Browsing by Subject "Leaching"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Open Access
    The batch and continuous bacterial leaching kinetics of a refractory gold-bearing pyrite concentrate
    (1989) Chapman, J T; Hansford, Geoffrey Spearing
    The recent focus on bacterial leaching as a preoxidation step in the treatment of refractory gold bearing sulphide ores and concentrates, has created the need for kinetic models to adequately describe bacterial leaching reactor performance. This work is a kinetic study of the bacterial leaching of a refractory gold bearing, pyrite concentrate. The study includes the presentation of two mechanistically based, the shrinking particle and propagating pore (Hansford and Drossou, 1986), batch reactor kinetic models. These models are derived for single stage continuous reactor description. In addition, the empirical logistic growth model (Pinches et al., 1987) is presented for both batch and continuous reactor description. The models are correlated with the experimental data. Three narrow size fractions of the pyrite concentrate were subjected to batch and continuous bacterial oxidation, using a Thiobacillus ferrooxidans culture. Time profile data of the pyrite oxidation were obtained for the batch reactor study. Similarly, retention time profile data of pyrite oxidation was obtained for the single stage continuous reactor. The .gold extraction as a function of sulphide oxidation as well as fraction arsenic leached, was established.
  • Thumbnail Image
    Item
    Restricted
    Determination of oxygen gas-liquid mass transfer rates in heap bioleach reactors
    (Elsevier, 2010) Petersen, J
    A detailed experimental study is described which was conducted to determine the rate of oxygen gas–liquid mass transfer within the packed bed of heap bioleach reactors at different temperatures (22–68 °C), using the Na2SO3 method. The raw data was analysed using a simplified film mass transfer model, making corrections for oxygen solubility in concentrated solution and for increased water vapour partial pressure at elevated temperatures. The results compared favourably against two independent experimental leach studies, indicating kLa values between 33 and 46 h−1. The value varied with the particle size distribution of the packing, with kLa assuming larger values for those packings that had a higher fines contents. While kLa increases with temperature, the solubility of oxygen decreases simultaneously, resulting in net mass transfer rates being relatively unaffected by temperature in the range studied. This indicates that thermophile heap bioleach reactors are likely to operate under gas–liquid mass transfer limitations, especially at high altitude.
  • Thumbnail Image
    Item
    Restricted
    The influence of applied potentials and temperature on the electrochemical response of Chalcopyrite in Bacterial Leaching
    (Elsevier, 2002) Tshilombo, A F; Petersen, J; Dixon, D G
    Electrochemical techniques were conducted to clarify the role of solution potential and temperature under a variety of experimental conditions similar to those found during the mesophilic and thermophilic biooxidation of chalcopyrite (CuFeS2). Despite a large number of publications dealing with the bacterial leaching of CuFeS2, three central aspects remain unclear: How to dissolve preferentially copper from CuFeS2, the effect of temperature on the extent of CuFeS2 passivation, and the behavior of ferric ions on a polarized CuFeS2 surface. Anodic characteristics showed that CuFeS2 passivation was more severe in the potential range 0.45–0.65 V saturated calomel electrode at 25 C. However, there was no evidence of CuFeS2 passivation at higher temperatures (45 and 65 C). Cu was preferentially dissolved from CuFeS2 at lower potentials and high temperatures at a ratio copper to iron of about 3:2. Cathodic characteristics showed that the ferric ions inhibited the leaching process when the CuFeS2 surface was polarized at high potentials and low temperatures.
  • Thumbnail Image
    Item
    Open Access
    Thermophilic Heap Leaching of a Chalcopyrite Concentrate
    (Elsevier, 2002) Petersen, J; Dixon, D G
    Thermophiles have been shown to be the only micro-organisms to leach chalcopyrite successfully. Heap leaching may be a feasible alternative to conventional bio-reactors, providing a high temperature environment can be maintained within the heap without external heating. In the present study thermophilic heap leaching of a chalcopyrite concentrate coated onto inert support rocks (the GEOCOAT™ process) was studied in sets of small heated columns. The temperature was gradually increased to 70 °C, while successively introducing various mesophile and thermophile cultures. Individual columns were dismantled after progressively longer leach periods and the residual concentrates analysed. Copper extractions in excess of 90% were achieved within 100 days. On the basis of head and residue analyses the rate of reaction heat generated was calculated. A comprehensive heap heat conservation model was used to determine whether the experimental temperatures can be achieved and maintained in a full scale heap. Results indicate that operating hot heaps successfully is possible within a certain range of process parameters.