Browsing by Author "Dorfling, C."

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    Characterization of precipitate formed during the removal of iron and precious metals from sulphate leach solutions
    (The Southern African Institute of Mining and Metallurgy, 2017-08) Coetzee, R.; Dorfling, C.; Bradshaw, S. M.
    ENGLISH ABSTRACT: Nickel sulphate leach solutions produced in the first leaching stage of base metal refineries contain impurities such as iron as well as precious metals (Rh, Ru, and Ir). Iron precipitation results in sludge formation, which needs to be controlled for efficient operation of downstream nickel recovery processes. Recovery of precious metals from the leach solution is also desired. This study aimed to evaluate the characteristics of the precipitate produced from a nickel sulphate leach solution containing 62.5–89.3 g/L Ni, 2.5 – 3.57 g/L Fe, and 10 mg/L of each of Rh, Ru, and Ir. Seeded precipitation from ferric-containing solutions resulted in precipitates with a d₅₀ particle size of 100.6 μm, which was two orders of magnitude larger than the reference goethite seed d₅₀particle size of 1.3 μm. The particle size distributions of the precipitates formed from ferrous solutions were similar to that of the reference goethite seed. The precipitates formed from ferrous-containing solutions at pH 2.5 and at pH 4 had increased micropore areas (72.8 m²/g and 87.1 m²/g, respectively) and decreased external specific surface areas (53.4 m²/g and 49.0 m²/g, respectively) compared to the goethite reference material (micropore surface area of 66.2 m2/g and external surface area of 64.8 m²/g). For ferric-containing solutions at pH 2.5, a decline in specific surface area from 131.0 m2/g to between 82.0 m²/g and 100.6 m²/g was caused by aggregation and molecular growth inside micropores. Instantaneous iron precipitation from ferric solutions at pH 4 resulted in an increased Brunauer-Emmett-Teller (BET) surface area of 156.5 m²/g due to poor ordering of crystal structure and a more amorphous surface structure. Iron oxide phases present in the precipitates had elemental compositions similar to ferrihydrite and schwertmannite. Sulphate inclusion was more prominent during the rapid precipitation from ferric solutions than during precipitation from ferrous solutions. The precipitate formed at pH 2.5 was overall more crystalline than the precipitate formed at pH 4.0; nickel entrainment also increased with an increase in pH. Rhodium- and rutheniumcontaining species were finely dispersed throughout the iron phases in the precipitates. Iridium precipitated primarily without the inclusion of iron or other precious metals; particles consisting of iridium (50–80 wt%), chloride, and oxygen were formed.
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    Expanding the semantic range to enable meaningful real-world application in chemical engineering
    (HESA, 2019) Dorfling, C.; Wolff, K.; Akdogan, G.
    ENGLISH ABSTRACT: Legitimation Code Theory has proven to be useful in analysing the relationship between theory and practice. Semantic gravity can be used to illustrate teaching and learning processes that move between different levels of abstraction and context-dependency. Effective engineering education entails moving both up and down the semantic range in a way that enables students to apply concepts to contextual practices. However, students seldom engage at the strongest level of semantic gravity. This study investigated the contextualisation of theory in a chemical engineering programme through industrial site visits. Final-year chemical engineering students participated in a voluntary field trip to visit industrial sites. Data obtained through written surveys showed that visits allowed participants to develop a better appreciation for the relevance of taught material to industrial applications and to better understand relationships between different modules and problem solving. Site visits were found to be an effective way of expanding the semantic range.
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    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.
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    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.
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    The recovery of copper from a pregnant sulphuric acid bioleach solution with developmental resin Dow XUS43605
    (Southern African Institute of Mining and Metallurgy, 2013-04) Liebenberg, C. J.; Dorfling, C.; Bradshaw, S. M.; Akdogan, G. A.; Eksteen, J. J.
    ENGLISH ABSTRACT: This paper focuses on the application of ion exchange technology for the recovery of copper from a leach solution originating from a heap bioleach in which base metals are leached from a low-grade ore that bears platinum group metals. Screening tests indicated that Dow XUS43605 has high selectivity for copper over the other metals in the solution, namely nickel, iron, cobalt, zinc, manganese, and aluminium. Batch adsorption kinetic experiments showed that copper adsorption equilibrium is attained at a fast rate. The kinetics of adsorption increased as the temperature was increased from 25°C to 60°C due to the decrease in solution viscosity and the subsequent improved intra-particle mass diffusion. Single-component Langmuir and Freundlich isotherm models were fitted to the batch copper adsorption equilibrium data, and a maximum copper capacity of 26 g/l was observed for Dow XUS43605. The effects of flow rate, temperature, pH, and initial metal concentration on the dynamic recovery of copper were investigated in fixed-bed columns, and it was determined that temperature and flow rate had the most significant impacts on the loading of copper on the resin at copper breakthrough. A 36% increase in copper loading at breakthrough was observed when the temperature was increased from 25°C to 60°C. Finally, it was determined that a split elution is possible by using different concentrations of H2SO4 to first elute co-loaded nickel from the resin, followed by the elution of copper.