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

Abstract

In this study, the removal of perchlorate (0.016mM) using Fe(0)-only (325 mesh, 10g L(-1)) and Fe(0) (10g L(-1)) with UV (254nm) 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 12h 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 9h. 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%, 9h), 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.