Arsenic removal effectiveness of iron oxide-based fibrous adsorbents and stability of granular iron oxide media

Abstract

This study focuses on two objectives to improve arsenic adsorptive capacities of iron oxide-based adsorbents. The first objective was to improve arsenic removal effectiveness of iron oxide-based adsorbent by investigating the potential of four types of fibrous materials, polypropylene, polyester, fiberglass, and cellulose for their ability to retain iron coatings and to remove arsenate. Arsenate adsorption densities were highest for iron-oxide coated fiberglass and cellulose, suggesting that these fibrous materials may offer advantages over iron-oxide-coated sand. Arsenate mass-transfer was observed to be limited by the external mass-transfer resistance initially and intra-particle mass-transfer resistance subsequently, which could be improved by introducing additional reactive sites on the fibers surface. Further experiments are warranted to make these coated fibers, particularly iron-oxide-coated fiberglass fibers, competitive with other commercially available arsenic adsorbents.The second objective of this work was to understand the combined effects of near-neutral solution pH levels, ion types, and concentrations typical of an arsenic contaminated groundwater on phase transformation of an iron oxide-based media. Batch studies were conducted using a granular iron hydroxide media and combined effects of time, pH, and ions were studied by observing changes in mineralogy of media and extent of crystallinity of iron oxide media. No major iron oxide phase change was observed during the aging studies and arsenic and other ions were not observed to be introduced in the XRD spectra of different iron oxide samples. Initial solution pH and aging time appear to be the significant factors affecting the extent of crystallization of different iron oxide samples, and the extent of crystallinity was observed to increase with aging time and low solution pH. The extent of crystallization of iron oxide was observed to decrease for samples, aged in the presence of 0.3 mg/L ferrous iron ions and increase during the intermediate pH adjustment studies. Further research work is required to understand the effects of ferrous iron and arsenic ions at near-neutral solution pH at room temperature for longer periods (i.e., > 1 years) on the crystalline structure of the iron oxide media, and their influence on its overall adsorptive capacity.%%%%Ph.D., Environmental Engineering – Drexel University, 2008