Addressing sustainability in the aluminum industry: a critical review of life cycle assessments
This article discusses the state of the practice, strength, and weakness of life cycle assessments (LCA) for achieving sustainability goals in the aluminum industry. Notable features of the reviewed LCAs include a limited geographical and life cycle scope and differentiated system boundaries, a common practice to use industry-wide inventory data, a polarized debate on allocation of aluminum recycling, and a predominant focus on energy and greenhouse gas emissions environmental metrics. Not surprisingly, the various studies have produced significantly different results, e.g., the greenhouse gas emissions per kilogram primary aluminum production range from 5.92 to 41.10 kg CO2-equivalent and the 'break-even point' (the point when the fuel economy benefits of the lighter aluminum vehicle offset added emissions from the production stage) of vehicles lightweighting ranges from 50,000 to 250,000 km. These variations relate not only to real world differences (e.g., temporal and geographical characteristics), but also partly to data uncertainties and methodological choices. Particularly, the recyclability, long lifetime, and environmental benefits in the use phase of aluminum pose great challenges for LCA methodology, especially for the allocation of recycling. The identified uncertainties and deficiencies can serve as an important base for further improvement of subsequent LCA applications in the aluminum industry.