CN106166474A - A kind of specific regulatory control nano zero valence iron corrosion product the method strengthening nano zero valence iron adsorption of Low Concentration arsenic - Google Patents

Abstract

The invention discloses a method for specifically regulating the corrosion products of nanometer zero-valent iron and strengthening the adsorption of low-concentration arsenic by nanometer zerovalent iron. In this method, the nZVI@Mg(OH) ₂ composite material is prepared by loading nano-zero-valent iron on the surface of magnesium hydroxide, which can control the corrosion products of nano-zero-valent iron and enhance the adsorption of low-concentration arsenic by nano-zero-valent iron. The method of the invention is simple and easy to operate, has wide sources of raw materials and low cost. The prepared nZVI@Mg(OH) ₂ composite fully amplifies the advantages of a single nZVI or Mg(OH) ₂ material, which can not only effectively reduce the concentration of As(Ⅴ) in water to the drinking water standard, but also have a relatively low level of As(Ⅴ) High adsorption capacity.

Description

A specific regulation of nano-ZVI corrosion products and enhanced nano-ZVI adsorption low arsenic method

technical field

The invention belongs to the technical field of arsenic adsorption in wastewater treatment, and relates to a method for controlling the generation of nano-zero-valent iron corrosion products and enhancing the adsorption of low-concentration arsenic by nano-zero-valent iron loaded on the surface of magnesium hydroxide.

Background technique

Arsenic is a ubiquitous element in nature, and its inorganic compounds are highly toxic. Because arsenic acid is similar to the molecular model of phosphoric acid, it can inhibit the oxidation of phosphate, thereby blocking the main energy metabolism system of living organisms. Long-term exposure or exposure to an environment containing excessive arsenic may cause lesions or cancer in multiple organs and tissues of the human body. The problem of excessive arsenic in drinking water has a wide range of influences in the world. Countries and regions such as Bangladesh, Chile, China, Hungary, India, Mexico, Romania, Vietnam, and the United States have reported that excessive arsenic in drinking water has been reported to varying degrees. In addition, it is worth noting that the pollution of arsenic in groundwater is a typical low-concentration pollution problem, and the concentration of arsenic in groundwater in most countries is in the range of 0-5200 μg/L. In order to reduce the harm of arsenic to human health, in 1993, WHO lowered the standard concentration of arsenic in drinking water from 50 μg/L to 10 μg/L.

Currently, the most common method for removing arsenic from water is adsorption. Nanoscale zero-valent iron (nZVI) is favored due to its large specific surface area, high reactivity, high adsorption capacity for arsenic, and easy magnetic separation, and has become a widely concerned material in the research of arsenic removal in water. The specific surface area of stable nZVI particles can reach more than 40m ² /g, the reaction rate is more than 1000 times higher than that of micron zero-valent iron ZVI, and the maximum adsorption capacity is 3.5mg/g (initial concentration is 1mg/L ^-1 ). However, the adsorption capacity of nZVI is limited due to its easy agglomeration, instability and poor strength. To overcome these limitations, nZVI was loaded onto other porous materials, such as activated carbon, chitosan-carboxymethyl β-cyclodextrin, chitosan nanospheres, and montmorillonite, etc. However, most studies on the arsenic removal performance of NZVI composites focus on improving the adsorption capacity of composites, but often ignore the actual environmental problems or water quality requirements after treatment. Either the concentration of arsenic in the treated water is much higher than the actual concentration in the environment, or the adsorption equilibrium concentration cannot meet the WHO drinking water standard. In addition, nZVI is easily corroded in an aerobic environment, and the corrosion products include magnetite/maghemite and lepidocite. Studies have shown that As(Ⅴ) is preferentially adsorbed on the magnetite/maghemite surface compared to lepidocite. If the reaction conditions of nZVI can be changed to specifically control the transformation of its corrosion products into magnetite/maghemite, the adsorption capacity of nZVI on As(Ⅴ) can be enhanced. However, there are no research reports in this area.

Contents of the invention

The purpose of the present invention is to provide a method for specifically regulating the corrosion products of nanometer zero-valent iron and strengthening the adsorption of low-concentration arsenic by nanometer zerovalent iron. The invention solves the above-mentioned problems in the prior art by loading nano-zero-valent iron on the surface of magnesium hydroxide to regulate the generation of nano-zero-valent iron corrosion products, and at the same time enhancing the adsorption of nano-zero-valent iron to low-concentration arsenic.

In order to realize the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is as follows.

A method for specifically regulating the corrosion products of nano-zero-valent iron and strengthening the adsorption of low-concentration arsenic by nano-zero-valent iron, comprising the following steps:

(1) Prepare Mg(OH) ₂ suspension: dissolve Mg(OH) ₂ in absolute ethanol and disperse by ultrasonic to obtain Mg(OH) ₂ suspension;

(2) Prepare Fe ₂ SO ₄ solution: Dissolve Fe ₂ SO ₄ ∙7H ₂ O in deionized water to obtain Fe ₂ SO ₄ solution;

(3) Prepare NaBH ₄ solution: dissolve NaBH ₄ solid in deionized water to obtain NaBH ₄ solution;

(4) Take the Mg(OH) ₂ suspension and place it in a three-necked flask, keep mechanical stirring, pass in an inert gas for isolation protection, add Fe ₂ SO ₄ solution, and immediately add NaBH ₄ solution dropwise at a rate of 3mL/min;

(5) After the dropwise addition, centrifuge to obtain a black solid, wash and dry to obtain the nZVI@ Mg(OH) ₂ composite material;

(6) Take the As(V) solution in a glass bottle at room temperature, adjust the pH with HCl solution and NaOH solution, add the nZVI@Mg(OH) ₂ composite material prepared in step (5), and place it in a constant temperature oscillator to vibrate at a constant speed After shaking, the solid-liquid sample was separated, and the As(V) content in the solution was tested.

Further, in step (1), the ultrasonic dispersion time is 5 minutes.

Further, the concentration of the Mg(OH) ₂ suspension is 0.1mol/L.

Further, the concentration of the Fe ₂ SO ₄ solution is 0.1 mol/L.

Further, the concentration of the _NaBH4 solution is 0.25mol/L.

Further, the speed of the mechanical stirring in step (4) is 300 r/min, and the mechanical stirring is maintained until the dropwise addition of the NaBH ₄ solution is completed.

Further, the inert gas in step (4) includes nitrogen or argon.

Further, in step (4), the molar ratio of the reactants added is Mg(OH) ₂ : Fe ₂ SO ₄ : NaBH ₄ =1:1:2.

Further, in step (5), the washing refers to washing with absolute ethanol and deionized water three times in sequence.

Further, in step (5), the drying is drying at 45° C. under vacuum.

Further, in step (6), the concentration of the As(V) solution is 1-8 mg/L.

Further, in step (6), the concentrations of the HCl solution and the NaOH solution are both 0.1 mol/L.

Further, in step (6), the pH value is 7.0±0.25.

Further, in step (6), the addition amount of the nZVI@Mg(OH) ₂ composite material is 0.1 g/L.

Further, in step (6), the oscillation speed is 200 r/min, and the oscillation time is 6 h.

The mechanism of the present invention is that the process of loading nZVI to Mg(OH) ₂ adopts a liquid phase reduction method, and nZVI is easily corroded in an aerobic environment, and the corrosion products include magnetite/maghemite and lepidocite. Studies have shown that As(Ⅴ) is preferentially adsorbed on the magnetite/maghemite surface compared to lepidocite. The corrosion product of nanometer zero-valent iron in the solution is mainly lepidocite, and also contains a small amount of magnetite/maghemite. After nanometer zero-valent iron is loaded onto the surface of magnesium hydroxide, since magnesium hydroxide is slightly soluble in water, during the corrosion process of nanometer zero-valent iron, magnesium hydroxide, as a solid alkali, continuously dissolves and releases OH ^- , thus making The content of magnetite/maghemite in the corrosion products of nanometer zero-valent iron increases, while the content of lepidocite decreases. The adsorption capacity of magnetite/maghemite to arsenic is stronger than that of lepidocite, so the adsorption capacity of nano zero-valent iron to arsenic is enhanced. If the reaction conditions of nZVI and As(Ⅴ) solution can be changed, the corrosion products can be specifically controlled to transform into magnetite/maghemite, thereby enhancing the adsorption capacity of nZVI to As(Ⅴ).

Experiments show that Mg(OH) ₂ can reduce the concentration of As(Ⅴ) in water to the standard of drinking water, but the adsorption capacity is small; nZVI has a large adsorption capacity for As(Ⅴ), but it cannot effectively reduce the concentration of As(Ⅴ) in the solution at low concentrations. As(Ⅴ) in the water; and the prepared nZVI@Mg(OH) ₂ composite material combines the advantages of the two, which can effectively reduce the concentration of As(Ⅴ) in the water to the drinking water standard, and has the effect on As(Ⅴ) High adsorption capacity.

Compared with the prior art, the present invention has the following advantages and technical effects:

(1) The method of the present invention is simple, easy to operate and control at normal temperature;

(2) The raw material source of the present invention is extensive, and cost is low;

(3) Fully amplify the advantages of a single material and make the best use of it. The obtained nZVI@Mg(OH) ₂ composite material can not only effectively reduce the concentration of As(Ⅴ) in water to the drinking water standard, but also reduce the concentration of As(Ⅴ) It also has a higher adsorption capacity.

Description of drawings

Figure 1 is a comparison of the equilibrium concentration of the prepared nZVI@Mg(OH) ₂ composite material and the single material after treatment with low concentration of arsenic.

detailed description

The present invention will be further described below in conjunction with specific examples, but the protection scope of the present invention is not limited to the examples.

Mg(OH) ₂ was synthesized by chemical precipitation method: at room temperature, 1M NaOH aqueous solution was added dropwise to an equal volume of 0.5M MgSO ₄ solution, and the dropwise addition was vigorously stirred at a speed of 300 r/min, wherein The MgSO ₄ solution was obtained by dissolving MgSO ₄ ∙7H ₂ O to 85wt% glycerol in water. After the dropwise addition was completed, continue to stir for 6 hours, let stand for 24 hours, then centrifuge, wash with deionized water and absolute ethanol three times in sequence, dry at 45°C, and set aside.

The arsenic removal experiment was carried out in a 25ml glass bottle: Take 20ml of As(Ⅴ) solution with a concentration of 1~8 mg/L in the glass bottle, adjust the pH to 7.0±0.25 with 0.1 M HCl solution and 0.1M NaOH solution, add 0.1 g /L prepared nZVI@Mg(OH) ₂ composite material, put it in a constant temperature oscillator and oscillate at a constant speed of 200 r/min, take it out after 6 hours, filter the supernatant through a 0.45 μm filter membrane, and measure the As content.

Example 1

(1) Prepare 0.1 mol/L Mg(OH) ₂ suspension: dissolve Mg(OH) ₂ in absolute ethanol, and disperse by ultrasonic for 5 minutes to obtain 0.1 mol/L Mg(OH) ₂ suspension;

(2) Prepare 0.1 mol/L Fe ₂ SO ₄ solution: Dissolve Fe ₂ SO ₄ ∙7H ₂ O in deionized water to obtain 0.1 mol/L Fe ₂ SO ₄ solution;

(3) Prepare 0.25 mol/L NaBH ₄ solution: dissolve NaBH ₄ solid in deionized water to obtain 0.25 mol/L NaBH ₄ solution;

(4) Take 75 ml of 0.1 mol/L Mg(OH) ₂ suspension and place it in a 500 ml three-necked flask, keep mechanical stirring at 300 r/min, pass through nitrogen for isolation protection, and add 75 ml of 0.1 mol/L Fe ₂ SO ₄ solution, and immediately dropwise add 0.25 mol/L NaBH ₄ solution 60ml at a rate of 3 mL/min;

(5) After the dropwise addition, the obtained black solid was centrifuged, washed three times with absolute ethanol and deionized water, and dried under vacuum at 45 °C to obtain the nZVI@ Mg(OH) ₂ composite material;

(6) At room temperature, take 20ml of As(Ⅴ) solution with a concentration of 1mg/L in a glass bottle, adjust the pH to 7.0 with 0.1mol/L HCl solution and 0.1mol/L NaOH solution, add 0.1g/L The obtained nZVI@Mg(OH) ₂ composite material was placed in a constant temperature oscillator and oscillated at a constant speed of 200 r/min. After 6 hours, the As(Ⅴ) concentration in the solution dropped to 3 μg/L; At ₂ , the residual concentration (18.7 μg/L) was low; the adsorption capacity of nZVI@Mg(OH) ₂ composites for arsenic was 0.996 mg/g, while the adsorption capacity of nanometer zero-valent iron was 0.981 mg/g, while magnesium hydroxide The adsorption capacity was 0.992 mg/g.

Example 2

Steps (1)-(5) are the same as in Example 1;

Arsenic removal experiment:

At room temperature, take 20 ml of As(V) solution with a concentration of 5 mg/L in a glass bottle, adjust the pH to 7.0 with 0.1 mol/L HCl solution and 0.1 mol/L NaOH solution, and add 0.1 g/L to prepare The nZVI@Mg(OH) ₂ composite material was placed in a constant temperature oscillator and oscillated at a constant speed of 200 r/min. After 6 h, the adsorption capacity of the nZVI@Mg(OH) ₂ composite material for As(V) was 4.94 mg/g; The adsorption capacity of nano zero-valent iron is 4.57 mg/g, while that of magnesium hydroxide is 3.04 mg/g.

Example 3

Steps (1)-(5) are the same as in Example 1;

Arsenic removal experiment:

At room temperature, take 20 ml of As(V) solution with a concentration of 8 mg/L in a glass bottle, adjust the pH to 7.0 with 0.1 mol/L HCl solution and 0.1 mol/L NaOH solution, and add 0.1 g/L to prepare The nZVI@Mg(OH) ₂ composite material was placed in a constant temperature oscillator and oscillated at a constant speed of 200 r/min. After 6 h, the adsorption capacity of the nZVI@Mg(OH) ₂ composite material for As(V) was 6.75 mg/g; The adsorption capacity of zero-valent iron is 6.68 mg/g, while that of magnesium hydroxide is 3.50 mg/g.

Figure 1 is a comparison of the prepared nZVI@Mg(OH) ₂ composite material and a single nZVI or Mg(OH) ₂ material after treating the equilibrium concentration of As(V) in low-concentration water. It can be seen from Figure 1 that when the initial concentration of As(V) gradually decreased from 8 mg/L to 1 mg/L, the equilibrium concentration gradually decreased. Compared with the adsorption effect of nZVI and Mg(OH) ₂ alone, the nZVI@Mg(OH) ₂ composite exhibited the best arsenic adsorption capacity. In addition, as shown by the black arrow on the way, when the initial concentration of As(V) is 1 mg/L, the equilibrium concentration corresponding to the nZVI@Mg(OH) ₂ composite material is 3.60 μg/L, which is lower than the WHO drinking water standard 10 μg/L. It shows that the composite material can effectively reduce the content of As(V) in water to the standard of drinking water.

Finally, it is necessary to explain here that: the above examples are only used to further describe the technical solutions of the present invention in detail, and cannot be interpreted as limiting the protection scope of the present invention. Non-essential improvements and adjustments all belong to the protection scope of the present invention.

Claims (10)

1. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic, characterized in that, comprising the following steps: (1) Prepare Mg(OH) ₂ suspension: dissolve Mg(OH) ₂ in absolute ethanol and disperse by ultrasonic to obtain Mg(OH) ₂ suspension; (2) Prepare Fe ₂ SO ₄ solution: Dissolve Fe ₂ SO ₄ ∙7H ₂ O in deionized water to obtain Fe ₂ SO ₄ solution; (3) Prepare NaBH ₄ solution: dissolve NaBH ₄ solid in deionized water to obtain NaBH ₄ solution; (4) Take the Mg(OH) ₂ suspension and place it in a three-necked flask, keep mechanical stirring, pass in an inert gas for isolation protection, add Fe ₂ SO ₄ solution, and immediately add NaBH ₄ solution dropwise at a rate of 3mL/min; (5) After the dropwise addition, centrifuge to obtain a black solid, wash and dry to obtain the nZVI@ Mg(OH) ₂ composite material; (6) Take the As(V) solution in a glass bottle at room temperature, adjust the pH with HCl solution and NaOH solution, add the nZVI@Mg(OH) ₂ composite material prepared in step (5), and place it in a constant temperature oscillator to vibrate at a constant speed After shaking, the solid-liquid sample was separated, and the As(V) content in the solution was tested. 2. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic according to claim 1, characterized in that the ultrasonic dispersion time in step (1) is 5 minutes . 3. a kind of specific regulation and control nano-zero-valent iron corrosion product according to claim 1 and strengthen the method for nano-zero-valent iron to adsorb low-concentration arsenic, it is characterized in that, described Mg(OH) _The concentration of suspension is 0.1 mol/L; the concentration of the Fe ₂ SO ₄ solution is 0.1 mol/L; the concentration of the NaBH ₄ solution is 0.25 mol/L. 4. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic according to claim 1, characterized in that the speed of mechanical stirring in step (4) is 300 r/min, mechanical stirring is maintained until the NaBH ₄ solution is added dropwise; the inert gas includes nitrogen or argon. 5. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic according to claim 1, characterized in that, in step (4), the molar ratio of the added amount of reactants It is Mg(OH) ₂ : Fe ₂ SO ₄ : NaBH ₄ =1:1:2. 6. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic according to claim 1, characterized in that, in step (5), the washing refers to using The water, ethanol and deionized water were washed three times in sequence; the drying was carried out at 45° C. under vacuum. 7. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic according to claim 1, characterized in that the As(V) solution described in step (6) The concentration is 1~8 mg/L. 8. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic according to claim 1, characterized in that, in step (6), the HCl solution and NaOH solution The concentrations are all 0.1 mol/L; the pH value is 7.0±0.25. 9. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic according to claim 1, characterized in that, in step (6), the nZVI@Mg(OH ) ₂ The amount of composite material added is 0.1 g/L. 10. A method for specifically regulating nano-zero-valent iron corrosion products and strengthening nano-zero-valent iron to adsorb low-concentration arsenic according to claim 1, characterized in that, in step (6), the oscillation speed is 200 r/min, the oscillation time is 6h.