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68 PCB007 MAGAZINE I DECEMBER 2018 Pyrometallurgical Recovery and Refining of PMs Chart 3 shows a generalized diagram of the pyrometallurgical process for PM recovery. This method is ideal for e-scrap with high-lev- els of precious metals, such as the recurring wastes as noted from electronic manufacturing operations. It can also be valuable for recycled electronic components that have been segre- gated for potential residual value such as high chip density circuit boards. Newer combustion processes typically use natural gas, which is cleaner and more cost-ef- fective than other fuels. Pyrolysis greatly reduc- es the volume of non-metallic residue [11] but generates combustion byproducts which must be controlled. Newly constructed facilities and process upgrades typically incorporate more stringent pollution controls to meet govern- ment standards and permitting requirement. Traditional incineration furnaces may oper- ate at temperatures in excess of 2,500°F. These high temperatures contribute to the formation of toxic compounds when processing plas- tics and other organic compounds. Older fur- naces may include a secondary afterburner to achieve more thorough burning of exhaust, but often lack other environmental controls or even basic filtration. Controlled temperature processing and ad- vanced controls can greatly reduce emissions Chart 3: Thermal recovery of PMs.