Method for preparing active magnesium oxide from low-grade magnesite

Abstract

The invention relates to the technical field of refractory materials, in particular to a method for preparing active magnesium oxide from low-grade magnesite, which comprises the following steps: 1) acid leaching and silicon removal: mixing low-grade magnesite with nitric acid, carrying out acid leaching reaction at the temperature of 80-90 DEG C to obtain acid leaching liquid and silicon sludge, and filtering out the silicon sludge; 2) impurity removal: cooling the pickle liquor to room temperature, adding a sodium hydroxide solution to adjust the pH value to 9-10, and filtering to remove precipitates; 3) precipitation separation: adding a sodium hydroxide solution into the filtrate, introducing excessive carbon dioxide gas into the mixed solution to convert calcium ions into calcium carbonate precipitates and magnesium ions into magnesium bicarbonate, and filtering to remove the calcium carbonate precipitates; and 4) preparation of active magnesium oxide: heating and decomposing the magnesium bicarbonate in the step 3) at 60-80 DEG C, filtering, washing with water, calcining at a low temperature of 500-600 DEG C, and calcining in air or inert atmosphere for 2-4 hours to obtain the active magnesium oxide. The active magnesium oxide prepared by the method has higher reaction activity.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractories, and particularly relates to a method for preparing active magnesium oxide from low-grade magnesite. Background Art

[0002] Magnesite is an important magnesium resource, and its main component is magnesium carbonate (MgCO3). However, low-grade magnesite usually contains a large amount of impurities such as iron, aluminum, calcium, silicon, etc. The presence of these impurities seriously affects the extraction and purification of magnesium. Traditional magnesite processing methods mostly use processes such as high-temperature calcination, which have high energy consumption and are difficult to effectively remove impurities, resulting in low product quality. Therefore, it is of great practical significance to develop a high-efficiency, energy-saving and impurity-removing low-grade magnesite processing technology. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing active magnesium oxide from low-grade magnesite, which can efficiently remove impurities, improve the extraction rate of magnesium, and has a simple process, low cost and environmental friendliness.

[0004] To achieve the above object, the present invention is realized by adopting the following technical solutions:

[0005] A method for preparing active magnesium oxide from low-grade magnesite, comprising the following steps:

[0006] 1) Acid leaching to remove silicon: Mix low-grade magnesite with nitric acid, carry out an acid leaching reaction at a temperature of 80 - 90 °C to obtain an acid leaching solution and silicon mud, and filter out the silicon mud;

[0007] 2) Impurity removal: After cooling the acid leaching solution to room temperature, add sodium hydroxide solution to adjust the pH to 9 - 10, so that iron ions and aluminum ions, and part of calcium ions in the solution are respectively precipitated as iron hydroxide, aluminum hydroxide and calcium hydroxide, and part of calcium ions and magnesium ions remain in the solution; Filter to remove the precipitate;

[0008] 3) Precipitation separation: Add sodium hydroxide solution to the filtrate again, and then pass excessive carbon dioxide gas into the mixed solution to convert calcium ions into calcium carbonate precipitate and magnesium ions into magnesium bicarbonate, and filter to remove the calcium carbonate precipitate;

[0009] 4) Preparation of active magnesium oxide: Heat and decompose magnesium bicarbonate in step 3) at 60 - 80 °C, filter and wash, and then carry out low-temperature calcination at 500 - 600 °C for 2 - 4 hours in air or an inert atmosphere to obtain active magnesium oxide.

[0010] In step 1), the MgCO3 content of the low-grade magnesite is < 76%, and the particle size of the magnesite is 1 - 3 mm.

[0011] Step 1) Mix low-grade magnesite with nitric acid at a mass ratio of 1:3 - 1:5, conduct acid leaching reaction for 1 - 2 hours, and the concentration of nitric acid is 25% - 30%.

[0012] Step 4) Use a fluidized bed calcination furnace to calcine for 2 - 4 hours in air or an inert atmosphere: the inert gas is nitrogen.

[0013] The specific surface area of the described active magnesium oxide is 50 - 200m 2 / g.

[0014] Compared with the existing technology, the beneficial effects of the present invention are:

[0015] The present invention efficiently removes impurities and optimizes the calcination process. The specific surface area of the prepared active magnesium oxide can reach 50 - 200m 2 / g, and it has relatively high reaction activity. By controlling the calcination temperature and time, the prepared magnesium oxide has a uniform particle size distribution, D50 = 1.5 - 3.0μm, D90 = 3.0 - 6.0μm, which helps to improve its dispersibility and application performance in composite materials. No harmful gases are generated during the whole preparation process, which is environmentally friendly. The generation of wastewater is reduced, and the main components in the wastewater can be recycled, reducing the impact on the environment. Specific embodiments

[0016] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship for the sole purpose of facilitating the description of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0017] Unless otherwise clearly defined and limited, the terms "installed", "connected", "connected to" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0018] A method for preparing active magnesium oxide from low-grade magnesite, comprising the following steps:

[0019] 1) Acid leaching for silicon removal: Mix low-grade magnesite with nitric acid at a mass ratio of 1:3 - 1:5, carry out an acid leaching reaction at a temperature of 80 - 90 °C for 1 - 2 hours to obtain an acid leaching solution and silicon mud, and filter out the silicon mud;

[0020] Particle size of magnesite: 1 - 3 mm; concentration of nitric acid: 25% - 30%; stirring intensity: 400 rpm is sufficient, and keep the solution in a peristaltic state for impregnation.

[0021] 2) Impurity removal: After cooling the acid leaching solution to room temperature, add sodium hydroxide solution to adjust the pH to 9 - 10, so that iron ions and aluminum ions, and part of calcium ions in the solution are respectively precipitated as iron hydroxide, aluminum hydroxide, and calcium hydroxide, and part of calcium ions and magnesium ions remain in the solution; filter to remove the precipitate;

[0022] Fe3+ + 3OH- → Fe(OH)3↓

[0023] Al3+ + 3OH- → Al(OH)3↓

[0024] Ca2+ + 2OH- → Ca(OH)2↓

[0025] 3) Precipitation separation: Add sodium hydroxide solution to the filtrate again, and then pass excessive carbon dioxide gas into the mixed solution to convert calcium ions into calcium carbonate precipitate and magnesium ions into magnesium bicarbonate, and filter to remove the calcium carbonate precipitate;

[0026] Ca2+ + 2OH- → Ca(OH)2↓

[0027] Ca(OH)2 + CO2 → CaCO3↓

[0028] Mg2+ + 2HCO3- → Mg(HCO3)2 (soluble in water)

[0029] 4) Preparation of active magnesium oxide: Heat and decompose magnesium bicarbonate in step 3) at 60 - 80 °C to decompose Mg(HCO3)2 into basic magnesium carbonate or magnesium carbonate and release CO2; maintain a weak alkaline pH of 8 - 10 to prevent incomplete hydrolysis of Mg 2+ hydrolysis.

[0030] Filtration: Remove soluble sodium salts, and water washing: further reduce sodium residue.

[0031] Low-temperature calcination: 500 - 600 °C, calcine for 2 - 4 hours in air or an inert atmosphere: Obtain highly specific surface area active MgO. Use a fluidized bed calcination furnace to enhance heat transfer and reduce sodium residue. Temperature ≤ 600 °C: Avoid sintering and maintain a high specific surface area. Avoid long-term calcination for 2 - 4 hours to cause sintering. Use air or an inert gas (N2) to prevent re-carbonation by CO2.

[0032] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Additionally, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods. Furthermore, any combination can be made between different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

[0033] To make the objectives, technical solutions, and technical effects of the present invention clearer, the technical solutions in the embodiments of the present invention will now be described clearly and completely. However, the embodiments described below are only a part of the embodiments of the present invention, rather than all of the embodiments. Combining the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0034] In the examples, the chemical composition of the low-grade magnesite is shown in Table 1;

[0035] Table 1:

[0036]

[0037]

[0038] Example 1:

[0039] A method for preparing active magnesium oxide from low-grade magnesite, comprising the following steps:

[0040] 1) Acid leaching to remove silicon: Mix low-grade magnesite with nitric acid. The mass ratio of low-grade magnesite to nitric acid is 1:3, and the concentration of nitric acid is 25%. Carry out the acid leaching reaction at a temperature of °C to obtain an acid leaching solution and silicon mud, and filter out the silicon mud;

[0041] 2) Impurity removal: After cooling the acid leaching solution to room temperature, add sodium hydroxide solution to adjust the pH to 9 - 9.5, so that iron ions, aluminum ions and part of calcium ions in the solution are respectively precipitated as iron hydroxide, aluminum hydroxide and calcium hydroxide, and part of calcium ions and magnesium ions remain in the solution; Filter to remove the precipitate;

[0042] 3) Precipitation separation: Add sodium hydroxide solution to the filtrate again, and then pass excessive carbon dioxide gas into the mixed solution to convert calcium ions into calcium carbonate precipitate and magnesium ions into magnesium bicarbonate, and filter to remove the calcium carbonate precipitate;

[0043] 4) Preparation of active magnesium oxide: In step 4), magnesium bicarbonate is heated and decomposed at 60 - 80 °C, filtered, washed with water, and then calcined at a low temperature of 580 °C in a fluidized bed calciner for 2.5 hours under a nitrogen atmosphere to obtain active magnesium oxide.

[0044] Example 2:

[0045] A method for preparing active magnesium oxide from low - grade magnesite, comprising the following steps:

[0046] 1) Acid leaching for silicon removal: Mix low - grade magnesite with nitric acid, the mass ratio of low - grade magnesite to nitric acid is 1:5, the concentration of nitric acid is 28%, and carry out acid leaching reaction at a temperature of °C to obtain an acid leaching solution and silicon mud, and filter out the silicon mud;

[0047] 2) Impurity removal: After cooling the acid leaching solution to room temperature, add sodium hydroxide solution to adjust the pH to 9.5 - 10, so that iron ions, aluminum ions and part of calcium ions in the solution are respectively precipitated as iron hydroxide, aluminum hydroxide and calcium hydroxide, and part of calcium ions and magnesium ions remain in the solution; Filter to remove the precipitate;

[0048] 3) Precipitation separation: Add sodium hydroxide solution to the filtrate again, and then pass excessive carbon dioxide gas into the mixed solution to convert calcium ions into calcium carbonate precipitate and magnesium ions into magnesium bicarbonate, and filter to remove the calcium carbonate precipitate;

[0049] 4) Preparation of active magnesium oxide: In step 4), magnesium bicarbonate is heated and decomposed at 75 °C, filtered, washed with water, and then calcined at a low temperature of 520 °C in a fluidized bed calciner for 3.2 hours under a nitrogen atmosphere to obtain active magnesium oxide.

[0050] Example 3:

[0051] A method for preparing active magnesium oxide from low - grade magnesite, comprising the following steps:

[0052] 1) Acid leaching for silicon removal: Mix low - grade magnesite with nitric acid, the mass ratio of low - grade magnesite to nitric acid is 1:4, the concentration of nitric acid is 30%, and carry out acid leaching reaction at a temperature of °C to obtain an acid leaching solution and silicon mud, and filter out the silicon mud;

[0053] 2) Impurity removal: After cooling the acid leaching solution to room temperature, add sodium hydroxide solution to adjust the pH to 9.2 - 9.6, so that ferric ions and aluminum ions, and part of calcium ions in the solution are respectively precipitated as ferric hydroxide, aluminum hydroxide, and calcium hydroxide, and part of calcium ions and magnesium ions remain in the solution; filter to remove the precipitate;

[0054] 3) Precipitation separation: Add sodium hydroxide solution to the filtrate again, and then pass excessive carbon dioxide gas into the mixed solution to convert calcium ions into calcium carbonate precipitate and magnesium ions into magnesium bicarbonate, and filter to remove the calcium carbonate precipitate;

[0055] 4) Preparation of active magnesium oxide: In step 4), magnesium bicarbonate is heated and decomposed at 70 °C, filtered, washed with water, and then calcined at 550 °C in a fluidized bed calciner for 3.8 hours under a nitrogen atmosphere to obtain active magnesium oxide.

[0056] The product performance indicators are shown in Table 2:

[0057] Table 2:

[0058]

[0059] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and deformations can be made to these embodiments without departing from the principles and basic spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing active magnesium oxide from low-grade magnesite, characterized in that, It includes the following steps: 1) Silicon removal by acid leaching: Mix low-grade magnesite with nitric acid, carry out acid leaching reaction at a temperature of 80 - 90 °C to obtain an acid leaching solution and silicon mud, and filter out the silicon mud; 2) Impurity removal: After cooling the acid leaching solution to room temperature, add sodium hydroxide solution to adjust the pH to 9 - 10, so that iron ions and aluminum ions, and part of calcium ions in the solution are respectively precipitated as iron hydroxide, aluminum hydroxide, and calcium hydroxide, and part of calcium ions and magnesium ions remain in the solution; Filter to remove the precipitate; 3) Precipitation separation: Add sodium hydroxide solution to the filtrate again, and then pass excessive carbon dioxide gas into the mixed solution to convert calcium ions into calcium carbonate precipitate and magnesium ions into magnesium bicarbonate, and filter out the calcium carbonate precipitate; 4) Preparation of active magnesium oxide: Magnesium bicarbonate in step 3) is heated and decomposed at 60 - 80 °C, filtered and washed, and then calcined at a low temperature of 500 - 600 °C for 2 - 4 hours in air or an inert atmosphere to obtain active magnesium oxide.

2. The method for preparing active magnesium oxide from low-grade magnesite according to claim 1, characterized in that , in step 1), the MgCO3 content of the low-grade magnesite is < 76%, and the particle size of the magnesite is 1 - 3 mm.

3. A method for preparing active magnesium oxide from low-grade magnesite according to claim 1, characterized in that , in step 1), the low-grade magnesite and nitric acid are mixed at a mass ratio of 1:3 - 1:5, the acid leaching reaction is carried out for 1 - 2 hours, and the nitric acid concentration is 25% - 30%.

4. A method for preparing active magnesium oxide from low-grade magnesite according to claim 1, characterized in that , in step 4), a fluidized bed calcination furnace is used, and calcination is carried out for 2 - 4 hours in air or an inert atmosphere: the inert gas is nitrogen.

5. A method for preparing active magnesium oxide from low-grade magnesite according to claim 1, characterized in that , the specific surface area of the active magnesium oxide is 50-200m 2 / g.

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