Open AccessDiffusive–Dispersive and Reactive Fronts in Porous Media: Iron(II) Oxidation at the Unsaturated–Saturated Interface
Author(s) -
Haberer Christina M.,
Muniruzzaman Muhammad,
Grathwohl Peter,
Rolle Massimo
Publication year - 2015
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2014.07.0091
Subject(s) - porous medium , anoxic waters , groundwater , chemistry , tracer , diffusion , permeable reactive barrier , mass transfer , precipitation , vadose zone , biogeochemical cycle , environmental chemistry , analytical chemistry (journal) , porosity , thermodynamics , geology , environmental remediation , chromatography , meteorology , ecology , physics , geotechnical engineering , organic chemistry , contamination , biology , nuclear physics
Diffusive–dispersive mass transfer is important for many groundwater quality problems as it drives the interaction between different reactants, thus influencing a wide variety of biogeochemical processes. In this study, we performed laboratory experiments to quantify O 2 transport in porous media, across the unsaturated–saturated interface, under both conservative and reactive transport conditions. As reactive system we considered the abiotic oxidation of Fe 2+ in the presence of O 2 . We studied the reaction kinetics in batch experiments and its coupling with diffusive and dispersive transport processes by means of one‐dimensional columns and two‐dimensional flow‐through experiments, respectively. A noninvasive optode technique was used to track O 2 transport into the initially anoxic porous medium at highly resolved spatial and temporal scales. The results show significant differences in the propagation of the conservative and reactive O 2 fronts. Under reactive conditions, O 2 , continuously provided from the atmosphere, was considerably retarded due to the interaction with dissolved Fe(II), initially present in the anoxic groundwater. The reaction between dissolved O 2 and Fe 2+ led to the formation of an Fe(III) precipitation zone in the experiments. Reactive transport modeling based on a kinetic PHREEQC module tested in controlled batch experiments allowed a quantitative interpretation of the experimental results in both one‐ and two‐dimensional setups.