Method for preparing a magnesium silicate hydrate cement using sepiolite

Abstract

The application discloses a method for preparing a magnesium silicate hydrate cement material by using sepiolite, and the method comprises the following steps: dissolving sepiolite by using a strong acid, and separating a solution and a residue; adding NaOH into the solution to obtain Mg(OH)2 precipitate; separating the Mg(OH)2 precipitate, and calcining to obtain MgO; mixing a water reducing agent, the residue and the MgO, and adding water to maintain, so as to obtain the magnesium silicate hydrate cement material. The method uses sepiolite which is rich in the earth's crust as a main raw material, and realizes low-cost and large-scale preparation of the magnesium silicate hydrate cement material.

Description

Technical Field

[0001] This invention belongs to the field of novel cementitious material preparation technology, and specifically relates to a method for preparing hydrated magnesium silicate cementitious material using sepiolite. Background Technology

[0002] Compared to traditional silicate cement, magnesium oxide-based cementitious materials are environmentally friendly. For example, the temperature required to calcine MgCO3 to produce MgO is lower than the decomposition temperature of CaCO3, thus saving energy. Furthermore, the ability of magnesium oxide to absorb atmospheric CO2 to form a series of carbonates and hydroxycarbonates during its service life is similar to the CO2 emitted during its manufacturing process.

[0003] Calcining magnesite (MgCO3) is the main way to obtain MgO, which is needed to prepare magnesium-based cementitious materials; however, this mineral resource has limited global distribution. MgO can also be obtained from salt lakes or seawater, but salt lakes are also concentrated in specific areas and not widely available. Precipitating Mg(OH)2 from seawater is considered energy-intensive unless the brine is highly concentrated.

[0004] The siliceous materials for preparing hydrated magnesium silicate are widely available, but primarily consist of highly reactive silica fume. Compared to silicate cement, the higher cost and relatively concentrated production locations of silica fume also limit its widespread application. In the foreseeable future, unless cheaper silica fume becomes available, hydrated magnesium silicate cementitious materials will remain a difficult-to-commercialize cementitious material.

[0005] The above factors result in high production costs and limited output of current hydrated magnesium silicate cementitious materials. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing hydrated magnesium silicate cementitious materials using sepiolite, with sepiolite, which is abundant in the earth's crust, as the main raw material, so as to achieve low-cost and large-scale preparation of hydrated magnesium silicate cementitious materials.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing hydrated magnesium silicate cementitious material using sepiolite includes the following steps:

[0009] Step 1: Immerse sepiolite in strong acid to dissolve it, and then separate the solution and residue.

[0010] Step 2: Add NaOH to the solution to obtain Mg(OH)2 precipitate;

[0011] Step 3: Separate the Mg(OH)2 precipitate, calcine to obtain MgO, mix the water-reducing agent, the residue and the MgO, and add water for curing to obtain hydrated magnesium silicate cementitious material.

[0012] In one embodiment, the sepiolite has the following chemical composition by weight: 0.1-5% CaO, 40-70% SiO2, 20-50% MgO, 0.5-3% Al2O3, 0.2-0.6% Fe2O3, 0.1-1% K2O, and the balance being impurities.

[0013] In one embodiment, step 1 involves first crushing and grinding sepiolite to obtain sepiolite powder, and then adding a strong acid to dissolve it; the strong acid is sulfuric acid, hydrochloric acid, or nitric acid, wherein the pH is <1.

[0014] In one embodiment, in step 1, the amount of strong acid added is 4500-5500 mL per 500 g of sepiolite powder; the dissolution conditions are: dissolving in a water bath at 83-87°C for 0.5-1.5 h; the separation conditions are: loading the solid-liquid mixture obtained after acid leaching into a centrifuge tube, then placing it in a centrifuge at a speed of 1800-2200 r / min and centrifuging for 13-17 min.

[0015] In one embodiment, the residue is dried, ground, and then used.

[0016] In one embodiment, the drying and grinding conditions are as follows: the precipitate obtained after thorough washing in the separation process is placed in a glass beaker and then placed in a vacuum drying oven and dried under vacuum at a temperature of 35-45°C; the dried residue is then ground again using a ball mill until the obtained powder passes through an 80-micron square hole sieve with less than 5% residue.

[0017] In one embodiment, in step 2, the amount of NaOH added is such that the pH value of the solution after addition is greater than 13.

[0018] In one embodiment, in step 3, the ratio of residue to MgO by weight is 0.3 to 6.0, the ratio of water to total solids is 0.2 to 3.0, the total solids are the total amount of residue and Mg(OH)2 precipitate, and the amount of water-reducing agent is 0.5% of the weight of the mixed system.

[0019] In one embodiment, step 3 involves curing the slurry obtained after adding water for 1 day to generate hydrated magnesium silicate gel material.

[0020] In one embodiment, step 3 involves using a Buchner funnel to separate the Mg(OH)2 precipitate from the mixture, drying it in a drying oven for 24 hours, and then calcining it in a muffle furnace at 740–760°C for 25–35 minutes to obtain MgO.

[0021] Compared with existing technologies, this invention uses strong acid and strong alkali to separate sepiolite, which is abundant in the earth's crust, to obtain high-silica residue and Mg(OH)2. It can simultaneously obtain the two raw materials required for hydrated magnesium silicate cementitious materials, solving the problems of high cost and limited output of silica fume used in the previous preparation of hydrated magnesium silicate. At the same time, it avoids the environmental problem of CO2 emission when using magnesite to obtain MgO. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the mineral composition of sepiolite in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the residue composition after sepiolite is corroded with sulfuric acid in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the MgO mineral composition obtained through precipitation and calcination in an embodiment of the present invention.

[0025] Figure 4 XRD patterns of slurries prepared from residue and MgO and cured at 50℃ for different times.

[0026] Figure 5 XRD patterns of slurries prepared from residue and MgO and cured at 80℃ for different times. Detailed Implementation

[0027] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0028] This invention provides a method for preparing hydrated magnesium silicate cementitious materials using sepiolite as the main raw material, with magnesium silicates from the Earth's crust as the primary raw material. Sepiolite mainly comprises SiO2, MgO, CaO, etc., see reference... Figure 1 As shown, by weight, the chemical composition of sepiolite used in the embodiments of the present invention is: 0.1-5% CaO, 40-70% SiO2, 20-50% MgO, 0.5-3% Al2O3, 0.2-0.6% Fe2O3, 0.1-1% K2O, and the balance being impurities.

[0029] The method for preparing hydrated magnesium silicate cementitious materials using sepiolite according to the present invention can be described in the following main steps:

[0030] Step 1: Dissolve sepiolite with a strong acid and separate the solution and residue.

[0031] In a specific embodiment, sepiolite is first crushed and ground to obtain sepiolite powder, then dissolved in a strong acid such as sulfuric acid, hydrochloric acid, or nitric acid. The amount of strong acid added is 5000 mL of a 40% (w / w) strong acid per 500 g of sepiolite powder. The dissolution conditions are: dissolving in a water bath at 85°C for 1 hour. For example, the crushing and grinding involves crushing 500 g of sepiolite using a jaw crusher and grinding it in a ball mill for 30 minutes. The residue on an 80-micron sieve after crushing and grinding is less than 10%.

[0032] The main purpose of using strong acid in this invention is that strong acid can destroy the crystal structure of sepiolite, causing it to decompose into soluble sulfate and silica gel. The silica gel needs further processing, but the main metal ions have already dissolved out, which facilitates subsequent extraction steps.

[0033] In this embodiment, the separation conditions are as follows: the solid-liquid mixture obtained after acid leaching is placed into a centrifuge tube, and then centrifuged at a speed of approximately 2000 r / min for approximately 15 min. Afterward, the supernatant obtained by centrifugation is stored in a narrow-mouthed bottle, and the sediment is repeatedly washed and centrifuged, vacuum dried at 40°C, and then stored in a self-sealing bag.

[0034] Figure 2 This is a schematic diagram of the composition of the residue after sepiolite is corroded with sulfuric acid in this embodiment. It can be seen that the peak of 2θ between 20° and 30° indicates that the residue is a typical amorphous SiO2.

[0035] Step 2: Add NaOH to the solution to obtain Mg(OH)2 precipitate.

[0036] In a specific embodiment, the amount of NaOH added is preferably such that the pH value of the solution is greater than 13, so as to ensure that Mg(OH)2 precipitates fully and quickly.

[0037] The main purpose of using the strong base NaOH in this invention is to neutralize the acidity in the acidolysis filtrate, increase the pH, and cause magnesium ions to precipitate as Mg(OH)₂, thereby separating them from other soluble substances. Simultaneously, the high concentration of NaOH may facilitate rapid precipitation and ensure complete precipitation of magnesium. Furthermore, excess NaOH helps dissolve other hydroxides such as Al(OH)₃, thereby increasing the purity of Mg(OH)₂.

[0038] Step 3: Separate the Mg(OH)2 precipitate, calcine to obtain MgO, mix the water-reducing agent, the residue, and the MgO, and add water for curing to obtain hydrated magnesium silicate cementitious material. Preferably, by weight, the ratio of residue to MgO is 0.3 to 6.0, and the ratio of water to total solids (residue and Mg(OH)2 precipitate) is 0.2 to 3.0.

[0039] This invention utilizes MgO, which is more conducive to the formation of hydrated magnesium silicate than Mg(OH)2. A mixed slurry is obtained by adding water, and curing this slurry for 1 day yields a hydrated magnesium silicate gel material. However, since the resulting residue has a high specific surface area, and MgO hydration also requires water, a water-reducing agent is introduced to reduce water consumption. The amount of water-reducing agent is approximately 0.5% of the weight of the mixed system. It can reduce the water-to-solid ratio while maintaining fluidity, increasing density and enhancing the strength of the final material. Simultaneously, the water-reducing agent adsorbs onto the particle surface, reducing agglomeration, increasing contact area, and promoting the reaction between MgO and silicates.

[0040] In a preferred embodiment of the present invention, the residue obtained in step 1 is dried and ground before use. Specifically, the sediment obtained after thorough washing in the separation process is placed in a glass beaker and then placed in a vacuum drying oven. It is then vacuum dried at 40°C for a certain period of time to ensure that the moisture content is less than 5%, which facilitates subsequent grinding. The dried residue is then ground again using a ball mill until the obtained powder has less than 5% on an 80-micron square hole sieve.

[0041] In a preferred embodiment of the present invention, in order to obtain MgO, Mg(OH)2 precipitate is separated from the mixture using a Buchner funnel, dried in a drying oven for 24 hours, and then calcined in a muffle furnace at 750°C for 30 minutes. Figure 3 The image shows the diffraction pattern of MgO obtained after calcining Mg(OH)2 precipitate at 750°C for 30 minutes in the example.

[0042] Figure 4 and Figure 5 The XRD patterns of the slurries prepared from the residue and MgO and cured at 50℃ and 80℃ for different times are shown. The figures show a rapid decrease in the diffraction peak between 5° and 15°, which is the first characteristic diffraction peak of hydrated magnesium silicate in the XRD pattern. The distinct peaks near 35° and 60° are the second and third characteristic diffraction peaks of hydrated magnesium silicate, respectively.

[0043] The principle of this invention is as follows: using sepiolite, which is abundant in the Earth's crust, as a raw material, the crystalline sepiolite is dissolved by strong acid to obtain an insoluble residue with a high SiO2 content and dissolved Mg. 2+ The solution contains Mg. 2+ Mg(OH)₂ precipitate is obtained by adding a strong alkali. Then, Mg(OH)₂ or MgO obtained from calcining Mg(OH)₂ is mixed with insoluble residues high in SiO₂ content, and water is added to obtain hydrated magnesium silicate cementitious material. Since the raw materials used are only sepiolite, water, and small amounts of strong alkali and acid, the preparation cost is significantly reduced compared to existing technologies. Furthermore, due to the abundant and widely distributed reserves of sepiolite, the process of this invention can be widely promoted, reducing dependence on specific mineral deposits.

Claims

1. A method for preparing hydrated magnesium silicate cementitious material using sepiolite, characterized in that, Includes the following steps: Step 1: Immerse sepiolite in strong acid to dissolve it, and separate the solution and residue. The amount of strong acid added is 4500-5500 mL per 500 g of sepiolite powder. The dissolution conditions are: dissolve in a water bath at 83-87℃ for 0.5-1.5 h. The separation conditions are: place the solid-liquid mixture obtained after acid immersion into a centrifuge tube, then centrifuge at 1800-2200 r / min for 13-17 min. The residue is then dried and ground for use. The drying and grinding conditions are: place the precipitate obtained after thorough washing in the separation process into a glass beaker, then place it in a vacuum drying oven at 35-45℃. The dried residue is then ground again using a ball mill until the powder passes through an 80-micron square-hole sieve with less than 5% residue. Step 2: Add NaOH to the solution to obtain Mg(OH)2 precipitate. The amount of NaOH added is such that the pH value of the solution after addition is greater than 13. Step 3: Separate the Mg(OH)2 precipitate, calcine to obtain MgO, mix the water-reducing agent, the residue and the MgO, and add water for curing to obtain hydrated magnesium silicate cementitious material. The ratio of residue to MgO by weight is 0.3~6.0, the ratio of water to total solids is 0.2~3.0, the total solids are the total amount of residue and Mg(OH)2 precipitate, and the amount of water-reducing agent is 0.5% of the weight of the mixed system.

2. The method for preparing hydrated magnesium silicate cementitious material using sepiolite according to claim 1, characterized in that, The chemical composition of the sepiolite, by weight, is: 0.1-5% CaO, 40-70% SiO2, 20-50% MgO, 0.5-3% Al2O3, 0.2-0.6% Fe2O3, 0.1-1% K2O, and the balance being impurities.

3. The method for preparing hydrated magnesium silicate cementitious material using sepiolite according to claim 1, characterized in that, In step 1, sepiolite is first crushed and ground to obtain sepiolite powder, and then dissolved in a strong acid; the strong acid is sulfuric acid, hydrochloric acid or nitric acid, wherein the pH is <1.

4. The method for preparing hydrated magnesium silicate cementitious material using sepiolite according to claim 1, characterized in that, In step 3, the slurry obtained after adding water is cured for 1 day to generate hydrated magnesium silicate gel material.

5. The method for preparing hydrated magnesium silicate cementitious material using sepiolite according to claim 1, characterized in that, In step 3, the Mg(OH)2 precipitate is separated from the mixture using a Buchner funnel, dried in a drying oven for 24 hours, and then calcined in a muffle furnace at 740~760℃ for 25~35 minutes to obtain MgO.

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