Preparation method and application of a fly ash-doped modified porous magnesium oxide adsorbent

Abstract

This invention relates to a method for preparing and applying a modified porous magnesium oxide adsorbent doped with fly ash, belonging to the field of inorganic adsorbent technology. The invention involves adding fly ash to a sodium hydroxide solution and leaching it with an alkaline solution for 1-5 hours under stirring to obtain alkaline-leached fly ash. Pyrolytic magnesium oxide, a surfactant, and deionized water are mixed evenly and added to a high-pressure reactor. A hydrothermal reaction is carried out at 80-200℃ for 0.5-6 hours, resulting in the hydration of magnesium oxide to form magnesium hydroxide. Magnesium hydroxide, alkaline-leached fly ash, and deionized water are then mixed evenly, heated under stirring, and evaporated to dryness at a constant temperature to obtain fly ash-doped hydrated magnesium hydroxide. The fly ash-doped hydrated magnesium hydroxide is then calcined in air at 400-800℃ for 0.5-4 hours to obtain the modified porous magnesium oxide adsorbent doped with fly ash. This invention, by doping with fly ash, uses fly ash as a structural framework, fundamentally reducing the agglomeration of magnesium oxide and increasing its porosity and specific surface area.

Description

Technical Field

[0001] This invention relates to a method for preparing and applying a modified porous magnesium oxide adsorbent doped with fly ash, belonging to the field of inorganic adsorbent technology. Background Technology

[0002] my country possesses extremely rich magnesium resources, and their effective utilization and development will bring enormous benefits to the ecology and environment. The lateritic nickel ore in Yunnan, China, is characterized by low nickel-iron content and high silicon-magnesium content. After pressure leaching with nitric acid, a leachate containing iron, chromium, aluminum, scandium, nickel, cobalt, manganese, and magnesium is obtained. Due to the difference in pH value, selective precipitation occurs, achieving the separation of magnesium metal ions from other metal ions. However, due to technological limitations, the magnesium oxide recovered from the lateritic nickel ore through acid leaching is of low purity and contains trace impurities, the contents of which are shown in Table 1.

[0003] Table 1-1. MgO element and its content.

[0004]

[0005] It is evident that the large amount of magnesium oxide containing trace impurities recovered from laterite nickel ore by acid leaching is limited in its use due to its low purity and cannot achieve high added value utilization. Summary of the Invention

[0006] To address the problem that existing technologies for recovering large quantities of magnesium oxide containing trace impurities from laterite nickel ore through acid leaching limit its use due to low purity and prevent its high-value-added utilization, this invention proposes a method for preparing a modified porous magnesium oxide adsorbent doped with fly ash. This invention uses high-silica magnesium-type laterite nickel ore as raw material, which is obtained by pressure leaching with nitric acid followed by magnesium precipitation and roasting to obtain pyrolytic magnesium oxide. Through a hydrothermal method, the hydration of large-particle pyrolytic magnesium oxide raw material is controlled to form magnesium hydroxide. Under the action of a surfactant, this hydroxide is dispersed and recrystallized to form a nanosheet structure. Then, alkaline-leached fly ash is used as a framework for doping followed by high-temperature treatment. As the moisture evaporates, a fly ash-doped modified porous magnesium oxide nanosheet adsorbent material is formed, realizing the high-value conversion and application of low-value magnesium oxide raw materials.

[0007] A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, comprising the following specific steps:

[0008] (1) Add fly ash to sodium hydroxide solution and leach it with an alkaline solution for 1 to 5 hours under stirring to obtain alkaline-leached fly ash;

[0009] (2) Pyrolytic magnesium oxide, surfactant and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 80-200℃ for 0.5-6 hours. Magnesium oxide is hydrated to form magnesium hydroxide.

[0010] (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash.

[0011] (4) Step (3) The hydrated magnesium hydroxide doped with fly ash is placed in an air atmosphere and calcined at a temperature of 400-800℃ for 0.5-4h to obtain modified porous magnesium oxide adsorbent doped with fly ash.

[0012] By mass percentage, the fly ash in step (1) contains 37.42–41.14% SiO2, 5.28–5.74% CaO, 13.12–16.42% Al2O3, and 3.25–3.65% Fe2O3.

[0013] In step (1), the concentration of the sodium hydroxide solution is 4-8 mol / L, and the solid-liquid ratio of fly ash to sodium hydroxide solution (g:mL) is 1-3:10.

[0014] The pyrolytic magnesium oxide in step (2) is obtained by leaching high-silica magnesium-type laterite nickel ore under pressure with nitric acid, followed by magnesium precipitation and roasting.

[0015] The pyrolytic magnesium oxide in step (2) contains Ca, Fe, Al and Si elements; the pyrolytic magnesium oxide is spherical with a particle size of 10-100 μm; the surfactant is one or more of sodium citrate, hexadecyltrimethylammonium bromide, N,N-dimethylformamide, dioxane, and urea.

[0016] In step (2), the mass ratio of pyrolyzed magnesium oxide, surfactant and deionized water is 1:0.01-0.2:20-40.

[0017] In step (3), the mass ratio of magnesium hydroxide, alkaline-leached fly ash, and deionized water is 1:0.01-0.1:1.5-2.

[0018] The temperature for constant temperature evaporation in step (3) is 60-80℃.

[0019] The application of the modified porous magnesium oxide adsorbent doped with fly ash in adsorbing heavy metal ions in the solution.

[0020] The heavy metal ion is Cr. 6+ Pb 2+ Zn 2+ Cu 2+ One or more of them.

[0021] The beneficial effects of this invention are:

[0022] (1) In view of the problem that the large amount of magnesium oxide containing trace impurities recovered from acid leaching in laterite nickel ore is limited in use due to its low purity and cannot achieve high added value utilization, this invention uses such pyrolytic magnesium oxide as raw material, and after modification and doping, prepares high-performance fly ash doped and modified porous magnesium oxide nanosheet adsorbent material, which can realize the high-value conversion and application of low-value magnesium oxide raw material.

[0023] (2) This invention addresses the problem that magnesium hydroxide is prone to structural collapse during sintering, leading to agglomeration and decreased porosity. By doping with fly ash, using fly ash as the structural framework, the agglomeration of magnesium oxide is fundamentally reduced, its porosity and specific surface area are improved, and it has a better adsorption effect.

[0024] (3) The modified porous magnesium oxide adsorbent doped with fly ash of the present invention has the characteristics of excellent adsorption effect and high removal rate for heavy metal ions in solution. Attached Figure Description

[0025] Figure 1 The XRD diffraction pattern of pyrolytic magnesium oxide;

[0026] Figure 2 SEM images of the adsorbents in Comparative Examples 1, 2, 4 and 1. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0028] In the embodiments and comparative examples of this invention, the fly ash contained 37.42% SiO2, 5.74% CaO, 13.12% Al2O3, and 3.65% Fe2O3 by mass percentage. The pyrolytic magnesium oxide was obtained by pressure leaching of high-silica magnesium-type laterite nickel ore with nitric acid, followed by magnesium precipitation and roasting. The XRD diffraction pattern of the pyrolytic magnesium oxide is shown below. Figure 1 Pyrolytic magnesium oxide contains trace amounts of Ca, Fe, Al and Si elements; pyrolytic magnesium oxide is spherical with a particle size of 10-100 μm.

[0029] Example 1: A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, the specific steps of which are as follows:

[0030] (1) Fly ash was added to a sodium hydroxide solution with a concentration of 6 mol / L and subjected to alkaline leaching for 3 h under stirring to obtain alkaline leached fly ash; the solid-liquid ratio of the fly ash to the sodium hydroxide solution was 1:10 g:mL.

[0031] (2) Pyrolytic magnesium oxide, surfactant (sodium citrate) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 120°C for 2 hours. Magnesium oxide is converted into magnesium hydroxide after the hydrothermal reaction. The mass ratio of pyrolytic magnesium oxide, surfactant (sodium citrate) and deionized water is 1:0.1:20.

[0032] (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat to 80°C under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash; the mass ratio of magnesium hydroxide, alkali-leached fly ash, and deionized water is 1:0.1:1.5.

[0033] (4) Step (3) hydrated magnesium hydroxide doped with fly ash was calcined in air at 600℃ for 2 hours to obtain modified porous magnesium oxide adsorbent doped with fly ash.

[0034] 0.5g of the modified porous magnesium oxide adsorbent doped with fly ash from this embodiment was added to 20mL of a Cr solution with a concentration of 300mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate;

[0035] This embodiment Cr 6+ The removal rate was 99.95%.

[0036] Comparative Example 1: Using pyrolytic magnesium oxide as an adsorbent, 0.5 g of pyrolytic magnesium oxide was added to 20 mL of a Cr solution with a concentration of 300 mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate.

[0037] Comparative Example 2: Preparation method of modified porous MgO, the specific steps are as follows:

[0038] (1) Pyrolytic magnesium oxide, surfactant (sodium citrate) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 120°C for 2 hours. Magnesium oxide is hydrated to form magnesium hydroxide. The mass ratio of pyrolytic magnesium oxide, surfactant (sodium citrate) and deionized water is 1:0.1:20.

[0039] (2) Hydrated magnesium hydroxide was calcined in air at 600°C for 2 hours to obtain modified porous magnesium oxide adsorbent;

[0040] 0.5 g of modified porous magnesium oxide adsorbent was added to 20 mL of Cr solution with a concentration of 300 mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate.

[0041] Comparative Example 3: Using fly ash as an adsorbent, 0.5 g of fly ash was added to 20 mL of a Cr solution with a concentration of 300 mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate.

[0042] Comparative Example 4: Using alkaline-leached fly ash as an adsorbent, 0.5 g of alkaline-leached fly ash was added to 20 mL of a Cr solution with a concentration of 300 mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate;

[0043] The specific steps for preparing alkaline-leached fly ash are as follows:

[0044] Fly ash was added to a 6 mol / L sodium hydroxide solution and subjected to alkaline leaching for 3 hours under stirring to obtain alkaline-leached fly ash; the solid-liquid ratio of the fly ash to the sodium hydroxide solution was 1:10 g:mL.

[0045] Comparative Example 5: Preparation method of modified porous magnesium oxide by doping with untreated fly ash, the specific steps are as follows:

[0046] (1) Pyrolytic magnesium oxide, surfactant (sodium citrate) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 120°C for 2 hours. Magnesium oxide is hydrated to form magnesium hydroxide. The mass ratio of pyrolytic magnesium oxide, surfactant (sodium citrate) and deionized water is 1:0.1:20.

[0047] (2) Mix magnesium hydroxide, fly ash raw material and deionized water from step (1) evenly, heat to 80°C under stirring and evaporate to dryness at constant temperature to obtain fly ash-doped hydrated magnesium hydroxide; the mass ratio of magnesium hydroxide, fly ash and deionized water is 1:0.1:1.5.

[0048] (3) Step (2) hydrated magnesium hydroxide doped with fly ash was calcined in air at 600°C for 2 hours to obtain modified porous magnesium oxide adsorbent doped with untreated fly ash.

[0049] 0.5 g of modified porous magnesium oxide adsorbent doped with untreated fly ash was added to 20 mL of Cr solution with a concentration of 300 mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate.

[0050] Comparative Example 6: A method for preparing adsorbents by directly doping alkaline-leached fly ash with magnesium oxide as raw material, the specific steps of which are as follows:

[0051] (1) Fly ash was added to a sodium hydroxide solution with a concentration of 6 mol / L and subjected to alkaline leaching for 3 h under stirring to obtain alkaline leached fly ash; the solid-liquid ratio of the fly ash to the sodium hydroxide solution was 1:10 g:mL.

[0052] (2) Mix magnesium oxide raw material, alkaline leached fly ash from step (1) and deionized water evenly, heat to 80°C under stirring and dry at constant temperature, and then calcine in air at 600°C for 2 hours to obtain an adsorbent for direct doping of magnesium oxide raw material with alkaline leached fly ash.

[0053] 0.5g of alkaline-leached fly ash directly mixed with magnesium oxide adsorbent was added to 20mL of a 300mg / L Cr solution. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate;

[0054] SEM images of the adsorbents in Comparative Examples 1, 2, 4 and 1 are shown below. Figure 2 Pyrolytic magnesium oxide adsorbent (a), modified porous MgO adsorbent of Comparative Example 2 (b), alkaline-leached fly ash adsorbent of Comparative Example 4 (c), and modified porous magnesium oxide doped with fly ash from Example 1 (d), from Figure 2 (a) It can be seen that pyrolytic magnesium oxide is generally spherical or nearly spherical and has severe agglomeration, resulting in poor dispersibility. (b) The MgO obtained after modification with the modifier exhibits hexagonal flakes with a rough surface and fine pores. (c) Alkali-leached fly ash exhibits a rounded spherical bead structure with a dense and smooth surface. In the modified porous magnesium oxide (d) with fly ash as the structural framework, magnesium oxide adheres to its surface, fundamentally reducing magnesium oxide agglomeration and achieving uniform dispersion, thereby improving its porosity and specific surface area.

[0055] Example 1 and Comparative Adsorbent Cr 6+ The removal rate is shown in Table 2.

[0056] Table 2. Cr content of the adsorbents in Example 1 and the comparative example. 6+ Removal rate

[0057]

[0058] As shown in Table 2, both raw materials MgO (Comparative Example 1) and fly ash (Comparative Example 3) exhibited poor adsorption effects without treatment. However, by controlling the hydration of large-particle pyrolytic magnesium oxide raw materials through a hydrothermal process to form magnesium hydroxide, and simultaneously dispersing and recrystallizing it under the action of surfactants to form a nanosheet structure, and then using alkaline-leached fly ash as a skeleton for doping and high-temperature treatment, the fly ash-doped and modified porous magnesium oxide nanosheet adsorbent material formed with the evaporation of water has excellent heavy metal ion adsorption effect, successfully realizing the high-value conversion and application of low-value magnesium oxide raw materials and waste fly ash resources.

[0059] Example 2: By mass percentage, the fly ash in this example contains 41.14% SiO2, 5.28% CaO, 16.42% Al2O3, and 3.65% Fe2O3. The pyrolytic magnesium oxide is obtained by leaching high-silica magnesium-type laterite nickel ore under pressure with nitric acid, followed by magnesium precipitation and roasting. The pyrolytic magnesium oxide contains trace amounts of Ca, Fe, Al, and Si elements. The pyrolytic magnesium oxide is spherical with a particle size of 10–100 μm.

[0060] A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, comprising the following specific steps:

[0061] (1) Fly ash was added to a sodium hydroxide solution with a concentration of 4 mol / L and subjected to alkaline leaching for 5 h under stirring to obtain alkaline-leached fly ash; the solid-liquid ratio of fly ash to sodium hydroxide solution was 2:10 g:mL.

[0062] (2) Pyrolytic magnesium oxide, surfactant (hexadecyltrimethylammonium bromide) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 80°C for 3 hours. The magnesium oxide is hydrated to form magnesium hydroxide. The mass ratio of pyrolytic magnesium oxide, surfactant (hexadecyltrimethylammonium bromide) and deionized water is 1:0.105:25.

[0063] (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat to 80°C under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash; the mass ratio of magnesium hydroxide, alkali-leached fly ash, and deionized water is 1:0.1:1.8.

[0064] (4) Step (3) hydrated magnesium hydroxide doped with fly ash was calcined in air at 400°C for 4 hours to obtain modified porous magnesium oxide adsorbent doped with fly ash.

[0065] 0.5g of the modified porous magnesium oxide adsorbent doped with fly ash from this embodiment was added to 20mL of a Cr solution with a concentration of 300mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated.6+ Removal rate;

[0066] This embodiment Cr 6+ The removal rate was 86%.

[0067] Example 3: By mass percentage, the fly ash in this example contains 39.45% SiO2, 5.64% CaO, 14.19% Al2O3, and 3.45% Fe2O3. The pyrolytic magnesium oxide is obtained by leaching high-silica magnesium-type laterite nickel ore under pressure with nitric acid, followed by magnesium precipitation and roasting. The pyrolytic magnesium oxide contains trace amounts of Ca, Fe, Al, and Si elements. The pyrolytic magnesium oxide is spherical with a particle size of 10–100 μm.

[0068] A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, comprising the following specific steps:

[0069] (1) Add fly ash to a sodium hydroxide solution with a concentration of 5 mol / L and alkali leaching for 3 h under stirring to obtain alkali-leached fly ash; the solid-liquid ratio of fly ash to sodium hydroxide solution is 3:10 g:mL.

[0070] (2) Pyrolytic magnesium oxide, surfactant (N,N-dimethylformamide) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 160°C for 1 hour. The magnesium oxide is hydrated to form magnesium hydroxide. The mass ratio of pyrolytic magnesium oxide, surfactant (N,N-dimethylformamide) and deionized water is 1:0.2:30.

[0071] (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat to 80°C under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash; the mass ratio of magnesium hydroxide, alkali-leached fly ash, and deionized water is 1:0.09:1.5.

[0072] (4) Step (3) hydrated magnesium hydroxide doped with fly ash was calcined in air at 500°C for 3 hours to obtain modified porous magnesium oxide adsorbent doped with fly ash.

[0073] 0.5g of the modified porous magnesium oxide adsorbent doped with fly ash from this embodiment was added to 20mL of a Cr solution with a concentration of 300mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate;

[0074] This embodiment Cr 6+ The removal rate was 80%.

[0075] Example 4: By mass percentage, the fly ash in this example contains 39.14% SiO2, 5.54% CaO, 15.12% Al2O3, and 3.54% Fe2O3. The pyrolytic magnesium oxide is obtained by leaching high-silica magnesium-type laterite nickel ore under pressure with nitric acid, followed by magnesium precipitation and roasting. The pyrolytic magnesium oxide contains trace amounts of Ca, Fe, Al, and Si elements. The pyrolytic magnesium oxide is spherical with a particle size of 10–100 μm.

[0076] A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, comprising the following specific steps:

[0077] (1) Fly ash was added to a sodium hydroxide solution with a concentration of 7 mol / L and subjected to alkaline leaching for 2 hours under stirring to obtain alkaline-leached fly ash; the solid-liquid ratio of the fly ash to the sodium hydroxide solution was 1:10 g:mL.

[0078] (2) Pyrolytic magnesium oxide, surfactant (dioxane) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 120°C for 2 hours. Magnesium oxide is hydrated to form magnesium hydroxide. The mass ratio of pyrolytic magnesium oxide, surfactant (dioxane) and deionized water is 1:0.1:40.

[0079] (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat to 80°C under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash; the mass ratio of magnesium hydroxide, alkali-leached fly ash, and deionized water is 1:0.01:1.5.

[0080] (4) Step (3) hydrated magnesium hydroxide doped with fly ash was calcined in air at 400°C for 4 hours to obtain modified porous magnesium oxide adsorbent doped with fly ash.

[0081] 0.5g of the modified porous magnesium oxide adsorbent doped with fly ash from this embodiment was added to 20mL of a Cr solution with a concentration of 300mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate;

[0082] This embodiment Cr 6+ The removal rate was 88%.

[0083] Example 5: By mass percentage, the fly ash in this example contains 40.18% SiO2, 5.64% CaO, 16.12% Al2O3, and 3.38% Fe2O3. The pyrolytic magnesium oxide is obtained by leaching high-silica magnesium-type laterite nickel ore under pressure with nitric acid, followed by magnesium precipitation and roasting. The pyrolytic magnesium oxide contains trace amounts of Ca, Fe, Al, and Si elements. The pyrolytic magnesium oxide is spherical with a particle size of 10–100 μm.

[0084] A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, comprising the following specific steps:

[0085] (1) Add fly ash to a sodium hydroxide solution with a concentration of 5 mol / L and alkali leaching for 4 h under stirring to obtain alkali-leached fly ash; the solid-liquid ratio of fly ash to sodium hydroxide solution is 1:10 g:mL.

[0086] (2) Pyrolytic magnesium oxide, surfactant (urea) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 180°C for 2 hours. Magnesium oxide is hydrated to form magnesium hydroxide. The mass ratio of pyrolytic magnesium oxide, surfactant (urea) and deionized water is 1:0.1:30.

[0087] (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat to 80°C under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash; the mass ratio of magnesium hydroxide, alkali-leached fly ash, and deionized water is 1:0.055:1.5.

[0088] (4) Step (3) hydrated magnesium hydroxide doped with fly ash was calcined in air at 800℃ for 3 hours to obtain modified porous magnesium oxide adsorbent doped with fly ash.

[0089] 0.5g of the modified porous magnesium oxide adsorbent doped with fly ash from this embodiment was added to 20mL of a Cr solution with a concentration of 300mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate;

[0090] This embodiment Cr 6+ The removal rate was 79%.

[0091] Example 6: The fly ash in this example is the same as that in Example 1 by mass percentage; the pyrolytic magnesium oxide is obtained by high-silica magnesium-type laterite nickel ore after pressure leaching with nitric acid, followed by magnesium precipitation and roasting. The pyrolytic magnesium oxide contains trace amounts of Ca, Fe, Al and Si elements; the pyrolytic magnesium oxide is spherical with a particle size of 10-100 μm.

[0092] A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, comprising the following specific steps:

[0093] (1) Add fly ash to a sodium hydroxide solution with a concentration of 4 mol / L and leach it under stirring for 5 h to obtain alkali-leached fly ash; the solid-liquid ratio of fly ash to sodium hydroxide solution is 1:10 g:mL.

[0094] (2) Pyrolytic magnesium oxide, surfactant (N,N-dimethylformamide) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 200°C for 1 hour. The magnesium oxide is hydrated to form magnesium hydroxide. The mass ratio of pyrolytic magnesium oxide, surfactant (N,N-dimethylformamide) and deionized water is 1:0.1:20.

[0095] (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat to 80°C under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash; the mass ratio of magnesium hydroxide, alkali-leached fly ash, and deionized water is 1:0.1:2.

[0096] (4) Step (3) hydrated magnesium hydroxide doped with fly ash was calcined in air at 400°C for 4 hours to obtain modified porous magnesium oxide adsorbent doped with fly ash.

[0097] 0.5g of the modified porous magnesium oxide adsorbent doped with fly ash from this embodiment was added to 20mL of a Cr solution with a concentration of 300mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate;

[0098] This embodiment Cr 6+ The removal rate was 76%.

[0099] Example 7: The fly ash in this example is the same as that in Example 2 by mass percentage; the pyrolytic magnesium oxide is obtained by high-silica magnesium-type laterite nickel ore after pressure leaching with nitric acid, followed by magnesium precipitation and roasting. The pyrolytic magnesium oxide contains trace amounts of Ca, Fe, Al and Si elements; the pyrolytic magnesium oxide is spherical with a particle size of 10-100 μm.

[0100] A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, comprising the following specific steps:

[0101] (1) Add fly ash to a sodium hydroxide solution with a concentration of 6 mol / L and alkali leaching for 2 h under stirring to obtain alkali-leached fly ash; the solid-liquid ratio of fly ash to sodium hydroxide solution is 1:10 g:mL.

[0102] (2) Pyrolytic magnesium oxide, surfactant (sodium citrate) and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 120°C for 2 hours. Magnesium oxide is hydrated to form magnesium hydroxide. The mass ratio of pyrolytic magnesium oxide, surfactant (sodium citrate) and deionized water is 1:0.1:20.

[0103] (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat to 80°C under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash; the mass ratio of magnesium hydroxide, alkali-leached fly ash, and deionized water is 1:0.1:1.75.

[0104] (4) Step (3) hydrated magnesium hydroxide doped with fly ash is calcined in air at 800℃ for 0.5h to obtain modified porous magnesium oxide adsorbent doped with fly ash.

[0105] 0.5g of the modified porous magnesium oxide adsorbent doped with fly ash from this embodiment was added to 20mL of a Cr solution with a concentration of 300mg / L. 6+ After adsorption by shaking in the solution for 3 hours, the Cr content in the solution was calculated. 6+ Removal rate;

[0106] This embodiment Cr 6+ The removal rate was 84%.

[0107] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing a modified porous magnesium oxide adsorbent doped with fly ash, characterized in that, The specific steps are as follows: (1) Add fly ash to sodium hydroxide solution and leach it with an alkaline solution for 1-5 hours under stirring to obtain alkaline-leached fly ash; (2) Pyrolytic magnesium oxide, surfactant and deionized water are mixed evenly and added to a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 80~200℃ for 0.5~6h. Magnesium oxide is hydrated to form magnesium hydroxide. (3) Mix magnesium hydroxide from step (2), alkali-leached fly ash from step (1), and deionized water evenly, heat under stirring conditions, and evaporate to dryness at a constant temperature to obtain hydrated magnesium hydroxide doped with fly ash; the mass ratio of magnesium hydroxide, alkali-leached fly ash, and deionized water is 1:0.01~0.1:1.5~2. (4) Step (3) Hydrated magnesium hydroxide doped with fly ash is placed in an air atmosphere and calcined at a temperature of 400~800℃ for 0.5~4h to obtain modified porous magnesium oxide adsorbent doped with fly ash.

2. The method for preparing the modified porous magnesium oxide adsorbent doped with fly ash according to claim 1, characterized in that: In terms of mass percentage, the fly ash in step (1) contains 37.42~41.14% SiO2, 5.28~5.74% CaO, 13.12~16.42% Al2O3, and 3.25~3.65% Fe2O3.

3. The method for preparing the modified porous magnesium oxide adsorbent doped with fly ash according to claim 1, characterized in that: Step (1) The concentration of sodium hydroxide solution is 4~8 mol / L, and the solid-liquid ratio of fly ash to sodium hydroxide solution is 1~3:10 g:mL.

4. The method for preparing the modified porous magnesium oxide adsorbent doped with fly ash according to claim 1, characterized in that: Step (2) The pyrolytic magnesium oxide contains Ca, Fe, Al and Si elements; the pyrolytic magnesium oxide is spherical with a particle size of 10~100μm; the surfactant is one or more of sodium citrate, hexadecyltrimethylammonium bromide, N,N-dimethylformamide, dioxane, and urea.

5. The method for preparing the modified porous magnesium oxide adsorbent doped with fly ash according to claim 1, characterized in that: In step (2), the mass ratio of pyrolyzed magnesium oxide, surfactant and deionized water is 1:0.01~0.2:20~40.

6. The method for preparing the modified porous magnesium oxide adsorbent doped with fly ash according to claim 1, characterized in that: The temperature for constant temperature evaporation in step (3) is 60~80℃.

7. The application of the fly ash-doped modified porous magnesium oxide adsorbent prepared by the preparation method according to any one of claims 1 to 6 in the adsorption of heavy metal ions in the solution.

8. The application according to claim 7, characterized in that: The heavy metal ion is Cr 6+ Pb 2+ Zn 2+ Cu 2+ One or more of them.

Images