THE WAELZ PROCESS: STATE OF THE ART AND INNOVATION TO DECREASE THE ENVIRONMENTAL IMPACT

Pontenossa S.p.A. recovers zinc oxide from Electric Arc Furnace Dusts (EAFD) through the Waelz Process. EAFD are classified as hazardous wastes, the Waelz process is notified in the BREF notes as the BAT for EAFD treatment. The EAFD are fed into a rotary kiln with coal and lime. Zinc and lead are reduced, volatilized, re-oxidized and then recovered from the gas flow through a filtration system. The product obtained is indicated as the Waelz oxide. The rest of the feed is discharged at the end of the kiln as Waelz slag. This slag is classified as hazardous waste and, currently, must be disposed in a landfill. Pontenossa has built a pilot plant to test a pyrometallurgical process to transform the slag into an inert material. The test has given positive results and the process has been patented. Moreover, Pontenossa continuously improves its plant to reduce its environmental impact. In 2015 Pontenossa has installed a new plant to reduce NO x emissions and in 2016 has completely revamped the RTO (regenerative thermal oxidizer) system for the abatement of CO and organic compounds. Nowadays, Pontenossa is building a plant to mix and pelletize EAF dusts, coal and lime before feeding the kiln. This new plant will provide a reduction of diffuse emissions and an increasing of the extraction yield of the kiln.