Method for preparing nano magnesium oxide

Abstract

The invention provides a method for preparing nano magnesium oxide, which belongs to the technical field of nano materials and comprises the following steps: evaporating and concentrating titanium-containing blast furnace slag magnesium enrichment to obtain magnesium enrichment concentrated solution; carrying out spray pyrolysis on the magnesium-enriched concentrated solution to obtain active magnesium oxide; the method comprises the following steps: adding active magnesium oxide into a reactor containing water and starting stirring, and then heating to carry out hydration reaction; after the hydration reaction is finished, cooling and filtering a product in sequence, and then washing and drying a filter cake to obtain magnesium-containing precursor powder; and calcining the magnesium-containing precursor powder in a muffle furnace to obtain the nano magnesium oxide. According to the method for preparing the nano magnesium oxide, a magnesium source comes from solid waste titanium-containing blast furnace slag, raw materials are easy to obtain and low in cost, the technological process is simple, used equipment is not high in price, the operation and maintenance requirements of the equipment are low, the method is green and environmentally friendly, the yield is large, the process is convenient to control, and industrialization is easy to achieve.

Description

Technical Field

[0001] The invention belongs to the technical field of nano materials, and in particular relates to a method for preparing nano magnesium oxide. Background Art

[0002] Compared with ordinary magnesium oxide, nano magnesium oxide is a new type of material with special and excellent properties. Due to the small size effect, macroscopic quantum tunneling effect and quantum size effect of nano materials, nano magnesium oxide has special electrical, optical, magnetic, thermal and mechanical properties, and is therefore widely used in catalysts, refractory materials, adsorbent materials, cosmetic fillers, toughening and reinforcing agents for plastics and rubber, antibacterial materials, ceramics and other fields. There are many preparation process technologies for nano magnesium oxide, but the existing various process technologies for preparing nano magnesium oxide have problems such as complex process flow, high raw material and preparation costs, expensive equipment cost and high operation and maintenance requirements, or inconvenient operation and control.

[0003] During the smelting process of vanadium-titanium magnetite, nearly half of the titanium enters the blast furnace for ironmaking along with the iron concentrate obtained from ore dressing. During the ironmaking process, almost all of the titanium enters the slag phase, forming titanium-containing blast furnace slag with a titanium content of about 20%. At present, only a small amount of titanium-containing blast furnace slag is used as concrete filler, resulting in a large amount of stockpiling in the Panxi area, which not only pollutes and damages the environment, but also makes it difficult to effectively utilize the remaining rich titanium resources and other valuable metal elements (aluminum, magnesium and calcium, etc.), resulting in serious waste of resources.

[0004] Therefore, it is in line with practical needs to provide a new method for preparing nano-magnesium oxide to solve various problems existing in existing process technologies and realize the high-value utilization of magnesium elements in titanium-containing blast furnace slag. Summary of the invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing nano-magnesium oxide to simplify the process flow and realize the high-value utilization of magnesium element in titanium-containing blast furnace slag.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A method for preparing nano magnesium oxide comprises the following steps:

[0008] S1, evaporating and concentrating the magnesium-enriched product of titanium-containing blast furnace slag to obtain a magnesium-enriched product concentrated solution;

[0009] S2, spray pyrolysis the magnesium-enriched concentrated solution obtained in S1 to obtain active magnesium oxide;

[0010] S3, adding the active magnesium oxide obtained in S2 into a reactor containing water and stirring, and then heating to carry out a hydration reaction;

[0011] S4, after the hydration reaction is completed, the product is cooled and filtered in sequence, and then the filter cake is washed with water;

[0012] S5, drying the filter cake obtained in S4 to obtain a magnesium-containing precursor powder;

[0013] S6. The magnesium-containing precursor powder obtained in S5 is placed in a muffle furnace and calcined to obtain nano magnesium oxide powder.

[0014] Furthermore, the titanium-containing blast furnace slag magnesium enrichment described in step S1 is obtained by first magnetically separating the titanium-containing blast furnace slag to remove iron, and then subjecting the titanium-containing blast furnace slag to nitric acid leaching and solid-liquid separation to obtain a solid phase silicon-titanium material (to prepare titanium dioxide and silicon-based products) and a nitric acid leachate, and then adding MgO as a neutralizing precipitant to the nitric acid leachate to sequentially neutralize, precipitate and separate elements such as Fe, Al and Mn, and then subjecting the nitric acid leachate to carbonization and precipitation to remove calcium, and finally obtaining a pure Mg(NO3)2 solution.

[0015] Furthermore, the mass percentage of the main components of the titanium-containing blast furnace slag is: TiO2 20-25%, CaO 20-35%, SiO2 18-30%, Al2O3 12-18%, MgO 5-10%, TFe 1-3%, MnO 0.2-0.8%, and the rest are inevitable impurities.

[0016] Furthermore, in the preparation process of the titanium-containing blast furnace slag magnesium concentrate in step S1, the nitric acid leaching solution mainly contains nitrates of Al, Mg, Fe, Mn, and Ca. When MgO is added to the nitric acid leaching solution to precipitate and separate metal elements such as Fe, Al, and Mn, the chemical reactions involved are as follows:

[0017] 2Fe(NO3)3 + 3H2O + 3MgO = 2Fe(OH)3 + 3Mg(NO3)2

[0018] 2Al(NO3)3 + 3H2O + 3MgO = 2Al(OH)3 + 3Mg(NO3)2

[0019] Mn(NO3)2 + H2O + MgO = Mn(OH)2 + Mg(NO3)2

[0020] Furthermore, in the preparation process of the titanium-containing blast furnace slag magnesium extract in step S1, not only carbon dioxide is introduced during carbonization and calcium precipitation, but also magnesium oxide or a suspension of magnesium oxide and water is added. The chemical reactions involved in carbonization and calcium precipitation are as follows:

[0021] Ca(NO3)2 + H2O + MgO = Ca(OH)2 + Mg(NO3)2

[0022] Ca(OH)2 + CO2 = CaCO3 + H2O

[0023] Further, the titanium-containing blast furnace slag magnesium concentrate described in step S1 has the following main metal element contents: Mg 40-60 g / L, Al 0.08-0.13 g / L, Ca 0.1-0.18 g / L, Fe 0.03-0.07 g / L, and Mn 0.01-0.03 g / L. It should be noted that the main element contents of the titanium-containing blast furnace slag magnesium concentrate are variable, on the one hand because the contents of each element in the titanium-containing blast furnace slag fluctuate; in addition, when magnesium oxide or magnesium oxide suspension is used as a neutralizing precipitant for separation, the amount of the neutralizing precipitant added needs to be adjusted according to the actual process conditions.

[0024] Furthermore, the temperature of the evaporation concentration in step S1 is 70-90°C.

[0025] Furthermore, when the titanium-containing blast furnace slag magnesium enriched material described in step S1 is evaporated and concentrated, the specific gravity of the concentrate is 1.25-1.45. It should be noted that when the specific gravity is too low, the water content in the concentrate is too high, which will increase the heat load of the subsequent spray pyrolysis and reduce the processing capacity of the spray pyrolysis; when the specific gravity is too high, the concentration of the solute in the concentrate is too high, and the viscosity of the concentrate is significantly increased, which is not conducive to the operation control of the subsequent spray pyrolysis step.

[0026] Furthermore, the temperature of the spray pyrolysis in step S2 is 500-800° C. If the spray pyrolysis temperature is too low, the magnesium-enriched material in the titanium-containing blast furnace slag cannot be completely and effectively decomposed, affecting the purity of the active magnesium oxide; if the spray pyrolysis temperature is too high, it may cause the magnesium oxide to burn, reduce the activity of the magnesium oxide, and affect the efficiency of the subsequent hydration reaction.

[0027] Furthermore, after the enriched concentrated solution in step S2 is spray-pyrolyzed, not only solid-phase active magnesium oxide is obtained, but also gas-phase nitrogen oxide compounds are obtained. The chemical reactions involved are as follows:

[0028] Mg(NO3)2·6H2O = Mg(NO3)2 + 6H2O

[0029] 2Mg(NO3)2 = 2MgO + 4NO2 + O2

[0030] Furthermore, the gaseous nitrogen oxides are absorbed by hydration to synthesize regenerated nitric acid, which is reused in the acid leaching step of preparing the titanium-containing blast furnace slag magnesium enrichment. The chemical reactions involved are as follows:

[0031] 3NO2 + H2O = 2HNO3 + NO

[0032] 2NO + O2 = 2NO2

[0033] 4NO2 + O2 + 2H2O = 4HNO3

[0034] Furthermore, the water used in the hydration reaction in step S3 is distilled water and / or deionized water.

[0035] Furthermore, in step S3, the solid-liquid mass ratio of the active magnesium oxide to water is 1:(8-15), and the stirring speed is ≥150 rpm.

[0036] Furthermore, the temperature of the hydration reaction in step S3 is 60-100° C., and the time is 60-120 minutes.

[0037] It should be noted that the hydration reaction of the active magnesium oxide in step S3 follows the chemical reaction mechanism of "dissolution-precipitation". The dissolution process is: MgO provides electrons in water to generate OH - , OH - Adsorbed on the positively charged solid surface, OH - Desorbed from the surface into the solution, releasing Mg 2+ ; The precipitation process is: the ion concentration gradually increases to form a supersaturated solution, generating magnesium hydroxide precipitation. The chemical reactions involved in the above "dissolution-precipitation" are as follows:

[0038] MgO(s)+H2O(l)→MgOH + (surface)+ OH - (aq)

[0039] MgOH + (surface)+OH - (aq)→MgOH + OH - (surface)

[0040] MgOH + OH - (surface)→Mg 2+ (aq)+2OH - (aq)

[0041] Mg 2+ (aq)+2OH - (aq)→Mg(OH)2(s)

[0042] Furthermore, the cooling in step S4 refers to cooling to room temperature under natural conditions.

[0043] Furthermore, the water used for washing in step S4 is distilled water and / or deionized water, and the mass ratio of washing water to filter cake in each washing process is (0.5-1):1, and the number of washing times is 1-3 times.

[0044] It should be noted that the reason why the hydration reaction in step S4 is to be cooled to room temperature first, filtered and washed at room temperature after completion is that the solubility of Ca(OH)2 is 0.165g / 100g H2O at 20°C under normal pressure, and the solubility of Ca(OH)2 gradually decreases with increasing temperature; while the solubility of Mg(OH)2 is 0.00064g / 100g H2O at 25°C. Therefore, according to the difference in solubility between Ca(OH)2 and Mg(OH)2, by cooling, filtering and washing at room temperature, calcium can be further removed, thereby improving the purity of the final nano-magnesium oxide product.

[0045] Furthermore, in step S5, the filter cake is dried at a temperature of 100-120° C. for 1-2 hours.

[0046] Furthermore, the calcination temperature in step S6 is 400-600°C, and the calcination time is 0.5-3 hours. The chemical reaction involved is as follows:

[0047] Mg(OH)2 = MgO + H2O

[0048] Furthermore, the nano magnesium oxide in step S6 has a purity of ≥99.3% and a particle size of ≤80 nm.

[0049] Compared with the existing process technology, the present invention has the following beneficial effects:

[0050] 1. The method for preparing nano-magnesium oxide proposed by the present invention uses a magnesium source from solid waste titanium-containing blast furnace slag. The raw materials are easily available and have low cost. The process flow is simple, the equipment used is not expensive, and the equipment operation and maintenance requirements are low. It is green and environmentally friendly, has a large output, is easy to control the process, and is easy to industrialize.

[0051] 2. The method of the present invention makes the magnesium element in the titanium-containing blast furnace slag become a high value-added product, improves the utilization efficiency of the titanium-containing blast furnace slag, and reduces the comprehensive development and processing cost of the titanium-containing blast furnace slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0053] Figure 1The present invention provides a process flow chart of a method for preparing nano magnesium oxide. DETAILED DESCRIPTION

[0054] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below in conjunction with the accompanying drawings, specific embodiments and comparative examples.

[0055] It should be noted that the titanium-containing blast furnace slag magnesium enriched material used in the following examples and comparative examples are all from the same batch, and the analysis results of its main components are as follows: Mg 49.43 g / L, Al 0.11 g / L, Ca 0.13 g / L, Fe 0.04 g / L, and Mn 0.02 g / L.

[0056] Example 1

[0057] The magnesium-enriched product of titanium-containing blast furnace slag is evaporated and concentrated at a temperature of 80° C. to obtain a magnesium-enriched concentrated solution, the specific gravity of which is 1.35; the magnesium-enriched concentrated solution is spray-pyrolyzed at a temperature of 600° C. to obtain active magnesium oxide; the active magnesium oxide is added to a reactor with distilled water and stirring, and then heated for hydration reaction, the stirring speed is set to 150 rpm, the solid-liquid mass ratio of active magnesium oxide to distilled water is 1:10, the hydration reaction temperature is 70° C., and the hydration reaction time is 60 minutes; after the hydration reaction is completed, it is cooled to room temperature under natural conditions, filtered, and then the filter cake is washed once with distilled water, and the mass ratio of washing water to filter cake in each washing process is 0.7:1; the filter cake is dried at 100° C. for 1 hour to obtain a magnesium-containing precursor powder; the magnesium-containing precursor powder is placed in a muffle furnace, the temperature is increased to 600° C. at a rate of 5° C. / min, and constant temperature calcined for 1.5 hours to obtain nano magnesium oxide powder.

[0058] The purity of the nano magnesium oxide is 99.5%, and the particle size is 10-50nm.

[0059] Example 2

[0060] The magnesium-enriched product of titanium-containing blast furnace slag is evaporated and concentrated at a temperature of 80° C. to obtain a magnesium-enriched concentrated solution, the specific gravity of which is 1.35; the magnesium-enriched concentrated solution is spray-pyrolyzed at a temperature of 600° C. to obtain active magnesium oxide; the active magnesium oxide is added to a reactor with distilled water and stirring, and then heated for hydration reaction, the stirring speed is set to 150 rpm, the solid-liquid mass ratio of active magnesium oxide to distilled water is 1:8, the hydration reaction temperature is 80° C., and the hydration reaction time is 80 minutes; after the hydration reaction is completed, it is cooled to room temperature under natural conditions, filtered, and then the filter cake is washed twice with distilled water, and the mass ratio of washing water to filter cake in each washing process is 0.8:1; the filter cake is dried at 120° C. for 0.8 hours to obtain a magnesium-containing precursor powder; the magnesium-containing precursor powder is placed in a muffle furnace, heated to 600° C. at a rate of 10° C. / min, and calcined at a constant temperature for 1 hour to obtain nano magnesium oxide powder;

[0061] The purity of the nano magnesium oxide is 99.6% and the particle size is 20-60nm.

[0062] Example 3

[0063] The magnesium-enriched product of titanium-containing blast furnace slag is evaporated and concentrated at a temperature of 70°C to obtain a magnesium-enriched concentrated solution, the specific gravity of which is 1.3; the magnesium-enriched concentrated solution is spray-pyrolyzed at a temperature of 450°C to obtain active magnesium oxide; the active magnesium oxide is added to a reactor with distilled water and stirring, and then heated for hydration reaction, the stirring speed is set to 200 rpm, the solid-liquid mass ratio of active magnesium oxide to distilled water is 1:12, the hydration reaction temperature is 90°C, and the hydration reaction time is 60 minutes; after the hydration reaction is completed, it is cooled to room temperature under natural conditions, filtered, and then the filter cake is washed 3 times with deionized water, and the mass ratio of washing water to filter cake in each washing process is 0.7:1; the filter cake is dried at 100°C for 1.2 hours to obtain a magnesium-containing precursor powder; the magnesium-containing precursor powder is placed in a muffle furnace, heated to 500°C at a rate of 8°C / min, and calcined at a constant temperature for 1.5 hours to obtain nano magnesium oxide powder;

[0064] The purity of nano magnesium oxide is 99.8% and the particle size is 10-40nm.

[0065] Comparative Example 1

[0066] This comparative example 1 is carried out with reference to Example 1, except that the evaporation and concentration time of the magnesium-enriched material from the titanium-containing blast furnace slag is prolonged, and the specific gravity of the final magnesium-enriched material concentrate is 1.5. At this time, the viscosity of the concentrate is relatively large, the fluidity is deteriorated, it is easy to adhere to the inner wall of the spray equipment, and it is difficult to be broken up into tiny droplets. This leads to insufficient heat exchange in the subsequent pyrolysis equipment, and the decomposition rate of magnesium nitrate hexahydrate is low, so the solid phase magnesium oxide obtained after decomposition cannot be used for the subsequent hydration and calcination process.

[0067] Comparative Example 2

[0068] This comparative example 2 is carried out with reference to Example 1, except that the active magnesium oxide is hydrated at room temperature of 30°C. This results in low hydration efficiency, and some of the original micron-sized active magnesium oxide is not converted into magnesium hydroxide, and nano-sized magnesium oxide cannot be generated through the calcination process at the back end, thereby affecting the subsequent particle size distribution of nano-magnesium oxide. The purity of nano-magnesium oxide in this comparative example 2 is 99.5%, and some magnesium oxide particles exceed 100nm, even reaching the micron level, and cannot be called a nano-magnesium oxide product.

[0069] Comparative Example 3

[0070] This comparative example 3 is carried out with reference to Example 1, except that after the hydration reaction is completed, it is not cooled to room temperature, but directly filtered and washed while hot. The solubility of Ca(OH)2 at this temperature is about 0.1 g / L, which is about 40% lower than the solubility at room temperature (20°C, 0.165 g / L). This results in a significant weakening of the decalcification effect of the filtration and washing steps, thereby affecting the purity of the subsequent nano-magnesium oxide. The purity of nano-magnesium oxide in this comparative example 3 is 99.1%, and the particle size is 10-50nm.

[0071] Comparative Example 4

[0072] This comparative example 4 is carried out with reference to Example 1, except that the magnesium enriched concentrate is spray pyrolyzed at 1000°C, resulting in the dead burning of the magnesium oxide generated by the pyrolysis. Since the activity of the magnesium oxide after dead burning is significantly reduced, it is difficult to convert it into magnesium hydroxide through a hydration reaction, and thus it is impossible to generate nano-magnesium oxide through the calcination process at the back end, thereby affecting the subsequent particle size distribution of nano-magnesium oxide. The purity of nano-magnesium oxide in this comparative example 2 is 99.5%, and some magnesium oxide particles exceed 100nm, even reaching the micron level, and cannot be called a nano-magnesium oxide product.

[0073] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing nano magnesium oxide, characterized in that: The steps include: S1, evaporating and concentrating the magnesium-enriched product of titanium-containing blast furnace slag to obtain a magnesium-enriched product concentrated solution; S2, spray pyrolysis the magnesium-enriched concentrated solution obtained in S1 to obtain active magnesium oxide; S3, adding the active magnesium oxide obtained in S2 into a reactor containing water and stirring, and then heating to carry out a hydration reaction; S4, after the hydration reaction is completed, the product is cooled and filtered in sequence, and then the filter cake is washed with water; S5, drying the filter cake obtained in S4 to obtain a magnesium-containing precursor powder; S6. The magnesium-containing precursor powder obtained in S5 is placed in a muffle furnace and calcined to obtain nano magnesium oxide powder.

2. The method for preparing nano magnesium oxide according to claim 1, characterized in that: The titanium-containing blast furnace slag magnesium enrichment described in step S1 is obtained by first magnetically separating the titanium-containing blast furnace slag to remove iron, then subjecting it to nitric acid leaching and solid-liquid separation to obtain solid-phase silicon-titanium material and nitric acid leaching solution, then adding MgO as a neutralizing precipitant to the nitric acid leaching solution, and sequentially neutralizing and precipitating and separating Fe, Al and Mn elements, and then subjecting the nitric acid leaching solution to carbonization precipitation and calcium removal, to finally obtain a pure Mg(NO3)2 solution.

3. The method for preparing nano magnesium oxide according to claim 2, characterized in that: The mass percentages of the main chemical components of the titanium-containing blast furnace slag are: TiO2 20-25%, CaO 20-35%, SiO2 18-30%, Al2O3 12-18%, MgO5-10%, TFe 1-3%, MnO 0.2-0.8%, and the rest are inevitable impurities.

4. The method for preparing nano magnesium oxide according to claim 2, characterized in that: The main metal element contents of the titanium-containing blast furnace slag magnesium enrichment in step S1 are: Mg 40-60 g / L, Al 0.08-0.13 g / L, Ca 0.1-0.18 g / L, Fe 0.03-0.07 g / L, and Mn 0.01-0.03 g / L.

5. The method for preparing nano magnesium oxide according to claim 1, characterized in that: The temperature of the evaporation concentration in step S1 is 70-90° C., and the specific gravity of the concentrated liquid is 1.25-1.

45.

6. The method for preparing nano magnesium oxide according to claim 1, characterized in that: The temperature of the spray pyrolysis in step S2 is 500-800°C.

7. The method for preparing nano magnesium oxide according to claim 1, characterized in that: The water used for the hydration reaction in step S3 is distilled water and / or deionized water, the solid-liquid mass ratio of the active magnesium oxide to water is 1:(8-15), the stirring speed is ≥150 rpm, the temperature of the hydration reaction is 60-100°C, and the time is 60-120 minutes.

8. The method for preparing nano magnesium oxide according to claim 1, characterized in that: The cooling in step S4 refers to cooling to room temperature under natural conditions. The water used for washing is distilled water and / or deionized water. The mass ratio of washing water to filter cake in each washing process is (0.5-1):1, and the number of washing times is 1-3 times.

9. The method for preparing nano magnesium oxide according to claim 1, characterized in that: The calcination temperature in step S6 is 400-600° C., and the calcination time is 0.5-3 hours.

10. The nano magnesium oxide prepared by the method according to any one of claims 1 to 9, characterized in that: The purity of the nano magnesium oxide is ≥99.3% and the particle size is ≤80nm.

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