Browsing by Author "Jones, Gavin C"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Restricted
    The generation of toxic reactive oxygen species (ROS) from mechanically activated sulphide concentrates and its effect on thermophilic bioleaching.
    (Elsevier, 2011) Jones, Gavin C; Corin, Kirsten C; van Hille, Robert P; Harrison, Susan T L
    Two types of laboratory mills, planetary and vibratory, were used to activate sulphide mineral concentrates mechanically before thermophilic (bio)leaching. These samples were analysed in terms of particle size, surface area, density, SEM, XRD line profile analysis and reactivity. The product particle size distributions indicated different particle breakage mechanisms of the two mills. The surface area for pyrite milled with the planetary mill was three fold that milled in the vibratory mill for the same length of time. Planetary milled samples showed lower densities, up to 4% less for pyrite samples, compared to vibratory milled samples. Particle surface oxidation, observed by SEM, occurred post milling. Surface oxidation products were more prevalent with planetary milled sulphide samples. XRD line profile analysis showed more line broadening effects with the planetary mill. This indicated that more bulk particle-related structural defects were present in the planetary milled samples. The reactivity in acidic solution was measured in terms of the generation of toxic reactive oxygen species (ROS): hydrogen peroxide and hydroxyl radicals. The ROS generation from milled sulphides, normalised to constant surface area loading, increased with increased mechanical activation. The planetary milled samples generated greater ROS per sample surface area than vibratory milled samples, more than 4-fold for pyrite after 60 min of milling. Increased ROS generation was postulated to result from increased surface area defects, solubilisation of iron oxidation products and bulk particle-related defects. The effect of mechanical activation on performance on thermophilic leaching and bioleaching tests was investigated using milled samples at 2% (w/v) pulp density. Short mill times improved leach rates from both mills, up to 7-fold cf. unactivated feed leach rates. Poor bioleaching performance resulted following long periods of mechanical activation (20–60 min). Pyrite and chalcopyrite bioleaching performance decreased dramatically above surface area loadings of 25 and 125 m2 /L respectively. Planetary milled samples were less amenable to bioleaching. For pyrite milled for 20 and 60 min and chalcopyrite milled for 40 min, no viable cells were observed following inoculation via fluorescence microscopy, suggesting culture death supported by compromised ferrous iron oxidation. The generation of ROS was postulated to cause poor bioleaching performance under these conditions.
  • Thumbnail Image
    Item
    Restricted
    A novel microwell-based analytical technique for studying ferrous iron biooxidation activity
    (Elsevier, 2014) Meissner, Murray P; Xu, Zhehua; Jones, Gavin C; Minnaar, Susanna H; Harrison, Susan T L
    The broad range of complexities in bioleaching includes the use of mixed microbial communities with diversity of species and strains with different windows of operating conditions. Empirical approaches to characterise these currently use cumbersome experimental systems; hence the need to develop a high throughput research tool, analogous to the techniques used in high throughput pharmaceutical research. In this study, a microwell research tool was evaluated as a growth and measurement tool for mixed autotrophic bioleaching cultures. The tool was assessed by comparing its performance to conventional shake flask apparatus. Mixed mesophilic cultures of predominantly Leptospirillum ferriphilum and Acidithiobacillus ferrooxidans were used. Growth and ferrous iron oxidation kinetics were quantified and assessed. Microwell plates performed similarly to conventional shake flasks with respect to growth and iron oxidation kinetics. The microwell plate apparatus was also used as a measurement system in combination with a microwell plate reader (measuring absorbance change at 428 nm over time). Progressive colour change of growth experiments correlated to ferrous iron oxidation within a defined operating window. We conclude that, using this measurement as a proxy for trends iron oxidation, the microwell research tool is well-suited for high throughput scoping studies to map operating windows for different cultures, in both an unadapted and adapted context. This was confirmed through an activity test utilising fluoride as an inhibitor. Where absorbance measurements at 428 nm are used to track oxidation progress, the research tool has limitations with respect to pH (<2.0) and total iron concentration (<8.0 g l−1).
  • Thumbnail Image
    Item
    Restricted
    The effect of sulfide concentrate mineralogy and texture on Reactive Oxygen Species (ROS) generation
    (Elsevier, ROS) Jones, Gavin C; Becker, Megan; van Hille, Robert P; Harrison, Susan T L
    The generation of Reactive Oxygen Species (ROS), H2O2 and radical dotOH, has been observed from sulfide mineral containing particles in acidic solutions. The implications of this phenomenon, as a potential microbial stress-causing effect, have been studied previously with respect to thermophilic bioleaching performance in the presence of finely milled pyrite and chalcopyrite concentrates. In this study, the effect of sulfide mineralogy on ROS generation in the absence of microbes under physicochemical conditions typical for the bioleach environment was investigated. The mineralogical and elemental composition of eleven different samples containing sulfide mineral was obtained. These Au, Cu and other base metal-containing sulfide mineral concentrates as well as a milled whole ore of low Cu grade were tested for ROS generation. The whole ore sample and two refractory Au concentrates containing approximately 50% pyrite, generated significantly less ROS compared to the base metal-containing concentrates when compared on a constant surface area loading basis. Sulfide mineral-related variables were correlated with ROS generation. A significant difference was observed between FeS2 and CuFeS2 grades separately, whereas a combined measure of both minerals present in samples showed a consistently strong correlation to ROS generation. The Cu grade, total Cu-containing sulfides and the chalcopyrite content of Cu-containing samples correlated well with ROS generation. However, a common deterministic variable with a strong association to increased ROS generation was not found. A sub-set of samples were subjected to QEMSCAN® for textural analysis. Results suggested that a decrease in sulfide mineral liberation, caused by gangue silicate mineral occlusion to solution, resulted in decreased reactivity as shown in one of the Au-containing samples. Well-liberated chalcopyrite and pyrite phases corresponded to increased reactivity of samples. Pyrite, which was present in all of the reactive samples, was shown to be associated with other sulfide minerals, implicating its importance in galvanic interactions. Micro-analysis of chalcopyrite and pyrite phases from highly reactive samples showed an abundance of particles with extensive cracking and the possible presence of secondary transformation phases (szomolnokite). These results suggest that sulfide mineralogy, liberation and extent of physical processing affect sulfide mineral concentrate reactivity in acidic solutions.