Browsing by Subject "Oxidation"

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    Biooxidation of a gold bearing arsenopyrite/pyrite concentrate
    (1990) Miller, D M; Hansford, Geoffrey Spearing
    The objectives of this project have been to characterise the biooxidation of an auriferous pyrite/arsenopyrite flotation concentrate, and to interpret laboratory batch and continuous pilot plant data in the light of the logistic model. Furthermore, the possibility of predicting continuous biooxidation plant performance from batch data was considered. The batch testing was carried out on five narrowly sized fractions of Fairview concentrate, as well as on the bulk concentrate. Extents of removal of iron, arsenic and sulphide-sulphur were described by the logistic equation and values of the kinetic parameters obtained. Maximum rates of removal of these components, predicted by the logistic parameters, correlated well with experimentally determined rates of removal obtained from the linear portions of the fractional removal versus time curves. Bibliography: pages 93-98.
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    Effect of culture conditions on the competition between lactate oxidisers and fermenters in a biological sulfate reduction system
    (Elsevier, 2012) Oyekola, Oluwaseun O; Harrison, Susan T L; van Hille, Robert P
    Kinetic constants (μmax and Ks) describing the predominance of lactate oxidation and fermentation were determined in chemostat cultures. The kinetics of sulfate reduction and lactate utilization were determined from 0.5 to 5 d residence times at feed sulfate concentrations of 1.0–10.0 g l−1. The kinetics of lactate fermentation in the absence of sulfate were investigated at residence times of 0.5–5 d. The lactate oxidizers (LO) were characterized by a μmax of 0.2 h−1 and Ks value of 0.6 g l−1 compared with a μmax of 0.3 h−1 and Ks of 3.3 g l−1 for the lactate fermenters (LF). Using mathematical models, it was shown that LO competed more effectively for lactate at low lactate concentrations (⩽5 g l−1) and high sulfide concentrations (0.5 g l−1). Lactate fermenters outcompeted the oxidizers under conditions of excess lactate (>5 g l−1) and low sulfide (0.014–0.088 g l−1).
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    Effect of culture conditions on the competitive interaction between lactate oxidizers and fermenters in a biological sulfate reduction system
    (Elsevier, 2012) Oyekola, Oluwaseun O; Harrison, Susan T L; Van Hille, Robert P
    Kinetic constants (lmax and Ks) describing the predominance of lactate oxidation and fermentation were determined in chemostat cultures. The kinetics of sulfate reduction and lactate utilization were determined from 0.5 to 5 d residence times at feed sulfate concentrations of 1.0–10.0 g l1 . The kinetics of lactate fermentation in the absence of sulfate were investigated at residence times of 0.5–5 d. The lactate oxidizers (LO) were characterized by a lmax of 0.2 h1 and Ks value of 0.6 g l1 compared with a lmax of 0.3 h1 and Ks of 3.3 g l1 for the lactate fermenters (LF). Using mathematical models, it was shown that LO competed more effectively for lactate at low lactate concentrations (65gl1 ) and high sulfide concentrations (0.5 g l1 ). Lactate fermenters outcompeted the oxidizers under conditions of excess lactate (>5 g l1 ) and low sulfide (0.014–0.088 g l1 ). 2011 E
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    The effect of heavy oxidation upon flotation and potential remedies for Merensky type sulfides
    (Elsevier, 2006) Newell, A J H; Bradshaw, D J; Harris, P J
    Surface oxidation of sulfide minerals, such as that found in the regions of a sulfide ore body near the water table, can have a significant impact upon flotation. This theme has been explored for Merensky ore type sulfides where an ore containing pyrrhotite, pentlandite and chalcopyrite was thermally oxidised and the role of potential remedies investigated. Back-scattered scanning electron microscope images are presented showing the oxidation layer which formed in the mineral surfaces. These oxidation layers were depleted in both sulfur and iron with incorporated oxygen. Flotation recovery rapidly decreased with increasing oxidation, particularly after 27 days and reached a plateau after 50 days. Up to 27 days, this effect could be partially overcome with higher collector additions. Oxidation had more impact upon the finer size fractions, particularly for pyrrhotite. For more heavily surface oxidised samples, ultrasonic treatment prior to collector conditioning was found to improve flotation recoveries. This treatment had the greatest effect upon chalcopyrite particles. Sulfidisation was successful in restoring the flotation recovery of the heavily oxidised sulfide minerals. Longer sulfidisation conditioning times were not conducive to good flotation recoveries of both oxidised pyrrhotite and pentlandite due to oxidation of the freshly formed sulfide surfaces. For maximum flotation recoveries of oxidised pyrrhotite, pentlandite and chalcopyrite, different sulfidisation conditions are indicated. It appears likely that in a mineral processing operation treating oxidised Merensky type ores, two stages of sulfidisation employing different conditions would be required.
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    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.