Sorption and transport of aqueous Fe^II in a goethite-coated sand column under anoxic conditions

Experiments were conducted under static batch and dynamic flow conditions to evaluate the sorption of Fe^II onto three goethites (G1, G2 and G3) having different crystal habits, morphologies and surface properties. Results reveal that G1 exhibited the highest Fe^II sorption extent and lowest kinetic rate constant, which may result from higher surface site density, surface roughness and edge surface faces. Surface complexation modeling parameters derived from batch experiments were combined with hydrodynamic parameters to simulate breakthrough curves in goethite-coated sand packed columns. The total sorbed amount of Fe^II at complete breakthrough was in agreement with that expected from the batch experiments, except for G1. Sorption breakthrough predictions that make use of surface complexation parameters accurately predicted Fe^II mobility in G2 and G3 columns, but poorly in G1 column. Experiments at various flow rates in G1 columns represented different amounts of Fe^II sorbed at complete breakthrough, thereby underscoring the impact of kinetic sorption. Moreover, Fe dissolution/re-precipitation or Fe^II-induced transformation of goethite was suspected at the lowest flow rate in the G1 column. The influence of goethite phase specific reactivity on Fe^II sorption under batch versus advective-dispersive flow is herein demonstrated. These findings have strong implications to assess transport of Fe^II and environmental contaminants both in natural and engineered systems.