Browsing by Author "Corin, Kirsten C"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Open Access
    Challenges Related to the Processing of Fines in the Recovery of Platinum Group Minerals (PGMs)
    (2021-05-18) Corin, Kirsten C; McFadzean, Belinda J; Shackleton, Natalie J; O’Connor, Cyril T
    In order to increase the recovery of PGMs by flotation, it is necessary to optimise the liberation of the key minerals in which the platinum group elements (PGEs) are contained which include sulphides, arsenides, tellurides, and ferroalloys among others, while at the same time ensuring the optimal depression of gangue minerals. In order to achieve this, comminution circuits usually consist of two or three stages of milling, in which the first stage is autogeneous, followed by ball milling. Further liberation is achieved in subsequent stages using ultra-fine grinding. Each comminution stage is followed by flotation in the so-called MF2 or MF3 circuits. While this staged process increases overall recoveries, overgrinding may occur, hence creating problems associated with fine particle flotation. This paper presents an overview of the mineralogy of most of the more significant PGM ores processed in South Africa and the various technologies used in comminution circuits. The paper then summarises the methodology used in flotation circuits to optimise recovery of fine particles in terms of the collectors, depressants, and frothers used. The effect of entrainment, slimes coating, changes in rheology caused by the presence of a significant amount of fines and of chromite recovery is addressed.
  • Thumbnail Image
    Item
    Open Access
    Considering Specific Ion Effects on Froth Stability in Sulfidic Cu-Ni-PGM Ore Flotation
    (Multidisciplinary Digital Publishing Institute, 2022-03-04) Manono, Malibongwe S; Corin, Kirsten C
    The mining and mineral processing of Cu-Ni-PGM sulfide ores in South Africa occurs in semi-arid regions. The scarcity of water resources in these regions has become one of the biggest challenges faced by mineral concentrators. As a result, concentrators are forced to find ways through which they can manage and control their water usage. The recycling and re-use of process water in mineral concentration plants has therefore become a common practice. This practice is beneficial in that it reduces reliance on municipal water and harnesses compliance to stringent environmental regulations on freshwater usage. This approach also offers a better response to the Sustainable Development Goals (SDGs) for the mining industry, as water and its preservation form part of the SDGs. This practice could, however, be somewhat concerning to a process operator because recirculated water often has higher concentrations of ions compared to fresh or potable water. This is because an unintended change in the process water quality may affect critical aspects of flotation such as the stability of the froth. This issue has led to the need for both the mining industry and researchers in the field to find the ions in process water that have the greatest impact on froth stability. Thus, the authors of this study investigated the effects of various ions common in the process water of a typical Cu-Ni-PGM ore on froth stability using a 3 L bench scale flotation cell. Solids and water recoveries were used as proxies for froth stability. These were further complemented by bubble size, water recoveries, foam height, and dynamic foam stability from two-phase flotation systems. A two-phase foam study resulted in observations that supported findings from a three-phase study. Generally, single salt solutions containing Ca2+ and Mg2+ ions resulted in higher water recoveries both in the two-phase foam and three-phase froth studies, increases in foam heights and dynamic foam stability, and a decrease in bubble size compared to the solutions that contained Na+ . SO4 2− also resulted in increased foam stability compared to Cl− and NO3 −. These results showed that the divalent inorganic electrolytes—Ca2+, Mg2+ , and SO4 2−—were more froth- and foam-stabilizing than the monovalent inorganic electrolytes—Cl−, NO3 −, and Na+ . This finding was in agreement with previous research. The findings of this study are deemed crucial in the development of a process water management protocol in sulfidic Cu-Ni-PGM ore concentrators. However, more comparative three-phase froth stability tests are needed as subjects of future investigative work to further ascertain specific ion effects on froth stability in sulfide ores.
  • 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.