Hydrometallurgical extraction of zinc and copper - A ⁵⁷Fe- Mössbauer and XRD approach

The most commonly used route in the hydrometallurgical extraction of zinc and copper from a sulphide ore is the concentrate-roast-leach-electro winning process. In the present investigation a zinc-copper ore from the Maranda mine, located in the Murchison Greenstone Belt, South Africa, containing sphalerite (ZnS) and chalcopyrite (CuFeS₂), was studied. The ⁵⁷Fe-Mössbauer spectrum of the concentrate yielded pyrite, chalcopyrite and clinochlore, consistent with XRD data. Optimal roasting conditions were found to be 900°C for 3 h and the calcine produced contained according to X-ray diffractometry equal amounts of franklinite (ZnFe ₂O₄) and zinc oxide (ZnO) and half the amount of willemite (Zn₂SiO₄). The Mössbauer spectrum showed predominantly franklinite (59%), hematite (6%) and other Zn- or Cu-depleted ferrites (35%). The latter could not be detected by XRD analyses as peak overlapping with other species occurred. Leaching was done with HCl, H ₂SO₄ and HNO₃, to determine which process would result in maximum recovery of Zn and Cu. More than 80% of both were recovered by using either one of the three techniques. From the residue of the leaching, the Fe-compounds were precipitated and <1% of the Zn and Cu was not recovered.