Arsenic continues to be a contaminant of concern due to its toxicity to living things and its wide occurrence in groundwater resources globally from both natural and anthropogenic causes. Previous studies have shown that nanoscale zerovalent iron (NZVI) is a promising sorbent for removing arsenic from water. However, the removal kinetics and mechanisms are not well understood. In this study, batch tests were conducted using 25-nm size nanoiron to remove the two predominant forms of arsenic: arsenate [As(V)] and arsenite [As(III)] from water under anaerobic conditions as a function of time and pH with or without phosphate and silicate. Both As(V) and As(III) removal increased with increasing time to approach a steady state after 4-5 days. There is generally more removal of As(III) than As(V). Complete or near complete removal of As(V) and As(III) was achieved at pH levels less than 10. Competition of phosphate and silicate against As(V) and As(III) was observed at alkaline pHs. New solid phases formed such as parasymplesite in the As(V) system and vivianite in the phosphate system. This study demonstrated that As(V) removal involves both solid precipitation and adsorption by NZVI; whereas, As(III) removal involves surface adsorption. Additional experiments were conducted using magnetite (20-30 nm), maghemite (20-50 nm), and hematite (20-50 nm) to remove As(V) and As(III) under aerobic conditions as a function of time and pH with or without phosphate and silicate. Surface adsorption is responsible for As removal by the iron oxides.

Arsenic removal from water by nanoscaled zerovalent iron and iron oxides

251st National Meeting (2016)

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