Browsing by Subject "Microbial ferrous iron oxidation"

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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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    Kinetic measurement of biological oxidation of ferrous iron at low ferric-to-ferrous ratios in a controlled potential batch reactor
    (Elsevier, 2008) Kazadi, Thierry Kamunga; Jochen, Petersen
    Traditionally, the kinetics of microbial ferrous iron oxidation have been studied in continuous or in batch culture. Both methods have drawbacks: in continuous culture experiments have to be repeated at a number of dilution rates to cover the entire spectrum of ferrous to ferric ratios, which is time-consuming. Furthermore, experiments at very low ferric-to-ferrous ratios require high dilution rates which are close to or exceed those at which wash-out occurs. In batch experiments, on the other hand, the prevalent ferric to ferrous ratio rapidly changes due to substrate depletion while the microbial population continually grows, making determination of specific momentary rates difficult. The present paper describes initial work with a novel device, the Redostat™, which allows careful electrochemical control of ferric to ferrous ratio in a batch reactor. A culture of Leptospirillum ferriphilum was grown at 35 °C and 5 g dm− 3 total iron by maintaining the ferric to ferrous ratio at 0.17, 0.51 and 1.65 (corresponding to redox potentials of 419, 452 and 482 mV vs. Ag/AgCl), respectively. The correlation of data obtained from off-gas and current measurements was excellent, and fitted Monod kinetics with ferric inhibition. A hitherto unobserved effect indicates the onset of ferric iron inhibition at the low redox potentials employed here. It was also noted that the biomass concentration has an effect on the biomass specific ferrous iron consumption rate and the biomass yield on ferrous iron.