Application of Fe(VI) in the treatment of Zn(II)-NTA complexes in aqueous solutions

摘要

The higher oxidation state of iron, i.e. Fe(VI), was exploited to treat the synthetic wastewater containing Zn(II)-NTA. The decomposition of Zn(II)-NTA by Fe(VI) was investigated with the help of analytical data obtained for the change in Fe(VI) concentration, dissolved organic carbon (DOC) and total soluble Zn(II) concentration as a function of time at various concentrations of Zn(II)-NTA and at constant Fe(VI) concentration. The UV-Visible data was used to explain the reaction kinetics for redox reactions between Fe(VI) and Zn(II)-NTA. The pseudo-first-order rate constant was calculated keeping the Zn(II)-NTA concentration in excess and hence the overall second-order-rate constant was obtained. Fe(VI) reduction was almost unaffected with the 1000 times increase in ionic strength (NaNO_3), as well as in the presence of completely oxidized background electrolytes. However, Fe(VI) reduction was greatly affected in the presence of both SO_3~(2-) and NO_2~- especially at higher concentrations, indicating a competitive reduction took place between Zn(II)-NTA and Na_2SO_3 or NaNO_2 in the Fe(VI) treatment. These results were again supported by the dissolved organic carbon observations since relatively very low removal of the dissolved organic carbon occurred in the presence of Na_2SO_3 and NaNO_2.