Method for regulating photocatalytic reduction removal of low concentration u by polycarboxylic acid and its derivatives

Abstract

The application discloses a method for removing low-concentration U by regulating photocatalysis through polycarboxylic acid and derivatives thereof, and comprises the following steps: adding TiO2 and a chelating hole trapping agent into a low-concentration uranium solution, adjusting the pH, and then performing high-pressure steam sterilization; placing the sterilized solution in a light-proof environment, stirring the solution to reach adsorption-desorption balance, and then performing light irradiation and stirring to form a polycarboxylic acid and derivative thereof regulated photocatalysis heterogeneous system; adding microorganisms into the polycarboxylic acid and derivative thereof regulated photocatalysis heterogeneous system to form a microorganism-photocatalysis heterogeneous system. The method has the beneficial effects that: by introducing the chelating hole trapping agent into the photocatalysis uranium removal system, the polycarboxylic acid and derivative thereof regulated photocatalysis heterogeneous system is constructed, and then the microorganism-photocatalysis heterogeneous system is constructed on the basis, the advantages of the bio-adsorption treatment and the photocatalysis treatment are better combined, and the uranium in the low-concentration uranium solution can be effectively removed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear waste water treatment, and particularly relates to a method for removing low-concentration U by regulating photocatalysis reduction through polycarboxylic acid and its derivatives. BACKGROUND

[0002] U(VI) is the main fuel of most commercial reactors at present, so a large amount of radioactive waste water containing U(VI) is released into the environment. The commonly used remediation technologies for uranium-contaminated waste water include traditional physical and chemical methods such as ion exchange, chemical precipitation and adsorption. Through TiO2 photocatalytic induced reduction deposition, toxic metal ions such as Ag + , Cr(VI), Hg 2+ , Fe 3+ and Cu 2+ can be effectively removed. Photocatalytic degradation of organic pollutants caused by light irradiation to a suspension containing a semiconductor organic oxidant as an alternative technology for waste water treatment continues to attract widespread attention. At present, the photocatalytic technology reduces the high mobility of U(VI) in the solution, thereby converting it into easily soluble U(IV), which is considered to be a reasonable method to eliminate uranium pollution. However, low-concentration U(VI) in the solution is difficult to remove by traditional methods. Bioremediation is a hot international research topic in recent years, but the effects of traditional biosorption and photocatalysis on the treatment of low-concentration uranium-containing waste water are not good. SUMMARY

[0003] An object of the present application is to solve at least the above problems and / or deficiencies, and to provide at least the advantages described later.

[0004] To achieve these objects and other advantages according to the present application, a method for removing low-concentration U by regulating photocatalysis through polycarboxylic acid and its derivatives is provided, comprising the following steps:

[0005] Step one, adding TiO2 and chelate hole trapping agent to low-concentration uranium solution, adjusting pH, and then performing high-pressure steam sterilization;

[0006] Step two, placing the sterilized solution in a light-proof environment and stirring to achieve adsorption-desorption equilibrium, and then turning on the LED lamp for light irradiation and stirring to form a polycarboxylic acid and its derivative-regulated photocatalysis heterogeneous system;

[0007] Step three, adding microorganisms to the polycarboxylic acid and its derivative-regulated photocatalysis heterogeneous system to form a microorganism-photocatalysis heterogeneous system.

[0008] Preferably, in the step one, before adjusting the pH, the optimal pH is determined through simulation analysis, and then HCl and NaOH are added to adjust the pH value.

[0009] Preferably, in the step one, the pH range of the simulation analysis is 3-7, and the optimal pH is 4.

[0010] Preferably, in the step one, the chelating hole trapping agent is one or more of polybasic carboxylic acid and its derivatives, including gluconic acid (HGH4), sodium gluconate (NaGH4), citric acid (CA), trisodium citrate (SC), tartaric acid (TA), sodium tartrate (ST), ethylenediaminetetraacetic acid (EDTA), or disodium ethylenediaminetetraacetate (EDTA-2Na), and the optimal chelating hole trapping agent is sodium gluconate (NaGH4).

[0011] Preferably, in the step one, the addition amount of TiO2 is 0.2 g / L, the chelating hole trapping agent is added according to the molar concentration ratio of the chelating hole trapping agent to U of 10:1-80:1, and the optimal molar concentration ratio of the chelating hole trapping agent to U is 30:1.

[0012] Preferably, in the step two, the light-shielded stirring time is 2-12 h, and the solution reaches adsorption-desorption equilibrium when the concentration of U is constant; the lighted stirring time is 50-60 h.

[0013] Preferably, in the step three, the method of adding microorganisms is:

[0014] S31, the chelating hole trapping agent and microorganisms are first placed in beef extract peptone culture medium for culture, and after a period of culture, bacterial liquid is obtained;

[0015] S32, the bacterial liquid is frozen and centrifuged, and then the precipitate after centrifugation is washed to obtain the bacterial body, which is refrigerated;

[0016] S33, the bacterial body obtained in S32 is added to the polybasic carboxylic acid and its derivatives regulated photocatalytic heterogeneous system obtained in step two, and then placed in a light-shielded environment and stirred to reach adsorption-desorption equilibrium, and after reaching the equilibrium, LED light is turned on for light stirring, thereby forming a microorganism-photocatalytic heterogeneous system.

[0017] Preferably, in the step three, the added microorganisms are one of actinomycetes, yeast, alkali-producing bacteria, Escherichia coli, and Bacillus spores.

[0018] Preferably, in the step one, the temperature of high-pressure steam sterilization is 110-130°C, and the sterilization time is 10-30 min.

[0019] Preferably, in the S31, the pH of the beef extract peptone liquid medium is 7.2, and the culture conditions are: temperature 30℃, 120rpm constant temperature shaker for 24h, and in the S32, the frozen centrifugation conditions are: temperature 4.0℃, 8000rpm frozen centrifuge for 10min, washed with 0.85wt% NaCl solution for three times, and stored in a 4℃ refrigerator.

[0020] Preferably, before adding TiO2 in step one, the TiO2 is modified, including the following steps:

[0021] a. Mix sulfuric acid and hydrogen peroxide in a volume ratio of 1:1, then put TiO2 into the mixture, soak, then wash and dry for standby;

[0022] b. Stir and mix anhydrous ethanol and phosphomolybdic acid, then add 20wt% glucose solution, continue to stir to further dissolve phosphomolybdic acid, then add treated TiO2 into the system, adjust the pH to 2 with sulfuric acid, then ultrasonic dispersion, then add AgNO3 and stir, drop 0.5mol / L Na2HPO4 solution while stirring, continue to stir until uniform, then transfer to a reaction kettle for reaction, after the reaction, wash the product with anhydrous ethanol and deionized water, then grind and dry;

[0023] c. Mix the dried product with 20g ethylene glycol, then put it into a tube furnace, protect it with nitrogen, and calcine to obtain modified TiO2.

[0024] Preferably, in the step a, the concentration of sulfuric acid is 2-10mol / L, and the soaking time is 2-8h;

[0025] Preferably, in the step b, the mass-volume ratio of anhydrous ethanol, phosphomolybdic acid, and 20wt% glucose solution is 1-30mL:0.1-5g:1-30mL, and the mass-volume ratio of phosphomolybdic acid, TiO2, AgNO3, and Na2HPO4 is 1g:10-25g:5-20g:10-100mL, the reaction temperature is 160-180℃, and the reaction time is 10-25h;

[0026] Preferably, in the step c, the mass ratio of the product to ethylene glycol is 1.2-1.8, and the calcination conditions are: heating to 250℃ at a rate of 2℃ / min for 1-3h, then continue to heat to 500℃ at a rate of 2℃ / min for 3-6h.

[0027] The present application at least comprises the following beneficial effects: by introducing a chelating hole trapping agent into a photocatalytic uranium removal system, a polycarboxylic acid and its derivative regulated photocatalytic heterogeneous system is constructed, then a microorganism is introduced into the polycarboxylic acid and its derivative regulated photocatalytic heterogeneous system, a microorganism-photocatalytic heterogeneous system is constructed, the advantages of biosorption treatment and photocatalytic treatment are better combined, uranium in a low-concentration uranium solution can be effectively removed, the uranium removal rate reaches 99%, the optimal chelating hole trapping agent NaGH4, the optimal pH is 4.0, and the optimal molar concentration ratio of NaGH4 to U(VI) is 30:1, compared with other treatment methods, the present application has the characteristics of low energy consumption and recyclability, the photocatalyst TiO2 is modified in the present application, so that the photocatalytic activity and the light absorption range of TiO2 are improved, and then the illumination stirring time is reduced, so that the speed of treating low-concentration U(VI) wastewater is improved.

[0028] Other advantages, objects, and features of the present application will be apparent from the following description, and will be understood by persons skilled in the art. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a continuous wavelength scanning diagram of the ultraviolet-visible light absorption spectrum of the present application;

[0030] Figure 2 is a fitting schematic diagram of a U(VI) solution concentration standard curve of the present application;

[0031] Figure 3 is a schematic diagram of U(VI) aqueous solution changes under different pH conditions of embodiments 1 to 4 of the present application (from left to right, pH is 3, 4, 5, and 7);

[0032] Figure 4 is a schematic diagram of the occurrence state of U(VI) in aqueous solution under different pH conditions of embodiments 1 to 4 of the present application;

[0033] Figure 5 is an electrochemical impedance spectrum (EIS) and equivalent circuit diagram of charge transfer resistance under different pH conditions of embodiments 1 to 4 of the present application;

[0034] Figure 6 is a time-current curve diagram of the system of reducing and removing low-concentration U(VI) of embodiments 5 to 10 and comparative example 1 of the present application;

[0035] Figure 7 is a diagram of the change of U(VI) removal efficiency of TiO2 photocatalysis with time under different molar concentration ratios of NaGH4 to U(VI) of embodiments 11 to 15 of the present application;

[0036] Figure 8Figure for effect of different molar concentration ratio of NaGH4 to U(VI) on TiO2 photocatalytic removal efficiency of U(VI) in embodiments 11-15 of the present application;

[0037] Figure 9 Figure for effect of different concentration of uranium solution on different chelate type hole trapping agents in embodiments 5-10 of the present application;

[0038] Figure 10 Figure for effect of different chelate type hole trapping agents on TiO2 photocatalytic removal efficiency of U(VI) in embodiments 5-10 of the present application;

[0039] Figure 11 XPS full spectrum of comparative example 2 and comparative example 3 of the present application;

[0040] Figure 12 U element fine spectrum of comparative example 2 and comparative example 3 of the present application;

[0041] Figure 13 Figure for removal efficiency of low concentration U(VI) containing wastewater by different microbial synergistic photocatalytic heterogeneous regulation in application examples 1-5 of the present application. DETAILED DESCRIPTION

[0042] The present application will be further described in detail below with reference to the accompanying drawings so as to enable those skilled in the art to implement the present application according to the description.

[0043] In the following examples, the determination method of U(VI) concentration is as follows: using arsenazo III as dye, the U(VI) concentration in solution is measured by ultraviolet spectrophotometer, and the wavelength of the ultraviolet spectrophotometer is set to 652 nm.

[0044] In the following examples, the removal rate of U(VI) is calculated as follows:

[0045] U(VI) removal rate (%) = (1 - C t / C0) x 100%

[0046] In the formula, C0(mg / L) is the initial concentration of U(VI) in the uranium containing solution, and C t (mg / L) is the concentration of U(VI) in the uranium containing solution after reaction time t.

[0047] In the following examples, the photocatalytic reaction kinetics Langmuir-Hinshelwood (LH) expression is as follows:

[0048]

[0049] In the formula, v represents the reaction rate changing with time, C is the concentration of reactant, k is the reaction rate constant, and K is the adsorption equilibrium constant.

[0050] The method for determining the scanning wavelength of the ultraviolet-visible light absorption spectrum and drawing the standard curve of the U(VI) solution concentration is as follows:

[0051] 0.05% azoarsenite III is configured as a complexing color developing agent with U(VI), 5.0 ml of the filtered supernatant containing U(VI) is taken, 0.1 mol / L HCl and 500 mg / L azoarsenite III solution are added, and the solution is subjected to continuous wavelength scanning of the ultraviolet-visible light absorption spectrum; the standard curve is drawn as follows: 0, 20, 40, 60, 80, 100, and 120 μL of 500 mg / L U(VI) solution is taken by a pipette, and 0.85% NaCl solution is added to make the solution volume 5 mL, and the corresponding U(VI) solution concentration is 0, 2, 4, 6, 8, 10, and 12 mg / L. 10, 25, 50, 75, 100, and 125 μL of 100 mg / L U(VI) solution is taken by a pipette, and 0.85% NaCl solution is added to make the solution volume 5 mL, and the corresponding U(VI) solution concentration is 0.2, 0.5, 1.0, 1.5, 2.0, and 2.5 mg / L. The blank solution is used as a reference, and the absorbance is measured at 652 nm. The concentration of uranyl ion CU(VI) is taken as the abscissa, and the absorbance A is taken as the ordinate, to obtain a linear regression equation. For example, Figure 1 、 Figure 2 When the U(VI) solution concentration is 2-12 mg / L, C U(VI) = 0.1101A-0.0641, R 2 = 0.9994; when the U(VI) solution concentration is 0.2-2 mg / L, C U(VI) = 0.0832A-0.0113, R 2 = 0.9995.

[0052] Examples 1-4

[0053] Before step one, simulation experiments are carried out at different pH values, the pH value of Example 1 is 4, the pH value of Example 2 is 3, the pH value of Example 3 is 5, and the pH value of Example 4 is 7. The method is as follows: the occurrence state of the uranium ion in the U(VI) solution with an initial concentration of 10 mg / L and a pH value of 4, 3, 5, and 7 is simulated and analyzed by using Visual MINTEQ 3.1 software, and the Electrochemical Impedance Spectroscopy (EIS) is determined, and the fitting is carried out by using ZView2 software. According to the simulation analysis, the best pH value is 4.

[0054] A method for regulating the reduction and removal of low-concentration U(VI) in a photocatalytic heterogeneous system by polycarboxylic acid and its derivatives, comprising:

[0055] Step one, 500mg / L of uranyl solution was prepared by adding 0.85wt% NaCl aqueous solution, then 10mg / L U(VI) low concentration uranium solution was prepared by adding HCl and NaOH to adjust pH to 4.0, then 250mL low concentration uranium solution was added into a conical flask, 50mg TiO2 and 68.75mg sodium gluconate (NaGH4) with molar ratio of 30:1 to U(VI) were added into the low concentration uranium solution, and the solution was sterilized in a high pressure steam sterilizer at 121℃ for 20min. The solution after sterilization was electrochemically characterized, the open circuit voltage was 0V, the initial frequency of the alternating current signal was set to 10000Hz, the end frequency was set to 0.1Hz, and the amplitude of the sinusoidal potential was set to 10mV RMS to record the electrochemical impedance spectroscopy (EIS); the voltage was set to 0V, the scanning time was set to 600s, and the recording time-current curve (i-t) was recorded to test the TiO2 photocurrent production amount;

[0056] Step two, the sterilized conical flask containing the solution was wrapped with tin foil to keep it in a light-proof environment, and stirred for 12h. The U(VI) concentration in the solution was detected until no change was observed, i.e. adsorption-desorption equilibrium was reached. After the equilibrium was reached, the LED light was turned on for illumination and stirring, and the stirring time was 60h to form a multi-carboxylic acid and its derivative regulated photocatalytic heterogeneous system. According to different sampling times, the supernatant was filtered through a 0.45μm needle filter after centrifugation at a speed of 8000rpm for 5min, and used to determine the U(VI) concentration in the supernatant. If the U concentration in the supernatant did not meet the discharge standard, step two was repeated until the discharge standard was met, and then the solution was directly discharged.

[0057] The results of the electrochemical impedance spectroscopy (EIS) determination of the systems with different pH values in step one of examples 1-4 are shown in Figure 5 The fitting results by ZView2 software are shown in table 1.

[0058] Table 1 Fitting values of each element in the equivalent circuit diagram

[0059]

[0060] It can be seen from Figure 3 that the solution is clear and transparent when the pH value is 3.0 and 4.0, the solution color changes to yellow-green when the pH value is 5.0 and 7.0, and the solution is turbid when the pH value is 7.0. It can be seen from Figure 4 that when the pH is 3.0, U(VI) mainly exists in the form of UO2 2 + in water. With the increase of pH, part of U(VI) in the solution reacts with OH- complexation, forming a series of positively charged hydrates, which help to adsorb on the surface of TiO2. When pH = 5.0, UO2 2+ gradually disappeared, and the main existing form of U(VI) became (UO2)3OH 5+ and (UO2)4OH 7+ and a small amount of yellow-green precipitate was produced, which was not easy to adsorb. From Figure 5 It can be seen that all the EIS curves are circular arcs, in which the circular arc is the largest when pH = 5, and the radii of the circular arcs are not much different when pH = 4 and 7. The size of the arc is related to the charge transfer resistance in the solution, and the larger the arc, the greater the resistance and the smaller the speed of charge transfer in the solution. The equivalent circuit diagram obtained by fitting the EIS curve is shown in the circuit diagram in Figure 5 , in which Rct is the electron transfer resistance in the solution. As can be seen from Table 1, when pH = 4.0, the value of the electron transfer resistance Rct is the smallest, 53653 Ω, which indicates that the charge transfer resistance is the smallest at this time, and the separation of photo-generated charges is easier, which is beneficial to the occurrence of redox reaction of the substrate adsorbed on the surface of the catalyst by the electron-hole pairs. At this time, the electron reduction kinetics is faster than that when pH = 3.0, 5.0 and 7.0, so the optimal pH is 4.0.

[0061] Examples 5-10

[0062] After determining the optimal pH of 4 based on Examples 1-4, different chelating hole trapping agents were selected for experiments according to the method of Example 1. The chelating hole trapping agent added in Example 5 was disodium ethylenediaminetetraacetate (EDTA-2Na), the chelating hole trapping agent added in Example 6 was gluconic acid (HGH4), the chelating hole trapping agent added in Example 7 was citric acid (CA), the chelating hole trapping agent added in Example 8 was trisodium citrate (SC), the chelating hole trapping agent added in Example 9 was tartaric acid (TA), and the chelating hole trapping agent added in Example 10 was sodium tartrate (ST). The experimental method includes:

[0063] Step one, 500mg / L of uranyl mother liquor is added to 0.85wt% NaCl aqueous solution to prepare 10mg / L U(VI) low concentration uranium solution, then HCl and NaOH are added to adjust pH to 4.0, then 6 groups of 250mL low concentration uranium solution are taken and added into conical flask respectively, then 50mg TiO2 and 68.75mg corresponding chelate type hole trapping agent are added into the low concentration uranium solution of examples 5-10 respectively, and sterilized in high pressure steam sterilizer at 121℃ for 20min. After sterilization, the solution is electrochemically characterized, the open circuit voltage is 0V, the initial frequency of alternating current signal is set to 10000Hz, the end frequency is 0.1Hz, the sinusoidal potential amplitude is 10mV RMS, and the alternating current impedance spectrum (EIS) is recorded; the voltage is set to 0V, the scanning time is 600s, and the time-current curve (i-t) is recorded for 3 times to test the TiO2 photocurrent production;

[0064] Step two, the sterilized conical flask containing solution is wrapped with tin foil paper to make it in the light-proof environment, and stirred for 12h, the U(VI) concentration in the solution is detected until no change, that is, the adsorption-desorption equilibrium is reached, after the equilibrium is reached, the LED lamp is turned on for light irradiation and stirring, and the stirring time is 60h, to form the polycarboxylic acid and its derivative regulated photocatalytic heterogeneous system; according to different time sampling, the supernatant is filtered through 0.45μm needle hole filter membrane after centrifugation at 8000rpm for 5min, and used for determining the U(VI) concentration in the supernatant, whether the U concentration in the supernatant reaches the discharge standard or not, if not, the step two is repeated until the discharge standard is reached and directly discharged.

[0065] Combination Figure 9 , Figure 10 It can be seen that when CH3OH exists in the system, the U(VI) concentration in the solution is obviously higher than that when NaGH4 or HGH4 exists, which shows that the addition of NaGH4 and HGH4 can enhance the effect of TiO2 adsorbing U(VI). The removal efficiency of U(VI) under light irradiation is obviously higher than that in the dark group, and the system adding NaGH4, ST and TA is better for improving the photocatalytic removal efficiency of U(VI), which is 58.8%, 55.4% and 48.8% respectively. Therefore, the hole trapping agent for TiO2 photocatalytic removal of U(VI) in the present application is selected as NaGH4.

[0066] In addition, from Figure 6It can be seen that the photoelectric current of the system adding four polycarboxylic acids and their derivatives is higher than that of adding artificially synthesized EDTA and EDTA-2Na. Among them, the current of the system adding NaGH4, SC and ST increases more obviously, especially the current of the system adding NaGH4 increases by about 5 times, the current of the system adding SC increases by about 3 times, and the current of the system adding ST increases by about 2 times, which indicates that the addition of NaGH4 can effectively excite more electron-hole pairs and improve the photoelectric conversion efficiency of TiO2. Therefore, the hole trapping agent is preferably selected as NaGH4.

[0067] Examples 11-15

[0068] After determining the optimal pH of 4 and the optimal chelated hole trapping agent of NaGH4 based on Examples 1-10, different amounts of NaGH4 are added to the system to set the molar concentration ratio of NaGH4 to U(VI) in the solutions of Examples 11-15, 10:1 for Example 11, 20:1 for Example 12, 40:1 for Example 13, 50:1 for Example 14, and 80:1 for Example 15. The method is as follows:

[0069] Step one, 0.85wt% NaCl aqueous solution is added to 500mg / L uranyl solution to prepare a low-concentration uranium solution of 10mg / L U(VI), then HCl and NaOH are added to adjust the pH to 4.0, then 5 groups of 250mL low-concentration uranium solution are taken and added to conical flasks, and then 50mg TiO2 and corresponding amount of NaGH4 are added to the low-concentration uranium solutions of Examples 11-15, and sterilized in a high-pressure steam sterilization pot at 121℃ for 20min. The solution after sterilization is electrochemically characterized, the open circuit voltage is 0V, the initial frequency of the alternating current signal is set to 10000Hz, the end frequency is 0.1Hz, and the sinusoidal potential amplitude is 10mV RMS to record the electrochemical impedance spectrum (EIS); the voltage is set to 0V, the scanning time is set to 600s, and the recording time-current curve (i-t) is recorded to test the TiO2 photoelectric current production;

[0070] Step two, the sterilized conical flask containing the solution is wrapped with tin foil paper to keep it in a light-proof environment, and stirred for 12h, and the U(VI) concentration in the solution is detected until no change is observed, i.e. adsorption-desorption equilibrium is reached. After the equilibrium is reached, the LED light is turned on for illumination and stirring, and the stirring time is 60h to form a polycarboxylic acid and its derivative regulated photocatalytic heterogeneous system. According to different time, the supernatant is centrifuged at a speed of 8000rpm for 5min, and then filtered through a 0.45μm needle hole filter membrane for determination of the U(VI) concentration in the supernatant. If the U concentration in the supernatant does not meet the discharge standard, step two is repeated until the discharge standard is met and the solution is directly discharged.

[0071] In combination Figure 7 , Figure 8 It can be seen that the photocatalytic removal efficiency is obviously different after adding different concentrations of NaGH4 in the photocatalytic reaction system. The photocatalytic efficiency is increasing with time. After 60 hours of photocatalytic treatment, the photocatalytic removal efficiency of U(VI) reaches 71% when the molar concentration ratio of NaGH4 to U(VI) is 30:1. With the increase of the molar concentration ratio, the photocatalytic removal efficiency of U(VI) shows a trend of first increasing and then decreasing, and the efficiency reaches the maximum at 30:1. It can be seen that under the light condition, the reaction of each U(VI) and molar concentration ratio does not show continuous reaction, but the U(VI) concentration decreases rapidly in the first 24 hours of light, and then the U(VI) removal efficiency of each different U(VI) and NaGH4 molar concentration ratio experiment group enters a stable period. Therefore, the preferred molar concentration ratio of NaGH4 to U(VI) in the system of the present application is 30:1.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 1 is that in Step 1, 0.85wt% NaCl aqueous solution is added to 500mg / L uranyl mother liquor to prepare a low-concentration uranium solution of 10mg / L U(VI), then HCl and NaOH are added to adjust the pH to 4.0, then 250mL of low-concentration uranium solution is added to a conical flask, and then 50mg TiO2 and 68.75mg methanol (CH3OH) are added to the low-concentration uranium solution, and sterilized in a high-pressure steam sterilization pot at 121℃ for 20min. The solution after sterilization is electrochemically characterized, the open circuit voltage is 0V, the initial frequency of the alternating current signal is set to 10000Hz, the final frequency is set to 0.1Hz, and the sinusoidal potential amplitude is recorded as 10mV RMS impedance spectrum (EIS); the voltage is set to 0V, the scanning time is set to 600s, and the recording time-current curve (i-t) is recorded to test the TiO2 photocurrent production amount;

[0074] The remaining steps are the same as those of Example 1.

[0075] Comparative Example 2

[0076] The comparative example differs from example 1 in that step two is: the sterilized conical flask containing the solution is wrapped with tin foil to make it in the light-avoiding environment, and stirred for 12 h, the U(VI) concentration in the solution is detected until there is no change, i.e. adsorption-desorption equilibrium is reached, and no light stirring treatment is carried out after light-avoiding stirring. According to different time sampling, the supernatant is filtered through a 0.45 pm needle hole filter membrane after centrifugation at a speed of 8000 rpm for 5 min, and is used for determining the U(VI) concentration in the supernatant to detect whether the U concentration in the supernatant reaches the discharge standard, and the precipitate after reaction is subjected to XPS test: the dried sample is subjected to full spectrum and narrow spectrum scanning of corresponding elements using a Thermo escalab 250Xi X-ray photoelectron spectrometer.

[0077] The other steps are consistent with example 1.

[0078] Comparative example 3

[0079] The comparative example differs from example 1 in that the test method is:

[0080] Step one: 0.85wt% NaCl aqueous solution is added to 500 mg / L uranyl mother liquor to prepare a low-concentration uranium solution of 10 mg / L U(VI), then HCl and NaOH are added to adjust the pH to 4.0, then 250 mL of the low-concentration uranium solution is added to a conical flask, and then 50 mg of Ti02 is added to the low-concentration uranium solution, which is sterilized in a high-pressure steam sterilization pot at 121°C for 20 min. The solution after sterilization is subjected to electrochemical characterization, the open circuit voltage is 0 V, the initial frequency of the alternating current signal is set to 10000 Hz, the end frequency is set to 0.1 Hz, and the sinusoidal potential amplitude is set to 10 mV RMS to record the electrochemical impedance spectrum (EIS); the voltage is set to 0 V, the scanning time is set to 600 s, and the recording is repeated 3 times to record the time-current curve (i-t) to test the Ti02 photocurrent production;

[0081] Step two is: the sterilized conical flask containing the solution is wrapped with tin foil to make it in the light-avoiding environment, and stirred for 12 h, the U(VI) concentration in the solution is detected until there is no change, i.e. adsorption-desorption equilibrium is reached, and no light stirring treatment is carried out after light-avoiding stirring. According to different time sampling, the supernatant is filtered through a 0.45 pm needle hole filter membrane after centrifugation at a speed of 8000 rpm for 5 min, and is used for determining the U(VI) concentration in the supernatant to detect whether the U concentration in the supernatant reaches the discharge standard, and the precipitate after reaction is subjected to XPS test: the dried sample is subjected to full spectrum and narrow spectrum scanning of corresponding elements using a Thermo escalab 250Xi X-ray photoelectron spectrometer.

[0082] From Figure 11 , Figure 12The precipitate contains Ti, C, O, and a large amount of U after the adsorption of U(VI). Among these, U(VI) contains U4f. 7 / 2 and U4f 5 / 2 The peaks were located in the range of 382.2±0.3 eV and 393.1±0.3 eV, while the U(IV) peaks were located in the range of 380.4±0.3 eV and 391.3±0.3 eV. After 60 hours of reaction under illumination, U(IV) was present in the precipitates with U(VI) to NaGH4 molar concentration ratios of 0:1 and 30:1. Calculations of the peak area ratios of U(IV) and U(VI) showed that at a molar concentration of 0:1, the peak area ratio of U(IV) was 12.8%, and that of U(VI) was 87.2%. At a molar concentration of 30:1, the peak area ratio of U(IV) was 18.6%, and that of U(VI) was 81.4%. Compared to the absence of NaGH4, the peak area ratio of U(VI) decreased, while that of U(IV) increased, indicating that NaGH4 promotes the photocatalytic reduction of U(VI) by TiO2.

[0083] Examples 16-20

[0084] After determining the optimal pH (4.0), optimal chelating hole scavenger (NaGH4), and optimal molar ratio of NaGH4 to U(VI) (30:1) through Examples 1-15, based on Example 1, different microorganisms were added to the photocatalytic heterogeneous system regulated by polycarboxylic acids and their derivatives. Example 16 used Bacillus, Example 17 used Escherichia coli, Example 18 used Alcaligenes faecalis, Example 19 used yeast, and Example 20 used Actinomycetes. The addition method was as follows:

[0085] S31. First, the microorganisms corresponding to Examples 16-20 were placed together with NaGH4 in beef extract peptone medium at pH 7.2 and cultured for 24 hours at 30°C and 120 rpm in a constant temperature shaker to obtain bacterial solution.

[0086] S32. Centrifuge the bacterial culture at 4℃ for 10 minutes at 8000 rpm. Then wash the precipitate three times with 0.85 wt% NaCl solution. The precipitate is the bacterial cell. Store it in a refrigerator at 4.0℃.

[0087] S33, adding the bacteria obtained in S32 to the photocatalytic heterogeneous system of the polycarboxylic acid and its derivatives, and adding an amount of 1 g of bacteria per 1 L of solution, and then continuing to perform electrochemical characterization on the solution, with an open circuit voltage of 0 V, an initial frequency of an alternating current signal of 10,000 Hz, an end frequency of 0.1 Hz, and a sine wave potential amplitude of 10 mV RMS, and recording an electrochemical impedance spectrum (EIS); setting a voltage of 0 V, a scanning time of 600 s, and repeating 3 times, and recording a time-current curve (i-t) to test the TiO2 photocurrent production amount; and then continuing to stir in the dark environment for 12 h, detecting the U(VI) concentration in the solution until no change is observed, i.e., adsorption-desorption equilibrium is reached, and after the equilibrium is reached, turning on an LED lamp for illumination and stirring and timing, with a stirring time of 60 h, to form a microbial-photocatalytic heterogeneous system.

[0088] In the microbial-photocatalytic heterogeneous system formed by the Bacillus used in Example 16, the removal rate of uranium in low-concentration U(VI)-containing wastewater reached 99%, and in the microbial-photocatalytic heterogeneous system formed by the Escherichia coli used in Example 17, the removal rate of uranium in low-concentration U(VI)-containing wastewater reached 98.8%.

[0089] Comparative Example 4

[0090] In this comparative example, only bacteria were added to the low uranium solution without adding NaGH4. The method was as follows: Bacillus was cultured in a beef extract peptone medium with a pH of 7.2, and after being cultured at 30°C for 24 h in a constant-temperature shaker with a rotation speed of 120 rpm, a bacterial solution was obtained. The bacterial solution was frozen and centrifuged at 8,000 rpm for 10 min, and then the precipitate after centrifugation was washed with a 0.85 wt% NaCl solution for three times to obtain the bacteria, which were stored in a refrigerator at 4.0°C.

[0091] Step one, 500 mg / L of uranyl solution was prepared by adding a 0.85 wt% NaCl aqueous solution to obtain a low-concentration uranium solution of 10 mg / L U(VI), and then HCl and NaOH were added to adjust the pH to 4.0. Then 250 mL of the low-concentration uranium solution was added to a conical flask, 50 mg of TiO2 was added to the low-concentration uranium solution, and then Bacillus was added to the low-concentration uranium solution at a bacteria addition amount of 1 g / L. Then the solution was subjected to electrochemical characterization, with an open circuit voltage of 0 V, an initial frequency of an alternating current signal of 10,000 Hz, an end frequency of 0.1 Hz, and a sine wave potential amplitude of 10 mV RMS, and an electrochemical impedance spectrum (EIS) was recorded; a voltage of 0 V was set, a scanning time of 600 s was set, and the process was repeated 3 times, and a time-current curve (i-t) was recorded to test the TiO2 photocurrent production amount.

[0092] Step two, the sterilized conical flask containing the solution is wrapped with tin foil, and it is in the light-proof environment and stirring for 12h, the concentration of U(VI) in the solution is detected until there is no change, that is, the adsorption-desorption equilibrium is reached, after reaching the equilibrium, the LED light is turned on for illumination and timing, and the stirring time is 60h.

[0093] The removal efficiency of low concentration U(VI) containing wastewater by microbial synergistic photocatalysis without adding NaGH4 is only 62.96%.

[0094] From Figure 13 It can be seen that the best removal efficiency of low concentration U(VI) containing wastewater by microbial synergistic photoelectron heterogeneous regulation is bacillus and escherichia coli, which reaches 99% and 98.8%, and the concentration of U(VI) ion in the solution is 27.32 and 45.28μg / L, respectively, which reaches the discharge standard. The removal efficiency of alkali producing bacteria reaches 98.0%, and the concentration of U(VI) ion in the solution is 67.1μg / L, which does not reach the discharge standard. The removal efficiency of yeast and actinomycete synergistic photoelectron for U(VI) is only 73.2% and 87.3%. The removal efficiency of low concentration U(VI) containing wastewater by microbial synergistic photocatalysis without adding NaGH4 is only 62.96%, which shows that the addition of NaGH4 can promote the removal efficiency of low concentration U(VI) containing wastewater by microbial synergistic photocatalysis heterogeneous regulation.

[0095] Example 21

[0096] A method for removing low concentration U by regulating photocatalysis with polycarboxylic acid and its derivatives, comprising:

[0097] a. 250mL of 3mol / L sulfuric acid and hydrogen peroxide are mixed in a volume ratio of 1:1, 20g of TiO2 is placed in it, soaked for 4h, then washed and dried for standby;

[0098] b. 15mL of anhydrous ethanol and 1g of phosphomolybdic acid are stirred and mixed uniformly, then 20wt% of glucose solution 15mL is added, and the phosphomolybdic acid is further dissolved by stirring, then the treated TiO2 is added to the system, the pH is adjusted to 2 with sulfuric acid, then ultrasonic dispersion is carried out for 3h, then 15AgNO3 is added and stirred, while 60mL of 0.5mol / L Na2HPO4 is added dropwise, continue to stir uniformly, then transfer to the reaction kettle, react at 180℃ for 20h, after the reaction is completed, the product is washed with anhydrous ethanol and deionized water, then ground and dried;

[0099] c. The dried product was mixed with 20 g of ethylene glycol and placed in a tube furnace, protected by nitrogen, and then heated to 250°C at a rate of 2°C / min for 1 h, and then heated to 500°C at a rate of 2°C / min for 3 h to obtain modified TiO2.

[0100] Step one, 0.85wt% NaCl aqueous solution was added to the 500mg / L uranyl liquor to prepare a low concentration uranium solution of 10mg / L U(VI), then HCl and NaOH were added to adjust the pH to 4.0, then 250mL of low concentration uranium solution was taken into a conical flask, then 50mg of modified TiO2 and 68.75mg of NaGH4 were added to the low concentration uranium solution, and then the solution was sterilized in a high-pressure steam sterilization pot at 121°C for 20min. The solution after sterilization was electrochemically characterized, the open circuit voltage was 0V, the initial frequency of the alternating current signal was set to 10000Hz, the end frequency was set to 0.1Hz, and the sinusoidal potential amplitude was set to 10mV RMS to record the electrochemical impedance spectrum (EIS); the voltage was set to 0V, the scan time was set to 600s, and the recording time-current curve (i-t) was recorded to test the TiO2 photocurrent production;

[0101] Step two, the sterilized conical flask containing the solution was wrapped with tin foil to keep it in a light-proof environment, and stirred for 12h, and the U(VI) concentration in the solution was detected until no change was observed, i.e. adsorption-desorption equilibrium was reached, after which the LED light was turned on for illumination and stirring, and the stirring time was 60h, forming a polycarboxylic acid and its derivative regulated photocatalytic heterogeneous system;

[0102] S31, NaGH4 and Bacillus were first placed in a beef extract peptone medium with a pH of 7.2 and cultured at 30°C in a constant temperature shaker at a speed of 120rpm for 24h to obtain a bacterial solution;

[0103] S32, the bacterial solution was frozen and centrifuged at 8000rpm for 10min, and then the precipitate after centrifugation was washed with 0.85wt% NaCl solution for three times to obtain the Bacillus cell, which was stored in a refrigerator at 4.0°C;

[0104] S33, the Bacillus cell obtained in S32 was added to the polycarboxylic acid and its derivative regulated photocatalytic heterogeneous system obtained in step two, and the addition amount was 1g of Bacillus per 1L of solution, then the solution was electrochemically characterized again, and the time-current curve (i-t) was recorded; then the solution was stirred in a light-proof environment for another 12h, and the U(VI) concentration in the solution was detected until no change was observed, i.e. adsorption-desorption equilibrium was reached, after which the LED light was turned on for illumination and stirring, and the stirring time was 30h, forming a microorganism-photocatalytic heterogeneous system.

[0105] The present embodiment uses the spore bacillus consistent with embodiment 16 to constitute a microorganism-photocatalysis heterogeneous system, and finally the removal rate of uranium in low concentration U(VI) containing wastewater reaches 99.5%, and because the present embodiment modifies TiO2, the photocatalytic activity of TiO2 is improved, after being added into the system, it can effectively improve the light absorption range of TiO2, and then reduce the light stirring time, so that the light stirring time is shortened from 60h to 30h, which is beneficial to form the microorganism-photocatalysis heterogeneous system as soon as possible, and improve the speed of treating low concentration U(VI) containing wastewater.

[0106] Although the embodiments of the present application have been disclosed as above, it is not limited to the application listed in the specification and the embodiments, and can be fully applied to various fields suitable for the present application, and additional modifications can be easily realized by those skilled in the art, and therefore the present application is not limited to specific details and the figures shown and described herein, without departing from the general concept defined by the claims and the equivalent scope.

Claims

1. A method for regulating photocatalytic reduction removal of low concentration U by polycarboxylic acids and their derivatives, characterized by, The method comprises the following steps: Step one, adding modified TiO2 and chelating hole trapping agent to low concentration uranium solution, adjusting pH, and then high pressure steam sterilization; Step two, placing the sterilized solution in a light-proof environment and stirring to reach adsorption-desorption equilibrium, then turning on the LED light for illumination and stirring to form a polycarboxylic acid and derivative regulated photocatalytic heterogeneous system; Step three, first placing the chelating hole trapping agent and microorganisms in a beef extract peptone culture medium for culture to obtain a bacterial solution; freezing and centrifuging the bacterial solution, then washing the precipitate after centrifugation to obtain the bacterial body, which is stored in a refrigerator; adding the bacterial body to the polycarboxylic acid and derivative regulated photocatalytic heterogeneous system, and then placing it in a light-proof environment and stirring to reach adsorption-desorption equilibrium, then turning on the LED light for illumination and stirring to form a microorganism-photocatalytic heterogeneous system; The preparation method of the modified TiO2 is as follows: a. mixing sulfuric acid and hydrogen peroxide at a volume ratio of 1:1, placing TiO2 in the mixture, soaking, then washing and drying, and storing for use; b. stirring and uniformly mixing anhydrous ethanol and phosphomolybdic acid, adding a 20wt% glucose solution, continuing to stir to further dissolve the phosphomolybdic acid, then adding the treated TiO2 to the system, adjusting the pH to 2 with sulfuric acid, then ultrasonic dispersion, adding AgNO3 and stirring, adding 0.5mol / L Na2HPO4 dropwise during stirring, stirring uniformly, then transferring to a reaction kettle for reaction, then washing the product with anhydrous ethanol and deionized water, then grinding and drying; c. mixing the dried product with 20g ethylene glycol, then placing it in a tube furnace for calcination under nitrogen protection to obtain the modified TiO2; The chelating hole trapping agent is polycarboxylic acid and its derivatives, including one or more of gluconic acid, sodium gluconate, tartaric acid, sodium tartrate, ethylenediaminetetraacetic acid, or disodium ethylenediaminetetraacetate.

2. The method of claim 1, wherein the photocatalytic reduction of low concentration U is removed by polycarboxylic acid and its derivatives, characterized in that, In step one, the optimal pH is determined by simulation analysis before adjusting the pH, then HCl and NaOH are added to adjust the pH value.

3. The method of claim 2, wherein the method is characterized by the reduction of low concentrations of U by photocatalysis modulated by polycarboxylic acids and their derivatives, In step one, the simulation analysis pH range is 3-7.

4. The method of claim 1, wherein the method of photocatalytic reduction removal of low concentration U is regulated by polycarboxylic acids and their derivatives. In step one, the addition amount of TiO2 is 0.2g / L, and the chelating hole trapping agent is added according to a molar concentration ratio of 10:1-80:1 of the chelating hole trapping agent to U.

5. The method of claim 1, wherein the method of photocatalytic reduction removal of low concentration U is regulated by polycarboxylic acids and their derivatives. In step two, the light-proof stirring time is 2-12h, and the U concentration in the solution remains unchanged to reach adsorption-desorption equilibrium, and the illumination and stirring time is 50-60h.

6. The method of claim 1, wherein the method of photocatalytic reduction removal of low concentration U is regulated by polycarboxylic acids and their derivatives. In step three, the added microorganism is one of actinomycetes, yeast, alkali-producing bacteria, Escherichia coli, and Bacillus spores.

7. The method of claim 1, wherein the method is characterized by the reduction of low concentration U by photocatalysis is regulated by polycarboxylic acids and their derivatives, In step one, the high pressure steam sterilization temperature is 110-130℃, and the sterilization time is 10-30min.

8. The method of claim 1, wherein the method is characterized by the reduction of low concentration U by photocatalysis is regulated by polycarboxylic acids and their derivatives, In step three, the pH of the beef extract peptone liquid medium is 7.2, the culture conditions are: temperature 30℃, 120 rpm constant temperature shaking bed culture for 24h, the freezing and centrifugation conditions are: temperature 4.0℃, 8000 rpm freezing centrifuge centrifugation for 10min, washing with 0.85wt% NaCl solution for three times, and storing in a 4℃ refrigerator.

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