AWWA ACE69067

The objective of this research was to understand the combined effects of pH, ion types and time on phase transformation of a commercially available granular iron hydroxide media, Bayoxide E33, exposed to a synthetic groundwater at pH 6 and pH 8 for 90 days in batch experiments, using X-ray diffraction (XRD) technique. No new iron/arsenic bearing mineral was observed for spent E33 media indicating that arsenic was not incorporated within the crystalline structure of the media. However, XRD peaks of spent media at 20 = 21.62º and 36.9º were observed to widen compared to fresh media. Greater widening of peaks was observed for samples exposed to pH 6 solutions than that exposed to pH 8 solutions. Observed changes in peak-widths of spent media suggest the possibility of structural changes in media over time, which may also influence its arsenic adsorptive capacity over time. These findings are relevant to small utilities that treat groundwater with high arsenic and ferrous iron concentrations. Concerns appear to be greater for reduced, alkaline groundwater as the pH 8 sample with ferrous iron present showed the greatest structural change. Further experiments are underway to collect more information about changes in degree of crystallinity and arsenic adsorption capacity of iron oxide media over time, which could be useful in understanding the combined effects of different environmental factors on its stability and time-dependent arsenic removal effectiveness. Includes 16 references, tables, figures.