Diffusion of HTO and cement pore fluids through host rock

SummaryIn the post-closure period of a deep disposal facility for low- to intermediate-level radioactive waste, highly alkaline pore-fluids chemically equilibrated with cementious components of the engineered barriers will migrate into the surroundings. Primary minerals in the host rock could dissolve and secondary calcium silicate hydrate (CSH) phases might be formed in the micro pore system of the rock and change the available porosity for radionuclides and hence the permeability. Since the retardation of radionuclides in the host rock depends on sorption and matrix diffusion, the study of the mineral reactions is of importance. Experiments with diffusion of HTO and synthetic cementitious pore-waters through 1 cm thick discs of Äspö diorite have been made in a nitrogen-flushed glovebox facility. Synthetic cementitious pore-waters representative of fresh and leached concrete were used. For the fresh pore-water the results show that hydroxide ion diffusion is retarded relative to HTO tracer, indicating that reactions between hydroxide and host rock take place. The result can be interpreted as hydroxide sorption in the rock.Al and Si did also accumulate on the sampling side which was attributed to mineral dissolution. For the evolved pore-water, no through-diffusion of hydroxide ions or accumulation of other elements in the sampling cell was observed during the sampling period, indicating that the through-diffusion of hydroxide is hindered by this type of pore-water.

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Significance of early-diagenetic water-rock interactions in a modern marine siliciclastic/evaporite environment: Salina Ometepec, Baja California

Geological Society of America Bulletin ◽

10.1130/0016-7606(2002)114<1055:soedwr>2.0.co;2 ◽

2002 ◽

Vol 114 (9) ◽

pp. 1055-1069 ◽

Cited By ~ 3

Author(s):

Anna M. Martini ◽

Lynn M. Walter ◽

Timothy W. Lyons ◽

Victoria C. Hover ◽

John Hansen

Keyword(s):

Sulfate Reduction ◽

Pore Water ◽

Gulf Of California ◽

Baja California ◽

Mineral Dissolution ◽

Pore Waters ◽

Near Surface ◽

Compositional Evolution ◽

Diagenetic Alteration ◽

Evaporative Concentration

Abstract Although marine brines are a significant component of pore waters in sedimentary basins, there are few geochemical studies of modern analogues of such systems, especially in siliciclastic settings. For these reasons, we chose the evaporite-associated siliciclastic sediments deposited in the salt flats of the Salina Ometepec, Baja California, for an integrated investigation of sediment, pore-water, and overlying brine geochemistry. Here, the detrital components include quartz, K-feldspar, plagioclase, chlorite, biotite, and smectite, and authigenic minerals are dominated by halite, gypsum, and K-rich magnesium smectite. Thermal and saline stresses on the sediments of the Salina Ometepec keep both organic and inorganic carbon concentrations in the sediments unusually low relative to other coastal marine environments. Sediment pore waters exhibit little microbial sulfate reduction, and dissolved inorganic C contents are also very low. As a result, we did not observe carbonate and sulfide mineral authigenesis in the Salina Ometepec sediments. Instead, pore-water geochemical evolution is largely controlled by evaporative concentration of seawater, evaporite-mineral dissolution and recrystallization, and diagenetic alteration of detrital aluminosilicates. Evaporite-mineral recycling affects the compositional evolution of surficial brines even before they infiltrate the sediment. Specifically, Na+ and Cl− concentrations are increased owing to halite dissolution. We see significant Br− enrichment relative to expected seawater evaporation trends in near-surface pore water, secondary to dissolution of K- and Mg salts. Because bacterial sulfate reduction is inhibited in the Salina Ometepec sediments, sulfate concentrations are more accurate indicators of the degree of evaporation than Br−, a usually conservative element during geochemical reactions. Pore waters exhibit down-core increases in dissolved Mg2+, K+, and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(H_{4}SiO_{4}^{0}\) \end{document} over the upper 1 m. Authigenic K-rich Mg-smectite formation is promoted by the concurrent processes of brine concentration, selective dissolution of K- and Mg-bearing salts, and dissolution of detrital aluminosilicates. Pore waters at a depth of 1 m have 87Sr/86Sr ratios that require input of Sr that is less radiogenic than that of Gulf of California seawater. This Sr is likely derived from weathering of detrital aluminosilicates from nearby volcaniclastic sources. These results show that significant chemical interactions among marine brines, evaporite minerals, and detrital aluminosilicates can occur relatively soon after sedimentation.

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Process Model of Gas-Related Phenomena Associated With a Proposed L/ILW Repository in Switzerland

MRS Proceedings ◽

10.1557/proc-506-999 ◽

1997 ◽

Vol 506 ◽

Author(s):

Rainer Senger ◽

Peter Gribi ◽

Markus Hugi ◽

Piet Zuidema

Keyword(s):

Radioactive Waste ◽

Host Rock ◽

Process Model ◽

Structural Integrity ◽

Gas Production ◽

Pore Waters ◽

Gas Generation ◽

Free Gas ◽

Intermediate Level Radioactive Waste ◽

National Cooperative

ABSTRACTNAGRA (National Cooperative for the Disposal of Radioactive Waste) has been investigating the feasibility for siting a low- and intermediate-level radioactive waste (L/ILW) repository in subsurface geologic environments. The design of the L/ILW repository consists of a horizontally accessed cavern system located beneath Wellenberg in the low-permeability unit of Valanginian marl. One of the concerns for the safety analysis is the effect of gas generation (primarily hydrogen) from anaerobic corrosion and degradation of waste material. The development of a free gas phase and the concomitant pressure buildup can result in the displacement of contaminated pore waters from the repository. Moreover, excess buildup of pressures in the repository can impact the structural integrity of the engineered barrier and of the surrounding host rock. For the investigation of the gas-related phenomena in a proposed L/ILW repository, a process model was developed to simulate the different performance periods of the repository which include: (1) construction/operation period of the repository resulting in desaturation of the host rock caused by pressure decline and ventilation in the cavern, and (2) post-closure period after backfilling and sealing of the caverns resulting in resaturation of the host rock and of the cavern, and in the release of waste-generated gas. Period (1) takes into account degassing of dissolved gas (methane) in the formation water due to the pressure decline around the cavern, and period (2) considers dissolution of free gas caused by the pressure increase associated with the resaturation and with the gas production in the cavern.

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Hydrochemistry of sediment pore water in the Bratsk reservoir (Baikal region, Russia)

Scientific Reports ◽

10.1038/s41598-021-90603-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

V. I. Poletaeva ◽

E. N. Tirskikh ◽

M. V. Pastukhov

Keyword(s):

Pore Water ◽

Ionic Composition ◽

Water System ◽

Water Reservoir ◽

Environmental Parameters ◽

Water Area ◽

Pore Waters ◽

Overlying Water ◽

Major Ion ◽

Bratsk Reservoir

AbstractThis study aimed to identify the factors responsible for the major ion composition of pore water from the bottom sediments of the Bratsk water reservoir, which is part of the largest freshwater Baikal-Angara water system. In the Bratsk reservoir, the overlying water was characterized as HCO3–Ca–Mg type with the mineralization ranging between 101.2 and 127.7 mg L−1 and pore water was characterized as HCO3–SO4–Ca, SO4–Cl–Ca–Mg and mixed water types, which had mineralization varying from 165.9 to 4608.1 mg L−1. The ionic composition of pore waters varied both along the sediment depth profile and across the water area. In pore water, the difference between the highest and lowest values was remarkably large: 5.1 times for K+, 13 times for Mg2+, 16 times for HCO3−, 20 times for Ca2+, 23 times for Na+, 80 times for SO42−, 105 times for Cl−. Such variability at different sites of the reservoir was due to the interrelation between major ion concentrations in the pore water and environmental parameters. The major factor responsible for pore water chemistry was the dissolution of sediment-forming material coming from various geochemical provinces. In the south part of the reservoir, Cl−, Na+ and SO42− concentrations may significantly increase in pore water due to the effect of subaqueous flow of highly mineralized groundwater.

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Dissolution and recrystallization in modern shelf carbonates: evidence from pore water and solid phase chemistry

Philosophical Transactions of the Royal Society of London Series A Physical and Engineering Sciences ◽

10.1098/rsta.1993.0072 ◽

1993 ◽

Vol 344 (1670) ◽

pp. 27-36 ◽

Cited By ~ 75

Keyword(s):

Organic Matter ◽

Pore Water ◽

Solid Phase ◽

Chemical Exchange ◽

Isotope Composition ◽

Geochemical Data ◽

Carbonate Sediments ◽

Pore Waters ◽

Carbonate Minerals ◽

Carbonate Production

We present an overview of geochemical data from pore waters and solid phases that clarify earliest diagenetic processes affecting modern, shallow marine carbonate sediments. Acids produced by organic matter decomposition react rapidly with metastable carbonate minerals in pore waters to produce extensive syndepositional dissolution and recrystallization. Stoichiometric relations among pore water solutes suggest that dissolution is related to oxidation of H 2 S which can accumulate in these low-Fe sediments. Sulphide oxidation likely occurs by enhanced diffusion of O 2 mediated by sulphide-oxidizing bacteria which colonize oxic/anoxic interfaces invaginating these intensely bioturbated sediments. Buffering of pore water stable isotopic compositions towards values of bulk sediment and rapid 45 Ca exchange rates during sediment incubations demonstrate that carbonate recrystallization is a significant process. Comparison of average biogenic carbonate production rates with estimated rates of dissolution and recrystallization suggests that over half the gross production is dissolved and/or recrystallized. Thus isotopic and elemental composition of carbonate minerals can experience significant alteration during earliest burial driven by chemical exchange among carbonate minerals and decomposing organic matter. Temporal shifts in palaeo-ocean carbon isotope composition inferred from bulk-rocks may be seriously compromised by facies-dependent differences in dissolution and recrystallization rates.

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Particulate organic carbon (POC) in relation to other pore water carbon fractions in drained and rewetted fens in Southern Germany

Biogeosciences ◽

10.5194/bg-5-1615-2008 ◽

2008 ◽

Vol 5 (6) ◽

pp. 1615-1623 ◽

Cited By ~ 18

Author(s):

S. Fiedler ◽

B. S. Höll ◽

A. Freibauer ◽

K. Stahr ◽

M. Drösler ◽

...

Keyword(s):

Organic Carbon ◽

Particulate Organic Carbon ◽

Pore Water ◽

Inorganic Carbon ◽

Dissolved Inorganic Carbon ◽

Relative Importance ◽

Pore Waters ◽

Calcareous Fens ◽

Essential Components ◽

The Individual

Abstract. Numerous studies have dealt with carbon (C) contents in Histosols, but there are no studies quantifying the relative importance of the individual C components in pore waters. For this study, measurements were taken of all the carbon components (particulate organic carbon, POC; dissolved organic carbon, DOC; dissolved inorganic carbon, DIC; dissolved methane, CH4) in the soil pore water of calcareous fens under three different water management regimes (re-wetted, deeply and moderately drained). Pore water was collected weekly or biweekly (April 2004 to April 2006) at depths between 10 and 150 cm. The main results obtained were: (1) DIC (94–280 mg C l−1) was the main C-component. (2) POC and DOC concentrations in the pore water (14–125 mg C l−1 vs. 41–95 mg C l−1) were pari passu. (3) Dissolved CH4 was the smallest C component (0.005–0.9 mg C l−1). Interestingly, about 30% of the POM particles were colonized by microbes indicating that they are active in the internal C turnover. Certainly, both POC and DOC fractions are essential components of the C budget of peatlands. Furthermore, dissolved CO2 in all forms of DIC appears to be an important part of peatland C-balance.

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DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles?

Biogeosciences ◽

10.5194/bg-10-891-2013 ◽

2013 ◽

Vol 10 (2) ◽

pp. 891-904 ◽

Cited By ~ 91

Author(s):

K.-H. Knorr

Keyword(s):

Ionic Strength ◽

Pore Water ◽

Surface Waters ◽

Iron Reduction ◽

Stream Water ◽

Riparian Wetlands ◽

Pore Waters ◽

Flow Paths ◽

Discharge Patterns ◽

Iron Concentrations

Abstract. Dissolved organic carbon (DOC) exports from many catchments in Europe and North-America are steadily increasing. Several studies have sought to explain this observation. As possible causes, a decrease in acid rain or sulfate deposition, concomitant reductions in ionic strength and increasing temperatures were identified. DOC often originates from riparian wetlands; but here, despite higher DOC concentrations, ionic strength in pore waters usually exceeds that in surface waters. In the catchment under study, DOC concentrations were synchronous with dissolved iron concentrations in pore and stream water. This study aims at testing the hypothesis that DOC exports are mediated by iron reduction/oxidation cycles. Following the observed hydrographs, δ18O of water and DOC fluorescence, the wetlands were identified as the main source of DOC. Antecedent biogeochemical conditions, i.e., water table levels in the wetlands, influenced the discharge patterns of nitrate, iron and DOC during an event. The correlation of DOC with pH was positive in pore waters, but negative in surface waters; it was negative for DOC with sulfate in pore waters, but only weak in surface waters. Though, the positive correlation of DOC with iron was universal for pore and surface water. The decline of DOC and iron concentrations in transition from anoxic wetland pore water to oxic stream water suggests a flocculation of DOC with oxidising iron, leading to a drop in pH in the stream during high DOC fluxes. The pore water did not per se differ in pH. There is, thus, a need to consider processes more thoroughly of DOC mobilisation in wetlands when interpreting DOC exports from catchments. The coupling of DOC with iron fluxes suggested that increased DOC exports could at least, in part, be caused by increasing activities in iron reduction, possibly due to increases in temperature, increasing wetness of riparian wetlands, or by a shift from sulfate dominated to iron reduction dominated biogeochemical regimes.

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Geochemistry of intertidal sediment pore waters from the industrialized Santos-Cubatão Estuarine System, SE Brazil

Anais da Academia Brasileira de Ciências ◽

10.1590/s0001-37652012005000021 ◽

2012 ◽

Vol 84 (2) ◽

pp. 427-442 ◽

Cited By ~ 6

Author(s):

Winston F.O. Gonçalves ◽

Wanilson Luiz-Silva ◽

Wilson Machado ◽

Erico C. Nizoli ◽

Ricardo E. Santelli

Keyword(s):

Surface Water ◽

Pore Water ◽

Surface Waters ◽

Water Concentration ◽

Point Sources ◽

Intertidal Sediment ◽

Estuarine System ◽

Pore Waters ◽

Geochemical Composition ◽

Se Brazil

The geochemical composition of sediment pore water was investigated in comparison with the composition of sediment particles and surface water in an estuary within one of the most industrialized areas in Latin America (Santos-Cubatão estuarine system, SE Brazil). Pore and surface waters presented anomalously high levels of F-, NH4+, Fe, Mn and P due to two industrial point sources. In the summer, when SO4(2-)/Cl- ratios suggested an enhanced sulfate reduction, the higher dissolved levels observed in pore waters for some metals (e.g., Cu and Ni) were attributed to reductive dissolution of oxidized phases. Results evidenced that the risks of surface water concentration increase due to diffusion or advection from pore water are probably dependent on coupled influences of tidal pumping and groundwater inputs.

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Migration of acidic pore waters at the Waite Amulet tailings site near Rouyn–Noranda, Quebec, Canada

Canadian Geotechnical Journal ◽

10.1139/t92-051 ◽

1992 ◽

Vol 29 (3) ◽

pp. 466-476 ◽

Cited By ~ 9

Author(s):

Ernest K. Yanful ◽

Luc C. St-Arnaud

Keyword(s):

Hydraulic Conductivity ◽

Pore Water ◽

Mine Drainage ◽

Geotechnical Properties ◽

Horizontal Flow ◽

Sulphide Mineral ◽

Saturated Zone ◽

Pore Waters ◽

Dissolved Metals ◽

Water Contents

Pore waters found in the unsaturated zone of the Waite Amulet tailings have been modified by sulphide mineral oxidation, resulting in acidic pH (near 4) and high concentrations of dissolved iron and sulphate at about 5 and 12 g/L, respectively. These pore waters have been displaced down into the shallow saturated zone of the tailings by infiltrating water. Most metals are removed from the pore water as a result of pH buffering before they reach the deeper saturated zone. However, some dissolved metals still remain in solution and are transported with the pore water through the tailings. Numerical flow modelling shows that an anisotropy in hydraulic conductivity (ratio of Kx/Ky is estimated to be 100) exists in the tailings, most likely due to the presence of horizontal fine-grained "slime" layers. The estimated horizontal pore-water velocity is almost 20 times higher than the vertical velocity. Anisotropy in hydraulic conductivity has the effect of promoting horizontal flow over vertical flow in the model. The geometry of the tailings impoundment and the assumed impermeability of the varved clay soil underlying the tailings also contribute to increased horizontal flow. To verify that a preferred horizontal flow exists and that the clay subsoil is indeed impermeable, the geotechnical properties and hydrogeochemistry of the clay are also evaluated. The results indicate that clay located beneath the tailings is slightly overconsolidated in the shallow zone but normally consolidated at greater depth by the weight of the tailings. Overconsolidation ratios reach a maximum value of 2.0. In the clay–tailings interface zone, the soil is characterized by lower in situ water contents and slightly higher undrained shear strengths Cu than the deeper clay. The water contents of the near-interface clay average about 40% and the Cu values 80 kPa, compared with an average water content of 55% and a Cu value of only 20 kPa for the clay at greater depths. These geotechnical properties confirm the presence of a desiccated oxidized upper zone identified in previous studies. It is hypothesized that fractures that could have appeared in the oxidized zone before the tailings deposition would have been closed due to consolidation by the tailings mass. Above-background sulphate concentrations observed in the clay layer at a depth of 1 m are believed to be controlled by diffusion and advection. The presence of fractures in the oxidized zone and excess pore-water pressures generated during consolidation of the clay by the tailings mass could have also influenced chemical transport. Key words : acid generation, acid mine drainage, diffusion, geotechnical, hydrogeochemistry, tailings.

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