ABSTRACT
Zero-valent iron (Fe0) is frequently used for the dechlorination of pesticides, because it is economical, easily acquired and stable. The kinetics of dechlorination by Fe0 are improved at low pH, but this requires additional acid addition, while dechlorination hardly occurs under basic conditions. Due to the buffer capacity of geological materials such as clay and sediment, however, the addition of acid to obtain a low pH may not be effective. In this research, the dechlorination constants of atrazine by Fe0 were measured with the addition of buffer solution to simulate the buffer capacity of sediment. In the presence of the buffer solution, the pH values remained neutral, while dechlorination occurred more slowly than that observed under acid additions but faster than that without any buffer. When the initial concentrations of atrazine were 10mg/L, 30 mg/L, and 50mg/L, its dechlorination was explained using pseudo-first order reaction kinetics. The pseudo-first order constants were 3.01 x 10(-2)d(-1) at 10 mg/L, 3.23 x 10(-2)d(-1) at 30 mg/L and 3.38 x 10(-2)d(-1) at 50mg/L. In addition, the half-lives of atrazine were 8.91 d at 10mg/L, 9.32 d at 30 mg/L, and 10.00 d at 50mg/L. Acid addition may not be omitted to obtain acidic pH conditions when dechlorination is necessary in geologic materials.
Subject(s)
Atrazine/chemistry , Chlorine/chemistry , Iron/chemistry , Buffers , Hydrogen-Ion Concentration , KineticsABSTRACT
This research investigated the role of the pH buffer capacity of sediment on the dechlorination of atrazine using zero valent iron (ZVI). The buffer capacity of the sediment was quantified by batch experiments and estimated to be 5.0 cmol OH(-) . pH(-1). The sediments were spiked with atrazine at 7.25-36.23 mg kg(-1) (6.21 x 10(-7)-3.09 x 10(-6) mol atrazine . g(-1) sediment) for the batch experiments. The buffer capacity of the sediment maintained the sediment suspension at neutral pH, thereby enabling continuous dechlorination until the buffer capacity of the sediment was depleted. The pseudo-first order dechlorination constants were estimated to be in the range of 1.19 x 10(-2)-7.04 x 10(-2) d(-1) for the atrazine-spiked sediments.
