Fixing agent, preparation method and application thereof

Abstract

The present application relates to the field of remediation of heavy metal pollution in sediments, and particularly relates to a fixing agent, a preparation method and application thereof. The fixing agent comprises electron shuttles and dissimilatory metal-reducing bacteria. The fixing agent is used for fixing heavy metals in water or remediation of heavy metal contaminated sediments. The heavy metals are selected from one or more of cadmium and lead. The dissimilatory metal-reducing bacteria used in the present application widely exist in river and lake sediments, and the sediments have strong adaptability and good heavy metal resistance. The electron shuttles are used to strengthen the dissimilatory metal-reducing bacteria to reduce and recrystallize the cadmium after reducing the iron and manganese oxides which exist in large quantities in the sediments. The sediments contain abundant organic matter which can provide carbon source for the dissimilatory metal-reducing bacteria, thereby avoiding the addition of iron source, manganese source and organic carbon source, reducing the risk of secondary pollution, and fully utilizing the abundant substances in the sediments to effectively fix the heavy metals.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of remediation of heavy metal pollution in sediments, in particular to a fixing agent and its preparation method and application. BACKGROUND

[0002] Cadmium (Cd) is one of the most concerned heavy metal pollutants due to its high biological toxicity and bioaccumulation. With the acceleration of industrialization and urbanization, a large amount of industrial wastewater and domestic sewage is discharged into rivers and lakes, and the heavy metal cadmium in the heavy metal contaminated sediments is enriched in the sediments through sedimentation, making the heavy metal cadmium pollution in the sediments a serious problem. High concentration of cadmium in the sediments may be re-released into the overlying water under changes in environmental conditions such as pH and ORP, causing secondary pollution. According to the literature results, the cadmium content in the sediments of many lakes and rivers in China exceeds the standard, and the cadmium content in the sediments of the lower reaches of the Pearl River reaches 10.6 mg / kg, with a 30-fold excess. Therefore, the remediation and fixation of cadmium in river and lake sediments is imminent.

[0003] In-situ remediation technology of heavy metals in sediments is divided into physical, chemical and biological remediation technology, among which microbially induced secondary mineralization technology has the advantages of stable fixation effect, no secondary pollution and low cost, and has become a research hotspot. Among them, dissimilatory metal-reducing bacteria widely exist in river and lake sediments, which can transmit electrons produced by intracellular oxidation of organic matter to the outside of the cell through the secretion of transmembrane protease, and then transfer the electrons to iron and manganese minerals through methods such as conductive pili and secretion of cytochrome. There is a high content of iron and manganese hydroxides in the sediments, and dissimilatory metal-reducing bacteria can convert high-valence iron and manganese hydroxides into low-valence iron and manganese ions, which can be recombined with anions in the sediments and interstitial water into more stable secondary minerals, which can fix cadmium in the process of recrystallization. Electron shuttles can change the rate of dissimilatory reduction of iron and manganese minerals, and thus change the morphology and crystal type of secondary minerals, directly affecting the secondary fixation effect of cadmium. In addition, the type of minerals has a significant impact on the fixation of cadmium. Due to the differences in crystallinity and thermodynamic stability of iron and manganese minerals, their dissimilatory reduction rates and degrees are different, which will also directly affect the secondary fixation effect of cadmium. Therefore, the present application attempts to find a method for efficient fixation of heavy metal cadmium in sediments by dissimilatory iron and manganese reduction. SUMMARY

[0004] In order to solve the problems existing in the prior art, the present application provides a fixing agent, which comprises an electron shuttle and a dissimilatory metal-reducing bacteria (DMRB).

[0005] Preferably, A1) the electron shuttles are selected from one or more of 9,10-anthraquinone disulfonate (AQDS), riboflavin, cytochrome c, cysteine, humic acid and fulvic acid;

[0006] Preferably, A2) the dissimilatory reducers are selected from one or more of Geobacter metallireducens GS-15, Shewanella MR-1, Geobacter sulfurreducens PCA;

[0007] The method for preparing the bacterial suspension of the dissimilatory metal-reducing bacteria GS-15 comprises the following steps: inoculating the bacterial suspension from the anaerobic vial storing the bacterial strain into the iron citrate culture medium, incubating at 30°C for 1-7 days to obtain the bacterial suspension with a dissolved Fe 2+ concentration of 20-35 mM, ready for use.

[0008] The iron citrate culture medium comprises the following components: NaHCO3 2.5 g / L, KCl 0.1 g / L, NH4Cl 0.25 g / L, NaH2PO4·2H2O 0.67 g / L, Na2SeO4 3.78 mg / L, iron citrate (C6H5FeO7) 50 mmol / L, sodium acetate 20 mmol / L, vitamin mixture and mineral mixture each 10 mL / L; the preparation method comprises: mixing all raw materials, adjusting the pH to 6.5-7.0, then aerating with mixed gas for 30 min, and sterilizing at 121°C for 30 min.

[0009] The mineral mixture per liter comprises the following components: trisodium nitrilotriacetate (C6H6NNa3O6) 1.5 g, MgSO4·7H2O 3 g, MnSO4·H2O 0.5 g, NaCl 1 g, FeSO4·7H2O 0.1 g, CaCl2·2H2O 0.1 g, CoCl2·6H2O 0.1 g, ZnCl2 0.13 g, CuSO4·5H2O 0.01 g, AlK(SO4)2·12H2O 0.01 g, H3BO3 0.01 g, Na2MoO4·2H2O 0.025 g, NiCl2·6H2O 0.024 g, Na2WO4·2H2O 0.025 g.

[0010] The vitamin mixture per liter comprises the following components: pyridoxal hydrochloride (C8H 11 NO3·HCl) 10 mg, vitamin B 12 (C 63 H 88 CoN 14 O 14 P) 0.1 mg, biotin (C 10 H 16 N2O3S) 2 mg, folic acid (C 19 H19 N7O6) 2mg, pantothenic acid (C6H) 11 NaO4) 5mg, thiamine (C 12 H 16 N4O2S) 5mg, Riboflavin (C 17 H 20 N4O6) 5mg, nicotinic acid (C6H4NNaO2) 5mg, p-aminobenzoic acid (C7H7NO2) 5mg, thioctic acid (C8H) 14 O2S2) 5mg;

[0011] The mixed gas is specifically: nitrogen to carbon dioxide in a volume ratio of 8:2;

[0012] Preferably, the mass-to-volume ratio of the electron shuttle to the dissimilatory reducing bacteria solution in A3) is 0.824–4.12 g / L, for example, it can be 0.824–1 g / L, 1–1.5 g / L, 1.5–2 g / L, 2–2.5 g / L, 2.5–3 g / L, 3–3.5 g / L, 4–4.12 g / L, 0.824–1 g / L,

[0013] Preferably, A4) also includes an iron source and a manganese source.

[0014] Preferably, in feature A2), the metal-reducing Geobacterium GS-15 has the accession number ATCC 53774.

[0015] Preferably, in feature A2), the Shewanella MR-1 has the accession number ATCC 700550;

[0016] Preferably, in feature A2), the sulfur-reducing Geobacterium PCA has the accession number ATCC 51573;

[0017] Preferably, in feature A3), the OD600 of the bacterial solution of the dissimilatory reducing bacteria is 0.4 to 1, for example, it can be 0.4 to 0.5, 0.5 to 0.6, 0.6 to 0.7, 0.7 to 0.8, 0.8 to 0.9, 0.9 to 1, etc.

[0018] Preferably, in feature A4), the iron source is selected from one or more of hematite, goethite, iron phosphate, ferrihydrite, magnetite, lepidocrocite, goethite, and iron-manganese copolymers.

[0019] Preferably, in feature A4), the manganese source is selected from one or more of manganese dioxide, pyrolusite, manganese potassium ore, calcium manganese ore, and iron-manganese copolymer;

[0020] Preferably, in A43), the concentration ratio of the iron source to the electron shuttle is (10:0.1) to (50:0.1).

[0021] Preferably, in A44), the concentration ratio of the manganese source to the electron shuttle is (1:0.1) to (5:0.1).

[0022] The second aspect of the present application provides the use of the above-mentioned fixing agent for fixing heavy metals in heavy metal contaminated bodies or for remediation of heavy metal contaminated sediments. Preferably, the heavy metal is selected from one or more of cadmium metal and lead metal.

[0023] The third aspect of the present application provides a method for fixing heavy metals in heavy metal contaminated bodies, using the above-mentioned fixing agent.

[0024] Preferably, in B1), the concentration ratio of the heavy metal to the electron shuttle is (1:1) to (3:1).

[0025] The concentration volume ratio of the heavy metal to the bacterial solution of the dissimilatory iron-reducing bacteria is (0.1 mM: 2.5 mL) to (3 mM: 2.5 mL).

[0026] Preferably, in B2), the concentration of the electron shuttle in the heavy metal contaminated body is 0.05 to 0.5 mmol / L, for example, it can be 0.05 to 0.1 mmol / L, 0.1 to 0.15 mmol / L, 0.15 to 0.2 mmol / L, 0.2 to 0.25 mmol / L, 0.25 to 0.3 mmol / L, 0.3 to 0.35 mmol / L, 0.35 to 0.4 mmol / L, 0.4 to 0.45 mmol / L, 0.45 to 0.5 mmol / L, etc.

[0027] Preferably, in B3), the volume fraction of the dissimilatory iron-reducing bacteria in the heavy metal contaminated body is 2% to 10%.

[0028] Preferably, in B4), the concentration of Fe in the bacterial solution of the dissimilatory iron-reducing bacteria in the heavy metal contaminated body is 20 to 35 mM, for example, it can be 20 to 25 mM, 25 to 30 mM, 30 to 36 mM, etc. 2+

[0029] Preferably, in B5), the heavy metal is selected from one or more of cadmium metal and lead metal.

[0030] Preferably, in C1), the heavy metal contaminated body contains an iron source.

[0031] Preferably, in C2), the heavy metal contaminated body contains a manganese source.

[0032] ​Preferably, C3) the heavy metal contaminated body contains a carbon source, which is a carbon source that can be utilized by dissimilatory metal-reducing bacteria;

[0033] Preferably, C4) the heavy metal contaminated body contains inorganic salt;

[0034] Preferably, C5) the heavy metal contaminated body contains vitamin;

[0035] Preferably, C6) the heavy metal contaminated body contains mineral;

[0036] Preferably, C7) the heavy metal contaminated body contains phosphorus source, preferably, the phosphorus source is insoluble phosphate;

[0037] Preferably, C8) the pH of the heavy metal contaminated body is 5-9, for example, it can be 5-6, 6-7, 7-8, 8-9, etc.

[0038] Preferably, C11) in feature C1), the iron source is selected from one or more of hematite, goethite, iron phosphate, ferrihydrite, magnetite, siderophite, limonite and iron-manganese coacervate.

[0039] Preferably, C21) in feature C2), the manganese source is selected from one or more of manganese dioxide, romanechite, todorokite, bixbyite and iron-manganese coacervate.

[0040] The manganese dioxide is prepared by mixing 0.1 mol / L KMnO4 solution with 0.2 mol / L NaOH solution to prepare manganese dioxide (MnO2), and the prepared solid precipitate is freeze-dried, ground and sieved for use.

[0041] The iron-manganese coacervate is prepared by mixing 0.1 mol / L KMnO4 solution with 0.3 mol / L FeCl2 solution to prepare iron-manganese coacervate (FeMn-Nodule), and the prepared solid precipitate is repeatedly washed with deionized water until the supernatant is clear, and then the prepared iron-manganese coacervate precipitate is freeze-dried, ground and sieved through a stainless steel sieve for use.

[0042] Preferably, C31) in feature C3), the carbon source is selected from sodium acetate or glucose.

[0043] The fourth aspect of the present application provides a method for repairing heavy metal contaminated sediment, which comprises culturing the above fixing agent with the heavy metal contaminated sediment under anaerobic conditions at constant temperature.

[0044] Preferably, the content of cadmium metal in D1) is 0.01-0.3 mM, for example, it can be 0.01-0.05 mM, 0.05-0.1 mM, 0.1-0.15 mM, 0.15-0.2 mM, 0.2-0.25 mM, 0.25-0.3 mM, etc.

[0045] Preferably, the content of lead metal in D2) is 0.5-8 mM, for example, it can be 0.5-1 mM, 1-2 mM, 2-3 mM, 3-4 mM, 4-5 mM, 5-6 mM, 6-7 mM, 7-8 mM, etc.

[0046] Preferably, the time of D3) is 10-270 days, for example, it can be 10-50 days, 50-100 days, 100-150 days, 150-200 days, 200-250 days, 250-270 days, etc.

[0047] Preferably, the temperature of D4) is 28-37℃, for example, it can be 28-29℃, 29-30℃, 30-31℃, 31-32℃, 32-33℃, 33-34℃, 34-35℃, 35-36℃, 36-37℃, etc.

[0048] The present application uses quinone compounds to mediate the dissimilatory iron and manganese reduction for the stabilization treatment of sediment heavy metals cadmium. Dissimilatory metal-reducing bacteria can reduce the tetravalent manganese and trivalent iron which are rich in the sediment to divalent manganese and divalent iron, and under the influence of phosphate, the types of secondary minerals will be changed, and phosphorus-containing iron and manganese (hydro) oxides will be generated, which will fix heavy metals in the process of recrystallization, and form more stable iron and manganese secondary minerals containing heavy metals, solving the problems of external repair materials and easy release of heavy metals under anaerobic conditions.

[0049] The present application has at least one of the following beneficial technical effects:

[0050] (1) The fixing agent and the method for fixing heavy metals provided by the present application are easy to prepare and implement, have low implementation cost, wide application range, and good sediment heavy metal fixing effect.

[0051] (2) The dissimilatory reduction bacteria used in the present application widely exist in river and lake sediments, have strong adaptability to sediments and good heavy metal resistance, and can fix cadmium after recrystallization after reducing the iron and manganese oxides which exist in large amounts in the sediments, and the sediments contain rich organic matter which can provide carbon source for the dissimilatory metal-reducing bacteria, avoiding the addition of iron source, manganese source and organic carbon source, reducing the risk of secondary pollution, and fully utilizing the substances rich in the sediments to effectively fix heavy metals.

[0052] (3) The low concentration of electron shuttles (for example, quinone compounds and the like) in the application can obviously promote the reduction effect of dissimilatory iron and manganese, effectively improve the dissimilatory iron and manganese reduction capacity of microorganisms, and obviously strengthen the effect, so that the secondary precipitation and fixation effect of heavy metals is more obvious. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 The figure is the change graph of the concentrations of soluble divalent iron, soluble divalent manganese, hydrochloric acid extractable divalent iron, hydrochloric acid extractable divalent manganese, soluble phosphorus and soluble cadmium in the process of quinone compound-mediated dissimilatory iron and manganese reduction and fixation of cadmium in Example 1 of the application.

[0054] Figure 2 The figure is the XRD spectrum of the secondary precipitation after 80 days of quinone compound-mediated dissimilatory iron and manganese reduction in Example 1 of the application.

[0055] Figure 3 The figure is the SEM spectrum of the secondary precipitation after 80 days of quinone compound-mediated dissimilatory iron and manganese reduction in Example 1 of the application (a: FeOOH, b: FeOOH-AQDS, c: MnO2, d: MnO2-AQDS, e: FeOOH-MnO2, f: FeOOH-MnO2-AQDS).

[0056] Figure 4 The figure is the comparison graph of cadmium forms of the secondary precipitation after 80 days of quinone compound-mediated dissimilatory iron and manganese reduction in Example 1 of the application.

[0057] Figure 5 The figure is the change graph of the concentrations of soluble divalent iron, soluble divalent manganese, hydrochloric acid extractable divalent iron, hydrochloric acid extractable divalent manganese, soluble phosphorus and soluble cadmium in the process of quinone compound-mediated dissimilatory reduction and fixation of cadmium in the coexisting group of iron phosphate-manganese dioxide and the iron-manganese copolymer group in Example 2 of the application. DETAILED DESCRIPTION

[0058] The embodiments of the application are explained hereinafter by specific examples, and other advantages and effects of the application can be easily understood by those skilled in the art from the disclosure of the specification. The application can also be implemented or applied by different specific embodiments, and various modifications or changes can be made to the details in the specification without departing from the spirit of the application.

[0059] It should be understood that the process equipment or device not specifically mentioned in the following examples is the conventional equipment or device in the art. The application is further described in detail in combination with the specific embodiments, and the examples are given only to illustrate the application, not to limit the scope of the application.

[0060] The experimental methods in the following examples are conventional methods, unless otherwise specified.

[0061] The materials, reagents and the like used in the following examples can be obtained from commercial sources unless otherwise specified.

[0062] The solvent of the culture medium used in the following examples is deionized water.

[0063] The dissimilatory metal-reducing bacteria (DMRB) used in the following examples is Geobacter metallireducens GS-15, which is obtained from the American Type Culture Collection and is commercially available, and the strain preservation number is ATCC 53774.

[0064] The method for preparing the bacterial suspension of the dissimilatory metal-reducing bacteria used in the following examples is as follows: shake the anaerobic vial containing the preserved strain, and then use a disposable syringe to take 2.5 mL of the bacterial suspension from the vial to inoculate the iron citrate culture medium, and incubate in a 30°C incubator for 1-7 days. The iron citrate culture medium changes from dark brown to light green, and the soluble Fe 2+ concentration in the iron citrate culture medium reaches 20-35 mM, and the bacterial suspension is obtained for storage. The method for testing the soluble Fe 2+ is as follows: shake the culture solution incubated for 1-7 days, and then filter through a 0.22 μm water filter membrane, and then use the o-phenanthroline spectrophotometry to determine the soluble Fe 2+ value.

[0065] The composition of the iron citrate culture medium is as follows: NaHCO3 2.5 g / L, KCl 0.1 g / L, NH4Cl 0.25 g / L, NaH2PO4·2H2O 0.67 g / L, Na2SeO4 3.78 mg / L, iron citrate (C6H5FeO7) 50 mmol / L, sodium acetate 20 mmol / L, vitamin mixture and mineral mixture each 10 mL / L. The preparation method comprises: mixing all the raw materials, adjusting the pH to 6.5-7.0, and then aerating with mixed gas for 30 min, and sterilizing at 121°C for 30 min.

[0066] The formula of each liter of vitamin mixture is as follows: pyridoxine hydrochloride (C8H 11 NO3·HCl) 10 mg, vitamin B 12 (C 63 H 88 CoN 14 O 14 P) 0.1 mg, biotin (C 10 H 16 N2O3S) 2 mg, folic acid (C 19 H 19 N7O6) 2 mg, pantothenic acid (C6H 11NaO4) 5 mg, thiamine (C12H17ClN4O3S) 5 mg, riboflavin (C17H20O6N4) 5 mg, nicotinic acid (C6H4NNaO2) 5 mg, p-aminobenzoic acid (C7H7NO2) 5 mg, lipoic acid (C8H 12 H 16 N4O2S) 5 mg, riboflavin (C17H20O6N4) 5 mg, nicotinic acid (C6H4NNaO2) 5 mg, p-aminobenzoic acid (C7H7NO2) 5 mg, lipoic acid (C8H 17 H 20 N4O6) 5 mg, nicotinic acid (C6H4NNaO2) 5 mg, p-aminobenzoic acid (C7H7NO2) 5 mg, lipoic acid (C8H 14 O2S2) 5 mg;

[0067] The formula of the mineral mixture solution is as follows: trisodium amino triacetate (C6H6NNa3O6) 1.5 g, MgSO4·7H2O 3 g, MnSO4·H2O 0.5 g, NaCl 1 g, FeSO4·7H2O 0.1 g, CaCl2·2H2O 0.1 g, CoCl2·6H2O 0.1 g, ZnCl2 0.13 g, CuSO4·5H2O 0.01 g, AlK(SO4)2·12H2O 0.01 g, H3BO3 0.01 g, Na2MoO4·2H2O 0.025 g, NiCl2·6H2O 0.024 g, Na2WO4·2H2O 0.025 g.

[0068] Example 1

[0069] Quinone-mediated immobilization of cadmium by dissimilatory reduction in goethite, manganese dioxide and coexistence of both

[0070] (1) 1 mL of 5 mM 9,10-anthraquinone disulfonate and 2.5 mL of metal-reducing Bacillus subtilis bacterial suspension were inoculated into 50 mL of goethite (FeOOH), manganese dioxide (MnO2) and goethite-manganese dioxide mineral coexistence (FeOOH-MnO2) culture medium respectively, and incubated at 30°C for 80 days.

[0071] The formula of the goethite culture medium is as follows: NaHCO3 2.5 g / L, NH4Cl 0.25 g / L, KCl 0.1 g / L, NaH2PO4·2H2O 0.67 g / L, Na2SeO4 3.78 mg / L, goethite (FeOOH) 10 mmol / L, 10 mL / L of vitamin mixture solution and mineral mixture solution, sodium acetate 20 mmol / L, pH 6.5-7.0, and then aerated with mixed gas for 30 min, and autoclaved at 121°C for 30 min;

[0072] The formula of the manganese dioxide culture medium is as follows: NaHCO3 2.5 g / L, NH4Cl 0.25 g / L, KCl 0.1 g / L, NaH2PO4·2H2O 0.67 g / L, Na2SeO4 3.78 mg / L, MnO2 2 mmol / L, vitamin mixture and mineral mixture 10 mL / L, sodium acetate 20 mmol / L, pH = 6.5-7.0, and then aeration with mixed gas for 30 min, high-temperature sterilization at 121 ℃ for 30 min;

[0073] The formula of the goethite-manganese dioxide coexisting culture medium is as follows: NaHCO3 2.5 g / L, NH4Cl 0.25 g / L, KCl 0.1 g / L, NaH2PO4·2H2O 0.67 g / L, Na2SeO4 3.78 mg / L, goethite (FeOOH) 10 mmol / L, MnO2 2 mmol / L, vitamin mixture and mineral mixture 10 mL / L, sodium acetate 20 mmol / L, pH = 6.5-7.0, and then aeration with mixed gas for 30 min, high-temperature sterilization at 121 ℃ for 30 min;

[0074] The formula of the vitamin mixture per liter is as follows: pyridoxine hydrochloride (C8H 11 NO3·HCl) 10 mg, vitamin B 12 (C 63 H 88 CoN 14 O 14 P) 0.1 mg, biotin (C 10 H 16 N2O3S) 2 mg, folic acid (C 19 H 19 N7O6) 2 mg, pantothenic acid (C6H 11 NaO4) 5 mg, thiamine (C 12 H 16 N4O2S) 5 mg, riboflavin (C 17 H 20 N4O6) 5 mg, nicotinic acid (C6H4NNaO2) 5 mg, p-aminobenzoic acid (C7H7NO2) 5 mg, lipoic acid (C8H 14 O2S2) 5 mg;

[0075] The formula for each liter of mineral mixture is as follows: trisodium triacetate (C6H6NNa3O6) 1.5g, MgSO4·7H2O 3g, MnSO4·H2O 0.5g, NaCl 1g, FeSO4·7H2O 0.1g, CaCl2·2H2O 0.1g, CoCl2·6H2O 0.1g, ZnCl2 0.13g, CuSO4·5H2O 0.01g, AlK(SO4)2·12H2O 0.01g, H3BO3 0.01g, Na2MoO4·2H2O 0.025g, NiCl2·6H2O 0.024g, Na2WO4·2H2O 0.025g;

[0076] The preparation method of manganese dioxide is as follows: Manganese dioxide (MnO2) is prepared by mixing 0.1 mol / L KMnO4 solution and 0.2 mol / L NaOH solution. The prepared solid precipitate is repeatedly washed with deionized water until the supernatant is clear. Then, the prepared MnO2 precipitate is freeze-dried, ground and passed through a stainless steel sieve for later use.

[0077] (2) Samples were taken and analyzed on days 0, 1, 4, 8, 15, 21, 30, 40, 60 and 80 respectively. Soluble ferrous iron and hydrochloric acid-extractable ferrous iron were tested by the o-phenanthroline method, soluble ferrous manganese and hydrochloric acid-extractable ferrous manganese were tested by the potassium periodate method, soluble phosphorus was tested by the ammonium molybdate colorimetric method, and soluble cadmium was determined by flame atomic absorption spectrophotometry.

[0078] Determination of soluble ferrous iron (Fe2+) and hydrochloric acid-extractable ferrous iron (Fe2+) in the culture medium: 2 mL of the suspension sample was filtered through a 0.22 μm aqueous membrane. Then, 0.2 mL of the filtrate was added to a 50 mL colorimetric tube, along with 5 mL of ammonium acetate-acetic acid buffer and 2 mL of o-phenanthroline chromogenic reagent. The mixture was allowed to develop for 15 min, and the absorbance was measured at 510 nm using ultrapure water as a reference, corrected with a blank control. Hydrochloric acid-extractable ferrous iron was extracted from 0.2 mL of the suspension by shaking with 1.8 mL of 0.5 mol hydrochloric acid for 4 h. The extract was then filtered through a 0.22 μm aqueous membrane, and the concentration of hydrochloric acid-extractable ferrous iron was tested using the same method described above.

[0079] Determination of soluble divalent manganese and hydrochloric acid-extractable divalent manganese in the culture medium: 2 mL of the suspension sample was filtered through a 0.22 μm aqueous membrane. Then, 0.2 mL of the filtrate was added to a 50 mL colorimetric tube, along with 10 mL of potassium pyrophosphate sodium acetate buffer and 2 mL of potassium periodate colorimetric reagent. The mixture was allowed to develop color for 15 min. The absorbance was measured at 525 nm using ultrapure water as a reference, and corrected using a blank control. Hydrochloric acid-extractable divalent manganese was extracted from 0.2 mL of the suspension by shaking with 1.8 mL of 0.5 mol hydrochloric acid for 4 h. The extract was then filtered through a 0.22 μm aqueous membrane, and the concentration of hydrochloric acid-extractable divalent manganese was tested using the same method described above.

[0080] Determination of soluble phosphorus in culture medium: Take 2 mL of suspension sample and filter it through a 0.22 μm aqueous filter membrane. Then take 0.1 mL of filtrate and add it to a 50 mL colorimetric tube and make up to 50 mL. Then add 1 mL of ascorbic acid and 2 mL of molybdate colorimetric reagent and develop the color for 15 min. Measure the absorbance at 700 nm with ultrapure water as a reference and use a blank control for correction.

[0081] Determination of soluble cadmium in culture medium: Take 2 mL of suspension sample and filter it through a 0.22 μm aqueous filter membrane, then take 0.2 mL and make up to 4 mL. Measure the cadmium using flame atomic absorption spectrophotometry.

[0082] Figure 1 The changes in the concentrations of soluble ferrous iron (Fe2+), soluble manganese (M2+), hydrochloric acid-extractable ferrous iron (Fe2+), hydrochloric acid-extractable M2+, soluble phosphorus (P), and soluble cadmium (C) during quinone-mediated dissimilatory iron-manganese reduction (FIG-M) fixation of cadmium are shown. Figure 1 It can be seen that, in the iron-manganese coexistence group mediated by quinone compounds, the concentrations of soluble ferrous iron, soluble ferrous manganese, hydrochloric acid-extractable ferrous iron, and hydrochloric acid-extractable ferrous manganese all increased rapidly in the early stage and remained relatively high after equilibrium, indicating that the dissimilatory reduction effect of the coexistence group was better after the addition of AQDS. The concentrations of soluble cadmium and phosphorus decreased rapidly over time and reached the lowest level after stabilization, indicating that the dissimilatory reduction of cadmium under the iron-manganese coexistence condition mediated by quinone compounds had the best effect on cadmium fixation. Moreover, the dissimilatory reduction generated higher concentrations of soluble ferrous iron and soluble ferrous manganese, which combined with more soluble phosphorus to produce secondary precipitation, and fixed more soluble cadmium during recrystallization.

[0083] Figure 2 The XRD patterns of secondary precipitates after 80 days of dissimilatory reduction of manganese by quinone compounds were obtained. The results showed that after 80 days of dissimilatory reduction with AQDS, manganese dioxide was added to generate red manganese ore (Mn5(PO4)2(PO3OH)2·4H2O). This indicates that AQDS enhanced cadmium fixation by promoting dissimilatory reduction of manganese and mineral recrystallization. In the iron-manganese coexistence group, the characteristic peaks of goethite masked the characteristic peaks of secondary manganese ore after the addition of AQDS.

[0084] Figure 3 The SEM images of secondary precipitates after 80 days of dissimilatory iron and manganese reduction mediated by quinone compounds (a: FeOOH, b: FeOOH-AQDS, c: MnO2, d: MnO2-AQDS, e: FeOOH-MnO2, f: FeOOH-MnO2-AQDS) showed that there was a significant difference between the manganese dioxide added AQDS group and the group without AQDS. The secondary precipitates after 80 days of dissimilatory reduction in the AQDS-containing group were needle-shaped crystals, and the morphology of the secondary minerals in the group without AQDS was cotton-like. After adding AQDS to the iron-manganese coexisting group, flaky substances appeared.

[0085] Figure 4 The results of the comparison of cadmium speciation of secondary precipitates after 80 days of dissimilatory iron and manganese reduction mediated by quinone compounds showed that the proportion of weak acid extractable cadmium was in the order of iron group > manganese group > iron-manganese coexisting group. After adding AQDS, the weak acid extractable state of the secondary precipitates in the iron-manganese coexisting group increased slightly after 80 days, but combined with the soluble cadmium data, it was known that the cadmium fixation effect of the iron-manganese coexisting group with AQDS was the best after 80 days of dissimilatory iron and manganese reduction.

[0086] Example 2

[0087] Fixation of cadmium by dissimilatory reduction of iron-manganese coexisting and iron-manganese coaggregates mediated by quinone compounds

[0088] (1) 2.5 mL of bacterial suspension of metal-reducing bacteria was centrifuged to retain the precipitate, and 1 mL of culture solution was used to resuspend the bacterial body. 1 mL of 5 mM 9,10-anthraquinone disulfonate and 1 mL of resuspended bacterial body were inoculated into 50 mL of iron phosphate-manganese dioxide (FePO4-MnO2) coexisting and iron-manganese coaggregates (FeMn-Nodule) culture medium, and incubated at 30°C for 80 days.

[0089] The formula of the iron phosphate-manganese dioxide mineral coexisting culture medium is as follows: NaHCO3 2.5 g / L, NH4Cl 0.25 g / L, KCl 0.1 g / L, NaH2PO4·2H2O 0.67 g / L, Na2SeO4 3.78 mg / L, iron phosphate (FePO4) 10 mmol / L, manganese dioxide (MnO2) 2 mmol / L, 10 mL / L of vitamin mixture and mineral mixture, sodium acetate 20 mmol / L, pH 6.5-7.0, then aerated with mixed gas for 30 min, and autoclaved at 121°C for 30 min.

[0090] The formula of the iron-manganese coagulation medium is as follows: NaHCO3 2.5 g / L, NH4Cl 0.25 g / L, KCl 0.1 g / L, NaH2PO4·2H2O 0.67 g / L, Na2SeO4 3.78 mg / L, iron concentration 10 mmol / L, manganese concentration 2 mmol / L, vitamin mixture and mineral mixture 10 mL / L, sodium acetate 20 mmol / L, pH 6.5-7.0, and then aeration with mixed gas for 30 min, high-temperature sterilization at 121 ℃ for 30 min;

[0091] The formula of the microbial mixture and the mineral mixture is the same as in Example 1, and the preparation method of the manganese dioxide is the same as in Example 1.

[0092] The preparation method of the iron-manganese coagulation is as follows: 0.1 mol / L KMnO4 solution and 0.3 mol / L FeCl2 solution are mixed to prepare the iron-manganese coagulation (FeMn-Nodule), the prepared solid precipitate is repeatedly washed with deionized water until the supernatant is clear, then the prepared iron-manganese coagulation precipitate is freeze-dried, ground and passed through a stainless steel sieve for standby use.

[0093] (2) Sampling and analysis are performed at 0, 1, 4, 8, 15, 21, 30, 40, 60 and 80 days, respectively, and the solubility of divalent iron and hydrochloric acid extractable divalent iron are tested by the o-phenanthroline method, the solubility of divalent manganese and hydrochloric acid extractable divalent manganese are tested by the potassium periodate method, the solubility of phosphorus is tested by the ammonium molybdate colorimetric method, and the solubility of cadmium is tested by the flame atomic absorption spectrophotometry.

[0094] Figure 5 The changes of the concentrations of the solubility of divalent iron, the solubility of divalent manganese, the hydrochloric acid extractable divalent iron, the hydrochloric acid extractable divalent manganese, the solubility of phosphorus and the solubility of cadmium in the process of the mediated dissimilatory reduction and fixation of cadmium by the quinone compound in the iron-manganese coagulation coexisting group and the iron-manganese coagulation group are shown. Figure 1 It can be seen that after the addition of AQDS, the concentrations of the solubility of divalent iron, the solubility of divalent manganese, the hydrochloric acid extractable divalent iron and the hydrochloric acid extractable divalent manganese in the iron-manganese coagulation group are relatively high, which indicates that the dissimilatory reduction effect of the coexisting group is better after the addition of AQDS; the solubility of cadmium and phosphorus decreases rapidly with time and the concentrations are the lowest after stabilization, which indicates that the dissimilatory reduction and fixation effect of cadmium by the iron-manganese coagulation is the best.

[0095] The above examples 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 examples 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 fixative, characterized in that, It includes an electron shuttle and dissimilar reducing bacteria; the dissimilar reducing bacteria are selected from one or more of metal-reducing bacteria GS-15 and sulfur-reducing bacteria PCA; it also includes an iron source and a manganese source; the manganese source is selected from one or more of manganese dioxide, pyrolusite, manganese potassium ore, calcium manganese ore or iron-manganese copolymer; the iron source is selected from one or more of hematite, goethite, ferric phosphate, ferrous ore, magnetite, lepidocrocite, goethite and iron-manganese copolymer.

2. The fixative according to claim 1, characterized in that, Includes at least one of the following technical features: The electron shuttle is selected from one or more of 9,10-anthraquinone disulfonate, riboflavin, cytochrome c, cysteine, humic acid and fulvic acid; The mass-to-volume ratio of the electron shuttle to the dissimilatory bacteria is 0.824~4.12 g / L.

3. The fixative according to claim 2, characterized in that, Includes at least one of the following technical features: The metal-reducing Geobacterium GS-15 has the accession number ATCC 53774; The accession number of the sulfur-reducing Geobacterium PCA is ATCC 51573; The OD600 of the bacterial culture of the dissimilatory reducing bacteria is 0.4~1; The concentration ratio of the iron source to the electron shuttle is (10:0.1) to (50:0.1); The concentration ratio of the manganese source to the electron shuttle is (1:0.1) to (5:0.1).

4. The application of a fixative as described in any one of claims 1-3 in the remediation of heavy metals or heavy metal contaminated deposits in a heavy metal contaminant; wherein the heavy metal is selected from one or more of cadmium and lead.

5. A method for immobilizing heavy metals in a heavy metal pollutant, characterized in that, The fixative according to any one of claims 1-3 is used, wherein the heavy metal is selected from one or more of cadmium and lead metals.

6. The method for immobilizing heavy metals in a heavy metal pollutant according to claim 5, characterized in that, Includes at least one of the following technical features: B1) The concentration ratio of the heavy metal to the electron shuttle is (1:1) to (3:1). B2) In the heavy metal pollutant, the concentration of the electron shuttle is 0.1~0.3 mmol / L; B3) In the heavy metal pollutant, the dissimilatory bacteria account for 2% to 10% of the volume of the heavy metal pollutant; B4) In the heavy metal pollutant, the Fe in the dissimilatory bacteria solution 2+ The concentration is 20~35 mM; B5) The concentration-to-volume ratio of the heavy metal to the bacterial solution of the dissimilatory reducing bacteria is (0.1 mM: 2.5 mL) ~ (3 mM: 2.5 mL).

7. The method for immobilizing heavy metals in a heavy metal pollutant according to claim 5, characterized in that, Includes at least one of the following technical features: C1) The heavy metal pollutants described contain a carbon source; C2) The heavy metal pollutants mentioned above contain inorganic salts; C3) The heavy metal pollutants mentioned above contain vitamins; C4) The heavy metal pollutants described contain minerals; C5) The heavy metal pollutants described contain a phosphorus source; The pH of the heavy metal pollutants described in C6 is 5-9.

8. The method for immobilizing heavy metals in a heavy metal pollutant according to claim 7, characterized in that, Includes at least one of the following technical features: In feature C1), the carbon source is selected from sodium acetate or glucose; In feature C5), the phosphorus source is a poorly soluble phosphate.

9. A method for remediating heavy metal contaminated sediments, characterized in that, The fixative according to any one of claims 2 or 3 is used to culture the heavy metal contaminated sediment under anaerobic conditions at a constant temperature.

10. The method for remediating heavy metal contaminated sediments according to claim 9, characterized in that, Includes at least one of the following technical features: D1) The cadmium content in the heavy metal is 0.01~0.3mM; D2) The lead content in the heavy metal is 0.5~8mM; The isothermal incubation period described in D3) is 10-270 days; The temperature for constant temperature culture described in D4 is 28~37℃.

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