Degradation of lead complex by photooxidation in the presence of hydrogen peroxide

Abstract

The degradation of Pb-EDTA in aqueous solution by hydrogen peroxide/UV process was studied. The UV radiation source was a medium-pressure mercury lamp (254 nm). The effect of hydrogen peroxide concentration, initial pH of solution, Pb-EDTA to hydrogen peroxide molar ratio and nitrate concentration have been investigated. Pb-EDTA can be rapidly degraded by hydrogen peroxide/UV process accompanied by simultaneous lead removal. A precipitation of lead during irradiation has been observed. From the experiments, the optimum conditions are Pb-EDTA: hydrogen peroxide molar ratio of 1:20 at initial solution pH of 3.0. NTA, IDA, oxalate and nitrate were found as by-products. It was found that the by-products like NTA itself can also be decomposed by photooxidation. The results indicated that nitrate in low concentration (0.004 M) has not effected Pb-EDTA degradation. In contrast, nitrate present at a relatively higher concentration (0.04 M) remarkably reducedPb-EDTA degradation and lead removal. The quantum yield of the photooxidation of Pb-EDTA was 0.30. The photooxidation of Zn-EDTA and Cd-EDTA have also been studied. It was found that Zn-EDTA and Cd-EDTA were decomposed rapidly but total zinc and cadmium concentration were not reduced. The quantum yield of the photooxidation of Zn-EDTA and Cd-EDTA are 0.21 and 0.22, respectively.