Implementation of an eco-innovative separation process for a cleaner chromium passivation in the galvanic industry

This paper reports the development and implementation of the eco-innovative process Emulsion Pertraction Technology (EPT) for the selective separation of zinc and iron impurities from used trivalent chromium passivation baths. The main goal was to purify the passivating formulations in order to extend their lifetime. Commercial hollow fibre membrane modules were used to provide the non-dispersive contact between the passivation bath and the emulsion extractant phase. Two passivation baths employed at two industrial facilities with initial concentration of metals in the range 3000 < [Cr](0) < 7000 mg/L, 11,000 <[Zn](0) < 20,500 mg/L and 15 < [Fe](0) < 100 mg/L were first analysed at a bench scale EPT system using a contactor with a membrane area of 1.4 m(2). The results showed that the effectiveness of EPT was enhanced by the countercurrent operational mode and high flow rates of the emulsion and passivation phases. The performance of the technology for purifying different commercial formulations of chromium (III) baths was proved to be comparable. The best experimental conditions resulted in a decrease of the feed concentration of Zn and Fe of 95% and 98%, respectively, and in a stripping solution enriched in Zn and Fe: 160,000 mg/L of Zn and 49 mg/L of Fe. The process scale-up was evaluated at industrial scale using an EPT unit with a membrane area of 40 m(2). The mass transfer flux of Zn was 4.5 g/m(2)h, while the flux of Fe was 0.025 g/m(2)h. These values can be used as reference for the scale-up of the process. This work concludes that the implementation at industrial scale indicated the great prospects of EPT on applications in the surface treatment sector. Zinc recovery by electrowinning is recommended. (C) 2013 Elsevier Ltd. All rights reserved.