Discrepancies persist in understanding and quantifying arsenate distribution in systems with ferrihydrite, despite a highly congested literature.  In this study the kinetics of As(V) sorption over ~ 3000 h in nine batch systems with varying pH and As(V)/Fe was undertaken in conjunction with an in situ ATRIR study.  The As(V) concentration in solution decreased linearly as a function of log(t) (termed Elovich kinetics) over the full 3000 h in most systems.  A stable [As(V)] was only observed in systems with low As(V)/Fe and low pH.  Ferrihydrite remained as the only detectable phase over the 3000 h in all systems even though ferrihydrite is not stable in the absence of As(V). Apparent As(V) sorption constants were derived from the data at specific times intervals using the Diffuse Layer Model and equations describing logKAs values as a function of time provide a way to describe this elusive equilibrium.  In situ ATRIR spectra measured over time as As(V) sorbed on ferrihydrite support the hypothesis that slow inter-particle diffusion is responsible for the slow approach to equilibrium.  This work resolves significant discrepancies in previous studies of As(V)-ferrihydrite in terms of quantifying As(V) distribution and understanding the processes responsible for the slow approach to equilibrium.

Arsenate-ferrihydrite systems from minutes to months: A macroscopic and ATRIR study of an elusive equilibrium

247th National Meeting (2014)

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