Biodepression of Copper-Activated Pyrite with Acidithiobacillus ferrooxidans in Flotation with Fresh and Seawater

Acidithiobacillus ferrooxidans has been shown to be a good depressant of pyrite in freshwater and seawater flotation. However, the effect of these bacteria over copper-activated pyrite has not been studied. At the industrial scale, the activation of pyrite with copper is a common process that occurs because Cu2+ ions, released from other minerals, react with pyrite. This is a problem because Cu2+ ions facilitate the reaction of pyrite with the xanthate collectors, becoming hydrophobic and reaching the froth. In this study, microflotation experiments in a Hallimond tube were conducted to evaluate the depressant effect of A. ferrooxidans over non-activated and Cu-activated pyrite in freshwater and seawater flotation. The experiments were carried out at pH 4, 6, 8, 10 and 12 and pyrite was mixed with CuSO4 at 2.5×10−5 and 5×10−5 M in order to activate its surface. Considering the results obtained in the microflotation tests, it is possible to conclude that Acidithiobacillus ferrooxidans is able to depress non-activated and Cu-activated pyrite at the entire pH range studied (4–12) in freshwater. On the other hand, the use of bacteria in flotation with seawater proved to be effective to depress non-activated and Cu-activated pyrite at pH 8 and 10 with better results achieved at pH 10. At this pH, the non-activated pyrite recovery dropped from 96% to 15%, and the recovery of Cu-activated pyrite dropped from 95% to 32% when the activation was carried out at 2.5×10−5 M, and from 87% to 50% when the activation was conducted at 5×10−5 M of CuSO4. The XPS analysis showed that chalcopyrite and copper (II) hydroxide were formed on the pyrite surface when it is contacted with CuSO4.

One year in situ incubation of pyrite at the deep seafloor and its microbiological and biogeochemical characterizations

In this study, we performed a year-long in situ incubation experiment of a common ferrous sulfide (Fe-S) mineral, pyrite, at the oxidative deep seafloor in the hydrothermal vent field in the Izu-Bonin arc, Japan, and characterized its microbiological and biogeochemical properties to understand the microbial alteration processes of the pyrite, focusing on the Fe(II) oxidation. The microbial community analysis of the incubated pyrite showed that the domain Bacteria heavily dominated over Archaea compared with that of the ambient seawater, and Alphaproteobacteria and Gammaproteobacteria distinctively co-dominated at the class level. The mineralogical characterization by surface-sensitive Fe X-ray absorption near-edge structure (XANES) analysis revealed that specific Fe(III) hydroxides (schwertmannite and ferrihydrite) were locally formed at the pyrite surface as the pyrite alteration products. Based on the Fe(III) hydroxide species and proportion, we thermodynamically calculated the pH value at the pyrite surface to be pH 4.9-5.7, indicating that the acidic condition derived from pyrite alteration was locally formed at the surface against neutral ambient seawater. This acidic microenvironment at the pyrite surface might explain the distinct microbial communities found in our pyrite samples. Also, the acidity at the pyrite surface indicates that abiotic Fe(II) oxidation rate was much limited at the pyrite surface kinetically, 3.9 × 10 3 −1.6 × 10 5 -fold lower than that in the ambient seawater. Moreover, the nanoscale characterization of microbial biomolecules using carbon near-edge X-ray absorption fine structure (NEXAFS) analysis showed that the sessile cells attached to pyrite excreted the acidic polysaccharide-rich extracellular polymeric substances at the pyrite surface, which can lead to the promotion of biogenic Fe(II) oxidation and pyrite alteration. Importance Pyrite is one of the most common Fe-S minerals found in submarine hydrothermal environments. Previous studies demonstrated that the Fe-S mineral can be a suitable host for Fe(II)-oxidizing microbes in hydrothermal environments; however, the details of microbial Fe(II) oxidation processes with Fe-S mineral alteration are not well known. The spectroscopic and thermodynamic examination in the present study suggests that moderately acidic pH condition was locally formed at the pyrite surface during pyrite alteration at the seafloor due to proton releases with Fe(II) and sulfidic S oxidations. Following previous studies, the abiotic Fe(II) oxidation rate significantly decreases with a decrease in pH, but the biotic (microbial) Fe(II) oxidation rate is not sensitive to the pH decrease. Thus, our findings clearly suggest the pyrite surface is a unique microenvironment where abiotic Fe(II) oxidation is limited and biotic Fe(II) oxidation is more prominent than that in neutral ambient seawater.

Pyrite (FeS2)-supported ultrafiltration system for removal of mercury (II) from water

This study investigated the Hg(II) removal efficiencies of the reactive adsorbent membrane (RAM) hybrid filtration process, a removal process that produces stable final residuals. The reaction mechanism between Hg(II) and pyrite and the rejection of the solids over time were characterized with respect to flux decline, pH change, and Hg and Fe concentration in permeate water. Effects of the presence of anions (Cl−, SO42−, NO3−) or humic acid (HA) on the rejection of the Hg(II)-contacted pyrite were studied. The presence of both HA and Hg(II) increased the rate of flux decline due to the formation of irreversible gel-like compact cake layers as shown in the experimental data and modeling related to the flux decline and the SEM images. Stability experiments of the final residuals retained on the membrane using a thiosulfate solution (Na2S2O3) show that the Hg(II)-laden solids were very stable due to little or no detection of Hg(II) in the permeate water. Experiment on the possibility of continuously removing Hg(II) by reusing the Hg/pyrite-laden membrane shows that almost all Hg(II) was adsorbed onto the pyrite surface regardless of the presence of salts or HA, and the Hg(II)-contacted pyrite residuals were completely rejected by the DE/UF system. Therefore, a membrane filter containing pyrite-Hg(II) could provide another reactive cake layer capable of further removal of Hg(II) without post-chemical treatment for reuse.

Pyrite/H2O2/hydroxylamine system for efficient decolorization of rhodamine B

To improve the efficiency of the Fe(II)/Fe(III) cycle and continuous reactivity of pyrite, a pyrite/H2O2/hydroxylamine (HA) system was proposed to treat rhodamine B (RhB). The results showed that near-complete decolorization and 52.8% mineralization 50 mg L−1 RhB were achieved under its optimum conditions: HA 0.8 mM, H2O2 1.6 mM, pyrite 0.4 g L−1, and initial pH 4.0. The degradation reaction was dominated by an •OH radical produced by the reaction of Fe2+ with H2O2 in solution. HA primarily had two roles: in solution, HA could accelerate the Fe(II)/Fe(III) cycle through its strong reducibility to enhance RhB decolorization; on the pyrite surface, HA could improve the continuous reactivity of pyrite by inhibiting the oxidation of pyrite. In addition, the dosing manner of HA had a significant effect on RhB decolorization. In addition, the high decolorization and mineralization efficiency of other dye pollutants suggested that the pyrite/H2O2/HA system might be widely used in textile wastewater treatment.

An XPS study of HCN-derived films on pyrite surfaces: a prebiotic chemistry standpoint towards the development of protective coatings

Alkaline hydrothermal environment led to a NH4CN-based film with protective corrosion properties on the highly reactive pyrite surface.

Two-stage fluid pathways generated by volume expansion reactions: insights from the replacement of pyrite by chalcopyrite

Volume expansion reactions involved in mineral–fluid interactions are linked to a number of geological processes, including silicate weathering, retrograde metamorphism, and mineralization. However, the effect of volume expansion on replacement reactions remains unclear. Here, we demonstrate that reactions associated with volume expansion during the replacement of pyrite by chalcopyrite involve two competing processes. The reaction is initially augmented because of the development of reaction-induced fractures in the pyrite. However, these fractures are subsequently filled by compacted products, which ultimately disrupts the contact and interaction between bulk fluids and the pristine pyrite surface. These competing processes indicate that replacement reactions are both augmented and inhibited by volume expansion reactions during pyrite replacement.

DFT-MD Dissolution of Oilfield Pyrite Scale using Borax

Introduction: Oilfield scales including pyrite form in oil and gas pipelines, underground tubing, and surface equipment thus blocking the flow of fluids and hindering production. Hence, the need for the development of effective chemicals in scale dissolution and removal. Materials and methods: A computational technique known as Density Functional Theory- Molecular Dynamics (DFT-MD) was employed to investigate the use of borax in scale dissolution. This method aids the understanding at the atomic level of scale dissolution by using Quantum ATK’s virtual Nano lab and VASP for model building and DFT-MD calculations respectively. Geometrical studies and radial distribution functions were carried out for data analysis. Results: The results show that potassium ion preferentially bonds to the sulfur atoms in the top layer of the pyrite surface rather than with iron. Hence, becoming the predominant factor that is responsible for pyrite dissolution. The K-S bonds evolve dynamically and expose the rest of the pyrite surface. Conclusions/future directions: The presence of a chelating agent alongside borax would prevent Fe-S bond formation. Hence, it is proposed that borax, in conjunction with chelating agents, would be efficient in pyrite scale dissolution and removal. This technique can be used to study other iron sulfide scales such as troilite and greigite, which have different iron to sulfur ratio compared to pyrite. This will consequently help boost production in the upstream sector.

Pyrite-induced uv-photocatalytic abiotic nitrogen fixation: implications for early atmospheres and Life

<p><strong>Pyrite-induced uv-photocatalytic abiotic nitrogen fixation: implications for early atmospheres and Life</strong></p> <p><strong> </strong></p> <ol> <li><strong> Mateo-Marti <sup>1</sup>, S. Galvez-Martinez<sup>1</sup>, C. Gil-Lozano<sup>1</sup> and María-Paz Zorzano <sup>1,2</sup></strong></li> </ol> <p> </p> <p><sup>1</sup>Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, Madrid, Spain.</p> <p><sup>2</sup>Department of Computer Science, Electrical and Space Engineering, Luleå Universit of Technology, Luleå, Sweden.</p> <p><br /><br />  Nitrogen is an essential element for life, a prerequisite for the origin and evolution of life on Earth, or in any other potentially habitable planet. The molecular form of nitrogen, N<sub>2</sub>, is universally available but is biochemically inaccessible for life due to the strength of its triple bond. Prior to the emergence of life, there must have been an abiotic process that could fix nitrogen in a biochemically usable form. The UV photo-catalytic effects of minerals such as pyrite on nitrogen fixation have to date been overlooked. Here we show experimentally, using X-ray photoemission and infrared spectroscopies that, under a standard earth atmosphere containing nitrogen and water vapour at Earth or Martian pressures, nitrogen is fixed to pyrite as ammonium iron sulfate after merely two hours of exposure to 2,3 W/m2 of ultraviolet irradiance in the 200–400 nm range [1]. Our experiments show that this process exists also in the absence of UV, although about 50 times slower. The experiments also show that carbonates species are fixed on pyrite surface [Figure 1]. We conclude that UV photocatalysis on pyrite may have been a natural mechanism of prebiotic fixation of nitrogen into ammonium sulfates which is then easily released upon contact with liquid water. This property of pyrite may have been incorporated naturally in the prebiotic chemistry evolution, leading to the inclusion of pyrite nano-clusters as reaction centres to generate ammonia from nitrogen, and then from ammonia to generate ammonium sulfates salts in the presence of oxygen. This process has furthermore implication for the abiotic nitrogen fixation on other planetary environments, and it has critical implications for the habitability of planet and the origin of life.</p> <p> </p> <p><strong>Fig. 1</strong>    Picture of the Planetary Atmosphere and Surfaces Chamber and XPS spectra of the presence of ammonium sulfate on pyrite surface (on the left). Schematic representation of the processes that lead nitrogen fixation on pyrite surface (on the right), (i) by UV photo-catalysis under low pressure conditions (on the top) and, (ii) by the catalytic effect of iron oxide-iron sulfide tandem under visible light conditions and standard earth atmosphere (on the bottom).</p> <p> </p> <p> </p> <p> </p> <p> </p> <p> </p> <p> </p> <p> </p> <p> </p> <p>[1]   E. Mateo-Marti, S. Galvez-Martinez, C. Gil-Lozano and M-P. Zorzano, Scientific Reports, <strong>9,</strong> 15311 (2019)</p>