Method for preparing hydrated magnesium silicate cementing material by using sepiolite

Abstract

The invention relates to a method for preparing a hydrated magnesium silicate cementing material by using sepiolite, which comprises the following steps: dissolving sepiolite by using strong acid, and separating to obtain a solution and residues; naOH is added into the solution, and Mg (OH) 2 sediment is obtained; and separating the Mg (OH) 2 precipitate, calcining to obtain MgO, mixing a water reducing agent, the residues and the MgO, and adding water for curing to obtain the hydrated magnesium silicate cementing material. Rich sepiolite in the earth crust is used as a main raw material, so that low-cost and large-scale preparation of the hydrated magnesium silicate cementing material is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of novel gelling materials, and in particular relates to a method for preparing hydrated magnesium silicate gelling material by using sepiolite. Background Art

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

[0003] Calcined magnesite (MgCO3) is the main way to obtain MgO for the preparation of magnesium-based cementitious materials, but this mineral resource is limited in global distribution. MgO can also be obtained from salt lakes or seawater, but salt lakes are also concentrated and not very common. Precipitating Mg(OH)2 from seawater is considered energy intensive unless the brine is already highly concentrated.

[0004] The siliceous materials for preparing hydrated magnesium silicate are widely available, but the main source is highly active silica fume. Compared with silicate cement, the higher cost of silica fume and the relatively concentrated production areas also limit the widespread application of this material. In the foreseeable future, unless there is cheaper silica fume, hydrated magnesium silicate cementitious material can only be a cementitious material that is difficult to commercialize.

[0005] The above factors make the current preparation cost of magnesium silicate hydrate cementitious materials high and the output limited. Summary of the invention

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

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing a hydrated magnesium silicate gelling material using sepiolite comprises the following steps:

[0009] Step 1, immersing the sepiolite in a strong acid to dissolve it, and separating to obtain a solution and a residue;

[0010] Step 2, adding NaOH to the solution to obtain Mg(OH)2 precipitation;

[0011] Step 3, separating the Mg(OH)2 precipitate, calcining to obtain MgO, mixing the water reducer, the residue and the MgO, and adding water for curing to obtain a hydrated magnesium silicate cementitious material.

[0012] In one embodiment, the chemical composition of the sepiolite is, 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 remainder impurities.

[0013] In one embodiment, in step 1, the sepiolite is first crushed and ground to obtain sepiolite powder, and then a strong acid is added 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 of strong acid is added to every 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: putting the solid-liquid mixture obtained after acid leaching into a centrifuge tube, and then putting it into a centrifuge with a speed set at 1800-2200 r / min, and centrifuging for 13-17 min.

[0015] In one embodiment, the residue is dried and ground before use.

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

[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, by weight, the ratio of residue to MgO is 0.3-6.0, the ratio of water to total solid is 0.2-3.0, the total solid is the total amount of residue and Mg(OH)2 precipitate, and the amount of water reducer is 0.5% of the weight of the mixed system.

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

[0020] In one embodiment, in step 3, the Mg(OH)2 precipitate is separated from the mixed solution using a Buchner funnel, dried in a drying oven for 24 hours, and then calcined in a muffle furnace at 740-760°C for 25-35 minutes to obtain MgO.

[0021] Compared with the prior art, the present invention uses strong acid and strong alkali to separate the sepiolite, which is abundant in the earth's crust, to obtain high-silicon residue and Mg(OH)2, and can simultaneously obtain the two raw materials required for the hydrated magnesium silicate cementitious material, thereby solving the problems of high cost and limited output of silica ash used in the preparation of hydrated magnesium silicate, and avoiding the environmental problem of CO2 emission when calcining magnesite to obtain MgO. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the mineral composition of sepiolite in the embodiments of the present invention.

[0023] Figure 2 Schematic diagram of the composition of the residue after sepiolite is corroded by sulfuric acid in an embodiment of the present invention.

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

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

[0026] Figure 5 XRD patterns of slurry prepared from residue and MgO and cured at 80℃ for different times. DETAILED DESCRIPTION

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

[0028] The present invention uses magnesium silicate in the earth's crust as the main raw material and provides a method for preparing hydrated magnesium silicate gelling material using sepiolite. Sepiolite mainly includes SiO2, MgO, CaO, etc. Figure 1 As shown, the chemical composition of the sepiolite used in the embodiment of the present invention is, 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 remainder impurities.

[0029] The method for preparing hydrated magnesium silicate gelling material using sepiolite of the present invention mainly comprises the following steps:

[0030] Step 1, using a strong acid to dissolve the sepiolite, and separating the solution and the residue.

[0031] In a specific embodiment, the sepiolite is first crushed and ground to obtain sepiolite powder, and then a strong acid such as sulfuric acid, hydrochloric acid or nitric acid is added to dissolve it. The amount of strong acid added is: 5000 mL of a strong acid with a mass fraction of 40% is added to every 500 g of sepiolite powder. The dissolution condition is: dissolving in a water bath at 85°C for 1 hour. For example, the crushing and grinding is to crush 500 g of sepiolite using a jaw crusher and grind it using a ball mill for 30 minutes. The product after crushing and grinding has a 80-micron sieve residue of less than 10%.

[0032] The main purpose of using strong acid in the present invention is that strong acidity can destroy the crystal structure of sepiolite and decompose it into soluble sulfate and silica gel. The silica gel needs further treatment, but the main metal ions have been dissolved, which is convenient for the subsequent extraction step.

[0033] The separation conditions in this embodiment are as follows: the solid-liquid mixture obtained after acid leaching is placed in a centrifuge tube, and then placed in a centrifuge with a speed of about 2000 r / min, and centrifuged for about 15 minutes. After that, the supernatant obtained by centrifugation is placed in a narrow-necked bottle for storage, and the sediment is repeatedly washed and centrifuged, and then vacuum-dried at 40°C and placed in a ziplock bag for storage.

[0034] Figure 2 Schematic diagram of the composition of the residue after sepiolite is corroded by sulfuric acid in this embodiment. It can be seen that the peak at 2θ is between 20°-30°, indicating that the residue is typical amorphous SiO2.

[0035] Step 2, adding NaOH to the solution to obtain Mg(OH)2 precipitation.

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

[0037] The main purpose of using the strong base NaOH in the present invention is to neutralize the acidity in the acid hydrolysis filtrate, increase the pH, and make the magnesium ions form Mg(OH)2 precipitation, thereby separating from other soluble substances. At the same time, the high concentration of NaOH may help to quickly precipitate and ensure the complete precipitation of magnesium. In addition, excessive NaOH helps to dissolve other hydroxides such as Al(OH)3, thereby improving the purity of Mg(OH)2.

[0038] Step 3, separating the Mg(OH)2 precipitate, calcining to obtain MgO, mixing the water reducer, the residue and the MgO, and curing with water to obtain a hydrated magnesium silicate cementitious material. Preferably, by weight, the ratio of the residue to MgO is 0.3 to 6.0, and the ratio of water to the total solid (residue to Mg(OH)2 precipitate) is 0.2 to 3.0.

[0039] The use of MgO in the present invention is more conducive to the formation of hydrated magnesium silicate than the use of Mg(OH)2. A mixed slurry is obtained by adding water, and the slurry is cured for 1 day to generate a hydrated magnesium silicate gel material. However, since the residue obtained here has a high specific surface area, and the hydration of MgO also requires water, in order to reduce the amount of water, the present invention introduces a water reducer, and the amount of the water reducer is about 0.5% of the weight of the mixed system. It can reduce the water-solid ratio while maintaining fluidity, improve density, and enhance the strength of the final material; at the same time, the water reducer is adsorbed on the surface of the particles, which can reduce agglomeration, increase the contact area, and promote the reaction of MgO and silicate.

[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 sufficient washing in the separation procedure is placed in a glass beaker, and then placed in a vacuum drying oven, and vacuum dried at a temperature of 40°C for a certain period of time to ensure that the water content is less than 5%, which is convenient for subsequent grinding; the dried residue is ground again using a ball mill until the obtained powder has a water content of less than 5% on an 80-micron square hole sieve.

[0041] In a preferred embodiment of the present invention, to obtain MgO, the Mg(OH)2 precipitate is separated from the mixed solution 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 This is the diffraction pattern of MgO obtained after calcining the Mg(OH)2 precipitate at 750°C for 30 minutes in the example.

[0042] Figure 4 and Figure 5 The XRD patterns of the slurry prepared from the residue and MgO at 50℃ and 80℃ for different curing times are shown in the figure. It can be seen from the figure that the diffraction peak drops rapidly between 5° and 15°, which is the first characteristic diffraction peak formed by hydrated magnesium silicate in the XRD pattern. The obvious peaks formed near 35° and 60° are the second and third characteristic diffraction peaks formed by hydrated magnesium silicate, respectively.

[0043] The principle of the present invention is to use the abundant sepiolite in the earth's crust as raw material, dissolve the crystalline sepiolite by strong acid, and obtain the insoluble residue with high SiO2 content and the Mg2O3 dissolved in the crystalline sepiolite. 2+ The solution contains Mg 2+ Mg(OH)2 precipitation is obtained by adding a strong base. Then, Mg(OH)2 or MgO obtained by calcining Mg(OH)2 is mixed with an insoluble residue with a high SiO2 content, and water is added to obtain a hydrated magnesium silicate gelling material. Since the raw materials used are only sepiolite, water and a small amount of strong alkali and strong acid, the preparation cost is greatly reduced compared with the prior art, and since sepiolite is abundant in reserves and widely distributed, the process of the present invention can be widely promoted, reducing the dependence on a specific mineral production area.

Claims

1. A method for preparing a hydrated magnesium silicate gelling material using sepiolite, characterized in that: The steps include: Step 1, immersing the sepiolite in a strong acid to dissolve it, and separating to obtain a solution and a residue; Step 2, adding NaOH to the solution to obtain Mg(OH)2 precipitation; Step 3, separating the Mg(OH)2 precipitate, calcining to obtain MgO, mixing the water reducer, the residue and the MgO, and adding water for curing to obtain a hydrated magnesium silicate cementitious material.

2. The method for preparing hydrated magnesium silicate gelling material using sepiolite according to claim 1, characterized in that: The chemical composition of the sepiolite is, 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 remainder impurities.

3. The method for preparing hydrated magnesium silicate gelling material using sepiolite according to claim 1, characterized in that: In the step 1, the sepiolite is first crushed and ground to obtain sepiolite powder, and then a strong acid is added to dissolve it; the strong acid is sulfuric acid, hydrochloric acid or nitric acid, wherein the pH value is less than 1.

4. The method for preparing hydrated magnesium silicate gelling material using sepiolite according to claim 1 or 3, characterized in that: In the step 1, the amount of strong acid added is: 4500-5500 mL of strong acid is added to every 500 g of sepiolite powder; the dissolution condition is: dissolving in a water bath at 83-87° C. for 0.5-1.5 h; the separation condition is: putting the solid-liquid mixture obtained after acid leaching into a centrifuge tube, then putting it into a centrifuge with a speed set at 1800-2200 r / min, and centrifuging for 13-17 min.

5. The method for preparing hydrated magnesium silicate gelling material using sepiolite according to claim 1, characterized in that: The residue is dried and ground before use.

6. The method for preparing hydrated magnesium silicate gelling material using sepiolite according to claim 5, characterized in that: The drying and grinding conditions are as follows: the sediment obtained after sufficient washing in the separation procedure is placed in a glass beaker, and then placed in a vacuum drying oven, and vacuum dried at a temperature of 35-45° C.; the dried residue is ground again using a ball mill until the obtained powder has less than 5% on an 80-micron square hole sieve.

7. The method for preparing hydrated magnesium silicate gelling material using sepiolite according to claim 1, characterized in that: In the step 2, the amount of NaOH added is such that the pH value of the solution after addition is greater than 13.

8. The method for preparing hydrated magnesium silicate gelling material using sepiolite according to claim 1, characterized in that: In step 3, by weight, the ratio of residue to MgO is 0.3-6.0, the ratio of water to total solid is 0.2-3.0, the total solid is the total amount of residue and Mg(OH)2 precipitation, and the amount of water reducer is 0.5% of the weight of the mixed system.

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

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

Images