Electrochemical oxidation of ethylenediaminetetraacetic acid in alkaline medium.

摘要

Bulk electrolysis of EDTA in alkaline medium suggested that stable organic intermediate species are formed. s-EDDA, glyoxal, formaldehyde and nitrate were identified in the partially electrolyzed EDTA solution. The oxidation products suggest that the initial breakdown of EDTA occurs via the Hofer-Moest type reaction. Complete oxidation reaction pathways to carbon dioxide are proposed.; In alkaline medium, very little EDTA oxidation was found to occur on bare platinum. Limiting-current-density behavior due to PtO formation was observed at potentials immediately positive of the rest potential. Tafel behavior (Tafel slope: 119 mV/decade) was observed in the potential region positive of the cessation of oxide film formation and negative of the onset of O{dollar}sb2{dollar} evolution. The reaction orders of EDTA and OH{dollar}sp-{dollar} were determined to be 0.54 and {dollar}sim{dollar}0, respectively. The reaction mechanism consistent with the observed experimental data involves Temkin-type adsorption and first-electron-transfer rate-determining step.; Polarization studies of EDTA and some of the intermediates species (ethylenediamine, glyoxal, glyoxalate, oxalate, formaldehyde, and formate) were carried out in alkaline medium using platinized titanium electrode. Formate and oxalate were found to be oxidized at rates significantly higher than the oxidation rates of other intermediate species. EDTA, glyoxalate, and ethylenediamine were found to oxidize at moderate rates. The aldehydes (formaldehyde and glyoxal) exhibited the slowest kinetics.; Bench scale parallel plate reactor experiments were carried out to study the effect of applied current density, flow rate, and cell configuration on EDTA destruction. The applied current density was found to have a significant effect on EDTA destruction rate. The flow rate at an applied current density of 200 mA/cm{dollar}sp2,{dollar} had very little effect on EDTA destruction rate. The divided cell configuration was found to decrease OH{dollar}sp-{dollar} concentration in the anolyte at a fast rate which resulted in the decrease in conductivity of the anolyte solution and an increase in cell potential. A simple mathematical model of the destruction of EDTA in an undivided parallel plate reactor is described which takes into account the reaction chemistry and the observed electrochemical kinetic behavior of the reactions.