Improvement of the electrochemical behaviour of Zn-electroplated steel using regenerated Cr (III) passivation baths

• Published in: Chemical engineering science Vol. 111; pp. 402 - 409
• Main Authors: García-Antón, J., Fernández-Domene, R.M., Sánchez-Tovar, R., Escrivà-Cerdán, C., Leiva-García, R., García, V., Urtiaga, A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 24.05.2014
• Subjects: Chemical engineering; Chromium; Conversion coating; Emulsion Pertraction Technology; Iron; Liquid wastes; Passivation; Passivation baths; Steels; Trivalent chromium; Zinc; Zn-electroplated steel; Zn-electroplated steel; Passivation baths; Emulsion Pertraction Technology; Trivalent chromium
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2014.03.005

Conversion coatings based on trivalent chromium are more sensitive to the presence of zinc and iron impurities than the chromate formulations. This fact contributes to a decrease in the quality of passivation and to the generation of a significant amount of hazardous liquid waste. Recently, a new eco-innovative process based on Emulsion Pertraction Technology (EPT) is being implemented at industrial scale for selectively removing Zn and Fe from spent passivation baths in order to enhance the lifetime of the Cr (III) baths. In this study, the effect of Zn and Fe removal on the electrochemical behaviour of Zn-electroplated steel samples was evaluated by means of polarisation curves and electrochemical impedance spectroscopy measurements at open circuit potential conditions in 3.5g/L NaCl solutions. The main objective was to assess the benefits brought by EPT using electrochemical methods. Cr (III) passivation baths regenerated using the EPT process have been compared to the bath used in a local industry as well as to fresh and spent baths. According to the results, the samples passivated in the EPT regenerated bath showed a significant improvement in their electrochemical behaviour compared to the samples passivated in the spent baths. This study concluded the suitability of EPT for regenerating Cr (III) passivation baths. •Emulsion Pertraction Technology (EPT) separates Zn and Fe from Cr (III) baths.•EPT step coupled to the passivation bath reduces the Zn and Fe impurities.•After using EPT the samples presented higher values of polarization resistance.•The EPT step improves the protective properties of the electroplated steels layers.