A mineralogical study of the reductive roasting of zinc ferrite residues: A potential zinc recycling technology : Special issue on recycling and high performance waste processing

A stockpiled zinc ferrite residue from Noranda Inc., CEZinc consists mostly of ZnFe 2 O 4 and Fe 2 O 3 , together with trace amounts of a number of other phases including Mn-bearing oxides and Sr sulphate. Reductive roasting of the zinc ferrite residue for 2 h at 800°C resulted in the extensive conversion of the ZnFe 2 O 4 to (Fe, Zn)O and ZnO; the (Fe, Zn)O phase contains about 16 mass%Zn. The particle sizes and shapes after reductive roasting are similar to those in the unroasted feed, but the roasted material may be slightly more porous. The copper impurity in the ferrite residue is reduced to an Ag-bearing copper alloy which occurs as inclusions along the grain boundaries of the (Fe, Zn)O phase. Some of the Sr sulphate present in the zinc ferrite residue is reduced to a Zn-Fe-Sr sulphide phase, and all of the initially present Fe 2 O 3 is reduced to (Fe, Zn)O. Reductive roasting converts the zinc ferrite residue into species which are soluble in dilute acid or alkaline media, thereby allowing the potential recycling of the Zn, Cu and Ag values.