Abstract: A process for purifying waste gases from smelting, resmelting or combustion plant furnaces and the use of the filter dusts produced. The invention is used in particular in the production or preparation of nonferrous metals. According to the invention, at least one alkali compound, in particular NaHCO.sub.3, is injected dry, optionally in the presence of activated carbon and/or open hearth coke, into the waste gas leaving the production process. The separated filter dust is fed back to the smelting or combustion process. It has unexpectedly been found that the returned filter dust can lower the dioxin and furan contents of the crude gas. Owing to the composition of the filter dust, it can also be used as protective salt in secondary aluminum production.