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The Maqarin Natural Analogue

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The Maqarin Natural Analogue The Maqarin Natural Analogue A E Milodowski . British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, United Kingdom Royal Society of Chemistry: Chemistry of Geological Disposal University of Manchester, 2nd December 2009 © NERC All rights reserved Contents 1. Introduction • Conceptual model of the alkaline disturbed zone (ADZ) • Why study natural analogue systems? 2. Background to the Maqarin Natural Analogue Project 3. Geological setting • Location of the Maqarin site and study areas • Origin of the hyperalkaline spring phenomenon 4. Groundwater chemistry 5. Mineralogical and petrological investigations • The primary metamorphic rock [“Cement Zone”] source • Interactions of the hyperalkaline plume [the “Alkali Disturbed Zone”] • Impacts on hydrogeological properties 6. Summary and conclusions © NERC All rights reserved Conceptual model of ADZ evolution Groundwater flow Leach hyperalkaline cement porewater Alkali plume migration Cementitious repository ‘later’ HPF K (Na) Ca Al, Si pH ‘early’ HPF concentration time/distance © NERC All rights reserved pH buffering Stage I Stage II Stage III 14 OPC: 100 cycles Low pH cement: 13 100 cycles 12 11 Na/K OH Ca(OH)2 10 leaching buffering pH 9 8 C-S-H 7 buffering 6 1 10 100 1000 Cycles of pore water exchange • In low permeability rocks, duration of a “cycle” may be in the order of thousands of years © NERC All rights• E reservedvolution may be accelerated by carbonation Cementitious wastes: the problem (1) • Extensive use of cementitious materials is standard in many waste repositories, ranging from tunnel liners to grouts to the waste itself • Cement porewaters initially have pH of 13.3, host rock groundwaters have pH of 7 to 10.....DISEQUILIBRIUM • Assuming an appropriate host rock, cementitious porewaters could be leaching out into the host rock for 104 to 106 years • Assuming the disequilibrium noted above, this means that the host rock conditions around a cementitious repository will be chemically disturbed - what are the PA implications? © NERC All rights reserved Cementitious wastes: the problem (2) • Some likely implications include: • Interaction of the cementitious leachates with the host rock will alter the rock mineralogy • Cement colloids produced in and around the interaction zone could migrate through the host rock • Sorption in the host rock will be altered (better or worse?) © NERC All rights reserved Natural analogues provide long-term understanding URL NA System Understanding Conceptual Models Field Lab Tests PA - Models Confidence studies © NERC All rights reserved Safety Case Background to the Maqarin Natural Analogue Project • Phase I 1989-1991 • funded by Nirex, Nagra, Ontario Hydro Alexander (ed.), 1992, Nagra Technical Report 91-10 • Phase II 1992-1994 • funded by Nirex, Nagra, SKB Linklater (ed.), 1998, Nirex Science Report S/98/003 • Phase III 1993-1996 • funded by Nirex, Nagra, SKB, UK Environment Agency Smellie (ed.), 1998, SKB Technical Report TR-98-04 • Phase IV 1999-2005 • Funded by Nirex, Nagra, SKB, ANDRA, CEA, JAEA Various reports © NERC All rights reserved Location and study areas Yarmouk Tertiary Basalt Adit 6 Bridge site Tert.-Cret. Maqarin Stn. chalks, clay biomicrites Western Springs Wadi Sijin Western Springs Eastern Springs © NERC All rights reserved Pyrometamorphism: Formation of the cement analogue Syrian [Hauran] Basalt Pleistocene O2 O2 Chalky Limestone Fm. Quaternary fluvial Lower Tertiary gravels and colluvium combustion Bituminous Limestone Fm. calcination R. Yarmouk Upper Cretaceous organic-rich, cherty, phosphatic, limestones and clay biomicrites with up to 20% organic C © NERC All rights reserved Saturation and groundwater penetration: Generation of an alkaline plume Ca-HCO3 groundwater percolates the marble Alteration (hydration) of marble Marble R. Yarmouk (larnite, spurrite, lime) and leaching of secondary portlandite, CSH minerals Hyperalkaline [pH >12.5] Ca-OH-SO4 groundwater reacts with host rocks A Natural Analogue for the long-term evolution of an alkaline leachate plume leaching from cementitious L/ILW radioactive waste repository © NERC All rights reserved Eastern Springs area Adit 6 (Unity Dam) Maqarin Station cutting Constructed in 1979 - photo 1990 Constructed in c.1905 - photo 1990 © NERC All rights reserved Western Springs area Yarmouk River: south bank Hyperalkaline springs discharge through Quaternary basalt-chert-limestone boulder gravels © NERC All rights reserved Groundwater chemistry Eastern Springs Western Springs • pH 12.3-12.5 12.5-12.7 • Ca 740-900 mg/l ~1060 mg/l • K 9-17.5 mg/l ~350 mg/l • OH 430-640 mg/l 630-650 mg/l • SO4 200-300 mg/l ~1510 mg/l • Se 100-300 µg/l ~1070 µg/l • Cr 0.5-1.5 mg/l ~5.08 mg/l* • Re ~1 µg/l 5.8 µg/l *Imparts yellow (chromate) colour to waters in the Western Springs © NERC All rights reserved Ca-OH-SO4 type groundwaters •pH>12.5 •Two distinct groups Eastern Springs 0100% Western Springs 100 0% - 2 M 3 SO O g 2 C 4 2 + - + + + + - K N 3 C O l - a + C H 100% 0% 0 100% 0 OH- 100% 100% Ca2+ 0% © NERC All rights reserved Primary metamorphic marbles (natural “cement zone”) •Metamorphosed phosphatic limestone - ellestadite-rich marbles •Metamorphosed cherty limestone -larnite,spurrite, wollastonite-rich marbles •Metamorphosed argillaceous limestones -brownmillerite, calcsilicates, calcaluminates spurrite, chrome-ferrite phases, brucite, periclase, portlandite, lime. © NERC All rights reserved Hydration of the “cement zone” Tobermorite CSH gels ettringite ettringite thaumasite thaumasite ettringite apophyllite afwillte © NERC All rights reserved Composition of CSH hydration products Ternary Ca-Al-Si mol% element plot of hydrated cement phases: microprobe data from Adit 6, phase IV Si GRID AXES Ettringite-thaumasite Tobermorite CSH Afwillite Ideal formulae Tacharanite Tobermorite Afw illite Thaumasite Al Ettringite Ca © NERC All rights reserved Early leaching of reactive K-bearing phases gives rise to early K-rich groundwaters Oldhamite CaS Cu-K-S-Se © NERC All rights reserved K-bearing Ca-silicate •0.3-3.3 % K2O present in primary spurrite- like calcium silicate-sulphate phase •Minor P also present in all primary thaumasite calcsilicates •K-rich ‘spurrite-like’ phase readily alters to thaumasite •K-free spurrite alters more slowly © NERC All rights reserved K leached during early alteration of primary K-bearing calcium silicate K Ca primary K-rich ‘spurrite’ secondary thaumasite alteration Se S Electron microprobe X-ray elemental maps of altered K-rich calcium silicate © NERC All rights reserved Cement zone alteration sequence Stage Event Description Minerals formed - - Ingress of Ca- HCO3 HCO3 water moves into marbles. Calcite ± aragonite 1 groundwater in marble Dissolution of Ca and K-bearing Barite (‘cement zone’) sulphides and selenides and Baritocelestite (Sr,Ca)SO4 available lime Hashemite Ba(CrO4 ,SO4) Initial hydration of ‘cement Alteration of most reactive Tobermorite, CSH gels 2 zone’ calcium silicates (larnite, lime and K-bearing ‘spurrite’) Hydration of calcium silico- Alteration of less reactive Afwillite, CSH gels 3 sulphates calcium slicates and silico- Ettringite-thaumasite phosphates (spurrite, ellestadite) Apophyllite Calcite, gypsum, silica gel 4 Interaction with bicarbonate groundwater Interaction with surface Atmospheric CO decomposes Calcite, gypsum, silica gel 5 2 atmosphere (dry periods + thaumasite on adit walls or post adit draining) and exposed in dry fractures © NERC All rights reserved bicarbonate groundwaters Reaction with host rocks: Chert/silica •CSH(I) formed by reaction with quartz (chert concretion) •Where CSH minerals are in sealed fractures, they tend to remain unaltered © NERC All rights reserved Reaction with host rocks: Bituminous Limestone Formation (marl) •Reaction with kaolinite, illite, quartz, carbonate minerals •Reaction products dominated by CSH gels, tobermorite and jennite- thaumasite-ettringite vein mineralisation •Secondary CSH phases altered by SO4 groundwaters •Complex oscillations of CSH minerals and sulphate minerals © NERC All rights reserved Calcium silicate hydrate (CSH) reaction products Si 100 % zeolite crystalline phases gels tobermorite‐like gels jennite‐like gels zeolitic gels jennite 100 % 100 % Al Ca Summary compositions (molar ratios) of crystalline and non-crystalline CSH and CASH alteration products, determined by EPMA and ATEM. © NERC All rights reserved Simplified mineral sequence produced by interaction of hyperalkaline with host rock Bituminous Limestone Formation (marl) calcite/ aragonite ettringite/thaumasite gypsum tobermorite/CSH(I) gel jennite/CSH(II) gel zeolite/zeolite gel smectite TIME © NERC All rights reserved Analogue trace element behaviour Uranium fission track registration studies U is remobilised when CSH mineral are altered by sulphate © NERC All rights reserved Impact on host-rock porosity in the ADZ: Enhanced porosity in wallrock Early stages of “ADZ” interaction: •Dissolution of silicate (silica, quartz, kaolinite) and carbonate minerals in the adjacent wallrock •Locallised enhanced porosity © NERC All rights reserved Impact on host-rock porosity in the ADZ: Sealing of fractures Reaction with hyperalkaline groundwater-rock Ett interaction tends to seal fractures in the natural “ADZ” CSH minerals appear to have existed for around 80- 100 Ka © NERC All rights reserved Conclusions 1. Good natural analogue for understanding the evolution of the ADZ – evolution of the Maqarin groundwater system mimics the evolution of OPC cement porewaters and conceptual model of alkali plume development.
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