Recovery of valuable materials from fine industrial waste streams

Abstract

The recycling of metals from waste streams is important since natural resources could be conserved by recovering metals from secondary sources. Moreover, environmental problems due to the waste disposal also could be alleviated by removing volatile and toxic materials from the wastes. In general, high-temperature materials processing generated off-gases contain a large amount of dust. Therefore, dust collection systems, such as baghouse and cyclones, are usually installed in these facilities to control the emission of air pollutants. Dust collected from various facilities usually contains some metal values; however, most fine wastes are landfilled currently. In this study, recovery of valuable metals from fine wastes is investigated by hydrometallurgical and pyrometallurgical processes from bottom ash from the municipal solid waste incinerator (MSWI), fly ashes from coal/oil fired power station, light fluff from end-of-life vehicle shredder, and baghouse dust from the secondary aluminum smelter and steel foundry. The elemental and mineralogical compositions of wastes are different depending on the industry where they come from. Therefore, these waste streams are initially analyzed by the inductively coupled plasma atomic emission spectroscopy (ICP-AES). Several wastes, which contain a relatively large amount of aluminum, silicon, calcium, and iron, could be used as a source of construction material since these elements are the major components of concrete. On the other hand, oil fly ash and aluminum smelter baghouse dust show a high concentration of vanadium and aluminum, respectively. For these reasons, this study mainly focuses on the recovery of vanadium and aluminum from these waste streams by hydrometallurgical and pyrometallurgical processes. In this research, aluminum smelter baghouse dust is treated by alkaline leaching followed by Al(OH)3 precipitation to extract aluminum selectively, and vanadium extraction from oil fly ash is investigated by salt-roasting followed by hot water leaching. Thermodynamic and kinetic modeling of the results also has been studied for a deeper understanding of experimental phenomena.