Chemical treatment of pesticide wastes. Evaluation of Fe(III) chelates for catalytic hydrogen peroxide oxidation of 2,4-D at circumneutral pH

A number of structurally diverse organic and inorganic polydentate chelators were tested for their ability to solubilize Fe(III) at pH 6 and catalyze the oxidation of 0.1 mM (22 ppm) 2,4-dichlorophenoxyacetic acid (2,4-D) by 10 mM (340 ppm) hydrogen peroxide in aerated aqueous solution. Of 50 compounds tested, 20 organic compounds gave soluble complexes capable of oxidizing 2,4-D in periods ranging from minutes to less than 5 h. The reaction rate was proportional to the concentration of H2O2 and inversely proportional to the concentration of chelator. 2,4-Dichlorophenol was a transient intermediate. Chloride was released concurrently with 2,4-D disappearance. Activities of individual complexes toward 2,4-D transformation and hydrogen peroxide decomposition were similar. Several of the most active complexes gave about 80% mineralization of [ring-14C]- or [carboxy-14C]-2,4-D within 4 h. Additional supplements of H2O2 increased the extent of mineralization. All active organic ligands were themselves oxidized, but in many cases the resulting iron complexes remained solubilized and reactive, often more reactive than the original complex. From a practical perspective, degradation of the ligand may be viewed as desirable