Removal of Lead and Zinc from Blast Furnace Sludge Through High Temperature Carbochlorination

Abstract

A new dual kiln processing route has been proposed and investigated for removal of heavy metals from the zinc-rich fraction of blast furnace (BF) sludge and recovery of ferrous materials. The zinc in BF sludge exists both as ZnO and ZnS. The thermodynamic analysis indicates that the carbochlorination of the sludge shows a selective heavy metal removal. Lead can be removed at a temperature below 900°C followed by the zinc removal at higher temperatures, producing an iron-rich clean residue free of heavy metals in the end feasible for recycling back to ironmaking. High temperature carbochlorination experiments have been conducted with designed mini-pellets. The experimental results prove that via the proposed dual kiln route, a valuable zinc-rich fraction and a clean iron-bearing residue can be achieved with addition of iron chloride, leaving a small stream of lead-rich residue for further processing. This newly developed recycling flowsheet provides a sequential carbochlorination in two inter-connected rotary kilns, incorporated with efficient dust-capturing systems. In total, over 98% heavy metal removal has been achieved. The Zn-rich dust contains more than 60% of zinc, and the quality of the iron-rich residue is sufficient for re-use in the integrated steel works.