Remediation of aquatic environment contaminated with the iminodiacetic acid metal complexes using ferrate(VI)

Abstract

The aim of this investigation is to assess the applicability of ferrate(VI) in the treatment of M(II)-complexed species viz., Cd(II)-IDA and Ni(II)-IDA from aqueous solutions. The batch reactor operations are performed for various physico-chemical parametric studies. The batch reactor studies indicate that a fast and efficient decomplexation/removal of Cd(II)/Ni(II)-IDA is occurred at varied molar concentrations (0.3–10.0mmol/L) of the complexed species treated with a constant dose of Fe(VI) (i.e., 1.0mmol/L). Moreover, decreasing the pH values from 10.0 to 8.0 is further favored the decomplexation/degradation of these pollutant species. The time dependence data is utilized further in demonstrating the kinetic studies conducted for various molar ratios of M(II)-IDA to Fe(VI) as studied at different pH values (i.e., pH 10.0–8.0). The kinetic results show that the decomplexation/oxidation of complexed species is followed with pseudo-first and pseudo-second order rate kinetics for both the systems studied. Further, these results indicate that the rate of decomposition is followed with first order rate kinetics for both the reactants i.e., Fe(VI) and M(II)-IDA species. This infers that a 1:1 stoichiometry prevails to the decomposition M(II)-IDA species by Fe(VI). The overall rate constant values indicate that decreasing the pH causes to increase the rate of degradation/decomplexation of M(II)-IDA by Fe(VI). Decomplexation/oxidation of the complexes shows that a significant degradation/oxidation of the IDA occurred since a significant decrease in total organic carbon (TOC) is obtained. Again, lower pH values favor the oxidation/mineralization of IDA. Remarkably, a significant removal of free cadmium or nickel is obtained simultaneously. The removal of metal ions is further enhanced raising the pH of the Fe(VI) treated samples to 12.0 and almost 100% of Cd(II) was removed whereas a significant percent of Ni(II) was also removed. These results indicate that the treatment of aqueous wastes contaminated with M(II)-IDA is efficient and effective by Fe(VI).