scholarly journals Reactive transport modelling of long-term interactions between iron and MX-80 bentonite

2021 ◽  
Vol 1 ◽  
pp. 169-170
Author(s):  
M. Carme Chaparro ◽  
Nicolas Finck ◽  
Volker Metz ◽  
Horst Geckeis
Keyword(s):  
Carbon Steel ◽  
Numerical Model ◽  
Reactive Transport ◽  
Transport Model ◽  
Corrosion Products ◽  
Mineral Dissolution ◽  
Secondary Phases ◽  
Short Term ◽  
Complexation Reactions

Abstract. The geological disposal in deep bedrock repositories is the preferred option for the management of high-level radioactive waste. In some of these concepts, carbon steel is considered as potential canister material and bentonites are planned as backfill material to protect metal waste containers. Therefore, a 1D radial reactive transport model has been developed in order to better understand the processes occurring during the long-term iron–bentonite interaction. The conceptual model accounts for diffusion, chemistry of the porewater and aqueous complexation reactions, mineral dissolution/precipitation and absorption, at a constant temperature of 25 ∘C under anoxic conditions. The geometry of the axisymmetric model reflects the canister–bentonite interface and the bentonite. The primary phases considered are montmorillonitic smectite, quartz, muscovite, albite, illite, pyrite and calcite. We assume that carbon steel is composed only of iron. The potential secondary phases considered are from reported experiments, such as magnetite, nontronitic smectite, greenalite, cronstedtite and siderite. The numerical model results suggest that at the iron–bentonite interface, Fe is adsorbed at the smectite surface via ion exchange in the short term and it is consumed by formation of the secondary phases in the long term. Furthermore, calcite precipitates are due to cation exchange in the short term and due to montmorillonitic smectite dissolution in the long term. The numerical model predicts the precipitation of nontronitic smectite, magnetite and greenalite as corrosion products. Results further reveal a significant increase in pH in the long term, whereas dissolution/precipitation reactions result in limited variations of the porosity. Progressing bentonite dissolution owing to the rising pH and concomitantly increasing silicate concentrations in the porewater induce formation of Fe-silicates as corrosion products at the expense of magnetite. A sensitivity analysis has also been performed to study the effect of selected parameters, such as corrosion rate, diffusion coefficient and composition of the porewater, on the corrosion products. Overall, outcomes suggest that pH and concentration of dissolved Si play an important role in corrosion mechanisms. The predicted main secondary phases in the long term are Fe-silicate minerals. Thus, such phases deserve further attention as possible chemical barriers for radionuclide migration in the repository near-field.

scholarly journals Reactive Transport Modelling of the Long-Term Interaction between Carbon Steel and MX-80 Bentonite at 25 ∘C

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1272
Author(s):  
M. Carme Chaparro ◽  
Nicolas Finck ◽  
Volker Metz ◽  
Horst Geckeis
Keyword(s):  
Carbon Steel ◽  
Numerical Model ◽  
Cation Exchange ◽  
Reactive Transport ◽  
Corrosion Products ◽  
Mineral Dissolution ◽  
Long Term Results ◽  
Short Term ◽  
Complexation Reactions

The geological disposal in deep bedrock repositories is the preferred option for the management of high-level radioactive waste (HLW). In some of these concepts, carbon steel is considered as a potential canister material and bentonites are planned as backfill material to protect metallic waste containers. Therefore, a 1D radial reactive transport model has been developed in order to better understand the processes occurring during the long-term iron-bentonite interaction. The numerical model accounts for diffusion, aqueous complexation reactions, mineral dissolution/precipitation and cation exchange at a constant temperature of 25 ∘C under anoxic conditions. Our results suggest that Fe is sorbed at the montmorillonite surface via cation exchange in the short-term, and it is consumed by formation of the secondary phases in the long-term. The numerical model predicts precipitation of nontronite, magnetite and greenalite as corrosion products. Calcite precipitates due to cation exchange in the short-term and due to montmorillonite dissolution in the long-term. Results further reveal a significant increase in pH in the long-term, while dissolution/precipitation reactions result in limited variations of the porosity. A sensitivity analysis has also been performed to test the effect of selected parameters, such as corrosion rate, diffusion coefficient and composition of the bentonite porewater, on the corrosion processes. Overall, outcomes suggest that the predicted main corrosion products in the long-term are Fe-silicate minerals, such phases thus should deserve further attention as a chemical barrier in the diffusion of radionuclides to the repository far field.

scholarly journals Arsenic in Petroleum-Contaminated Groundwater near Bemidji, Minnesota Is Predicted to Persist for Centuries

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1485
Author(s):  
Brady A. Ziegler ◽  
G.-H. Crystal Ng ◽  
Isabelle M. Cozzarelli ◽  
Aubrey J. Dunshee ◽  
Madeline E. Schreiber
Keyword(s):  
Reactive Transport ◽  
Transport Model ◽  
Oxygen Demand ◽  
Leading Edge ◽  
Contaminated Aquifer ◽  
Drinking Water Standard ◽  
Attenuation Mechanism ◽  
Complexation Reactions ◽  
Fe Reduction

We used a reactive transport model to investigate the cycling of geogenic arsenic (As) in a petroleum-contaminated aquifer. We simulated As mobilization and sequestration using surface complexation reactions with Fe(OH)3 during petroleum biodegradation coupled with Fe-reduction. Model results predict that dissolved As in the plume will exceed the U.S. and EU 10 µg/L drinking water standard for ~400 years. Non-volatile dissolved organic carbon (NVDOC) in the model promotes As mobilization by exerting oxygen demand, which maintains anoxic conditions in the aquifer. After NVDOC degrades, As re-associates with Fe(OH)3 as oxygenated conditions are re-established. Over the 400-year simulation, As transport resembles a “roll front” in which: (1) arsenic sorbed to Fe(OH)3 is released during Fe-reduction coupled to petroleum biodegradation; (2) dissolved As resorbs to Fe(OH)3 at the plume’s leading edge; and (3) over time, the plume expands, and resorbed As is re-released into groundwater. This “roll front” behavior underscores the transience of sorption as an As attenuation mechanism. Over the plume’s lifespan, simulations suggest that As will contaminate more groundwater than benzene from the oil spill. At its maximum, the model simulates that ~5.7× more groundwater will be contaminated by As than benzene, suggesting that As could pose a greater long-term water quality threat than benzene in this petroleum-contaminated aquifer.

scholarly journals Mineralogical, numerical and analytical studies of the coupled oxidation of pyrite and coal

2003 ◽  
Vol 67 (2) ◽  
pp. 381-398 ◽  
Author(s):  
K. A. Evans ◽  
C. J. Gandy ◽  
S. A. Banwart
Keyword(s):  
Reactive Transport ◽  
Transport Model ◽  
Pyrite Oxidation ◽  
Spoil Heap ◽  
Reaction Fronts ◽  
Order Of Magnitude ◽  
Magnitude Variation ◽  
Discharge Chemistry ◽  
Analytical Expressions

Mineralogical, bulk and field leachate compositions are used to identify important processes governing the evolution of discharges from a coal spoil heap in County Durham. These processes are incorporated into a numerical one-dimensional advective-kinetic reactive transport model which reproduces field results, including gas compositions, to within an order of magnitude. Variation of input parameters allows the effects of incorrect initial assumptions on elemental profiles and discharge chemistry to be assessed. Analytical expressions for widths and speeds of kinetic reaction fronts are developed and used to predict long-term development of mineralogical distribution within the heap. Results are consistent with observations from the field site. Pyrite oxidation is expected to dominate O2 consumption in spoil heaps on the decadal timescale, although C oxidation may stabilize contaminants in effluents on the centennial scale.

Interactions of corrosion products and bentonite: An extended multicomponent reactive transport model

2011 ◽  
Vol 36 (17-18) ◽  
pp. 1661-1668 ◽  
Author(s):  
Chuanhe Lu ◽  
Javier Samper ◽  
Bertrand Fritz ◽  
Alain Clement ◽  
Luis Montenegro
Keyword(s):  
Reactive Transport ◽  
Transport Model ◽  
Corrosion Products ◽  
Reactive Transport Model ◽  
Multicomponent Reactive Transport

scholarly journals Modelling Long-Term Durability Performance of Cementitious Materials under Sodium Sulphate Interaction

2018 ◽  
Vol 8 (12) ◽  
pp. 2597 ◽  
Author(s):  
Yogarajah Elakneswaran ◽  
Eiji Owaki ◽  
Toyoharu Nawa
Keyword(s):  
Waste Disposal ◽  
Reactive Transport ◽  
Power Plants ◽  
Transport Model ◽  
Cementitious Materials ◽  
Sodium Sulphate ◽  
High Concentration ◽  
Essential Components ◽  
Term Performance

Cementitious materials are one of the essential components for low- and intermediate-level waste disposal sites. Low-level nuclear waste from power plants consists of highly concentrated (~25 wt %) Na2SO4, and the wastes are solidified with cementitious materials. Degradation of cementitious materials that result from chemical and physical sulphate attack is a major concern in the safety of the waste disposal. In this study, hydration and reactive transport models, developed in previous works by the authors, were applied with Pitzer interactions coefficients to evaluate the long-term performance of Portland cement (PC) solidified with high concentration of Na2SO4. Expansive sulphate-bearing products of ettringite and mirabilite were formed and filled the pores in the hydrating PC with 25% of Na2SO4 by weight, but they were destabilised as temperature increased. Influence of Na2SO4 concentration and temperature on mineralogical changes is discussed. The simulation results from the reactive-transport model showed that the degradation of solidified Na2SO4 waste by cementitious materials exposed to 10% Na2SO4 for 1000 years is due to dissolution of mirabilite and secondary formation of ettringite, but not Na2SO4 crystallisation. The phases and porosity became stable close to exposure surface after 10 years, although the deterioration progressed from the surface to core with exposure time.

Assessing the durability of nuclear glass with respect to silica controlling processes in a clayey underground disposal

2006 ◽  
Vol 932 ◽  
Author(s):  
Laurent De Windt ◽  
Stéphanie Leclercq ◽  
Jan van der Lee
Keyword(s):  
Host Rock ◽  
Reactive Transport ◽  
Transport Model ◽  
Glass Block ◽  
High Level Waste ◽  
Residual Rate ◽  
Glass Dissolution ◽  
Underground Disposal ◽  
High Level

ABSTRACTThe long-term behaviour of vitrified high-level waste in an underground clay repository was assessed by using the reactive transport model HYTEC with respect to silica diffusion, sorption and precipitation processes. Special attention was given to the chemical interactions between glass, corroded steel and the host-rock considering realistic time scale and repository design. A kinetic and congruent dissolution law of R7T7 nuclear glass was used assuming a first-order dissolution rate, which is chemistry dependent, as well as a long-term residual rate. Without silica sorption and precipitation, glass dissolution is diffusion-driven and the fraction of altered glass after 100,000 years ranges from 5% to 50% depending on the fracturation degree of the glass block. Corrosion products may limit glass dissolution by controlling silica diffusion, whereas silica sorption on such products has almost no effect on glass durability. Within the clayey host-rock, precipitation of silicate minerals such as chalcedony may affect glass durability much more significantly than sorption. In that case, however, a concomitant porosity drop is predicted that could progressively reduce silica diffusion and subsequent glass alteration.

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