During the production of pig iron in a blast furnace, a Zn- and Pb-containing sludge is generated in the air pollution control system. This toxic waste can be landfilled after dewatering and pretreatment, which is very costly. The sludge particles contain large amounts of Fe and C that could be recycled in the furnace. However, the Zn content of the sludge is high, and the Zn input to the blast furnace must be limited, so Zn has to be removed. This paper describes a hydrometallurgical process whereby the sludge is leached under both acid (HCl) and oxidizing conditions. After the separation of the solids, which mainly contain C and Fe, from the leaching solution, the latter is passed through an anion exchanger to remove Zn and Pb and is recirculated to the reactor. Investigation of the leaching behavior showed that a pH below 1.5 and a redox potential above 650 mV are required to obtain high leaching efficiencies for Zn and Pb. Sequential extraction showed that the largest part of Zn and Ph is extracted in acid medium, whereas an additional 16-18% is extracted in oxidizing acid medium. XRD analysis showed that after acid leaching, Zn partially occurs as sfalerite and as Franklinite. Comparison of the leaching behavior of the sludge with that of sfalerite and Franklinite geochemical standards confirmed this and showed that sfalerite dissolves in acid oxidizing conditions, whereas the Franklinite does not. Calculations with the geochemical speciation program MINTEQA2 were compared with experimental results, and the process developed was tested in a pilot plant.