Browsing by Subject "Leptospirillum ferriphilum"

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    Attachment of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum cultured under varying conditions to pyrite, chalcopyrite, low-grade ore and quartz in a packed column reactor
    (Springer Verlag, 2012) Africa, Cindy-Jade; van Hille, Robert P; Harrison, Susan T L
    The attachment of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum spp. grown on ferrous medium or adapted to a pyrite mineral concentrate to four mineral substrata, namely, chalcopyrite and pyrite concentrates, a low-grade chalcopyrite ore (0.5 wt%) and quartzite, was investigated. The quartzite represented a typical gangue mineral and served as a control. The attachment studies were carried out in a novel particle-coated column reactor. The saturated reactor containing glass beads, which were coated with fine mineral concentrates, provided a quantifiable surface area of mineral concentrate and maintained good fluid flow. A. ferrooxidans and Leptospirillum spp. had similar attachment characteristics. Enhanced attachment efficiency occurred with bacteria grown on sulphide minerals relative to those grown on ferrous sulphate in an ore-free environment. Selective attachment to sulphide minerals relative to gangue materials occurred, with mineral adapted cultures attaching to the minerals more efficiently than ferrous grown cultures. Mineral-adapted cultures showed highest levels of attachment to pyrite (74% and 79% attachment for A. ferrooxidans and L. ferriphilum, respectively). This was followed by attachment of mineral-adapted cultures to chalcopyrite (63% and 58% for A. ferrooxidans and L. ferriphilum, respectively). A. ferrooxidans and L. ferriphilum exhibited lower levels of attachment to low-grade ore and quartz relative to the sulphide minerals.
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    Biooxidation kinetics of Leptospirillum ferriphilum under heap bioleach conditions
    (Metallurgy and Exploration Inc, 2008) Ojumu, T V; Harrison, S T L; Hansford, G S; Petersen, J
    Although the kinetics of biological oxidation of ferrous to ferric iron–the key step in any bioleaching process–have been studied for a variety of organisms, the focus has always been on conditions typical of tank-bioleaching. In heaps, parameters such as pH and temperature vary widely across the heap and are usually far from optimal. Total iron concentrations are usually much lower than the tanks(except in gold heaps), and the presence of dissolved gangue mineral is usually much more significant.
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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.
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    The kinetics of ferrous-iron oxidation by Leptospirillum ferriphilum in continuous culture: the effect of pH
    (Elsevier, 2011) Ojumu, T V; Petersen, J
    The kinetics of ferrous ion oxidation by Leptospirillum ferriphilum were studied in continuous culture with a focus on the effect of solution pH (pH 0.8–2.0), assuming that the effect of pH on cell metabolism can be independently studied of reactor context and other reactions common in bioleach heaps. A simplified competitive ferric ion inhibition model and the Pirt Equation were used to analyze the experimental data. The results showed that the maximum specific activity of L. ferriphilum has a symmetrical bell-shaped curve relationship with pH. The maximum specific ferrous-iron oxidation rate,qFe2 +maxgave a highest value of 14.54 mmol Fe2+(mmol C h)− 1 at pH 1.3, and was described by a quadratic function. The steady state carbon biomass in the reactor and the apparent affinity constant, K′Fe2 +, also increased with increase in pH; however, a slight increase in the carbon biomass was observed beyond pH 1.6. The results also showed that ferric ion precipitation is significant beyond pH 1.3 and about 13% total iron from the feed was lost at pH 2.0. The maximum biomass yield increased linearly with pH, while the culture maintenance coefficient was significantly small in all experiments and was minimum at pH 1.3. The values are indicative of actively growing chemostat cultures. This study shows that microbial ferrous ion oxidation by L. ferriphilum may be sustained at pH lower than pH 0.8 as the microbial activity is much higher than reported values for common mesophilic acidophiles. This may have implications on how bioleach heap operations can be started-up to improve metal recovery.
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    The kinetics of ferrous-iron oxidation by Leptospirillum ferriphilum in continuous culture: the effect of temperature
    (Elsevier, 2009) Ojumu, T V; Hansford, G S; Petersen, J
    A typical bioleach heap is characterized by wide variation of temperature across the heap bed, leading to oxidation of target minerals occurring at different rates. Previous studies on the effect of temperature on the microbial oxidation of ferrous-iron were limited to a narrow range of temperatures (30–40 °C) near optimum conditions and mostly toAcidithiobacillus ferrooxidans. The kinetics of ferrous-iron oxidation by Leptospirillum ferriphilum were studied in continuous culture. In this paper we focus on the effect of temperature (18–45 °C) on these kinetics. The study was based on the assumption that the effect of temperature can be studied independently of other, equally important factors such as pH, dissolved salts, etc. and independent of the reactor context. The experimental data were correlated using both, a simplified ferric-iron inhibitory model and the Pirt Equation. The results showed that the maximum specific ferrous-iron oxidation rate, increased with increasing temperature to a maximum at 42 °C. This trend can be described adequately by the Arrhenius Equation with an activation energy, Ea of 34.46 kJ mol−1 and frequency factor,K0 of 1.05 × 107 mmol Fe2+(mmolC)−1 h−1. An increase in temperature slightly reduces the steady state carbon biomass in the reactor, while the apparent affinity constant, K′Fe2+ increases. The investigation further suggests that at low temperature (18 °C) and beyond the maximum temperature (42 °C), the culture cannot be sustained in a continuous mode. The maximum biomass yield followed a linear decline with increasing temperature, while cell maintenance on ferrous-iron followed a quadratic trend, although the small values indicates that it is not significant, as would be expected in continuous culture. The results indicate that L. ferriphilum is likely to perform optimally, at warm temperatures (25–42 °C) in heap bioleach operations before being taken over by thermophiles at higher temperatures.