CN111063469A - Method for removing radionuclide strontium in water - Google Patents

Method for removing radionuclide strontium in water Download PDF

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CN111063469A
CN111063469A CN201911342834.XA CN201911342834A CN111063469A CN 111063469 A CN111063469 A CN 111063469A CN 201911342834 A CN201911342834 A CN 201911342834A CN 111063469 A CN111063469 A CN 111063469A
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activated carbon
water
sbac
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strontium
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董丽华
潘淑杰
伍成梁
侯立安
张光辉
顾平
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Tianjin University
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    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21FPROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
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Abstract

The invention discloses a method for removing radionuclide strontium in water, which comprises the steps of measuring the effluent quality of a BAC process, and testing, characterizing and actually applying an activated carbon sample used by the BAC process. The method does not need to reconstruct the BAC process or add steps of pretreatment, post-treatment and the like, saves energy, and realizes the in-situ recycling of the activated carbon used by the BAC process; the method for removing the radionuclide strontium (Sr) in the water by utilizing the BAC process can fully consider the practical factors of the traditional water treatment, thereby achieving the purposes of making the best use of the materials and saving resources. Compared with a single treatment process, the method is combined with the traditional water treatment process, has low cost, is environment-friendly, has good economic benefit, saves resources and has positive significance for promoting social sustainable development.

Description

Method for removing radionuclide strontium in water
Technical Field
The invention relates to the field of removal of radionuclide strontium (Sr) in water, in particular to Sr removal by a water supply advanced treatment process of a Biological Activated Carbon (BAC) method.
Background
1. Radioactive strontium and its hazard
Strontium atom number 38, relative molecular mass 87.62, belonging to alkaline earth metal, and density 2.60g/cm3Melting point 769 deg.C, boiling point 1384 deg.C. It is an active positive metal and is easily oxidized into stable colorless Sr2+The chemical property is similar to calcium and barium. Exists in nature84Sr、86Sr、87Sr、88Four stable isotopes of Sr, with the most common of the 16 radioactive isotopes being90Sr。
In general terms, the amount of the solvent to be used,90sr in soluble ionic form2+Is present in the water body and is,90in addition, strontium is a second main group element, and has similar biochemical properties to calcium, so that the strontium participates in metabolic processes and exchanges with calcium ions in bones to form Sr (PO)4)2The Sr in water is removed, so that the Sr is removed2+Arouse the wide attention of scholars at home and abroad.
With the development of the nuclear industry, radioactive wastes are produced in large quantities, and the discharge of radioactive waste water is an important source of radioactive nuclides into the environment, wherein radioactive strontium (x), (b), (c), and (d)90Sr) is235U and239one of the fission products of Pu has a half-life of 30 years, occupies a large radioactive share, and is a main nuclide in radioactive wastewater. In 2011, when an explosion accident occurs in a nuclear power station in the Fudao of Japan, dangerous radioactive substances rapidly diffuse around, about 520 tons of high-radioactivity sewage leaks into the sea shortly after the accident, and more than 30 ten thousand tons of polluted wastewater is pumped out from a reactor and discharged into the sea. There are documents showing that a large amount of radioactive waste water containing strontium is discharged at that time, wherein90The release amount of Sr flowing into nearby ocean is up to 1 x 1015~6×1015And Bq. Moreover, in 2011 after radiation leakage, a large amount of radiation sewage in Japan remains untreated later, and one of 9, 10 and 9 months in 2019The secondary reporter will be in the Japan environment minister and even directly that "Japan has no choice but to discharge the sewage into the sea and dilute the sewage". Radioactive water contamination, including radioactive strontium, has received much global attention.
2. Current state of the art for radioactive strontium in water
Heretofore, techniques for removing radioactive strontium from an aqueous solution include adsorption, chemical precipitation, extraction, ion exchange, membrane separation, evaporative concentration, biological methods, and the like. That is, the removal method is the same as the removal of heavy metal lead in water except for the evaporation concentration method. The evaporative concentration method is to utilize the non-volatile property of radioactive nuclide to send the radioactive wastewater into an external heating device to be heated to boiling, so that the volatile solvent is continuously vaporized, and the radioactive wastewater is concentrated. The method is mainly used for treating the medium-high level radioactive wastewater, has the advantages of higher flexibility, higher safety and reliability and Decontamination Factor (DF) as high as 104~106. But the method is not suitable for treating wastewater containing tritium, iodine, ruthenium and other volatile nuclides and wastewater containing organic matters and easy to foam, and meanwhile, the method has high heat energy consumption and high operation cost, and potential threats such as corrosion, scaling, explosion and the like need to be considered in design and operation, so that the method is not generally applied. The biological treatment method is suitable for radioactive wastewater with low radioactivity or high organic content, and comprises a microbiological method and a phytoremediation method. The microorganism method is to absorb, enrich and transfer the radioactive nuclide through the microorganism between the soil and the plant root system, and the plant restoration method is to absorb the radioactive nuclide in the soil and the water while the green plant absorbs the nutrient, thereby fixing and transferring the radioactive nuclide in the polluted body and achieving the purpose of removal. As a new method for removing strontium, the biological adsorption has the advantages of high adsorption capacity, low cost and the like. However, the method has low efficiency, and the used plants or microorganisms are limited by the environment, so that the strontium-containing wastewater treated by the biological method is only in the laboratory research stage at present. In addition, some extracting agents in the extraction method have strong toxicity; the resin in the ion exchange method needs to be regenerated by acid or alkali according to time, a large amount of regenerated wastewater can be generated, and secondary pollution is caused; the membrane separation method has lower yield and the like. All of these factors contribute toThe technical choice of physically radioactive strontium wastewater is increasingly favored by adsorption processes.
Researchers at home and abroad have tested strontium removal with a variety of organic and inorganic adsorbents, including diatomaceous earth, goethite, hematite, bentonite, kaolinite, montmorillonite, clay minerals, pecan shells, zeolites, activated carbon, and some novel adsorbents, and the like. Among them, the activated carbon has been studied less to adsorb strontium and the effect is not satisfactory. The Shanwabkeh et al use pecan shells to prepare a novel carbon material, and the nitrogen adsorption isotherm test shows that the average pore diameter of the pore structure is
Figure BDA0002332081700000021
The research result shows that the removal rate of the strontium by the carbon is only 56.3 percent when the carbon adding amount is 1 g/L. Chegroch et al verified various factors such as pH, initial concentration of strontium, particle size and temperature in a granular activated carbon (merck, germany) adsorption experiment, and the best conditions to obtain the experiment were: the pH value is 4.0, the contact time is 8h, the initial concentration of strontium is 100mg/L, the particle size of the adsorbent is 270 mu m, and the temperature is 293.15K; the strontium adsorption obtained under the experimental condition follows quasi-first-order kinetics, a Langmuir model is well fitted, and the maximum adsorption capacity of the granular activated carbon to the strontium is 44.42 mg/g; however, the adding amount of the adsorbent is not given, so that the strontium removal effect of the activated carbon under specific conditions cannot be calculated from data in the text, and assuming that the adding amount is 10.0g/L, the strontium adsorption removal rate of the used activated carbon under the optimal conditions can be calculated to reach 60%. Moluukhia uses H2O2And HNO3The coconut shell carbon is oxidized and modified, a plurality of radioactive elements are adsorbed after surface chemical modification, and research shows that Eu is adsorbed3+,Ce3+,Sr2+And Cs+The selective order of the ions is Eu3+>Ce3+>Sr2+>Cs+Wherein, when the carbon adding amount is 10g/L and the contact time is 4h, the strontium solution with the initial concentration of 50mg/L can not be absorbed by 40 percent. Studies by Caccin and Kubota even showed that the activated carbon used had little strontium removal. The traditional adsorbent has not ideal strontium adsorption effect, the research and development of the novel adsorbent has high energy consumption and high cost, and therefore, the research and development of the novel adsorbent are closedThe adsorption of strontium also requires finding an adsorbent with low cost and ideal effect.
Reference documents:
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[4]Hong H J,Kim B G,Ryu J,et al.Preparation of highly stable zeolite-alginate foam composite for strontium(90Sr)removal from seawater andevaluation of Sr adsorption performance[J].Journal of EnvironmentalManagement,2018,205:192-200.
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[10]Wen T,Zhao Z,Shen C,et al.Multifunctional flexible free-standingtitanate nanobelt membranes as efficient sorbents for the removal ofradioactive90Sr2+and137Cs+ions and oils[J].Scientific Reports,2016,6:20920.
[11] the research progress of the low-level radioactive wastewater treatment technology in Yangqing, Houlian, Wang you Jun, J. environmental science and management, 2007(09): 107-.
[12] Wenxiangyi, a polymer auxiliary ultrafiltration method for removing cobalt [ D ] in the medium-low level radioactive wastewater: shanghai university of transportation, 2011.
[13] General technical overview of Miao Junting. Radioactive wastewater treatment [ J ] scientific and technical information, 2011(23):480.
[14]Huang C P,Lin T Y,Chiao L H,et al.Characterization of radioactivecontaminants and water treatment trials for the Taiwan Research Reactor’sspent fuel pool[J].Journal of Hazardous Materials,2012,233-234:140-147.
[15]O'Day P A,Newville M,Neuhoff P S,et al.X-Ray AbsorptionSpectroscopy of Strontium(II)Coordination[J].Journal of Colloid and InterfaceScience,2000,222(2):184-197.
[16]Karasyova O N,Ivanova L I,Lakshtanov L Z,et al.Strontium Sorptionon Hematite at Elevated Temperatures[J].Journal of Colloid&Interface Science,1999,220(2):419-428.
[17]Liang T J,Hsu C N,Liou D C.Modified Freundlich sorption of cesiumand strontium on Wyoming bentonite[J].Appl Radiatisotopes,1993,44(9):1205-1208.
[18]Jeong C H,Mineralogical and hydrochemical effects on adsorptionremoval of cesium-137and strontium-90by kaolinite[J].Journal of EnvironmentalScience and Health,Part A,2001,36(6):1089-1099.
[19]Papachristodoulou C A,Assimakopoulos P A,Gangas N H J.Strontiumadsorption properties of an aluminum-pillared montmorillonite carryingcarboxylate functional groups[J].Journal of Colloid&Interface Science,2002,245(1):32-39.
[10]Cole T,Bidoglio G,Soupioni M,et al.Diffusion mechanisms ofmultiple strontium species in clay[J].Geochimica et Cosmochimica Acta,2000,64(3):385-396.
[21]Shawabkeh R A,Rockstraw D A,Bhada R K.Copper and strontiumadsorption by a novel carbon material manufactured from pecan shells[J].Carbon,2002,40(5):781-786.
[22]Al-Jubouri S M,Curry N A,Holmes S M.Hierarchical porousstructured zeolite composite for removal of ionic contaminants from wastestreams and effective encapsulation of hazardous waste[J].Journal ofHazardous Materials,2016,320:241-251.
[23]Mingdong Z,Ping G,Zhenguo Z,et al.Effective,rapid and selectiveadsorption of radioactive Sr 2+,from aqueous solution by a novel metalsulfide adsorbent[J].Chemical Engineering Journal,2018,351:668-677.
[24]Chegrouche S,Mellah A,Barkat M.Removal of strontium from aqueoussolutions by adsorption onto activated carbon:kinetic and thermodynamicstudies[J].Desalination,2009,235(1-3):306-318.
[25]Moloukhia H,Hegazy W S,Abdel-Galil E A,et al.Removal of Eu3+,Ce3+,Sr2+,and Cs+ions from radioactive waste solutions by modified activated carbonprepared from coconut shells[J].Chemistry and Ecology,2016,32(4):324-345.
[26]Caccin M,Giacobbo F,Da Ros M,et al.Adsorption of uranium,cesiumand strontium onto coconut shell activated carbon[J].Journal ofRadioanalytical and Nuclear Chemistry,2013,297(1):9-18.
[27]Kubota T,Fukutani S,Ohta T,et al.Removal of radioactive cesium,strontium,and iodine from natural waters using bentonite,zeolite,andactivated carbon[J].Journal of Radioanalytical and Nuclear Chemistry,2013,296(2):981-984.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method for removing radionuclide strontium in water, and solves the problem that the removal effect of radioactive strontium in water is not ideal in the prior art.
The technical scheme of the invention is as follows:
a method for removing radionuclide strontium in water adopts a two-stage BAC feedwater advanced treatment process, when the first-stage effluent quality of the BAC process does not reach the standard and the pH of the used activated carbon is less than 7 or the zeta potential is less than 0 or the content of surface acidic functional groups is higher than the content of surface basic functional groups, the first-stage effluent quality is changed into a second-stage adsorption tank, namely the first-stage activated carbon adsorption tank has the function of the BAC process, and the used activated carbon as the second-stage adsorption tank can be used for removing radionuclide Sr in water, so that the existing BAC process has the function of removing the radionuclide Sr.
The method for removing the radionuclide strontium in the water specifically comprises the following steps:
(1) the effluent quality of the first-stage activated carbon adsorption tank is periodically detected;
(2) when the quality of the effluent water does not reach the standard, sampling and testing an activated carbon sample, wherein the sampling and testing mainly comprises the characterization of the pH, the isoelectric point and the surface functional group of the activated carbon;
(3) when the pH of the used activated carbon is less than 7 or the zeta potential is less than 0 or the content of the surface acidic functional groups is higher than that of the surface alkaline functional groups, the used activated carbon is changed into a second-stage adsorption tank; namely, the first-stage adsorption pool has the function of the BAC process, and SBAC as the second-stage adsorption pool can be used for removing the radionuclide Sr in the water, so that the conventional BAC process has the function of removing the radionuclide Sr.
In the step (2), characterization methods of pH, isoelectric point and surface functional group of the activated carbon are adopted to characterize the activated carbon mutually.
The invention has the beneficial effects that:
1. the method makes full use of the characteristics of the BAC process, finds a new removing scheme for removing the radionuclide Sr, effectively solves the possible sudden water pollution event, saves the cost, avoids secondary pollution, realizes the sustainable and full utilization of resources, and achieves the purposes of making the best use of things and saving resources.
2. The SBAC is arranged at the rear end of the adsorption pool, so that the BAC process has the functions of adsorption, biodegradation and radionuclide removal; the method has important significance for further understanding the BAC mechanism and the development of the BAC process; meanwhile, a backup guarantee is provided for emergency treatment of a BAC process water plant, and the functions of the activated carbon and the purpose of saving resources are fully exerted.
3. The invention is combined with the traditional water treatment process, has low cost, good environmental friendliness and economic benefit, saves resources and has positive significance for promoting the sustainable development of society.
Drawings
FIG. 1 shows the results of isoelectric point measurements of three types of carbon;
FIG. 2 is a FT-IR spectrum of the novel activated carbon with SBAC;
FIG. 3 SBAC vs. Sr in three adsorption tanks2+Langmuir adsorption isotherm and adsorption thermodynamic parameter fitting (C)05-250 mg/L; 2g/L of dosage; t is 25 ℃; pH 6.0; t is 120 min); wherein a.SBAC-5 adsorption isotherm; SBAC-6 adsorption isotherm; SBAC-7 adsorption isotherm; d. fitting adsorption thermodynamic parameters;
FIG. 4 SBAC vs. Sr2+Adsorption kinetics and model fitting (C)05.78 mg/L; W/V is 2.0 g/L; t is 25 ℃; pH 6.1; t is 1-90 min); wherein a is the adsorption rate; b. a quasi-first order kinetic model; c. a quasi-second order kinetic model; d. an intra-particle diffusion model;
FIG. 5 addition of adsorbent to SBAC adsorption of Sr2+Influence of (C)0=5.315mg/L&0.513mg/L;dosage=0-8g/L;T=25℃;pH=6.1;t=120min);
FIG. 6 Sr2+Initial concentration to SBAC adsorption of Sr2+Influence of (C)05-100 mg/L; 2g/L of dosage; t is 25 ℃; pH 6.1; t is 120 min); wherein a. Sr at different initial concentrations2+The equilibrium concentration of (a); SBAC vs. different initial concentrations of Sr2+The removal rate of (3).
Detailed Description
The invention is further illustrated by the following specific examples and the accompanying drawings. The examples are intended to better enable those skilled in the art to better understand the present invention and are not intended to limit the present invention in any way.
Example 1: after the two-stage BAC process for 5 years is operated, the first-stage adsorption tank can not meet the requirement of the internal control index of the water plant, and the first-stage adsorption tank is set as a second-stage adsorption tank. The plant uses coagulation, precipitation, two-stage BAC (O)3GAC) and filtration combined water treatment process with a capacity of (200,000 m)3And/d), the empty bed contact time EBCT of the AC bed is 14 minutes, the height of the AC bed is 2.0 meters, the ozone dosage is 2.0-2.5mg/L, and the contact time is 24 minutes. The water source of the water plant is from HP river, and the average effluent quality of the water plant is superior to the quality standard of Chinese drinking water.
Example 2: after the two-stage BAC process for 6 years is operated, the first-stage adsorption tank can not meet the requirement of the internal control index of the water plant, and the first-stage adsorption tank is set as a second-stage adsorption tank. The plant used coagulation, sedimentation, filtration and two stage BAC (O)3GAC) combined water treatment process flow with production capacity of (260,000 m)3And/d), the empty bed contact time EBCT of the AC bed is 14 minutes, the height of the AC bed is 1.8 meters, the ozone dosage is 1.8-2.0mg/L, and the contact time is 20 minutes. The water source of the water plant comes from CJ river, and the average effluent quality of the water plant is superior to the quality standard of Chinese drinking water.
Example 3: after 7 years of two-stage BAC process is operated, the first-stage adsorption tank can not meet the requirement of the internal control index of the water plant, and the first-stage adsorption tank is set as a second-stage adsorption tank. The plant used coagulation, sedimentation, filtration and two stage BAC (O)3GAC) combined water treatment process flow with production capacity of (100,000 m)3And/d), the empty bed contact time EBCT of the AC bed is 14 minutes, the height of the AC bed is 2.0 meters, the ozone dosage is 2.0-2.5mg/L, and the contact time is 22 minutes. The water source of the water plant is from HP river, and the average effluent quality of the water plant is superior to the quality standard of Chinese drinking water.
Example 4: the two-stage BAC process is operated for 3 years, and the first-stage adsorption tank can not reach the internal control index of the water plantAnd setting the adsorption tank as a second-stage adsorption tank. The plant uses coagulation, sedimentation, filtration, two-stage BAC (O)3GAC) and ultrafiltration combined water treatment process with a capacity of (150,000 m)3And/d), the empty bed contact time EBCT of the AC bed is 12 minutes, the height of the AC bed is 1.8 meters, the ozone dosage is 2.0-2.5mg/L, and the contact time is 20 minutes. The water source of the water plant is from certain lake water, and the average outlet water quality of the water plant is superior to the water quality standard of Chinese drinking water.
Example 5: and (3) operating a two-stage BAC process for 2 years, setting the first-stage adsorption tank as a second-stage adsorption tank when the first-stage adsorption tank cannot meet the requirement of the internal control index of the water plant. The plant used coagulation, sedimentation, filtration and two stage BAC (O)3GAC) combined water treatment process flow with production capacity of (500,000 m)3And/d), the empty bed contact time EBCT of the AC bed is 14 minutes, the height of the AC bed is 2.0 meters, the ozone dosage is 2.0-2.5mg/L, and the contact time is 26 minutes. The water source of the water plant is river water, and the average outlet water quality of the water plant is superior to the water quality standard of Chinese drinking water.
Example 6: the two-stage BAC process is operated for 4 years, the first-stage adsorption tank can not meet the requirement of the internal control index of the water plant, and the first-stage adsorption tank is set as a second-stage adsorption tank. The plant used coagulation, sedimentation, filtration and two stage BAC (O)3GAC) combined water treatment process flow with production capacity of (250,000 m)3And/d), the empty bed contact time EBCT of the AC bed is 14 minutes, the height of the AC bed is 2.0 meters, the ozone dosage is 2.0-2.5mg/L, and the contact time is 22 minutes. The water source of the water plant is from reservoir water, and the average outlet water quality of the water plant is superior to the water quality standard of Chinese drinking water.
Examples of the experiments
The results of characterization and application of the activated carbon in the first stage activated carbon adsorption cells of examples 1, 2 and 3 above are as follows:
samples taken from the first stage activated carbon in examples 1, 2 and 3 were designated as SBAC-5, SBAC-6 and SBAC-7, respectively.
Surface characterization of 1 SBAC
1.1 pH value
The pH of the fresh activated carbon in the water plant sampled here was 11, while the pH of SBAC-5, SBAC-6 and SBAC-7 was reduced to 6.0, 6.5 and 5.7, respectively. That is, due to the complex physical, chemical and biological processes (ozone oxidation, adsorption and biodegradation) in the BAC process, the pH of SBAC decreases with increasing activated carbon usage time. The slightly higher pH value of the SABC-6 is probably caused by unstable process operation in a water treatment plant, larger fluctuation of inlet water quality, supplement of new active carbon and the like.
1.2 surface functional groups
The surface functionality of SBAC-5, SBAC-6 and SBAC-7 was tested using Boehm titration to quantify the amount of acidic and basic functionality, respectively, and the results are shown in Table 1.
TABLE 1 acidic and basic functional groups of SBAC surface
Figure BDA0002332081700000081
As can be seen from table 1 above, the content of acidic groups (carboxyl, lactone and phenolic) was higher than that of basic groups for all SBAC samples of different service life, which is consistent with the results of the pH test described above. Test results demonstrate that SBAC has the potential to remove metal ions by chelation, with SBAC-6 having the highest carboxyl content, followed by SBAC-7 and SBAC-5; SBAC-5 has the highest lactone group content; SBAC-7 has the highest phenolic hydroxyl content.
1.3 surface ZETA potential
The results of isoelectric point measurements of the three carbons are shown in FIG. 1.
The isoelectric points of the three types of active carbon are respectively 2.86, 1.69 and 1.61 by utilizing an interpolation method. When the pH value of the solution is less than the isoelectric point of each activated carbon, the surface of the activated carbon is positively charged; when the pH of the solution is higher than the isoelectric point of the activated carbon, the surface of the activated carbon is negatively charged, and the positively charged metal ions, such as Pb, can be favorably adsorbed2+、Sr2+And the like. That is, the SBAC is negatively charged in aqueous solution except for the strongly acidic environment, which proves the feasibility of experimental studies on metal ion adsorption by SBAC.
1.4 FT-IR surface functional group analysis
The surface functional groups of SBAC-5, SBAC-6 and SBAC-7 were analyzed by Fourier Infrared spectroscopy with reference to a new activated carbon from the same water plant, and the results are shown in FIG. 2.
As can be seen from FIG. 2, the most significant differences compared to the new activated carbon are the appearance of several characteristic peaks in SABC-5, SABC-6 and SABC-7, which are attributed to the complex physical, chemical and biological reactions during BAC water treatment. That is, the BAC process does significantly change the surface properties of the activated carbon, consistent with the results of pH and Boehm titration surface functional group analysis. Compared with the new activated carbon, the following new peaks appear in SBAC-5, SBAC-6 and SBAC-7. 1385cm-1To NO3 Adsorption peak of (4); the asymmetric stretching vibration of the carboxylate is 1565-1665 cm-1Visible adsorption peaks generated within the range; the C-O stretching vibration is 1020-1300 cm-1The appearance of a large absorption peak value; the wave number resulting from free and hydrogen-bonded O-H groups is 3200 to 3600cm-1Absorption peak in the range. Furthermore, it can also be seen that SBAC-5, SBAC-6 and SBAC-7 exhibit the same characteristic peaks, i.e., the surface functional groups of SBAC show stability with increasing age.
Adsorption isotherm and thermodynamics of 2 SBAC on strontium
Based on the strontium ion concentration C at equilibriume(mg/L) and strontium ion equilibrium adsorption amount qe(mg/g) data (298K), adsorption isotherms of SBAC were fitted using a Langmuir adsorption model and a Freundlich adsorption model, respectively. The fitting results show that the adsorption isotherms of SBAC-5, SBAC-6 and SBAC-7 all fit better with the Langmuir model, as shown in FIG. 3(a) (b) (c), with the correlation coefficient R2Are all greater than 0.976, indicating Sr2+Monolayer adsorption occurs on the SBAC surface. As for the adsorption capacity, SBAC-5, SBAC-6 and SBAC-7 are comparable, as can be seen from Table 2, and the maximum saturated adsorption capacity of SABC-7 is 30.98mg/g, 30.41mg/g for SBAC-6 times, and 29.33mg/g for SBAC-5 times, at room temperature of 25 deg.C (298K).
At the same time, to explore the SBAC vs Sr2+The adsorption thermodynamic properties of (1) are respectively tested at 283K and 313K, and SBAC adsorption Sr is fitted2+Langmuir adsorbs isotherms and the results are shown in FIGS. 3(a) (b) (c) (d), with the corresponding model parameters shown in Table 2.
TABLE 2 Sr2+Isotherm, thermodynamic parameters of ions on SBAC
Figure BDA0002332081700000101
From FIG. 3(d), lnK of van't Hoff equation corresponding to SBAC-5, SBAC-6 and SBAC-7CThe curve for 1/T is a linear equation with a higher regression coefficient, R2The values are 0.9765, 0.8574, and 0.9509, respectively, and thus thermodynamic parameters can be derived from this equation, and the results of the calculations are shown in table 2. As can be seen from Table 2, the adsorption capacity q of SBACmDecreases with increasing temperature, indicating that lower temperatures are more favorable for SBAC vs Sr2+This is consistent with the thermodynamic parameter of negative value of enthalpy change △ H2+Gibbs free energy of adsorption on SBAC becomes negative, indicating Sr2+Adsorption on activated carbon is a spontaneous process. The enthalpy change value is negative, indicating that the adsorption process is exothermic, and therefore lowering the temperature favors adsorption.
Adsorption kinetics of 3 SBAC for strontium
FIG. 4(a) shows Sr2+Adsorption kinetics curves on SBAC-5, SBAC-6 and SBAC-7. From the figure, Sr in solution2+The concentration drops rapidly in the first few minutes of the adsorption process, almost within 3 minutes of Sr2+The removal rate of (3) reaches 85 percent, as the adsorption time continues to increase, Sr2+The removal rate of (2) is not changed greatly, and is only increased to about 86.6%. This indicates Sr2+The reaction with SBAC is transient and is characterized by chemical reactions.
The kinetics were fitted using a quasi-primary model, a quasi-secondary model and an intraparticle diffusion model, respectively, and the results are shown in fig. 4(b) (c) (d), with the results of the parameter fit shown in table 3. As can be seen from FIG. 4 and Table 3, SBAC-5, SBAC-6 and SBAC-7 are used for Sr2+The adsorption kinetics of (A) completely conforms to a quasi-second-order model, the rate constant K of SBAC-62Highest, fastest adsorption, followed by SBAC-7 and SBAC-5, andq is obtained from a quasi-second-order model of three kinds of carbone,cThe values are all the same as q detected in the experimenttThe values were identical and were 2.51mg/g, 2.50mg/g and 2.50mg/g, respectively.
TABLE 3 Sr2+Kinetic parameters on SBAC
Figure BDA0002332081700000111
Influence factor of strontium adsorption of 4 SBAC
4.1 Effect of adsorbent dosage
FIG. 5 shows the SBAC addition versus Sr removal2+The influence of (c). As can be seen from FIG. 5, when Sr is used2+When the initial concentration of the solution is 5mg/L, SBAC to Sr with different service lives are added as the dosage of SBAC is increased from 0 to 2g/L2+The removal rate of the adsorbent is increased to more than 85 percent, the dosage of the adsorbent is continuously increased from 2 to 8g/L, Sr2+The removal rate is slowly increased to 89%, and the amplification is not large; when is Sr2+When the initial concentration of the solution is 0.5mg/L, the amount of SBAC is increased from 0 to 0.5g/L, SBAC-5, SBAC-6 and SBAC-7 are added to Sr2+The removal rate of ions is increased to more than 78 percent, the carbon adding amount is continuously increased to 1g/L, Sr2+The removal was nearly at equilibrium and the removal increased to 82%. The above results indicate that SBAC at low addition (less than 1g/L) for low concentrations of Sr2+The adsorption removal rate of (a) is greater than the higher concentration. Comparative Pb2+Under the conditions that the initial lead concentration is about 5mg/L and the adding amount is 0.2g/L, the removal rate of 99 percent can be achieved, and SBAC can be used for Sr2+The adsorption capacity of (b) is slightly weak.
4.2 Effect of initial strontium ion concentration
The experiment examines the Sr removal of SBAC by different initial strontium ion concentrations (5-100mg/L)2+The effect, equilibrium concentration and removal rate results are shown in fig. 6(a) and (b), respectively. As can be seen from FIG. 6(a), SBAC adsorbs Sr as the initial concentration increases2+The latter equilibrium concentration also increased, indicating that the adsorbent dosage (2g/L) was insufficient in the high concentration strontium solution. When the initial concentration is lower than 30mg/L, the removal effects of the SABC-5, the SABC-6 and the SABC-7 are not greatly different; when the initial concentration increased to 30mg/LAt the above time, the removal effect of the three carbons began to show differences, with SBAC-7 being superior to SBAC-6 and SBAC-5 being the least desirable due to the lowest content of acid groups and Ca on the surface of SBAC-5.
As can be seen from FIG. 6(b), when the initial concentration is 5mg/L and the addition amount of the adsorbent is 2g/L, the SBAC samples with three different service lives can effectively adsorb Sr2+The removal rate reaches more than 87.0 percent, and is a great breakthrough compared with the removal rate of 16 percent of new active carbon. With the increase of the initial concentration, the adding amount is kept to be 2.0g/L, and the removal rate is gradually reduced but still has greater advantages than the new activated carbon, which proves that the BAC process really changes the surface characteristics of the new activated carbon to ensure that the BAC process has the function of removing heavy metals.

Claims (3)

1. A method for removing radionuclide strontium in water is characterized in that a two-stage BAC water supply advanced treatment process is adopted, when the first-stage effluent quality of the BAC process does not reach the standard and the pH of the used activated carbon is less than 7 or the zeta potential is less than 0 or the content of surface acidic functional groups is higher than the content of surface basic functional groups, the BAC process is changed into a second-stage adsorption tank, namely the first-stage activated carbon adsorption tank has the function of the BAC process, and the used activated carbon serving as the second-stage adsorption tank can be used for removing radionuclide Sr in water, so that the existing BAC process has the function of removing radionuclide Sr.
2. The method for removing the radionuclide strontium in the water according to claim 1, comprising the following steps:
(1) the effluent quality of the first-stage activated carbon adsorption tank is periodically detected;
(2) when the quality of the effluent water does not reach the standard, sampling and testing an activated carbon sample, wherein the sampling and testing mainly comprises the characterization of the pH, the isoelectric point and the surface functional group of the activated carbon;
(3) when the pH of the used activated carbon is less than 7 or the zeta potential is less than 0 or the content of the surface acidic functional groups is higher than that of the surface alkaline functional groups, the used activated carbon is changed into a second-stage adsorption tank; namely, the first-stage adsorption pool has the function of the BAC process, and SBAC as the second-stage adsorption pool can be used for removing the radionuclide Sr in the water, so that the conventional BAC process has the function of removing the radionuclide Sr.
3. The method for removing the radionuclide strontium in water according to claim 2, wherein in the step (2), the activated carbon is characterized by mutual verification by at least two of pH, isoelectric point and surface functional group characterization methods of the activated carbon.
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