Browsing by Author "Lottering, C."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Investigation of secondary zinc oxides as an alternative feed to the Skorpion Zinc process : Part 1 — leaching alternative zinc oxides
    (Southern African Institute of Mining and Metallurgy, 2018) Lottering, C.; Dorfling, C.
    ENGLISH ABSTRACT: Skorpion Zinc processes zinc oxide ore using a sulphuric acid leaching, solvent extraction, and electrowinning process to produce Special High Grade zinc. The company investigated the possibility of supplementing ore with alternative zinc oxide sources to extend the life of mine and maximize zinc production. In part 1 of this two-part communication we report on experimental investigations to assess the technical feasibility of recovering zinc from electric arc furnace (EAF) dust, zinc dross, and zinc fume under the current Skorpion Zinc leaching conditions. The metal dissolution and acid consumption were determined at temperatures between 40 and 70°C and pH values between 1.2 and 2.1 for slurries containing 20% solids. With the current Skorpion Zinc operating conditions of 50°C and pH 1.8, zinc dissolution from the EAF dust, zinc dross, and zinc fume was 93, 96.9, and 98.5 %, respectively. The rate of zinc leaching from dross and from zinc fume decreased as the pH was increased to 1.5 and 1.8, respectively. The rate-determining step for zinc leaching from zinc dross gradually changed with an increase in pH from porous layer mass transport to chemical reaction and/or boundary layer mass transport. In the case of EAF dust, increasing the temperature to 70°C significantly reduced the zinc leaching rate due to the precipitation of calcium sulphate, which inhibited the zinc leaching reactions. The overall acid consumptions for all three alternative oxides investigated were below the current target consumption of 1.5 t acid per ton of Zn in the feed. It would be technically feasible to use EAF dust, zinc dross, and/or zinc fume as supplementary feed to the Skorpion Zinc process.
  • Thumbnail Image
    Item
    Investigation of secondary zinc oxides as an alternative feed to the Skorpion Zinc process : Part 2 - process considerations and economic analysis
    (Southern African Institute of Mining and Metallurgy, 2018) Lottering, C.; Dorfling, C.
    ENGLISH ABSTRACT: Skorpion Zinc is investigating the possibility of using secondary zinc oxides as an alternative feed to supplement the zinc oxide ore feed and to extend the life of mine. Part 1 of this communication provides the technical background on the leaching performance at the typical Skorpion Zinc operating conditions. This study reports on the process modelling and economic analysis that were performed to determine appropriate feed blending strategies for electric arc furnace (EAF) dust, zinc dross, and zinc fume dust based on process limitations and economic considerations. The zinc fume dust had the highest zinc and lowest impurity content of the alternative oxide sources investigated; as a result, this alternative source resulted in the highest zinc production and profitability. At a blending ratio of 50% zinc fume in the solids feed, more than three times the current zinc production from ore could theoretically be achieved. Production from the zinc dross samples was limited by the amount of contained nickel; the maximum production was achieved at a blending ratio of 10% and was 20% higher than the current production from ore. Zinc production from EAF dust was very low at blending ratios exceeding 30%, due to Mg and Mn impurity limitations as well as the relatively low zinc content. Both zinc dross and EAF dust can also be processed economically to yield profit for Skorpion Zinc and the alternative oxide suppliers. Zinc dross was generally more profitable to process than EAF dust, despite its higher freight costs.