Pure Pyrite Research Articles

An investigation on pyrite floatability using stable micro-nanobubble-assisted flotation

This study critically examines the impact of micro-nanobubble (MNB)-assisted flotation on pyrite recovery in bulk ore, and clarifies the intricate relationship between pyrite and its associated ore. The physicochemical properties of MNBs and the interaction mechanisms between xanthate collector and pure pyrite mineral were evaluated using advanced analytical techniques, including Dynamic Light Scattering (DLS), Field-Emission Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy (FESEM-EDX), and Ultraviolet-Visible Spectroscopy (UV-Vis), in the absence and the presence of MNBs. MNBs were created through hydrodynamic cavitation, and their characteristics revealed a size increase from 600 nm to 3 µm over 25 days. Notably, the zeta potential measurements indicated an increase from -2.5 to 0 mV at a constant pH of 8, correlating with the geometric mean size of MNBs coarsening from 600 nm to 2-3 µm. The FESEM and EDS analyses disclosed that ultrasonic treatment effectively dispersed ultrafine surface coatings on pyrite particles, increasing iron and sulfur purity by 8% and 6%, respectively, and significantly reducing surface oxygen by 53%. Micro-flotation and batch rougher kinetic flotation experiments were conducted with and without MNBs, leading to a 7% and 8% improvement in recovery for pyrite mono-minerals (-105+53 µm) and its ore (d<sub>80</sub>=150 µm), respectively. The sorption behavior of sodium isopropyl xanthate (SIPX) collector on the particle surface was also investigated at various concentrations (ca. 10-160 µM) in the presence and absence of stable MNBs and demonstrated that the presence of MNBs resulted in a 1.6-fold increase in collector absorption on the pyrite surface, confirming the findings obtained from micro-flotation. Moreover, adsorption behavior is up to 1.3 times compared to the scenario without MNBs. The adsorption process was controlled by a pseudo-second-order model, indicating a chemical sorption mechanism.

Mechanism investigation of food waste compost as a source of passivation agents for inhibiting pyrite oxidation

Pyrite oxidation causes the generation of acid mine drainage (AMD), posing significant challenges in the management of sulfide tailings. Passivation agents such as humic acid have been tested to prevent pyrite oxidation. The potential of using humate rich food waste compost as a source of passivation agents to suppress pyrite oxidation was explored in this study. Batch leaching tests were conducted at room temperature, involved oxidatively leaching a pure pyrite and a pyrite-containing coal refuse sample, respectively, with and without adding the compost at acidic pH. The involved passivation mechanisms were investigated by solution leaching tests and spectroscopic (XPS) and microscopic (SEM) analysis of the pure pyrite sample and its leaching residues. Compared to the control, adding the compost led to the increases in solution pH, removal of the Fe2+/Fe3+ ions from the solutions by adsorption, and remarkable decreases (≥58 %) in sulfur concentration in both samples. Both SEM and XPS analysis indicated that a coating layer was successfully established on pyrite surface after being leached in the presence of the compost. The coating layer comprised a mixture of organic species (e.g., O-CO and N-H/C groups) and phosphate, potentially improving the likelihood of providing antioxidant protection over acidic pH. As a low-cost material, food waste compost can benefit the source control of AMD not only in terms of its surface passivation, but also its intrinsic alkalinity, metal immobilization, and low environmental risk.

Characterizing the Stoichiometry of Individual Metal Sulfide and Phosphate Colloids in Soils, Sediments, and Industrial Processes by Inductively Coupled Plasma Time-of-Flight Mass Spectrometry.

Size and purity of metal phosphate and metal sulfide colloids can control the solubility, persistence, and bioavailability of metals in environmental systems. Despite their importance, methods for detecting and characterizing the diversity in the elemental composition of these colloids in complex matrices are missing. Here, we develop a single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS) approach to characterize the elemental compositions of individual metal phosphate and sulfide colloids extracted from complex matrices. The stoichiometry was accurately determined for particles of known composition with an equivalent spherical diameter of ≥∼200 nm. Assisted by machine learning (ML), the new method could distinguish particles of the copper sulfides covellite (CuS), chalcocite (Cu2S), and chalcopyrite particles (CuFeS2) with 75% (for Cu2S) to 99% (for CuFeS2) accuracy. Application of the sp-icpTOF-MS method to particles recovered from natural samples revealed that iron sulfide (FeS) particles in lake sediment contained ∼4% copper and zinc impurities, whereas pure pyrite (FeS2) was identified in hydraulic fracturing wastewater and confirmed by selected area electron diffraction. Colloidal mercury in an offshore marine sediment was present as pure mercury sulfide (HgS), whereas geogenic HgS recovered from an industrial process contained ∼0.08 wt % silver per Hg, enabling source apportionment of these colloids using ML. X-ray absorption spectroscopy confirmed that Hg was predominantly present as metacinnabar (β-HgS) in the industrial process sample. The determination of impurities in individual colloids, such as zinc and copper in FeS, and silver in HgS may enable improved assessment of their origin, reactivity, and bioavailability potential.

Experimental timing of pyrite oxidation under various leaching conditions: consequences for rates of weathering in geological profiles

Pyrite (FeS2) is one of the most abundant sulfides on Earth and has already been studied in numerous ways for decades because of its rapid oxidation and the associated environmental impacts. This study proposes a new experimental physico-chemical approach (air, tridistilled water and water drip exposure) to determine the oxidation rate of pyrite using surface and depth data via XPS (X-ray Photoelectron Spectroscopy) analyses. Our experimental study of almost pure pyrite reveals a maximum oxidation rate of 11.7 ± 1.8 nm day−1 for drip exposure with precipitation of sulfates or Fe-oxides depending on the experimental condition. The oxidation rates obtained under various experimental conditions may be extrapolated to weathering rates of different zones of supergene profiles/ores (leached zone, saprolite and cementation zone). The extrapolation suggests a maximum rate of 4.3 ± 0.6 m Ma−1, which is consistent with data obtained by isotope dating of weathering profiles. Under geological conditions however, the oxidation rate of pyrite may be influenced by additional parameters, such as the nature of the host rock, its porosity/permeability, the climate, the influence of an oxidizing environment, and the mineralization of secondary minerals.

Study on Grinding Behavior Characteristics under Low-Speed Grinding Condition

In order to explore the crushing mechanism of minerals, this paper attempts to eliminate the throwing effect of media and study the grinding characteristics of minerals only under the action of abrasion force. In this paper, the method of removing the throwing state of media is to adjust the mill to a lower rotational speed, so that the grinding media are all in a cascading state. Three single-component pure minerals, quartz, pyrrhotite, and pyrite, commonly found in complex ores, were selected as research objects to study the grinding behavior characteristics of the three minerals only under the force of abrasion. The effects of mineral species, feed-particle sizes, grinding time, and other factors on the particle-size distribution and product-generation rate of grinding products are studied. The results show that from the particle-size distribution of grinding products, the yield of coarse particles is the highest, while the yield and t10 value of other fine particles are very low. The feed-particle size and the hardness of the mineral sample affect the grinding behavior. The product particle size is mainly 0.71 times the feed-particle size, and the other fine particle sizes generated are less than 0.5 times the feed-particle size.

Study on Impact Crushing Characteristics of Minerals Based on Drop Weight Tests

The degree of difficulty in crushing an ore depends on the composition of the ore itself. Due to different types and compositions of ores, the crushing mechanism of ores during the crushing process is also different. In order to quantitatively analyze the impact crushing characteristics of mineral components in ores, this paper takes pure mineral quartz, pyrrhotite, and pyrite as the research objects and uses the universal drop weight impact crushing test equipment and standard test methods developed by the JK Mineral Research Center of the University of Queensland, Australia, to conduct JK drop weight tests on these three pure mineral samples. The results show that the particle size distribution of impact crushing products is wide, covering all particle sizes from “0” to close to the feed particle size, and the yield distribution of each product particle size is relatively uniform. There are critical values and “energy barrier” effects for the impact-specific crushing energy. The impact-specific crushing energy has a significant impact on the particle size composition and crushing effect of the crushing product, and there is an interactive effect between the impact-specific crushing energy and the feed particle size and mineral type. The impact crushing resistance of the sample can be characterized by using Mohs hardness, impact crushing characteristic parameters, impact crushing resistance level, and the yield limit value t10 of the characteristic crushing particle size. The overall characterization results have good consistency.

Synergetic effects of pyrrhotite and biochar on simultaneous removal of nitrate and phosphate in autotrophic denitrification system.

In the trend of upgrading wastewater treatment plants, developing advanced treatment technologies for more efficient nutrient removal is crucial. This study prepared a pyrrhotite-biochar composite (Fex Sy @BC) to investigate its potential for simultaneous removal of nitrate and phosphate under autotrophic denitrification conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to characterize the novel composite of Fex Sy @BC, which exhibited 9.2mg N/(L·d) NO3 - -N reduction rate, 97.3% N2 production, and 81.8mmol N/(kg·d) NO3 - -N material load with small solid/liquid ratio (0.008). The NO3 - -N removal with Fex Sy @BC was 1.2-2.2 times higher than that with pure iron sulfides or biochar or their mixtures, whereas the Δn(S)/Δn(N) of Fex Sy @BC was the lowest (1.80). Moreover, the PO4 3- -P reduction rate of Fex Sy @BC reached 3.23 mg P/(L·d), as high as that of pure pyrite or pyrrhotite. Thiobacillus was the most dominant denitrifying bacterium. Fex Sy @BC exhibited great promise for enhancing nutrient removal from secondary effluent without additional carbon source. PRACTITIONER POINTS: FexSy@BC enhanced nitrate and phosphate removal simultaneously. First-order kinetics and Monod model were fitted for denitrification with FexSy@BC. FexSy@BC had smaller molar ratio of sulfate release to nitrate removal. Thiobacillus was the dominant bacterium in FexSy@BC autotrophic denitrification. Synergistic effects on nutrients removal existed between biochar and pyrrhotite.

Pyrite with lower cubic symmetry from Lavrion, Greece

In this study, we examined the morphological, chemical, and structural details of tetrahedral pyrite crystals from the Jean Baptiste mine in Lavrion, Greece. Pyrite occurs in three generations. Tetrahedral crystals of the first generation are left- or right-handed with the lowest cubic 23 symmetry. In this generation, there are twins with higher cubic m_3 and hexagonal 6 symmetry. All crystals of the second generation are primarily interpenetrated into twins with a cubic _4m3 symmetry. Some, however, continue to twin up to crystals with the highest cubic m_3m and hexagonal 6mm symmetry. Third-generation crystals overgrow second-generation crystals in a non-oriented manner. Chemical analysis confirms chemically pure pyrite, and single-crystal X-ray analysis of the first- and the second-generation crystals confirms the pyrite-specific m__3 symmetry. The morphology of the single crystals and twins indicates that first generation of single pyrite crystals should have the lowest cubic 23 symmetry, which is not confirmed by the structural analysis. This discrepancy may be due to changed pT conditions and the consequent transformation of the original pyrite structure with symmetry 23 into a secondary structure with m__3 symmetry, or to suboptimal conditions in determining the structure by X-ray diffraction.

Investigation into pyrite autotrophic denitrification with different mineral properties

Pyrite autotrophic denitrification (PAD) is considered a promising method for nitrate removal from wastewater and groundwater. However, the results of PAD studies have been contradictory for two decades, and the mechanism is unclear. Here, we investigated mineral properties of two kinds of natural pyrite (YP and TP), their PAD performances, and microbial community shift in their column reactors in parallel. Both pyrite are highly pure crystalline pyrite, but their other mineral properties are quite different. Both batch and column experiments found that PAD of YP occurred but that of TP did not. Thus, the contradictory results of PAD were presented for the first time at the same study. The dominant bacteria in YP and TP columns finally were Thiobacillus (24.55±8.67%) and Flavobacterium (21.11±10.59%), respectively, though their initial microbial communities cultured were similar. Reduced sulfur species and oxide impurities on the surface of pyrite, and small DO in water did not change autotrophic denitrification characteristic of the pyrite itself. This research indicates that mineral property of pyrite caused the contradictory result of PAD. Among pyrite properties, the main crystal plane exposed and chemical state of surficial sulfur and iron were considered the decisive parameters for PAD. The study provides guidelines for selection of pyrite minerals for PAD applications.

A comparison study of the structural, electronic and mechanical properties of the pure pyrite FeS2 and oxygen doped pyrite FeO0.25S1.75 under pressure range from 0 to 25 GPa

Despite pure pyrite FeS2 has a very high optical absorption coefficient about 105cm−1, its smaller band gap about 0.95eV leads to a lower than 3% photoelectric conversion efficiency and thus limits its semiconductor photovoltaic applications. In this paper, we make a comparison study of the structural, electronic and mechanical properties of the pure pyrite FeS2 and oxygen doped pyrite FeO0.25S1.75 under pressure range of 0–25 GPa by first-principles calculations within GGA + U method. With increasing the pressure from 0 to 25 GPa, the band gap of the pure pyrite FeS2 oscillation decreases from 0.936eV at zero pressure to 0.682eV at 25 GPa and thus is not suitable for semiconductor photovoltaic application. Fortunately, the band gap of the oxygen doped FeO0.25S1.75 increases firstly from 1.080eV at zero pressure to the maximum value of 1.290eV at 13 GPa and then decreases slightly but is still larger than that of the pure pyrite FeS2. Especially, this maximum band gap value of 1.290eV at 13 GPa closes to the value of 1.340eV of Shockley-Queisser limit for semiconductor photovoltaic applications. Furthermore, the oxygen doped FeO0.25S1.75 is mechanical stable under pressure range of 0–25 GPa based on Born stability criteria. Our study shows that it is feasible to further increase the band gap of the oxygen doped pyrite FeO0.25S1.75 by applying a suitable pressure.

Reduction in Urbach energy and density of states for pyrite (FeS2) thin films: Healing of sulfur vacancies during hematite to pyrite transformation

Pyrite, an inexpensive, earth-abundant photovoltaic material has potential to compete with silicon. Unfortunately, pyrite based devices suffer from low power conversion efficiencies and open-circuit voltages, which can be overcome by improved understanding of electronic and optical properties of pyrite. In the electronic and optical properties of pyrite role of sulfur vacancies is very crucial but less explored and still ambiguous. In the present study, effect of sulfur vacancies on the optical and charge transport properties of phase pure pyrite films has been investigated where the sulfur vacancies have been tamed by increasing the sulfurization pressure from subatmospheric to overatomspheric value. Lower Urbach energy in the pyrite films indicates a decrease in density of localized states, which is believed to be due to reduced sulfur vacancies at higher sulfurization pressure. Temperature dependent transport properties reveal the presence of Mott-variable range hoping conduction through the high density of localized states arising from sulfur vacancies. Decreased density of localized states reflects in increased hoping energy associated with longer hoping distance in the pyrite films.

Distinct effects of transition metal (cobalt, manganese and nickel) ion substitutions on the abiotic oxidation of pyrite: In view of hydroxyl radical production

The abiotic oxidation of pyrite (FeS2) is a geochemically crucial reaction involved in acid mine drainage, the release of toxic trace elements and the generation of hydroxyl radicals (•OH) that can oxidize environmental substances. Studies on •OH generation from the abiotic oxidation of pyrite have drawn wide interest, but the effects of the common substitution of transition metal ions on •OH generation are still largely unknown, and worthy of comprehensive comparison. We therefore synthesized and comprehensively characterized micron-sized pyrites containing low concentrations of cobalt (Co), nickel (Ni), or manganese (Mn) ions, and tested the relative ability of these transition metal ion-substituted pyrites to generate •OH under abiotic oxidation. We found that transition metal ion substitutions inhibited the growth of pyrite crystals to various extents and increased Fe–S bond distances, leading to distinct alterations in surface chemical composition, conductivity, and the exposure of active faces. These differences resulted in an increase in •OH generation by the oxidation of transition metal ion-substituted pyrites, relative to pure pyrite, with the order of increase being Mn2+-substituted < Ni2+-substituted < Co2+-substituted pyrites. These substituent-dependent differences were explored by linking the crystal properties and physical chemistry of these pyrites to various reaction pathways that were possible in such contexts. For pure pyrite, the heterogeneous Fenton reaction was the chief generator of •OH. The substitution of pyrite with Co2+, which was redox-active, increased the conductivity of pyrite and accelerated the reduction of surface Fe3+ to Fe2+, resulting in a significant increase in H2O2 and •OH production. The substitution of pyrite with Mn2+, which was also redox-active, likewise increased the conductivity; however, the high oxidizing ability of surface Mn4+ inhibited the reduction of Fe3+ and thus decreased •OH generation. By contrast, the substitution of pyrite with Ni2+ did not affect electron transfer but led to absolute exposure of the (111) face of pyrite, which increased its activity toward O2 and H2O, slightly increasing H2O2 and •OH generation. These results highlight the vital role of transition metal ion-substituted pyrite in various geochemical processes.

Fabrication of Iron Pyrite Thin Films and Photovoltaic Devices by Sulfurization in Electrodeposition Method.

Iron pyrite is a cheap, stable, non-toxic, and earth-abundant material that has great potential in the field of photovoltaics. Electrochemical deposition is a low-cost method, which is also suitable for large-scale preparation of iron pyrite solar cells. In this work, we prepared iron pyrite films by electrochemical deposition with thiourea and explored the effect of sulfurization on the synthesis of high-quality iron pyrite films. Upon sulfurization, the amorphous precursor film becomes crystallized iron pyrite film. Optical and electrical characterization show that its band gap is 0.89 eV, and it is an n type semiconductor with a carrier concentration of 3.01 × 1019 cm−3. The corresponding photovoltaic device shows light response. This work suggests that sulfurization is essential in the electrochemical preparation for fabricating pure iron pyrite films, and therefore for low-cost and large-scale production of iron pyrite solar cells.

A DFT investigation into the effects of As-doping on the electronic structure and electrochemical activity of pyrite (FeS2)

Pyrite (FeS2) is a semiconductor mineral with electronic structural properties that are heavily influenced by trace elements in its composition. It has been demonstrated experimentally that the reduction of Fe3+ ions is significantly enhanced in the presence of trace arsenic (As) atoms in FeS2. Using density functional theory calculations, we compare the geometric and electronic structural properties of pure and As-doped (110) pyrite surfaces. The interaction of the Fe3+ ion, a common oxidant of sulfides in acidic solution and acid mine drainage, with the aforementioned surfaces is thoroughly investigated. The findings reveal that the addition of an As atom alters the electronic structure of pyrite and decreases its band gap. The adsorption energy of the Fe3+ ion on As-doped pyrite is greater than that on pure pyrite. The calculated Gibbs free energy changes show that the reduction of Fe3+ to Fe2+ ion on the As-modified surface is thermodynamically more favorable than on pure pyrite.

New insights related to the flotation of covellite in porphyry ores

Covellite usually occurs accompanying other copper minerals, like chalcopyrite and chalcocite, but there are few studies on covellite flotation. The effect of collectors O-isopropyl-N-ethyl thionocarbamate (IPETC) and potassium amyl xanthate (PAX) and pH on covellite and pyrite flotation was investigated through a Hallimond tube test using pure covellite and pyrite and a Denver cell test using porphyry ore. Pure covellite and pyrite were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR). Moreover, the covellite was characterized using scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS). Porphyry ore was characterized by automated mineralogy using scanning electron microscopy (QEMSCAN®). Design of experiments was utilized to identify the factors with a statistical influence (ANOVA) and obtain the optimal flotation conditions using response surface methodology (RSM) and desirability function. ANOVA test demonstrated that the factors that influence covellite behavior are the collector type and dosage. The results obtained on pure minerals shows that with a high PAX concentration and low pH, it is possible to carry out bulk flotation with recoveries of 93% covellite and 90 % pyrite, and with a low IPETC dosage and high pH, it is possible to get a selective flotation with around 81% covellite and 20% pyrite recoveries. These results were determined using RSM and desirability function, and corroborated with the Hallimond tube test. Then, the flotation results of mixture covellite-pyrite show that selective flotation is feasible with IPETC at alkaline pH with a low dosage displaying recoveries of 97 % covellite and 53 % pyrite. Also, bulk flotation is feasible with PAX at a pH of 8 and a high collector concentration with recoveries of 96% covellite and 88% pyrite. The results show that covellite recovery is not pH-dependent. The Denver cell test with a porphyry ore shows a selective flotation with IPETC at a pH of 11 with a low collector dosage (5 g/ton), achieving recoveries of 92% covellite and 39% pyrite. Also, recoveries of 85% covellite and 75% pyrite were observed for a bulk flotation with IPETC at pH = 8 at the same collector dosage. Therefore, the IPETC can be used as a selective or bulk collector when varying the pH and collector concentration. These results demonstrate that covellite flotation performances remain constant over a wide range of pH values, which allows a selective separation from other sulfides such as pyrite.

Fingerprinting fluid evolution by trace elements in epithermal pyrite, Vatukoula Au-Te deposit, Fiji

Tellurium (Te) is an important element for green technologies, including thin film photovoltaic panels. Stagnating supply caused by its by-product dependency together with an increasing demand will likely lead to a shortage in the near future. Pyrite may represent a potential target for the direct recovery of Te, since the concentrations of Te can reach weight percent levels under specific, but poorly constrained hydrothermal conditions. The Vatukoula (formerly Emperor) epithermal Au-Te deposit is currently mined for Au and ~ 75% are recovered from Au-tellurides and pyrite. Tellurium has been processed in the past, but is now sent to tailings despite of concentrations reaching 1.4 wt. % in pyrite, which makes this system a natural laboratory to investigate key Te enrichment processes.The epithermal mineralisation at Vatukoula consists of an early low-grade disseminated host-rock and a later high-grade Ag-Au-Te vein-type stage. Pyrite occurs in both ore-types with diverse As contents including concentrations < 0.5 wt. % in pure pyrite, 0.5 to 13 wt. % in low-As and 23 to 43 wt. % in high-As pyrite, reflecting increasing fluid As with system evolution towards the high-grade mineralisation. Tellurium contents in pyrite increase from pure pyrite (up to 220 ppm) to low-As pyrite (up to 1.4 wt. %), but with a decrease towards high-As pyrite (up to 185 ppm). This is a yet unknown relation, since trace element incorporation in pyrite is usually facilitated by increasing As. Instead, the presented results suggest a threshold between 13 and 23 wt. % As, above which the incorporation of Te and related elements (e.g., Ag, Au) may be less favourable. Mineral stabilities, trace element ratios (e.g., Sb/Pb, Tl/Pb) and LA-ICP-MS mapping of texturally distinct pyrite indicate that fluid boiling was a critical process for the Ag, Au and Te enrichment in the Vatukoula epithermal system. Fluid sulphidation states decreased with proceeding evolution of the epithermal system from initially intermediate- to late low-sulphidation conditions, which led to the diverse chemical character of pyrite. Early pure pyrite primarily formed as a replacement product of magnetite in the altered host rocks, whereas low- and high-As pyrite precipitated in the direct vicinity of Ag-Au-telluride veins, from which most of the As, Ag, Te and Au hosted in pyrite was derived from. Consequently, the trace element composition of pyrite allows the fingerprinting of the fluid evolution of Te-rich ore-forming systems like Vatukoula, Fiji.

A green solar photo-Fenton process for the degradation of carbamazepine using natural pyrite and organic acid with in-situ generated H2O2

Pyrite is widely used in Fenton reaction for degradation of pollutants and exhibits great potential for environmental remediation, however, its efficiency is greatly compromised by extra H2O2 and pH adjustment. Herein, a pyrite based green solar photo-Fenton system for carbamazepine (CBZ) treatment is constructed, involving the use of simulated sunlight and natural organic acids with in situ-generated H2O2 and without extra pH adjustment. The addition of organic acids including tartaric acid (TA), citric acid (CA), and ascorbic acid (AA) can form complex with iron in pyrite, which promotes the Fe(II) dissolution. Upon irradiation, pyrite could be excited to produce photoelectrons, which would reduce oxygen to produce H2O2 through a two-step route assisted by organic acids. The simulated sunlight and organic acids promoted the in-situ production of H2O2 and Fe(II) species, sustaining an efficient Fenton reaction. This produced massive hydroxyl radical (OH), as demonstrated by the active species capture experiment. Compared with no degradation of CBZ under pure pyrite, the degradation efficiency of CBZ reached to 70%, 60%, and 53% in pyrite/TA, pyrite/CA, pyrite/AA within 30 min under simulated solar light irradiation, respectively. This work reports the first use of natural pyrite, a typical Fe-mineral semiconductor, to produce OH for CBZ degradation through natural additive assisted Fenton reaction excluding the adding extra H2O2 and pH adjustment.

Defect mediated improved charge carrier dynamics in hybrid bulk-heterojunction solar cell induced by phase pure iron pyrite nanocubes

In this article, the synthesis of phase pure iron pyrite nanocubes (FeS2 NCs) and their various effects on the charge carrier dynamics and photovoltaic performances of P3HT:PC71BM based hybrid bulk-heterojunction solar cells have been studied. The optimum doping concentration of FeS2 NCs was found to be 0.3 wt%. For the optimally doped devices, the short-circuit current density was found to have improved from 5.47 to 7.99 mA cm−2 leading to an overall cell efficiency improvement from 2.10% to 3.22% as compared to the undoped reference devices. The enhancement in photovoltaic performance is mainly attributed to the formation of localized energy states near the band edges leading to higher carrier generation rate by 72% whereas carrier dissociation probability is also increased by 13%. Urbach energy estimation reveals that the optimally doped devices have achieved a relatively balanced amount of localized states resulting in reduced non-radiative recombination. Such localized defect states formation with FeS2 NCs doping was also found to have significant influence over the charge carrier dynamics of the active layer. Transient photocurrent and photovoltage studies revealed that FeS2 NCs assist in faster carrier extraction by reducing the transport time from 1.4 to 0.6 μs and by enhancing carrier recombination time from 51.7 to 78.9 μs for the reference and optimum devices respectively. Such an unorthodox approach of defect state assisted efficiency improvement demonstrates the importance of simultaneously understanding the charge carrier dynamics and photovoltaic performance for rational device optimization, and opens new prospects for developing high-efficiency solution processable hybrid devices.

Crystal chemistry of arsenian pyrites: A Raman spectroscopic study

AbstractA Raman spectroscopic study on the nature of As-S substitution in natural arsenian pyrite [Fe(S,As)2] is presented, covering a compositional range of 0.01–4.6 at% As. Three Raman-active modes were identified in the Raman spectrum of a nearly pure pyrite: Eg (344 cm−1), Ag (379 cm−1), and Tg(3) (432 cm−1). The Raman vibrational modes exhibit one-mode behavior, and the wavenumbers of optical modes vary approximately linearly with As content, correlating with the change in bond constants with increasing substitution of As for S. The linewidth of the Ag mode increases with increasing As substitution, which may be attributed to the increase in lattice strain associated with the substitution of As for S. This study provides experimental evidence for As-induced structural evolution of pyrite from being stable to metastable before decomposing into other phases. Our results, together with those of another Raman study of arsenian pyrite whose As substitution is more complex, indicate that one cannot use Raman band shifts to determine As content, but for a given As content, can characterize the nature of As substitution, i.e., As for S or As for Fe or both.

Study of pyrite transformation during coal samples heated in CO2 atmosphere

Pyrite transformation in two coals heated in CO2 was investigated. It was found that the pyrite experienced two visibility DTG peaks at temperature above 840 °C in CO2. It may be due to the pyrite decomposed products further reacting with CO2 to form iron oxides, sulfur oxide and CO as temperature increased. There are two main parts during the coal-pyrite blends heated to 1300 °C in CO2, which are the main pyrolysis part and the main gasification part, respectively. It shown that the coal decomposition processes did influence the pyrite transformation behaviors. During the main pyrolysis part, two DTG peaks were significantly observed related to the devolatilization of acid-washed coal and the pyrite pyrolysis desulfurization, respectively. The pyrite in coal-pyrite blends decomposed at lower temperature than the pure pyrite. The decomposition temperature of pyrite in coal-pyrite blends are decreased as the pyrite content in blends decreased in the main pyrolysis part. The flue gas analysis shows that, H2S is the main sulfur-containing gaseous product in the main pyrolysis part, SO2 and CO are the major gas products in the main gasification part of the coal-pyrite blends. During the main gasification process, the SO2 and CO release peaks move to high temperature zone as the pyrite content decreased. The ashes from the fix-bed reactor were also analyzed. It was shown that the iron oxide (magnetite) may be formed at temperature as low as 600 °C in the coal-pyrite blends. At higher temperature (main gasification part), it suggested the pyrite in coal-pyrite blends may be transformed together with char gasification and the co-transformation temperature is different with the coal type.