Complexing capacity of electroplating rinsing baths?a twist to the resolution of two ligand families of similar strength

GRISELDA L. SOSA; SILVANA RAMIREZ; ANITA ZALTS

Journal of Analytical Science and Technology

Springer

Año: 2016

2093-3371

AbstractBackground: The presence of ligands affects metal behavior when removing metals from wastewaters. So far, mostof the attention has been paid to strong ligands; however, experimental observations indicate that also weakercomplexing agents may play a key role in the availability of metals in waters and in the success of the treatment tobe applied. In particular, we have analyzed wastewaters of an electroplating facility during an 8-h workday. Totalmetal content (copper, zinc, cadmium, and lead) was determined; ligands were characterized by concentration (Lt)and strength (conditional stability constant, K´f). This work focuses on ligands of moderate strength which, as far aswe know, have been overlooked in the literature.Methods: A two-moderate-ligand system was used to mimic the wastewaters. N-(2-hydroxyethyl)iminodiacetic acidand nitrilotriacetic acid were used as model ligands. Electrochemical titration data (obtained by square wave anodicstripping voltammetry) were analyzed combining the Scatchard linearization method with a standard non-linearcurve fitting function to focus on the resolution of two ligand families of similar strength. Correctness was testedboth for the analytical procedure and data analysis.Results: Most significant changes in metal concentration were related to zinc and lead that increased along theworkday. Copper and cadmium contents were negligible. The model system and wastewater samples were successfullycharacterized by this methodology. Two ligand families of constants K´f1 (4.07 ± 0.69 )× 106 and K´f2 (5.56 ± 0.78) × 105were discriminated in the micromolar range using zinc in the titration of the wastewater sample.Conclusions: A combined strategy involving electrochemical techniques, the Scatchard linearization, and a non-linearcurve fitting function was successfully applied to the model system, within experimental error. Our main goal was tocharacterize two moderate ligand families of similar strength in the wastewater samples by means of the same strategy,a task that so far has not been described. The combined strategy used in this particular case may be of interest fordifferent environmental matrixes.Keywords: Complexing capacity, Moderate ligands, Electroplating bath, Zinc, Cadmium