Steel slag modified magnesium oxysulfate cement and preparation method thereof

Abstract

The invention relates to the field of building materials, and provides steel slag modified magnesium oxysulfate cement and a preparation method thereof. The preparation raw materials of the steel slag modified magnesium oxysulfate cement comprise the following components in parts by weight: 300-500 parts of light calcined magnesia, 150-350 parts of magnesium sulfate, 0-5 parts of a modifier, 45-150 parts of pretreated steel slag and 140-250 parts of water, wherein the pretreated steel slag is obtained by pretreating the steel slag by adopting a composite pretreatment method of low-temperature drying and mechanical grinding. The resource utilization range of the steel slag can be widened, and the performance of the magnesium oxysulfate cement can be effectively improved. And meanwhile, a convenient and low-cost technical approach is provided for recycling and productization of the material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building materials, in particular to a steel slag modified magnesium oxysulfate cement and a preparation method thereof. BACKGROUND

[0002] The magnesium resources in China have the characteristics of concentrated distribution, large reserves, high grade and shallow burial. The magnesite resources in China are also rich in Liaoning Province, Hebei Province, Sichuan Province and Tibet Autonomous Region. Industrial grade magnesium sulfate heptahydrate (MgSO4·7H2O) is mostly a by-product generated after industrial manufacturing and processing.

[0003] Magnesium oxysulfate cement (MOS) is a rigid gel material made of light burned magnesium powder and a certain concentration of magnesium sulfate heptahydrate solution according to the designed molar ratio. Magnesium oxysulfate material has the advantages of light weight, high strength, wear resistance, stability, sound insulation, etc. It has a wide application space in building decoration materials.

[0004] Steel slag is a waste generated during the smelting of crude steel in a steel smelting plant. The steel slag contains various components such as metallic iron, CaO, MgO, SiO2, MnO, etc. The large discharge of steel slag leads to the random piling of a large amount of untreated steel slag, which not only occupies a large amount of land, pollutes the environment, but also wastes a large amount of resources. Due to the requirements of environmental protection and recycling of industrial waste, the recycling technology of steel slag has gradually formed and is widely carried out. The application of steel slag in the field of building materials is one of the important ways of resource utilization of steel slag. However, due to the presence of free calcium oxide and magnesium oxide in steel slag, volume expansion occurs during the hydration process, which has volume stability problems, further limiting the resource utilization way of steel slag in the field of building materials. SUMMARY

[0005] The purpose of the present application is to provide a steel slag modified magnesium oxysulfate cement and a preparation method thereof.

[0006] In order to achieve the purpose of the present application, in a first aspect, the present application provides a steel slag modified magnesium oxysulfate cement, and the preparation raw materials include the following components in weight parts: light burned magnesium oxide 300-500 parts, magnesium sulfate 150-350 parts, modifier 0-5 parts, pretreated steel slag 45-150 parts and water 140-250 parts.

[0007] Preferably, the preparation raw materials include the following components in weight parts: light burned magnesium oxide 300-405 parts, magnesium sulfate 173-217 parts, modifier 2-3 parts, pretreated steel slag 45-150 parts and water 159-207 parts.

[0008] The pretreated steel slag is obtained by pretreating the steel slag by a composite pretreatment method of low-temperature drying and mechanical grinding.

[0009] Further, the preparation method of the pretreated steel slag comprises: drying the steel slag at a temperature of ≤80℃, and then grinding the dried steel slag to a particle size D50<20μm by using a ball mill.

[0010] Further, the content of the main component CaO in the steel slag is 30%-40%, the content of Fe2O3 is 15%-25%, the content of SiO2 is 10%-20%, and the content of MgO is 5%-10%; the content is a mass percentage. In addition to the above four oxides, the steel slag also contains other oxides in low content, and the sum of the mass percentages of all oxides is 100%.

[0011] Further, the content of magnesium oxide in the light-burned magnesium oxide is 70%-90%, and the content of active magnesium oxide is ≥45%; the content is a mass percentage.

[0012] Further, the magnesium sulfate is selected from at least one of anhydrous magnesium sulfate, monohydrate magnesium sulfate, hexahydrate magnesium sulfate, and heptahydrate magnesium sulfate, and is preferably heptahydrate magnesium sulfate.

[0013] Further, the modifier is selected from at least one of citric acid, sodium citrate, and ammonium citrate, and is preferably citric acid.

[0014] In the second aspect, the application provides a preparation method of the modified sulfur-oxygen-magnesium cement with steel slag, which comprises the following steps: dissolving magnesium sulfate in water to prepare a magnesium sulfate solution, adding a modifier to the magnesium sulfate solution, putting the obtained mixed solution, light-burned magnesium oxide, and pretreated steel slag into a cement mortar stirrer, uniformly stirring to form a modified sulfur-oxygen-magnesium cement slurry, pouring and shaping the modified sulfur-oxygen-magnesium cement slurry, and then curing for a period of time to obtain the modified sulfur-oxygen-magnesium cement.

[0015] Further, the specific method of curing comprises the following steps: curing for 1-3 days under the conditions of a temperature of 5-45℃ and a humidity of 50%-70%, then removing the mold, and then continuing to cure for 28-30 days under the same conditions.

[0016] By means of the above technical scheme, the application has at least the following advantages and beneficial effects: (1) The application provides a method for modifying sulfur-oxygen-magnesium cement with steel slag, which not only can broaden the resource utilization range of steel slag, but also can effectively improve the performance of sulfur-oxygen-magnesium cement. At the same time, it provides a convenient and low-cost technical approach for resource utilization and productization.

[0017] (2) In the application, the technical index of the modified sulfur-oxygen-magnesium cement with pretreated steel slag meets the requirements of the standard “Sulfur-oxygen-magnesium-based cementitious material” (T-CECS 10397-2024).

[0018] (Three) the process for preparing the steel slag modified magnesium oxysulfate cement is simple and suitable for industrial production. DETAILED DESCRIPTION

[0019] The present application aims at the problem of difficulty in recycling of steel slag in the field of building materials in China at present, and provides a method for modifying magnesium oxysulfate cement by using steel slag.

[0020] The present application adopts the following technical scheme: 1. Steel slag pretreatment: a combined pretreatment method of low-temperature drying and mechanical grinding is adopted to pretreat the steel slag, and the pretreated steel slag is used to modify the magnesium oxysulfate cement.

[0021] The low-temperature drying is T≤80℃, and the purpose is to remove free water in the steel slag.

[0022] The dried steel slag is ground to a particle size D50<20μm by using a ball mill, and the purposes include: (1) homogenizing the components of the ground steel slag; (2) increasing the specific surface area to play a filling and promoting hydration role.

[0023] 2. The ratio of the modified magnesium oxysulfate cement, including the following components in parts by weight: light-burned magnesium oxide 300-500 parts, magnesium sulfate heptahydrate 150-350 parts, modifier 0-5 parts, pretreated steel slag 45-150 parts, and water 140-250 parts.

[0024] The light-burned magnesium oxide has a magnesium oxide content of 70%-90% and an active magnesium oxide content of ≥45%; the content is a mass percentage.

[0025] The content of the main component CaO in the steel slag is 30%-40%, the content of Fe2O3 is 15%-25%, the content of SiO2 is 10%-20%, and the content of MgO is 5%-10%; the content is a mass percentage. In addition to the above four oxides, the steel slag also contains other oxides in low content, and the sum of the mass percentages of all oxides is 100%.

[0026] The magnesium sulfate includes analytical pure magnesium sulfate and industrial grade magnesium sulfate, and mainly includes anhydrous magnesium sulfate, monohydrate magnesium sulfate, hexahydrate magnesium sulfate and / or heptahydrate magnesium sulfate.

[0027] The modifier includes citric acid, sodium citrate and / or ammonium citrate.

[0028] 3. Preparation of modified magnesium oxysulfate cement: accurately weigh each solid material according to the above ratio, dissolve magnesium sulfate heptahydrate in water to prepare a magnesium sulfate solution, add citric acid to the magnesium sulfate solution, put light-burned magnesium oxide, pretreated steel slag and the above solution into a cement mortar stirrer, refer to the stirring method provided in "Cement mortar strength test method" (GB / T 17671-2021), uniformly stir to form a modified magnesium oxysulfate cement slurry. Pour the modified magnesium oxysulfate cement slurry into a mold, mold, and maintain it for a certain period of time to obtain the modified magnesium oxysulfate cement.

[0029] It should be noted that in the magnesium oxysulfate cement slurry prepared in the MgO-MgSO4-H2O mixed system, four basic magnesium oxysulfates, namely 5Mg(OH)2·MgSO4·3H2O (513), 3Mg(OH)2·MgSO4·8H2O (318), Mg(OH)2·2MgSO4·3H2O (123) and Mg(OH)2·MgSO4·5H2O (115), will appear in the system. After modification by adding citric acid in the system, a new product 5Mg(OH)2·MgSO4·7H2O (denoted as 517 phase) will appear in the system. The presence of the 517 phase can ensure the strength and performance of the hardened magnesium oxysulfate cement slurry. The mass ratio of different light-burned magnesium oxide, magnesium sulfate, water and citric acid produces different contents of 517 phase, and the best range produces the highest content of 517 phase.

[0030] In the MgO-MgSO4-H2O system, the treated steel slag is uniformly distributed in the hardened magnesium oxysulfate cement slurry in the early hardening stage, fills the pores of the hardened slurry, improves the density of the hardened slurry, and increases the strength of the hardened slurry. At the same time, the addition of steel slag can provide nucleation sites for the hydration products of magnesium oxysulfate cement, reduce the nucleation barrier of magnesium oxysulfate cement hydration products, increase the generation amount of hydration products, improve the density of the hardened slurry, and increase the strength of the hardened slurry. With the increase of the amount of steel slag, excessive steel slag adheres to the surface of the hydration product, causing changes in the micro-morphology of the hydration product. At the same time, the introduction of excessive free CaO and free MgO by excessive steel slag will consume water in the magnesium oxysulfate cement slurry, generate gypsum, cause volume expansion, destroy the stable structure of the system, and cause strength loss. At the same time, the reduction of sulfate in the system is not conducive to the generation of hydration product 517 phase, resulting in strength loss.

[0031] The following examples are used to illustrate the present application, but are not intended to limit the scope of the present application. If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art, and the raw materials used are commercially available.

[0032] The steel slag used in the following examples was purchased from Hebei Shougang Qianan Iron and Steel Co., Ltd., and its main components include CaO at a content of 40%, Fe2O3 at a content of 23%, SiO2 at a content of 14%, and MgO at a content of 7%; the content is a mass percentage. In addition to the above four oxides, the steel slag also includes other oxides at low contents, and the sum of the mass percentages of all oxides is 100%.

[0033] The pretreated steel slag is prepared by drying the steel slag at a temperature of ≤80°C, and then grinding the dried steel slag to a particle size D50<20μm using a ball mill.

[0034] The light-burned magnesium oxide (main components are shown in Table 1) used in the following examples was purchased from Haicheng Danhai Chemical Powder Co., Ltd., and the magnesium oxide content is 87.51%, of which the active magnesium oxide content is 62.5%; the content is a mass percentage.

[0035] Table 1

[0036] Example According to the detection requirements provided in “Cement Mortar Strength Test Method” (GB / T 17671-2021), test samples were prepared (see Table 2 for the formula), and the test blocks were removed after curing for a certain period of time according to the standard specification requirements (the curing conditions were temperature 30°C and humidity 65%); the mold was removed after 1 day of curing, and then the curing was continued for 28 days under the same conditions.

[0037] Table 2

[0038] Note: Standard sand needs to be added according to the test standard requirements during performance testing.

[0039] The test sample (modified magnesium oxysulfate cement) was prepared as follows: each solid material was accurately weighed according to the proportions in Table 2, magnesium sulfate heptahydrate was dissolved in water to prepare a magnesium sulfate solution, citric acid was added to the magnesium sulfate solution, and light-burned magnesium oxide, standard sand, and pretreated steel slag were placed in a cement mortar stirrer with the above solution, and the stirring mode was provided in “Cement Mortar Strength Test Method” (GB / T 17671-2021), and the modified magnesium oxysulfate cement slurry was formed after uniform stirring. The modified magnesium oxysulfate cement slurry was cast, molded, and cured for a certain period of time to obtain the modified magnesium oxysulfate cement.

[0040] Its mechanical properties were tested (Tables 3 and 4).

[0041] Table 3

[0042] Table 4

[0043] From the above experimental results, compared with the comparative example 1 (KB group) without adding citric acid and pretreated steel slag, the SS-0 to SS-3 groups with citric acid and pretreated steel slag have better fluidity and higher mechanical properties. Compared with the comparative example 2 (SS-0), the SS-1 to SS-3 with pretreated steel slag have better fluidity and significantly higher mechanical properties. Compared with the comparative example 3 (DB-1), the SS-1 to SS-3 with pretreated steel slag have better fluidity and significantly higher mechanical properties.

[0044] Although the present application has been described in detail with general description and specific embodiments above, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of the present application claimed.

Claims

1. A steel slag modified magnesium oxysulfide cement, characterized in that, The raw materials for its preparation include the following components in parts by weight: 300-500 parts of lightly calcined magnesium oxide, 150-350 parts of magnesium sulfate, 0-5 parts of modifier, 45-150 parts of pretreated steel slag, and 140-250 parts of water. The pretreated steel slag is obtained by pretreating the steel slag using a combined pretreatment method of low-temperature drying and mechanical grinding.

2. The steel slag modified magnesium oxysulfide cement according to claim 1, characterized in that, The raw materials for its preparation include the following components by weight: 300-405 parts of lightly calcined magnesium oxide, 173-217 parts of magnesium sulfate, 2-3 parts of modifier, 45-150 parts of pretreated steel slag, and 159-207 parts of water.

3. The steel slag modified magnesium oxysulfide cement according to claim 1, characterized in that, The pretreated steel slag is prepared by drying the steel slag at a temperature of ≤80℃, and then grinding the dried steel slag into a particle size D50 <20μm using a ball mill.

4. The steel slag modified magnesium oxysulfide cement according to any one of claims 1-3, characterized in that, The main components of the steel slag are CaO (30%~40%), Fe2O3 (15%~25%), SiO2 (10%~20%), and MgO (5%~10%); the contents are by mass percentage.

5. The steel slag modified magnesium oxysulfide cement according to any one of claims 1-3, characterized in that, The lightly calcined magnesium oxide has a magnesium oxide content of 70% to 90% and an active magnesium oxide content of ≥45%; the content is a mass percentage.

6. The steel slag modified magnesium oxysulfide cement according to any one of claims 1-3, characterized in that, The magnesium sulfate is selected from at least one of magnesium sulfate monohydrate, magnesium sulfate hexahydrate, and magnesium sulfate heptahydrate.

7. The steel slag modified magnesium oxysulfide cement according to any one of claims 1-3, characterized in that, The modifier is selected from at least one of citric acid, sodium citrate, and ammonium citrate.

8. The method for preparing steel slag modified magnesium oxysulfide cement according to any one of claims 1-7, characterized in that, Magnesium sulfate is dissolved in water to prepare a magnesium sulfate solution. A modifier is added to the magnesium sulfate solution. The resulting mixture, along with lightly calcined magnesium oxide and pretreated steel slag, is placed in a cement mortar mixer and stirred evenly to form a modified magnesium sulfate-oxygenated cement slurry. Then, the modified magnesium sulfate-oxygenated cement slurry is poured into molds, placed in a mold, and cured for a period of time to obtain modified magnesium sulfate-oxygenated cement.

9. The method according to claim 8, characterized in that, The specific curing methods include: curing for 1 to 3 days at a temperature of 5℃ to 45℃ and a humidity of 50% to 70%, then removing the mold, and continuing to cure for 28 to 30 days under the same conditions.

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