Even though a large number of European primary lead-zinc processing plants have closed over the last 20 years, their remains in the form slag heaps are still present. These landfills must not only be seen as a potential hazard for the environment and the population, but also as a future source of metals. In the scope of this thesis, the reprocessing of the lead- and zinc-containing slag from Veles, North Macedonia, is investigated. Using a carbon-saturated iron bath, acting as a carbon carrier for the reduction reactions and as a collector for the iron and copper contained, the proposed process is tested in lab-scale and in technical-scale. Reprocessing the lead- and zinc-containing residue, three different product streams are generated: a zinc oxide-rich flue dust, an iron alloy, and a clean residual slag. The flue dust represents a saleable product that can directly be used in primary zinc production. The residual slag shows a high potential to be accepted as a primary raw material substitute for construction purposes. Due to the enrichment in sulphur, copper and arsenic, the iron alloy generated only shows limited applications for a further use. To describe the principal reaction mechanisms and evaluate the influence of the FeO content and the temperature on the reduction rates, a generally valid kinetic model is developed. This model is validated within reduction trials using a synthetic slag and the industrial slag from Veles. Conducting trials in technical-scale, the prospect of processing landfilled slag in a combined reduction treatment in order to recover valuables and remove harmful compounds is confirmed.