Voltammetric evaluation of binding abilities of tannery effluents by competing ligand exchange method using model solutions of Cr(VI), Ni(II), Cu(II) and Pb(II)

Metal complexation capacity (CC) is an important parameter in assessing the quality of wastewaters. In this study, CC and complexation kinetics of tannery wastewater was evaluated using the competing ligand exchange approach with model solutions of Cr(VI), Ni(II), Cu(II) and Pb(II). Ethylenediaminete-traactic acid (EDTA) was used as competing ligand in complexation studies of Cu and Pb while dimethylglyoxime (DMG) and diethylenetriaminepentaacetic acid (DTPA) were used in the case of Ni and Cr, respectively. Determination of labile metal fraction was done using differential pulse anodic stripping voltammetry (DPASV) (Cu and Pb) and differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) (Ni and Cr) at a hanging mercury drop electrode (HMDE). Flame atomic absorption spectrophotometry (FAAS) was used to determine total and dissolved chromium in the tannery wastewater samples. Results show high complexation capacities (9.03–436.81 μM) and fast kinetics of the tannery effluent, with most of the inert metal species being formed within the first two minutes. The kinetic curves for all the metals showed two kinetically distinguishable components, except for nickel which had an extra component. Speciation results revealed that less than 3% of the chromium in the wastewater was present in the dissolved phase, while no labile forms were detected. The study has demonstrated the role of CC of wastewater in metal speciation and environmental remediation.