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

Abstract 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 0 -only reaction, and reduced by 40% in the Fe 0 /UV reaction, within 9 h. The pseudo-first-order rate constant ( k 1 ) was 1.63 × 10 −3  h −1 in Fe 0 -only and 4.94 × 10 −3  h −1 in Fe 0 /UV reaction under anoxic conditions. Under oxic conditions, k 1 was 776.9 × 10 −3  h −1 in Fe 0 -only reaction and 35.1 × 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/co-precipitation 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 /H 2 O system.