Utilization of blast furnace sludge for the removal of zinc from steelmaking dusts using microwave heating

Utilization of dusts generated by steelmaking industries prevents the disposal of wastes and enhances the use of secondary raw material. This work aimed to study the simultaneous recycling of steelmaking dust and blast furnace sludge (BFS) by using microwave heating. The possibility of utilizing BFS as a reducing agent to remove zinc from the dusts was studied. Three steelmaking dusts obtained from steel plants in Finland with varying zinc concentrations and zinc-containing phases were studied. Mixtures of the dusts and graphite, bulk BFS, > 250 mu m BFS, and > 125-250 mu m BFS reductants were heated for 20 min at the microwave power of 1100 W. The results indicated that the zinc removal efficiency depends on the amounts of iron oxide and calcium oxide in the mixtures. The highest zinc removal was observed for mixtures with high calcium oxide and low iron oxide contents. Zinc removal of 92.79-96.06% was achieved for mixtures with > 125-250 mu m BFS and > 250 mu m BFS reductants. Therefore, to achieve efficient zinc removal, coarser fractions (> 125 mu m) of BFS should be utilized. Owing to the excellent microwave absorption and high carbon content of the sludge, BFS can be applied effectively in the processing of steelmaking dusts.