Browsing by Subject "Chalcopyrite"

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    Competitive Bioleaching of Pyrite and Chalcopyrite
    (Elsevier, 2006) Petersen, Jochen; Dixon, David G
    An experimental study was conducted to investigate the heap bioleaching of a copper-gold concentrate using the Geocoat™ technique. Small-scale columns were operated at selected temperatures using bacterial consortia suited to these temperatures. In all experiments secondary copper sulfides would leach more rapidly than pyrite. Chalcopyrite, however, appeared to leach only in the presence of extremely thermophile microbes and selectivity towards chalcopyrite decreased with leach time. Analysis of the leach tailings showed that, surprisingly, the overall rate of bio-oxidation did not significantly increase with temperature. Further, analysis of ferric demand for mineral oxidation vs. ferric supply by microbial oxidation suggests that chalcopyrite leaching is promoted by extreme thermophiles due to a favourable interplay between reaction kinetics, solution potential and chalcopyrite ‘passivation’ phenomena, whereas pyrite leaching is favoured at lower temperatures. This analysis also explains why selectivity towards chalcopyrite decreases with time. The results are of some significance for the development of a high temperature whole ore chalcopyrite heap bioleach process.
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    Conventional and electrochemical bioleaching of chalcopyrite concentrates by moderately thermophilic bacteria at high pulp density
    (Elsevier, 2011) Ahmadi, Ali; Schaffi, Mahine; Petersen, Jochen; Schippers, Axel; Ranjbar, Mohammad  
    Conventional and electrochemical bioleaching were investigated to extract copper from Sarcheshmeh chalcopyrite concentrate at high pulp densities. Experiments were conducted in the presence and absence of a mixed culture of moderately thermophilic iron- and sulphur oxidizing bacteria using a 2-L stirred electro-bioreactor at 20% (w/v) pulp density, an initial pH of 1.4–1.6, a temperature of 50 °C, a stirring rate of 600 rpm and Norris nutrient medium with 0.02% (w/w) yeast extract addition. The results of 10 day leaches showed that, when using electrochemical bioleaching in an ORP range of 400 to 430 mV, copper recovery reaches about 80% which is 3.9, 1.5 and 1.17 times higher than that achieved in abiotic electrochemical leaching, conventional bioleaching, and electrochemical bioleaching at 440–480 mV ORP, respectively. It appears that applying current directly to the slurry optimises both, the biological and chemical subsystems, leading to an increase in both, the dissolution rate and the final recovery of copper from the concentrate. Mineralogical analysis of the solid residues of electrochemical leaching in both, biotic and abiotic media, showed the formation of chalcocite and covellite minerals on the surface of not leached chalcopyrite. It is postulated that the reduction of refractory chalcopyrite to more soluble minerals such as chalcocite and covellite is achieved through both, electron transfer upon electrode contact and by ferrous reduction at the low ORP of the slurry. These secondary minerals are then rapidly dissolved through bioleaching, while at the same time a formation of a passive layer of jarosites is minimised. This process also appears to promote an increased bacteria–solid ratio due to favourable growth conditions.
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    Effect of inoculum size on the rates of whole ore colonisation of mesophilic, moderate thermophilic and thermophilic acidophiles
    (Elsevier, 2012) Tupikina, Olga V; Minnaar, Susanna H; Rautenbach, George F; Dew, David W; Harrison, Susan T L
    Bioheap leaching of low grade copper sulphides has been applied successfully at the commercial scale for the extraction of copper from secondary sulphide minerals. It is important to optimise the inoculation of heaps in order to minimise the residence time required for the heap and to maximise extraction.Thermophilic bioleaching of the primary sulphide chalcopyrite poses an additional challenge of rising temperatures inside the heap demanding microbial succession. After heap start up, rising heap core temperatures make conditions less favourable for mesophilic microbial species, and the moderately thermophilic community succeeds them in the consortium. In turn, thermophilic microorganisms succeed the moderately thermophilic microbes as the higher temperatures are reached.A detailed understanding of the microbial colonisation of whole ore is necessary to optimise microbial succession during thermophilic bioleaching, as is that of microbial growth kinetics on whole ore. Most published research is focused on microbial growth rates of bioleaching organisms in liquid cultures; little work is reported on microbial colonisation of whole ore and subsequent microbial activity. To extend the information available on the microbial diversity and succession in a bioleaching habitat, a study of bioleaching microbes colonising the ore body is required.The aim of this work was to explore aspects of colonisation of low grade chalcopyrite ore at 23 °C, 50 °C and 65 °C by acidophilic micro-organisms. Laboratory column packed bed reactors were designed to simulate heap leach environments and to provide a systematic way of studying microbial dynamics on whole ore. The effect of inoculum size and inoculation strategies on microbial activity established and the subsequent leaching performance were investigated under conditions that support mesophilic, moderately thermophilic and thermophilic microorganisms. A relationship was shown between the inoculum size and the culture time required to achieve Eh values greater than 700 mV, especially at 23 °C and 65 °C. However, the culture time required to establish an active iron- (and sulphur-) oxidising culture was also influenced by ore type, irrigation rate and inoculum adaptation. The effect on effluent Eh, pH and dissolved iron levels is also discussed.
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    Effect of inoculum size on the rates of whole ore colonisation of mesophilic, moderate thermophilic;thermophilic acidophiles
    (Elsevier, 2014) Tupikina, O V; Minnaar, S H; Rautenbach, G F; Dew, D W; Harrison, S T L
    Bioheap leaching of low grade copper sulphides has been applied successfully at the commercial scale for the extraction of copper from secondary sulphide minerals. It is important to optimise the inoculation of heaps in order to minimise the residence time required for the heap and to maximise extraction. Thermophilic bioleaching of the primary sulphide chalcopyrite poses an additional challenge of rising temperatures inside the heap demanding microbial succession. After heap start up, rising heap core temperatures make conditions less favourable for mesophilic microbial species, and the moderately thermophilic community succeeds them in the consortium. In turn, thermophilic microorganisms succeed the moderately thermophilic microbes as the higher temperatures are reached. A detailed understanding of the microbial colonisation of whole ore is necessary to optimise microbial succession during thermophilic bioleaching, as is that of microbial growth kinetics on whole ore. Most published research is focused on microbial growth rates of bioleaching organisms in liquid cultures; little work is reported on microbial colonisation of whole ore and subsequent microbial activity. To extend the information available on the microbial diversity and succession in a bioleaching habitat, a study of bioleaching microbes colonising the ore body is required. The aim of this work was to explore aspects of colonisation of low grade chalcopyrite ore at 23 °C, 50 °C and 65 °C by acidophilic micro-organisms. Laboratory column packed bed reactors were designed to simulate heap leach environments and to provide a systematic way of studying microbial dynamics on whole ore. The effect of inoculum size and inoculation strategies on microbial activity established and the subsequent leaching performance were investigated under conditions that support mesophilic, moderately thermophilic and thermophilic microorganisms. A relationship was shown between the inoculum size and the culture time required to achieve Eh values greater than 700 mV, especially at 23 °C and 65 °C. However, the culture time required to establish an active iron- (and sulphur-) oxidising culture was also influenced by ore type, irrigation rate and inoculum adaptation. The effect on effluent Eh, pH and dissolved iron levels is also discussed.
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    Investigation and in situ visualisation of interfacial interactions of thermophilic microorganisms with metal-sulphides in a simulated heap environment
    (Elsevier, 2013) Africa, Cindy-Jade; van Hille, Robert P; Sand, Wolfgang; Harrison, Susan T L
    This study sought to provide a better understanding of the dynamics of microbial-metal sulphide interfacial processes relevant to heap bioleaching. Attachment and subsequent biofilm formation by Metallosphaera hakonensis (M. hakonensis) on the surface of massive chalcopyrite and pyrite samples, as well as a low-grade chalcopyritic whole ore were investigated. The method made use of a biofilm reactor in which thin sections of mineral ore were mounted. Operating conditions in the reactor simulated those of a bioheap in terms of fluid-flow and mineralogy, where the low-grade chalcopyrite ore sections were used. Pure cultures of M. hakonensis were used to inoculate the reactors and the attachment and subsequent biofilm development visualised in situ after 2, 4 and 8 days using a combination of atomic force and epifluorescent microscopy (AFM–EFM) as well as confocal scanning laser microscopy (CSLM). This revealed insights into biofilm structure and architecture. The effect of varying temperature on the extent of attachment and biofilm development was also assessed after 4 days using three temperature regimes: room temperature (20 ± 1 °C), 45 °C and 65 °C. The density of the attached micro–colonies increased with an increase in time, indicative of an actively growing biofilm. The extent of surface coverage and proliferation of the biofilm was dependent on the temperature, with surface coverage being more extensive at 65 °C, near the optimal temperature for growth. Preferential attachment and biofilm formation to sulphide minerals was observed, with increased surface coverage of pyrite mineral surfaces relative to chalcopyrite and low-grade ore. The AFM–EFM technique enhanced the level of detail at which site specific associations of microorganisms with mineral surfaces could be assessed. Spatial orientation and density of attached micro-colonies were noted.