Browsing by Subject "Bioleaching"
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- ItemRestrictedAttachment 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 LThe 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.
- ItemRestrictedCarbon dioxide and oxygen consumption during the bioleachingof a copper ore in a large isothermal column(Elsevier, 2010) Petersen, J; Minaar, S H; du Plessis, C ADuring large-scale column tests at BHP Billiton's Johannesburg Technology Centre (JTC) on a low-grade copper ore during 2005/6, the concentrations of both oxygen and CO2 were continuously monitored in feed and exit gas as well as at various intermediate positions over the height of the column. This paper describes results from a test run at 40 °C fed with an air stream enriched to between 1000 and 2000 ppm CO2. Oxygen consumption very closely tracks iron and copper leaching. CO2 is consumed rapidly from the bottom up, resulting in significant depletion midway through the column, even though an enriched feed was used. Oxidation rates decline in CO2 depleted zones, but were not observed to cease completely. This decline is postulated to be linked to a slowly decaying population unable to regenerate itself, and a relative rate of decay in the absence of oxygen has been estimated to be around 3%/day. A comparison between O2 and CO2 consumption rates shows a linear correlation beyond a minimum oxidation rate. This minimum rate corresponds to a non-growth maintenance energy requirement, and the slope of the linear correlation to the growth yield. Both are functions of available CO2 in the range 50 to 1000 ppm, with maintenance declining and yield increasing. The findings of this study imply that CO2 supplementation in bioheaps will stimulate microbial growth and CO2 consumption, but not necessarily increase the rate of oxygen uptake and hence leaching. Absence of CO2 is expected to result in gradual population decline, but a degree of oxidation continues on the basis of maintenance. In tall heaps, CO2 depletion with height is likely and may therefore result in impaired leaching in the upper zones.
- ItemRestrictedA comparative study on thermophilic and mesophilic biooxidation of ferrous iron(Elsevier, 2000) Nemati, M; Harrison, S T LHigh temperature biooxidation of ferrous iron was studied in a batch system, using the acidophilic thermophile Acidianus brierleyi. The effect of ferrous iron initial concentration on the growth and activity of the cells was investigated. A. brierleyi was able to grow on ferrous iron at concentrations below 7.5 kg m−3. The values of specific growth rate and yield were 0.043 h−1 and 2.2×1014 cells/kg iron respectively. At ferrous iron concentrations of 7.5 kg m−13 and higher the growth of the cells was prohibited, however the non-growing cells were able to oxidise iron. The maximum biooxidation rate of ferrous iron, 0.105 kg m −3 h−1, was achieved in a culture initially containing 7.5 kg m−3 Fe2+. The mesophilic iron oxidiser Thiobacillus ferrooxidans was capable of growing on ferrous iron at concentrations as high as 30 kg m−3. Moreover the rate of mesophilic biooxidation offerrous iron was significantly higher than that observed in the presence of A. brierleyi.
- ItemRestrictedCompetitive Bioleaching of Pyrite and Chalcopyrite(Elsevier, 2006) Petersen, Jochen; Dixon, David GAn 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.
- ItemRestrictedConventional 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, MohammadConventional 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.
- ItemRestrictedThe Effect of CO2 Availability on the Growth, Iron Oxidation and CO2-Fixation Rates of Pure Cultures of Leptospirillum ferriphilum and Acidithiobacillus ferrooxidans(Wiley, 2012) Bryan, C G; Davis-Belmar, C S; van Wyk, N; Fraser, M K; Dew, D; Rautenbach, G F; Harrison, S T LUnderstanding how bioleaching systems respond to the availability of CO2 is essential to developing operating conditions that select for optimum microbial performance. Therefore, the effect of inlet gas and associated dissolved CO2 concentration on the growth, iron oxidation and CO2-fixation rates of pure cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum was investigated in a batch stirred tank system. The minimum inlet CO2 concentrations required to promote the growth of At. ferrooxidans and L. ferriphilum were 25 and 70 ppm, respectively, and corresponded to dissolved CO2 concentrations of 0.71 and 1.57 mM (at 308C and 378C, respectively). An actively growing culture of L. ferriphilum was able to maintain growth at inlet CO2 concentrations less than 30 ppm (0.31–0.45 mM in solution). The highest total new cell production and maximum specific growth rates from the stationary phase inocula were observed with CO2 inlet concentrations less than that of air. In contrast, the amount of CO2 fixed per new cell produced increased with increasing inlet CO2 concentrations above 100 ppm. Where inlet gas CO2 concentrations were increased above that of air the additional CO2 was consumed by the organisms but did not lead to increased cell production or significantly increase performance in terms of iron oxidation. It is proposed that At. ferrooxidans has two CO2 uptake mechanisms, a high affinity system operating at low available CO2 concentrations, which is subject to substrate inhibition and a low affinity system operating at higher available CO2 concentrations. L. ferriphilum has a single uptake system characterised by a moderate CO2 affinity. At. ferrooxidans performed better than L. ferriphilum at lower CO2 availabilities, and was less affected by CO2 starvation. Finally, the results demonstrate the limitations of using CO2 uptake or ferrous iron oxidation data as indirect measures of cell growth and performance across varying physiological conditions. Biotechnol. Bioeng. 2012;109: 1693–1703
- ItemRestrictedEffect 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 LBioheap 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.
- ItemRestrictedEffect 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 LBioheap 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.
- ItemRestrictedThe effect of temperature and culture history on the attachment of Metallosphaera hakonensis to mineral sulphides with application to heap bioleaching(Elsevier, 2011) Bromfield, L; Africa, C-J; Harrison, S T L; van Hille, R PTemperatures in excess of 60 °C are required for efficient bioleaching of chalcopyrite. Within heaps, colonisation of the mineral with thermophilic archaea is important in reaching and maintaining these high temperatures. The effect of temperature and culture history on the attachment of Metallosphaera hakonensis, an extreme thermophilic acidophile identified as a key player in heap bioleaching, to sulfide concentrates and low-grade ore was investigated in shake flasks and packed beds. Attachment studies were conducted at 25 °C, 45 °C and 65 °C. The results show a clear relationship between increasing temperature and attachment efficiency for both suspended and packed bed systems. Attachment at 25 °C was low. Increasing the temperature to 45 °C improved attachment efficiency by between 50% and 100% while a further increase to 65 °C improved attachment by an additional 20–50%. Cells cultured on elemental sulfur as energy source prior to contacting showed 1.3 times greater affinity for the mineral concentrate than those cultured on sulphide mineral concentrates or ferrous sulphate. In contrast to previous studies using mesophilic organisms the selective attachment ofMetallosphaera to sulfide minerals, relative to gangue, was less pronounced. Attachment efficiency was lower in the packed bed system which more closely mimicked flow through a heap. The cell surface properties surface charge and hydrophobicity as well as metabolic activity were investigated to provide insight into the observed phenomena. The data suggest that retention of thermophiles within the heap could be enhanced by a secondary inoculation following elevation of the temperature above 40 °C by the mesophilic pioneer species.
- ItemRestrictedThe 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 LTwo 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.
- ItemRestrictedIn situ investigation and visualisation of microbial attachment and colonisation in a heap bioleach environment: the novel biofilm reactor(Elsevier, 2010) Africa, Cindy-Jade; Harrison, Susan T L; Becker, Megan; van Hille, Robert PIn this paper, the development of a novel means of investigating the attachment and subsequent biofilm formation of mineral bioleaching micro-organisms to mineral surfaces in situ is described. The protocol was developed to investigate the interactions of micro-organisms with sulfide minerals and low-grade chalcopyrite ore under conditions resemblant of a bioheap environment. The method makes use of a biofilm reactor in which thin sections of mineral ore are mounted. The reactor is operated as a continuous flow-through system. Attachment of pure and mixed cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum is assessed. The technique allows for the investigation of microbial ecology with special regard to microbe–mineral attachment, site and mineral specific associations of micro-organisms and spatial organisation of microbial communities present through the use of fluorescent microscopy techniques. Preliminary fluorescent in situ hybridisation (FISH) analysis of the attachment of L. ferriphilum and A. ferrooxidans to massive chalcopyrite sections, as well as to low-grade chalcopyrite containing ore sections is presented. In the case of both low-grade and massive sulfide mineral samples, attachment of mixed micro-colonies was observed in regions where surface defects were prevalent. In low-grade samples, preferential attachment was observed in regions where sulfide minerals were present. The density of the attached micro-colonies increased with an increase in contacting time (from 20, 72 and 96 h) and was indicative of an actively growing mono-layered biofilm.
- ItemRestrictedInvestigating heap leaching – the effect of feed iron concentration on bioleaching performance(Elsevier, 2010) van Hille, Robert P; van Zyl, Andries W; Spurr, Nicholas R L; Harrison, Susan T LThis paper describes an investigation into the effect of iron concentration in the leach solution on the bioleaching of a low grade copper ore, where chalcopyrite was the dominant copper sulphide. The concentration of dissolved iron is primarily controlled by pH and the relative proportion of ferric to ferrous iron, with significant jarosite precipitation occurring above pH ≈ 1.8 in a highly oxidised system. The solution pH may be increased by the dissolution of acid soluble gangue and when iron oxidation is significantly higher than sulphur oxidation. The study was approached using two experimental systems. In the former, the leach solution was recycled through an ore bed of low aspect (reactor height divided by diameter) ratio for a portion of the experiment. During the recycle phase, no acid was added to the system and acid consumption by gangue material led to a pH increase (1.6–2.2). The resulting jarosite precipitation reduced soluble iron from 2.5 g/l to less than 250 mg/l. Copper recovery decreased, but not in proportion to the decrease in iron. This was partly attributed to adsorption on, or entrainment within, the jarosites. To study the effect of reduced iron concentration on leach performance under more controlled conditions, bioleaching was performed in packed bed column reactors with feed iron concentrations ranging from 5 g/l to 200 mg/l. Observations indicated an initial decreased rate of copper liberation with reduced iron concentration in the feed. The relationship between available Fe3+ concentration and copper liberation was not proportional. However, with time, the liberation of copper became independent of iron concentration in the percolation liquor. Further, the specific rate of copper liberation was consistently below the theoretical value on a basis of ferric iron concentration. The highest values of copper liberation were reported at the lowest iron concentrations. In summary, while increased iron concentration in solution may enhance the initial rate of leaching, mineral availability appears to dominate CuFeS2 leach kinetics through the majority of the leach. Furthermore, high iron concentrations in solution aggravate jarosite formation with concomitant retention of copper in the ore bed.
- ItemRestrictedInvestigation 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 LThis 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.
- ItemRestrictedKinetic modeling of bioleaching of copper sulfide concentrates in conventional and electrochemically controlled systems(Elsevier, 2012) Ahmadi, Ali; Ranjbar, Mohammad; Schaffie, Mahin; Petersen, JochenIn this paper a model of conventional and electrochemical bioleaching of high grade complex copper sulfide ores or flotation concentrates in isothermal stirred tank reactors is presented and compared to experimental data. Experiments were conducted in an electrobioreactor using a mixed culture of moderate thermophile microorganisms at pulp density 20% (w/v), leaching time 10 days, stirring rate 600 rpm and temperature 50 °C. The behavior of conventional and electrochemical bioleaching processes was described with a combined reaction-based kinetic model. The model considers the effects of mineralogical composition of the feed, the properties of the initial solution, the presence of iron- and sulfur oxidizing microorganisms and both the passivation and electroreduction of chalcopyrite on the values of copper recovery, pH and redox potential during the processes. Comparing the values obtained from the integrated semi-empirical model with the experimental data showed that the model results are in good agreement with the real leaching data of copper recovery, ORP (oxidation reduction potential) and pH for the mentioned processes under different experimental conditions.
- ItemRestrictedThe kinetics of ferrous-iron oxidation by Leptospirillum ferriphilum in continuous culture: the effect of pH(Elsevier, 2011) Ojumu, T V; Petersen, JThe 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.
- ItemRestrictedMicrobial leaching of a low-grade sphalerite ore using a draft tube fluidized bed bioreactor(Elsevier, 2009) Soleimani, M; Hosseini, S; Roostaazad, R; Petersen, J; Mousavi, S M; Vasiri, Kazemi AThe use of a draft tube fluidized bed bioreactor (DTFBB) has been successfully demonstrated for the bioleaching of a chalcopyrite concentrate (Mousavi, et. al., 2005). In the present paper this technique was used for the bioleaching of zinc from a sphalerite bearing low-grade ore. A strain of the thermophilic bacterium, Sulfobacillus, has been isolated from the Kooshk lead and zinc mine near the city of Yazd (Iran) and is tested at temperatures 47 °C–72 °C. This is compared to leaching with a strain of the mesophileAcidithiobacillus ferrooxidans, which has been adapted to the high levels of zinc and the presence of the low-grade ore, and which was tested at temperatures 18 °C–42 °C. The effects of using the two temperature ranges, as well as varying pH in the range 1.2 to 1.8, and solid concentration in the range 1–20% w/v, on Zn recovery, ferrous, ferric and total iron concentrations and cells number were investigated in two batch DTFBBs with external recycling streams. The best conditions for leaching by mesophilic and thermophilic strains occurred at 10% w/v pulp density, giving 87% and 91.4% Zn recovery respectively, after 9 days.
- ItemRestrictedModelling of bioleach processes: connection between science and engineering(Elsevier, 2010) Petersen, JThis paper gives a brief introduction to the modelling of bioleach processes, developed from a careful analysis of the fundamental process steps at the gas–liquid, biological and mineral interfaces, and how these interact in a given reactor environment (tanks and heaps). The insights gained from such modelling work can guide both engineers in the optimisation of processes and scientist in directing their research at areas not yet well understood. From this perspective, some future directions of the bioleaching field are discussed.
- ItemRestrictedModelling zinc heap bioleaching(Elsevier, 2007) Petersen, J; Dixon, D GA comprehensive modelling study of the HydroZinc™ heap bioleach process, using the HeapSim modelling tool, is described. The model was calibrated on the basis of a small number of column leach experiments and compared against pilot heap test results. The model calibration thus confirmed, a detailed sensitivity study was conducted in order to establish the key parameters that determine the overall rate of Zn extraction. In the present case these were found to be oxygen gas–liquid mass transfer, various factors affecting the delivery of acid into the heap, and factors affecting the temperature distribution within the heap. A set of improved design parameters are proposed that would almost double the zinc conversion rate measured in the pilot plant – from 83% in 740 days to 78% in 383 days – and increase zinc production rate from 1.77 to 4.35 kg/m2/day. However, this improvement must be evaluated in the context of various implications for the downstream process.
- ItemRestrictedModification of the ferric chloride assay for the spectrophotometric determination of ferric and total iron in acidic solutions containing high concentrations of copper(Elsevier, 2012) Govender, E; Harrison, S T L; Bryan, C GDuring heap bioleaching for copper recovery, solution containing high concentrations of copper is recycled to the heaps. The commonly used 1,10-phenanthroline assay is not suitable in such situations; the presence of 6 g L−1 copper in a solution containing 50 mg L−1 ferrous iron resulted in the complete loss of the absorbance band associated with the tris(1,10-phenanthroline)iron(II) complex. The colorimetric determination of soluble ferric iron concentration using the ferric chloride assay is simple and rapid. However, it offers relatively low resolution and cannot be used to determine total iron concentrations. The detection wavelength was changed to improve resolution and the assay further modified to include an oxidation step using potassium persulfate. Therefore, both ferric and total iron concentrations can be determined rapidly using the same aliquot. There was minimal interference of copper (<5% deviation) on the modified assay with copper concentrations of 10 g L−1 and below. At greater copper concentrations the deviation increased. However, a linear relationship between absorbance and ferric iron concentration was maintained for all the solutions tested allowing correction through appropriate calibration.
- ItemRestrictedA 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 LThe 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).