Environmental Sustainability Assessment of an Innovative Cr (III) Passivation Process Veró nica García,* María Margallo, Rube ́ n Aldaco, Ane Urtiaga, and Angel Irabien Departamento de Ingeniería Química y Química Inorga ́ nica, Universidad de Cantabria, Av de los Castros, s/n., 39005, Santander, Cantabria, Spain * S Supporting Information ABSTRACT: A life cycle assessment was conducted for the Zn-electroplating products passivated by different processes in a small and medium enterprise. The goal was to evaluate and to compare the environmental impact associated to the conventional and alternative passivation process from a “cradle to grave” analysis. The assessment was divided into “cradle to gate”, “gate to gate”, and “gate to grave” steps for natural resources usage and environmental burdens. The innovative process was based on the integration of emulsion pertraction technology to the passivation bath in order to extend its lifetime. Results showed that the transferred hazardous waste from the process to the landfill was the major contributor to the environmental impact of the conventional and innovative passivation. The manufacture of the sodium hydroxide needed in the wastewater treatment process had a main role in the impacts of the “cradle to gate” cycle. This work concluded that the innovative passivation decreased most of the generated waste (92%) during the manufacture cycle of the passivated product as a consequence of the extension of the lifetime of the passivation bath. A reduction of the total environmental burdens to air and to water and the resource usage during the whole manufacture cycle of the product was stated. The environmental burdens to air and to water were mainly connected to the environmental impacts: human health effects and ecotoxicity to aquatic life, respectively. KEYWORDS: Life cycle assessment, Chromium (III) passivation, Emulsion pertraction technology, Hazardous waste minimization, Material recovery ■ INTRODUCTION Trivalent chromium(III) baths are commonly used in the passivation or conversion of zinc-electroplated surfaces. The main aim of these formulations is to provide the surface with an extra protective film against corrosion and/or a decorative finishing. The immersion of electroplated pieces during the passivation step causes the release of Zn (II) and iron (III) to the bath, while a layer of chromium salts covers the metallic piece. The Zn (II) and Fe (III) contamination negatively affects the effectiveness of the Cr (III) formulation reducing its lifetime. The bath is replaced when it does not fulfill its purpose, and it is managed as a hazardous waste due to its high content of heavy metals and nitrates. The effluent is commonly treated by means of physical- chemical processes that consume high amounts of chemicals and generate considerable quantities of metallic sludge. 1 Diban et al. estimated that the amount of sludge generated in the treatment of a passivation bath was 1240 kg per m 3 of spent formulation. 2 Consequently, the traditional passivation implies an inefficient use of resources and materials and exhibits an important environmental impact. The in situ removal of Zn (II) and Fe (III) impurities from the Cr (III) bath during the passivation is essential in order to avoid the loss of efficiency, reduce waste, and promote the resource efficiency of the process. Emulsion pertraction technology (EPT) enables the separation of Zn (II) and Fe (III) in acidic media while maintaining the concentration of Cr (III) constant. 3-5 EPT is a liquid-liquid extraction technology in which the extraction and back-extraction are conducted in a single membrane contactor. The membrane contactor consists of hollow fiber membranes that are microporous and hydrophobic, allowing the nondispersive contact between the passivation fluid and extractant phase. In EPT (Figure 1), the solution containing the targeted heavy metals is circulated through the shell side of the membrane module while an emulsion is circulated through the inside of the hollow fibers. The emulsion is formed by the dispersion of a stripping acid into an organic extractant phase. The pores of the fiber are filled with the extractant because of the hydrophobic character of the membrane material. 7 The fact that the target components are extracted while others remain in the solution is based on the selection of the operational variables (pH) and the extractant. 4 Added advantages are its flexible and compact design. The main benefit of passivating the Zn-electroplated piece by the integrated EPT passivation process is that the lifetime of the chemical formulation is extended. The need for bath replacement diminishes; hence, the environmental impact of Received: November 6, 2012 Revised: March 7, 2013 Published: March 18, 2013 Research Article pubs.acs.org/journal/ascecg © 2013 American Chemical Society 481 dx.doi.org/10.1021/sc3001355 | ACS Sustainable Chem. Eng. 2013, 1, 481-487