Zinc casting and recycling

Abstract

Aim, Scope and Background. Metal die casting is a highly energy-intensive industry. In addition to that, the production of primary zinc by smelting consumes huge amounts of energy as well as generates many types of pollution. This paper uses LCA to investigate the environmental performance of a zinc cast product. The areas of environmental concern are focused on the direct and indirect air emissions that arise from the Zinc Smelting, Casting and Recycling, as well as transportation. Main Features. The LCA case study employs a cradle-to-gate approach, which starts with the purchasing of primary zinc from abroad, casting, inspection, and ends when the scrap metal is sent back for recycling by truck. Based on a 'generic' zinc casting product, the objective of the LCA was to compare the air emissions from the material cycle due to: i) the increased content of recycled metal in the final cast product; and ii) the choice of selecting between two Remelters (A and B), the first located near the company and the other in a neighbouring country, to send zinc scrap for recycling. The LCA SimaPro software (version 5.0) Eco-indicator '99 method is used to perform an impact assessment for Climate Change, Acidification, Ecotoxicity, Respiratory Inorganics, and Respiratory Organics was performed. Results. The results from direct (process) and indirect (power plants) air emissions confirmed that the major air pollution occurs during Zinc Smelting, that is up to approximately 65-70%. Although an increase in recycling rates resulted in higher levels of air pollution from transportation as well as heavy metals from dross, these two issues were insignificant compared to the huge amount of energy consumed for primary metal production. Based on air pollution from transportation alone, a significant reduction of greenhouse gases and VOCs of 90% each was appreciated when Remelter A was selected. Conclusion. The results verified that efforts to recycle zinc and consume the material in a more sustainable manner have become highly important. Also, a second LCA investigation that was made to compare zinc cast products that consists of: 100% primary zinc, mixtures of 50-50% and 40-60% primary-to-recycled zinc, and finally 100% recycled zinc; further emphasized the need for using recycled metal, as opposed to using primary metal. © 2005 ecomed publishers (Verlagsgruppe Hüthig Jehle Rehm GmbH).