Papers by Keyword: Acidophiles

Abstract: The goal of the present work was to compare the rates of pyrite oxidation by different microorganisms, representatives of the groups predominating in biohydrometallurgical processes. The experiments were conducted in flasks with 100 mL of the medium containing mineral salts, 0.02% of yeast extract, and 2 g of pyrite at 45°C on rotation shaker (200 rpm) for 30 days. Strains Acidithiobacillus caldus MBC-1, Sulfobacillus thermosulfidooxidans VKMV 1269^T, and Acidiplasma sp. MBA-1 were used in the study. Different combinations of the strains were used in the experiments (pure cultures of S. thermosulfidooxidans VKMV 1269^T, Aсidiplasma sp. MBA-1, A. caldus MBC-1, as well as mixed cultures S. thermosulfidooxidans VKMV 1269^T + A. caldus MBC-1, Aсidiplasma sp. MBA-1 + A. caldus MBC-1, S. thermosulfidooxidans VKMV 1269^T + Aсidiplasma sp. MBA-1). Iron concentrations in the medium were the highest in the variants “S. thermosulfidooxidans VKMV 1269^T + A. caldus MBC-1”, “Aсidiplasma sp. MBA-1 + A. caldus MBC-1”, and “Sb. thermosulfidooxidans VKMV 1269^T + Aсidiplasma sp. MBA-1” and achieved 3.8, 3.5, and 3.3 g/L, respectively. Iron concentration in sterile control as well as in the experiments with pure cultures of Aсidiplasma sp. MBA-1 and A. caldus MBC-1 were very low. It demonstrated that in these variants pyrite was almost not oxidized. In the experiment with the pure culture of S. thermosulfidooxidans VKMV 1269^T, the rate of oxidation was high during 10 d of the experiment but then the oxidation activity drastically decreased. The ferric iron concentration achieved a maximum of 1.8 g/L and then decreased, whereas the ferrous iron concentration began to increase. Revealed differences in pyrite oxidation rates can be explained by differences in the physiological properties between the microorganisms. Results of the present work suggest that different groups of microorganisms have different impact in pyrite biooxidation.

Abstract: Detailed descriptions of the consortia present in commercial mineral processing operations have emerged in recent years, improving our understanding of the biology and the ecology of bioleaching. In spite of this progress, one of the aspects of biomining microbial ecology that remains un-tackled is that of virus-host interactions. The effects of viruses on the dynamics of the bioleaching microbial consortia and their impact in metal recovery is presently unknown. To begin addressing this issue we asked a basic question: ¿Are there viruses in industrial bioleaching econiches In this work, we answer that question experimentally, assessing the number and types of viral particles recovered in the leachates from different industrial settings, using epifluorescence and transmission electron microscopy. Findings emerging from this work point to an almost null presence of viral particles in the leachates from mineral processing operations, possibly due to structural stability issues of the particles in the extreme acidic and highly oxidant conditions favoured by their potential microbial hosts. In turn, DNA-loaded viral-size vesicles of presently unknown function are frequent and abundant in all samples analysed.

Abstract: Solid waste from sulfuric acid production may contain relatively high levels of metals such as Fe, Zn, Co, Cu and As that are harmful if inappropriately disposed of in the environment, but may be a valuable resource if metals can be recovered. The objective of this research was to investigate the pilot-scale acid bioleaching of metals from pyritic ashes, originating from the roasting of pyrite ores for sulfuric acid production and consisting mainly of hematite. Bioleaching was carried out at 25 °C in pilot-scale continuously stirred tank reactors (CSTR), with 50 L working volume in mineral salts medium supplemented with trace elements, 1 % (w/v) elemental sulfur and with pyritic ash pulp densities 10 % and 20 %. The reactors were inoculated with a mixed culture of iron- and sulfur-oxidising acidophiles containing Acidithiobacillus (At.) ferrooxidans, At. thiooxidans/albertensis, At. caldus, Leptospirillum ferrooxidans, Sulfobacillus (Sb.) thermosulfidooxidans, Sb. thermotolerans and some members of Alicyclobacillus genus. Metal leaching yields from pyritic ashes in the CSTR after 32 days were 54.6-56.7 % Cu, 41.7-43.2 % Zn, 1.7-1.8 % Co, 3.0-5.4 % As and 0.3-0.5 % Fe. Solution pH decreased during the experiment from 2.9 to 1.9-2.2. Elemental analysis using X-ray fluorescence showed that the contents of metals, except for As, in the leach residue were below the higher guideline values given in the Government decree on the assessment of the soil contamination and remediation needs by the Ministry of the Environment, Finland. Bioleaching facilitated the extraction of metals from pyritic ashes and the mitigation of environmental risks related to the residue disposal for other metals except for As.

Abstract: A composed mixed acidophilic, iron-oxidizing culture (FIGB) and a thermo-acidophilic enrichment culture (TK65) were used to evaluate microbial iron(III) reduction coupled to oxidation of reduced inorganic sulfur compounds (RISCs) under high pressure. Experiments were done in batch culture in high pressure vessels at 1 and 100 bar. Microbial abundance and activity were determined by measuring iron(II) concentration, direct cell counting, T-RFLP and quantitative real-time PCR. The data indicate that both cultures are able to reduce soluble iron(III) by oxidation of sulfur compounds under anaerobic conditions. At high pressure (100 bar) these acidophiles were capable of growing and microbial ferric iron reduction was only partially inhibited. These results indicate that acidophiles can be barotolerant and their activities are contributing to sulfur and iron cycling in anaerobic environments including deep ore deposits which is highly relevant for in situ leaching operations.

Abstract: Arsenic (As) is a major impurity contaminated in metal refinery wastewaters. To immobilize As ions, we have previously reported microbial scorodite (FeAsO₄·2H₂O) crystallization using the thermo-acidophilic iron-oxidizing archaeon, Acidianus brierleyi. In order to extend the applicable range of As (III)-bearing metal refinery wastewaters (especially for dilute As (III) concentrations of 250–1500 ppm), this study investigated the effect of several factors possibly affecting the bioscorodite crystallization efficiency; (i) [Fe (II)]_ini/[As (III)]_ini molar ratio at different target As (III) concentrations, (ii) initial pH, and (iii) seed scorodite with different morphologies. The [Fe (II)]_ini/[As (III)]_ini molar ratio strongly affected the bioscorodite crystallization efficiency at each target As (III) concentration. Whilst the [Fe (II)]_ini/[As (III)]_ini molar ratio of 1.4 was most effective at 500–1500 ppm As (III), the optimal molar ratios for treating more dilute concentrations (< 500 ppm) were shown to be relatively higher. However, further increasing the [Fe (II)]_ini/[As (III)]_ini molar ratio resulted in formation of unwanted potassium jarosite (KFe₃(OH)₆(SO₄)₂) together with scorodite. Lowering the initial pH from 1.5 to 1.2 resulted in earlier scorodite nucleation, but lesser overall As immobilization. Feeding chemical-and bio-scorodite seed crystals differently affected the reaction speed and the stability of newly-precipitated bioscorodite. The TCLP test indicated that scorodite formed on bioscorodite seeds is more stable than that formed on chemically-synthesized scorodite seeds.

Abstract: The major objective of the EU Horizon 2020 project “BioMOre” is the technical realization of indirect in situ leaching of Kupferschiefer sandstone and black shale ore by a ferric iron lixiviant generated by a mixed culture of autotrophic, acidophilic, iron-oxidizing bacteria and archaea in a ferric iron-generating bioreactor (FIGB). These organisms could colonize the deeply buried geological formations even under anaerobic conditions as most are able to grow by coupling the reduction of ferric iron to the oxidation of reduced sulfur compounds in the absence of oxygen. Development of an inhibition protocol to eliminate these allochthonous microbial bioreactor populations subsequent to the completion of in situ bioleaching was therefore investigated. Column bioleaching experiments using a laboratory-scale FIGB confirmed not only that metals were solubilised from both the sandstone and shale ores, but also that significant numbers of bacteria were released from the FIGB. The efficacy of 13 different chemical compounds in inhibiting microbial iron oxidation has been tested at different concentrations in shake flask and FIGB-coupled columns. Iron-oxidation activity, microcalorimetrically-determined activity and ATP measurements, in combination with microscopic cell counts and biomolecular analysis (T-RFLP, qPCR), plate counts and most-probable-number (MPN), were used to monitor the inhibiting effects on the acidophiles. Complete inhibition of metabolic activity of iron-oxidizing acidophiles was achieved in the presence of 0.4 mM formate, 300 mM chloride, 100 mM nitrate, 10 mM of primary C₆ to C₈ alcohols, 100 mM 1-butanol, 100 mM 1-pentanol, 0.1 mM SDS or 0.35 mM benzoic acid. No inhibition was found for 0.6 mM acetic acid and 200 mM methanol. Based on these results a recipe for the chemical composition of the “decommissioning solution” is proposed.

Abstract: Kupferschiefer-type ore represents an important source for base metals and several studies concerning the bioleaching of black shale ores and Cu concentrates have been carried out with focus on various microbial communities and processing parameters. However, the incomplete dissolution of chalcopyrite remains a key issue for copper ore bioleaching improvement and requires further investigations in order to ensure an optimal control of the process for upscaling. Our study clearly showed that bioleaching tests are characterized by two separate phases with a distinct optimal temperature. A distinct effect of the temperature on the copper recovery and the advantage of temperature ramp in order to enhance copper bioleaching and chalcopyrite dissolution were demonstrated.

Abstract: Río Tinto (Iberian Pyrite Belt, SW Spain) is a natural extreme acidic environmentwith a constant acidic pH and high concentration of toxic heavy metals. The characterization of the Tinto basin performed by our group during more than thirty years has provided evidences on the importance of the iron and sulfur cycles in generating the extreme conditions of theriver and maintaining the high level of prokaryotic and eukaryotic diversity detected on it.It has also proven that the extreme conditions of the Tinto basin are not generated by the long record of mining activities in the area, but the consequence of an underground bioreactor sustained by the massive sulfidic minerals existing in the Iberian Pyrite Belt. To test this hypothesis two drilling projects, MARTE (NASA Ames and Centro de Astrobiología, 2003-2006) and IPBSL (Centro de Astrobiología, 2011-2015) have beenperformed to provide evidences ofchemolithotrophicmicrobial activities operating in thisunderground bioreactor.Considering all the information collected from this natural ARD and AMD model system, its biohydrometallurgical interest is discussed

Abstract: This European Union ERASysApp funded study will investigate one of the major drawbacks of bioleaching of the copper containing mineral chalcopyrite, namely the long lag phase between construction and inoculation of bioleaching heaps and the release of dissolved metals. In practice, this lag phase can be up to three years and the long time period adds to the operating expenses of bioheaps for chalcopyrite dissolution. One of the major time determining factors in bioleaching heaps is suggested to be the speed of mineral colonization by the acidophilic microorganisms present. By applying confocal microscopy, metatranscriptomics, metaproteomics, bioinformatics, and computer modeling the authors aim to investigate the processes leading up to, and influencing the attachment of three moderately thermophilic sulfur-and/or iron-oxidizing model species: Acidithiobacillus caldus, Leptospirillum ferriphilum, and Sulfobacillus thermosulfidooxidans. Stirred tank reactors containing chalcopyrite concentrate will be inoculated with these species in various orders and proportions and the effects on the lag phase and rates of metal release will be compared. Meanwhile, confocal microscopy studies of cell attachment to chalcopyrite mineral particles, as well as metatranscriptomics and metaproteomics of the formed biofilms will further increase understanding of the attachment process and help develop a model thereof. By fulfilling our goal to decrease the length of the lag phase of chalcopyrite bioleaching heaps we hope to increase their economic feasibility and therefore, industrial interest in bioleaching as a sustainable technology.

Abstract: Pregnant leach solutions (PLS) resulting from bioleaching of copper concentrate from Kupferschiefer are characterized by low pH values and high concentrations of mainly ferric iron, copper, zinc and sulfate, as well as significant amounts of nickel and cobalt. In order to recover the valuable metals for further processing, a novel technique that promotes selective metal recovery and sulfate removal from acidic liquors, described in this study, is proposed.