天然土壤胶体对U(Ⅵ)迁移的影响
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摘要
以石英砂为填充介质,采用动态柱实验方法研究了某中低放处置场地表土壤胶体对U(Ⅵ)在石英砂柱中迁移行为的影响,并结合静态批式实验探究了土壤胶体对U(Ⅵ)迁移的影响机制。结果表明,当U(Ⅵ)进样质量浓度从1.0 mg/L增大至5.0 mg/L时,U(Ⅵ)在石英砂柱中的穿透速率显著增大,且达到洗脱平衡时所需淋洗液的体积从250 PVs(孔隙体积)增大至400 PVs。与U(Ⅵ)相比,土壤胶体在石英砂柱内迁移较快,这可能是由于土壤胶体与石英砂之间相互作用较弱所致。土壤胶体与U(Ⅵ)共存体系中,U(Ⅵ)的迁移速率明显增大,而土壤胶体迁移速率无显著变化,表明共存体系中U(Ⅵ)的迁移行为主要受土壤胶体所控制。静态吸附实验表明,在石英砂-U(Ⅵ)二元体系中,pH≈6.0时石英砂对U(Ⅵ)的吸附率最大,而在胶体-石英砂-U(Ⅵ)三元体系中,U(Ⅵ)主要在土壤胶体表面发生吸附。本研究所用土壤中胶体的质量分数仅约占0.04%,但可吸附20%U(Ⅵ)(初始质量浓度为5.0 mg/L);由此可见,土壤胶体可与U(Ⅵ)发生强的相互作用,进而对U(Ⅵ)在真实环境体系中的吸附、迁移和扩散等行为产生至关重要的影响。
The transport behavior of U(Ⅵ) in the presence of soil colloids was investigated by column experiments using quartz sand as the porous media, and batch technique was further applied to explore the mechanism of U(Ⅵ) transport in the presence of soil colloids. The results show that when the initial mass concentration of U(Ⅵ) increases from 1.0 mg/L to 5.0 mg/L, the transport rate of U(Ⅵ) significantly increases, and the required leachate volume increases from 250 PVs(pore volume) to 400 PVs, reaching the elution equilibrium. Compared with U(Ⅵ), the soil colloids transport much faster in the quartz column, mainly owing to the weak interaction between the soil colloids and the quartz sand. In the presence of soil colloids, the transport rate of U(Ⅵ) is remarkably improved, while the breakthrough curve of soil colloids do not change obviously, which indicates that the transport behavior of U(Ⅵ) in the ternary system of colloid-U(Ⅵ)-quartz is mainly controlled by soil colloids. In the binary system of U(Ⅵ)-quartz, the sorption of U(Ⅵ) on quartz is maximized at pH≈6.0, while in the ternary system of colloid-U(Ⅵ)-quartz almost all U(Ⅵ) is absorbed on the soil colloids, and the contribution of quartz can be negligible. It is noted that about 20% U(Ⅵ)(initial mass concentration is 5.0 mg/L) is adsorbed on soil colloids, which only accounts for 0.04% of the studied soil. The strong interaction between soil colloids and U(Ⅵ) suggests that soil colloids have a crucial impact on U(Ⅵ) adsorption, transport and diffusion in the environment.
The transport behavior of U(Ⅵ) in the presence of soil colloids was investigated by column experiments using quartz sand as the porous media, and batch technique was further applied to explore the mechanism of U(Ⅵ) transport in the presence of soil colloids. The results show that when the initial mass concentration of U(Ⅵ) increases from 1.0 mg/L to 5.0 mg/L, the transport rate of U(Ⅵ) significantly increases, and the required leachate volume increases from 250 PVs(pore volume) to 400 PVs, reaching the elution equilibrium. Compared with U(Ⅵ), the soil colloids transport much faster in the quartz column, mainly owing to the weak interaction between the soil colloids and the quartz sand. In the presence of soil colloids, the transport rate of U(Ⅵ) is remarkably improved, while the breakthrough curve of soil colloids do not change obviously, which indicates that the transport behavior of U(Ⅵ) in the ternary system of colloid-U(Ⅵ)-quartz is mainly controlled by soil colloids. In the binary system of U(Ⅵ)-quartz, the sorption of U(Ⅵ) on quartz is maximized at pH≈6.0, while in the ternary system of colloid-U(Ⅵ)-quartz almost all U(Ⅵ) is absorbed on the soil colloids, and the contribution of quartz can be negligible. It is noted that about 20% U(Ⅵ)(initial mass concentration is 5.0 mg/L) is adsorbed on soil colloids, which only accounts for 0.04% of the studied soil. The strong interaction between soil colloids and U(Ⅵ) suggests that soil colloids have a crucial impact on U(Ⅵ) adsorption, transport and diffusion in the environment.
引文
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[27] Khamseh A G,Ghorbanian S A.Experimental and modeling investigation of thorium biosorption by orange peel in a continuous fixed-bed column[J].J Radioanal Nucl Chem,2018,317(2):871-879.
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[31] Yang Y,Saiers J E,Xu N,et al.Impact of natural organic matter on uranium transport through saturated geologic materials:from molecular to column scale[J].Environ Sci Technol,2012,46(11):5931-5938.
[32] Mibus J,Sachs S,Pfingsten W,et al.Migration of uranium(Ⅳ)/(Ⅵ) in the presence of humic acids in quartz sand:a laboratory column study[J].J Contam Hydrol,2007,89(3-4):199-217.
[2] Jerden J L,Sinha A K.Geochemical coupling of uranium and phosphorous in soils overlying an unmined uranium deposit;Coles Hill,Virginia[J].J Geochem Explor,2006,91(1-3):56-70.
[3] Bachmaf S,Merkel B J.Sorption of uranium(Ⅵ) at the clay mineral-water interface[J].Environ Earth Sci,2011,63(5):925-934.
[4] Bekhit H M,Hassan A E.Subsurface contaminant transport in the presence of colloids:effect of nonlinear and nonequilibrium interactions[J].Water Resour Res,2007,43(8):1050-1056.
[5] Duff M C.Uranium co-precipitation with iron oxide minerals[J].Geochim Cosmochim Acta,2002,66(20):3533-3547.
[6] Kurttio P,Auvinen A,Salonen L,et al.Renal effects of uranium in drinking water[J].Environ Health Perspect,2002,110(4):337-342.
[7] Vicente-Vicente L,Quiros Y,Pérez-Barriocanal,et al.Nephrotoxicity of uranium:pathophysiological,diagnostic and therapeutic perspectives[J].Toxicol Sci,2010,118(2):324-347.
[8] 张伟,董发勤,杨杰,等.三种非活性微生物对铀的吸附行为及其受γ辐照的动力学影响[J].核化学与放射化学,2018,40(4):258-265.
[9] Du L,Li S,Li X,et al.Effect of humic acid on uranium(Ⅵ) retention and transport through quartz columns with varying pH and anion type[J].J Environ Radioact,2017,177:142-150.
[10] Kar A S,Kumar S,Tomar B S.U(Ⅵ) sorption by silica:effect of complexing anions[J].Colloids Surf,A,2012,395:240-247.
[11] Jin Q,Su L,Montavon G,et al.Surface complexation modeling of U(Ⅵ) adsorption on granite at ambient/elevated temperature:experimental and XPS study[J].Chem Geol,2016,433:81-91.
[12] CrancOn P,Pili E,Charlet L.Uranium facilitated transport by water-dispersible colloids in field and soil columns[J].Sci Total Environ,2010,408(9):2118-2128.
[13] M?ri W R,Alexander W R,Geckeis H,et al.The colloid and radionuclide retardation experiment at the Grimsel Test Site:influence of bentonite colloids on radionuclide migration in a fractured rock[J].Colloids Surf,A,2003,217(1-3):33-47.
[14] Murphy R J,Lenhart J J,Honeyman B D.The sorption of thorium(Ⅳ) and uranium(Ⅵ) to hematite in the presence of natural organic matter[J].Colloids Surf,A,1999,157(1-3):47-62.
[15] Tran E L,Teutsch N,Klein-Bendavid O,et al.Uranium and cesium sorption to bentonite colloids under carbonate-rich environments:implications for radionuclide transport[J].Sci Total Environ,2018,643:260-269.
[16] Chen C,Zhao K,Shang J,et al.Uranium(Ⅵ) transport in saturated heterogeneous media:influence of kaolinite and humic acid[J].Environ Pollut,2018,240:219-226.
[17] Wang Q,Cheng T,Wu Y.Influence of mineral colloids and humic substances on uranium(Ⅵ) transport in water-saturated geologic porous media[J].J Contam Hydrol,2014,170:76-85.
[18] Ge M,Wang D,Yang J,et al.Co-transport of U(Ⅵ) and akaganéite colloids in water-saturated porous medium:role of U(Ⅵ) concentration,pH and ionic strength[J].Water Res,2018,147:350-361.
[19] Degueldre C,Grauer R,Laube A,et al.Colloid properties in granitic groundwater systems Ⅱ:stability and transport study[J].Appl Geochem,1996,11(5):697-710.
[20] Baek I,Pitt Jr W W.Colloid-facilitated radionuclide transport in fractured porous rock[J].Waste Manage,1996,16(4):313-325.
[21] Kretzschmar R,Sch?fer T.Metal retention and transport on colloidal particles in the environment[J].Elements,2005,1(4):205-210.
[22] Kalbitz K,Wennrich R.Mobilization of heavy metals and arsenic in polluted wetland soils and its dependence on dissolved organic matter[J].Sci Total Environ,1998,209(1):27-39.
[23] Krawczyk-BaRsch E,Arnold T,Reuther H,et al.Formation of secondary Fe-oxyhydroxide phases during the dissolution of chlorite:effects on uranium sorption[J].Appl Geochem,2004,19(9):1403-1412.
[24] Wang X K,Dong W M,Dai X X,et al.Sorption and desorption of Eu and Yb on alumina mechanisms and effect of fulvic acid[J].Appl Radiat Isot,2000,52(2):165-173.
[25] 熊毅.土壤胶体[M].第二册.北京:科学出版社,1985.
[26] Wang J J,He B H,Wei X Y,et al.Sorption of uranyl ions on TiO2:effects of pH,contact time,ionic strength,temperature and HA[J].J Environ Sci,2019,75:115-123.
[27] Khamseh A G,Ghorbanian S A.Experimental and modeling investigation of thorium biosorption by orange peel in a continuous fixed-bed column[J].J Radioanal Nucl Chem,2018,317(2):871-879.
[28] Stumm W.Chemistry of the solid-water interface:processes at the mineral-water and particle-water interface in natural systems[M].John Wiley & Son Inc.,1992.
[29] Davis J A,Curti G P.Application of surface complexation modeling to describe uranium(Ⅵ) adsorption and retardation at the uranium mill tailings site at Naturita,Colorado[M].Washington,D.C.,US:Nuclear Regulatory Commission,2003.
[30] Sylwester E R,Hudson E A,Allen P G.The structure of uranium(Ⅵ) sorption complexes on silica,alumina,and montmorillonite[J].Geochim Cosmochim Acta,2000,64(14):2431-2438.
[31] Yang Y,Saiers J E,Xu N,et al.Impact of natural organic matter on uranium transport through saturated geologic materials:from molecular to column scale[J].Environ Sci Technol,2012,46(11):5931-5938.
[32] Mibus J,Sachs S,Pfingsten W,et al.Migration of uranium(Ⅳ)/(Ⅵ) in the presence of humic acids in quartz sand:a laboratory column study[J].J Contam Hydrol,2007,89(3-4):199-217.
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