Method for preparing fly ash-based layered double hydroxides through molybdenum sulfide intercalation modification

Abstract

The invention discloses a method for preparing fly ash-based layered double hydroxides through molybdenum sulfide intercalation modification. The method comprises the following steps: mixing washed fly ash with AlCl3 and hydrochloric acid, and adding NaOH to adjust the pH value so as to prepare the fly ash-based layered double hydroxides; on the basis, MoS < 2-> is coupled by a mechanochemical method to prepare a single-phase material molybdenum sulfide intercalation modified fly ash-based layered double-metal hydroxide. According to the method, the adsorption capacity of the LDHs prepared from the fly ash on heavy metals Pb < 2 + >, Ag < + >, Hg < 2 + > and Cu < 2 + > can be remarkably improved, meanwhile, heavy metal adsorption selectivity can be brought to LDHs materials, the selectivity is that Ag < + > is larger than Hg < 2 + >, Cu < 2 + > is larger than Pb < 2 + >, and the selectivity is larger than others, in addition, by adopting a mechanochemical method, precipitation of Mo can be remarkably reduced, the harmfulness of the materials is reduced, and meanwhile the cost, the energy consumption and the environmental harm are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection, and in particular relates to a method for preparing fly ash-based layered double metal hydroxides by intercalation modification of molybdenum sulfide. Background Art

[0002] With the rapid development of my country's urban economy and the enhancement of public environmental awareness, the amount of urban domestic waste generated and the proportion of incineration treatment have continued to rise. This change has also led to an increase in the production of fly ash from domestic waste incineration, making the treatment and resource utilization of fly ash an important issue that needs to be solved urgently. At present, fly ash from waste incineration is mainly disposed of by landfill and cement kiln co-disposal. However, with the continuous improvement of government policies, it is particularly important to improve the treatment and resource utilization capacity of fly ash. Traditional methods are difficult to meet the needs due to factors such as environmental risks and treatment volume. Therefore, it is necessary to develop more high-value-added, low-cost green resource technologies to effectively treat waste incineration fly ash. Layered double hydroxides (LDHs) are anionic clay materials composed of main layer structures, interlayer anions and water molecules. The most common synthesis method is to combine coprecipitation with hydrothermal method. At present, LDHs are mainly used in the research of catalysts, adsorbents, flame retardants and corrosion inhibitors.

[0003] The preparation of layered double hydroxides using fly ash as raw material is a green resource technology that can meet the needs, has high added value and is low-cost. At present, layered double hydroxides have some applications in the adsorption of heavy metals, and the adsorption capacity of LDHs made from fly ash is not much different from that of LDHs on the market. However, in some specific cases, when a single heavy metal needs to be adsorbed, LDHs lack selectivity. Based on this, there is an urgent need to provide a modified fly ash-based layered double hydroxide with heavy metal selective adsorption on the market. Summary of the invention

[0004] In order to solve at least one of the above problems, the present invention provides a method for preparing fly ash-based layered double metal hydroxides by intercalation modification of molybdenum sulfide.

[0005] In order to achieve the above object, the present invention adopts the following technical means: The first aspect of the present invention provides a method for preparing fly ash-based layered double metal hydroxide by intercalation modification of molybdenum sulfide, comprising the following steps: S1. Add sodium hydroxide solution to the waste incineration fly ash for 1-2 times, and the liquid-solid ratio of sodium hydroxide solution to fly ash is (10-12) ml:1g; after solid-liquid separation, the solid is taken to obtain the washed fly ash; S2, mixing the washed fly ash solid, deionized water, hydrochloric acid solution and aluminum chloride, wherein the mass ratio of the washed fly ash solid to the aluminum chloride is (5-20):1, deionized water is added at a liquid-solid ratio of (10-14) ml:1g, and the pH is adjusted to 11-13 with sodium hydroxide. After fully stirring, a mixture is obtained, and the mixture is transferred to a ball mill for temperature-controlled ball milling. The solid-liquid mixture obtained after ball milling is centrifuged, washed with water, and dried to obtain a fly ash-based layered double metal hydroxide, recorded as: CaAl-Cl-LDH; S3, adding ammonium tetrathiomolybdate to the fly ash layered double metal hydroxide obtained in S2, with a mass ratio of (1.1-1.5):1, and then adding deionized water, and performing temperature-controlled ball milling treatment; S4. Centrifuge the mixed solution in S3, filter, wash and dry to obtain a molybdenum sulfide intercalated fly ash modified layered double metal hydroxide, recorded as: CaAl-MoS4-LDH.

[0006] In some embodiments of the present invention, in step S1, the solid-liquid separation is performed by filtering the mixture through a 0.45 μm filter membrane.

[0007] In some embodiments of the present invention, in step S1, the concentration of the sodium hydroxide solution is 0.5-1 mol / L.

[0008] In some embodiments of the present invention, in step S1, the rinsing method is: fully shaking for 6 to 8 hours, and standing for 22 to 24 hours.

[0009] In some embodiments of the present invention, in step S2, the concentration of the hydrochloric acid solution is 1-1.2 mol / L.

[0010] In some embodiments of the present invention, in step S2, the ball mill rotation speed is 700-900 rpm, the ball-to-material ratio is (4-7):1, the ball milling time is 4-6 hours, and the ball milling temperature is controlled at 100-120°C.

[0011] In some embodiments of the present invention, in step S3, the liquid-to-solid ratio of the mixture of deionized water and the fly ash-based layered double metal hydroxide and ammonium tetrathiomolybdate is (8-12) ml: 1 g.

[0012] In some embodiments of the present invention, in step S3, the ball milling conditions are: ball-to-material ratio (8-10): 1, ball milling time 6-8h, rotation speed 400-500rpm, and ball milling temperature controlled at 80-100°C.

[0013] In some embodiments of the present invention, in step S4, the washing process is two water washes and one ethanol wash.

[0014] In some embodiments of the present invention, in step S4, the drying process is performed at 80-105° C. under a nitrogen atmosphere.

[0015] The second aspect of the present invention provides a molybdenum sulfide intercalated modified fly ash layered double metal hydroxide prepared by the method described in the first aspect.

[0016] The present invention also provides the use of the molybdenum sulfide intercalated fly ash-modified layered double metal hydroxide prepared by the method described in the first aspect in the adsorption of heavy metals in wastewater.

[0017] The use of the molybdenum sulfide intercalated fly ash-modified layered double metal hydroxide prepared by the method described in the first aspect in the selective adsorption of heavy metals in wastewater.

[0018] In some embodiments of the present invention, the selectively adsorbed heavy metals include Ag, Hg, Cu, and Pb. In some embodiments of the present invention, the selectively adsorbed heavy metal is preferably Ag, followed by Hg.

[0019] Beneficial Effects of the Invention Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention utilizes the effective components in fly ash and synthesizes fly ash-based LDHs to adsorb heavy metal ions in wastewater, thereby achieving the purpose of treating waste with waste.

[0020] (2) The present invention optimizes the structure of LDHs made from fly ash and uses a temperature-controlled ball milling process to generate interlaminar band Cl - The LDHs were then used to accelerate the spontaneous MoS4 2- Replacement of interlayer Cl - The process of inserting MoS4 between LDHs layers 2- , achieving the purpose of increasing the heavy metal adsorption capacity of LDHs made from fly ash, and at the same time bringing about the adsorption selectivity of specific heavy metal cations, which can meet the adsorption of a single heavy metal under specific circumstances.

[0021] (3) The present invention utilizes the mechanochemical method to reduce energy consumption, shorten the reaction time and bring about better material adsorption performance. The material made by utilizing the performance of the mechanochemical method is not easy to precipitate the Mo element during use, thereby reducing the harm of the material itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The electron microscope image of LDHs obtained in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0023] The following examples are used to demonstrate preferred embodiments of the present invention. It will be appreciated by those skilled in the art that the techniques disclosed in the following examples represent techniques discovered by the inventors that can be used to implement the present invention and therefore can be considered as preferred embodiments of the present invention. However, it will be appreciated by those skilled in the art based on this specification that many modifications may be made to the specific embodiments disclosed herein and still achieve the same or similar results without departing from the spirit or scope of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs, and the materials cited herein and those cited by them are incorporated by reference. Those skilled in the art will recognize or will learn through routine experimentation that there are many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the claims.

[0025] The technical solution of the present application is further described in detail below in conjunction with specific implementation methods.

[0026] A method for preparing fly ash-based layered double metal hydroxide by intercalation modification of molybdenum sulfide, the process steps are as follows: S1. Add 0.5~1mol / L sodium hydroxide solution to the waste incineration fly ash for 1~2 times, and the liquid-solid ratio of the sodium hydroxide solution to the fly ash is (10~12) ml:1g; fully shake for 6~8h, let it stand for 22~24h, filter it, and take the solid to obtain the washed fly ash; S2, the washed fly ash solid, deionized water, a hydrochloric acid solution with a concentration of 1-1.2 mol / L and aluminum chloride are mixed, the mass ratio of the washed fly ash solid to the aluminum chloride is (5-20):1, deionized water is added at a liquid-solid ratio of (10-14) ml:1g, the pH is adjusted to 11-13 with sodium hydroxide, and the mixture is fully stirred, and the mixture is transferred to a ball mill and the temperature is controlled to 100-120°C, and ball milled, the ball mill speed is 700-900rpm, the ball-to-material ratio is (4-7):1, and the ball milling time is 4-6h; the solid-liquid mixture obtained after ball milling is centrifuged, washed with water, and dried to obtain a fly ash-based layered double metal hydroxide, recorded as: CaAl-Cl-LDH; S3, adding ammonium tetrathiomolybdate to the fly ash-based layered double metal hydroxide obtained in S2, with a mass ratio of (1.1-1.5):1; then adding deionized water according to a liquid-solid ratio of (8-12) ml:1g, controlling the temperature to 80-100°C, and performing ball milling treatment; the ball milling treatment conditions are: ball-to-material ratio (8-10):1, ball milling time 6-8h, and rotation speed 400-500rpm; S4. The mixed solution in S3 is centrifuged, filtered, washed twice with water, and dried at 80-105° C. under a nitrogen atmosphere to obtain a molybdenum sulfide intercalated modified fly ash layered double metal hydroxide, recorded as: CaAl-MoS4-LDH.

[0027] The second aspect of the present invention provides a molybdenum sulfide intercalated modified fly ash layered double metal hydroxide prepared by the method described in the first aspect.

[0028] The present invention also provides the use of the molybdenum sulfide intercalated fly ash-modified layered double metal hydroxide prepared by the method described in the first aspect in the adsorption of heavy metals in wastewater.

[0029] The use of the molybdenum sulfide intercalated fly ash-modified layered double metal hydroxide prepared by the method described in the first aspect in the selective adsorption of heavy metals in wastewater.

[0030] In some embodiments of the present invention, the selectively adsorbed heavy metals include Ag, Hg, Cu, and Pb. In some embodiments of the present invention, the selectively adsorbed heavy metal is preferably Ag, followed by Hg.

[0031] Example 1 A method for preparing fly ash-based layered double metal hydroxide by intercalation modification of molybdenum sulfide comprises the following steps: S1: Add waste incineration fly ash into 1 mol / L NaOH solution with a liquid-to-solid ratio of 10 ml:1 g, stir for 6 h, and let stand for 24 h; filter the resulting mixture through a 0.45 μm filter membrane to extract the solid; S2: Take the fly ash and aluminum chloride treated by S1 at a mass ratio of 10:1, add 1 mol / L hydrochloric acid solution at a liquid-solid ratio of 3 ml:1 g and mix evenly, add deionized water at a liquid-solid ratio of 10 ml:1 g, add 2 M NaOH solution to adjust the pH to 12, transfer the mixture to a ball mill, set the speed to 900 rpm, control the temperature at 110 ° C, ball mill for 6 hours, centrifuge the obtained mixture with water, dry it at 105 ° C for 24 hours, and obtain a fly ash-based layered double metal hydroxide, recorded as: CaAl-Cl-LDH; S3: Add the obtained fly ash-based layered double metal hydroxide and ammonium tetrathiomolybdate into a ball mill at a mass ratio of 1.2:1, add deionized water at a liquid-solid ratio of 8ml:1g, and perform mechanochemical treatment at a ball-to-material ratio of 10:1 and a ball mill speed of 400rpm for 6h at a ball mill temperature of 80°C; S4: The solid phase was separated at a centrifugal speed of 5500 rpm, washed with deionized water twice and ethanol once, and dried at 100°C for 12 h under a nitrogen atmosphere to obtain a molybdenum sulfide intercalated modified fly ash layered double metal hydroxide.

[0032] Example 2 The preparation method steps are the same as those in Example 1, except that: in step S2, 2M NaOH solution is added to adjust the pH to 13.

[0033] Example 3 The preparation method steps are the same as those in Example 1, except that in step S2, the mass ratio of fly ash to aluminum chloride is set to 15:1.

[0034] Example 4 The preparation method steps are the same as those in Example 1, except that in step S2, the mass ratio of fly ash to aluminum chloride is set to 20:1.

[0035] Example 5 The difference from Example 1 is that the ball milling speed in step S2 is set to 800 rpm.

[0036] Example 6 The difference from Example 1 is that the ball milling speed in step S3 is set to 500 rpm.

[0037] Example 7 The difference from Example 1 is that the ball milling time in step S2 is set to 4 hours.

[0038] Example 8 The difference from Example 1 is that the ball milling time in step S3 is set to 8 hours.

[0039] Example 9 The difference from Example 1 is that the liquid-to-solid ratio in step S2 is 12 ml: 1 g.

[0040] Example 10 The difference from Example 1 is that the liquid-solid ratio added in step S3 is 10 ml:1 g.

[0041] Comparative Example 1 The difference from Example 1 is that in step S2, 2M NaOH solution is added to adjust the pH to 10.

[0042] Comparative Example 2 The difference from Example 1 is that in step S2, the mass ratio of fly ash to aluminum chloride is set to 25:1.

[0043] Comparative Example 3 The difference from Example 1 is that the ball milling speed in step S2 is set to 500 rpm.

[0044] Comparative Example 4 The difference from Example 1 is that in step S3, the ratio of balls to materials is 10:1.

[0045] Comparative Example 5 The difference from Example 1 is that in step S3, the ball milling speed is set to 900 rpm.

[0046] Comparative Example 6 The difference from Example 1 is that the ball milling time in step S2 is set to 2 h.

[0047] Comparative Example 7 The difference from Example 1 is that the ball milling temperature in step S2 is set to 80°C.

[0048] Comparative Example 8 The difference from Example 1 is that the ball milling temperature in step S3 is set to 120°C.

[0049] Comparative Example 9 The difference from Example 1 is that the liquid-to-solid ratio added in step S3 is 5 ml:1 g.

[0050] Comparative Example 10 The difference from Example 1 is that in step S3, the mass ratio of the fly ash-based layered double metal hydroxide to ammonium tetrathiomolybdate is 2:1.

[0051] Adsorption experiments were conducted using the molybdenum sulfide intercalated modified fly ash layered double metal hydroxides prepared in Examples 1 to 10 and Comparative Examples 1 to 9, and the method is as follows: (1) 0.05 g of the molybdenum sulfide intercalated modified fly ash layered double hydroxide material prepared above was mixed with 100 ml of simulated liquid respectively. The initial concentrations of silver nitrate, mercuric nitrate, lead nitrate and copper nitrate in the four simulated liquids were all 500 mg / L. The mixture was shaken and stirred at 400 rpm for 6 h at room temperature (25 °C). The mixture was centrifuged at 7000 rpm for 5 min to obtain a supernatant and a separation slurry. The supernatant was filtered through a 0.22 μm filter to obtain a filtrate. The concentrations of heavy metal ions in the liquid phase before and after adsorption were determined by ICP-OES.

[0052] The adsorption results of the materials prepared in the examples and comparative examples are shown in Table 1.

[0053] Table 1 Heavy metal adsorption results of materials prepared by Examples 1-10 and Comparative Examples 1-9

[0054] The results show that: using the preparation method of the present application, under appropriate conditions, the adsorption of Ag, Hg, Cu, and Pb by the product prepared is significantly greater than that of the product prepared under the comparative example. Among them, inappropriate conditions affect the synthesis and structural optimization of LDHs in step S2, which leads to the MoS4 in S3. 2- Substitute Cl between layers -Formation of LDHs intercalated with MoS4 2- Failure will greatly affect the heavy metal adsorption capacity of LDHs prepared from fly ash.

[0055] The product of step S2 and the final product in the embodiment were tested for adsorption effect, and the results are shown in Table 2.

[0056] Table 2 MoS4 2- Adsorption effect of fly ash-based layered double hydroxides before and after intercalation modification

[0057] The results show that LDHs produced from waste incineration fly ash can be processed by MoS4 2- After intercalation modification, the adsorption capacity for heavy metals is significantly improved, especially for silver ions.

[0058] (2) 0.05 g of the molybdenum sulfide intercalated modified fly ash layered double hydroxide material prepared in Example 1 was mixed with 100 ml of a simulated liquid, in which the initial concentrations of silver nitrate, mercuric nitrate, lead nitrate and copper nitrate were all 500 mg / L, and the mixture was stirred at 400 rpm for 6 h at room temperature of 25°C, and centrifuged at 7000 rpm for 5 min to obtain a supernatant and a separation slurry. The supernatant was filtered through a 0.22 μm filter to obtain a filtrate, and the concentration of heavy metal ions in the liquid phase before and after adsorption was determined by ICP-OES. The results are shown in Table 3.

[0059] Table 3 Adsorption effect of molybdenum sulfide intercalated modified fly ash layered double metal hydroxide prepared in Example 1

[0060] The results show that LDHs produced from waste incineration fly ash can be processed by MoS4 2- After intercalation modification, the adsorption of heavy metals is selective, and the selectivity is Ag. + >Hg 2+ >Cu 2+ >Pb 2+ .

[0061] (3) 0.1 g of the molybdenum sulfide intercalated modified fly ash layered double hydroxide material prepared in Example 1 and the LDHs before ball milling in step S3 in the preparation process of Example 1 were placed in 100 ml of water respectively, and stirred at 400 rpm for 6 h at room temperature 25°C. After suction filtration through a 0.45 um membrane, the amount of Mo element precipitation was analyzed by ion chromatography, and the results were shown in Table 4.

[0062] Table 4 Comparison of Mo element precipitation in LDHs materials before and after ball milling

[0063] The results show that the amount of Mo precipitated in LDHs before ball milling is 1.94 times that in LDHs after ball milling. The amount of Mo precipitated in the modified LDHs material obtained after S3 ball milling is nearly 1 times less than that in the material before ball milling. The Mo in the modified LDHs material obtained after S3 ball milling is more stable and not easy to precipitate, which reduces the harm of the material itself.

[0064] All documents mentioned in the present invention are cited as references in this application, just as each document is cited as references separately. In addition, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined in the present application.

Claims

1. A method for preparing fly ash-based layered double metal hydroxides by intercalation modification of molybdenum sulfide, characterized in that: The steps include: S1. Add sodium hydroxide solution to the waste incineration fly ash for 1-2 times, and the liquid-solid ratio of the sodium hydroxide solution to the fly ash is (10-12) ml:1 g; filter and take out the solid to obtain the washed fly ash; S2, mixing the washed fly ash solid, deionized water, hydrochloric acid solution and aluminum chloride, wherein the mass ratio of the washed fly ash solid to the aluminum chloride is (5-20):1, deionized water is added at a liquid-solid ratio of (10-14) ml:1g, and the pH is adjusted to 11-13 with sodium hydroxide, and the mixture is fully stirred to obtain a mixture, and the mixture is transferred to a ball mill for temperature-controlled ball milling in a ball mill, and the solid-liquid mixture obtained after ball milling is centrifuged, washed with water, and dried to obtain a fly ash-based layered double metal hydroxide; S3, adding ammonium tetrathiomolybdate to the fly ash layered double metal hydroxide obtained in S2, with a mass ratio of (1.1-1.5):1, and then adding deionized water, and performing temperature-controlled ball milling treatment; S4. Centrifuge the mixed solution in S3, filter, wash and dry to obtain the molybdenum sulfide intercalated modified fly ash layered double metal hydroxide.

2. The method according to claim 1, characterized in that: In step S1, the concentration of the sodium hydroxide solution is 0.5-1 mol / L.

3. The method according to claim 1, characterized in that: In step S1, the rinsing method is: fully shaking for 6 to 8 hours and standing for 22 to 24 hours.

4. The method according to claim 1, characterized in that: In step S2, the concentration of the hydrochloric acid solution is 1-1.2 mol / L.

5. The method according to claim 1, characterized in that: In step S2, the rotation speed of the ball mill is 700-900 rpm, the ball-to-material ratio is (4-7):1, the ball milling time is 4-6 hours, and the ball milling temperature is controlled at 100-120°C.

6. The method according to claim 1, characterized in that: In step S3, the liquid-to-solid ratio of the mixture of deionized water and the fly ash-based layered double metal hydroxide and ammonium tetrathiomolybdate is (8-12) ml: 1 g.

7. The method according to claim 1, characterized in that: In step S3, the ball milling conditions are: ball-to-material ratio (8-10): 1, ball milling time 6-8 hours, rotation speed 400-500 rpm, and ball milling temperature controlled at 80-100°C.

8. The method according to claim 1, characterized in that: In step S4, the washing process is two water washes and one ethanol wash.

9. The method according to claim 1, characterized in that: In step S4, the drying process is performed at 80-105° C. under a nitrogen atmosphere.

10. A molybdenum sulfide intercalated fly ash-modified layered double metal hydroxide prepared by the method described in any one of claims 1 to 9.

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