CN115228432A - Preparation and application of biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment - Google Patents
Preparation and application of biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment Download PDFInfo
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Abstract
The invention discloses a preparation and application of a biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment, which comprises the following steps: carbonizing the konjac glucomannan derivative carbon precursor to obtain konjac glucomannan derivative carbon KGMC; adding konjac glucomannan derived carbon into a ferric salt solution, and stirring to obtain a suspension of nZVI @ KGMC; directionally freezing and drying the nZVI @ KGMC suspension to obtain a 3DnZVI @ KGMC precursor; and (3) carrying out high-temperature in-situ reduction on the precursor of 3D nZVI @ KGMC, and cooling to obtain nZVI @ KGMC, namely the biomass derived carbon-coated nano zero-valent iron material for radionuclide treatment. The biomass-derived carbon-coated nano zero-valent iron material nZVI @ KGMC for radionuclide enrichment prepared by the invention shows 90.1% of effective U (VI) enrichment rate within 60 minutes. Meanwhile, nzvi @ kgmc shows good U (VI) enrichment efficiency in the presence of interfering ions and organic matter.
Description
Technical Field
The invention relates to the technical field of preparation of radionuclide enrichment materials, in particular to preparation and application of a biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment.
Background
Uranium (U) is a radioactive metal element that is widely used in the nuclear industry. With the development of the nuclear industry, the discharge amount of uranium-containing wastewater is rapidly increasing. Uranium-containing wastewater having high fluidity and complex composition is continuously flowed into human habitats through groundwater. Uranium has a strong chemical toxicity, causing irreversible damage to the ecological environment and human health. In addition, the radioactive uranium-bearing wastewater produced by the nuclear industry also contains various ions and organic substances, and the presence of the substances greatly influences the concentration of uranium by the adsorbent.
In addition, the radioactive uranium-bearing wastewater produced by the nuclear industry also contains various ions and organic substances, and the presence of the substances greatly influences the concentration of uranium by the adsorbent. Notably, U (VI) enrichment and separation are problems to be solved in uranium-containing wastewater.
Reduction of high mobility U (VI) to low mobility U (IV) to achieve uranium fixation in radioactive wastewater is an effective way to treat U contamination. To date, various methods of reducing U (IV) have been developed, including biological reduction (enzymatic reduction), electrochemistry, photocatalysis, and zero-valent iron reduction (ZVI). Among them, bioreduction, electrochemistry and photocatalysis are inefficient, requiring the introduction of additional power and light sources, which limits their further applications. Notably, ZVI has significant utility and reactivity and can be used in a variety of different environments without the addition of additional conditions. Therefore, ZVI-based materials have been extensively studied for uranium enrichment and separation. More importantly, the particle size of the ZVI particles is adjusted to be nano-scale, so that the ZVI particles have larger specific surface area, higher redox performance and abundant surface active centers. Nano zero-valent iron (nZVI) particles exhibit excellent efficiency and reaction rate in radionuclide enrichment, but their practical applications are limited due to the disadvantages of easy agglomeration and surface oxidation. Loading nZVI particles onto various substrates, including clay minerals, metal (hydr) oxides, and carbon-based materials, is an effective strategy to improve the dispersibility and reactivity of nZVI particles. The nZVI particles prepared in the prior art have the problems of uneven size, low dispersity and the like. Konjac Glucomannan (KGM) in biomass materials is a potential assembly material because it has excellent biocompatibility and gelling properties. The gelling property of KGM and the oxygen-containing functional groups on the surface can effectively improve the dispersibility of iron ions through a biological assembly technology, and then the nZVI is encapsulated in the biomass-derived carbon through in-situ reduction, so that the stability of the nZVI is enhanced.
Disclosure of Invention
An object of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
To achieve these objects and other advantages in accordance with the present invention, there is provided a method for preparing a biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment, comprising the steps of:
step one, adding konjac glucomannan into water, stirring to obtain a suspension, and freeze-drying to obtain a konjac glucomannan derived carbon precursor;
secondly, leading the carbon precursor derived from konjac glucomannan to be in Ar/H 2 Carbonizing at high temperature in the atmosphere, and cooling to room temperature to obtain konjac glucomannan derived carbon KGMC;
step three, adding Fe (NO) 3 ) 3 ·9H 2 Adding O into water, and stirring to obtain an iron salt solution; adding konjac glucomannan derived carbon into a ferric salt solution, and stirring to obtain a suspension of nZVI @ KGMC; directionally freezing the nZVI @ KGMC suspension, and drying in vacuum to obtain a 3D nZVI @ KGMC precursor;
step four, mixing3D nZVI @ KGMC precursor in Ar/H 2 And carrying out in-situ reduction at high temperature in the atmosphere, and cooling to obtain nZVI @ KGMC, namely the biomass derived carbon-coated nano zero-valent iron material for radionuclide treatment.
Preferably, in the first step, the mass ratio of the konjac glucomannan to the water is 1; the stirring time is 10 to 15 hours.
Preferably, in the second step, the temperature rise rate of the high-temperature carbonization is 8-12 ℃/min, the temperature of the high-temperature carbonization is 900-1100 ℃, and the time of the high-temperature carbonization is 1-3 hours; ar/H 2 Ar and H in the atmosphere 2 Is 95.
Preferably, in the second step, the obtained konjac glucomannan derived carbon KGMC and absolute ethyl alcohol are added into a high-temperature high-pressure reaction kettle, the high-temperature high-pressure reaction kettle is sealed, the sealed high-temperature high-pressure reaction kettle is heated to reach the supercritical temperature and pressure of the ethyl alcohol, the temperature and pressure are kept for 5-10 min, the cooling and pressure relief are carried out, a solid product is taken out, and the vacuum drying is carried out.
Preferably, the supercritical temperature and pressure for reaching the ethanol are 225-235 ℃ and 10-15 MPa respectively; the mass ratio of the konjac glucomannan derived carbon KGMC to the absolute ethyl alcohol is 1.
Preferably, in step three, fe (NO) 3 ) 3 ·9H 2 The mass ratio of O to water is 0.8-1.2; said Fe (NO) 3 ) 3 ·9H 2 The mass ratio of the O to the konjac glucomannan derived carbon is 0.8-1.2; the stirring time is 10 to 15 hours.
Preferably, in the third step, the process of directionally freezing the suspension of nzvi @ kgmc is as follows: adding the nZVI @ KGMC suspension into a mould, fixing the bottom of the mould on a steel plate, and placing the steel plate in liquid nitrogen for freezing so as to realize the directional freezing of the nZVI @ KGMC suspension; the vacuum drying time is 6-8 days.
Preferably, the resulting suspension of nzvi @ kgmc is subjected to hermetic pressure sonication; the pressure ultrasonic treatment adopts gradient ultrasonic treatment, and the process comprises the following steps: stopping ultrasound for 5min after each ultrasonic reaction for 10-15 min, and circulating sequentially, wherein the total time of gradient ultrasound treatment is 3-4 h, the frequency is 5-8 MHz, the pressure is 10-20 MPa, and the temperature is 45-55 ℃.
Preferably, in the fourth step, the temperature rise speed of the high-temperature in-situ reduction is 8-12 ℃/min, the temperature of the high-temperature in-situ reduction is 900-1100 ℃, and the time of the high-temperature in-situ reduction is 1-3 hours; ar/H 2 Ar and H in the atmosphere 2 Is 95.
The invention also provides application of the biomass-derived carbon-coated nano zero-valent iron material prepared by the preparation method in radionuclide enrichment.
The invention at least comprises the following beneficial effects: the biomass-derived carbon-coated nano zero-valent iron material nZVI @ KGMC for radionuclide enrichment is prepared by a biological assembly technology and an in-situ reduction method, wherein KGM-derived carbon can prevent nZVI particles from agglomerating, and the passivation rate of the carbon-coated nZVI particles is reduced; nZVI @ KGMC showed an effective U (VI) enrichment of 90.1% within 60 minutes. Meanwhile, nzvi @ kgmc showed good U (VI) enrichment efficiency in the presence of interfering ions and organics.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Description of the drawings:
FIG. 1 is an SEM image of nZVI @ KGMC of the present invention;
FIG. 2 is an SEM image of nZVI @ KGMC of the present invention at another magnification;
FIG. 3 is an SEM image of a 3D nZVI @ KGMC precursor;
FIG. 4 is a TEM image of nZVI @ KGMC;
FIG. 5 is an HRTEM image of nZVI @ KGMC;
FIG. 6 is a TEM image of nZVI @ KGMC and the corresponding elements; FIG. 7 is a TEM image of a commercially available nano-iron powder (C-nZVI, 99.9% metal base, 100nm, available from Aladdin);
FIG. 8 is a TEM image of konjac glucomannan-derived carbon KGMC;
FIG. 9 shows X-ray diffraction (XRD) patterns of KGMC, C-nZVI and nZVI @ KGMC, respectively.
FIG. 10a shows the FT-IR spectrum of KGMC and nZVI @ KGMC;
FIG. 10b is a Raman spectrum of KGMC and nZVI @ KGMC according to the present invention;
FIG. 11 is an XPS total spectrum of KGMC and nZVI @ KGMC;
FIG. 12 is an XAS spectrum of nZVI @ KGMC;
FIG. 13 shows the U (VI) enrichment curve versus time for KGMC and nZVI @ KGMC in a U (VI) -containing wastewater environment (U (VI) concentration of 200mg/L, pH = 5.0);
FIG. 14 shows the relationship between U (VI) enrichment curves of nZVI @ KGMC, nZVI @ KGMC-1, and nZVI @ KGMC-2 in U (VI) -containing wastewater environment and time (U (VI) concentration is 200mg/L, pH = 5.0);
FIG. 15 shows the removal rate of U (VI) by nZVI @ KGMC, nZVI @ KGMC-1 and nZVI @ KGMC-2 at different initial concentrations (reaction time 60 min);
FIG. 16 is the removal efficiency of nZVI @ KGMC on U (VI) and the degradation rate on organics in a simulated radioactive wastewater system containing organics;
FIG. 17 is an ESR spectrum of nZVI @ KGMC;
FIG. 18 is a graph showing the U (VI) removal efficiency of nZVI @ KGMC at different pH;
FIG. 19 is the removal efficiency of nZVI @ KGMC on U (VI) in the presence of other interfering ions;
FIG. 20 shows FT-IR spectra of nZVI @ KGMC and nZVI @ KGMC + U (VI);
FIG. 21 shows an XPS spectrum summary for nZVI @ KGMC and nZVI @ KGMC + U (VI);
FIG. 22 shows the Fe L-edge XAS spectra of nZVI @ KGMC before and after the reaction.
The specific implementation mode is as follows:
the present invention is described in further detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description text.
It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
Example 1:
a preparation method of biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment comprises the following steps:
step one, adding 1g of konjac glucomannan into 100mL of deionized water, stirring for 12 hours at room temperature to obtain a suspension, and freeze-drying to obtain a konjac glucomannan derived carbon precursor;
secondly, the precursor of the carbon derived from konjac glucomannan is placed in Ar/H 2 (95);
step three, adding 0.9g of Fe (NO) 3 ) 3 ·9H 2 Adding O into 100mL of water, and stirring to obtain an iron salt solution; adding 1g of konjac glucomannan derived carbon into an iron salt solution, and stirring for 12h to obtain an nzvi @ KGMC suspension; directionally freezing the nZVI @ KGMC suspension (adding the nZVI @ KGMC suspension into a mold, fixing the bottom of the mold on a steel plate, placing the steel plate in liquid nitrogen for directional freezing), and performing vacuum drying for 7 days to obtain a 3D nZVI @ KGMC precursor;
step four, the precursor of 3D nZVI @ KGMC is put in Ar/H 2 (95).
Example 2:
a preparation method of biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment comprises the following steps:
step one, adding 1g of konjac glucomannan into 100mL of deionized water, stirring for 12 hours at room temperature to obtain a suspension, and freeze-drying to obtain a konjac glucomannan derived carbon precursor;
secondly, leading the carbon precursor derived from konjac glucomannan to be in Ar/H 2 (95n, heating to 950 ℃, carbonizing for 3 hours, and then cooling to room temperature to obtain konjac glucomannan derived carbon KGMC;
step three, adding 0.9g of Fe (NO) 3 ) 3 ·9H 2 Adding O into 100mL of water, and stirring to obtain an iron salt solution; adding 1g of konjac glucomannan derived carbon into an iron salt solution, and stirring for 12h to obtain an nzvi @ KGMC suspension; directionally freezing the nZVI @ KGMC suspension (adding the nZVI @ KGMC suspension into a mould, fixing the bottom of the mould on a steel plate, placing the steel plate in liquid nitrogen for directional freezing), and performing vacuum drying for 7 days to obtain a 3D nZVI @ KGMC precursor;
step four, the precursor of 3D nZVI @ KGMC is put in Ar/H 2 (95).
Example 3:
a preparation method of biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment comprises the following steps:
step one, adding 1g of konjac glucomannan into 100mL of deionized water, stirring for 12 hours at room temperature to obtain a suspension, and freeze-drying to obtain a konjac glucomannan derived carbon precursor;
secondly, leading the carbon precursor derived from konjac glucomannan to be in Ar/H 2 (95); adding 1g of konjac glucomannan derivative carbon KGMC and 10mL of absolute ethyl alcohol into a high-temperature high-pressure reaction kettle, sealing, and heating the sealed high-temperature high-pressure reaction kettle to the temperature of 230 ℃ and the pressure of 13MPa; reaching the supercritical temperature and pressure of ethanol, keeping the temperature and pressure for 10min, cooling and decompressing, taking out the solid product, and drying in vacuum to obtain the treated konjac glucomannan derivative carbon KGMC;
step three, adding 0.9g of Fe (NO) 3 ) 3 ·9H 2 Adding O into 100mL of water, and stirring to obtain an iron salt solution; mixing 1g of treated konjac glucomannanAdding the derived carbon into the ferric salt solution, and stirring for 12h to obtain nZVI @ KGMC suspension; directionally freezing the nZVI @ KGMC suspension (adding the nZVI @ KGMC suspension into a mould, fixing the bottom of the mould on a steel plate, placing the steel plate in liquid nitrogen for directional freezing), and performing vacuum drying for 7 days to obtain a 3D nZVI @ KGMC precursor;
step four, putting the precursor of 3D nZVI @ KGMC in Ar/H 2 (95).
Example 4:
a preparation method of biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment comprises the following steps:
step one, adding 1g of konjac glucomannan into 100mL of deionized water, stirring for 12 hours at room temperature to obtain a suspension, and freeze-drying to obtain a konjac glucomannan derived carbon precursor;
secondly, the precursor of the carbon derived from konjac glucomannan is placed in Ar/H 2 (95); adding 1g of konjac glucomannan derived carbon KGMC and 10mL of absolute ethyl alcohol into a high-temperature high-pressure reaction kettle, sealing, and heating the sealed high-temperature high-pressure reaction kettle to the temperature of 230 ℃ and the pressure of 13MPa; reaching the supercritical temperature and pressure of ethanol, keeping the temperature and pressure for 10min, cooling and decompressing, taking out a solid product, and performing vacuum drying to obtain the treated konjac glucomannan derived carbon KGMC;
step three, adding 0.9g of Fe (NO) 3 ) 3 ·9H 2 Adding O into 100mL of water, and stirring to obtain an iron salt solution; adding 1g of treated konjac glucomannan derived carbon into a ferric salt solution, and stirring for 12h to obtain an nZVI @ KGMC suspension; carrying out sealed pressurized ultrasonic treatment on the obtained nZVI @ KGMC suspension; the pressure ultrasonic treatment adopts gradient ultrasonic treatment, and the process comprises the following steps: stopping ultrasound for 5min after each ultrasound reaction for 10min, and circulating sequentially, wherein the total time of gradient ultrasound treatment is 3h, the frequency is 5MHz, the pressure is 15MPa, and the temperature is 45 ℃; directionally freezing the ultrasonically treated nZVI @ KGMC suspension (adding the nZVI @ KGMC suspension into a mold, fixing the bottom of the mold on a steel plate, and placing the steel plate in liquid nitrogen for directional freezing), and performing vacuum drying for 7 days to obtain a 3D nZVI @ KGMC precursor;
step four, the precursor of 3D nZVI @ KGMC is put in Ar/H 2 (95).
The microstructure and surface elemental composition of nzvi @ kgmc were characterized by SEM and TEM. FIGS. 1 and 2 are SEM images of nZVI @ KGMC at different magnifications, respectively. The low power SEM images showed the 3D honeycomb structure of nzvi @ kgmc, mainly due to the formation of ice crystals during the directional freezing process; meanwhile, high power SEM images show that a layer of nanoparticles is uniformly grown on the KGMC surface, which is due to the pyrolysis of the ferric salt precursor at high temperature to produce nZVI. FIG. 3 is an SEM image of the 3D nZVI @ KGMC precursor;
FIG. 4 is a TEM image of nZVI @ KGMC, and FIG. 5 is a HRTEM image of nZVI @ KGMC; FIG. 6 is a TEM image of nZVI @ KGMC and the corresponding elements; FIG. 7 is a TEM image of a commercially available nano-iron powder (C-nZVI, 99.9% metal base, 100nm, available from Aladdin); FIG. 8 is a TEM image of konjac glucomannan-derived carbon KGMC;
as shown in FIG. 4, nZVI particles with a diameter of 50-100 nm are uniformly wrapped in KGMC, so that the oxidation of nZVI can be effectively slowed down. HRTEM image of nZVI @ KGMC shows clear grains with a layer spacing of 0.21nm, corresponding to Fe 0 The (111) lattice plane of (fig. 5). In addition, fe elements corresponded to the entire selected region of TEM and the associated energy dispersive X-ray (EDX) element mapping picture of nZVI @ kgmc, indicating that nZVI is uniformly distributed on the surface of nZVI @ kgmc (fig. 6). This is also supported by comparing TEM images of KGMC and nZVI @ KGMC with commercially available nano-iron (C-nZVI) (fig. 7 and 8).
FIG. 9 shows X-ray diffraction (XRD) patterns of KGMC, C-nZVI and nZVI @ KGMC, respectively. XRD pattern for KGMC, weak peaks at 44 ° and 24.The broad peaks at 2 ° represent the reflection of the (101) plane and graphite packing of the (002) plane, respectively, indicating that pyrolysis completely carbonizes KGM to graphite. For nZVI @ KGMC, the XRD pattern is related to the mixture of metallic iron, i.e. C with face-centered cubic structure 0.05 Fe 0.95 (JCPDS: 00-023-0298) and alpha-Fe (PDF # 87) -0721) have a body centered cubic structure, indicating that the KGMC-loaded metallic iron is mainly gamma-Fe and a small fraction of alpha-Fe. The presence of the high temperature phase γ -Fe may be due to the inability to achieve volume expansion during the cooling phase due to encapsulation of nZVI particles in the KGMC. Wherein the presence of a metastable iron phase (gamma-Fe) at ambient temperature means Fe 0 The particles have thermodynamically stable carbon shells.
FIG. 10a shows the FT-IR spectrum of KGMC and nZVI @ KGMC. 3432. 2923, 1636, 1385 and 1045cm -1 The peaks at (a) were due to stretching vibrations of the O-H, C = C, C-OH and C-O-C groups, respectively, indicating that KGMC still maintains the enriched post-pyrolysis group of oxygen-containing functional groups. Furthermore, the D according to KGMC and nZVI @ KGMC (1349.7 cm) -1 ) And G (1599.2 cm) -1 ) The relative intensity (ID/IG) ratios of the bands, 0.933 and 1.047, respectively, revealed Fe loading 0 The degree of order of KGMC is reduced.
FIG. 11 is an XPS total spectrum of KGMC and nZVI @ KGMC, with the major components of the surface of nZVI @ KGMC being Fe, C and O. FIG. 12 is an XAS spectrum of nZVI @ KGMC, in which one set of peaks at about 710.4eV and another set of peaks at about 722.2eV are observed in an Fe L-edge XAS spectrum of nZVI @ KGMC, which is attributed to (L) 3 Region) 2p 3/2 → 3d transition sum (L2 region) 2p 1/2 → 3d conversion. Notably, fe in nZVI @ KGMC 0 The presence of (a) is confirmed by the appearance of its characteristic peak at 708.0 eV.
An enrichment experiment for radionuclides was performed in which 5mg of prepared KGMC, nZVI @ KGMC or commercially available C-nZVI particles were added to 20mL of U (VI) solutions of different initial concentrations (CU (VI) =8mg/L, 50mg/L, 100mg/L, 200mg/L and 400mg/L, pH = 5.0) and reacted thoroughly in an air bath constant temperature shaker. The pH of the suspension is then adjusted with 0.1M HCl and NaOH solutions, and the volume is then negligible. The U (VI) concentrations before and after reduction were measured by arsine-III spectrophotometryMeasured at a wavelength of 651.8 nm. For the pH effect, the initial pH of the U (VI) (8 mg/L) solution was adjusted to 3.0-9.0 using a pH benchtop. Experiments with interfering ions were performed in 8mg/L U (VI) solution (pH = 5.0) at 10 times the interfering ion dose. And the experiment with organic was performed in a 100mg/L U (VI) solution (pH = 5.0) with an organic concentration of 10 mg/L. The U (VI) removal rate (Ads,%) was calculated as Ads = [ (C) 0 -C t )/C 0 ]×100％；
Usually, the enrichment experiment is carried out in an air atmosphere with a solid-to-liquid ratio of 0.25 g/L. FIG. 13 shows the U (VI) enrichment curve of KGMC and nZVI @ KGMC in a U (VI) -containing wastewater environment versus time (U (VI) concentration of 200mg/L, pH = 5.0). After the reaction time reaches 60min, the adsorption of KGMC to U (VI) reaches equilibrium, the removal rate is only 25.2%, and when the initial concentration is 200mg/L, the enrichment rate of nZVI @ KGMC to U (VI) reaches 75.7% after the reaction time reaches 10 min. The above results indicate that nZVI @ KGMC has faster U (VI) removal rate and higher enrichment capacity. FIG. 14 shows the U (VI) enrichment curves of nZVI @ KGMC, nZVI @ KGMC-1, nZVI @ KGMC-2 in U (VI) -containing wastewater environment as a function of time (U (VI) concentration of 200mg/L, pH = 5.0). It can be seen that nZVI @ KGMC-1 and nZVI @ KGMC-2 have higher enrichment capacity than nZVI @ KGMC, because the agglomeration of KGM derived carbon itself can be prevented by treating the KGM derived carbon, and the agglomeration of nZVI particles can be further prevented, and meanwhile, the treated KGM derived carbon can play an auxiliary role in enriching U (VI); simultaneously to nZVI @ KGMC suspension seal pressurization ultrasonic treatment, improved the misce bene degree of KGM derived carbon with molysite solution, further improved nZVI @ KGMC's enrichment ability.
FIG. 15 shows the removal rate of U (VI) by nZVI @ KGMC, nZVI @ KGMC-1 and nZVI @ KGMC-2 at different initial concentrations (reaction time 60 min); specifically, nzVI @ KGMC-1 and nzVI @ KGMC-2 still showed a significant U (VI) removal capacity of more than 90% for U (VI) at initial U (VI) concentrations of 8mg/L to 200 mg/L. Even if the concentration of the U (VI) solution is 400mg/L, high removal rate of 49.3% is still maintained at nzvi @ KGMC, while high removal rates of greater than 55% are maintained at nzvi @ KGMC-1 and nzvi @ KGMC-2.
FIG. 16 is the removal efficiency of nZVI @ KGMC on U (VI) and the degradation rate on organics in a simulated radioactive wastewater system containing organics; as shown in FIG. 16, application of nZVI @ KGMC to 100mg/L uranium-containing wastewater containing organic matter [10mg/L Tannic Acid (TA), methylene Blue (MB), bisphenol A (BPA) and rhodamine B (RhB) ], indicates that the presence of organic matter hardly affects the concentration of uranium. Meanwhile, nZVI @ KGMC can degrade more than 80% of organic matters within 60 minutes. These results are mainly due to the reaction of nZVI particles in the above solution system to produce OH (as shown in fig. 17).
FIG. 18 is a graph showing the U (VI) removal efficiency of nZVI @ KGMC at different pH; for the influence of pH, the U (VI) species are predominantly UO at pH 3 2 2+ Exist in the form of (1). Therefore, the main reason why the removal rate is low at pH =3 may be H in the solution + Or H 3 O + Competes with the surface active site of nzvi @ kgmc for U (VI), resulting in decreased uranium removal rates. Then, the removal rate gradually increased as the pH value increased from 3.0 to 5.0, and then at pH>After 5.0, there is a slight decrease. Meanwhile, the U (VI) removing capacity of the nZVI @ KGMC can be kept at 85% under the alkaline pH.
FIG. 19 is the removal efficiency of nZVI @ KGMC on U (VI) in the presence of other interfering ions; when other interfering ions exist, nZVI @ KGMC still shows high anti-interference capability.
The changes in the surface functionality and composition of nZVI @ KGMC before and after the reaction were described using FT-IR, XPS and XAS. FIG. 20 shows FT-IR spectra of nZVI @ KGMC and nZVI @ KGMC + U (VI). Notably, U (VI) is at 908.1cm -1 U-O bond and U (IV) 567.9cm -1 The U-O bond at (A) is due to two new peaks in the FT-IR spectrum after the reaction. The results show that Fe 0 The transfer of electrons can reduce U (VI) adsorbed on KGMC to U (IV).
FIG. 21 shows the FT-IR XPS spectra of nZVI @ KGMC and nZVI @ KGMC + U (VI). After the reaction, XPS spectrum of nZVI @ KGMC showed U peak.
FIG. 22 shows the Fe L-edge XAS spectra of nZVI @ KGMC before and after the reaction. Fe in comparison with nZVI @ KGMC 0 The characteristic peak at 708.0eV disappears after the reaction, and these phenomena are mainly attributed to Fe 0 And Fe (II) reduces U (VI) to U (IV).
While embodiments of the invention have been described above, it is not intended to be limited to the details shown, described and illustrated herein, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed, and to such extent that such modifications are readily available to those skilled in the art, and it is not intended to be limited to the details shown and described herein without departing from the general concept as defined by the appended claims and their equivalents.
Claims (10)
1. A preparation method of biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment is characterized by comprising the following steps:
step one, adding konjac glucomannan into water, stirring to obtain a suspension, and freeze-drying to obtain a konjac glucomannan derived carbon precursor;
secondly, leading the carbon precursor derived from konjac glucomannan to be in Ar/H 2 Carbonizing at high temperature in the atmosphere, and cooling to room temperature to obtain konjac glucomannan derived carbon KGMC;
step three, adding Fe (NO) 3 ) 3 ·9H 2 Adding O into water, and stirring to obtain an iron salt solution; adding konjac glucomannan derived carbon into a ferric salt solution, and stirring to obtain a suspension of nZVI @ KGMC; directionally freezing the nZVI @ KGMC suspension, and drying in vacuum to obtain a 3D nZVI @ KGMC precursor;
step four, putting the precursor of 3D nZVI @ KGMC in Ar/H 2 And carrying out in-situ reduction at high temperature in the atmosphere, and cooling to obtain nZVI @ KGMC, namely the biomass derived carbon-coated nano zero-valent iron material for radionuclide treatment.
2. The method for preparing a biomass-derived carbon-encapsulated nano zero-valent iron material for radionuclide enrichment according to claim 1, wherein in the first step, the mass ratio of konjac glucomannan to water is 1; the stirring time is 10 to 15 hours.
3. The biomass-derived carbon-encapsulated nano-zeros for radionuclide enrichment of claim 1The preparation method of the iron material is characterized in that in the second step, the temperature rise speed of high-temperature carbonization is 8-12 ℃/min, the temperature of the high-temperature carbonization is 900-1100 ℃, and the time of the high-temperature carbonization is 1-3 hours; ar/H 2 Ar and H in the atmosphere 2 Is 95.
4. The method for preparing the biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment according to claim 1, wherein in the second step, the obtained konjac glucomannan-derived carbon KGMC and absolute ethanol are added into a high-temperature high-pressure reaction kettle, the reaction kettle is sealed, the sealed high-temperature high-pressure reaction kettle is heated to reach the supercritical temperature and pressure of ethanol, the temperature and pressure are maintained for 5-10 min, the cooling and pressure relief are carried out, a solid product is taken out, and the vacuum drying is carried out.
5. The method of claim 4, wherein the supercritical temperature and pressure to ethanol are 225-235 ℃ and 10-15 MPa, respectively; the mass ratio of the konjac glucomannan derivative carbon KGMC to the absolute ethyl alcohol is 1.
6. The method of claim 1, wherein in step three, fe (NO) is used in the preparation of the biomass-derived carbon-encapsulated nanoscale zero-valent iron material for radionuclide enrichment 3 ) 3 ·9H 2 The mass ratio of O to water is 0.8-1.2; said Fe (NO) 3 ) 3 ·9H 2 The mass ratio of the O to the konjac glucomannan derived carbon is 0.8-1.2; the stirring time is 10 to 15 hours.
7. The method for preparing the biomass-derived carbon-encapsulated nanoscale zero-valent iron material for radionuclide enrichment according to claim 1, wherein in the third step, the directional freezing of the suspension of nzvi @ kgmc comprises the following steps: adding the nZVI @ KGMC suspension into a mould, fixing the bottom of the mould on a steel plate, and placing the steel plate in liquid nitrogen for freezing so as to realize the directional freezing of the nZVI @ KGMC suspension; the vacuum drying time is 6-8 days.
8. The method for preparing the biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment according to claim 1, wherein the obtained nzvi @ kgmc suspension is subjected to sealed pressure ultrasonic treatment; the pressure ultrasonic treatment adopts gradient ultrasonic treatment, and the process comprises the following steps: stopping ultrasound for 5min after every 10-15 min of ultrasound reaction, and circulating sequentially, wherein the total time of gradient ultrasound treatment is 3-4 h, the frequency is 5-8 MHz, the pressure is 10-20 MPa, and the temperature is 45-55 ℃.
9. The method for preparing the biomass-derived carbon-coated nano zero-valent iron material for radionuclide enrichment according to claim 1, wherein in the fourth step, the temperature rise rate of the high-temperature in-situ reduction is 8 to 12 ℃/min, the temperature of the high-temperature in-situ reduction is 900 to 1100 ℃, and the time of the high-temperature in-situ reduction is 1 to 3 hours; ar/H 2 Ar and H in the atmosphere 2 Is 95.
10. The use of the biomass-derived carbon-coated nano zero-valent iron material prepared by the preparation method according to any one of claims 1 to 9 in radionuclide enrichment, wherein the biomass-derived carbon-coated nano zero-valent iron material is added into wastewater containing radioactive nuclides and stirred to realize the enrichment of the radioactive nuclides by the biomass-derived carbon-coated nano zero-valent iron material.
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