The effect of environmental factors (e.g., pH, solution composition, and temperature) that affect the longevity of Fe(0) barriers in the subsurface are difficult to quantify independently from changes that occur to the passivating layer. Therefore, to quantify the rate of Fe(0) dissolution under conditions which maintain the pO2 at a relatively constant level and minimize the formation of a passivating layer on the metal surface, a series of experiments have been conducted with the single-pass flow-through (SPFT) apparatus. These experiments were conducted over the pH range from 7.0 to 12.0 at 90°C in the presence of 5 mM EDDHA or 5 mM EDTA. The organic acids, EDDHA and EDTA, helped to maintain the aqueous Fe concentration below saturation with respect to Fe-bearing alteration phases and minimize the formation of a partially oxidized surface film. Results suggest the corrosion of Fe(0) is relatively insensitive to pH and the forward or maximum dissolution rate is 3 to 4 orders of magnitude higher than when a passive film and corrosion products are present.
Revised: March 5, 2008 |
Published: March 25, 2007
Citation
Lodge A.M., E.M. Pierce, D.M. Wellman, and E.A. Cordova. 2007.Effect of pH on the dissolution kinetics of zero-valent iron in the presence of EDDHA and EDTA. In Preprints of extended abstracts presented at the 233rd ACS National Meeting, American Chemical Society, Division of Environmental Chemistry, edited by G. Coimbatore, 47, 101-109. Washington, D.C., District Of Columbia:American Chemical Spciety, Division of Environmental Chemistry.PNNL-SA-57100.