Zinc recovery from blast furnace flue dust

Abstract

Blast furnace flue dusts are a mixture of oxides expelled from the top of the blast furnace, whose major components are iron oxides. They also contain zinc, silicon, magnesium and other minor element oxides in lesser amounts. The direct recycling of flue dust is not usually possible since it contains some undesirable elements (zinc and alkaline metals) that can cause operational difficulties in the blast furnace. Furthermore, in some cases the dust contains toxic elements (zinc, cadmium, chromium and arsenic) that make it hazardous and unacceptable for landfill. The fact that it is not possible to recycle this dust directly or to reject it as landfill, makes it necessary to consider the recovery of the valuable elements contained in it and to obtain a non-hazardous residue that can be stored without problem or can be used in agglomeration units in iron-making industries. To reach this objective a sequence of unit operations which consists of leaching, filtration, purification, extraction, stripping and electrolysis processes is required. In this research a blast furnace flue dust which principally consists of iron, with some zinc and other elements oxides has been examined. The preliminary results show that it is possible to leach selectively the valuable elements of the dust by sulphuric acid at low acid concentration and room temperature, giving high recovery using zinc (about 80%). The pregnant solution obtained is subjected to purification and extraction for eliminating its contaminants, and increasing its zinc concentration before electrowinning the zinc.