Method for preparing hydrated magnesium silicate cementing material by dissolving magnesium silicate mineral with waste acid

Abstract

A method for preparing a hydrated magnesium silicate cementing material by dissolving magnesium silicate minerals with waste acid comprises the following steps: dissolving the magnesium silicate minerals such as serpentine, olivine and sepiolite with the waste acid, and then filtering to obtain filtrate and residues; when the filtrate contains Mg < 2 + >, NaOH is added to obtain a precipitate Mg (OH) 2; the hydrated magnesium silicate is prepared by the following steps: mixing the main component SiO2 of filtered residues with the Mg (OH) 2 precipitate, and then adding water for curing, thereby obtaining the hydrated magnesium silicate cementing material. Magnesium silicate minerals such as serpentine, olivine and sepiolite in the earth crust are used as raw materials, the raw materials are simple in source and low in price, and technical theoretical guidance is provided for preparation of hydrated magnesium silicate cementing materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of novel cementitious materials, and particularly relates to a method for preparing magnesium hydrosilicate cementitious materials by dissolving magnesium silicate minerals with waste acid. Background Art

[0002] The preparation cost of traditional magnesium hydrosilicate cementitious materials is high, and the output is limited.

[0003] A Chinese invention patent titled "Method for Preparing Magnesium Hydrosilicate Cementitious Materials by Using Sepiolite (Application No. CN202510259333.4)" submitted by the applicant on March 6, 2025, has solved the above problems to a certain extent, but there are still some areas for improvement, mainly manifested in:

[0004] 1. Strong acid is used to dissolve sepiolite in this patent. On the one hand, the cost of strong acid is relatively high, and large-scale use will increase the preparation cost, which is contrary to the goal of achieving low-cost preparation and is not conducive to large-scale industrial production. On the other hand, the high corrosiveness of strong acid determines that its operation requirements are relatively high, and the subsequent pollution risk is relatively large.

[0005] 2. Water reducing agents are still used in this patent to reduce water consumption, and the reagent cost of water reducing agents has not been reduced.

[0006] 3. Only sepiolite is used as the raw material in this patent, and the scope is relatively narrow. Summary of the Invention

[0007] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a method for preparing magnesium hydrosilicate cementitious materials by dissolving magnesium silicate minerals with waste acid, using abundant magnesium silicate minerals such as serpentine, olivine, and sepiolite in the earth's crust as the main raw materials, using waste acid to replace strong acid, and not requiring the use of water reducing agents, ultimately achieving low-cost and large-scale preparation of magnesium hydrosilicate cementitious materials.

[0008] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0009] A method for preparing magnesium hydrosilicate cementitious materials by dissolving magnesium silicate minerals with waste acid, comprising the following steps:

[0010] Step 1, dissolving magnesium silicate minerals with waste acid, and separating to obtain a solution and a residue, wherein the magnesium silicate minerals are one or more of serpentine, olivine, and sepiolite;

[0011] Step 2, adding NaOH to the filtrate to react to obtain Mg(OH)₂ precipitate;

[0012] Step 3, directly adding water for curing after mixing the residue and the Mg(OH)₂ precipitate to obtain magnesium hydrosilicate cementitious materials.

[0013] In terms of weight, the chemical composition of the magnesium silicate mineral is as follows: 0.08 - 2.80% of CaO, 35 - 60% of SiO2, 25 - 50% of MgO, 0.2 - 12% of Al2O3, 0.4 - 8% of Fe2O3, 0.01 - 1% of K2O, and the balance being impurities.

[0014] In one embodiment, in step 1, the magnesium silicate mineral is first crushed and ground to obtain mineral powder, and then waste acid is added for dissolution; the waste acid is a mixture of sulfuric acid and hydrochloric acid. In the present invention, the waste acid is from the laboratory, with a pH of 3 ± 0.5. The molar concentrations of HCl and H2SO4 in the waste acid mixture are 6.20 mol / L and 7.77 mol / L respectively, and the waste acid used in the experimental process is all from the same batch.

[0015] In one embodiment, in step 1, the addition amount of the waste acid is: 2500 mL ± 1 mL of waste acid is added to every 500 g ± 1 g of mineral powder; the dissolution conditions are: dissolution at 90°C for 3 h; the separation conditions are: the solid-liquid mixture obtained after acid leaching is filled into a centrifuge tube, and then placed in a centrifuge with a set rotation speed of about 2000 r / min and centrifuged for about 15 min.

[0016] In one embodiment, the obtained residue is washed with water multiple times to wash off the residual waste acid on the surface, and then dried and ground for use. The drying and grinding conditions can be: the centrifuge separates to obtain filtrate and residue. The sediment obtained after the residue is fully washed with deionized water is placed in a glass beaker, and then put into a vacuum drying oven and vacuum dried at a temperature of 40°C for about 48 h.

[0017] In one embodiment, in step 2, the addition amount of NaOH is: after addition, the pH value of the filtrate is greater than 13.

[0018] In one embodiment, in step 3, in terms of weight:

[0019] The ratio of the residue to the Mg(OH)2 precipitate is 1.0, and the ratio of water to the total amount of solids (residue and Mg(OH)2 precipitate) is 10.0.

[0020] In one embodiment, in step 3, the slurry obtained after adding water is cured for 1 d to generate a hydrated magnesium silicate gel material.

[0021] The hydrated magnesium silicate cementitious material obtained in the present invention has a mortar strength of 12 MPa at 3 d, a compressive strength exceeding 40 MPa at 28 d. Measured using a vibrating table, its mortar fluidity is 157, 162, and 181 mm respectively.

[0022] Compared with the prior art, the present invention chemically separates high-silica residue and Mg(OH)₂ from magnesium silicate minerals such as serpentine, olivine, and sepiolite that are abundant in the earth's crust, and can simultaneously obtain two raw materials required for the hydrated magnesium silicate cementitious material. It uses waste acid to replace strong acid, optimizes the process to achieve mineral dissolution, and the product waste residue is mainly silica gel, without the need to use water-reducing agents. Therefore, it solves the problems of high cost and limited output of silica fume used in the preparation of hydrated magnesium silicate in the past, and at the same time avoids the environmental problem of CO₂ emissions when obtaining MgO by calcining magnesite. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the mineral composition of serpentine, olivine, and sepiolite in the embodiment of the present invention.

[0024] Figure 2 It is a flow chart for preparing hydrated magnesium silicate using serpentine, olivine, and sepiolite in the embodiment of the present invention.

[0025] Figure 3 It is a schematic diagram of the residue composition after serpentine, olivine, and sepiolite are corroded by waste acid in the embodiment of the present invention.

[0026] Figure 4 It is a schematic diagram of the mineral composition of Mg(OH)₂ obtained by precipitation in the embodiment of the present invention.

[0027] Figure 5 It is an XRD diagram of the slurry cured at 20 °C, 50 °C, and 80 °C for different times prepared from the residue and Mg(OH)₂. DETAILED DESCRIPTION OF THE INVENTION

[0028] The embodiments of the present invention will be described in detail below with reference to the drawings and examples.

[0029] The present invention uses magnesium silicate in the earth's crust as the main raw material and provides a method for preparing a hydrated magnesium silicate cementitious material using magnesium silicate minerals such as serpentine, olivine, and sepiolite. Magnesium silicate minerals such as serpentine, olivine, and sepiolite mainly include SiO₂, MgO, CaO, etc., as shown in reference Figure 1 shown.

[0030] Reference Figure 2 shown, the method for preparing a hydrated magnesium silicate cementitious material using magnesium silicate minerals in the present invention can be mainly described as follows:

[0031] Step 1, dissolve the magnesium silicate mineral with waste acid and separate to obtain a solution and a residue.

[0032] In a specific embodiment, by weight, the magnesium silicate mineral used in the embodiment of the present invention is olivine, and its chemical composition is: 0.08 - 2.80% of CaO, 35 - 60% of SiO2, 25 - 50% of MgO, 0.2 - 12% of Al2O3, 0.4 - 8% of Fe2O3, 0.01 - 1% of K2O, and the balance is impurities.

[0033] First, crush and grind olivine to obtain olivine powder, and then add waste acid for dissolution. The addition amount of the waste acid is: 2500 mL (±1 mL) of waste acid is added to every 500 g (±1 g) of olivine powder. The dissolution conditions are: dissolve in a 90°C water bath for 3 h. Exemplarily, for the said crushing and grinding, 500 g of olivine is crushed using a jaw crusher and ground using a ball mill for 30 minutes. The residue on a 80-micron sieve of the product after crushing and grinding is less than 10%.

[0034] Compared with the patent described in the background art (application number CN202510259333.4), the waste acid is used in this step. The waste acid usually comes from industrial production processes or laboratories, such as industries like metal processing and chemical engineering. It has a wide source and low cost, can reduce the raw material cost, and reduce environmental pollution. And due to the relatively high chemical activity of magnesium silicate minerals such as serpentine, olivine, sepiolite, and chlorite, even if the dissolution ability of the waste acid is weak, the magnesium element in them can be dissolved out under certain conditions, separated from insoluble silicon dioxide, meeting the requirements for preparing hydrated magnesium silicate cementitious materials.

[0035] The present invention can improve the dissolution efficiency of waste acid by controlling process conditions such as the dosage of waste acid, reaction temperature, and time. For example, the limitation of the addition amount and dissolution conditions of the aforementioned waste acid can achieve a good dissolution effect. In actual industrial production, if the dissolution ability of the waste acid is insufficient, some auxiliary reagents can be appropriately added to enhance the dissolution effect. For example, adding an appropriate amount of catalyst can accelerate the reaction rate and promote the dissolution of magnesium silicate minerals, making up for the problem that the dissolution ability of waste acid is not as good as that of strong acids.

[0036] Furthermore, the present invention can also make olivine into fine powder by crushing and grinding it, reducing the particle size, increasing the specific surface area of the material, creating favorable conditions for shortening the chemical reaction time of the material, and the particles of the ground material are uniform, which is beneficial to the progress of the reaction.

[0037] After the waste acid dissolution, since olivine contains 20 - 50% of MgO, magnesium in the olivine enters the waste acid solution during the dissolution process, and SiO2 that is insoluble in acid can be separated by a centrifuge, effectively separating MgO and SiO2 through the acid leaching method.

[0038] In this embodiment, the separation conditions are set as follows: The solid-liquid mixture obtained after acid leaching is filled into a centrifuge tube, and then placed in a centrifuge with a rotation speed of about 2000 r / min and centrifuged for about 15 min. After that, the supernatant obtained by centrifugation is filled into a narrow-mouth bottle for storage. The sediment is repeatedly washed and centrifuged, vacuum dried at 40 °C, and then filled into a self-sealing bag for storage.

[0039] In more embodiments, serpentine and sepiolite are also used as raw materials.

[0040] Figure 3 It is a schematic diagram of the residue composition of serpentine, olivine and sepiolite after being corroded by waste acid in this embodiment. It can be seen that the peak envelope between 2θ of 20° - 30° indicates that the residue is typical amorphous SiO2.

[0041] Step 2: Add NaOH to the obtained filtrate to obtain Mg(OH)2 precipitate.

[0042] The filtrate is a magnesium solution. In a specific embodiment, the addition amount of NaOH is preferably such that the pH value of the filtrate is greater than 13 after addition to ensure the full and rapid precipitation of Mg(OH)2.

[0043] Step 3: Perform in the following manner:

[0044] The residue after filtration is SiO2. After mixing with the above-mentioned Mg(OH)2 precipitate, direct water curing can obtain a hydrated magnesium silicate cementitious material; preferably, by weight, the ratio of the residue to the Mg(OH)2 precipitate is 1.0, and the ratio of water to the total solid amount (residue and Mg(OH)2 precipitate) is 10.0.

[0045] Since the residue prepared in Step 2 is mainly SiO2, that is, mainly silica gel, and the silica gel contains a certain amount of water, there is no longer a need for the water required to wet the silica fume particles when using silica fume. Using this method, directly using the prepared Mg(OH)2 also does not require the water required to wet and hydrate the MgO particles. Therefore, a water reducing agent does not need to be added to the raw materials.

[0046] In the above manner, using Mg(OH)2 is more conducive to the formation of hydrated magnesium silicate. In a specific project, how to choose depends on comprehensive considerations such as product requirements and costs. In the above manner, adding water to obtain a mixed slurry, and curing this slurry for 1 day can generate a hydrated magnesium silicate gel material.

[0047] 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 process is placed in a glass beaker and then put into a vacuum drying oven. It is 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 less than 5% of the obtained powder passes through a 80-micron square-hole sieve.

[0048] In a preferred embodiment of the present invention, to obtain Mg(OH)2, a Buchner funnel is used to separate the Mg(OH)2 precipitate from the mixed solution and placed in a drying oven for 24 h of drying. Figure 4 XRD pattern of the Mg(OH)2 precipitate in the example.

[0049] Figure 5 XRD patterns of the slurry prepared from the residue and Mg(OH)2 cured at 20 °C, 50 °C and 80 °C for 3 d, 7 d, 14 d, 28 d. It can be seen from the figure that the diffraction peaks rapidly decrease between 5° and 15°, which is the first characteristic diffraction peak for the formation of magnesium silicate hydrate in the XRD pattern. The obvious peak envelopes formed near 35° and 60° are the second and third characteristic diffraction peaks for the formation of magnesium silicate hydrate, respectively.

[0050] The principle of the present invention is as follows: Using abundant serpentine, olivine and sepiolite in the earth's crust as raw materials, the crystalline serpentine, olivine and sepiolite are dissolved by waste acid to obtain an insoluble residue with a high SiO2 content and a solution containing dissolved Mg 2+ The Mg in the solution 2+ is obtained as a Mg(OH)2 precipitate by adding a strong base. Then, Mg(OH)2 is mixed with the insoluble residue with a high SiO2 content and water is added to obtain a magnesium silicate hydrate gelling material. Since the raw materials used are only serpentine, olivine and sepiolite, water and a small amount of strong base waste acid, compared with the prior art, its preparation cost is greatly reduced. Moreover, due to the rich reserves and wide distribution of serpentine, olivine and sepiolite, the process of the present invention can be widely promoted, reducing the dependence on specific mineral producing areas.

Claims

1. A method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid, characterized in that, It includes the following steps: Step 1: Dissolve the magnesium silicate mineral with waste acid and separate to obtain a filtrate and a residue, where the magnesium silicate mineral is one or more of serpentine, olivine and sepiolite; Step 2: Add NaOH to the filtrate and react to obtain Mg(OH)₂ precipitate; Step 3: Mix the residue with the Mg(OH)₂ precipitate and directly add water for curing to obtain the hydrated magnesium silicate cementitious material.

2. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid according to claim 1, characterized in that, The pH of the waste acid is 3±0.5, which comes from the laboratory and is a mixture of sulfuric acid and hydrochloric acid. The molar concentrations of HCl and H₂SO₄ in the mixture are 6.20mol / L and 7.77mol / L respectively, and the waste acid used in the experimental process is all from the same batch.

3. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid according to claim 1, characterized in that, By weight, the chemical composition of the magnesium silicate mineral is: 0.08 - 2.80% of CaO, 35 - 60% of SiO₂, 25 - 50% of MgO, 0.2 - 12% of Al₂O₃, 0.4 - 8% of Fe₂O₃, 0.01 - 1% of K₂O and the balance of impurities.

4. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid according to claim 1, characterized in that, In Step 1, first crush and grind the magnesium silicate mineral to obtain mineral powder, and then add waste acid for dissolution.

5. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid according to claim 1 or 2 or 3 or 4, characterized in that, In Step 1, the addition amount of waste acid is: add 2500mL±1mL of waste acid to every 500g±1g of mineral powder; the dissolution conditions are: dissolve at 90±1°C for 3±0.5h; the separation conditions are: put the solid-liquid mixture obtained after acid leaching into a centrifuge tube, and then put it into a centrifuge and set the rotation speed to 2000±200r / min and centrifuge for 15±3min.

6. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid according to claim 1, characterized in that, In Step 1, wash the obtained residue with water for multiple times to wash off the residual waste acid on the surface, and then dry and grind it for use. The drying and grinding conditions are: separate the filtrate and the residue by a centrifuge, put the sediment obtained after the residue is fully washed with deionized water into a glass beaker, and then put it into a vacuum drying oven and vacuum dry at a temperature of 40±5°C for 48±1h.

7. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid according to claim 1, characterized in that, In Step 2, the addition amount of NaOH is: after adding, make the pH value of the filtrate greater than 13.

8. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid according to claim 1, wherein In Step 3, by weight: The ratio of the residue to the Mg(OH)₂ precipitate is 1.0, and the ratio of water to the total solid is 10.0; the total solid refers to the total amount of the residue and the Mg(OH)₂ precipitate.

9. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals with waste acid according to claim 1, characterized in that, In Step 3, cure the slurry obtained after adding water for 1d to generate the hydrated magnesium silicate gel material.

10. The method for preparing a hydrated magnesium silicate cementitious material by dissolving magnesium silicate minerals in waste acid according to claim 1, characterized in that, For the hydrated magnesium silicate cementitious material, the 3d mortar strength is 12MPa, the 28d compressive strength exceeds 40MPa, measured by a vibrating table, and its mortar fluidities are 157, 162 and 181mm respectively.

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