Utilization of Biomass at the Recycling of Heavy Metal Containing Wastes

Metal production and recycling industries are typically characterized by a high demand on energy. Besides this, in the reduction processes necessary in metallurgy, high amounts of reducing agents are also used in this field of the industry. Normally this high demand on carbon is covered by fossil carbonaceous materials, which results in high amounts of greenhouse gas emissions, which in turn enhance global warming. For that reason, companies are being forced by environmental legislation to reduce their carbon footprint. Therefore, one option would be the substitution of fossil based materials with carbon-neutral alternatives. In order to describe some approaches, two options for the utilization of reducing agents based on biomass in heavy metal recycling processes are described in this paper. For that reason biomasses from agriculture like different tree cuttings were converted into metallurgical charcoal by means of a special carbonization reactor. With these charcoals electric arc furnace dust (EAFD) was reduced and recycled in a lab-scale rotary kiln. Furthermore, the by-product of the carbonization process-the pyrolysis gas-was used for the treatment of Waelz slag in a retort process. In both cases, nearly the entire zinc contained in the residue (EAFD and Waelz slag) could be recovered by means of alternative reducing agents. In the retort process also the iron in the remaining slag could be highly metalized. With such a replacement of fossil materials, the CO2 emissions from current dirty industry sectors such as heavy metal recycling can be dramatically reduced. This could lead special industries to be pioneers in matters of environmental protection.