Browsing by Author "Ojumu, Tunde V"

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    The effect of dissolved cations on microbial ferrous-iron oxidation by Leptospirillum ferriphilum in continuous culture
    (Elsevier, 2008) Ojumu, Tunde V; Petersen, Jochen; Hansford, Geoffrey S
    In heap bioleaching the dissolution of gangue minerals from igneous ore materials can lead to the build-up of considerable concentrations of Mg and Al sulphates in the recycled leach solution. This may interfere with microbial ferrous iron oxidation, which drives the oxidation of the target minerals. In the present study the effect of solution concentrations of Mg and Al as sulphate at individual concentrations of 0 to 10 g•dm− 3 and combined concentrations 0 to 16 g•dm− 3each (or total ionic strength from 0.2 to 1.3 M) has been investigated in continuous culture using Leptospirillum ferriphilum. Increasing the concentrations of the salts increasingly depresses the specific rate of ferrous iron oxidation and also shifts the viable range more and more into the low potential region. Aluminium significantly reduces the amount of carbon biomass maintained in the reactor, whereas magnesium actually enhances it at low concentrations. The experimental data was correlated using the Pirt equation and a simplified substrate utilisation model. The results suggest that the maximum microbial growth rate and growth yield decline significantly only at total ionic strengths above about 1 mol•dm−3. The implications of this study are that heap cultures are likely to perform sub-optimally in those operations where build-up of dissolved gangue minerals is not controlled.
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    Investigating the effect of acid stress on selected mesophilic micro-organisms implicated in bioleaching
    (Elsevier, 2015-05-01) Ngoma, I Emmanuel; Ojumu, Tunde V; Harrison, Susan T L
    During start-up of heap bioleaching, low grade ores are typically treated with acid for agglomeration and to combat the acid neutralising capacity of the gangue minerals. This may stress the bioleaching inocula, particularly upon inoculation during ore agglomeration. Acid addition for agglomeration varies across operations, ore types and their neutralising capacity, with limited information published on recommended concentrations. The initial pH in the agglomeration mix is typically below pH 1.0 and may be as low as pH 0.5. This paper investigates the effect of acid stress in terms of initial acid concentration and exposure duration in submerged culture on mesophilic bacteria typically implicated in mineral sulphide bioleaching and critical for heap colonisation at start-up. Following acid stress, cultures were returned to standard operating conditions in batch stirred slurry reactors and their performance assessed in terms of mineral leach rates, ferrous oxidation and the rate of microbial growth. Increasing acid stress resulted in an increase in the lag period before onset of microbial growth and iron oxidation. Following adaptation, typical growth and ferrous iron oxidation rates were observed under low stress conditions while reduction in the rate and extent of microbial growth and ferrous iron oxidation persisted at extreme conditions. A reduction in yield (microbial cells produced per kg iron oxidised) was observed with increased acid concentration over comparative times. Microbial speciation analysis indicated a substantial decrease in the diversity of surviving bacterial species.