Transformation Of Pyrite Research Articles

A scale-integrated exploration model for orogenic gold deposits based on a mineral system approach

Concept-based orogenic gold exploration requires a scale-integrated approach using a robust mineral system model. Most genetic hypotheses for orogenic gold deposits that involve near-surface or magmatic-hydrothermal fluids are now negated in terms of a global mineral system model. Plausible models involve metamorphic fluids, but the fluid source has been equivocal. Crustal metamorphic-fluid models are most widely-accepted but there are serious problems for Archean deposits, and numerous Chinese provinces, including Jiaodong, where the only feasible fluid source is sub-crustal. If all orogenic gold deposits define a coherent mineral system, there are only two realistic sources of fluid and gold, based on their syn-mineralization geodynamic settings. These are from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package, or release from mantle lithosphere that was metasomatized and fertilized during a subduction event, particularly adjacent to craton margins. In this model, CO2 is generated during decarbonation and S and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 ​°C. This orogenic gold mineral system can be applied to conceptual exploration by first identifying the required settings at geodynamic to deposit scales. Within these settings, it is then possible to define the critical gold mineralization processes in the system: fertility, architecture, and preservation. The geological parameters that define these processes, and the geological, geophysical and geochemical proxies and responses for these critical parameters can then be identified. At the geodynamic to province scales, critical processes include a tectonic thermal engine and deep, effective, fluid plumbing system driven by seismic swarms up lithosphere-scale faults in an oblique-slip regime during uplift late in the orogenic cycle of a convergent margin. At the district to deposit scale, the important processes are fluid focussing into regions of complex structural geometry adjacent to crustal-scale plumbing systems, with gold deposition in trap sites involving complex conjugations of competent and/or reactive rock sequences and structural or lithological fluid caps. Critical indirect responses to defined parameters change from those generated by geophysics to those generated by geochemistry with reduction in scale of the mineral system-driven conceptual exploration.

Electrochemical gold precipitation to explain extensive vertical and lateral mineralization in the world‐class Poderosa‐Pataz district, Peru

AbstractThe world‐class Poderosa‐Pataz district is famous for its gold endowment in vertically and laterally extensive quartz‐sulphide veins. Precipitating mechanisms are investigated to determine why gold is so laterally and vertically distributed. Micro‐XRF and LA‐ICP‐MS element mapping of pyrites surrounding gold grains reveals systematic enrichment of As around or near visible gold accumulations. These As‐enriched zones define discordant rims and corridors overprinting pyrites. LA‐ICP‐MS spot analyses performed within and outside the As enrichment zones indicate that As is enriched on average by two orders of magnitude in association with gold. Secondary pyrite transformation by hydrothermal fluids with elevated As‐Au induced a change in the semiconducting properties of pyrite grains, resulting in the precipitation of visible gold particles at the interfaces of As‐enriched zones. The electrochemical precipitation mechanism acted as a filter to extract gold in solution regardless of variations in pressure and temperature, hence explaining the vertically and laterally extensive gold mineralization.

Trace-element systematics of pyrite and its implications for refractory gold mineralisation within the carbonaceous metasedimentary units of Palaeoproterozoic South Purulia shear zone, eastern India

Globally, refractory gold occurs in significant proportions in many types of gold deposits. The present work reports the occurrence of sulphide-hosted refractory gold within the carbonaceous phyllites of the South Purulia shear zone in the Singhbhum crustal province, eastern India. Detailed textural characteristics, paragenesis and trace-element concentrations of different generations of pyrites were studied to understand their evolutionary stages and the mechanism of gold incorporation in pyrites. Four types of pyrites, which are closely associated with gold mineralisation were identified in the host rock, i.e., carbonaceous phyllite. Py I is of diagenetic origin, whereas Py II, Py III and Py IV are of hydrothermal origin. Laser ablation inductively coupled plasma mass spectrometry studies confirm the presence of invisible/refractory gold concentration up to 110.55 ppm within these pyrites. The positive correlation between Au and As in pyrite indicates the significant role of As in the incorporation of gold in pyrite. Fourier transform infrared spectroscopy confirms the presence of organic matter that provided suitable redox conditions for the precipitation of auriferous pyrites. The refractory gold mineralisation is attributed to widespread sulphidation during both sedimentation and hydrothermal ore-forming processes. Transformation of diagenetic pyrite to pyrrhotite during prograde metamorphism of carbonaceous rocks promoted the liberation of sulphur and Au from the lattice of abundant diagenetic pyrites to the hydrothermal fluid which later precipitated sulphides in the quartz ± carbonate veins.

Fate of cobalt and nickel in mackinawite during diagenetic pyrite formation

AbstractAs iron sulfide mineral phases are important sedimentary sinks for naturally occurring or contaminant metals, it is important to know the fate of metals during the diagenetic transformation of primary sulfide minerals into more stable phases, such as pyrite (FeS2). Furthermore, the trace metal content of pyrite has been proposed as a marine paleoredox proxy. Given the diverse low-temperature diagenetic formation pathways for pyrite, this use of pyrite requires validation. We, therefore, studied nickel (Ni) and cobalt (Co) incorporation into freshly precipitated mackinawite (FeSm), and after experimental diagenesis to pyrite (FeS2) using S0 as an oxidant at 65 °C. Metal incorporation was quantified on bulk digests using ICP-OES or ICP-AES. Bulk mineralogy was characterized with micro-X-ray diffraction (micro-XRD), documenting the transformation of mackinawite to pyrite. Epoxy grain mounts were made anoxically of mackinawite and pyrite grains. We used synchrotron-based micro-X-ray fluorescence (μXRF) to map the distribution of Co and Ni, as well as to collect multiple energy maps throughout the sulfur (S) K-edge. Iron (Fe) and S K-edge micro-X-ray absorption near edge spectroscopy (μXANES) was used to identify the oxidation state and mineralogy within the experimentally synthesized and diagenetically transformed minerals, and map end-member solid phases within the grain mounts using the multiple energy maps. Metal-free FeSm transformed to pyrite, with residual FeSm detectable. Co- and Ni-containing FeSm also transformed to pyrite, but with multiple techniques detecting FeSm as well as S0, implying less complete transformation to pyrite as compared to metal-free FeSm. These results indicate that Co and Ni may inhibit transformation for FeSm to pyrite, or slow it down. Cobalt concentrations in the solid diminished by 30% during pyrite transformation, indicating that pyrite Co may be a conservative tracer of seawater or porewater Co concentrations. Nickel concentrations increased several-fold after pyrite formation, suggesting that pyrite may have scavenged Ni from the dissolution of primary FeSm grains. Nickel in pyrites thus may not be a reliable proxy for seawater or porewater metal concentrations.

A holistic model for the origin of orogenic gold deposits and its implications for exploration

The term orogenic gold deposits has been widely accepted, but there has been continuing debate on their genesis. Early syn-sedimentary or syn-volcanic models and hydrothermal meteoric-fluid models are now invalid. Magmatic-hydrothermal models fail because of the lack of consistent spatially associated granitic intrusions and inconsistent temporal relationships. The most plausible models involve metamorphic fluids, but the source of these fluids is equivocal. Intra-basin sources within deeper segments of the hosting supracrustal successions, the underlying continental crust, subducted oceanic lithosphere with its overlying sediment wedge, and metasomatized lithosphere are all potential sources. Several features of Precambrian orogenic gold deposits are inconsistent with derivation from a continental metamorphic-fluid source. These include the presence of hypozonal deposits in amphibolite-facies domains, their anomalous multiple sulfur isotopic compositions, and problems of derivation of gold-related elements from devolatilization of dominant basalts in the sequences. The Phanerozoic deposits are largely described as hosted in greenschist-facies domains, consistent with supracrustal devolatilization models. A notable exception is the Jiaodong gold deposits of China, where ca. 120-Ma gold deposits are hosted in Precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization. Other deposits in China are comparable to those in the Massif Central and elsewhere in France, in that they are hosted in amphibolite-facies domains or clearly post-date regional metamorphic events imposed on hosting supracrustal sequences. If all orogenic gold deposits have a common genesis, the only realistic source of fluid and gold is from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package, or the associated metasomatized mantle wedge, with CO2 released during decarbonation and S- and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 °C. Although this model satisfies all geological, geochronological, isotopic, and geochemical constraints, and is consistent with limited computer-based modeling of fluid release from subduction zones, the precise mechanisms of fluid flux are model-driven and remain uncertain. From an exploration viewpoint, the model re-emphasizes the ubiquitous occurrence of orogenic gold deposits in subduction-related orogenic belts and importance of continental-scale lithosphere-tapping fault and shear zones to focus large volumes of auriferous fluid. It confirms the importance of the consistent spacing between world-class deposits, broadly equivalent to the depth of the Moho, as derived from empirical observations.

Using the high-temperature phase transition of iron sulfide minerals as an indicator of fault slip temperature

The transformation of pyrite into pyrrhotite above 500 °C was observed in the Chelungpu fault zone, which formed as a result of the 1999 Chi-Chi earthquake in Taiwan. Similarly, pyrite transformation to pyrrhotite at approximately 640 °C was observed during the Tohoku earthquake in Japan. In this study, we investigated the high-temperature phase-transition of iron sulfide minerals (greigite) under anaerobic conditions. We simulated mineral phase transformations during fault movement with the aim of determining the temperature of fault slip. The techniques used in this study included thermogravimetry and differential thermal analysis (TG/DTA) and in situ X-ray diffraction (XRD). We found diversification between 520 °C and 630 °C in the TG/DTA curves that signifies the transformation of pyrite into pyrrhotite. Furthermore, the in situ XRD results confirmed the sequence in which greigite underwent phase transitions to gradually transform into pyrite and pyrrhotite at approximately 320 °C. Greigite completely changed into pyrite and pyrrhotite at 450 °C. Finally, pyrite was completely transformed into pyrrhotite at 580 °C. Our results reveal the temperature and sequence in which the phase transitions of greigite occur, and indicate that this may be used to constrain the temperature of fault-slip. This conclusion is supported by field observations made following the Tohoku and Chi-Chi earthquakes.

Metamorphic mineral assemblages in fossils in the contact metamorphic rocks of the Portrush Sill, Northern Ireland

Ammonites and other metafossils have been identified in hornfelsed Jurassic clay from Portrush, Northern Ireland. Thermal metamorphism due to intrusion of a large sill complex produced zoned high temperature mineral assemblages due to reaction between the calcite and calcite/pyrite shells and the clay matrix. Modelling of hornfels compositions using Theriak – Domino gives a minimum temperature for metamorphism of ~600 °C at 200 bars. The metafossils comprise an inner wollastonite-rich core that also contains pyrrhotite and fayalite in the ammonites (zone 1), surrounded by iron-rich wollastonite, hedenbergite, titanite and feldspar (zone 2). The matrix in contact with the metafossil (zone 3) comprises magnesian hedenbergite, plagioclase and potassium feldspar and matrix distant from the fossils (zone 4) comprises augite, plagioclase, potassium feldspar, fayalite, ilmenite and quartz. These assemblages developed by metasomatic exchange of silica, sourced from the matrix with CaO sourced from the calcite shells. The metamorphic transformations, in particular reaction of calcite with silica-bearing fluids to form wollastonite and transformation of pyrite to pyrrhotite result in large volume changes which may have distorted the shape of the fossils, nevertheless original morphological features, particularly of the ammonites can be detected.

Fe-rich microspheres pseudomorphs after pyrite framboids in Holocene fluvial deposits from NE Spain: Relationship with environmental conditions and bacterial activity

Three iron oxides-rich microsphere types (Type I to III) were detected in an Holocene 17 m-thick stratigraphic succession located in the Iberian Range (NE Spain). Lithofacies features indicate that the studied materials were generated in an alluvial-dominated setting, with a channeled area fringed by floodplain zones. During high water levels and high-energy floods, gravels and sands deposited in the active area and in lateral overbank areas. In these lateral areas, mud settling took place when flood decreased and then anoxic conditions could be reached due to microbial oxidation of organic matter and the low permeability of the marly sediment. X-ray diffraction (XRD) analysis of 32 samples and microtextural observation of 10 samples by Field Emission Scanning Electron Microscopy (FESEM) revealed the occurrence of Fe oxi-hydroxides microspheres showing different surficial structure. These microspheres are pseudomorphs after pyrite framboids although the formation of some primary Fe oxy-hydroxides aggregates cannot be rejected. Pyrite framboids genesis in sediments underlying oxic-dysoxic water column would have been favored by anoxic conditions reached in lateral overbank areas after main flooding, involving the activity of Fe reducing bacteria and sulfate-reducing bacteria (SRB), given the high SO4= availability provided by the highly mineralized groundwater from the upstream Baños de Ariño spring. Subsequent change to oxic conditions during the exposition of the floodplain enhanced the transformation of pyrite into Fe oxy-hydroxides, as well as in microenvironments around cracks and roots. Pyrite oxidation likely took place with the implication of neutrophilic iron oxidizing Bacteria and Archaea living in microaerophilic conditions, as well as cyanobacteria, given the close association of Fe oxides framboids with microbial features. In addition, pyrite and/or Fe oxi-hydroxides framboids from marl levels could have been incorporated to sand sediments during further overbank flooding episodes. Under these new oxic conditions pyrite oxidation would have been favored and even the formation of primary Fe oxy-hydroxides.

Effect of steam on the transformation of sulfur during demineralized coal pyrolysis

This study focused on the effect of steam on the transformation of sulfur during pyrolysis of demineralized coal in a horizontal tube furnace within the range of temperatures from 300 to 800 °C. The main sulfur-containing products in the resulting pyrolysis gases including H2S, SO2, and COS were quantitatively measured using ion chromatography combined with Fourier-transform infrared spectroscopy gas analyzer. The transformation of pyrite in char was assessed based on X-ray diffraction, while the organic sulfur was determined using both an infrared sulfur analyzer and X-ray photoelectron spectroscopy. The experimental results indicated that sulfur in the demineralized coal was primarily converted to H2S during pyrolysis under both argon and steam/argon atmospheres. During steam/argon pyrolysis, the steam promoted the formation of H2S while inhibiting the formation of SO2, thus increasing and decreasing the yields of these two compounds, respectively. In the argon atmosphere, the pyrite decomposed completely into pyrrhotite at 500 °C and was then converted to troilite at 600 °C. In the steam/argon atmosphere, different iron-containing compounds (Fe1−xS, Fe3O4, and FeO) were formed during the demineralized coal pyrolysis. The promotion of the pyrite transformation by steam was especially pronounced at temperatures above 500 °C. The organic sulfur removal was found to increase likely because the addition of steam above 500 °C promoted the decomposition of thiophenic sulfur.

Pyrite cloning: a single tube and programmed reaction cloning with restriction enzymes

BackgroundInsertion of engineered DNA fragments into bacterial vectors is the foundation of recombinant DNA technology, yet existing methods are still laborious, require many steps, depend on specific vector configuration, or require expensive reagents.ResultsWe have developed a method, called “Pyrite” cloning that combines the traditional restriction enzyme digestion and ligation reaction in a single tube and uses a programmed thermocycler reaction, allowing rapid and flexible cloning in a single tube. After the Pyrite reaction and transformation, approximately 50% colonies contain the expected insert, which can be easily and quickly determined by colony PCR or blue-white colony screening. We also demonstrated that Pyrite cloning can be applied for different cloning purposes.ConclusionsThe Pyrite cloning method reported here is a single tube and programmed reaction cloning with restriction enzymes. Compared to other cloning methods, Pyrite cloning is flexible, inexpensive, simple, and highly efficient.

Genesis and evolution of framboidal pyrite and its implications for the ore-forming process of Carlin-style gold deposits, southwestern China

Southwestern Guizhou, an indispensable component of the “golden triangle” area of southwestern China, is famous for its numerous Carlin-style gold deposits. Unlike other sulfides in the deposits that have been well studied, the genesis of framboidal pyrite is still controversial because of its tiny size. Here, we first determined the chemical and in situ sulfur isotopic compositions of framboidal pyrites from three typical Carlin-style gold deposits (namely Shuiyindong, Taipingdong and Nibao) using secondary electron image (SEI), back scattered electron (BSE), electron probe micro analysis (EPMA), and nanometer-scale secondary ion mass spectroscopy (Nano-SIMS) methods. Our EPMA data show that the framboidal pyrites contain a minor amount of trace elements (Ni < 0.344 wt%, Co = 0.017–0.295 wt%, Cr = 0.009–0.292 wt% and As < 1.479 wt%). Incorporation of the trace elements into the framboidal pyrites resulted in a slight decrease in S and Fe concentrations compared to the theoretical values. The in situ δ34S values of the framboidal pyrites, ranging from −53.2‰ to −30.9‰, are in good agreement with the sulfur isotopic fractionation triggered by the bacterial sulfate reduction (BSR) process in an open-SO42− ocean condition. Combined with SEI, BSE, and Nano-SIMS high-resolution multiple elemental mapping, four consecutive processes responsible for their genesis and evolution are summarized as follows: (1) initial microcrystal nucleation via the BSR process, (2) abundant microcrystal aggregation to form individual framboid and multiple-framboids during sedimentation or diagenesis, (3) partial replacement and recrystallization of preexisting framboids by As-rich ore fluids, and (4) eventual framboidal pyrite transformation to larger euhedral grains via continuous recrystallization. These processes not only present compelling mechanisms responsible for the variations in morphology and chemical composition of the framboidal pyrites, from the initial framboid with a low 75As32S signal (Py1) to the framboid with a recrystallization origin (Py3), but also indicate that their genesis and evolution may have an intimate correlation with the formation of Carlin-style gold deposits.

Structure–Composition Relationship of Skeletal and Dendritic Ferrospheres Isolated from Calcium-Rich Power Plant Ash

This paper presents a systematic SEM–EDS study of polished sections of individual skeletal and dendritic ferrospheres in the–0.04 + 0.032 mm size fraction, isolated from fly ash from the combustion of brown coal from the Berezovskoe field. The ferrospheres are characterized by a wide range of variations in the macrocomponent composition of local areas. We have identified groups of globules whose overall composition as well as the composition of local areas on their polished sections can be represented by general equations for component concentrations: SiO2 = f(FeO), SiO2 = f(Al2O3), and CaO = f(SiO2). Such equations make it possible to identify the nature of the mineral precursors involved in the formation of the globules. FeO-rich skeletal ferrospheres with low CaO concentration originate from the thermochemical transformation of pyrite and illite associates. Skeletal and dendritic ferrospheres with monotonically increasing CaO and SiO2 concentrations are formed from pyrite and montmorillonite associates, with the participation of a melt containing quartz and decomposition products of Ca-humates of the initial coal. Skeletal and dendritic spinel ferrite crystallization is due to a magnesium aluminate spinel “seed,” resulting from the thermal transformation of illite and montmorillonite from the parent coal. The observed increase in glass phase concentration and the change from the skeletal type of crystallization to a dendritic in the ferrospheres containing ≤64 wt % FeO and ≥6.5 wt % CaO are due to the low concentration of the spinel-forming cations Fe2+ and Fe3+ in the melt and the increase in the percentage of [Fe3+O2]− and [Fe23+ O5]4− ferrite complexes with an increase in the degree of oxidation of the melt.

Transformations of Pyrite and Pyrrhotite in Supercritical Water

The interaction of pyrite (FeS2) with water at the uniform heating (1.5 K/min) of the reaction mixture to 923 K and its subsequent cooling (about 3 K/min) to 423 K is studied. The reaction products are analyzed using the methods of mass-spectrometry, elemental and X-ray diffraction analyses, and scanning electron microscopy. It is established that H2S, SO2, and rhombic and hexagonal pyrrhotite (FeS) are formed while heating, and the subsequent cooling of the reaction system gives rise to the formation of H2S, H2, cubic pyrite, and monoclinic pyrrhotite exhibiting ferromagnetic properties. It is shown that the transformations FeS2 → FeS → FeS x (1 < x ≤ 2) are accompanied by changes in the morphology and size of particles.

Microbial acceleration of aerobic pyrite oxidation at circumneutral pH.

Pyrite (FeS2 ) is the most abundant sulfide mineral on Earth and represents a significant reservoir of reduced iron and sulfur both today and in the geologic past. In modern environments, oxidative transformations of pyrite and other metal sulfides play a key role in terrestrial element partitioning with broad impacts to contaminant mobility and the formation of acid mine drainage systems. Although the role of aerobic micro-organisms in pyrite oxidation under acidic-pH conditions is well known, to date there is very little known about the capacity for aerobic micro-organisms to oxidize pyrite at circumneutral pH. Here, we describe two enrichment cultures, obtained from pyrite-bearing subsurface sediments, that were capable of sustained cell growth linked to pyrite oxidation and sulfate generation at neutral pH. The cultures were dominated by two Rhizobiales species (Bradyrhizobium sp. and Mesorhizobium sp.) and a Ralstonia species. Shotgun metagenomic sequencing and genome reconstruction indicated the presence of Fe and S oxidation pathways in these organisms, and the presence of a complete Calvin-Benson-Bassham CO2 fixation system in the Bradyrhizobium sp. Oxidation of pyrite resulted in thin (30-50nm) coatings of amorphous Fe(III) oxide on the pyrite surface, with no other secondary Fe or S phases detected by electron microscopy or X-ray absorption spectroscopy. Rates of microbial pyrite oxidation were approximately one order of magnitude higher than abiotic rates. These results demonstrate the ability of aerobic microbial activity to accelerate pyrite oxidation and expand the potential contribution of micro-organisms to continental sulfide mineral weathering around the time of the Great Oxidation Event to include neutral-pH environments. In addition, our findings have direct implications for the geochemistry of modern sedimentary environments, including stimulation of the early stages of acid mine drainage formation and mobilization of pyrite-associated metals.

Long-term sequestration of nickel in mackinawite formed by Desulfovibrio capillatus upon Fe(III)-citrate reduction in the presence of thiosulfate

In euxinic sediments, the reaction between iron and sulfides results in the formation of Fe(II)-sulfides, which are known to play a key role in trace metal sequestration. The present study investigates the sequestration of nickel during Fe(II)-sulfide formation mediated by the (thio)sulfate-reducing bacterium Desulfovibrio capillatus in the presence of soluble Fe(III)-citrate and thiosulfate as the terminal electron acceptor. XRD, HRTEM and Fe K-edge EXAFS data indicate that biogenic mackinawite (FeS) was the sole mineral formed in our experiments. These data also show that the kinetics of mackinawite crystal growth was significantly accelerated when nickel was present in the starting solution. In addition, the lack of detection of other Fe(II)-sulfides indicates inhibition of the mackinawite (FeS) to greigite (Fe3S4) and/or pyrite (FeS2) transformation that is likely related to (i) the efficiency of Desulfovibrio capillatus in reducing S(0) to H2S and (ii) the absence of O2 during the experiments. Finally, chemical analyses show that 98% of the nickel is associated with biogenic mackinawite and no release of nickel from mackinawite was observed after up to 10 months of incubation under anoxic conditions. This finding is consistent with Ni K-edge EXAFS data which show that Ni(II) substitutes for Fe(II) in the structure of biogenic mackinawite. This study shows that (thio)sulfate-reducing bacteria can efficiently promote the formation of mackinawite in euxinic sedimentary environments and that these Fe(II)-sulfides can act as efficient and long-term trapping minerals for nickel in such settings. Considering the capacity of mackinawite at incorporating other trace metals such as Mn, Co, Cu and Zn, this iron sulfide could also serve as a host for these elements as well. This study suggests that mackinawite likely plays a more important role in the biogeochemical cycles of Fe, S, and associated trace metals than considered up to now.

Destruction of Kerogen in the Presence of Pyrite and Cobalt-Based Catalyst

Objectives: The investigation of the process of the kerogen in situ catalytic transformation accompanied by the synthetic oil production. Methods: To develop kerogen-rich deposits, such technologies as in situ combustion and retorting, presupposing productive layers warming-up, can be employed. The intensification of the light hydrocarbon generation under the kerogen cracking is achieved while using nano-dimensional catalysts based on the transition metals. Finding: The cracking catalyst on the cobalt basis alongside with the impact on the organic substance can promote to the transformation of pyrite into mixed iron oxides, the latter also being the catalysts of the processes under discussion. Under the thermocatalytic effect on the kerogen-containing rocks, the processes of the destructive hydrogenation with the formation of liquid hydrocarbons take place. The processes above are quite catalytic, accompanied by the hydrocarbons molecules activation with power and chemical methods. Iron-containing minerals of all other ones found in the thermal transformation of kerogen. Pyrite under thermal treatment transforms into hematite which is a hydrocracking process. Conclusion: The influence of the nano-dimensional catalyst based on cobalt aims at the organic substance cracking.

Destruction of Kerogen in the Presence of Pyrite and Cobalt-Based Catalyst

Objectives: The investigation of the process of the kerogen in situ catalytic transformation accompanied by the synthetic oil production. Methods: To develop kerogen-rich deposits, such technologies as in situ combustion and retorting, presupposing productive layers warming-up, can be employed. The intensification of the light hydrocarbon generation under the kerogen cracking is achieved while using nano-dimensional catalysts based on the transition metals. Finding: The cracking catalyst on the cobalt basis alongside with the impact on the organic substance can promote to the transformation of pyrite into mixed iron oxides, the latter also being the catalysts of the processes under discussion. Under the thermocatalytic effect on the kerogen-containing rocks, the processes of the destructive hydrogenation with the formation of liquid hydrocarbons take place. The processes above are quite catalytic, accompanied by the hydrocarbons molecules activation with power and chemical methods. Iron-containing minerals of all other ones found in the thermal transformation of kerogen. Pyrite under thermal treatment transforms into hematite which is a hydrocracking process. Conclusion: The influence of the nano-dimensional catalyst based on cobalt aims at the organic substance cracking.

Transformation of pyrite to pyrrhotite in the presence of Au-Ag alloys at 500 °C

Dry annealing of Au x Ag 1−x alloys (х = 0.19, 0.35, 0.56 or of fineness 300, 500, 700‰) and pyrite was used to reveal the solubility of Au (Ag) in FeS 2 and study phase equilibria in the FeS 2 -Au x Ag 1−x system at 500 °C. Pyrrhotite, acanthite, and uytenbogaardtite and Au-Ag alloys with increased fineness were established at the contacts of pyrite blocks with Au-Ag plates. The obtained results evidence the absence of solubility between FeS 2 and Au (Ag) at 500 °C. The Ag content in alloys influences the stability of pyrite and contributes to its transformation in pyrrhotite and sulfidation and ennobling of Au-Ag alloys. Au-Ag sulfides and pyrrhotite may be present in the sulfide ores of metamorphogene deposits as annealing products of Au-Ag-pyrite-bearing ores.

A mechanistic study of the effects of CO2 on pyrrhotite oxidation

The high levels of CO2 in oxy-fuel combustion are expected to have important effects on the transformation of pyrite, a major contributor to ash deposition. As a successive work to the previous study that explored the chemical role of CO2 in pyrite decomposition, this paper is purposely designed to investigate the effects of CO2 on the oxidation of pyrrhotite generated from pyrite decomposition. Pyrrhotite oxidation in pure CO2 was respectively investigated at 900, 950 and 1000°C on a well-designed thermo-gravimetric reactor (TGR). The time-resolved data of sample weight loss and gas evolution were collected online by a data collection module and a Horiba PG-350 gas analyzer, respectively. The solid products were characterized by X-ray diffraction (XRD). The results demonstrate that the influence of CO2 on the oxidation of pyrrhotite is chemical in nature. The transformation of pyrrhotite in CO2 consists of three stages, i.e., the fast weight loss stage, the slow weight loss stage and the slow weight gain stage. The mechanisms involving CO2 at these three distinct stages are quite different. At the first stage, ferrous sulfide is formed by the decomposition reaction of pyrrhotite with CO2. At the second stage, the oxidation reactions of ferrous sulfide with CO2 are responsible for the formation of magnetite or hematite. Hematite may also be formed through further oxidation of magnetite by CO2. The third stage is dominated by the oxidation of magnetite to form hematite with CO as the only gas product.

The Effect of Microwave Heating on the Mineralogical Phase Transformation of Pyrite and Fe Leaching

In order to study the phase transformation of pyrite and to determine the maximum Fe leaching factors, pyrite samples were an electric furnace and microwave oven and then ammonia leaching was carried out. The rim structure of hematite was observed in the sample exposed in an electric furnace, whereas a rim structure consisting of hematite and pyrrhotite were found in the microwave treated sample. Numerous interconnected cracks were only formed in the microwave treated sample due to the arcing effect, and these cracks were not found in the electric furnace treated sample. Under XRD analysis, pyrite and hematite were observed in the electric furnace treated sample, whereas pyrite, hematite and pyrrhotite were found in the microwave treated sample. The results of the pyrite sample leaching experiments showed that the Fe leaching was maximized with the particle size of -325 mesh, sulfuric acid of 2.0 M, ammonium sulfate of 1.0 M, and hydrogen peroxide of 1.0 M. The electric furnace and microwave treated samples were tested under the maximum leaching conditions, the Fe leaching rate was much greater in the microwave treated sample than in the electric furnace treated sample and the maximum Fe leaching time was also faster in the microwave treated sample than in the electric furnace treated sample. Accordingly, it is expected that the microwave heating can enhance (or improve) Fe leaching in industrial minerals as well as pyrite decomposition in gold ores.