No. 382: Collecting zinc from plating wastes for recycling (December 16, 2011)

JFE Engineering will start the business to recycle zinc contained in the acid waste fluid from hot-dip galvanization plants next April. Its subsidiary, JFE Kankyo, developed and established a technology to separate zinc and iron from waste acid fluid produced in the plating process. The subsidiary will buy waste fluid from plating plants and sell collected zinc to zinc smelting companies. Acid waste fluid used to rinse metals before plating contains 5-15% zinc and 5-10% iron. It is currently neutralized by alkaline fluid and dehydrated, and subsequently buried as a solid mixed with zinc and iron because it is hard to separate iron and zinc from the acid waste fluid. About 900 tons of zinc is discarded in the East Japan area alone.

The company focused on the difference of deposition conditions between zinc and iron depending on the concentration of hydrogen ion, and developed a processing system by controlling the concentration of hydrogen ion. Alkaline fluid is put in the reaction tank of waste fluid to increase the pH from less than one to five that is suitable for the oxidation of iron. Subsequently, air is instilled into the fluid tank to oxygenate the iron ion, and the oxygenated iron ion is extracted as a solid. Subsequently alkaline fluid is put into the iron-free waste tank, and solid zinc is collected through dehydration. It takes 12-24 hours to collect zinc, and the concentration of zinc is higher than 50%. The company plans to process 1,700 tons of acid waste fluid of this kind in 2012. The cost of processing is expected to be lower than the cost required for landfill disposal.