Geometallurgical characterisation of non-ferrous historical slag in Tasmania: determining reprocessing options

Pyrometallurgical processing of the ore from the Zeehan ore field was performed intermittently from 1896 to 1948 recovering Pb, Ag and Cu. Zinc recovery was attempted but not possible using the available technology, thus Zn reported to the slag. Today, the former smelter site consists of two large slag piles (North and South). Using a range of mineralogical and geochemical techniques (e.g., XRD, SEM, LA-ICPMS, XRF and static testing) the geometallurgical and geoenvironmental properties of the slag (n = 303) were determined. The South and North piles contain on average 18 % and 12 % Zn respectively. A range of mineral phases have been identified and are dominated by olivines, Fe oxides, sulphides and glass. Microtexturally, the slag is heterogeneous, with five main textural groups identified (euhedral to subhedral/ lath-like to skeletal crystals, bleb inclusions, dendrites, spinifex textures and glass); these vary in scale and abundance and can be further separated based on compositional differences. Zinc is most concentrated in the dendritic textured wurtzite/sphalerite phase (21. 4 wt. % to 59 wt. %) and the glass phase (30.3 wt. % to 33.4 wt. %) and is refractory in both. Zinc is also concentrated in olivine and pyroxene phases but has a much greater range (BDL to 40.8 wt. %; and 11.1 wt. % to 41.3 wt. %) and is also refractory. These slags also contain elevated levels of As, Cd, Co, Cu, Pb and Sb. Geoenvironmental assessments indicate these materials are potentially acid forming thus slag reprocessing, via leaching, may be a feasible management option for this contaminated site.