Volatilisation of major, minor, and trace elements during thermal processing of fly ashes from waste- and wood-fired power plants in oxidising and reducing gas atmospheres. (1st February 2020)

• Record Type: Journal Article
• Authors: Lane, Daniel J.; Sippula, Olli; Koponen, Hanna; Heimonen, Mikko; Peräniemi, Sirpa; Lähde, Anna; Kinnunen, Niko M.; Nivajärvi, Taina; Shurpali, Narasinha; Jokiniemi, Jorma
• Is Part Of: Waste management. Volume 102(2020)
• Page Start: 698
• Page End: 709
• Publication Date: 2020-02-01
• Subjects: Fly ash -- Thermal treatment -- Waste-to-energy -- Volatility -- Reducing gas -- Wood-combustion ash; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2019.11.025
• Languages: English
• ISSNs: 0956-053X

Abstract

Highlights: Impact of atmosphere varied greatly depending on fly ash type and temperature. Low release of heavy metals from wood combustion fly ash in an oxidising atmosphere. Several impurities, including Cl, have high volatilities in both atmospheres. Zn, Sn, Sb, and Bi were significantly more volatile in the reducing atmosphere. These elements were selectively volatilised in a two-step thermal process. Abstract: This study assesses the volatility of 15 elements (As, Bi, C, Cd, Cl, Cu, K, Mn, Na, P, Pb, S, Sb, Sn, and Zn) during thermal processing of fly ashes obtained from four waste-to-energy plants and one wood-combustion plant. Differences in volatility in oxidising and reducing atmospheres (air and 10% H2 /90% N2 ) were assessed at two temperatures, 700 and 1000 °C. P and Mn were predominately retained in all ashes regardless of the operating atmosphere and temperature. Other elements showed significant variation in volatility depending on the type of fly ash, atmosphere, and temperature. Heat-treatment of the wood-combustion fly ash in the air atmosphere resulted in low release of K, Na, and all investigated heavy metals and metalloids. Several valuable elements, including Zn, Sb, Sn, and Bi, were significantly more volatile in the reducing atmosphere than in the oxidising atmosphere, particularly at 1000 °C. Other elements were either less volatile, equally volatile, or only marginally more volatile when the ashes were heated at 1000 °C in the reducing atmosphere. These elements include C, Cl, Cu, and, in the case of fly ashes derived from municipal solid waste, Cd and Pb. A two-step process, in which municipal solid waste incineration fly ash is first heated in an oxidising atmosphere and then in a reducing atmosphere, is proposed for production of a chloride-free zinc concentrate. Evaluation of the two-step process at 880 °C shows good potential for selective volatilisation of Zn with other valuable elements, including Sn, Sb, and Bi.