A new roasting process slated for commercialization

Outotec Oyj (Espoo, Finland; www.outotec.com) has introduced a new partial roasting process to purify copper and gold concentrates that are contaminated with arsenic, antimony and carbon. The process is a pretreatment stage for Cu- and Au-extraction plants, and enables the extraction of metals from ores that had previously been unattractive because the impurities create a “huge problem” of handling dust laden with As and other intermediate products formed in conventional Cu or Au smelters, says Lars Hedstrom, head of Outotec’s Roasting Competence Center in Skelleftea, Sweden. In the new process (flowsheet), ore concentrate is fed to the top of a fluidized-bed roaster. Preheated air is added through a large numbers of tuyeres at the furnace bottom. The air acts as fluidization media and supplies oxygen to the roasting reactions. Heat is generated by exothermic combustion reactions whereby iron sulfide in the concentrate is oxidized to magnetite and a SO2-rich process gas. Impurities, such as As and Sb, are vaporized at the high reaction temperature, and thus removed from the solid calcine that contains the valuable metals (normally Cu, Au and Ag). Most of the calcine is pneumatically transported out from the roaster…