Iron Oxide Phase Transformation of a Commercial Granular Iron Oxyhydroxide Based Arsenic Adsorbent: A Mineralogical Investigation

摘要

The objective of this research work was to understand the combined effects of pH, ionrntypes and time on phase transformation of a commercially available granular ironrnhydroxide media, Bayoxide E33, exposed to a synthetic groundwater at pH 6 and pH 8rnfor 90 days in batch experiments, using X-ray diffraction (XRD) technique. No newrniron/arsenic bearing mineral was observed for spent E33 media indicating that arsenicrnwas not incorporated within the crystalline structure of the media. However, XRD peaksrnof spent media at 2θ = 21.62° and 36.9° were observed to widen compared to freshrnmedia. Greater widening of peaks was observed for samples exposed to pH 6 solutionsrnthan that exposed to pH 8 solutions. Observed changes in peak-widths of spent mediarnsuggest the possibility of structural changes in media over time, which may also influencernits arsenic adsorptive capacity over time. These findings are relevant to small utilities thatrntreat groundwater with high arsenic and ferrous iron concentrations. Concerns appear tornbe greater for reduced, alkaline groundwater as the pH 8 sample with ferrous iron presentrnshowed the greatest structural change. Further experiments are underway to collect morerninformation about changes in degree of crystallinity and arsenic adsorption capacity ofrniron oxide media over time, which could be useful in understanding the combined effectsrnof different environmental factors on its stability and time-dependent arsenic removalrneffectiveness.