Acid/base front propagation in saturated porous media: 2D laboratory experiments and modeling.
We perform laboratory scale reactive transport experiments involving acid-basic reactions between nitric acid and sodium hydroxide. A two-dimensional experimental setup is designed to provide continuous on-line measurements of physico-chemical parameters such as pH, redox potential (Eh) and electrical conductivity (EC) inside the system under saturated flow through conditions. The electrodes provide reliable values of pH and EC, while sharp fronts associated with redox potential dynamics could not be captured. Care should be taken to properly incorporate within a numerical model the mixing processes occurring inside the electrodes. The available observations are modeled through a numerical code based on the advection-dispersion equation. In this framework, EC is considered as a variable behaving as a conservative tracer and pH and Eh require solving the advection dispersion equation only once. The agreement between the computed and measured pH and EC is good even without recurring to parameters calibration on the basis of the experiments. Our findings suggest that the classical advection-dispersion equation can be used to interpret these kinds of experiments if mixing inside the electrodes is adequately considered.
Laboratoire d'Hydrologie et de Géochimie de Strasbourg, Université de Strasbourg/EOST-CNRS, 1 rue de Blessig, 67000 Strasbourg, France.
Stéphanie
S
Loyaux-Lawniczak
François
F
Lehmann
Philippe
P
Ackerer
D007700:Kinetics; D008956:Models, Chemical; D017942:Nitric Acid / Q000737:chemistry*; D016062:Porosity; D012972:Sodium Hydroxide / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D014874:Water Pollutants, Chemical; D017942:Nitric Acid; D012972:Sodium Hydroxide