CN113441108B - A kind of preparation method of modified attapulgite loaded nano zero-valent iron heavy metal adsorbent, product and application thereof - Google Patents

Abstract

The invention relates to the technical field of heavy metal adsorbents, in particular to a preparation method of a modified attapulgite-loaded nano zero-valent iron heavy metal adsorbent, its products and applications. The preparation method comprises the following steps: ATP is treated with acid to obtain modified attapulgite; a mixed solution obtained by mixing ferrous salt and modified ATP and then adding a solvent to mix evenly; adding a reducing agent solution to the mixed solution under stirring conditions for reaction and then centrifuging , washing and drying to obtain modified attapulgite-loaded nano-zero-valent iron heavy metal adsorbent. In the present invention, ATP is modified to make it have good dispersing ability and high mechanical strength, so as an excellent solid phase carrier, nZVI is loaded on ATP, the nZVI particles are dispersed, and the bond with heavy metals is increased. The contact area can solve the problem that nZVI is easy to agglomerate and oxidize. The prepared modified attapulgite-loaded nano-zero-valent iron adsorbent will greatly improve its adsorption capacity for heavy metals.

Description

A kind of preparation method of modified attapulgite-loaded nano-zero-valent iron heavy metal adsorbent, product and application thereof

technical field

The invention relates to the technical field of heavy metal adsorbents, in particular to a preparation method of a modified attapulgite-loaded nano zero-valent iron heavy metal adsorbent, its products and applications.

Background technique

With the sharp increase of industrial production, a large number of heavy metal elements enter the water body through electroplating, mining, metallurgy, tanning and other industrial methods, causing their content to exceed the standard and seriously pollute the water resources. In addition, human activities such as the use of pesticides and fertilizers, domestic waste disposal, and vehicle traffic are also directly or indirectly increasing the content of heavy metals in water bodies. The current situation of water resources is becoming more and more severe, not only in the shortage of water sources, but also in the deterioration of water pollution. How to solve the shortage of water resources and deal with the problem of water pollution reasonably has become an important issue facing the world today. In the face of increasingly strict heavy metal pollution regulations, how to efficiently and reasonably solve the problem of heavy metal pollution in water is the focus of scientific researchers.

Attapulgite (ATP) has a specific crystal structure and special surface charge distribution characteristics, strong adsorption and ion exchange performance, and low cost, non-toxic, wide application range, and has a wide range of applications in the treatment of heavy metal pollution in water prospect. Gansu is rich in ATP mineral resources and has the largest reserves in the world. However, the content of attapulgite in the original ore is only 20% to 30%, with low grade and many impurities. The pore structure is hindered by carbonate cements. Its physical and chemical properties are weakened, the adsorption efficiency is not ideal, and it cannot meet various application requirements as an adsorbent, resulting in it has not been developed and utilized on a large scale.

Nano Zero Valent Iron (nZVI) has become the preferred functional material for the treatment of heavy metal pollution in water. nZVI refers to zero-valent iron (Fe ⁰ ) particles with a particle size ranging from 1 to 100 nm. Due to the small particle size, it can produce unique surface effect and small size effect, which makes it have better adsorption; while Fe ⁰ itself has reducibility, and nanomaterials have surface effect, which makes nZVI have stronger reducibility. Therefore, it is used to remove various pollutants from water, such as heavy metals, organic compounds, chlorinated organic compounds and radioactive substances, and has great application potential in the field of wastewater treatment. Iron is a common metal element in nature, with abundant resources, low cost, non-toxic and harmless, and less secondary pollution. Although nZVI particles have strong reactivity and large specific surface area, their performance is reduced due to their own shortcomings such as easy agglomeration, easy oxidation and poor electron selectivity, which limits the popularization and application of nZVI. To enhance the reactivity of nZVI particles during wastewater treatment, additional metal catalysts, such as copper, platinum, palladium, and nickel, can be incorporated into these particles. These bimetallic particles can improve removal rates by providing hydrogen catalysts or active electron donors. These bimetals also have the advantages of faster reaction kinetics and slower corrosion product deposition compared to nZVI.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a preparation method of a modified attapulgite-loaded nano-zero-valent iron heavy metal adsorbent, its product and its application. ATP is modified to make it have a specific needle structure, good dispersing ability and high mechanical strength, so that it can be used as an excellent solid-phase carrier. When nZVI is loaded on ATP, it is expected to disperse the nZVI particles and increase the size of the particles. The contact area with heavy metals can solve the problems of easy agglomeration and oxidation of nZVI, and the prepared modified attapulgite-supported nano-zero-valent iron (nZVI@ATP) adsorbent will greatly improve its adsorption capacity for heavy metals.

One of the technical solutions of the present invention, a preparation method of a modified attapulgite-loaded nano-zero-valent iron heavy metal adsorbent, comprises the following steps:

(1) attapulgite is acid-treated to obtain modified attapulgite;

(2) under oxygen-free atmosphere, the mixed solution of adding ethanol and mixing after mixing ferrous salt and modified attapulgite;

(3) In an oxygen-free atmosphere, the reducing agent solution is added dropwise to the mixed solution under stirring condition, and the reaction is carried out after centrifugation, cleaning and drying to obtain the modified attapulgite-loaded nano-zero-valent iron heavy metal adsorbent.

Further, the step (1) specifically includes: placing the attapulgite raw ore powder in a hydrochloric acid solution with a concentration of 1-3 mol/L, ultrasonicating after stirring, leaving it to stand to remove the supernatant, precipitation cleaning, drying, and grinding. Modified attapulgite.

Further, the particle size of the attapulgite raw ore powder is to pass a 200-mesh sieve; the mixing mass and volume ratio of the attapulgite raw ore powder and the hydrochloric acid solution is 1g:10mL; the stirring speed is 1000r/min and stirring for 3h, and the ultrasonic time is 1h; the The drying temperature is 70-100° C., and the grinding is passed through a 200-mesh sieve.

Further, in the step (2), the ferrous salt is in terms of iron content, and the mixed mass ratio of the ferrous salt and the modified attapulgite is (1-3): (1-3); ethanol is added to limit the The size of the nanoscale zero-valent iron forms a finite structure with a restricted shape.

In the step (3), the reducing agent solution is a 0.5mol/L sodium borohydride solution (configured by dissolving the reducing agent sodium borohydride in a 0.1% sodium hydroxide solution); sodium borohydride and ferrous salt The molar ratio is 2:1.

Further, before performing step (2), the modified attapulgite is also subjected to the following treatment: after mixing the modified attapulgite and the copper salt solution, adding starch and hexadecyl amine under stirring conditions and then performing a hydrothermal reaction , the product is filtered, and directly transferred to 50-80 ℃ environment for drying without cleaning.

Further, the concentration of the copper salt solution is 0.05-0.2 mol/L, and the mixed mass volume ratio of the modified attapulgite and the copper salt solution is (1-5) g: (10-20) mL; the The added amount of starch and the mixed mass volume ratio of the copper salt solution are (5-10) g: (10-20) mL; the added amount of cetylamine and the mixed mass volume ratio of the copper salt solution are (0.05-0.1 ) g: (10-20) mL; the hydrothermal reaction temperature is 160-180° C., and the hydrothermal reaction time is 1-3 h.

Further, bentonite is also added to the mixed solution in the step (2), and the mass ratio of the bentonite to the modified attapulgite is 1:(30-50).

The second technical solution of the present invention is the modified attapulgite-loaded nano-zero-valent iron heavy metal adsorbent prepared by the above-mentioned preparation method of the modified attapulgite-loaded nano-zero-valent iron heavy metal adsorbent.

The third technical solution of the present invention is the application of the above-mentioned modified attapulgite-loaded nano-zero-valent iron heavy metal adsorbent in the treatment of heavy metal polluted wastewater.

Further, the heavy metals in the heavy metal pollution wastewater are cadmium ions and/or lead ions, wherein the cadmium ion concentration is 50-200 mg/L, and the lead ion concentration is 500-1000 mg/L; the pH value of the heavy metal pollution wastewater is 3.5-6.

Compared with the prior art, the beneficial effects of the present invention:

The attapulgite raw ore powder has uneven particle size and poor dispersion. It exists in the form of agglomeration of crystal bundles, the arrangement is discontinuous, and there are impurities on the surface. Mainly due to the existence of van der Waals force and the hydrogen bond generated on the surface, ATP tends to polymerize with itself and other impurities; therefore, in the present invention, the attapulgite is acidified in an acid solution ^. The carbonate minerals in ATP react, and part of H ⁺ can directly replace the cations in ATP, and the soluble metal oxides and calcium carbonate impurities blocked in the ATP pores and inside can be removed in large quantities. The pore size and porosity of ATP were improved, so that the main elements of ATP did not change significantly, while the structure became loose, the surface gap increased and the surface impurities were significantly reduced; the acid-treated ATP contained a large amount of -OH, Si-O- Si and Si-O bonds can provide active sites for heavy metal ions; Zeta potential shows that the surface of ATP presents a permanent negative charge, which can generate electrostatic attraction between heavy metal ions and promote the adsorption reaction. Therefore, using the acid-treated attapulgite as a heavy metal adsorbent can adsorb heavy metal ions in heavy metal wastewater and purify the water source. However, in the acid treatment process, if a higher acid environment is used, the regular octahedral structure of attapulgite may be destroyed, resulting in an increase in the bulk density of attapulgite, thereby reducing the specific surface area and reducing the number of binding sites . Therefore, in the preferred solution of the present invention, the acid solution is defined as a hydrochloric acid solution with a concentration of 1-3 mol/L.

In the invention, the acid-treated attapulgite is used as a carrier, and nano-zero-valent iron is prepared on the surface of the in-situ redox reaction, and the pure nZVI particles are easy to agglomerate, so that the contact opportunity with pollutants is limited, and its adsorption performance cannot be fully exerted. Causes waste of adsorption sites, and after loading to ATP, the agglomeration of nZVI can be improved due to the steric barrier effect of ATP, and the removal rate can be increased; however, due to the limited steric barrier effect of ATP, too much nZVI will cover the surface of ATP to continue. Aggregates into long chains, inhibiting the transfer process of heavy metal ions on its surface, resulting in a reduction in removal rate, so a high iron-soil ratio is not conducive to the removal of heavy metals by nZVI@ATP, so the present invention defines the iron-soil ratio as (1-3): (1 -3).

In the present invention, sodium borohydride is used as a reducing agent to reduce the surface of attapulgite modified by acid treatment in situ to prepare nano-zero-valent iron. The nano-zero-valent iron synthesized by sodium borohydride has B element on the surface, which can be loaded with nano-zero-valent iron on the surface. The chemical adsorption of iron attapulgite for heavy metal wastewater adsorption provides a certain catalytic effect and improves the adsorption efficiency of the material.

In a preferred solution of the present invention, the attapulgite is firstly placed in a copper salt solution, and the hydrothermal reduction reaction is carried out under the condition of starch as a reducing agent and the action of cetylamine, thereby pre-growing on the surface of the attapulgite Copper nanowires, and then on the basis of copper nanowires, the in-situ reduction and loading of nano-zero-valent iron is carried out, thereby forming copper/iron bimetallic nanomaterials with nano-zero-valent iron-coated copper nanowires on the surface of attapulgite , on the one hand, the pre-loading of nano-copper provides a new loading site for attapulgite material, which avoids the aggregation of nano-iron caused by high iron-soil ratio, thereby improving the loading of nano-iron; on the other hand, in heavy metal adsorption During the process, nZVI acts as a reducing agent, and copper metal acts as a catalyst. By providing a hydrogen catalyst or an active electron donor, the adsorption efficiency of nZVI can be further improved. At the same time, starch is used as a reducing agent in the copper reduction process, which can be attached to the surface of the nanoparticles through the hydrogen bond between the hydroxyl groups in the starch and the nZVI on the surface of the nanoparticles, providing higher stability for the nanoparticles.

In the preferred solution of the present invention, a certain amount of bentonite is also introduced during the nano-iron loading, and the two form a mixed reaction medium and play a synergistic effect. The adsorption of heavy metal ions is enhanced by ion exchange and co-precipitation. powerful.

Description of drawings

1 is a simple preparation device for preparing nZVI@ATP(a) and nZVI(b) in Example 1 of the present invention;

2 is a scanning electron microscope image of nZVI@ATP(a) and pure nZVI(b) prepared in Example 1 of the present invention.

Detailed ways

Various exemplary embodiments of the present invention will now be described in detail, which detailed description should not be construed as a limitation of the invention, but rather as a more detailed description of certain aspects, features, and embodiments of the invention.

It should be understood that the terms described in the present invention are only used to describe particular embodiments, and are not used to limit the present invention. Additionally, for numerical ranges in the present disclosure, it should be understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated value or intervening value in that stated range is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

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 this invention relates. Although only the preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials in connection with which the documents are referred. In the event of conflict with any incorporated document, the content of this specification controls.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the present invention. The description and examples of the present invention are exemplary only.

As used herein, "comprising," "including," "having," "containing," and the like, are open-ended terms, meaning including but not limited to.

Example 1

(1) Preparation of modified ATP

Take 300g of ATP raw ore powder that has passed a 200-mesh sieve and put it into a 5L beaker, add 3000mL of hydrochloric acid with a concentration of 2mol/L, stir with an electric stirrer at room temperature at 1000r/min for 3h, and then use ultrasonic treatment for 1h. After standing for a period of time, the supernatant was poured out, and the lower sediment was washed with ultrapure water until the pH became neutral. Finally, it was dried in an oven at 70-100 °C, and ground through a 200-mesh sieve to obtain modified ATP, which was sealed and stored. ,spare;

SEM analysis of the modified ATP raw ore powder and the prepared ATP found that the particle size of the raw soil was uneven and the dispersion was not good. , the bonding phenomenon on ATP still exists but has been improved, the structure becomes loose, the surface gap increases and the surface impurities are significantly reduced. The main constituent elements of the ATP were C, O, Si, Mg, Al, Fe, Ca by EDS analysis. After pretreatment, the mass percentage of Ca decreased from 14.06% to 11.02%, the mass percentage of Al decreased from 3.8% to 1.85%, the mass percentage of Si decreased from 10.03% to 6.05%, and the mass percentage of Fe decreased from 3.4% to 1.75% , impurities are partially removed. The main elements of ATP did not change significantly after pickling, indicating that the pretreatment did not change the structure of ATP, but only removed the surface impurities;

After XRD analysis, the main phase composition of modified ATP is attapulgite, silica and dolomite: characteristic diffraction peaks of ATP appear at 2θ=27.5°, 30.89°, 35.1° and 40.01°, and at 2θ=20.81° , 26.58° and 39.5° appear characteristic diffraction peaks of silica, 2θ=29.49° and 33.41° are characteristic diffraction peaks of dolomite.

(2) Preparation of nZVI@ATP and nZVI

Add 27.802g FeSO ₄ ·7H ₂ O (in which iron accounts for 5.561g) to the three-necked flask containing 100mL of distilled water, according to the mass of iron soil of 3:1, 2:1, 1:1, 1:2, 1:3 A certain amount of modified ATP prepared in step (1) was added separately, stirred for 2 h under the protection of N ₂ to make it fully mixed, and then 100 mL of absolute ethanol was added, and stirred for 30 min. Then add 400mL of 0.5mol/L NaBH ₄ solution (prepared by dissolving the reducing agent sodium borohydride in 0.1% sodium hydroxide solution) at a rate of 1 to 2 drops/second, and continue to stir after the addition is complete. 15min, to ensure that NaBH ₄ and Fe ²⁺ fully react. The above reaction processes were all carried out under _N2 atmosphere. Then the solution was centrifuged, the supernatant was discarded, washed with oxygen-free ultrapure water and oxygen-free absolute ethanol in turn, and separated with a centrifuge. Dry at ℃ and pass through a 200-mesh sieve to obtain nZVI@ATP, which is vacuum-sealed and stored in the freezer layer of the refrigerator for use.

There is no need to add ATP during the preparation of pure nZVI, and the rest of the steps are the same as those for the preparation of nZVI@ATP. The experimental setup is shown in Figure 1. The SEM images of the as-prepared nZVI@ATP(a) and pure nZVI(b) are shown in Figure 2.

By comparing the SEM images of nZVI@ATP(a) and pure nZVI(b), it can be concluded that the pure nZVI particles are generally smooth and spherical, and the particle size reaches the nanometer level, mostly 50-100 nm. Due to the effect of its own magnetic force, the pure nZVI particles showed obvious agglomeration and were distributed in a chain bead shape, confirming that nZVI has a tendency to form aggregates under normal conditions. In nZVI@ATP, after the nZVI was loaded on ATP, the single spherical nZVI particles were uniformly dispersed on the surface and in the voids of ATP, and the agglomeration phenomenon was weakened, which overcomes the shortcomings of nZVI’s reduced specific surface area and adsorption performance due to its large agglomeration tendency. This unique microstructure promotes the enhanced adsorption performance of nZVI@ATP for heavy metals.

The introduction of ATP can make nZVI disperse well, mainly because due to the existence of van der Waals forces and hydrogen bonds, ATP will be intertwined and stacked, and nZVI will be interrupted and dispersed by the intertwined and stacked ATP during the aggregation process. The resistance will also hinder the agglomeration between nZVI; and in the process of synthesizing nZVI@ATP, Fe ²⁺ in the solution will undergo ion exchange with part of Mg ²⁺ and Ca ²⁺ in ATP, and when NaBH ₄ is added, it will It is reduced to a single nZVI and embedded into the ATP structure; in addition, the Fe ions contained in ATP itself will also be reduced to nZVI by NaBH ₄ to directly precipitate or be embedded in ATP. Further EDS analysis showed that the mass percentage of Fe in the elemental composition of nZVI@ATP increased significantly, from 1.79% to 56.56%, indicating that nZVI was successfully loaded on ATP. However, due to the limited steric barrier effect of ATP, too much nZVI will cover the surface of ATP and continue to aggregate into long chains, inhibiting the transfer process of heavy metal ions on its surface, resulting in a decrease in the removal rate. High iron-soil ratio is not conducive to the removal of nZVI@ATP. heavy metal.

(3) Effect verification

① Preparation of experimental solution: Weigh 2.7442g Cd(NO ₃ ) ₂ ·4H ₂ O solid and 11.1895g lead nitrate (Pb(NO ₃ ) ₂ ) solid powder and dissolve them in an appropriate amount of 0.01mol/L NaNO ₃ solution, respectively. Move it to a 1L volumetric flask and continue to dilute it with 0.01mol/L NaNO ₃ solution to prepare a cadmium stock solution with a concentration of 1000mg/L and a lead stock solution of 7000mg/L, and further dilute it to a specific concentration of 100mg/L. Cadmium solution and 700mg/L lead solution.

②Take 8 50mL centrifuge tubes, add ATP raw ore powder, modified ATP, pure nZVI, nZVI@ATP (iron-soil mass ratio=3:1), nZVI@ATP (iron-soil mass ratio=3:1) at a dosage of 1 g/L. After mass ratio=2:1), nZVI@ATP (iron-soil mass ratio=1:1), nZVI@ATP (iron-soil mass ratio=1:2), nZVI@ATP (iron-soil mass ratio=1:3) , and then add 30 mL of anoxic Cd ²⁺ solution whose pH is adjusted to 5.0 and whose concentration is 100 mg/L, shake at a speed of 200 r/min for 24 hours, and then pass through a 0.45 μm microporous membrane to measure the Cd ²⁺ concentration in the filtrate;

③Take 8 50mL centrifuge tubes, add ATP raw ore powder, modified ATP, pure nZVI, nZVI@ATP (iron-soil mass ratio=3:1), nZVI@ATP (iron-soil mass ratio=3:1) at a dosage of 1 g/L. After mass ratio=2:1), nZVI@ATP (iron-soil mass ratio=1:1), nZVI@ATP (iron-soil mass ratio=1:2), nZVI@ATP (iron-soil mass ratio=1:3) , and then add 30 mL of anaerobic Pb ²⁺ solution whose pH is adjusted to 5.0 and whose concentration is 700 mg/L, shake at a speed of 200 r/min for 24 hours, and then pass through a 0.45 μm microporous membrane to measure the Pb ²⁺ concentration in the filtrate;

②③ The results showed that the removal rate of Cd ²⁺ from ATP raw ore was only 9.66%, and the removal rate of Pb ²⁺ was 44.26%. After pickling, the removal rate of Cd ²⁺ and Pb ²⁺ by ATP increased slightly, respectively 11.82% and 52.72%, the reason is that in the acidification process, a part of H ⁺ can react with carbonate minerals in ATP, and a part of H ⁺ can directly replace cations in ATP, blocking the soluble metal oxides in ATP pores and inside The impurities such as calcium carbonate and calcium carbonate can be removed in large quantities, and the acid washing dredges the internal pores and improves the pore size and porosity of ATP. Compared with nZVI or ATP, the adsorption performance of nZVI@ATP composites for Cd ²⁺ was significantly improved, and the adsorption performance was the best when the iron-soil ratio was 1:1 and 1:2, and the removal rates reached 99.1% and 98.38%, respectively. The removal rate was higher than that of pure nZVI (93.66%), and the removal rates were 90.2%, 91.8% and 59.2% when the iron-soil ratio was 3:1, 2:1 and 1:3, respectively. The removal rate of Pb ²⁺ by the composite material first increased and then decreased with the decrease of Fe ratio in the iron-soil ratio. Similarly, the adsorption performance was the best when the iron-soil ratio was 1:1 and 1:2, and the removal rates reached 85.2% and 84.5%, respectively. %, which was also higher than the removal rate of pure nZVI (78.18%), and the removal rates were 61.7%, 69.8% and 60.5% when the iron-soil ratio was 3:1, 2:1 and 1:3, respectively. Since the removal rates of Cd ²⁺ and Pb ²⁺ were not much different when the iron-soil ratio was 1:1 and 1:2, the experiments in ④⑤⑥⑦ were carried out on the basis of 1:2 iron-soil ratio.

④Take 11 50mL centrifuge tubes, add nZVI@ATP at a dosage of 1g/L, and then add 30mL of anaerobic Cd ²⁺ solution with a pH adjusted to 5.0 and a concentration of 100mg/L in turn, and shake in a constant temperature water bath at 25°C. Vibrate in the device at a speed of 200r/min for 0.25, 0.5, 1, 2, 3, 4, 6, 8, 12, 20 and 24 hours, respectively, and then pass through a 0.45 μm microporous membrane to determine the concentration of Cd ²⁺ in the filtrate.

⑤ Take 11 50mL centrifuge tubes, add nZVI@ATP at a dosage of 1g/L, and then add 30mL of anaerobic Pb ²⁺ solution whose pH is adjusted to 5.0 and the concentration is 700mg/L, and shake in a constant temperature water bath at 25°C. In the device, vibrate at a speed of 200r/min for 0.25, 0.5, 1, 2, 3, 4, 6, 8, 12, 20 and 24 hours, respectively, and then pass through a 0.45 μm microporous membrane to measure the concentration of Pb ²⁺ in the filtrate.

④⑤ The results showed that the adsorption process of Cd ²⁺ in solution by nZVI@ATP can be roughly divided into three stages: fast adsorption stage (0～1h), slow adsorption stage (1～6h) and adsorption equilibrium stage (after 6h). The correlation coefficient R ² of the pseudo-second-order kinetic equation is 0.9949, which is better than the pseudo-first-order kinetic model, and the equilibrium adsorption capacity (q _m ) obtained by the pseudo-second-order kinetic model fitting is 98.0 mg/g, and the experimental The results are similar, indicating that the pseudo-second-order kinetic model can describe the adsorption process of Cd ²⁺ by nZVI@ATP well, and the model includes all the adsorption processes, indicating that the adsorption of Cd ²⁺ by nZVI@ATP is a multi-step reaction , and chemisorption dominates the adsorption process, and the main mechanism of adsorption is electron sharing or transfer between nZVI@ATP and Cd ²⁺ . The adsorption capacity of nZVI@ATP for Pb ²⁺ increased rapidly within 0-2 h, which could reach more than 90% of the equilibrium adsorption capacity. This is because a large number of vacant sites on the surface of nZVI@ATP facilitate the adsorption of Pb ²⁺ at the initial stage of adsorption, and the mass transfer driving force generated under the concentration difference of Pb ²⁺ will push Pb ²⁺ to nZVI@ATP rapidly Diffusion, there is a high chance of being attached to the adsorption site. With the progress of the reaction, the number of vacant adsorption sites on the surface of nZVI@ATP gradually decreased, and the mass transfer driving force caused by the concentration difference of Pb ²⁺ decreased, and Pb ²⁺ had to overcome a large resistance to enter the nZVI@ The interior of ATP is bound to the adsorption site, resulting in a decrease in the adsorption rate, a small increase in the adsorption amount, and a gradual saturation. The pseudo-second-order kinetic fitting model is more suitable for the fitting curve of nZVI@ATP to Pb ²⁺ , and the adsorption process of nZVI@ATP to Pb ²⁺ is controlled by chemisorption involving electron transfer or sharing.

⑥ Take nine 50mL centrifuge tubes, add nZVI@ATP at a dosage of 1g/L, and then add 30mL of pH to 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, and the concentration is 100mg/ L of anaerobic Cd ²⁺ solution, the pH of the Cd ²⁺ solution was adjusted with 0.1mol/L HNO ₃ and 0.1 mol/L NaOH, in a constant temperature water bath shaker at 25°C constant temperature shaking at a speed of 200r/min for 24h, and then passed through a 0.45μm micropore filter and measure the remaining Cd ²⁺ concentration in the solution.

⑦Take nine 50mL centrifuge tubes, add nZVI@ATP at a dosage of 1g/L, and then add 30mL of pH to 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, and the concentration is 100mg/ L of anaerobic Pb ²⁺ solution, the pH of Cd ²⁺ solution was adjusted with 0.1mol/L HNO ₃ and 0.1 mol/L NaOH, and it was shaken at 200r/min in a constant temperature water bath shaker at 25℃ for 24h and then passed through a 0.45μm micropore filter and measure the remaining Pb ²⁺ concentration in the solution.

⑥⑦ The results show that the pH value of the solution will affect the adsorption effect by affecting the existence of heavy metals in the solution. At low pH, Cd mainly exists in the form of Cd ²⁺ in water, and when the pH is higher, Cd(OH) ₂ precipitates. The adsorption performance of nZVI@ATP for Cd ²⁺ in water was greatly affected by the pH of the solution. In the range of pH 2.0～3.5, the adsorption capacity of Cd ²⁺ increased sharply with the increase of pH, from 75.72mg/g to 98.3mg/g; in the range of pH 3.5～6, the adsorption capacity of Cd ²⁺ fluctuated with the increase of pH Not much. The lower Cd adsorption performance of nZVI@ATP under strongly acidic conditions ^is mainly attributed to the competition between H ⁺ and Cd ²⁺ for vacant adsorption sites ^. Under acidic conditions, Fe ⁰ is oxidized to generate a large amount of OH ^- , which increases the pH value of the solution and promotes the chemical precipitation of Cd ²⁺ to be removed, which increases the ability of nZVI@ATP to remove Cd ²⁺ . Through further analysis, it can be seen that the isoelectric point of nZVI@ATP in solution is about 7.35. When pH<7.35, the surface of nZVI@ATP is positively charged, and the electrostatic repulsion between it and Cd ²⁺ is large, which is not conducive to nZVI@ The adsorption of Cd ²⁺ by ATP, but the experimental results show that the adsorption performance of nZVI@ATP on Cd ²⁺ is good at pH 3.5-6. It can be seen that the adsorption between nZVI@ATP and Cd ²⁺ in solution is more affected by electrostatic attraction. It is not a pure physical adsorption process, but mainly a chemical adsorption process.

Example 2

(1) prepare modified attapulgite according to step (1) of Example 1;

(2) The modified attapulgite and 0.2mo/L copper salt solution were mixed according to the mass-volume ratio of 1g:15mL, and then 8g of starch and 0.08g of cetylamine were added under stirring conditions of 200r/min. After thermal reaction for 2 hours, the product was filtered and directly transferred to 70°C for drying without cleaning to obtain modified attapulgite loaded with copper nanowires.

(3) Add 27.802g FeSO ₄ ·7H ₂ O (among which iron accounts for 5.561g) into the three-necked flask containing 100mL of distilled water, and according to the ratio of 3:1, 2:1, 1:1, 1:2, 1:3 A certain amount of the modified attapulgite loaded with copper nanowires prepared in step (2) was added to the iron-earth mass ratio, stirred for 2 h under the protection of _N2 to make it fully mixed, and then added 100 mL of anhydrous ethanol, and stirred for 30 min to obtain a mixed solution . Then add 400 mL of the 0.5 mol/L NaBH ₄ solution prepared at a rate of 1 to 2 drops/second, and continue stirring for 15 min after the dropwise addition to ensure that NaBH ₄ and Fe ²⁺ react fully. The above reaction processes were all carried out under _N2 atmosphere. Then the solution was centrifuged, the supernatant was discarded, washed with oxygen-free ultrapure water and oxygen-free absolute ethanol in turn, and separated with a centrifuge. Dry at ℃ and pass through a 200-mesh sieve to obtain nZVI/Cu@ATP, which is vacuum-sealed and stored in the freezer layer of the refrigerator for use.

(4) The nZVI/Cu@ATP prepared in step (3) of this example was tested and verified according to the verification method of step (3)②③ of Example 1, and the removal rate results are shown in Table 1.

Table 1

iron-to-earth ratio 3:1 2:1 1:1 1:2 1:3 Cd²⁺ solution 100% 99.5% 99.8% 99.1% 86.4% Pb²⁺ solution 90.5% 91.1% 89.6% 88.3% 72.7%

It can be seen from Table 1 that after the loading of copper nanowires, the overall adsorption capacity of heavy metal ions is improved, but the adsorption performance of nZVI/Cu@ATP with high iron-soil ratio is more obvious. Therefore, copper nanowires The loading of nZVI plays a role in increasing the loading of nZVI, avoiding the technical problem of the decline of adsorption performance caused by the aggregation of nano-iron due to the high iron-soil ratio.

The nZVI/Cu@ATP prepared in step (3) of the present example was tested and verified according to the verification method of step (3) (4) and (5) of Example 1. The removal rate results are shown in Table 2 (the mass ratio of iron to soil is 3:1).

Table 2

Cd²⁺ solution Pb²⁺ solution Adsorption time 0.25h 88.3% 60.1% Adsorption time 0.5h 94.0% 71.8% Adsorption time 1h 98.9% 74.4% Adsorption time 2h 99.1% 84.1% Adsorption time 3h 99.1% 85.9% Adsorption time 4h 99.2% 88.2% Adsorption time 6h 99.3% 89.7% Adsorption time 8h 99.5% 90.6% Adsorption time 12h 99.6% 90.9% Adsorption time 20h 100.0% 91.0% Adsorption time 24h 100.0% 91.0%

From Table 2, it can be concluded that the adsorption process of nZVI/Cu@ATP and nZVI@ATP for Cd ²⁺ and Pb ²⁺ is basically the same, but the time for nZVI/Cu@ATP to reach the adsorption equilibrium is shorter. The adsorption of Cd ²⁺ and Pb ²⁺ by nZVI/Cu@ATP can be described by pseudo-second-order kinetic model, and the adsorption process is mainly chemical adsorption. Due to the loading of Cu nanowires, the adsorption efficiency of nZVI/Cu@ATP was significantly improved compared with that of nZVI@ATP.

Example 3

The method steps are the same as the scheme in which the iron-to-clay ratio is 3:1 in Example 2, the difference is that when carrying out the load of step (3), bentonite (200 meshes) is also added to the mixed solution, and the mass ratio of bentonite and modified attapulgite is is 1:40.

Take a centrifuge tube, add the prepared materials at a dosage of 1 g/L, and then add 30 mL of anaerobic Cd ²⁺ solution with a pH adjusted to 5.0 and a concentration of 100 mg/L. After shaking at the speed of /min for 12h, it was passed through a 0.45 μm microporous membrane, and the concentration of Cd ²⁺ in the filtrate was determined. The results showed that the removal rate of Cd ²⁺ by the mixed adsorbent reached 100%.

Take a centrifuge tube, add the prepared materials at a dosage of 1 g/L, and then add 30 mL of anaerobic Pb ²⁺ solution with a pH adjusted to 5.0 and a concentration of 700 mg/L. The speed of /min was shaken for 12h, and then passed through a 0.45 μm microporous membrane, and the concentration of Pb ²⁺ in the filtrate was determined. The results showed that the adsorption rate of Pb ²⁺ by the mixed adsorbent reached 95.8%.

Therefore, the adsorption efficiency and adsorption capacity of the material can be improved by adding an appropriate amount of bentonite to the modified attapulgite.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention. within.

Claims (8)

1. A preparation method of a modified attapulgite loaded nano zero-valent iron heavy metal adsorbent is characterized by comprising the following steps:

(1) treating attapulgite with acid to obtain modified attapulgite;

(2) mixing ferrous salt and the modified attapulgite in an oxygen-free atmosphere, and adding ethanol to obtain a mixed solution;

(3) under the oxygen-free atmosphere, dropwise adding a reducing agent solution into the mixed solution under the stirring condition, reacting, centrifuging, cleaning and drying to obtain the modified attapulgite loaded nano zero-valent iron heavy metal adsorbent;

the preparation method of the modified attapulgite loaded nano zero-valent iron heavy metal adsorbent is characterized in that before the step (2), the modified attapulgite is further treated by the following steps: mixing the modified attapulgite and the copper salt solution uniformly, adding starch and hexadecylamine under stirring, mixing uniformly, carrying out hydrothermal reaction, filtering the product, and drying in an environment at 50-80 ℃;

the preparation method of the modified attapulgite-loaded nano zero-valent iron heavy metal adsorbent is characterized in that the concentration of the copper salt solution is 0.05-0.2mol/L, and the mixing mass-volume ratio of the modified attapulgite to the copper salt solution is (1-5) g: (10-20) mL; the mixing mass volume ratio of the starch to the copper salt solution is (5-10) g: (10-20) mL, and the mixing mass-to-volume ratio of the hexadecylamine to the copper salt solution is (0.05-0.1) g: (10-20) mL; the hydrothermal reaction temperature is 160-180 ℃, and the hydrothermal reaction time is 1-3 h.

2. The preparation method of the modified attapulgite-loaded nano zero-valent iron heavy metal adsorbent according to claim 1, wherein the step (1) specifically comprises: putting the attapulgite raw ore powder into a hydrochloric acid solution with the concentration of 1-3mol/L, stirring, performing ultrasonic treatment, standing to remove supernatant, precipitating, cleaning, drying, and grinding to obtain the modified attapulgite.

3. The preparation method of the modified attapulgite-loaded nano zero-valent iron heavy metal adsorbent according to claim 2, wherein the particle size of the attapulgite raw ore powder is 200 mesh; the mixing mass volume ratio of the attapulgite crude ore powder to the hydrochloric acid solution is 1g:10 mL; the ultrasound after the stirring treatment is specifically as follows: stirring for 3 hours at the stirring speed of 1000r/min, and carrying out ultrasonic treatment for 1 hour; the drying temperature is 70-100 ℃, and the grinding and 200-mesh sieving are carried out.

4. The preparation method of the modified attapulgite loaded nano zero-valent iron heavy metal adsorbent according to claim 1, wherein in the step (2), the mixing mass ratio of the ferrous salt to the modified attapulgite is (1-3) in terms of the iron content: (1-3);

in the step (3), the reducing agent solution is 0.5mol/L sodium borohydride solution; the molar ratio of the sodium borohydride to the ferrous salt is 2: 1.

5. The preparation method of the modified attapulgite loaded nano zero-valent iron heavy metal adsorbent according to claim 1, wherein bentonite is further added into the mixed solution obtained in the step (2), and the mass ratio of the bentonite to the modified attapulgite is 1: (30-50).

6. The modified attapulgite-loaded nano zero-valent iron heavy metal adsorbent prepared by the preparation method of the modified attapulgite-loaded nano zero-valent iron heavy metal adsorbent according to any one of claims 1 to 5.

7. The application of the modified attapulgite-loaded nano zero-valent iron heavy metal adsorbent of claim 6 in treatment of heavy metal-polluted wastewater.

8. The application of the modified attapulgite-loaded nanoscale zero-valent iron heavy metal adsorbent in treatment of heavy metal polluted wastewater according to claim 7, wherein heavy metals in the heavy metal polluted wastewater are cadmium ions and/or lead ions, wherein the concentration of the cadmium ions is 50-200mg/L, and the concentration of the lead ions is 500-1000 mg/L;

the pH value of the heavy metal polluted wastewater is 3.5-6.

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