RESUMEN
The development of cost-effective environmentally friendly technologies is of current importance for the intensification of metal recovery. Here, we propose a new direction in the use of a two-step process for the treatment of complex sulfidic ores. In the first step, ore flotation allows the obtainment of a bulk copper-zinc concentrate and low-toxicity waste. In the second step, zinc is selectively extracted by chemical leaching with a biogenic ferric iron solution, while copper is accumulated in the leach residue. Importantly, the efficiency of this step depends on the chemical and mineralogical composition of polymetallic concentrates. Four samples of the copper-zinc sulfide concentrate with various contents of copper and zinc have been leached in multiple cycles at 80 °C, 10% of pulp density, and pH 1.3-1.5. The leaching of the concentrate that contained 14.7% of copper and 5.0% of zinc for three leaching cycles (total duration, 5.75 h) allowed the obtainment of a leach residue containing 15.3 and 0.14% of copper and zinc, respectively. At the same time, the leaching of another concentrate that contained 19.2% of copper and 2.64% of zinc after one leaching cycle (total duration, 0.67 h) led to copper and zinc contents of 19.1 and 0.72%, respectively, in the leach residue. Therefore, the treatment of only two concentrates allowed the obtainment of high-grade copper concentrates containing low amounts of zinc. Ferric iron, the oxidant of sulfide minerals, was fully regenerated in leachate within 30-35 h at 40 °C using an acidophilic microbial community dominated by Leptospirillum ferriphilum, Sulfobacillus spp., and Ferroplasma acidiphilum. The loss of copper and zinc in solid waste of the bioregeneration did not exceed 1.0% and 1.8%, respectively. The proposed flowsheet of bulk concentrate processing has several important advantages over conventional technologies, including short duration of leaching, formation of low-toxicity solid waste, and pyrometallurgical processing of only high-grade copper concentrates. This approach can be a promising solution for the efficient processing of polymetallic bulk concentrates.
Asunto(s)
Cobre , Residuos Sólidos , Cobre/química , Hierro/química , Sulfuros , Zinc/químicaRESUMEN
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.
RESUMEN
Biooxidation of gold-bearing arsenopyrite concentrates, using acidophilic microbial communities, is among the largest commercial biohydrometallurgical processes. However, molecular mechanisms of microbial responses to sulfide raw materials have not been widely studied. The goal of this research was to gain insight into the defense strategies of the acidophilic bacterium Sulfobacillus thermotolerans, which dominates microbial communities functioning in industrial biooxidation processes at >35 °C, against the toxic effect of the high-arsenic gold-bearing sulfide concentrate. In addition to extreme metal resistance, this acidophile proved to be one of the most As-tolerant microorganisms. Comparative proteomic analysis indicated that 30 out of 33 differentially expressed proteins were upregulated in response to the ore concentrate, while the synthesis level of the functional proteins required for cell survival was not negatively affected. Despite a high level of cellular metal(loid) accumulation, no specific metal(loid)-resistant systems were regulated. Instead, several proteins involved in the metabolic pathways and stress response, including MBL fold metallo-hydrolase, sulfide:quinone oxidoreductase, and GroEL chaperonin, may play crucial roles in resistance to the sulfide ore concentrate and arsenic, in particular. This study provides the first data on the microbial responses to sulfide ore concentrates and advances our understanding of defense mechanisms against toxic compounds in acidophiles.
RESUMEN
A two-step process, which involved ferric leaching with biologically generated solution and subsequent biooxidation with the microbial community, has been previously proposed for the processing of low-grade zinc sulfide concentrates. In this study, we carried out the process of complete biological oxidation of the product of ferric leaching of the zinc concentrate, which contained 9% of sphalerite, 5% of chalcopyrite, and 29.7% of elemental sulfur. After 21 days of biooxidation at 40°C, sphalerite and chalcopyrite oxidation reached 99 and 69%, respectively, while the level of elemental sulfur oxidation was 97%. The biooxidation residue could be considered a waste product that is inert under aerobic conditions. The results of this study showed that zinc sulfide concentrate processing using a two-step treatment is efficient and promising. The microbial community, which developed during biooxidation, was dominated by Acidithiobacillus caldus, Leptospirillum ferriphilum, Ferroplasma acidiphilum, Sulfobacillus thermotolerans, S. thermosulfidooxidans, and Cuniculiplasma sp. At the same time, F. acidiphilum and A. caldus played crucial roles in the oxidation of sulfide minerals and elemental sulfur, respectively. The addition of L. ferriphilum to A. caldus during biooxidation of the ferric leach product proved to inhibit elemental sulfur oxidation.
RESUMEN
The first complete genome of the biotechnologically important species Sulfobacillus thermotolerans has been sequenced. Its 3â 317â 203-bp chromosome contains an 83â 269-bp plasmid-like region, which carries heavy metal resistance determinants and the rusticyanin gene. Plasmid-mediated metal resistance is unusual for acidophilic chemolithotrophs. Moreover, most of their plasmids are cryptic and do not contribute to the phenotype of the host cells. A polyphosphate-based mechanism of metal resistance, which has been previously unknown in the genus Sulfobacillus or other Gram-positive chemolithotrophs, potentially operates in two Sulfobacillus species. The methylcitrate cycle typical for pathogens and identified in the genus Sulfobacillus for the first time can fulfill the energy and/or protective function in S. thermotolerans Kr1 and two other Sulfobacillus species, which have incomplete glyoxylate cycles. It is notable that the TCA cycle, disrupted in all Sulfobacillus isolates under optimal growth conditions, proved to be complete in the cells enduring temperature stress. An efficient antioxidant defense system gives S. thermotolerans another competitive advantage in the microbial communities inhabiting acidic metal-rich environments. The genomic comparisons revealed 80 unique genes in the strain Kr1, including those involved in lactose/galactose catabolism. The results provide new insights into metabolism and resistance mechanisms in the Sulfobacillus genus and other acidophiles.
