Papers by Keyword: Bioleaching

Abstract: Acidophilic leaching microorganisms have been reported to be in general intolerant to high salinity, namely high concentrations of chloride. At present this restriction hampers the use of sea water for bioleaching technology. Enrichment cultures obtained in this study from a former ore deposit near the Spanish coast oxidize ferrous iron in the presence of up to 50 gL-1 NaCl at pH 2.5 and 37°C. The presence of at least 5 gL-1 NaCl was shown to be an obligate requirement for iron oxidation. The major microbial groups comprise Alicyclobacillus and Arthrobacter. The findings may be of biotechnological relevance.

Abstract: In the commercial BIOX^® process, an acidophilic mixed bacterial and archaeal community dominated by iron and sulphur oxidising microorganisms is used to facilitate the recovery of precious metals from refractory gold-bearing sulphidic mineral concentrates. Characterisation of the microbial communities associated with commercial BIOX^® reactors from four continents revealed a significant shift in the microbial community structure compared to that of the seed culture, maintained at SGS (South Africa). This has motivated more detailed study of the microbial community dynamics in the process. Microbial speciation of a subset of the BIOX^® reactors at Fairview mines (Barberton, South Africa) and two laboratory maintained reactors housed at Centre for Bioprocess Engineering Research, University of Cape Town, has been performed tri-annually for three years by quantitative real-time polymerase chain reaction. The laboratory BIOX^® culture maintained on Fairview concentrate was dominated by the desired iron oxidiser, Leptospirillum ferriphilum, and sulphur oxidiser, Acidithiobacillus caldus, when operated under standard BIOX^® conditions. Shifts in the microbial community as a result of altered operating conditions were transient and did not result in a loss of the microbial diversity of the BIOX^® culture. The community structure of the Fairview mines BIOX^® reactor tanks showed archaeal dominance of these communities by organisms such as the iron oxidiser Ferroplasma acidiphilum and a Thermoplasma sp. for the period monitored. Shifts in the microbial community were observed across the monitoring period and mapped to changes in performance of the commercial process plant. Understanding the effect of changes in the plant operating conditions on the BIOX^® community structure may assist in providing conditions that support the desired microbial consortium for optimal biooxidation to maximize gold recovery.

Abstract: Bioleaching of copper sulfides is catalyzed by iron-and sulfur-oxidizing acidophilic microorganisms attached to the mineral surface forming a biofilm. However, the link between copper sulfides bioleaching and biofilm formation is not yet fully understood. Understanding the factors that are limiting the bioleaching kinetics for different copper sulfide minerals through exhaustive mineralogical analysis of the mineral surface with concomitant biofilm formation during the leaching process will deliver new process conditions with enhanced kinetics and higher copper recovery. In this work we have developed and standardized a reproducible flow cell method able to mimic heap/dump bioleaching laminar flow conditions to study the mineralogical dynamics by advanced mineralogical analysis including QEMSCAN and SEM-EDS coupled to biofilm formation analysis. Based on this method, the bioleaching mineralogical dynamics of primary copper sulfides (enargite (Cu₃AsS₄), chalcopyrite (CuFeS₂) and bornite (Cu₅FeS₄)) have been determined in the presence of biofilm formation. Supported by the observed mineralogical dynamics, different mechanisms of dissolution for bioleaching were observed as well as selective biofilm formation over the mineral surface, showing enhanced conditions for copper recovery.

Abstract: In the course of the decline of high-grade ore deposits, new effective and eco-friendly bioleaching techniques are of interest. In-situ leaching is an auspicious method, but composition of leaching community should be adapted to the respective external conditions and the ore material. In this study several sulfidic minerals were inoculated into acidic mine water of a mine in eastern Germany, housing members of well-known iron oxidizing bacteria like Acidithiobacillus, Leptospirillum and Ferrovum. The attachment tests were performed in batch and in a continuous way at different temperatures. The analysis of the extracted DNA from adhered cells showed an enrichment of Ferrovum spp. on chalcopyrite surface under in-situ conditions at 11°C. For laboratory batch conditions an accumulation of Leptospirillum spp. was detected for adhered cells probably due to the changes of the physicochemical parameter of the mine water. In more detailed analyses we aim to elucidate possible preferential attachment of the mine water community members to certain minerals.

Abstract: Acidithiobacillus thiooxidans is one of the most stable components in the consortium of microorganisms inhabiting the copper bioleaching heap of Minera Escondida Limitada. CalvinBenson-Bassham (CBB) is the CO2 fixation pathway most used by aerobic bacteria, and is the exclusive pathway used by A. thiooxidans. In this work, the population dynamics and the transcriptomic dynamics of five key genes involved in the A. thiooxidans CBB pathway were studied in bioleaching column and pure culture tests at different concentrations of CO2 availability. Association between CO2 level, population dynamics and relative expression of CBB-genes was discovered. Differences between CBB pathways from closely related species were reported. The transcription profile modelling could provide useful knowledge for improving industrial bioleaching operations.

Abstract: The objective of this study is to improve the understanding of copper sulfides dissolution and to use this knowledge for optimization of process parameters for commercial application of electrochemical bioleaching of chalcopyrite concentrates in stirred bioreactors. From the results of this study, the importance of the oxidation reduction potential (ORP) on the catalytic interaction between chalcopyrite and pyrite can be pointed out as the main parameters for successful bioprocessing of chalcopyrite concentrates. Under these conditions, the optimization of the average particle size of feed (D80) and adjusting the ORP in the range between 400-450 mV are important criteria for increasing the electrochemical bioleaching rate of chalcopyrite concentrates. It seems that the main reason for the increased copper recovery could be the control and prevention of chalcopyrite passivation resulting from improved galvanic interaction between copper sulfide minerals, here especially chalcopyrite and pyrite in the selected ORP range and the right particle size distribution of feed. At optimum conditions, the copper extraction from chalcopyrite flotation concentrate during 7 days of continuous electrochemical bioleaching operations in stirred tanks was about 95%, which should be high enough to justify the process economically.

Abstract: Heap and dump leaching of sulphide minerals have become well-established techniques for the processing of low grade ores, especially of copper, over the past 30 years. The oxidative dissolution of sulphides in heaps can be significantly enhanced by microbial colonies, but the complexities of the heap leach process overall often counteract the potential advantages, or prevent microbial colonisation and bioleaching in the first place. This overview discusses the multiple layers of complexities that govern percolation leaching processes, such as the interactions between mineral grains, particle pores and leach solution, microbial responses to solution chemistry typical of heaps, solution and solute transport in heterogeneous unsaturated ore beds, as well as heap aeration and microbial response to CO₂ supply. It becomes clear that economically successful heap bioleaching hinges on careful engineering and operation of the heap process as a whole to create an environment in which microbial colonies can thrive and the value metal is released sufficiently rapidly into solution.

Abstract: In bioleaching processes using autotrophic bacteria, CO₂ is the carbon source for the growth of the microorganisms and its availability is dependent on gas mass transfer. The objective of this study was to investigate the demand in CO₂ in complex copper concentrate bioleaching operations and to optimize CO₂ supply. Batch tests in 2L-stirred reactors at 10%_w/v solid load were performed to study the need for CO₂-supplementation and to determine the adequate CO₂ partial pressure in the gas inlet. The results show that Fe oxidation (and thus microbial activity) is delayed when air is injected without CO₂-supplementation. CO₂-supplementation improves leaching kinetics since Cu dissolution rate increases from 84 mg/L/h with air solely to 120 mg/L/h when CO₂ is added to air. The study proposes also a methodology to determine G/L transfer components and to asses CO₂ limitations in the system. It shows that the microorganisms are not only sensitive to the transfer rate of CO₂ from the gas to the liquid phase, but also to the availability of CO₂ in solution.

Abstract: The FAME (Flexible and Mobile Economic Processing Technologies) project targets the development of flexible and economic processing technologies for small and low-grade European ore deposits with complex mineralogy, targeting greisen, skarn and pegmatite ores. Amongst the valuable elements to be recovered are W, Sn, Li and minor constituents like In, Ge, Ga, Nb or Ta. To improve the processing of by-product sulfides to recover critical elements like In or Ga and to develop innovative processing strategies for raw materials, biohydrometallurgical technologies are investigated. There are different approaches in FAME for the biohydrometallurgical recovery of valuable metals from low grade ores: 1) the extraction of Li from zinnwaldite and lepidolite, 2) the heap leaching of low grade sulfide ore unsuitable for conventional processing to recover Zn and In, and 3) the bioleaching of sulfide concentrates in a two-stage tank process for recovery of Zn and Cu. So far the most promising results were achieved for heap-leaching of low-grade Zn-In ores achieving 7.4 ppm In in the leaching solution and for Li extraction (28%) from zinnwaldite.

Abstract: The application of acidophilic iron oxidizing bacteria is an established technique in tank and heap leaching of mainly sulfidic minerals. Even though bioleaching is broadly studied, there are still several issues to solve. Especially, the formation of iron precipitates, leading to co-precipitation of valuable metals, as well as the inhibition due to coating, considerably decrease the leaching efficiency. Consequently, the addition of chelating agents should result in an increased dissolution rate.However, organic acids, which have chelating characteristics, are generally regarded as highly toxic for leaching bacteria. Nonetheless, we found that both the addition of sodium citrate and citric acid leads to an increased iron oxidation rate of 42% and 84%, respectively, compared to standard culture medium without citrate. Chemical leaching tests with ZnS and ferric iron showed similar concentrations of dissolved zinc with and without citrate. However, the actual leaching efficiency is yet to be evaluated.