scholarly journals Improved parameterization of the weathering kinetics module in the PROFILE and ForSAFE models

2020 ◽  
Author(s):  
Harald Ulrik Sverdrup ◽  
Eric H. Oelkers ◽  
Martin Erlandsson Lampa ◽  
Salim Belyazid ◽  
Daniel Kurz ◽  
...  
Keyword(s):  
Mineral Water ◽  
Dissolution Kinetics ◽  
Base Cation ◽  
Mineral Dissolution ◽  
Soil Evolution ◽  
Groundwater Systems ◽  
Level Model ◽  
Kinetic Expression ◽  
Improved Model ◽  
Mineral Dissolution Kinetics

Abstract. Although the PROFILE and ForSAFE model can accurately reproduce the chemical and mineralogical evolution of the soil unsaturated zone, it overestimates weathering rates in deeper soil layers and in groundwater systems. This overestimation has been corrected by improving the kinetic expression describing mineral dissolution by adding or upgrading braking functions. The base cation and aluminium brakes have been strengthened, and an additional silicate brake has been developed, improving the ability to describe mineral- water reactions in deeper soils. These brakes are developed from a molecular-level model of the dissolution mechanisms. Equations, parameters and constants describing mineral dissolution kinetics have now been obtained for 113 minerals from 12 major structural groups, comprising all types of minerals encountered in most soils. The PROFILE and ForSAFE weathering sub-model was extended to cover two-dimensional catchments, both in the vertical and the horizontal direction, including the hydrology. Comparisons between this improved model and field observations are available in Erlandsson Lampa et al. (2019, This special issue). The results showed that the incorporation of a braking effect of silica concentrations was necessary and helps obtain more accurate descriptions of soil evolution rates at greater depths and within the saturated zone.

scholarly journals Reviews and syntheses: Weathering of silicate minerals in soils and watersheds: Parameterization of the weathering kinetics module in the PROFILE and ForSAFE models

2019 ◽  
Author(s):  
Harald Ulrik Sverdrup ◽  
Eric Oelkers ◽  
Martin Erlandsson Lampa ◽  
Salim Belyazid ◽  
Daniel Kurz ◽  
...  
Keyword(s):  
Mineral Water ◽  
Dissolution Kinetics ◽  
Base Cation ◽  
Mineral Dissolution ◽  
Soil Evolution ◽  
Groundwater Systems ◽  
Level Model ◽  
Kinetic Expression ◽  
Improved Model ◽  
Mineral Dissolution Kinetics

Abstract. The PROFILE model, now incorporated in the ForSAFE model can accurately reproduce the chemical and mineralogical evolution of the soil unsaturated zone. However, in deeper soil layers and in groundwater systems, it appears to overestimate weathering rates. This overestimation has been corrected by improving the kinetic expression describing mineral dissolution by adding or upgrading breaking functions. The base cation and aluminium brakes have been strengthened, and an additional silicate brake has been developed, improving the ability to describe mineral-water reactions in deeper soils. These brakes are developed from a molecular-level model of the dissolution mechanisms. Equations, parameters and constants describing mineral dissolution kinetics have now been obtained for 102 different minerals from 12 major structural groups, comprising all types of minerals encountered in most soils. The PROFILE and ForSAFE weathering sub-model was extended to cover two-dimensional catchments, both in the vertical and the horizontal direction, including the hydrology. Comparisons between this improved model and field observations is available in Erlandsson Lampa et al. (2019, This special issue). The results showed that the incorporation of a braking effect of silica concentrations was necessary and helps obtain more accurate descriptions of soil evolution rates at greater depths and within the saturated zone.

Experimental Determination of Chlorite Dissolution Rates

1994 ◽  
Vol 353 ◽  
Author(s):  
Christopher A. Rochelle ◽  
Keith Bateman ◽  
Robert MacGregor ◽  
Jonathan M. Pearce ◽  
David Savage ◽  
...  
Keyword(s):  
Dissolution Kinetics ◽  
Research Programme ◽  
Mineral Dissolution ◽  
Dissolution Rates ◽  
Disturbed Zone ◽  
Ph Conditions ◽  
Engineered Barriers ◽  
The Uk ◽  
Mineral Dissolution Kinetics

AbstractCurrent concepts of the geological disposal of low- and intermediate-level radioactive wastes in the UK envisage the construction of a mined facility (incorporating cementitious engineered barriers) in chlorite-bearing rocks. To model accurately the fluid-rock reactions within the ‘disturbed zone’ surrounding a repository requires functions that describe mineral dissolution kinetics under pH conditions that vary from near neutral to highly alkaline.Therefore, an experimental study to determine the dissolution rates of Fe-rich chlorite has been undertaken as part of the Nirex Safety Assessment Research Programme. Four experiments have been carried out at 25 °C and four at 70 °C, both sets using a range of NaCl/NaOH solutions of differing pH (of nominal pH 9.0,10.3, 11.6 and 13.0 [at 25 °C]).Dissolution rates have been calculated and were found to increase with increasing pH and temperature. However, increased pH resulted in non-stoichiometric dissolution possibly due to preferential dissolution of part of the chlorite structure relative to another, or reprecipitation of some elements as thin hydroxide or oxyhydroxide surface coatings on the chlorite.These results also show that chlorite dissolution is appreciably slower than that of albite and quartz at both 25 and 70 °C, but slightly faster than that of muscovite at 70 °C.

Avoiding unrealistic behaviour in coupled reactive-transport simulations of cation exchange and mineral kinetics in clays

Clay Minerals ◽  
2019 ◽  
Vol 54 (1) ◽  
pp. 83-93
Author(s):  
Steven Benbow ◽  
James Wilson ◽  
Richard Metcalfe ◽  
Jarmo Lehikoinen
Keyword(s):  
Cation Exchange ◽  
Reactive Transport ◽  
Bentonite Clay ◽  
Dissolution Kinetics ◽  
Mineral Dissolution ◽  
Common Component ◽  
Coupling Approach ◽  
Mineral Dissolution Kinetics ◽  
End Members ◽  
Long Timescales

AbstractBentonite clay is often included as a buffer, backfill and/or sealing material in designs for deep geological repositories for radioactive wastes. It is expected that bentonite materials may undergo some mineralogical alteration as they interact with in situ groundwaters over long timescales on the order of thousands to millions of years. Long-term modelling of these materials is therefore important in order to demonstrate confidence that the engineered designs will continue to perform as required over their intended lifetimes (required assessment timescales can be up to 1 million years). The key geochemical processes that must be considered in such modelling are mineral dissolution and precipitation and cation exchange. These processes are expected to occur simultaneously and so modelling of their coupled effects and their rates (kinetics) is necessary. Illustrative reactive-transport models of the geochemical alteration of montmorillonite (the primary mineral in bentonite exhibiting cation exchange) are presented which demonstrate that one possible approach to fully coupling cation exchange and clay mineral dissolution kinetics, referred to here as the ‘all-component coupling’ approach, may lead to unrealistic behaviour due to feedback that may occur in the formulation. This feedback can be avoided if a ‘common-component’ conceptual model for the dissolution of exchanger end members is adopted, where only the saturation of the exchanger ‘structural unit’ is considered when evaluating the potential for dissolution of the mineral. Such considerations have been proposed historically in stability analyses for montmorillonite, but have not been explored widely in the modelling literature.

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