EDTA degradation induced by oxygen activation in a zerovalent iron/air/water system

A method for the removal of ethylenediaminetetraacetic acid (EDTA) at room temperature and 1 atm is demonstrated. EDTA (1 mM, 50 mL) containing 2.5 g of granular zerovalent iron (ZVI) (20-40 mesh) was degraded in 2.5 h. Using a recently developed form Of 02 activation, reactive oxygen species are generated in situ, resulting in the degradation of EDTA when complexed with Fe-II. ESI-MS measurements indicate that degradation of EDTA yields low-molecular carboxylic acids. The presence of oxygen is crucial: the observed pseudo-first-order rate constants for EDTA removal are k(obs) = 1.02 +/- 0.26 h(-1) (k(SA) = 1.85 +/- 0.046 L h(-1) m(-2)) and k(obs) = 0.04 h(-1) (kSA = 0.00724 +/- 0.002 L h(-1) m(-2)) under air and under N-2 purge, respectively. kSA represents surface area normalized rate constants. Large excesses of EDTA in,the reaction mixture slow the rate of degradation. Increasing the concentration of EDTA from 1.0 to 10.0 mM while holding all other parameters constant gave observed rates of k(obs) = 1.02 +/- 0.26 h(-1) (k(SA) = 1.85 +/- 0.046 L h(-1) m(-2)) and k(obs) = 0.044 +/- 0.01 h(-1) (k(SA) = 0.00796 +/- 0.002 L h(-1) m(-2)), respectively. The rate-limiting step is determined to be homogeneous oxygen activation.