Impact of groundwater quality on adsorption of arsenate onto iron-oxide-based adsorbent: Case study in Chiayi, Taiwan

Removal of arsenic using an iron-oxide-based adsorbent (IBA) was examined for the groundwater near a black foot disease epidemic area, Chiayi, Taiwan. The groundwater was first characterized for arsenic speciation and water quality that may influence arsenic removal. Arsenic in the present groundwater was predominately the pentavalent species and dissolved form (<1 kDa) and with a concentration of ~30 μg/L. Adsorption uptake of arsenate onto the studied IBA in the groundwater was only two-thirds of that in deionized water. Among the 10 ions, metals, and organics examined, only phosphate and natural organic matter (NOM) influenced the adsorption of arsenate onto iron-oxide-coated diatomite (IOCD). To further identify the governing factor for the suppression of arsenate uptake on IOCD, adsorption experiments were conducted using coagulated groundwater, which may remove phosphate and NOM to different degrees. Experimental results confirmed that phosphate was the only important factor to suppress arsenate adsorption to IOCD in the studied groundwater.