HR: 14:10h
AN: H23I-03 INVITED    [Abstracts]
TI: A Formulation to Solve Mixing-Driven Reactive Transport Problems
AU: * DeSimoni, M
EM: michela.de.simoni@eni.it
AF: ENI-E&P Division, Via Emilia 1, San Donato Milanese, MI 20097, Italy
AU: Sanchez-Vila, X
EM: xavier.sanchez-vila@upc.edu
AF: Department of Geotechnical Engineering and Geosciences - Technical University of Catalonia, C/ Jordi Girona 1-3, Barcelona, BCN 08034, Spain
AU: Carrera, J
EM: jcarrera@ija.csic.es
AF: Institut de Ciencies de la Terra Jaume Almera - CSIC, C/ Lluís Solé i Sabarís, Barcelona, BCN 08028, Spain
AU: Guadagnini, A
EM: alberto.guadagnini@polimi.it
AF: Dipartimento di Ingegneria Idraulica, Ambientale, Infrastrutture Viarie, Rilevamento - Politecnico di Milano, Piazza L. Da Vinci 32, Milano, MI 20133, Italy
AU: Saaltink, M
EM: maarten.saaltink@upc.edu
AF: Department of Geotechnical Engineering and Geosciences - Technical University of Catalonia, C/ Jordi Girona 1-3, Barcelona, BCN 08034, Spain
AB: Several reactive transport phenomena are driven by mixing. Therefore, quantification of the mixing rate is essential for evaluating the fate of reactive solutes in rivers, lakes and aquifers. Mixing-driven chemical processes are generally highly non-linear; the resulting complexity has inhibited the development of analytical solutions for multi-component heterogeneous reactions (such as precipitation/dissolution) and led to analyze reactive transport processes mainly using advanced numerical codes. We propose a novel mixing ratios-based formulation to evaluate solute concentrations and reaction rates when equilibrium aqueous reactions and precipitation-dissolution of minerals are driven by mixing of different waters. The approach decouples solute transport and chemical speciation, so that mixing ratios are obtained solving a conservative transport problem and then used to evaluate species concentrations. One key point of the methodology is constituted by the general expression for reaction rates which clearly demonstrates that the amount of reactants evolving into products depends on the rate at which solutions mix. The methodology is a useful tool to derive analytical solutions highlighting the relative importance of involved phenomena and parameters. The derived analytical solutions may also be used as benchmark for reactive transport codes or in designing/interpreting experimental analyses devoted to study mixing-driven reactive transport processes. We apply the developed formulation to provide an analytical solution of the reactive transport process resulting from mixing different CaCO3-saturated waters in a two-dimensional set-up. The derived solution reproduces the non-linear behaviour of calcite precipitation/dissolution in the fresh-saltwater mixing zone of coastal aquifers, with modest computational effort if compared to reactive transport numerical codes. The obtained solution is thus a promising tool to investigate carbonate system evolution.
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting