The Development of Innovated Complex Process for Treatment of Old Flotation Tailings of Copper-Zinc Sulfide Ore.

The possibility of selective Cu and Zn leaching from the sample of old pyrite tailings, which is one of the most widespread types of solid waste forming during non-ferrous metal production, using sulfuric acid solutions and water was studied. It was shown that water leaching provided selective extraction of Cu and Zn and comparatively low iron ion extraction. At the same time, acid leaching provided the obtainment of pregnant solutions with high ferric ion concentration, which can be used for oxidative leaching of substandard copper concentrates. Water and acid leaching also provided increased Au recovery by cyanidation. The results suggest that acid leaching can be an effective approach for processing old flotation tailings, which allows the extraction of base metals from these wastes and treating flotation tailings for subsequent cyanidation. Effective flotation treatment methods should also provide environmental load reduction, which is caused by the long-term storage of metal-bearing wastes.

Draft genome sequence of Acidiplasma cupricumulans strain BH2T, isolated from a pregnant leachate solution of heap bioleaching.

We report the draft genome sequence of a type strain Acidiplasma cupricumulans Strain BH2T, isolated from a pregnant leachate solution of industrial-scale chalcocite bioleach heap (Monywa, Myanmar). The genome is 1.7 Mbp long with a GC content of 34.2%.

Shifts in the Microbial Populations of Bioleach Reactors Are Determined by Carbon Sources and Temperature.

In the present study, the effect of additional carbon sources (carbon dioxide and molasses) on the bio-oxidation of a pyrite-arsenopyrite concentrate at temperatures of 40-50 °C was studied, and novel data regarding the patterns of the bio-oxidation of gold-bearing sulfide concentrates and the composition of the microbial populations performing these processes were obtained. At 40 °C, additional carbon sources did not affect the bio-oxidation efficiency. At the same time, the application of additional carbon dioxide improved the bio-oxidation performance at temperatures of 45 and 50 °C and made it possible to avoid the inhibition of bio-oxidation due to an increase in the temperature. Therefore, the use of additional carbon dioxide may be proposed to prevent the negative effect of an increase in temperature on the bio-oxidation of sulfide concentrates. 16S rRNA gene profiling revealed archaea of the family Thermoplasmataceae (Acidiplasma, Ferroplasma, Cuniculiplasma, and A-plasma group) and bacteria of the genera Leptospirillum, with Sulfobacillus and Acidithiobacillus among the dominant groups in the community. Temperature influenced the composition of the communities to a greater extent than the additional sources of carbon and the mode of operation of the bioreactor. Elevating the temperature from 40 °C to 50 °C resulted in increases in the shares of Acidiplasma and Sulfobacillus and decreases in the relative abundances of Ferroplasma, Leptospirillum, and Acidithiobacillus, while Cuniculiplasma and A-plasma were more abundant at 45 °C. A metagenomic analysis of the studied population made it possible to characterize novel archaea belonging to an uncultivated, poorly-studied group of Thermoplasmatales which potentially plays an important role in the bio-oxidation process. Based on an analysis of the complete genome, we propose describing the novel species and novel genus as "Candidatus Carboxiplasma ferriphilum" gen. nov., spec. nov.

Two-Stage Oxidative Leaching of Low-Grade Copper-Zinc Sulfide Concentrate.

Bioleaching may be effectively used to extract nonferrous metals from sulfide ores and concentrates. At the same time, some minerals are refractory and their bioleaching rate is often comparatively low that does not allow the required metal extraction rate to be achieved. In the present work, we studied the two-stage process, which included stages of biological and chemical leaching, to improve copper extraction from low grade Cu-Zn sulfide concentrate containing chalcopyrite, tennantite, pyrite, and sphalerite. Bioleaching was conducted in the continuous mode in three laboratory scale reactors connected in series. The pulp density was 10% and the residence time was 7 days. The temperature was 40 °C in the 1st reactor and 50 °C in the 2nd and 3rd reactors. Bioleaching allowed the extraction of 29.5 and 78% of Cu and Zn, respectively. The solid bioleach residue obtained was then treated for additional Cu and Zn recovery using high temperature leaching at 90 °C for 25 h. The liquid phase of the bioleaching pulp contained Fe3+ ions, which is the strong oxidant, and the leach solution was supplemented with NaCl. In the presence of the maximal NaCl concentration (1 M), Cu and Zn extraction reached 48 and 84%. Thus, two-stage leaching may allow to increase bioleaching efficiency and may be used to improve the bioleaching rate of refractory minerals, such as chalcopyrite.

Draft Genome Sequence of Acidiplasma aeolicum Strain V1T, Isolated from a Hydrothermal Pool.

We report the draft genome sequence of Acidiplasma aeolicum strain V1T, isolated from a hydrothermal pool (Vulcano Island, Italy). The genome is 1.8 Mbp long with a GC content of 34%. The genome sequence was found to be closely related to those of other known strains of Acidiplasma genus.

Biogeochemical Niches of Fe-Cycling Communities Influencing Heavy Metal Transport along the Rio Tinto, Spain.

In the mining-impacted Rio Tinto, Spain, Fe-cycling microorganisms influence the transport of heavy metals (HMs) into the Atlantic Ocean. However, it remains largely unknown how spatial and temporal hydrogeochemical gradients along the Rio Tinto shape the composition of Fe-cycling microbial communities and how this in turn affects HM mobility. Using a combination of DNA- and RNA-based 16S rRNA (gene) amplicon sequencing and hydrogeochemical analyses, we explored the impact of pH, Fe(III), Fe(II), and Cl- on Fe-cycling microorganisms. We showed that the water column at the acidic (pH 2.2) middle course of the river was colonized by Fe(II) oxidizers affiliated with Acidithiobacillus and Leptospirillum. At the upper estuary, daily fluctuations of pH (2.7 to 3.7) and Cl- (6.9 to 16.6 g/L) contributed to the establishment of a unique microbial community, including Fe(II) oxidizers belonging to Acidihalobacter, Marinobacter, and Mariprofundus, identified at this site. Furthermore, DNA- and RNA-based profiles of the benthic community suggested that acidophilic and neutrophilic Fe(II) oxidizers (e.g., Acidihalobacter, Marinobacter, and Mariprofundus), Fe(III) reducers (e.g., Thermoanaerobaculum), and sulfate-reducing bacteria drive the Fe cycle in the estuarine sediments. RNA-based relative abundances of Leptospirillum at the middle course as well as abundances of Acidihalobacter and Mariprofundus at the upper estuary were higher than DNA-based results, suggesting a potentially higher level of activity of these taxa. Based on our findings, we propose a model of how tidal water affects the composition and activity of the Fe-cycling taxa, playing an important role in the transport of HMs (e.g., As, Cd, Cr, and Pb) along the Rio Tinto. IMPORTANCE The estuary of the Rio Tinto is a unique environment in which extremely acidic, heavy metal-rich, and especially iron-rich river water is mixed with seawater. Due to the mixing events, the estuarine water is characterized by a low pH, almost seawater salinity, and high concentrations of bioavailable iron. The unusual hydrogeochemistry maintains unique microbial communities in the estuarine water and in the sediment. These communities include halotolerant iron-oxidizing microorganisms which typically inhabit acidic saline environments and marine iron-oxidizing microorganisms which, in contrast, are not typically found in acidic environments. Furthermore, highly saline estuarine water favored the prosperity of acidophilic heterotrophs, typically inhabiting brackish and saline environments. The Rio Tinto estuarine sediment harbors a diverse microbial community with both acidophilic and neutrophilic members that can mediate the iron cycle and, in turn, can directly impact the mobility and transport of heavy metals in the Rio Tinto estuary.

Effect of Carbon Sources on Pyrite-Arsenopyrite Concentrate Bio-oxidation and Growth of Microbial Population in Stirred Tank Reactors.

Tank bio-oxidation is a biohydrometallurgical technology widely used for metal recovery from sulfide concentrates. Since carbon availability is one of the key factors affecting microbial communities, it may also determine the rate of sulfide concentrate bio-oxidation. The goal of the present work was to evaluate the effect of carbon sources on the bio-oxidation of the concentrate containing 56% pyrite and 14% arsenopyrite at different temperatures (40 and 50 °C) in stirred tank reactors. CO2 was supplied into the pulp of the first reactor (about 0.01 L/min) and 0.02% (w/v) molasses was added to the pulp of the second one, and no additional carbon sources were used in the control tests. At 40 °C, 77% of pyrite and 98% of arsenopyrite were oxidized in the first reactor, in the second one, 73% of pyrite and 98% of arsenopyrite were oxidized, while in the control reactor, 27% pyrite and 93% arsenopyrite were oxidized. At 50 °C, in the first reactor, 94% of pyrite and 99% of arsenopyrite were oxidized, in the second one, 21% of pyrite and 94% of arsenopyrite were oxidized, while in the control reactor, 10% pyrite and 92% arsenopyrite were oxidized. The analysis of the microbial populations in the reactors revealed differences in the total number of microorganisms and their species composition. Thus, it was shown that the use of various carbon sources made it possible to increase the intensity of the concentrate bio-oxidation, since it affected microbial populations performing the process.

Unraveling the Central Role of Sulfur-Oxidizing Acidiphilium multivorum LMS in Industrial Bioprocessing of Gold-Bearing Sulfide Concentrates.

Acidiphilium multivorum LMS is an acidophile isolated from industrial bioreactors during the processing of the gold-bearing pyrite-arsenopyrite concentrate at 38-42 °C. Most strains of this species are obligate organoheterotrophs that do not use ferrous iron or reduced sulfur compounds as energy sources. However, the LMS strain was identified as one of the predominant sulfur oxidizers in acidophilic microbial consortia. In addition to efficient growth under strictly heterotrophic conditions, the LMS strain proved to be an active sulfur oxidizer both in the presence or absence of organic compounds. Interestingly, Ac. multivorum LMS was able to succeed more common sulfur oxidizers in microbial populations, which indicated a previously underestimated role of this bacterium in industrial bioleaching operations. In this study, the first draft genome of the sulfur-oxidizing Ac. multivorum was sequenced and annotated. Based on the functional genome characterization, sulfur metabolism pathways were reconstructed. The LMS strain possessed a complicated multi-enzyme system to oxidize elemental sulfur, thiosulfate, sulfide, and sulfite to sulfate as the final product. Altogether, the phenotypic description and genome analysis unraveled a crucial role of Ac. multivorum in some biomining processes and revealed unique strain-specific characteristics, including the ars genes conferring arsenic resistance, which are similar to those of phylogenetically distinct microorganisms.

Role of biogenic Fe(III) minerals as a sink and carrier of heavy metals in the Rio Tinto, Spain.

Oxidation of sulfide ores in the Iberian Pyrite Belt region leads to the presence of extremely high concentration of dissolved heavy metals (HMs) in the acidic water of the Rio Tinto. Fe(II) is microbially oxidized resulting in the formation of suspended particulate matter (SPM) consisting of microbial cells and Fe(III) minerals with co-precipitated HMs. Although substantial amount of HM-bearing SPM is likely deposited to river sediment, a portion can still be transported through estuary to the coastal ocean. Therefore, the mechanisms of SPM formation and transport along the Rio Tinto are important for coastal-estuarine zone. In order to reveal these mechanisms, we performed diurnal sampling of Rio Tinto water, mineralogical and elemental analysis of sediment from the middle course and the estuary of the river. We identified two divergent but interrelated pathways of HM transfer. The first longitudinal pathway is the transport of SPM-associated metals such as As (6.58 µg/L), Pb (3.51 µg/L) and Cr (1.30 µg/L) to the coastal ocean. The second sedimentation pathway contributes to the continuous burial of HMs in the sediment throughout the river. In the middle course, sediment undergoes mineralogical transformations during early diagenesis and traps HMs (e.g. 1.6 mg/g of As, 1.23 mg/g of Pb and 0.1 mg/g of Cr). In the estuary, HMs are accumulated in a distinct anoxic layer of sediment (e.g. 1.5 mg/g of As, 2.09 mg/g of Pb and 0.04 mg/g of Cr). Our results indicate that microbially precipitated Fe(III) minerals (identified as ferrihydrite and schwertmannite) play a key role in maintaining these divergent HM pathways and as a consequence are crucial for HM mobility in the Rio Tinto.

Enrichment and genome sequence of the group I.1a ammonia-oxidizing Archaeon "Ca. Nitrosotenuis uzonensis" representing a clade globally distributed in thermal habitats.

The discovery of ammonia-oxidizing archaea (AOA) of the phylum Thaumarchaeota and the high abundance of archaeal ammonia monooxygenase subunit A encoding gene sequences in many environments have extended our perception of nitrifying microbial communities. Moreover, AOA are the only aerobic ammonia oxidizers known to be active in geothermal environments. Molecular data indicate that in many globally distributed terrestrial high-temperature habits a thaumarchaeotal lineage within the Nitrosopumilus cluster (also called "marine" group I.1a) thrives, but these microbes have neither been isolated from these systems nor functionally characterized in situ yet. In this study, we report on the enrichment and genomic characterization of a representative of this lineage from a thermal spring in Kamchatka. This thaumarchaeote, provisionally classified as "Candidatus Nitrosotenuis uzonensis", is a moderately thermophilic, non-halophilic, chemolithoautotrophic ammonia oxidizer. The nearly complete genome sequence (assembled into a single scaffold) of this AOA confirmed the presence of the typical thaumarchaeotal pathways for ammonia oxidation and carbon fixation, and indicated its ability to produce coenzyme F420 and to chemotactically react to its environment. Interestingly, like members of the genus Nitrosoarchaeum, "Candidatus N. uzonensis" also possesses a putative artubulin-encoding gene. Genome comparisons to related AOA with available genome sequences confirmed that the newly cultured AOA has an average nucleotide identity far below the species threshold and revealed a substantial degree of genomic plasticity with unique genomic regions in "Ca. N. uzonensis", which potentially include genetic determinants of ecological niche differentiation.