Pollution prevention in a zinc die casting company: a 10-year case study

In this project, pollution prevention methodologies were applied to a mass finishing process used for the cleaning and polishing of miniature zinc die-casts. While the original project objective had been to rely on the use of acids and filtration methods (cartridge and membrane) to minimize waste discharges, development testing and improvement data obtained throughout the year-long project indicated that acid use and cartridge filtration were no longer required; pH levels were found to be the key to simplifying the entire operation. Pollution prevention was achieved through (1) the elimination of mineral spirits to preclean parts; (2) the elimination of hydrochloric acid used to settle and remove sludge; (3) the elimination of a 100,000 l/month sewer discharge of metal-bearing wastewater; (4) the recovery of zinc metal for off-site recycling; and (5) the recycling of an aqueous-based soap. Favorable economic payback and reduced liabilities were also realized while product rejection rates decreased. The company has been using the process for 10 years.