Physico-chemical and biological coupled method and device for removing heavy metal vanadium from soil

Abstract

The application relates to the field of environmental governance technology, in particular to a physicochemical-biological coupling method and device for removing heavy metal vanadium from soil, which comprises the following steps: adding soil contaminated by pentavalent vanadium [V(V)] into a reactor provided with magnetic pyrite particles and anaerobic sediment, then adding synthetic groundwater into the reactor and stirring uniformly to obtain a test water sample; curing the test water sample under anaerobic and light-shielded conditions for at least eight days, so that the microorganisms in the anaerobic sediment convert soluble pentavalent vanadium into tetravalent vanadium precipitate by taking the magnetic pyrite as an electron donor, and the tetravalent vanadium precipitate is attached to unreacted magnetic pyrite; obtaining a solid soil sample after reduction through mud-water separation, and recycling the metal vanadium in the soil through an external magnetic field, wherein the magnetic force strength of the external magnetic field is 1200-3000Gs.

Description

TECHNICAL FIELD

[0001] The one or more embodiments of the specification relate to the technical field of environmental governance, in particular to a physico-chemical-biological coupling method and device for removing heavy metal vanadium from soil. BACKGROUND

[0002] Vanadium (V) is a heavy metal pollutant, due to its unique multivalent state, it is widely distributed in various spheres of the earth, among which the most toxic is pentavalent vanadium [V(V)]. With the increase of intensive industrial activities such as smelting, mining, fossil fuel combustion, etc., the environmental release of vanadium dispersed and universal in global circulation, causing serious pollution to soil.

[0003] Traditional soil remediation technologies include chemical reduction, electrokinetic process, ion exchange method and phytoremediation technology. In recent years, in-situ remediation of vanadium contaminated soil by delivering biologically active substances into soil and using indigenous microorganisms is considered a very promising technology. There have been extensive studies on the use of gaseous electron donors, organic matter, zero-valent iron and elemental sulfur to remediate vanadium pollution.

[0004] However, these materials usually have high cost and toxicity. In order to reduce and fix V(V) in contaminated soil, other low-cost and eco-friendly materials are needed. In addition, V(V) is easily re-oxidized after reduction and remains in the soil. Therefore, it is still a difficult problem to completely reduce V(V) to separate it from the soil. SUMMARY

[0005] The embodiments of the specification describe a physico-chemical-biological coupling method and device for removing heavy metal vanadium from soil, which can efficiently and completely reduce pentavalent vanadium [V(V)] to separate it from vanadium contaminated soil, with low energy consumption and no secondary pollution.

[0006] In a first aspect, the embodiments of the specification provide a physico-chemical-biological coupling method for removing heavy metal vanadium from soil, comprising the following steps:

[0007] The soil contaminated with pentavalent vanadium [V(V)] is added to a reactor with pyrrhotite particles and anaerobic sediment, then synthetic groundwater is added to the above reactor and stirred uniformly to obtain a test water sample; the test water sample contains 20.0 ml of anaerobic sediment and 5.00 g of pyrrhotite particles in every 250.0 ml of synthetic groundwater; the anaerobic sediment is an aquifer sediment contaminated with pentavalent vanadium [V(V)], which is used to inoculate and construct a microbial community in the reactor;

[0008] The test water sample is maintained under anaerobic and light shielding conditions for at least eight days, and the microorganisms in the anaerobic sediment use the magnetite as an electron donor to convert the soluble pentavalent vanadium into a tetravalent vanadium precipitate and attach it to the unreacted magnetite;

[0009] The reduced solid soil sample is obtained by mud-water separation, and the metallic vanadium in the soil is recovered by an external magnetic field with a magnetic strength of 1200-3000Gs.

[0010] In some embodiments, the external magnetic field is generated by a neodymium magnet.

[0011] In some embodiments, the average particle size of the magnetite particles is 1.0mm.

[0012] In some embodiments, the initial pH of the test water sample is 5.5-8.5.

[0013] In some embodiments, the concentration of pentavalent vanadium [V(V)] in the test water sample is 25.0-100.0mg / L.

[0014] In some embodiments, NaHCO3 is added to the test water sample as a carbon source.

[0015] In some embodiments, the microorganisms in the anaerobic sediment include iron-oxidizing bacteria and sulfur-oxidizing bacteria.

[0016] In the second aspect, the embodiments of the present specification also provide a physicochemical-biological coupling device for removing heavy metal vanadium from soil, which is applied to the method described above and includes a reactor and a neodymium magnet; wherein the reactor contains synthetic groundwater, magnetite particles and anaerobic sediment, and contains 20.0ml of anaerobic sediment and 5.00g of magnetite particles per 250.0ml of synthetic groundwater; the anaerobic sediment is aquifer sediment contaminated by pentavalent vanadium [V(V)], which is used to inoculate and construct a microbial community in the reactor, and the microorganisms in the anaerobic sediment include iron-oxidizing bacteria and sulfur-oxidizing bacteria; the neodymium magnet is located outside the reactor, and the magnetic strength of the neodymium magnet is 1200-3000Gs.

[0017] In some embodiments, the reactor is a device for maintaining the microorganisms in the anaerobic sediment in a light-shielding and anaerobic environment.

[0018] In some embodiments, the reactor is a glass bottle with an aluminum foil wrapped around the body.

[0019] The scheme provided by the embodiment of the present specification constructs a microbial community by adding anaerobic sediment with pyrrhotite as an electron donor, the microbial uses the pyrrhotite to convert soluble pentavalent vanadium into tetravalent vanadium precipitate, which is attached to unreacted pyrrhotite, and then uses the magnetism of the pyrrhotite and an external magnetic field to remove vanadium from the soil, so as to reduce the potential harm caused by the re-release (or re-oxidation) of vanadate to the surrounding soil environment, and provide reference support for soil remediation projects. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 The removal efficiency of V(V) in biotic and abiotic reactors with pyrrhotite as an electron donor is shown;

[0022] Figure 2 The schematic diagram of magnetic recovery of metallic vanadium in soil is shown;

[0023] Figure 3a The vanadium content recovered by magnetism in the reactor with added pyrrhotite is shown;

[0024] Figure 3b The magnetic recovery efficiency in the reactor with added pyrrhotite is shown;

[0025] Figure 4 The change of vanadium occurrence form in soil in the bioreactor with added pyrrhotite in different reaction periods is shown;

[0026] Figure 5a The vanadium content recovered by magnetism using magnets with different magnetic strengths for magnetic recovery of metallic vanadium in soil is shown

[0027] Figure 5b The magnetic recovery efficiency using magnets with different magnetic strengths for magnetic recovery of metallic vanadium in soil is shown;

[0028] Figure 6 The concentration change of V(V) in the bioreactor with different initial pH values is shown;

[0029] Figure 7a The vanadium content recovered by magnetism using magnets from different pH reactors by magnetic recovery is shown;

[0030] Figure 7b The magnetic recovery efficiency using magnets from different pH reactors by magnetic recovery is shown;

[0031] Figure 8 Concentration of V(V) in different initial V(V) concentration bioreactors is shown;

[0032] Figure 9a Vanadium content recovered by magnetic recovery from different initial vanadium concentration bioreactors with magnets is shown;

[0033] Figure 9b Magnetic recovery efficiency of vanadium recovered by magnetic recovery from different initial vanadium concentration bioreactors with magnets is shown.

[0034] Figure 10a Microbial community composition and abundance of phylum level in different initial pH (P1, P2, P3 and P4 represent reactors with initial pH of 5.5, 6.5, 7.5 and 8.5, respectively) bioreactors is shown;

[0035] Figure 10b Microbial community composition and abundance of phylum level in different initial V(V) concentration (V1, V2, V3 and V4 represent reactors with initial V(V) concentration of 25.0, 50.0, 75.0 and 100.0 mg / L, respectively) bioreactors is shown;

[0036] Figure 11a Microbial community composition and abundance of genus level in different initial pH (P1, P2, P3 and P4 represent reactors with initial pH of 5.5, 6.5, 7.5 and 8.5, respectively) bioreactors is shown;

[0037] Figure 11b Microbial community composition and abundance of genus level in different initial V(V) concentration (V1, V2, V3 and V4 represent reactors with initial V(V) concentration of 25.0, 50.0, 75.0 and 100.0 mg / L, respectively) bioreactors is shown. DETAILED DESCRIPTION

[0038] It should be understood that the scope of protection of the present application is not limited to the specific embodiments described below; it should also be understood that the terms used in the embodiments of the present application are used to describe specific embodiments and are not intended to limit the scope of protection of the present application; in the specification and claims of the present application, the singular forms "a", "an" and "the" include the plural forms unless the context clearly indicates otherwise.

[0039] When the embodiments give numerical ranges, it is understood that, unless the present invention indicates otherwise, each numerical range's two endpoints, and any number between the two endpoints, can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by one of ordinary skill in the art. Except in the examples, or where otherwise explicitly indicated, 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 belongs. The present invention can be implemented using any methods, devices, and materials similar or equivalent to those described in the embodiments of the present invention according to the skill in the art, and according to the description of the present invention.

[0040] The "room temperature" described in the present invention has the meaning commonly known in the art, and generally refers to 24-28℃.

[0041] Pyrrhotite is a common natural iron sulfide, and its non-stoichiometric composition is Fe 1-x S, Fe(II) and S(-II) in the crystal lattice can act as electron donors, so that pyrrhotite is a natural reducing agent in nature, and pyrrhotite is also a mineral material with magnetism.

[0042] Vanadium is widely used in the steel industry, batteries, aerospace, medicine and other fields due to its excellent industrial performance. In the supergene environment sample (refers to the environmental sample collected from the surface or shallow underground, such as soil, sediment, river water, lake water, seawater, vegetation, etc., which usually contains rich microbial communities and biological active substances), vanadium generally exists in the form of V(IV) and V(V) oxidation state, and V(V) is generally more mobile than V(IV) compounds and has greater toxicity to animals and plants.

[0043] In order to efficiently and completely reduce pentavalent vanadium [V(V)] to separate it from the soil, the present embodiment provides a physicochemical-biological coupling method and device for removing heavy metal vanadium from soil. The present embodiment mainly verifies the effectiveness of pyrrhotite in fixing vanadium in soil, and detects the ability of pyrrhotite to reduce and fix V(V) and the efficiency of recovering soil metal vanadium by an external magnetic field through a series of solution experiments and influence factor tests. Finally, the microbial community in the reaction process is analyzed to explore the influence of different influence factors on the structure and abundance of the microbial community.

[0044] Microorganisms in anaerobic sediments can reduce V(V) to V(IV) using magnetite as an electron donor under the condition of sodium bicarbonate (NaHCO3) as the sole carbon source, and finally exist in the soil in the form of V(IV). Although V(IV) exists in a stable form in the soil for a short period of time, high concentrations of V(IV) may eventually re-enter the groundwater environment through microbial oxidation, Fe(III) oxidation, or self-dissolution. Therefore, it is necessary to consider separating high concentrations of V(IV) in the soil. The magnetic recovery in the embodiments of the present application is a technology that can separate pollutants in the soil from the soil using magnetic materials. Therefore, the present application recovers metal vanadium from the soil using natural magnetite ore with magnetism. The occurrence form of metal vanadium in the soil is measured by continuous extraction method, and the effects of different magnetic force sizes, pH, and initial concentrations of vanadium on the efficiency of magnetic recovery of metal vanadium in the soil and the response of microbial communities are explored, which has important practical significance for addressing the challenges of V(V) contaminated soil remediation.

[0045] Embodiment 1

[0046] Materials and methods

[0047] The anaerobic sediment (the anaerobic sediment refers to a sediment formed under anoxic or extremely low oxygen conditions) is a V(V)-contaminated aquifer sediment in Panzhihua, Sichuan Province. It should be noted that since the anaerobic sediment is a V(V)-contaminated aquifer sediment, the anaerobic sediment is used as the reactor inoculum and the V(V)-contaminated soil to be purified in the embodiments. That is, in the embodiments of the present application, V(V)-contaminated soil is not added. Of course, based on the wide application range of the removal method of the present application, V(V)-contaminated soil can also be added in some embodiments, which is not limited by the present application.

[0048] Magnetite (Fe 1-x S) was purchased from Guangzhou, China. The magnetite was ground and sieved to obtain particles with a diameter of about 1.0 mm for standby use.

[0049] All experiments were conducted at room temperature (24-28 °C) using 250.0 ml glass bottles as the main body of the bioreactor, and wrapped with aluminum foil to prevent the effect of light. Pyrrhotite was used as the preferred inorganic electron donor. In the bioreactor, pyrrhotite (5.00 g), anaerobic sediment sample (20.0 ml) was mixed with 250.0 ml of simulated synthetic groundwater, which was prepared by dissolving the following ingredients in deionized water (per liter): 0.246 g CaCl2, 1.0572 g MgCl2-6H2O, 0.4459 g NaCl, 0.0283 g KCl, 0.8082 g NaHCO3, 0.1557 g NH4Cl, 0.0299 g KH2PO4. NaHCO3 was used as the sole carbon source, V(V) was added to the synthetic groundwater in the form of NaVO3 (Aldrich, Shanghai, China) with an initial concentration of 50.0 mg / L. In order to maintain an anaerobic environment, the bioreactor was purged with nitrogen for 20.0 min, and then the bioreactor was sealed with a butyl rubber stopper in turn.

[0050] Neodymium magnets with different magnetic strengths were prepared, with magnetic strengths of 1200, 1800, 2400, and 3000, units Gauss (Gs).

[0051] Two groups of reactors were set up for the experiment: 1) biotic group of reactors with the addition of anaerobic sediment; 2) abiotic group of reactors with the addition of pyrrhotite only. The biotic group of reactors was set up with six parallel reactors, and the reactors were kept stable under their respective conditions, with each cycle being 8 days. The synthetic groundwater was replaced at the end of each cycle, and the continuous batch experiment was stable for 15 cycles, a total of 143 days. At the 1st, 3rd, 6th, 9th, 11th, and 15th cycles, destructive sampling was carried out, the magnetic iron in the reactor was recovered, and the recovered pyrrhotite and anaerobic sediment were subjected to physicochemical characterization.

[0052] Test method

[0053] All aqueous samples were pretreated by 0.22 μM filter before analysis. The concentration of V(V) was determined at a wavelength of 510 nm using a UV spectrophotometer (UV-8000S, Shanghai, China). The content of dissolved total vanadium was determined by inductively coupled plasma mass spectrometry (ICP-MS, X series, Thermo Fisher, Germany). The measurement of SO4 2- was determined by anion chromatograph (Basic IC 792, Metrohm, Switzerland).

[0054] Microbial samples were collected from the inoculum (anaerobic sediment) and different operating bioreactors. The Viable Count Kit (BIOLOG, USA) was used according to the manufacturer's instructions. DNA of microorganisms was extracted by PowerSoil® DNA Isolation Kit (MO BIO®, Arup, California, USA). Bacterial and archaeal 16S rRNA genes were amplified using PCR primers 515F (5'-gtgccagcmgccgg-3') and 806R (5'-GGACTACHVGGGTWTCTAAT-3'). The resulting DNA was used for high-throughput 16S rRNA gene sequencing on the MiSeq platform (Illumina, USA), which was provided by Majorbio Technology (Shanghai, China). Microbial information was obtained by processing sequencing data according to the standard channel.

[0055] Determination of soil vanadium forms: The improved BCR heavy metal form extraction method was used to extract the chemical forms of vanadium in soil samples.

[0056] (1) Acid extractable state: 0.50 g of sieved air-dried soil was weighed, 20.0 mL of glacial acetic acid (CH3COOH, 0.11 mol / L) solution was added, and after oscillation at 25.0 °C for 16 h, centrifugation was performed at 4000.0 rpm for 20.0 min, and the supernatant was collected and filtered through a 0.45 μM filter for preservation. 20.0 mL of deionized water was added to the residue, and oscillation, centrifugation, and discarding of the supernatant were performed.

[0057] (2) Reducible state: 20.0 mL of hydroxylamine hydrochloride (NH3OHCl, 0.50 mol / L, adjusted to pH 1.50 with 2.00 mol / L nitric acid) was added to the residue of the previous step, oscillated for 16 h, then centrifuged at 4000.0 rpm for 20.0 min, and the supernatant was collected and filtered through a 0.45 μM filter for preservation. 20.0 mL of deionized water was added to the residue, and oscillation, centrifugation, and discarding of the supernatant were performed.

[0058] (3) Oxidizable state: 5.00 mL of hydrogen peroxide (H2O2, 30.0%) was added to the residue of the previous step, covered, and reacted at room temperature for 1 h with intermittent shaking, then heated in a water bath at 85.0 °C for 1 h, and when the volume of H2O2 was reduced to 1.00-2.00 mL, 5.00 mL of H2O2 was added, uncovered, and heated in a water bath at 85.0 °C for 1 h, until H2O2 was evaporated to near dryness. After the sample was cooled, 25.0 mL of ammonium acetate (1.00 mol / L, pH = 2.00) was added, oscillated at 25.0 °C for 16 h, then centrifuged at 4000.0 rpm for 20.0 min, and the supernatant was collected and filtered through a 0.45 μM filter for preservation. 20.0 mL of deionized water was added to the residue, and oscillation, centrifugation, and discarding of the supernatant were performed.

[0059] (4) Residue state: The remaining sample was freeze-dried and placed in a muffle furnace digestion tube. Concentrated nitric acid, perchloric acid, and hydrofluoric acid were sequentially added to the digestion tube. The digestion tube was placed in a graphite digestion instrument for digestion. After the sample was completely digested, the digestion solution was diluted to 50.0 mL with ultrapure water, and then the digestion solution was filtered. The content of vanadium metal in the filtrate was determined by inductively coupled plasma optical emission spectrometry (ICP-OES, Prodigy XP, Leeman Labs Inc, USA).

[0060] Example 2

[0061] Influencing factor experiment of magnetic recovery of soil metal vanadium by pyrrhotite

[0062] The related influencing factors include: different magnetic strength of the magnet, initial pH, and initial V(V) concentration, and the change trend of V(V) in the reaction period is determined synchronously. The following influencing factor experiments are carried out under the condition that bicarbonate is the inorganic carbon source:

[0063] (1) Different magnetic strength of the magnet: Four groups of parallel bioreactors with the same initial conditions were set up and operated stably, and then three operation periods were continuously carried out. Then, the destructive sampling was carried out by using neodymium magnets with different magnetic strengths (1200, 1800, 2400, and 3000 GS), and the recovery efficiency of soil metal vanadium by the neodymium magnets with different magnetic strengths was measured.

[0064] (2) Initial pH: Four groups of parallel bioreactors with the same initial pH of 5.5, 6.5, 7.5, and 8.5 were set up and operated stably, and then three operation periods were continuously carried out. The experiment of magnetic recovery of soil metal vanadium was carried out.

[0065] (3) Initial V(V) concentration: Four groups of parallel bioreactors with the same initial V(V) concentration of 25.0, 50.0, 75.0, and 100.0 mg / L were set up and operated stably, and then three operation periods were continuously carried out. The experiment of magnetic recovery of soil metal vanadium was carried out.

[0066] Example 3

[0067] Feasibility study of magnetic recovery of metal vanadium

[0068] As a Fe(II)-containing mineral, pyrrhotite can be dissolved by microorganisms, and the dissolved Fe(II) and S(-II) can be used as electron donors to promote the reduction of V(V). In addition, pyrrhotite has obvious magnetism compared with other Fe(II)-containing minerals, so the feasibility of pyrrhotite as a magnet for recovering metal vanadium from soil was verified.

[0069] Figure 1The removal efficiency of V(V) by pyrrhotite as an electron donor in biotic and abiotic reactors was investigated as a function of experimental period. The continuous batch experiment was stable for 15 periods, a total of 143 days, and the results again verified that pyrrhotite is a reliable electron donor, not only can microorganisms utilize the electrons provided by it to bioreduce V(V), but also has the ability to chemically reduce V(V) itself.

[0070] The destructive sampling was performed at different periods of the bioreactor, and the magnetic recovery of vanadium in the soil was performed by applying a magnetic field (as shown in Figure 2 The neodymium magnet was rotated around the reactor and the reactor was vibrated to magnetically recover vanadium in the soil, as shown in Figure 3a The soil in the reactor and the soil after magnetic adsorption were destructively sampled from the bioreactor running to the 1st, 3rd, 6th, 9th, 11th and 15th periods, respectively, and then digested with concentrated nitric acid, perchloric acid and hydrofluoric acid to determine the content of vanadium. As can be seen from FIG. 3, the dissolved vanadium in the reactor will eventually enter the sediment in the form of solid, further verifying that V(V) is reduced to solid V(IV) under the action of biology. Interestingly, the soil after magnetic separation was detected to contain vanadium elements, indicating that pyrrhotite as a material for magnetic recovery of vanadium from soil is feasible, and pyrrhotite itself can adsorb a certain amount of vanadium. In addition, the magnetic recovery efficiency (the proportion of the content of vanadium recovered by magnetism to the total vanadium content in the soil) was analyzed and calculated, as shown in Figure 3b The magnetic recovery efficiencies of different periods were 48.4±5.90%, 43.2±4.60%, 45.5±3.50%, 39.2±1.50%, 43.3±1.40% and 47.4±2.50%, respectively, indicating that under the action of the external magnetic field, the vanadium-containing product separates from the soil along with the pyrrhotite, thereby completely reducing the vanadium content in the soil and fundamentally solving the problem of re-oxidation of vanadium after remediation. Therefore, the magnetic recovery of vanadium using pyrrhotite is stable and feasible.

[0071] In summary, the use of natural magnetic minerals can effectively achieve the in-situ reduction of V(V) in soil, and it is easy to separate and remove from contaminated soil by an external magnetic field. This provides a new method for the clean remediation of soil contaminated by V(V).

[0072] Example 4

[0073] Occurrence of vanadium in soil

[0074] In this experiment, the chemical forms of vanadium in the soil at different reaction periods were studied by the improved BCR sequential extraction method, involving acid extractable, reducible, oxidizable and residual forms, and the results are shown in Figure 4The results show that vanadium in soil is mainly in the acid extractable and reducible fractions, indicating that vanadium is mainly present in soil under the action of microbial reduction and ore adsorption, and is easily re-entered into the aqueous solution with environmental changes. The complex interaction between (bio) geochemical processes will control the occurrence state and distribution of vanadium in soil. For example, biological activity in soil can increase the availability of vanadium. On the other hand, the reducible fraction is sensitive to environmental changes, and when the redox potential of the soil decreases or is in an anaerobic state, vanadium is released into the soil pore water, thereby increasing its potential health risk. Therefore, it is generally believed that the reducible fraction in BCR contributes more to the potential mobility and effectiveness of vanadium than the oxidizable fraction.

[0075] In addition, with the increase of the reaction period, the proportion of the residual fraction gradually increases, indicating that the metal vanadium in the soil exists in the form of a low-bioavailability residual fraction or a more stable form Figure 4 The different occurrence forms of metals in soil can directly affect the ability of the element to activate and migrate in soil and its bioavailability. The main form of vanadium in the farmland soil near the vanadium smelter is the reducible fraction with high bioavailability. In general, vanadium in the residual fraction does not participate in the biogeochemical processes of the soil. However, it is particularly important to note that most of the vanadium samples in previous studies are in the form of residual fraction in soil.

[0076] Example 5

[0077] Study on the efficiency of recovering metal vanadium by magnetic force

[0078] As Figure 5a -b is the content of soil metal vanadium and the magnetic recovery efficiency using magnets with different magnetic field strengths. When the magnetic field strength is 1200, 1800, 2400 and 3000 Gs, the content of recovered metal vanadium in soil is 196.5 ± 32.1, 213.2 ± 43.3, 214.4 ± 51.2 and 223.7 ± 33.7 mg / kg, respectively. Among them, the magnetic recovery efficiency of different magnetic field strengths is 44.0 ± 3.71%, 45.4 ± 4.93%, 48.1 ± 4.62% and 49.0 ± 4.73%, respectively. The results show that the higher the magnetic field strength of the external magnetic field, the higher the recovery efficiency of vanadium in soil, which is mainly because the surface of the pyrrhotite is corroded and oxidized under the participation of microorganisms, and the increase of surface oxides will weaken the magnetism of pyrrhotite to a certain extent, so the greater the magnetic field strength of the external magnetic field, the more unreacted pyrrhotite can be adsorbed.

[0079] Example 6

[0080] Effect of different pH on the efficiency of recovering metal vanadium

[0081] As Figure 6The removal efficiency of V(V) in the reactor was 47.3 ± 1.32%, 55.3 ± 2.53%, 49.1 ± 1.40%, and 39.0 ± 2.41% when the initial pH in the system was 5.5, 6.5, 7.5, and 8.5, respectively. The reduction performance of V(V) in the reactor was poor under strong acidic or basic conditions, and the removal efficiency was the highest at pH 6.5. The optimal pH for the reactor to reduce V(V) was pH 6.5, and too high or too low pH would inhibit the removal of V(V) and reduce the removal efficiency. The reason could be that the activity of enzymes in microorganisms would change with the change of pH, and too high or too low pH would inhibit the activity of enzymes and affect the metabolic activity of microorganisms. In addition, under weak acidic conditions, Fe(II) would be leached from the ore, and the reaction zone would be expanded from the surface to the liquid, thereby enhancing the chemical action of the pyrrhotite.

[0082] As Figure 7a The content of recovered metal vanadium in the soil and the magnetic recovery efficiency at different initial pH values in the bioreactor. When the initial pH was 5.5, 6.5, 7.5, and 8.5, the content of recovered metal vanadium in the soil was 166.5 ± 34.5, 207.2 ± 45.3, 189.4 ± 52.3, and 143.7 ± 32.1 mg / kg, respectively. Among them, the magnetic recovery efficiency in the reactor at different pH values was 46.7 ± 4.61%, 50.1 ± 4.50%, 48.6 ± 3.42%, and 43.2 ± 4.52%, respectively, indicating that the magnetic recovery efficiency was the highest in the reactor at pH 6.5, which was consistent with the change of V(V) removal rate Figure 5a The reactor at pH 6.5 had a higher V(V) removal rate, on the one hand because the microbial activity was relatively high, and on the other hand because the dissolution of Fe(II) on the surface of the mineral at lower pH promoted chemical reduction, and vanadium could complex with iron oxides, making it easy to separate by magnetic separation. Therefore, the content of vanadium in the deposited soil was the highest in the reactor at pH 6.5, and the magnetic recovery efficiency was the highest. In addition, the high or low pH could affect the positive or negative charge of the mineral surface, changing the electrostatic adsorption force on the mineral surface. Therefore, at low pH, the surface of pyrrhotite would attract negatively charged V(V) substances. At higher pH, the negatively charged surface of pyrrhotite would repel negatively charged V(V) substances.

[0083] Example 7

[0084] Effect of different initial concentrations of vanadium on the efficiency of recovering metal vanadium

[0085] As Figure 8As shown, when the V(V) concentration is 25.0, 50.0, 75.0 and 100.0 mg / L, the reduction efficiency of V(V) in the reactor is 94.7 ± 4.20%, 55.3 ± 7.41%, 43.4 ± 4.12% and 32.8 ± 3.53% respectively, and the removal efficiency is the highest when the initial V(V) concentration is 25.0 mg / L, and the removal efficiency of V(V) gradually decreases with the increase of the initial V(V) concentration, indicating that the higher the V(V) concentration, the more obvious the inhibition of microorganisms, but the removal rate of V(V) increases from 3.00 mg / (L·d) to 4.10 mg / (L·d). The results show that the microbial system constructed by anaerobic sediment has good removal effect on V(V), and can adapt to higher concentration of V(V) pollution environment.

[0086] As Figure 9a -b is the content of soil metal vanadium and the magnetic recovery efficiency in the bioreactor with different initial V(V) concentrations. When the initial V(V) concentration is 25.0, 50.0, 75.0 and 100.0 mg / L, the content of recovered metal vanadium in the soil is 156.3 ± 36.1, 182.1 ± 42.2, 209.3 ± 53.4 and 211.3 ± 33.3 mg / kg respectively. Among them, the magnetic recovery efficiency in the reactor with different initial V(V) concentrations is 47.1 ± 4.72%, 48.2 ± 4.60%, 48.5 ± 3.51% and 46.4 ± 4.53% respectively. The analysis of the results shows that there is no significant difference in the magnetic recovery efficiency of soil metal vanadium in the bioreactor with different initial V(V) concentrations. Therefore, different initial V(V) concentrations do not affect the magnetic recovery efficiency of soil metal vanadium. At the same time, it also shows that the removal of heavy metal vanadium physico-chemical-biological coupling method provided in the application is suitable for purifying V(V) contaminated soil with a wide concentration range.

[0087] Example 8

[0088] Microbial community evolution and functional microorganism identification

[0089] As Figure 10aAs shown, the main phyla in the system under different pH conditions were Proteobacteria (30.0%-41.5%), Bacteroidota (13.9%-18.7%), Firmicutes (10.7%-15.0%), Actinobacteriota (7.80%-11.2%), and Chloroflexi (4.00%-7.20%). Proteobacteria was the dominant phylum, accounting for over 30.0% of the total. In this system, the proportion of the most dominant phylum, Proteobacteria, remained the highest as the initial pH increased from 5.5 to 8.5. The proportion of Proteobacteria was particularly high at pH 6.5, indicating that weakly acidic conditions favored the enrichment of the most dominant phylum. Microbial succession analysis showed that the relative abundance of Bacteroidota was higher in acidic or alkaline environments than in neutral environments, indicating that acidic or alkaline environments were more suitable for the enrichment of Bacteroidota. Furthermore, the relative abundance of Chloroflexi increased along the pH gradient. In summary, pH affects bacterial community composition and microbial abundance, thereby leading to changes in community structure stability and V(V) removal performance.

[0090] like Figure 10b As shown, the dominant phyla in the system under different initial V(V) concentrations were Proteobacteria, Bacteroidota, and Firmicutes. Among them, Bacteroidota (13.8%–18.4%) and Firmicutes (12.3%–13.9%) were significantly enriched in the reactor with added V(V) compared to the original inoculum, suggesting a potential role in promoting V(V) reduction. Notably, Chloroflexi and Synergistota showed higher abundance in reactor V4 compared to other reactors with increasing V(V) concentration. Chloroflexi was found to be the dominant phylum in severely vanadium-contaminated soils and showed a positive correlation with vanadium concentration. This indicates the adaptive ability of microorganisms under vanadium stress, suggesting the shaping effect of vanadium on soil microbial community structure. The preferential enrichment of microorganisms in samples under strong vanadium stress and their potential V(V) reduction activity may lead to the formation of highly correlated metal-tolerant or detoxification communities.

[0091] It should be noted that, Figure 10aIn the single column chart of b, the phyla from bottom to top are Proteobacteria, Bacteroidota, Firmicutes, Actinobacteriota, Chloroflexi, Desulfobacterota, Planctomycetota, Armatimonadota, Synergistota and others.

[0092] As Figure 11a , the composition and abundance of functional microorganisms at the genus level in different initial pH reactors were revealed. Under all pH conditions, the relative abundance of Thiobacillus was the highest, maintaining at 8.90%-12.2%. Thiobacillus not only has the dual oxidation ability of iron and sulfur, but also has good ability to reduce V(V), so it is most likely to remove V(V) in the current proposed biological system. Interestingly, the relative abundance of Thiobacillus in P2 reactor(12.2%) was significantly higher than that in other reactors, which may be the reason for the good V(V) removal performance of the system at pH 6.5 Figure 6 ). In addition, Thermomonas and Arenimonas were also found to have higher relative abundance than other reactors. Among them, Thermomonas and Arenimonas, as iron-oxidizing bacteria, mainly participate in the oxidation of Fe(II) in pyrrhotite, which is conducive to the electron transfer of V(V) reduction process. These results show that pH has a significant impact on the bacterial community of the reactor, and the results confirm that pH=6.5 may be more conducive to bacterial metabolism than other pH values. In addition, Proteiniphilum and Fermentimonas were found to be significantly enriched in P1 reactor, and their relative abundance was also higher than that in other reactors. This indicates that Proteiniphilum and Fermentimonas are more adaptable to acidic environments. Among them, Proteiniphilum as an acid-producing microorganism has a wider range of pH adaptation. It is worth noting that Limnobacter and Desulfurivibrio were significantly enriched in P4 reactor, indicating that the bacteria can adapt to alkaline environments. Desulfurivibrio, as a sulfur-oxidizing bacteria, was originally isolated from an alkaline lake and later found in other alkaline environments. Therefore, in alkaline environments, Desulfurivibrio may play a key role in the coupling of pyrrhotite oxidation and V(V) reduction.

[0093] As Figure 11bThe composition and abundance of functional microorganisms at genus level in different initial V(V) concentration reactors were revealed. At genus level, Thiobacillus (6.91%-14.08%), Desulfatitalea (1.73%-3.06%), Lentimicrobium (1.48%-2.84%), Vulcanibacillus (1.57%-2.3%) and Gemmatimonas (0.57%-0.91%) were significantly enriched compared with the original inoculum. Interestingly, Thiobacillus, Desulfatitalea and Lentimicrobium were enriched in V1 reactor, and their relative abundance was found to be negatively correlated with the initial vanadium concentration, suggesting that high concentration of vanadium had a significant inhibitory effect on the activity of microorganisms, resulting in a decrease in microbial abundance. However, Sumerlaea, LNR_A2-18, Truepera and Vulcanibacillus were found to be significantly enriched in V4 reactor. Among them, Truepera was reported to have denitrification ability and participate in the biological transformation of Cr(VI) to Cr(III), and may have the potential to reduce V(V).

[0094] In summary, the examples of the present application verify the effectiveness of natural magnetic mineral material (magnetic pyrite) in fixing vanadium in soil and the feasibility of using magnetic separation. The examples of the present application test the ability of magnetic material to reduce V(V) and the efficiency of using magnet to recover vanadium from the sediment soil through a series of continuous batch experiments and influence factor experiments, and the following conclusions are drawn:

[0095] (1) In Example 3, the continuous batch experiment was stable for 15 cycles, a total of 143 days, and the results again verified that magnetic pyrite is a reliable electron donor, not only can microorganisms utilize the electrons provided by it to bioreduce V(V), but also has the ability to chemically reduce V(V) itself.

[0096] (2) In Example 4, the BCR sequential extraction method was improved to study the chemical forms of metal vanadium in soil at different reaction periods, and the results showed that vanadium in soil was mainly in acid extractable and reducible states, indicating that vanadium in solution mainly exists in the form of high bioavailability (acid extractable and reducible states) in soil under the action of microbial reduction and ore adsorption, and is easy to re-enter the aqueous solution with environmental changes.

[0097] (3) As shown in Examples 5-7, the destructive sampling was performed at different periods of the bioreactor, and the magnet was used to magnetically recover vanadium in the soil, which showed that under the action of the external magnetic field, the vanadium-containing product was separated from the soil along with the magnetic pyrite, and the recovery efficiency of vanadium was as high as 50.1±4.50%. Therefore, the natural magnetic mineral can be used to effectively realize the in-situ reduction of V(V) in the soil, and it is easy to separate and remove from the contaminated soil by the external magnetic field. This provides a new method for the clean remediation of the soil contaminated by V(V).

[0098] (4) Examples 5-7 demonstrate that through the exploration of the influencing factors of the magnetic recovery of vanadium in the soil by the magnetic pyrite, it is found that different magnetic strengths and pH values will affect the recovery efficiency of vanadium in the reactor. Among them, the stronger the magnetic strength, the higher the recovery efficiency, the main reason is that the larger the magnetic strength, the more magnetic mineral materials can be adsorbed; and when the pH is 6.5, the removal rate and recovery rate of V(V) in the reactor are the highest, the main reason is that the pH will affect the activity of microorganisms and the dissolution leaching of Fe(II) on the surface of the ore. However, different initial V(V) concentrations will not affect the magnetic recovery efficiency of vanadium in the soil.

[0099] (5) The microbial community analysis in Example 8 shows that the pH value has a significant effect on the bacterial community in the reactor. Among them, Thiobacillus has the highest relative abundance under all pH conditions, Proteiniphilum and Fermentimonas are more suitable for acidic environment, and Desulfurivibrio as a sulfur-oxidizing bacteria plays a key role in the coupling of pyrite oxidation and V(V) reduction in alkaline environment. Sulfur-oxidizing bacteria and iron-oxidizing bacteria (such as Desulfurivibrio and Thermomonas) together accelerate the dissolution and oxidation of pyrite to generate Fe(III) and SO4 2- , and use V(V) as an electron acceptor to couple the biological reduction process of V(V). In addition, the vanadium content will affect the composition and abundance of the microbial community. Among them, Thiobacillus, Desulfatitalea and Lentimicrobium have a negative effect on the vanadium content, while Truepera adapts to high concentration of vanadium stress and has the potential to reduce V(V).

[0100] Based on the above-mentioned scheme, the present specification provides a physico-chemical and biological coupled method for removing heavy metal vanadium, comprising the following steps: adding soil contaminated by pentavalent vanadium [V(V)] into a reactor with pyrrhotite particles and anaerobic sediment, then adding synthetic groundwater into the above-mentioned reactor and stirring uniformly to obtain a test water sample; the test water sample contains 20.0 ml of anaerobic sediment and 5.00 g of pyrrhotite particles in every 250.0 ml of synthetic groundwater; the anaerobic sediment is aquifer sediment contaminated by pentavalent vanadium [V(V)], which is used to inoculate and construct microbial community in the reactor; the test water sample is cured under anaerobic and light-shielded conditions for at least eight days, and the microorganism in the anaerobic sediment utilizes the pyrrhotite as an electron donor to convert the soluble pentavalent vanadium into tetravalent vanadium precipitate and attach it to the unreacted pyrrhotite; the reduced solid soil sample is obtained by mud-water separation, and the metal vanadium in the soil is recovered by an external magnetic field with a magnetic strength of 1200-3000 Gs.

[0101] In some embodiments, the external magnetic field is generated from a neodymium magnet.

[0102] In some embodiments, the average particle size of the pyrrhotite particles is 1.0 mm.

[0103] In some embodiments, the initial pH of the test water sample is 5.5-8.5.

[0104] In some embodiments, the concentration of pentavalent vanadium [V(V)] in the test water sample is 25.0-100.0 mg / L.

[0105] In some embodiments, NaHCO3 is added as a carbon source in the test water sample.

[0106] In some embodiments, the microorganism in the anaerobic sediment includes iron-oxidizing bacteria and sulfur-oxidizing bacteria.

[0107] The present specification also provides a physico-chemical and biological coupled device for removing heavy metal vanadium from soil, which is applied to the above-mentioned method and comprises a reactor and a neodymium magnet; wherein the reactor contains synthetic groundwater, pyrrhotite particles and anaerobic sediment, and contains 20.0 ml of anaerobic sediment and 5.00 g of pyrrhotite particles in every 250.0 ml of synthetic groundwater; the anaerobic sediment is aquifer sediment contaminated by pentavalent vanadium [V(V)], which is used to inoculate and construct microbial community in the reactor, and the microorganism in the anaerobic sediment includes iron-oxidizing bacteria and sulfur-oxidizing bacteria; the neodymium magnet is located outside the reactor, and the magnetic strength of the neodymium magnet is 1200-3000 Gs.

[0108] In some embodiments, the reactor is a device that maintains the microorganisms in the anaerobic deposit in a light-tight and anaerobic environment.

[0109] In some embodiments, the reactor is a glass bottle with an aluminum foil wrapped around the body of the bottle.

[0110] The embodiments of the present application can effectively achieve in-situ reduction of V(V) in soil using pyrrhotite, and the pyrrhotite is easy to separate and remove from the contaminated soil by applying a magnetic field. The occurrence form of vanadium in soil is mainly in acid extractable state and reducible state, and when the magnetic field strength is 3000Gs, the recovery efficiency of soil metal vanadium can be up to 49.0±4.73%.

[0111] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A physico-chemical-biological coupled method for removing heavy metal vanadium from soil, characterized in that, The method comprises the following steps: The soil contaminated by pentavalent vanadium [V(V)] is added into a reactor with pyrrhotite particles and anaerobic sediment, and then synthetic groundwater is added into the reactor and stirred to obtain a test water sample; the test water sample contains 20.0 ml of anaerobic sediment and 5.00 g of pyrrhotite particles in every 250.0 ml of synthetic groundwater; the anaerobic sediment is aquifer sediment contaminated by pentavalent vanadium [V(V)], which is used to inoculate and construct a microbial community in the reactor; the microorganisms in the anaerobic sediment include iron-oxidizing bacteria and sulfur-oxidizing bacteria; the iron-oxidizing bacteria include Thermomonas and Arenimonas; the sulfur-oxidizing bacteria include Desulfurivibrio and Thiobacillus; the average particle size of the pyrrhotite particles is 1.0 mm; the initial pH of the test water sample is 5.5-8.5; and the concentration of pentavalent vanadium [V(V)] in the test water sample is 25.0-100.0 mg / L; The test water sample is cured under anaerobic and light-shielded conditions for at least eight days, and the microorganisms in the anaerobic sediment use the pyrrhotite as an electron donor to convert the soluble pentavalent vanadium into tetravalent vanadium precipitate and adhere to the unreacted pyrrhotite; The reduced solid soil sample is obtained by mud-water separation, and the metallic vanadium in the soil is recovered by an external magnetic field with a magnetic strength of 1200-3000 Gs.

2. The method of claim 1, wherein, The external magnetic field is generated by a neodymium magnet.

3. The method of claim 1, wherein, NaHCO3 is added as a carbon source in the test water sample.

4. A physico-chemical-biological coupled device for removing heavy metal vanadium from soil, applied to the method according to any one of claims 1-3, characterized by, The method comprises a reactor and a neodymium magnet; the reactor contains synthetic groundwater, pyrrhotite particles and anaerobic sediment, and contains 20.0 ml of anaerobic sediment and 5.00 g of pyrrhotite particles in every 250.0 ml of synthetic groundwater; the anaerobic sediment is aquifer sediment contaminated by pentavalent vanadium [V(V)], which is used to inoculate and construct a microbial community in the reactor; the microorganisms in the anaerobic sediment include iron-oxidizing bacteria and sulfur-oxidizing bacteria; the neodymium magnet is located outside the reactor, and the magnetic strength of the neodymium magnet is 1200-3000 Gs.

5. The apparatus of claim 4, wherein, The reactor is a device for keeping the microorganisms in the anaerobic sediment in a light-shielded and anaerobic environment.

6. The apparatus of claim 5, wherein, The reactor is a glass bottle with an aluminum foil wrapped around the column body.

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