Perchlorate removal in Fe0/H2O systems: Impact of oxygen availability and UV radiation

In this study, the removal of perchlorate (0.016 mM) using Fe-0-only (325 mesh, 10 g L-1) and Fe-0 (10 g L-1) with UV (254 nm) reactions were investigated under oxic and anoxic conditions (nitrogen purging). Under anoxic conditions, only 2% and 5.6% of perchlorate was removed in Fe-0-only and Fe-0/UV reactions, respectively, in a 12 h period. However, under oxic conditions, perchlorate was removed completely in the Fe-only reaction, and reduced by 40% in the Fe-0/UV reaction, within 9h. The pseudo-first-order rate constant (k(1)) was 1.63 x 10(-3) h(-1) in Fe-0-only and 4.94 x 10(-3) h(-1) in Fe-0/UV reaction under anoxic conditions. Under oxic conditions, k(1) was 776.9 x 10(-3) h(-1) in Fe-only reaction and 35.1 x 10(-3) h(-1) in the Fe-0/UV reaction, respectively. The chlorine in perchlorate was recovered as chloride ion in Fe-0-only and Fe-0/UV reactions, but lower recovery of chloride under oxic conditions might due to the adsorption/coprecipitation of chloride ion with the iron oxides. The removal of perchlorate in Fe-0/UV reaction under oxic conditions increased in the presence of methanol (73%, 9 h), a radical scavenger, indicating that OH radical can inhibit the removal of perchlorate. The removal of perchlorate by Fe-0-only reaction under oxic condition was highest at neutral pH. Application of the Langmuir-Hinshelwood model indicated that removal of perchlorate was accelerated by adsorption/co-precipitation reactions onto iron oxides and subsequent removal of perchlorate during further oxidation of Fe-0. The results imply that oxic conditions are essential for more efficient removal of perchlorate in Fe-0/H2O system. (C) 2011 Elsevier B.V. All rights reserved.