Susceptibility of Goethite to Fe2+-Catalyzed Recrystallization over Time

Recent work has shown that iron oxides, such as goethite and hematite, may recrystallize in the presence of aqueous Fe2+ under anoxic conditions. This process, referred to as Fe2+-catalyzed recrystallization, can influence water quality by causing the incorporation/release of environmental contaminants and biological nutrients. Accounting for the effects of Fe2+-catalyzed recrystallization on water quality requires knowing the time frame over which recrystallization occurs. Here, we tested the hypothesis that nanoparticulate goethite becomes less susceptible to Fe2+-catalyzed recrystallization over time. We set up two batches of reactors in which55Fe2+ tracer was added at two different time points, and tracked the 55Fe partitioning in the aqueous and solid phases over 60 days. Less 55Fe uptake occurred between days 30 and 60 than between days 0 and 30, suggesting goethite recrystallization slowed with time. Fitting the data with a box model indicated that 15% of the goethite recrystallized after 30 days o...