed with the calcium ions released by cement hydration can also promote the hydration of cement clinker and improve the strength. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation thereof. Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings.

[0020] Figure 1 The following is a diagram of the compressive strength test in Example 1.

[0021] Figure 2 The following is a diagram of the compressive strength test in Example 2.

[0022] Figure 3 The following is a diagram of the compressive strength test in Example 3.

[0023] Figure 4 The following is a diagram of the compressive strength test in Example 4.

[0024] Figure 5 The following is a diagram of the compressive strength test in Example 5. Detailed Implementation

[0025] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. The preferred methods and materials described herein are for illustrative purposes only.

[0026] In addition, the reagents or raw materials used in this invention can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in this invention shall be used in accordance with conventional methods in the field or in accordance with the product instructions.

[0027] The main components (based on oxides) of the siliceous phosphate tailings in the following examples are shown in the table below: Example 1 A process for preparing a cement chromium removal mineral admixture includes the following steps: (1) The specific surface area is 416.8 m² 2 / kg of siliceous phosphate tailings powder was mixed with 5mol / L sulfuric acid at a ratio of 1g:10ml and stirred evenly. The mixture was then leached at 60℃ for 12 hours. After leaching, the solid product and the leachate were obtained by filtration. The solid product was washed with water to remove residual acid. Then, the solid product was mixed with potassium dihydrogen phosphate solution at a mass ratio of magnesium content (calculated as MgO) to dihydrogen phosphate of 4:1. The mixture was then dried at 60℃ to remove moisture, yielding activated siliceous phosphate tailings powder for later use.

[0028] (2) The specific surface area is 427.4 m² 2 / kg of coal gangue powder is heated to 580℃ for 1.5 hours in a nitrogen protective atmosphere, and after cooling to room temperature, the obtained calcined product is mixed with the leaching solution of step (1) at a ratio of 1g:1.3ml, then stirred uniformly, and then left to stand for 20min, after completion, neutralized with sodium hydroxide solution, the obtained mixture is dried to remove water at 110℃, then heated to 480℃ for 55min in a nitrogen protective atmosphere, to obtain the pretreated coal gangue powder.

[0029] (3) According to the proportion of 8.5% of calcium nitrite to the mass of the pretreated coal gangue powder, calcium nitrite solution is added to the pretreated coal gangue powder, stirred uniformly, then dried to remove water at 110℃ in a nitrogen protective atmosphere, then the obtained powder is mixed with the active siliceous phosphorus tailings powder at a mass ratio of 1:1, and stirred uniformly, to obtain the cement chromium removal mineral admixture.

[0030] Performance test: 1. The cement chromium removal mineral admixture of the present embodiment is added to 42.5 ordinary portland cement clinker (the amount of admixture is 20% of the mass of the clinker), then water is added to make cement slurry, which is then poured into a mold, then cured under standard conditions for 28 days to obtain a test piece. Then the test piece is soaked in deionized water for 7 days, and the amount of chromium(VI) dissolved n1 is tested. At the same time, the test piece without the addition of the cement chromium removal mineral admixture is used as a control group, and the amount of chromium(VI) dissolved n2 is tested, and then the chromium(VI) removal rate=(n2-n1) / n2 is calculated. 2. The cement chromium removal mineral admixture of the present embodiment is added to 42.5 ordinary portland cement clinker (the amount of admixture is 20% of the mass of the clinker), then according to the "Cement mortar strength test method (ISO method)" (GB / T 17671-2021) to test the 7d compressive strength (such as Figure 1 shown), the results are: chromium(VI) removal rate=94.13%, compressive strength=25.27MPa.

[0031] Example 2 A preparation process of a cement chromium removal mineral admixture, comprising the following steps: (1) 4mol / L nitric acid is mixed with siliceous phosphorus tailings powder with a specific surface area of 380.2m 2 / g at a ratio of 1g:30ml, then stirred uniformly, and then leached at 80℃ for 11 hours. After completion, the solid product and the leaching solution are obtained by filtration, the solid product is washed with clean water to remove residual acid, then the solid product is mixed with potassium dihydrogen phosphate solution according to the proportion of 3.5:1 of the magnesium content (calculated as MgO) in the leaching solution to the mass of the dihydrogen phosphate, then dried to remove water at 60℃, to obtain active siliceous phosphorus tailings powder, for standby use.

[0032] (2) 4mol / L nitric acid is mixed with siliceous phosphorus tailings powder with a specific surface area of 380.7m2 / kg of coal gangue powder is heated to 500°C in a nitrogen protective atmosphere for 2 hours, and after cooling to room temperature, the obtained calcined product is mixed with the leaching solution of step (1) at a ratio of 1 g:0.8 ml, and then stirred uniformly, and then left for 30 min, and then neutralized by adding sodium hydroxide solution, and then the obtained mixture is dried at 110°C to remove water, and then heated to 450°C in a nitrogen protective atmosphere for 60 min, to obtain the pretreated coal gangue powder.

[0033] (3) According to the proportion of 7% of calcium nitrite to the mass of the pretreated coal gangue powder, calcium nitrite solution is added to the pretreated coal gangue powder, and then stirred uniformly, and then dried at 110°C in a nitrogen protective atmosphere to remove water, and then the obtained powder is mixed with the active siliceous phosphorus tailings powder at a mass ratio of 1:1.2, and then stirred uniformly, to obtain the cement chromium removal mineral admixture.

[0034] Performance test: 1. The cement chromium removal mineral admixture of the present embodiment is added to the same 42.5 ordinary portland cement clinker as in Example 1 (the amount of addition is 15% of the mass of the clinker), and then the chromium(VI) removal rate is calculated by the same method as in Example 1. 2. The cement chromium removal mineral admixture of the present embodiment is added to the 42.5 ordinary portland cement clinker (the amount of addition is 15% of the mass of the clinker), and then the 7d compressive strength is tested according to the "Cement mortar strength test method (ISO method)" (GB / T17671-2021) (as shown in Table 1), and the results are: chromium(VI) removal rate = 97.52%, compressive strength = 21.86 MPa. Figure 2

[0035] Example 3 A preparation process of a cement chromium removal mineral admixture, comprising the following steps: (1) 463.6m 2 / kg of siliceous phosphorus tailings powder is mixed with 3 mol / L sulfuric acid at a ratio of 1 g:35 ml, and then stirred uniformly, and then incubated at 40°C for 14 hours. After completion, the solid product and the leaching solution are obtained by filtration, and then the solid product is washed with water to remove residual acid, and then the solid product is mixed with potassium dihydrogen phosphate solution at a ratio of 3:1 of the magnesium content (calculated as MgO) in the leaching solution to the mass of the dihydrogen phosphate, and then dried at 60°C to remove water, to obtain the active siliceous phosphorus tailings powder, for standby.

[0036] (2) 459.1m 2 ​ / kg of coal gangue powder is heated to 650℃ in a nitrogen protective atmosphere for 1 hour, and after cooling to room temperature, the obtained calcined product is mixed with the leaching solution of step (1) at a ratio of 1 g:1.5 ml, and then stirred uniformly, and then left for 20 min, and then neutralized by adding sodium carbonate solution, and then the obtained mixture is dried to remove water at 110℃, and then heated to 520℃ in a nitrogen protective atmosphere for 45 min, to obtain a pretreated coal gangue powder.

[0037] (3) According to the proportion of 12% of calcium nitrite to the mass of the pretreated coal gangue powder, calcium nitrite solution is added to the pretreated coal gangue powder, and then stirred uniformly, and then dried to remove water at 110℃ in a nitrogen protective atmosphere, and then the obtained powder is mixed with the active siliceous phosphorus tailings powder at a mass ratio of 1:1.35, and then stirred uniformly, to obtain a cement chromium removal mineral admixture.

[0038] Performance test: 1. The cement chromium removal mineral admixture of the present embodiment is added to the same 42.5 ordinary portland cement clinker as in Example 1 (the amount of addition is 25% of the mass of the clinker), and then the chromium(VI) removal rate is calculated by the same method as in Example 1. 2. The cement chromium removal mineral admixture of the present embodiment is added to the 42.5 ordinary portland cement clinker (the amount of addition is 25% of the mass of the clinker), and then the 7d compressive strength is tested according to the "Cement Mortar Strength Test Method (ISO Method)" (GB / T17671-2021) (as shown in Table 1), and the results are: chromium(VI) removal rate = 98.24%, compressive strength = 22.93MPa. Figure 3

[0039] Example 4 A preparation process of a cement chromium removal mineral admixture, comprising the following steps: (1) 416.8m 2 / kg of siliceous phosphorus tailings powder is mixed with 5mol / L sulfuric acid at a ratio of 1g:10ml, and then stirred uniformly, and then soaked at 60℃ for 12 hours. After completion, the solid product and the leaching solution are obtained by filtration, and then the solid product is washed with water to remove residual acid, and then the solid product is mixed with potassium dihydrogen phosphate solution according to the proportion of 4:1 of the magnesium content (calculated as MgO) in the leaching solution to the mass of the dihydrogen phosphate, and then dried to remove water at 60℃, to obtain active siliceous phosphorus tailings powder, for standby use.

[0040] (2) 427.4m 2 ​ / kg of coal gangue powder is heated to 580℃ for 1.5 hours in a nitrogen protective atmosphere, and after cooling to room temperature, the obtained calcined product is mixed with the leaching solution of step (1) at a ratio of 1g:1.3ml, stirred uniformly, then placed for 20min, after completion, neutralized with sodium hydroxide solution, the obtained mixture is dried to remove water at 110℃, then heated to 480℃ for 55min in a nitrogen protective atmosphere, to obtain a pretreated coal gangue powder.

[0041] (3) The pretreated coal gangue powder is mixed with the active siliceous phosphorus tailings powder at a mass ratio of 1:1, and then stirred uniformly to obtain a cement chromium removal mineral admixture.

[0042] Performance test: 1. The cement chromium removal mineral admixture of the present embodiment is added to the same 42.5 ordinary portland cement clinker as in Example 1 (the amount of addition is 20% of the mass of the clinker), and then the chromium(VI) removal rate is calculated by the same method as in Example 1. 2. The cement chromium removal mineral admixture of the present embodiment is added to the 42.5 ordinary portland cement clinker (the amount of addition is 20% of the mass of the clinker), and then the 7d compressive strength is tested according to the "Cement mortar strength test method (ISO method)" (GB / T17671-2021) (as shown in Figure 4 The results are: chromium(VI) removal rate = 81.08%, compressive strength = 19.32MPa.

[0043] Example 5 A preparation process of a cement chromium removal mineral admixture, comprising the following steps: (1) 416.8m 2 / kg of siliceous phosphorus tailings powder is mixed with 5mol / L sulfuric acid at a ratio of 1g:10ml, then stirred uniformly, and then leached at 60℃ for 12 hours. After completion, the solid product and the leaching solution are obtained by filtration, the solid product is washed with water to remove residual acid, then the solid product is mixed with potassium dihydrogen phosphate solution at a ratio of 4:1 of the magnesium content (calculated as MgO) in the leaching solution to the mass of the dihydrogen phosphate, then dried at 60℃ to remove water, to obtain active siliceous phosphorus tailings powder, for standby use.

[0044] (2) 427.4m 2 / kg of coal gangue powder is mixed with the leaching solution of step (1) at a ratio of 1g:1.3ml, then stirred uniformly, and then placed for 20min, after completion, neutralized with sodium hydroxide solution, the obtained mixture is dried to remove water at 110℃, then heated to 480℃ for 55min in a nitrogen protective atmosphere, to obtain a pretreated coal gangue powder.

[0045] (3) According to the proportion of 8.5% of calcium nitrite in the mass of the pretreated coal gangue powder, calcium nitrite solution is added to the pretreated coal gangue powder, and after stirring uniformly, it is dried at 110°C under a nitrogen protective atmosphere to remove water, and then the obtained powder is mixed with the active siliceous phosphorite tailings powder in a mass ratio of 1:1, and stirred uniformly to obtain the cement chromium removal mineral admixture.

[0046] Performance test: 1. The cement chromium removal mineral admixture of the present embodiment is added to the same 42.5 ordinary portland cement clinker as in Example 1 (the amount of addition is 20% of the mass of the clinker), and then the chromium(VI) removal rate is calculated by the same method as in Example 1. 2. The cement chromium removal mineral admixture of the present embodiment is added to the 42.5 ordinary portland cement clinker (the amount of addition is 20% of the mass of the clinker), and then the 7d compressive strength is tested according to the "Cement mortar strength test method (ISO method)" (GB / T17671-2021) (as shown in Figure 5 The results are: chromium(VI) removal rate = 89.46%, compressive strength = 20.14 MPa.

[0047] Example 6 A preparation process of a cement chromium removal mineral admixture, comprising the following steps: (1) The siliceous phosphorite tailings powder with a specific surface area of 380.2 m 2 / kg is mixed with 4 mol / L nitric acid in a ratio of 1 g:30 ml, and then stirred uniformly, and then soaked at 80°C for 11 hours. After completion, the solid product and the soaking solution are obtained by filtration, the solid product is washed with water to remove residual acid, and then the solid product is mixed with potassium dihydrogen phosphate solution in a ratio of 3.5:1 of the magnesium content (calculated as MgO) in the soaking solution to the mass of the dihydrogen phosphate, and then dried at 60°C to remove water to obtain the active siliceous phosphorite tailings powder for standby.

[0048] (2) The coal gangue powder with a specific surface area of 380.7 m 2 / kg is heated to 500°C under a nitrogen protective atmosphere for 2 hours, and then cooled to room temperature to obtain a pretreated coal gangue powder.

[0049] (3) According to the proportion of 8.5% of calcium nitrite in the mass of the pretreated coal gangue powder, calcium nitrite solution is added to the pretreated coal gangue powder, and after stirring uniformly, it is dried at 110°C under a nitrogen protective atmosphere to remove water, and then the obtained powder is mixed with the active siliceous phosphorite tailings powder in a mass ratio of 1:1, and stirred uniformly to obtain the cement chromium removal mineral admixture.

[0050] Performance test: 1. The cement chromium removal mineral admixture of the present example is added to the same 42.5 ordinary portland cement clinker as in Example 1 above (the amount is 15% of the mass of the clinker), and then the chromium(VI) removal rate is calculated by the same method as in Example 1 above. 2. The cement chromium removal mineral admixture of the present example is added to the 42.5 ordinary portland cement clinker (the amount is 15% of the mass of the clinker), and then the 7d compressive strength is tested according to "Cement mortar strength test method (ISO method)" (GB / T17671-2021), and the results are: chromium(VI) removal rate = 86.37%, compressive strength = 16.71 MPa.

[0051] Example 7 A preparation process of a cement chromium removal mineral admixture, comprising the following steps: (1) The siliceous phosphorus tailings powder with a specific surface area of 463.6 m 2 / kg is mixed with 3 mol / L sulfuric acid at a ratio of 1 g:35 ml, then stirred uniformly, and then soaked at 40℃ for 14 hours. After completion, the solid product and the soaking solution are obtained by filtration, the solid product is washed with clean water to remove residual acid solution, and then dried at 60℃ to remove water, to obtain active siliceous phosphorus tailings powder for standby.

[0052] (2) The coal gangue powder with a specific surface area of 459.1 m 2 / kg is heated to 650℃ for 1 hour in a nitrogen protective atmosphere, and then cooled to room temperature. The calcined product obtained is mixed with the soaking solution of step (1) at a ratio of 1 g:1.5 ml, then stirred uniformly, and then placed for 20 min. After completion, sodium carbonate solution is added for neutralization, and then the obtained mixture is dried at 110℃ to remove water, and then heated to 520℃ for 45 min in a nitrogen protective atmosphere, to obtain pretreated coal gangue powder.

[0053] (3) According to the proportion of 12% of calcium nitrite to the mass of the pretreated coal gangue powder, calcium nitrite solution is added to the pretreated coal gangue powder, stirred uniformly, and then dried at 110℃ in a nitrogen protective atmosphere to remove water. Then the obtained powder is mixed with the active siliceous phosphorus tailings powder at a mass ratio of 1:1.35, and then stirred uniformly, to obtain the cement chromium removal mineral admixture.

[0054] Performance test: 1. The cement chromium removal mineral admixture of the present example is added to the same 42.5 ordinary portland cement clinker as in the above example 1 (the amount of admixture is 25% of the mass of the clinker), and then the chromium(VI) removal rate is calculated by the same method as in the above example 1. 2. The cement chromium removal mineral admixture of the present example is added to the 42.5 ordinary portland cement clinker (the amount of admixture is 25% of the mass of the clinker), and then the 7d compressive strength is tested according to the "Cement mortar strength test method (ISO method)" (GB / T17671-2021), and the results are: chromium(VI) removal rate = 91.03%, compressive strength = 18.22 MPa.

[0055] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation process for a cement chromium removal mineral admixture, characterized in that, Includes the following steps: (1) The silica-phosphorus tailings powder is placed in an acid solution for acid leaching treatment. After the treatment, solid and liquid separation is performed to obtain solid product and leaching solution. The solid product is washed and mixed with dihydrogen phosphate solution and dried to obtain active silica-phosphorus tailings powder. (2) The coal gangue powder is calcined in a protective atmosphere to carbonize the organic matter therein. Then the calcined product is mixed with the extract and allowed to stand. After completion, an alkaline solution is added to neutralize it. The mixture is dried and then heated in a protective atmosphere for decomposition treatment to obtain pretreated coal gangue powder. (3) After mixing the pretreated coal gangue powder with calcium nitrite solution, dry it in a protective atmosphere or vacuum dry it. Then mix the obtained powder with the active siliceous phosphorus tailings powder to obtain cement chromium removal mineral admixture.

2. The preparation process of the cement chromium removal mineral admixture according to claim 1, characterized in that, In step (1), the ratio of the siliceous phosphorus tailings powder to the acid solution is 1g: 10~35ml; Optionally, in step (1), the acid solution includes at least one of hydrochloric acid, sulfuric acid, and nitric acid; Optionally, in step (1), the concentration of the acid solution is 3~5 mol / L.

3. The preparation process of the cement chromium removal mineral admixture according to claim 1, characterized in that, In step (1), the acid leaching time is 11 to 14 hours and the temperature is 40 to 80°C.

4. The preparation process of the cement chromium removal mineral admixture according to claim 1, characterized in that, In step (1), the solid product is mixed with the dihydrogen phosphate solution at a ratio of 3 to 4:1, where the magnesium content in the extract is calculated as magnesium oxide. Optionally, in step (1), the dihydrogen phosphate salt includes at least one of potassium dihydrogen phosphate and ammonium dihydrogen phosphate.

5. The preparation process of the cement chromium removal mineral admixture according to claim 1, characterized in that, In step (1), the specific surface area of ​​the activated siliceous phosphorus tailings powder is not less than 380 m². 2 / kg.

6. The preparation process of the cement chromium removal mineral admixture according to claim 1, characterized in that, In step (2), the calcination temperature is 500~650℃ and the time is 1~2 hours; Optionally, the protective atmosphere includes at least one of nitrogen and argon.

7. The preparation process of the cement chromium removal mineral admixture according to claim 1, characterized in that, In step (2), the ratio of the calcined product to the extract is 1g: 0.8~1.5ml; Optionally, in step (2), the settling time shall not be less than 20 minutes; Optionally, in step (2), the alkaline solution includes at least one of sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, and ammonia water.

8. The preparation process of the cement chromium removal mineral admixture according to claim 1, characterized in that, In step (2), the decomposition process is carried out at a temperature of 450~520℃ for 45~60 min.

9. The preparation process of cement chromium removal mineral admixture according to any one of claims 1-8, characterized in that, In step (3), the calcium nitrite is 7-12% of the mass of the pretreated coal gangue powder; Optionally, in step (3), the mass ratio of the powder to the active siliceous phosphorus tailings powder is 1:1~1.35; Optionally, in step (3), the specific surface area of ​​the powder is not less than 380 m². 2 / kg.

10. The application of the cement chromium-removing mineral admixture obtained by the preparation process according to any one of claims 1-9 in silicate cement clinker; optionally, the admixture is 15-25% of the mass of cement clinker.

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