Active magnesium oxide as well as preparation method and application thereof

Abstract

The invention relates to active magnesium oxide as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) reversely injecting a magnesium-containing solution into a carbonate solution to obtain a mixed solution; (2) reacting the mixed solution, and then performing dynamic gradient drying to obtain a basic magnesium carbonate precursor; the dynamic gradient drying comprises at least two drying stages; and (3) carrying out two-stage roasting on the basic magnesium carbonate precursor to obtain the active magnesium oxide. According to the preparation method of the active magnesium oxide provided by the invention, the reverse injection method, the solution reaction, the dynamic gradient drying and the two-stage roasting process are combined, and the crystallization kinetics and interface engineering in the preparation process are controlled, so that the prepared magnesium oxide has the characteristics of high activity, high specific surface area and high bulk density at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic materials, and particularly to an active magnesium oxide, a preparation method thereof and an application thereof. Background Art

[0002] It can be foreseen that magnesium oxide has significant advantages as a precipitant in the acid leaching solution for nickel and cobalt precipitation: its slow-release characteristic enables mild pH regulation, improves the selective precipitation rate of nickel and cobalt (>90%), and simultaneously reduces the entrainment of manganese impurities. The formation of magnesium hydroxide can avoid the problem of local over-alkalinity in the solution, which is beneficial to the growth of crystal grains and the formation of coarse particles that are easy to filter. In a copper-cobalt ore project in the Democratic Republic of the Congo, magnesium oxide is used in the cobalt precipitation process, which can achieve selective cobalt precipitation, effectively inhibit the doping of copper and manganese impurities, and reduce the moisture content of the filter cake and the reagent cost. With the development of the new energy industry, at present, the demand for nickel and cobalt in the new energy field has increased sharply. Due to its environmental protection and economy, the magnesium oxide precipitation method will accelerate the replacement of traditional strong base processes in the hydrometallurgy field.

[0003] The preparation of traditional active magnesium oxide mostly adopts the uniform concentration precipitation method or the single-stage calcination process, which has a contradiction between activity and compaction density: high-activity materials have fine particles (specific surface area > 80 m 2 / g), but the bulk density is low (<0.5 g / cm 3 ), while the high compaction process (bulk density > 0.8 g / cm 3 ) often leads to a decrease in activity (citric acid activity > 80 s).

[0004] The prior art CN104724734A discloses a method for manufacturing light, high specific surface area, flower ball-shaped nano magnesium hydroxide, which includes the following steps: (1) preparing an aqueous magnesium salt solution with a certain concentration in a reaction vessel; (2) preparing an alkali solution with a certain concentration in the vessel; (3) adding a certain amount of dispersant to the solution in step (1) or the solution in step (2) before the reaction; (4) slowly dropping the solution in step (2) into the solution in step (1), or slowly dropping the solution in step (1) into the solution in step (2), reacting to obtain a white precipitate, and after aging, centrifuging and washing the white precipitate (magnesium hydroxide) to remove other impurity ions, obtaining a white gel-like solid. The magnesium hydroxide obtained through the coprecipitation reaction and low-temperature calcination shows a high specific surface area, but the bulk density is relatively low, less than 0.15 g / cm 3 .

[0005] The prior art CN119263316A discloses a kind of active magnesium oxide and its preparation method, which relates to the technical field of magnesium oxide preparation. The method includes the following steps: obtaining calcium carbonate and active low-calcium magnesium-rich solution after calcining and dissociating, intensively leaching and carbonizing and separating the first magnesium ore; obtaining fine materials after calcining and dissociating and mechanically fine grinding the second magnesium ore, or directly mechanically fine grinding the second magnesium ore to obtain fine materials; pumping the active low-calcium magnesium-rich solution into a hydration activation tank, starting stirring and then transporting the fine materials to the hydration activation tank, and the active low-calcium magnesium-rich solution reacts with the fine materials to form a composite magnesium salt; drying and dispersing the composite magnesium salt and then transporting it to a calcining furnace, and obtaining active magnesium oxide after calcining and cooling and discharging through a screw. The prepared magnesium oxide has high activity, but the bulk density does not exceed 0.6g / cm 3 .

[0006] High activity often means a high specific surface area. For low-concentration magnesium-containing solutions, such as the post-liquid of high-pressure acid leaching and nickel-cobalt precipitation, the method of increasing supersaturation by concentration to refine crystal grains is obviously inappropriate. At the same time, for the magnesium oxide obtained by roasting from a high-activity precursor, although it has a large specific surface area and high activity, its bulk density is relatively low.

[0007] Therefore, it is necessary to optimize the synthesis process to prepare active magnesium oxide with both high activity, high specific surface area and high bulk density, and improve its advantages in the application of extracting mixed nickel-cobalt hydroxide from laterite nickel ore. Summary of the Invention

[0008] To solve the above technical problems, the purpose of the present invention is to provide a kind of active magnesium oxide and its preparation method and application. The preparation method of the active magnesium oxide provided by the present invention combines the processes of reverse injection method, solution reaction, dynamic gradient drying and two-stage roasting, and controls the crystallization kinetics and interface engineering in the preparation process to improve the activity, specific surface area and bulk density of magnesium oxide at the same time.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a preparation method of active magnesium oxide, and the preparation method includes the following steps:

[0011] (1) Reverse-injecting a magnesium-containing solution into a carbonate solution to obtain a mixed solution;

[0012] (2) Reacting the mixed solution, and then performing dynamic gradient drying to obtain a basic magnesium carbonate precursor; the dynamic gradient drying includes at least two drying stages;

[0013] (3) Performing two-stage roasting on the basic magnesium carbonate precursor to obtain the active magnesium oxide.

[0014] In the present invention, the "reverse injection" refers to an injection process that is completely opposite to the conventional process of injecting a carbonate solution into a magnesium-containing solution in the prior art, that is, injecting the magnesium-containing solution into the carbonate solution.

[0015] In the present invention, the "dynamic gradient drying" refers to drying the product in multiple stages with different temperatures.

[0016] The preparation method of active magnesium oxide provided by the present invention uses a specific reverse injection method to add a magnesium-containing solution into a carbonate solution to form a locally supersaturated region, then reacts the mixed solution and controls the homogenization of the solution during the reaction. Next, a dynamic gradient drying process is designed to continuously dry the reaction product in multiple stages, which can avoid the agglomeration phenomenon during the preparation of precursor particles. By controlling the crystallization kinetics of substances during the reaction and drying processes, a specific basic magnesium carbonate precursor is formed. Then, by controlling the interface engineering through a calcination process, the precursor particles are converted into magnesium oxide with a high defect state during a single calcination process, and a secondary calcination is continued to bond the interfaces between the particles to improve the bonding strength between the particles, while increasing the particle size, to obtain active magnesium oxide with a high bulk density. The present invention designs a preparation method with a specific process, and through controlling the crystallization kinetics and interface engineering between substances during the overall reaction process, the two cooperate with each other to prepare magnesium oxide with high activity, high specific surface area and high bulk density, making it effectively applicable to nickel-cobalt precipitation while being beneficial to the transportation and transfer of materials.

[0017] Preferably, the concentration of magnesium ions in the magnesium-containing solution in step (1) is 5-7 g / L, such as 5 g / L, 5.2 g / L, 5.4 g / L, 5.6 g / L, 5.8 g / L, 6 g / L, 6.2 g / L, 6.4 g / L, 6.6 g / L, 6.8 g / L or 7 g / L, etc.

[0018] Preferably, the magnesium-containing solution in step (1) includes a magnesium sulfate solution.

[0019] Preferably, the carbonate solution in step (1) includes any one or a combination of at least two of sodium carbonate, potassium carbonate, ammonium carbonate, ammonium bicarbonate, potassium bicarbonate or ammonium bicarbonate.

[0020] Preferably, the concentration of the carbonate solution in step (1) is 1-2 mol / L, such as 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2 mol / L, etc.

[0021] In the present invention, if the concentration of the carbonate solution is too low, the concentration of carbonate ions in the solution is too low, which will lead to a decrease in the specific surface area and activity of the prepared active magnesium oxide; if the concentration is too high, not only is there difficulty in dissolution, but also due to the too high concentration of carbonate ions in the solution, the bulk density of the prepared active magnesium oxide will decrease.

[0022] Preferably, the rate of the reverse injection in step (1) is 100 - 200 mL / min, such as 100 mL / min, 110 mL / min, 120 mL / min, 130 mL / min, 140 mL / min, 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min or 200 mL / min, etc.

[0023] Preferably, the molar ratio of magnesium ions to carbonate ions in the mixed solution obtained in step (1) is 1:(1 - 1.5), such as 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5, etc.

[0024] The present invention regulates the molar ratio of magnesium ions to carbonate ions in the mixed solution to form a locally supersaturated region, which is beneficial to the preparation of a specific whisker-like basic magnesium carbonate precursor, thereby improving the performance of the obtained active magnesium oxide.

[0025] Preferably, during the reverse injection in step (1), first stirring and first ultrasonic treatment are also carried out.

[0026] Preferably, the rotation speed of the first stirring is 250 - 400 rpm, such as 250 rpm, 275 rpm, 300 rpm, 325 rpm, 350 rpm, 375 rpm or 400 rpm, etc.

[0027] Preferably, the frequency of the first ultrasonic treatment is 30 - 50 kHz, such as 30 kHz, 32 kHz, 34 kHz, 36 kHz, 38 kHz, 40 kHz, 42 kHz, 44 kHz, 46 kHz, 48 kHz or 50 kHz, etc.; the power is 80 - 120 W, such as 80 W, 85 W, 90 W, 95 W, 100 W, 105 W, 110 W, 115 W or 120 W, etc.

[0028] Preferably, during the reaction in step (2), second stirring and second ultrasonic treatment are carried out.

[0029] In the present invention, the ultrasonic process is used to assist the stirring process during the reverse injection process and the reaction process, which can effectively improve the homogenization of the solution, is not only beneficial to the formation of whisker-like basic magnesium carbonate, but also beneficial to the growth of particles.

[0030] Preferably, the reaction time in step (2) is 0.5 - 5 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, etc.

[0031] Preferably, the rotation speed of the second stirring is 100 - 200 rpm, such as 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm or 200 rpm, etc.

[0032] Preferably, the frequency of the second ultrasonic wave is 30 - 50 kHz, such as 30 kHz, 32 kHz, 34 kHz, 36 kHz, 38 kHz, 40 kHz, 42 kHz, 44 kHz, 46 kHz, 48 kHz or 50 kHz, etc.; the power is 80 - 120 W, such as 80 W, 85 W, 90 W, 95 W, 100 W, 105 W, 110 W, 115 W or 120 W, etc.

[0033] Preferably, aging is carried out after the reaction in step (2).

[0034] Preferably, the aging time is 0.5 - 5 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, etc.

[0035] Preferably, solid - liquid separation and washing are carried out before the dynamic gradient drying in step (2) to obtain a solid product for dynamic gradient drying.

[0036] The solid product obtained after solid - liquid separation and washing in the present invention is the wet residue of basic magnesium carbonate.

[0037] Preferably, the dynamic gradient drying in step (2) is carried out under vacuum conditions.

[0038] The dynamic gradient drying process provided by the present invention dries the basic magnesium carbonate precursor, controls the moisture residue in the obtained product, and at the same time prevents particle aggregation, effectively improving the activity and specific surface area of the obtained magnesium oxide.

[0039] Preferably, the dynamic gradient drying in step (2) is a three - stage continuous drying, including a first drying stage, a second drying stage and a third drying stage carried out in sequence.

[0040] In the present invention, the specific process of the "dynamic gradient drying" includes: drying the separated and washed product using three drying stages with different temperatures.

[0041] Preferably, the temperature of the first drying stage is 60 - 90 °C, such as 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C or 90 °C, etc.

[0042] Preferably, the time of the first drying stage is 0.5 - 2 h, such as 0.5 h, 1 h, 1.5 h, or 2 h, etc.

[0043] Preferably, the temperature of the second drying stage is 100 - 150 °C, such as 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, or 150 °C, etc.

[0044] Preferably, the time of the second drying stage is 1 - 3 h, such as 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, etc.

[0045] Preferably, the temperature of the third drying stage is 50 - 70 °C, such as 50 °C, 55 °C, 60 °C, 65 °C, or 70 °C, etc.

[0046] Preferably, in the third drying stage until the moisture residue in the product obtained by the dynamic gradient drying is below 2 wt%, such as 2 wt%, 1.8 wt%, 1.6 wt%, 1.4 wt%, 1.2 wt%, or 1 wt%, etc.

[0047] In the present invention, the "moisture residue" refers to the percentage of the mass of water contained in the dried product to the total mass of the product.

[0048] Preferably, after the dynamic gradient drying in step (2), the structure of the magnesium basic carbonate precursor obtained is a whisker structure.

[0049] Preferably, the two-stage calcination in step (3) includes a first calcination and a second calcination carried out in sequence.

[0050] Preferably, the first calcination is carried out in an air atmosphere.

[0051] Preferably, the temperature of the first calcination is 400 - 500 °C, such as 400 °C, 420 °C, 440 °C, 460 °C, 480 °C, or 500 °C, etc.

[0052] Preferably, the time of the first calcination is 1 - 5 h, such as 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, etc.

[0053] In the first stage of calcination of the present invention, the whisker-like magnesium basic carbonate precursor material is calcined in an air atmosphere to generate magnesium oxide whiskers with high defects, improving the activity of magnesium oxide.

[0054] Preferably, the second calcination is carried out in a mixed gas.

[0055] Preferably, the mixed gas includes carbon dioxide.

[0056] Preferably, the mixed gas further includes any one of nitrogen or inert gas.

[0057] Preferably, in the mixed gas, the content of carbon dioxide accounts for 3-10 vol% of the total volume of the mixed gas, such as 3 vol%, 4 vol%, 5 vol%, 6 vol%, 7 vol%, 8 vol%, 9 vol% or 10 vol%, etc.

[0058] In the present invention, if the content of carbon dioxide in the mixed gas is too low, the bonding effect of the material interface will be poor, the particle size will be low, and the bulk density of the obtained active magnesium oxide cannot be effectively improved; if the content of carbon dioxide in the mixed gas is too high, the proportion of magnesium carbonate in the product will be relatively high, reducing the performance of active magnesium oxide.

[0059] Preferably, the temperature of the second calcination is 700-900 °C, such as 700 °C, 725 °C, 750 °C, 775 °C, 800 °C, 825 °C, 850 °C, 875 °C or 900 °C, etc.

[0060] Preferably, the time of the second calcination is 2-3 h, such as 2 h, 2.4 h, 2.6 h, 2.8 h or 3 h, etc.

[0061] In the present invention, higher temperature calcination is continued in the mixed gas containing carbon dioxide to form a magnesium carbonate coating layer on the surface of magnesium oxide, improve the particle bonding strength through MgCO3-MgO interface bonding, and at the same time, high temperature is beneficial to increasing the particle size. Continuing to calcine at high temperature, the magnesium carbonate in the coating layer will be converted into magnesium oxide, thereby preparing active magnesium oxide with high bulk density.

[0062] As a preferred technical method of the present invention, the preparation method of the active magnesium oxide includes the following steps:

[0063] S1. Inject the magnesium-containing solution reversely into the carbonate solution at a rate of 100-200 mL / min. During the reverse injection process, first stirring with a rotation speed of 250-400 rpm is carried out, and at the same time, first ultrasound with a frequency of 30-50 kHz and a power of 80-120 W is carried out to obtain a mixed solution; the molar ratio of magnesium ions to carbonate ions in the mixed solution is 1:(1-1.5), the concentration of magnesium ions in the magnesium-containing solution is 5-7 g / L, and the concentration of the carbonate solution is 1-2 mol / L.

[0064] S2. React the mixed solution under a second stirring at a rotation speed of 100 - 200 rpm for 0.5 - 5 h, with the assistance of a second ultrasound at a frequency of 30 - 50 kHz and a power of 80 - 120 W. Then, age the product obtained from the reaction for 0.5 - 5 h. Next, after solid-liquid separation and washing, a wet precursor residue is obtained.

[0065] S3. Perform dynamic gradient drying on the wet precursor residue. First, conduct a first drying at 60 - 90 °C for 0.5 - 2 h. Then, conduct a second drying at 100 - 150 °C for 1 - 3 h. Next, conduct a third drying at 50 - 70 °C until the moisture residue in the dried product is below 2 wt%, obtaining a whisker-like basic magnesium carbonate precursor.

[0066] S4. First, conduct a first calcination on the dried whisker-like basic magnesium carbonate precursor in an air atmosphere at a temperature of 400 - 500 °C for 1 - 5 h. Then, conduct a second calcination in nitrogen or an inert gas with a carbon dioxide content of 3 - 10 vol% at a temperature of 700 - 900 °C for 2 - 3 h to obtain the active magnesium oxide.

[0067] In a second aspect, the present invention provides an active magnesium oxide, which is prepared by the preparation method described in the first aspect.

[0068] The active magnesium oxide provided by the present invention is prepared by a specific preparation method and has the characteristics of high activity, high specific surface area, and high bulk density. It is suitable for nickel-cobalt precipitation and is conducive to the transportation and transfer of materials.

[0069] In a third aspect, the present invention provides an application of the active magnesium oxide described in the second aspect, and the active magnesium oxide is applied to the process of extracting mixed nickel-cobalt hydroxide from laterite nickel ore.

[0070] The active magnesium oxide provided by the present invention is applicable to any application field that those skilled in the art can think of.

[0071] Compared with the prior art, the present invention has at least the following beneficial effects:

[0072] The present invention designs a preparation method with a specific process. By designing processes such as reverse injection method, solution reaction, dynamic gradient drying, and two-stage calcination, the crystallization kinetics and interface engineering between substances in the overall reaction process are controlled. All processes cooperate with each other to jointly promote the preparation of magnesium oxide with high activity, high specific surface area, and high bulk density, enabling the obtained active magnesium oxide to be suitable for nickel-cobalt precipitation and facilitating the transportation and transfer of materials. Description of the Drawings

[0073] Figure 1It is the scanning electron microscope image of the active magnesium oxide prepared in Example 1 of the present invention.

[0074] Figure 2 It is the X-ray diffraction pattern of the active magnesium oxide prepared in Example 1 of the present invention.

[0075] Figure 3 It is the scanning electron microscope image of the magnesium oxide prepared in Comparative Example 1 of the present invention. Detailed implementation manners

[0076] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation manners. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0077] Example 1

[0078] This example provides a method for preparing active magnesium oxide, which includes the following steps:

[0079] S1. Inject the magnesium-containing solution reversely into the sodium carbonate solution at a rate of 150 mL / min. During the reverse injection process, it is accompanied by a first stirring at a rotation speed of 300 rpm, and at the same time, a first ultrasound with a frequency of 40 kHz and a power of 100 W is carried out to obtain a mixed solution; the molar ratio of magnesium ions to carbonate ions in the mixed solution is 1:1. The magnesium-containing solution is a magnesium sulfate solution, in which the concentration of magnesium ions is 6 g / L, and the concentration of the sodium carbonate solution is 2 mol / L.

[0080] S2. React the mixed solution obtained in step S1 under a second stirring at a rotation speed of 150 rpm for 2 h, and be assisted by a second ultrasound with a frequency of 40 kHz and a power of 100 W. Then, age the product obtained from the reaction for 2 h. Next, after solid-liquid separation and washing, a precursor wet residue is obtained.

[0081] S3. Carry out dynamic gradient drying on the precursor wet residue obtained in step S2. First, carry out a first drying at 80 °C for 1 h, then carry out a second drying at 120 °C for 2 h, and then carry out a third drying at 60 °C until the water residue in the dried product is 2 wt%, to obtain a whisker-like basic magnesium carbonate precursor.

[0082] S4. First, carry out a first calcination on the dried whisker-like basic magnesium carbonate precursor obtained in step S3 in an air atmosphere at a temperature of 450 °C for 3 h, and then carry out a second calcination in a nitrogen mixed gas with a carbon dioxide content of 3 vol% at a temperature of 800 °C for 2.5 h to obtain active magnesium oxide.

[0083] Example 2

[0084] This embodiment provides a method for preparing active magnesium oxide, which includes the following steps:

[0085] S1. Inject the magnesium-containing solution reversely into the sodium carbonate solution at a rate of 100 mL / min. During the reverse injection process, a first stirring with a rotation speed of 250 rpm is also carried out, and at the same time, a first ultrasonic wave with a frequency of 30 kHz and a power of 80 W is applied to obtain a mixed solution; the molar ratio of magnesium ions to carbonate ions in the mixed solution is 1:1. The magnesium-containing solution is a magnesium sulfate solution, in which the concentration of magnesium ions is 6 g / L, and the concentration of the sodium carbonate solution is 1.5 mol / L.

[0086] S2. React the mixed solution obtained in step S1 under a second stirring with a rotation speed of 100 rpm for 5 h, and assist it with a second ultrasonic wave with a frequency of 30 kHz and a power of 80 W. Then, age the product obtained from the reaction for 0.5 h. Next, after solid-liquid separation and washing, a precursor wet residue is obtained.

[0087] S3. Perform dynamic gradient drying on the precursor wet residue obtained in step S2. First, carry out a first drying at 60 °C for 2 h, then carry out a second drying at 100 °C for 3 h, and then carry out a third drying at 50 °C until the moisture residue in the dried product is 1.5 wt%, to obtain a dried whisker-like basic magnesium carbonate precursor.

[0088] S4. First, carry out a first calcination on the dried whisker-like basic magnesium carbonate precursor obtained in step S3 in an air atmosphere at a temperature of 400 °C for 5 h, and then carry out a second calcination in a nitrogen mixed gas with a carbon dioxide content of 10 vol% at a temperature of 750 °C for 3 h to obtain active magnesium oxide.

[0089] Example 3

[0090] This embodiment provides a method for preparing active magnesium oxide, which includes the following steps:

[0091] S1. Inject the magnesium-containing solution reversely into the sodium carbonate solution at a rate of 200 mL / min. During the reverse injection process, a first stirring with a rotation speed of 400 rpm is also carried out, and at the same time, a first ultrasonic wave with a frequency of 50 kHz and a power of 120 W is applied to obtain a mixed solution; the molar ratio of magnesium ions to carbonate ions in the mixed solution is 1:1. The magnesium-containing solution is a magnesium sulfate solution, in which the concentration of magnesium ions is 6 g / L, and the concentration of the sodium carbonate solution is 1 mol / L.

[0092] S2. React the mixed solution obtained in step S1 under the second stirring at a rotational speed of 200 rpm for 0.5 h, assisted by the second ultrasonic wave with a frequency of 50 kHz and a power of 120 W. Then, age the product obtained from the reaction for 5 h. Next, after solid-liquid separation and washing, a wet precursor residue is obtained.

[0093] S3. Perform dynamic gradient drying on the wet precursor residue obtained in step S2. First, conduct the first drying at 90 °C for 0.5 h, then conduct the second drying at 150 °C for 1 h, and then conduct the third drying at 70 °C until the moisture residue in the dried precursor product is 1 wt%, obtaining a dried whisker-shaped basic magnesium carbonate precursor.

[0094] S4. First, conduct the first calcination on the dried whisker-shaped basic magnesium carbonate precursor obtained in step S3 in an air atmosphere at a temperature of 500 °C for 3 h, and then conduct the second calcination in a nitrogen mixed gas with a carbon dioxide content of 5 vol% at a temperature of 900 °C for 2 h to obtain active magnesium oxide.

[0095] Example 4

[0096] This example provides a method for preparing active magnesium oxide, including the following steps:

[0097] S1. Inject the magnesium-containing solution reversely into the potassium carbonate solution at a rate of 160 mL / min. During the reverse injection process, it is also accompanied by the first stirring at a rotational speed of 350 rpm, and at the same time, the first ultrasonic wave with a frequency of 45 kHz and a power of 90 W is carried out to obtain a mixed solution; the molar ratio of magnesium ions to carbonate ions in the mixed solution is 1:1.5. The magnesium-containing solution is a magnesium sulfate solution, in which the concentration of magnesium ions is 5 g / L, and the concentration of the potassium carbonate solution is 1.6 mol / L.

[0098] S2. React the mixed solution obtained in step S1 under the second stirring at a rotational speed of 160 rpm for 2 h, assisted by the second ultrasonic wave with a frequency of 35 kHz and a power of 90 W. Then, age the product obtained from the reaction for 4 h. Next, after solid-liquid separation and washing, a wet precursor residue is obtained.

[0099] S3. Perform dynamic gradient drying on the wet precursor residue obtained in step S2. First, conduct the first drying at 80 °C for 2 h, then conduct the second drying at 110 °C for 3 h, and then conduct the third drying at 60 °C until the moisture residue in the dried precursor product is 1 wt%, obtaining a dried whisker-shaped basic magnesium carbonate precursor.

[0100] S4. The dried whisker-shaped basic magnesium carbonate precursor obtained in step S3 is first calcined in an air atmosphere at a temperature of 450 °C for 4 h, and then calcined in a nitrogen mixed gas with a carbon dioxide content of 7 vol% at a temperature of 850 °C for 2.5 h to obtain active magnesium oxide.

[0101] Example 5

[0102] The difference between this example and Example 1 is only that: the molar ratio of magnesium ions to carbonate ions in the mixed solution obtained in step S1 is 1:0.5. The rest are the same as in Example 1.

[0103] Example 6

[0104] The difference between this example and Example 1 is only that: the molar ratio of magnesium ions to carbonate ions in the mixed solution obtained in step S1 is 1:2. The rest are the same as in Example 1.

[0105] Example 7

[0106] The difference between this example and Example 1 is only that: the concentration of the sodium carbonate solution used in step S1 is 0.5 mol / L. The rest are the same as in Example 1.

[0107] Example 8

[0108] The difference between this example and Example 1 is only that: the concentration of the sodium carbonate solution used in step S1 is 2.5 mol / L. The rest are the same as in Example 1.

[0109] Example 9

[0110] The difference between this example and Example 1 is only that: steps S2 and the second ultrasound and second ultrasound-assisted process used in step S1 are omitted, and only the stirring process is carried out. The rest are the same as in Example 1.

[0111] Example 10

[0112] The difference between this example and Example 1 is only that: the third drying in step S3 is omitted, and only the first drying is carried out at 80 °C for 1 h, and then the second drying is carried out at 120 °C for 2 h. The rest are the same as in Example 1.

[0113] Example 11

[0114] The difference between this example and Example 1 is only that: the carbon dioxide in the second calcination mixed gas is omitted in step S4, and the second calcination is directly carried out in nitrogen at a temperature of 800 °C for 2.5 h. The rest are the same as in Example 1.

[0115] Comparative Example 1

[0116] The difference between this comparative example and Example 1 is only that in step S1, the sodium carbonate solution is added to the magnesium-containing solution at a rate of 150 mL / min. The rest of the content is the same as that of Example 1.

[0117] Comparative Example 2

[0118] The difference between this comparative example and Example 1 is only that in step S3, the wet precursor slag obtained in step S2 is directly dried at 100 °C for 8 h, and the residual moisture content in the dried product is below 2 wt% to obtain the dried basic magnesium carbonate precursor; meanwhile, in step S4, the second calcination process is omitted, and it is directly calcined in an air atmosphere at a temperature of 450 °C for 2 h. The rest of the content is the same as that of Example 1.

[0119] Comparative Example 3

[0120] The difference between this comparative example and Example 1 is only that in step S3, the wet precursor slag obtained in step S2 is directly dried at 100 °C for 8 h, and the residual moisture content in the dried product is below 2 wt% to obtain the dried basic magnesium carbonate precursor. The rest of the content is the same as that of Example 1.

[0121] Comparative Example 4

[0122] The difference between this comparative example and Example 1 is only that in step S4, the first calcination process is omitted, and the dried whisker-like basic magnesium carbonate precursor is directly calcined in a nitrogen mixed gas with a carbon dioxide content of 3 vol% at a temperature of 800 °C for 2.5 h. The rest of the content is the same as that of Example 1.

[0123] The products obtained by the preparation methods provided in Examples 1 - 11 and Comparative Examples 1 - 4 were tested for citric acid activity, specific surface area, and bulk density. The specific test conditions were as follows: For the determination of citric acid activity, refer to "Method for Determining the Chemical Activity of Light-Burned Magnesium Oxide" (YB / T 4019 - 2020). The specific surface area was measured using a specific surface area analyzer, and the bulk density was obtained by the vibration method to measure the volume and mass of the sample, and finally the bulk density was calculated. The test results are shown in Table 1:

[0124] Table 1

[0125]

[0126]

[0127] It can be seen from the test results that:

[0128] (1) It can be seen from Examples 1 to 4 that the preparation method of active magnesium oxide provided by the present invention combines the processes of reverse injection method, solution reaction, dynamic gradient drying and two-stage calcination. By controlling the crystallization kinetics and interface engineering in the preparation process, the activity, specific surface area and bulk density of magnesium oxide are improved simultaneously.

[0129] Figure 1 The scanning electron microscope image of the active magnesium oxide prepared in Example 1 is given. It can be Figure 1 seen that the active magnesium oxide prepared in Example 1 is a whisker structure with relatively large size, and the morphology is regular and uniform.

[0130] Figure 2 The X-ray diffraction pattern of the active magnesium oxide prepared in Example 1 is given. It can be Figure 2 seen that the preparation method provided in Example 1 successfully prepares magnesium oxide with good crystallinity.

[0131] (2) By comparing Example 1 with Examples 5-6, it can be seen that if the molar ratio of magnesium ions to carbonate ions in the mixed solution of the present invention is too high, there will be no excess carbonate for particle growth after rapid nucleation. Although the specific surface area of the obtained product is relatively large, the bulk density is low; if the molar ratio of magnesium ions to carbonate ions in the mixed solution is too low, the precursor grows excessively, resulting in relatively large particles. Although the bulk density of the obtained magnesium oxide is high, its activity and specific surface area are both small.

[0132] (3) By comparing Example 1 with Examples 7-8, it can be seen that if the concentration of the carbonate solution is too low, the specific surface area and activity of the prepared active magnesium oxide will decrease; if the concentration is too high, the bulk density of the prepared active magnesium oxide will decrease.

[0133] (4) By comparing Example 1 with Example 9, it can be seen that if the second ultrasonic-assisted process is omitted in step S2 of the present invention, the homogenization of the solution will become poor, thus affecting the performance of the obtained magnesium oxide.

[0134] (5) By comparing Example 1 with Example 10, it can be seen that if the third drying process is omitted and only the first drying and second drying processes are carried out in the present invention, the dehydration of the precursor will be incomplete, reducing the activity of magnesium oxide.

[0135] (6) By comparing Example 1 with Example 11, it can be seen that if the carbon dioxide gas used in the secondary calcination in the two-stage calcination process is omitted in the present invention, the particles will be fine, resulting in a low bulk density.

[0136] (7) It can be seen from the comparison between Example 1 and Comparative Example 1 that if the carbonate solution is added to the magnesium-containing solution in the present invention, the activity of the obtained magnesium oxide will decrease sharply, and the specific surface area and bulk density will decrease significantly.

[0137] Figure 3 The scanning electron microscope image of the magnesium oxide prepared in Comparative Example 1 is given. It can be seen from the figure that in the forward addition method, that is, adding the carbonate solution to the magnesium-containing solution, the shape of the obtained magnesium oxide is irregular and uneven.

[0138] (8) It can be seen from the comparison between Example 1 and Comparative Examples 2-4 that if the three-stage dynamic gradient drying in the present invention is replaced by one-stage drying, or the two-stage calcination is replaced by any one-time calcination, the activity, specific surface area and bulk density of the prepared magnesium oxide will all decrease.

[0139] In summary, the present invention designs a preparation method with a specific process. By designing the process of reverse injection method, solution reaction, dynamic gradient drying and two-stage calcination, the crystallization kinetics and interface engineering between substances in the overall reaction process are controlled. All processes cooperate with each other to jointly promote the preparation of magnesium oxide with high activity, high specific surface area and high bulk density, so that the obtained active magnesium oxide can be applicable to nickel-cobalt precipitation while being beneficial to the transportation and transfer of materials.

[0140] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A preparation method of active magnesium oxide, characterized in that, The preparation method includes the following steps: (1) Inject the magnesium-containing solution into the carbonate solution in a reverse direction to obtain a mixed solution; (2) React the mixed solution, and then perform dynamic gradient drying to obtain a basic magnesium carbonate precursor; the dynamic gradient drying includes at least two drying stages; (3) Perform two-stage calcination on the basic magnesium carbonate precursor to obtain the active magnesium oxide.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of magnesium ions in the magnesium-containing solution is 5-7 g / L; Preferably, in step (1), the concentration of the carbonate solution is 1-2 mol / L; Preferably, in step (1), the reverse injection rate of the magnesium-containing solution is 100-200 mL / min; Preferably, in step (1), the molar ratio of magnesium ions to carbonate ions in the obtained mixed solution is 1:(1-1.5).

3. The preparation method according to claim 1 or 2, characterized in that, During the reverse injection in step (1), first stirring and first ultrasonic treatment are also carried out; Preferably, the rotation speed of the first stirring is 250-400 rpm; Preferably, the frequency of the first ultrasonic treatment is 30-50 kHz, and the power is 80-120 W.

4. The preparation method according to any one of claims 1-3, characterized in that, During the reaction in step (2), second stirring and second ultrasonic treatment are also carried out; Preferably, the reaction time in step (2) is 0.5-5 h; Preferably, the rotation speed of the second stirring is 100-200 rpm; Preferably, the frequency of the second ultrasonic treatment is 30-50 kHz, and the power is 80-120 W; Preferably, aging is carried out after the reaction in step (2); Preferably, the aging time is 0.5-5 h.

5. The preparation method according to any one of claims 1-4, characterized in that, Before the dynamic gradient drying in step (2), solid-liquid separation and washing are also carried out to obtain a solid product for dynamic gradient drying.

6. The preparation method according to any one of claims 1-5, characterized in that, The dynamic gradient drying in step (2) is carried out under vacuum conditions; Preferably, the dynamic gradient drying in step (2) is three-stage continuous drying, including a first drying stage, a second drying stage, and a third drying stage carried out sequentially in order; Preferably, the temperature of the first drying stage is 60-90 °C; Preferably, the time of the first drying stage is 0.5-2 h; Preferably, the temperature of the second drying stage is 100-150 °C; Preferably, the time of the second drying stage is 1-3 h; Preferably, the temperature of the third drying stage is 50-70 °C; Preferably, until the water residue in the product obtained by the dynamic gradient drying in the third drying stage is below 2 wt%; Preferably, after the dynamic gradient drying in step (2), the structure of the obtained basic magnesium carbonate precursor is a whisker structure.

7. The preparation method according to any one of claims 1-6, characterized in that, The two-stage calcination in step (3) includes a first calcination and a second calcination carried out sequentially; Preferably, the first calcination is carried out in an air atmosphere; Preferably, the temperature of the first calcination is 400-500 °C; Preferably, the time of the first calcination is 1-5 h.

8. The preparation method according to claim 7, characterized in that, The second calcination is carried out in a mixed gas; Preferably, the mixed gas includes carbon dioxide; Preferably, the mixed gas further includes any one of nitrogen or inert gas; Preferably, in the mixed gas, the content of the carbon dioxide accounts for 3-10 vol% of the total volume of the mixed gas; Preferably, the temperature of the second roasting is 700-900 °C; Preferably, the time of the second roasting is 2-3 h.

9. An active magnesium oxide, characterized in that, The active magnesium oxide is prepared by the preparation method described in any one of claims 1-8.

10. The application of the active magnesium oxide according to claim 9, characterized in that, The active magnesium oxide is applied to the process of extracting mixed nickel-cobalt hydroxide from laterite nickel ore.

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