Blast Furnace sludge accumulates during production of pig iron which is an intermediate product in iron industry. During production of pig iron in large blast furnaces a preheated air flow is introduced into the lower part of the furnace. The air that leaves the furnace at the top is a dusty gas flow, which may contain N2, CO2, CO and H2 as well as high amounts of fine solids (dust). The material is first dry cleaned and subsequently washed so that a wet, muddy waste is generated, the so-called blast furnace sludge. Generally the material consists of iron ores, metallurgical coke and flux and is enriched in elements like Na, K, and Zn (Mansfeldt and Dohrmann, 2004).