膨润土受热作用后的水-力性能研究
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摘要
受核废料衰变热影响,处置库内缓冲层的膨润土会长期处于高温状态。经历持续高温作用后,膨润土的膨胀自愈能力能否得以保持,还没有明确的结论。利用马弗炉维持105℃恒温环境,对粉状膨润土持续加热到预定周期;然后,获得不同加热周期试样的水-力性能。结果表明,随着加热时间增长,膨润土水-力性能出现大幅衰减。借助X射线衍射仪测试发现持续加热90d其晶面间距缩合,出现了硅质氧化物胶结,导致颗(团)粒集聚。其红外光谱和热重特征表明,持续加热作用脱去了蒙脱石层间离子水合水,引起部分Na、Mg离子随水分蒸发而逃逸,两者共同作用导致蒙脱石颗(团)粒发生缩合作用。通过观察其扫描电镜图片也能发现,经过90d持续加热后,蒙脱石颗(团)粒表面不再层次分明,而是紧密地相互搭接,发生了显著的缩合行为。粒度分布特征进一步证实,膨润土经历90d加热后,即使浸泡28d,其颗(团)粒依然未被分散,可初步推断上述缩合行为不可逆。
Bentonite, as buffer materials in disposal repository, will be under long term effect of decay heat which released from nuclear waste sealed in the canister. Whether the expansion self-healing ability of bentonite can be maintained after sustained high temperature has not been clearly concluded. The powdery bentonite was heated in muffle furnace at a constant temperature(105 ℃). But the heating periods were different, and the longest one was 90 d. A series of tests was carried out on the heated samples. The results show that the free swelling ratio and swelling pressure decrease dramatically with heated time. X-ray diffraction spectrums of montmorillonite demonstrate that the adjacent lattice distances is shortened, silica oxide cementation occurs after continuous heating for 90 d, which results in aggregation of montmorillonite particles. It can be inferred from infrared spectrum and thermogravimetric testing results that the hydration of interlayer ions of montmorillonite is removed by continuous heating, and some Na and Mg ions escape with the evaporation of water. The combination of the two causes the condensation of montmorillonite particles. This phenomenon is also found by SEM that montmorillonite particles closely linked to each other instead of distinctly stacked as original state. Moreover, this condensation or cluster behaviors are irreversible, which could be confirmed from particle size distribution curves of heated bentonite. Because the clusters of bentonite(heated 90 d) were not dispersed obviously, even after soaking 28 d.
Bentonite, as buffer materials in disposal repository, will be under long term effect of decay heat which released from nuclear waste sealed in the canister. Whether the expansion self-healing ability of bentonite can be maintained after sustained high temperature has not been clearly concluded. The powdery bentonite was heated in muffle furnace at a constant temperature(105 ℃). But the heating periods were different, and the longest one was 90 d. A series of tests was carried out on the heated samples. The results show that the free swelling ratio and swelling pressure decrease dramatically with heated time. X-ray diffraction spectrums of montmorillonite demonstrate that the adjacent lattice distances is shortened, silica oxide cementation occurs after continuous heating for 90 d, which results in aggregation of montmorillonite particles. It can be inferred from infrared spectrum and thermogravimetric testing results that the hydration of interlayer ions of montmorillonite is removed by continuous heating, and some Na and Mg ions escape with the evaporation of water. The combination of the two causes the condensation of montmorillonite particles. This phenomenon is also found by SEM that montmorillonite particles closely linked to each other instead of distinctly stacked as original state. Moreover, this condensation or cluster behaviors are irreversible, which could be confirmed from particle size distribution curves of heated bentonite. Because the clusters of bentonite(heated 90 d) were not dispersed obviously, even after soaking 28 d.
引文
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[19]PUSCH R.On the effect of hot water vapor on MX-80clay[R].Stockholm,Sweden:SKB,2000.
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[23]YE W M,WAN M,CHEN B,et al.Temperature effects on the swelling pressure and saturated hydraulic conductivity of the compacted GMZ01 bentonite[J].Environmental Earth Science,2013,68(1):281-288.
[24]YE W M,ZHENG Z J,CHEN B,et al.Effects of pH and temperature on the swelling pressure and hydraulic conductivity of compacted GMZ01 bentonite[J].Applied Clay Science,2014,101(1):192-198.
[25]ESTABRAGH A R,KHOSRAVI F,JAVADI A A.Effect of thermal history on the properties of bentonite[J].Environmental Earth Science,2016,75(8):648-657.
[26]南京水利科学院.SL 237―1999土工试验规程[S].北京:中国水利水电出版社,1999.Nanjing Hydraulic Research Institute.SL 237―1999Specification of soil test[S].Beijing:China Water and Power Press,1999.
[27]HEILMAN M D,CARTER D L,GONZALEZ C L.The ethylene glycol monoethyl ether(EGME)technique for determining soil-surface area[J].Soil Science,1965,100(6):409-413.
[28]PUSCH R.Bentonite clay environmental and applications[M].London:Taylor&Francis Group,2015.
[29]BISHOP J L.Infrared spectroscopic analyses on the nature of water in montmorillonite[J].Clays and Clay Minerals,1994,42(6):702-716.
[30]CHO J W,WHANG J H,CHUN K S.Thermal effects on the physicochemical properties of domestic bentonite as a buffer material of spent fuel repository[J].Journal of the Korean Nuclear Society,1991,23(4):456-464.
[31]章庆和.膨润土差热曲线与物理化学特性的关系[J].矿物学报,1989,9(2):177-180.ZHANG Qing-he.Relation between differential thermal curve and physical and chemical properties of bentonite[J].Journal of Mineral Sciences,1989,9(2):177-180.
[2]SKB.SR 97-Post-closure safety[R].Stockholm:SKB,1999.
[3]KARNLAND O,OLSSON S,NILSSON U.Mineralogy and sealing properties of various bentonites and smectite-rich clay materials[R].Stockholm,Sweden:Swedish Nuclear Fuel and Waste Management Co.,2006.
[4]王驹,陈伟明,苏锐,等.高放废物地质处置及其若干关键科学问题[J].岩石力学与工程学报,2006,25(4):801-812.WANG Ju,CHEN Wei-ming,SU Rui,et al.Geological disposal of high-level radioactive waste and its key scientific issues[J].Chinese Journal of Rock Mechanics and Engineering,2006,25(4):801-812.
[5]NAGRA.The Nagra research,development and demonstration(RD&D)plan for the disposal of radioactive waste in Switzerland[R].Nagra,Wettingen:National Cooperative for the Disposal of Radioactive Waste,2009.
[6]张虎元,张明,崔素丽,等.混合型缓冲回填材料土水特征曲线测试与修正[J].岩石力学与工程学报,2011,30(2):382-390.ZHANG Hu-yuan,ZHANG Ming,CUI Su-li,et al.Determination and modification of soil-water characteristic curves of bentonite-sand mixtures highlevel waste backfill/buffer material[J].Chinese Journal of Rock Mechanics and Engineering,2011,30(2):382-390.
[7]PUSCH R,YONG R N.Microstructure of smectite clays and engineering performance[M].London:Taylor&Francis,2006.
[8]LEE J Y,CHO D K,CHOI H J,et al.Analysis of disposal efficiency based on nuclear spent fuel cooling time and disposal tunnel/pit spacing for the design of a geological repository[J].Progress in Nuclear Energy,2011,53(4):361-367.
[9]LEE J O,BIRCH K,CHOI H-J.Coupled thermal-hydro analysis of unsaturated buffer and backfill in a high-level waste repository[J].Annals of Nuclear Energy,2014,72:63-75.
[10]JOHNSON L H,LENEVEU D M,SHOESMITH D W,et al.The vault model for postclosure assessment[R].Ottawa:AECL,1994:404.
[11]Japan Nuclear Cycle Development Institute.H12:Project to establish the scientific and technical basis for HLWdisposal in Japan.Supporting Report 2.Repository design and engineering technology[R].Tokai,Japan:Japan Nuclear Cycle Development Institute,2000:435.
[12]BEL J,BERNIER F.Temperature criterion related to clay-based backfill materials in the framework of a geological repository of heat producing radioactive waste[C]//Proceedings of ICEM 2001.Bruges:[s.n.],2001.
[13]COUTURE R A.Steam rapidly reduces the swelling capacity of bentonite[J].Nature,1985,318:50-52.
[14]OSCARSON D W,DIXON D A.Effect of heating unsaturated bentonite on the swelling and hydraulic properties of subsequently saturated clay[C]//Proceedings of the Annual Conference and 1st Biennial Environmental Speciality Conference of the Canadian Society of Civil Engineering.Hamilton,Ontario:[s.n.],1990:312-323.
[15]PUSCH R,BLUEMLING P,JOHNSON L H.Performance of strongly compressed MX-80 pellets under repository-like conditions[J].Applied Clay Science,2003,23(1):239-244.
[16]INOUE A,WATANABE T,KOHYAMA N,et al.Characterization of illitization of smectite in bentonite beds at Kinnekulle,Sweden[J].Clays Clay Mineral,1990,38(3):241-249.
[17]MULLER-VONMOOS M,KAHR G,BUCHER F,et al.Investigation of Kinnekulle K-bentonite aimed at assessing the long term stability of bentonites under repository conditions[J].Engineering Geology,1990,28(3):269-280.
[18]OSCARSON D W,DIXON D A.The effect of steam on montmorillonite[J].Applied Clay Science,1989,4(3):279-292.
[19]PUSCH R.On the effect of hot water vapor on MX-80clay[R].Stockholm,Sweden:SKB,2000.
[20]VILLAR M V,LLORET A.Influence of temperature on the hydro-mechanical behavior of a compacted bentonite[J].Applied Clay Science,2004,26(1):337-350.
[21]LLORET A,VILLAR M V.Advances on the knowledge of the thermo-hydro-mechanical behaviour of heavily compacted“FEBEX”bentonite[J].Physical Chemistry Earth,2007,32(8):701-715.
[22]SHIRAZI S M,KAZAMA H,KUWANO J,et al.The influence of temperature on swelling characteristics of compacted bentonite for waste disposal[J].Environment Asia,2010,3(1):60-64.
[23]YE W M,WAN M,CHEN B,et al.Temperature effects on the swelling pressure and saturated hydraulic conductivity of the compacted GMZ01 bentonite[J].Environmental Earth Science,2013,68(1):281-288.
[24]YE W M,ZHENG Z J,CHEN B,et al.Effects of pH and temperature on the swelling pressure and hydraulic conductivity of compacted GMZ01 bentonite[J].Applied Clay Science,2014,101(1):192-198.
[25]ESTABRAGH A R,KHOSRAVI F,JAVADI A A.Effect of thermal history on the properties of bentonite[J].Environmental Earth Science,2016,75(8):648-657.
[26]南京水利科学院.SL 237―1999土工试验规程[S].北京:中国水利水电出版社,1999.Nanjing Hydraulic Research Institute.SL 237―1999Specification of soil test[S].Beijing:China Water and Power Press,1999.
[27]HEILMAN M D,CARTER D L,GONZALEZ C L.The ethylene glycol monoethyl ether(EGME)technique for determining soil-surface area[J].Soil Science,1965,100(6):409-413.
[28]PUSCH R.Bentonite clay environmental and applications[M].London:Taylor&Francis Group,2015.
[29]BISHOP J L.Infrared spectroscopic analyses on the nature of water in montmorillonite[J].Clays and Clay Minerals,1994,42(6):702-716.
[30]CHO J W,WHANG J H,CHUN K S.Thermal effects on the physicochemical properties of domestic bentonite as a buffer material of spent fuel repository[J].Journal of the Korean Nuclear Society,1991,23(4):456-464.
[31]章庆和.膨润土差热曲线与物理化学特性的关系[J].矿物学报,1989,9(2):177-180.ZHANG Qing-he.Relation between differential thermal curve and physical and chemical properties of bentonite[J].Journal of Mineral Sciences,1989,9(2):177-180.