Pyrite Biooxidation by Acidophilic Archaea AcidiplasmaSp. MBA-1 Under Varied Conditions

The goal of this research was to study pyrite (FeS2 ) bioleaching by a strain of the genus Acidiplasma under different conditions (temperature, pH) to evaluate the potential role of Acidiplasma representatives in biooxidation of this sulfide mineral. To compare the role of Acidiplasma archaea in pyrite biooxidation with other acidophilic microorganisms, the experiments were also performed with representatives of othergroups of microorganisms predominant in biohydrometallurgical processes.Pure and mixed cultures of moderately thermophilic acidophilic microorganisms, including strains Acidithiobacillus caldus MBC-1, Sulfobacillusthermosulfidooxidans VKMV 1269T and Acidiplasmasp. MBA-1, were used. The experiments were carried out in flasks with 100 mL of mineral nutrient medium supplemented with 0.02% yeast extract and 1 g of pyrite on a rotary shaker for 20 days. Bioleaching was performed at 45, 55, and 60∘С. The results demonstrated that the representatives of the genus Acidiplasmaprovided a comparatively higher rate of pyrite bioleaching at high temperatures (55 and 60∘C) and low pH of the medium (1.0). Thus, according to the results, strains of thegenus Acidiplasma may provide a high rate of pyrite bioleaching at low levels ofpH. Therefore, the results suggest that archaea of the genus Acidiplasma may be promising microorganisms to improve bioleaching processes with an increase in the operational temperature, which is usually maintained at 40–45∘C in industrial-scale reactors. Keywords: biomining, bioleaching, acidophilic microorganisms, sulfide minerals, pyrite

Industrial Heap Bioleaching of Copper Sulfide Ore Started with Only Water Irrigation

Sulfuric acid solution containing ferric iron is the extractant for industrial heap bioleaching of copper sulfides. To start a heap bioleaching plant, sulfuric acid is usually added to the irrigation solution to maintain adequate acidity (pH 1.0–2.0) for copper dissolution. An industrial practice of heap bioleaching of secondary copper sulfide ore that began with only water irrigation without the addition of sulfuric acid was successfully implemented and introduced in this manuscript. The mineral composition and their behavior related to the production and consumption of sulfuric acid during the bioleaching in heaps was analyzed. This indicated the possibility of self-generating of sulfuric acid in heaps without exogenous addition. After proving by batches of laboratory tests, industrial measures were implemented to promote the sulfide mineral oxidation in heaps throughout the acidifying stages, from a pH of 7.0 to 1.0, thus sulfuric acid and iron was produced especially by pyrite oxidation. After acidifying of the heaps, adapted microbial consortium was inoculated and established in a leaching system. The launch of the bioleaching heap and finally the production expansion were realized without the addition of sulfuric acid, showing great efficiency under low operation costs.

Polarization-dependent optical responses in natural 2D layered mineral teallite

Multi-element layered materials enable the use of stoichiometric variation to engineer their optical responses at subwavelength scale. In this regard, naturally occurring van der Waals minerals allow us to harness a wide range of chemical compositions, crystal structures and lattice symmetries for layered materials under atomically thin limit. Recently, one type of naturally occurring sulfide mineral, ternary teallite has attained significant interest in the context of thermoelectric, optoelectronic, and photovoltaic applications, but understanding of light-matter interactions in such ternary teallite crystals is scarcely available. Herein, polarization-dependent linear and nonlinear optical responses in mechanically exfoliated teallite crystals are investigated including anisotropic Raman modes, wavelength-dependent linear dichroism, optical band gap evolution, and anisotropic third-harmonic generation (THG). Furthermore, the third-order nonlinear susceptibility of teallite crystal is estimated using the thickness-dependent THG emission process. We anticipate that our findings will open the avenue to a better understanding of the tailored light-matter interactions in complex multi-element layered materials and their implications in optical sensors, frequency modulators, integrated photonic circuits, and other nonlinear signal processing applications.

Sulfide mineral chemistry and platinum-group minerals of the UG-2 chromitite in the northern limb of the Bushveld Igneous Complex, South Africa

ABSTRACT The UG-2 chromitite layer, with its elevated platinum-group element content, is a key marker horizon in the eastern and western limbs of the Bushveld Igneous Complex and the largest platinum-group element chromite-hosted resource of its kind in the world. In contrast, much less is known about its stratigraphic equivalent in the northern limb, the “UG-2 equivalent” (UG-2E) chromitite. Recent studies on chromite mineral chemistry show similarities between the UG-2 and sections of the UG-2E, but also that the UG-2E was partially contaminated by assimilation of local metasedimentary rocks. Here, we provide a detailed characterization of sulfide minerals and platinum-group minerals in a suite of samples from the UG-2E and compare the results with data obtained from a reference suite of samples from the UG-2. Results from petrographic observations, electron probe microanalysis, laser ablation-inductively coupled plasma-mass spectrometry, quantitative evaluation of materials by scanning electron microscopy, and δ34S isotopes show that: (1) sulfide minerals in the UG-2E and UG-2 consist mainly of pentlandite-chalcopyrite-pyrrhotite, but pyrrhotite is significantly more abundant in the UG-2E and almost absent in the UG-2; (2) iron contents in pentlandite from the UG-2E are significantly higher than in the UG-2; (3) platinum-group element contents within sulfide minerals are different between the two chromitites; (4) UG-2E platinum-group minerals are dominated by arsenides and bismuthotellurides, and by alloys and platinum-group element-sulfide minerals in the UG-2; (5) sulfide mineral chemistry and δ34S values indicate some crustal contamination of the UG-2E; and (6) sulfide mineral and secondary silicate mineral textures in both the UG-2E and UG-2 are indicative of minor, millimeter- to centimeter-scale, hydrothermal alteration. From our observations and results, we consider the UG-2E chromitite in the northern limb to be the equivalent to the UG-2 in the eastern and western limbs that has been contaminated by assimilation of Transvaal Supergroup footwall rocks during emplacement. The contamination resulted in UG-2E sulfide mineral elemental contents and platinum-group mineral types and abundances that are distinct from those of the UG-2 in the rest of the Bushveld.

Flotation and Tailing Discarding of Copper Cobalt Sulfide Ores Based on the Process Mineralogy Characteristics

The mineral composition of copper–cobalt ores is more complex than that of copper sulfides, and it is also difficult to discard tailing efficiently in primary flotation for the fine-grained disseminated of ore. In this work, a mineral liberation analyzer (MLA) was employed to study the characteristics of minerals. As a significant mineralogical characteristic, the liberation degree of useful mineral aggregates was determined after grinding, and a correlation was established between the ore grinding size and mineralogical characteristics. The results showed that the adopted ore occurred in sulfide form. However, the particle size of the mineral’s monomer was fine grained, whereas its aggregate was coarse. The sulfide mineral aggregate obtained after primary grinding was selected as the recovery object, and its mineralogical characteristics, such as liberation degree and particle size, were investigated to promote total recovery in primary flotation. The copper–cobalt sulfide concentration was obtained at the following optimal conditions: the grinding size of −0.074 mm (65%), the aggregate’s liberation degree of 67%, a collector dosage of 50 g·t−1, a collector combination of 35% aerofloat + 65% butyl xanthate, a pH of 8.5, and 2# oil (a terpineol type foaming agent) dosage of 60 g·t−1. The recovered rough Cu and Co concentrates were 89.45% and 88.03%, respectively. Moreover, the grades of Cu and Co were 13.4% and 4.81%, respectively, with 85.07% of the ore weight discarded as tailing. The consideration of sulfide aggregates instead of singeral minerals mineralogy characters in primary grinding and primary flotation provides an effective theoretical guide for the sorting of sulfide minerals and reduction in the power consumption of grinding.

Evolution of a hydrothermal ore-forming system recorded by sulfide mineral chemistry: a case study from the Plaka Pb–Zn–Ag Deposit, Lavrion, Greece

Laser ablation-inductively coupled plasma-mass spectrometry and electron-probe microanalysis were used to investigate the trace-element contents of sphalerite, chalcopyrite and pyrite from the Plaka Pb–Zn–Ag deposit. Using petrographic observations, the analytical results could be linked to the temporal evolution of the Plaka ore-forming system. Sphalerite chemistry reliably records the temperature and fS2 evolution of the system, with estimated formation temperatures reproducing the microthermometric results from previous fluid-inclusion studies. Chalcopyrite chemistry also shows systematic variations over time, particularly for Cd, Co, Ge, In, Sn and Zn concentrations. Measurable pyrite was only found in association with early high-temperature mineralisation, and no clear trends could therefore be identified. We note, however, that As and Se contents in pyrite are consistent with formation temperatures estimated from co-existing sphalerite. Statistical analysis of the sphalerite data allowed us to identify the dominant geological controls on its trace-element content. The three investigated factors temperature, fS2, and sample location account for > 80% of the observed variance in Mn, Fe, Co, Ga, Ge, In, Sb and Hg concentrations, and > 60% of the observed variance in Cd and Sn concentrations. Only for Cu and Ag concentrations is the explained variance < 50%. A similarly detailed analysis was not possible for chalcopyrite and pyrite. Nevertheless, comparison of the results for all three investigated minerals indicates that there are some systematic variations across the deposit which may be explained by local differences in fluid composition.

Diffusible signal factor signaling controls bioleaching activity and niche protection in the acidophilic, mineral-oxidizing leptospirilli

Bioleaching of metal sulfide ores involves acidophilic microbes that catalyze the chemical dissolution of the metal sulfide bond that is enhanced by attached and planktonic cell mediated oxidation of iron(II)-ions and inorganic sulfur compounds. Leptospirillum spp. often predominate in sulfide mineral-containing environments, including bioheaps for copper recovery from chalcopyrite, as they are effective primary mineral colonizers and oxidize iron(II)-ions efficiently. In this study, we demonstrated a functional diffusible signal factor interspecies quorum sensing signaling mechanism in Leptospirillum ferriphilum and Leptospirillum ferrooxidans that produces (Z)-11-methyl-2-dodecenoic acid when grown with pyrite as energy source. In addition, pure diffusible signal factor and extracts from supernatants of pyrite grown Leptospirillum spp. inhibited biological iron oxidation in various species, and that pyrite grown Leptospirillum cells were less affected than iron grown cells to self inhibition. Finally, transcriptional analyses for the inhibition of iron-grown L. ferriphilum cells due to diffusible signal factor was compared with the response to exposure of cells to N- acyl-homoserine-lactone type quorum sensing signal compounds. The data suggested that Leptospirillum spp. diffusible signal factor production is a strategy for niche protection and defense against other microbes and it is proposed that this may be exploited to inhibit unwanted acidophile species.

Examining pathways of iron and sulfur acquisition, trafficking, deployment, and storage in mineral-grown methanogen cells

Methanogens have a high demand for iron (Fe) and sulfur (S); however, little is known of how they acquire, deploy, and store these elements and how this, in turn, affects their physiology. Methanogens were recently shown to reduce pyrite (FeS 2 ) generating aqueous iron-sulfide (FeS (aq) ) clusters that are likely assimilated as a source of Fe and S. Here, we compare the phenotype of Methanococcus voltae when grown with FeS 2 or ferrous iron (Fe(II)) and sulfide (HS - ). FeS 2 -grown cells are 33% smaller yet have 193% more Fe than Fe(II)/HS - -grown cells. Whole cell EPR revealed similar distributions of paramagnetic Fe, although FeS 2 -grown cells showed a broad spectral feature attributed to intracellular thioferrate-like nanoparticles. Differential proteomic analyses showed similar expression of core methanogenesis enzymes, indicating that Fe and S source does not substantively alter the energy metabolism of cells. However, a homolog of the Fe(II) transporter FeoB and its putative transcriptional regulator DtxR were up-expressed in FeS 2 -grown cells, suggesting that cells sense Fe(II) limitation. Two homologs of IssA, a protein putatively involved in coordinating thioferrate nanoparticles, were also up-expressed in FeS 2 -grown cells. We interpret these data to indicate that, in FeS 2 -grown cells, DtxR cannot sense Fe(II) and therefore cannot down-regulate FeoB. We suggest this is due to the transport of Fe(II) complexed with sulfide (FeS (aq) ) leading to excess Fe that is sequestered by IssA as a thioferrate-like species. This model provides a framework for the design of targeted experiments aimed at further characterizing Fe acquisition and homeostasis in M. voltae and other methanogens. IMPORTANCE FeS 2 is the most abundant sulfide mineral in the Earth’s crust and is common in environments inhabited by methanogenic archaea. FeS 2 can be reduced by methanogens, yielding aqueous FeS (aq) clusters that are thought to be a source of Fe and S. Here, we show that growth of Methanococcus voltae on FeS 2 results in smaller cell size and higher Fe content per cell, with Fe likely stored intracellularly as thioferrate-like nanoparticles. Fe(II) transporters and storage proteins were up-regulated in FeS 2 -grown cells. These responses are interpreted to result from cells incorrectly sensing Fe(II) limitation due to assimilation of Fe(II) as FeS (aq) . These findings have implications for our understanding of how Fe/S availability influences methanogen physiology and the biogeochemical cycling of these elements.