Pyrite Material Research Articles

Understanding some regularities of gold extraction from secondary pyrite materials using sulphate-sulphite leach solutions

Understanding some regularities of gold extraction from secondary pyrite materials using sulphate-sulphite leach solutions

Rapid preparation and characterization of pyrite materials under HPHT: A new method

This paper reports the synthesis of bulk pyrite (FeS2) polycrystals at high pressure and high temperature (HPHT) for the first time. The HPHT method markedly improves the speed of synthesis, reducing the time for synthesizing bulk pyrite from several hundred hours to several hours. A unique honeycomb-type structure was introduced into the system by the primary reaction to refine the size of the reactants. On this basis, the sulfur-deficient contamination phase Fe7S8 was effectively eliminated by secondary synthesis. Using Raman spectroscopy and X-ray diffraction (XRD), the crystalline phase of the product was confirmed to be the cubic pyrite phase. The crystal structure and initial crystal parameters of pyrite crystals synthesized under HPHT conditions were obtained for the first time by Rietveld refinement with GASA software. In combination with a scanning electron microscope (SEM) assay, the reaction process was traced, and the significance of secondary synthesis for HPHT was analyzed. Seebeck data showed that as the temperature increased, the sample changed from p-type to an n-type semiconductor and the conductivity increased monotonically, revealing the typical semiconductor characteristics of pyrite. UV reflectance spectra and VSM tests revealed the bandgap width and magnetic properties of pyrite.

Topological transformations in hyperuniform pentagonal two-dimensional materials induced by Stone-Wales defects

We discover two distinct topological pathways through which the pentagonal Cairo tiling (P5), a structural model for single-layer $AB_2$ pyrite materials, respectively transforms into a crystalline rhombus-hexagon (C46) tiling and random rhombus-pentagon-hexagon (R456) tilings, by continuously introducing the Stone-Wales (SW) topological defects. We find these topological transformations are controlled by the orientation correlations among neighboring $B$-$B$ bonds, and exhibit a phenomenological analogy of the (anti)ferromagnetic to paramagnetic transition in two-state Ising systems. Unlike the SW defects in hexagonal 2D materials such as graphene, which cause distortions, the defects in pentagonal 2D materials preserve the shape and symmetry of the fundamental cell of P5 tiling and are associated with a minimal energy cost, making the intermediate R456 tilings realizable metastable states at room temperature. Moreover, the intermediate structures along the two pathways are neither crystals nor quasicrystals, and yet these random tilings preserve hyperuniformity of the P5 or C46 crystal (i.e., the infinite-wavelength normalized density fluctuations are completely suppressed), and can be viewed as 2D analogs of disordered Barlow packings in three dimensions. The resulting 2D materials possess metal-like electronic properties, making them promising candidates for forming Schottky barriers with the semiconducting P5 material.

Distribution of pyrite depth and soil properties in fresh water swampland in North Candi Laras Sub-district, South Kalimantan Province

One of the challenges of swamp land utilization for agricultural uses is the existence of pyrite (FeS2), especially in the top soil. The aim of this research was to study the distribution of pyrite position with depth and soil properties in fresh water swamp land in North Candi Laras Sub-district, Tapin Regency, South Kalimantan Province. Pyrite layer was determined by using hydrogen peroxide (H2O2) and its unique reaction was marked by foam existence with soil pH <2.5. Ten soil samples analyzed to determine physical and chemical properties. The result of this research showed that pyrite depth varied from 25 cm to >100 cm. The depths of pyrite material were grouped into 25 to 50 cm, 51 to 75 cm, 76 to100 cm, and 101 to 150 cm. The closer to the river, pyrite depth in the soil was deeper. The pyrite depth affected soil pH and cations. Soils containing pyrite material were very acidic with an average field soil pH 4.0 to 4.5. Cation Ca, K, Na levels were higher with the shallower pyrite depth in the soil, meanwhile Mg was almost same in all pyrite depth groups. The information of pyrite position within the soil is useful for controlling water table management to prevent pyrite oxidation.

Characterization and identification of Au pathfinder minerals from an artisanal mine site using X-ray diffraction

Gold-associated pathfinder minerals have been investigated by identifying host minerals of Au for samples collected from an artisanal mining site near a potential gold mine (Kubi Gold Project) in Dunkwa-On-Offin in the central region of Ghana. We find that for each composition of Au powder (impure) and the residual black hematite/magnetite sand that remains after gold panning, there is a unique set of associated diverse indicator minerals. These indicator minerals are identified as SiO2 (quartz), Fe3O4 (magnetite) and Fe2O3 (hematite), while contributions from pyrite, arsenopyrites, iridosmine, scheelite, tetradymite, garnet, gypsum and other sulfate materials are insignificant. This constitutes a confirmative identification of Au pathfinding minerals in this particular mineralogical area. The findings suggest that X-ray diffraction could also be applied in other mineralogical sites to aid in identifying indicator minerals of Au and the location of ore bodies at reduced environmental and exploration costs.

Synthesis of Thin-Film Metal Pyrites by an Atomic Layer Deposition Approach.

Late 3d transition metal disulfides (MS2 , M=Fe, Co, Ni, Cu, Zn) can crystallize in an interesting cubic-pyrite structure, in which all the metal cations are in a low-spin electronic configuration with progressive increase of the eg electrons for M=Fe-Zn. These metal pyrite compounds exhibit very diverse and intriguing electrical and magnetic properties, which have stimulated considerable attention for various applications, especially in cutting-edge energy conversion and storage technologies. The synthesis of the metal pyrites is certainly very important, because highly controllable, reproducible, and reliable synthesis methods are virtually essential for both fundamental materials research and practical engineering. In this Concept, a new approach of (plasma-assisted) atomic layer deposition (ALD) to synthesize the thin-film metal pyrites (FeS2 , CoS2 , NiS2 ) is introduced. The ALD synthesis approach allows for atomic-precision control over film composition and thickness, excellent film uniformity and conformality, and superior process reproducibility, and therefore it is of high promise for uniformly conformal metal pyrite thin-film coatings on complex 3D structures in general. Details and implications of this ALD approach are discussed in this Concept, mainly from a conceptual perspective, and it is envisioned that, with this new ALD synthesis approach, a significant amount of new studies will be enabled on both the fundamentals, and novel applications of the metal pyrite materials.

Influence of substrate temperature on properties of pyrite thin films deposited using a sequential coevaporation technique

A series of pyrite thin films were deposited in-situ in a monolayer-by-monolayer fashion using sequential evaporation of iron under high vacuum, followed by sulfidation at a sulfur pressure of 133 Pa, as a function of substrate temperature. The stoichiometry, crystallinity, topographic smoothness, and phase purity of the deposited pyrite thin films improve with increasing substrate temperature up to 420 °C, the highest temperature studied. Characterization of the films deposited at 420 °C using selected-area precession electron diffraction, Raman Spectroscopy, and conventional X-ray diffraction indicated that the pyrite layer is phase pure, with no evidence of a secondary marcasite phase, and grew in columnar grains with a preferential (100) orientation on the (100) silicon substrates. This novel sequential evaporation technique has the potential to make useful low-cost semiconducting pyrite materials for large-area electronic applications.

Low temperature synthesis of iron pyrite (FeS2) nanospheres as a strong solar absorber material

Phase pure iron pyrite (FeS2) nanosphere morphology was synthesized by a solvothermal route an alternative to colloidal synthesis by utilizing an ethylene glycol and benzylamine as a solvent and structure directing ligand at 160 °C for 12 h in Teflon lined autoclave. The as obtained nanospheres were in average ∼50 nm diameter with a smooth surface and well mono-disperse as observed by the FESEM images. The XRD analysis shows a typical iron pyrite crystal phase with 2θ position at 28.23°, 32.76°, 36.84°, 40.48°, 47.32° and 56.01° without any impurity peaks. The Raman spectra further confirmed the phase pure pyrite structure. The UV-Vis and PL spectra shows excellent solar absorbance with a band gaps of 1.35 eV close to the direct band gap (1.38 eV) of pyrite materials, however the photoluminescence spectra shows a band gap of 1.39 eV close to the direct band gap. The obtained nanosphere morphology was highly promising as an excellent solar absorber material for the photovoltaic application.

Anisotropic Growth of Iron Pyrite FeS2 Nanocrystals via Oriented Attachment

Pyrite (FeS2) material is attractive for applications in solar cells, lithium batteries, and hydrogen production because of its abundant, nontoxic features as well as the extraordinary electrical and optical properties. Pyrite (FeS2) nanocrystals (NCs) were synthesized via hot injection method, and the crystalline structure and morphologic evolution of pyrite NCs were investigated. We found that pyrite (FeS2) NCs were generated from a mackinawite FeS0.94 nanosheets template. The initial anisotropic growth of NCs was dominated by oriented attachment mechanism. Ostwald ripening growth became obvious as time progressed, resulting in faceted NCs. In accordance with the analysis of high-resolution transmission electron microscopy (HRTEM) images and surface free energies, we found that the attachment occurs between the opposite facets with high surface free energies including (210)-Fe and (210)-2S as well as (001)-Fe and (001)-2S. The attachment could also happen through a “point-contact” followed by interparti...

Hydrothermal synthesized micro/nano-sized pyrite used as cathode material to improve the electrochemical performance of thermal battery

In this paper, single-phase pyrite with different particle sizes is prepared by hydrothermal method with the reactants of Na2S, S, and FeSO4. Compared with natural pyrite powder, synthesized pyrite nanocubes with small particle sizes and fine distribution have lower resistance, higher specific capacity and power density during the discharging process. The enlarging contacting surface area of pyrite with electrolytes will reduce the concentration polarization caused by the discharging current and improve the utilization efficiency of the pyrite materials. When pulse currents are loaded, compared with natural pyrite single-cell thermal battery, synthetic ones have smaller voltage drops and higher power density during the pulse discharging process. Influences of particle sizes on the thermal stability of the pyrite powders have also been investigated.

Theoretical Expectation of Large Seebeck Effect in PtAs2 and PtP2

Motivated by a recent observation of good thermoelectric properties in %a %pyrite material PtSb$_2$, we theoretically study related pyrites %materials in an attempt to %find a %better thermoelectric material. %Our aim is to seek for a material which overcomes the suppression of the Seebeck coefficient at high temperatures.% in PtSb$_2$. We find that PtAs$_2$ and PtP$_2$ are good candidates, where a larger band gap than in PtSb$_2$ combined with the overall flatness of the band top gives rise to a monotonically increasing Seebeck coefficient up to high temperatures. This expectation has been confirmed quite recently for hole doped PtAs$_2$, where a very large power factor of $\sim$ 65$\mu$W/cmK$^2$ at T=440 K is observed.

Optimization of Limited-Entry Matrix Acid Stimulations in the Danish Central Graben

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 157429, ’Optimization of Limited-Entry Matrix Acid Stimulations With Laboratory Testing and Treatment Pressure Matching’ by Mary S. Van Domelen, SPE, and Mohamad abd Hammoud, Maersk Oil Denmark; Gerard Glasbergen, SPE, Shell; and Noor Talib, SPE, Maersk Oil Qatar, prepared for the 2012 SPE International Production and Operations Conference and Exhibition, Doha, Qatar, 14-16 May. The paper has not been peer reviewed. In the Danish central graben, tight chalk reservoirs have been developed successfully through drilling, completion, and stimulation of long horizontal wells. These fields, developed since the early 1970s, are operated on behalf of a joint venture, the Dansk Undergrunds Consortium (DUC). One of the most successful technologies used in these fields is the controlled-acid-jetting (CAJ) technique. Lower Cretaceous Formation, Central Graben Fig. 1 shows the major producing fields of the DUC area. The Lower Cretaceous reservoir contains significant in-place oil volumes. Fig. 2 shows the thickness map of the Tuxen and Sola Lower Cretaceous formation in the central graben. This formation historically has posed a challenge to development because of its extremely low permeability; in addition, the formation is soft, highly heterogeneous, and has significant clay content in some areas. Thicker Lower Cretaceous reservoir sections in the Valdemar field have been propped-fracture stimulated successfully. Acid stimulation is preferred for the thinner sections; however, early attempts at matrix acid stimulation were very disappointing. Recently, the need to re-enter a well for maintenance allowed three zones to be selectively restimulated with improved execution techniques and a more appropriate acid formulation. Production increase following restimulation of this first well was very encouraging, and the lessons learned were applied to a second well. The Lower Cretaceous formation is characterized by a high content of insoluble residue (IR), consisting mainly of clay with subordinate amounts of quartz, rare pyrite, and organic material. Porosity correlations were developed from core data and by petrophysical evaluation of logs. The porosity varies considerably, but is generally remarkably high. While the primary variation in porosity was linked directly to the IR content of the facies, factors such as pore pressure and depth of burial/compaction also had an influence. On the basis of the formation core data, the Lower Cretaceous would not be considered a good candidate for matrix acid stimulation. It is well established, however, that low-permeability reservoirs can be economically produced by long, horizontal wellbores that effectively maximize reservoir contact.

Iron isotope heterogeneity in pyrite fillings of Holocene worm burrows

We present 54Fe and 56Fe data on pyrite from burrow-like and irregularly shaped pyrite concretions from Holocene postglacial lacustrine clays in the northern Baltic Sea collected using a secondary ion mass spectrometry (SIMS) microanalysis technique. The burrow-like concretions were formed in reducing, mucus-coated worm burrows in oxic surface sediments. Framboidal pyrite in the cores of the burrow-like concretions shows extensively fractionated δ56Fe values down to −3.1‰. The framboids are cemented by poorly crystalline FeS2 with δ56Fe values between −2.1‰ and +1.4‰. The irregularly shaped concretions with microcrystalline textures were formed in organic-poor sediment pore spaces, and display a wide spread of δ56Fe values up to +4.1‰. The measured δ56Fe values reflect the preferential capture of 54Fe to pyrite in the diagenetic sequence and the 56Fe enrichment of remaining pore water. The diagenetic sequence of the pyrite materials is supported by previous petrographical study and 34S/32S microanalysis of the same samples. Our results demonstrate substantial early-diagenetic δ56Fe and δ34S heterogeneity within individual pyrite grains, underlining the necessity of high spatial resolution measurements in studying biological and abiological isotopic signatures.

Electrochemical Analysis of Highly Reactive Pyrite

Samples of highly reactive pyritic material, exposed during the construction of the Pennsylvania Interstate Highway 99 (I-99) has been characterized by X-ray diffraction, Raman microprobe spectroscopy, electron microscopy and electrochemical methods. Mineral standards of marcasite, arsenopyrite and pyrite were compared in order to determine the cause of rapid generation of acid and liberation of dissolved metals observed in the exposed pyritic material. Linear sweep voltammetry found no significant differences in the electrochemical activity, however, a significantly lower open circuit potential was found in the reactive pyrite material than in the pyrite or marcasite standards. A high concentration of zinc and aluminium impurities was observed in Energy Dispersive X-ray analysis of the finest iron sulfide crystals found in the reactive pyritic material.

Research Progress in Ionic Functional Materials Used for Energy Saving and Emission Reduction

The application of ionic functional materials for energy saving and emission reduction in China was introduced in this paper. Firstly, the application of mine materials in the field of architectural energy saving, including heat insulation materials, combustion energy saving materials and enhancing heat emission materials,etc, was introduced. Secondly, the application of ionic functional materials in the field of automobile energy saving was introduced. The product technology of promoting energy saving through activating fuel, air and cycling water by activative bed technology was also introduced, aimed at industry boiler. Finally, the application in battery field of lithium-ion storage materials, including natural pyrite and lithium iron phosphate materials was introduced.

Controlled electrochemical dissolution of hydrothermal and sedimentary pyrite

Electrochemically controlled pyrite dissolution was performed with three pyrite materials from different geological origins under mixed potential and high overpotential conditions. Both solid electrodes and C paste electrodes of powdered pyrite were used. The rate of pyrite dissolution increased with applied positive potential and was strongly affected by temperature. Current density measurements over the applied potential range successfully described the rate of pyrite dissolution of each pyrite electrode. Controlled dissolution performed under mixed potential conditions on the solid electrodes successfully reflected the same pyrite reactivity and dissolution rate order as in batch reactor dissolution studies with the same pyrite materials. Therefore, the relative reactivity of different pyrite materials can be determined through current density measurements on their solid electrodes under mixed potential conditions. This technique could be a useful tool to compare rapidly the relative reactivity for different pyrite materials. In contrast, electrochemically controlled dissolution studies with C paste electrodes constructed with fine-grained pyrite and paraffin/graphite mixture did not result in accurate ranking of pyrite samples by dissolution rate.

Electrochemical study of hydrothermal and sedimentary pyrite dissolution

The dissolution of pyrite is of interest in the formation of acid mine drainage and is a complex electrochemical process. Being able to measure the rate of dissolution of particular pyrite samples under particular conditions is important for describing and predicting rates of AMD generation. Electrochemical techniques offer the promise of performing such measurements rapidly and with small samples. The oxidation of pyrite and the reduction of Fe3+ ions and/or O2 half reactions involved in the pyrite dissolution process were investigated by cyclic voltammetry and steady-state voltammetry using three pyrite materials formed in both sedimentary and hydrothermal environments. For each sample, two kinds of pyrite working electrodes (conventional constructed compact solid electrode, and carbon paste electrode constructed from fine-grained pyrite particles) were employed. Results indicated that for both the hydrothermal and sedimentary pyrite samples the oxidation and reduction half reactions involved in dissolution were governed by charge transfer processes, suggesting that hydrothermal and sedimentary pyrites obey the same dissolution mechanism despite their different formation mechanisms. In addition, the results showed that it is feasible to use a C paste electrode constructed from fine-grained or powdered pyrite to study the pyrite dissolution process electrochemically and to derive approximate rate expressions from the electrochemical data.

Fluvial geomorphology and hydrology in the dispersal and fate of pyrite mud particles released by the Aznalcóllar mine tailings spill

The Agrio-Guadiamar River reach affected by the Aznalcóllar mine tailings spill can be divided into three main sectors taking account of geomorphic characteristics and human-induced changes. Along the first 15 km, the valley presents the characteristics of a middle fluvial reach of moderate sinuosity and gradient; the floodplain declines gently towards the main channel and is built up mainly by lateral accretion deposits, which are mined by open pits. The second sector is located between 15 and 30 km downstream of the mine, and is characterised by higher channel sinuosity and a lower gradient; the floodplain is built on overbank deposits, separated from the main channel by natural levees, showing some low sinuosity flood channels. Finally, the lowest reach, with a similar low gradient, can be described as the proximal area of the Doñana marshlands, whose geomorphology has been modified by agricultural practices for the last 40 years. The spread of mining tailings deposited a mat of pyrite mud (fine milled heavy metal-rich ore) over the main channel and floodplain with a thickness of up to 50 cm in the first sector and then, progressively decreasing downstream. The pyrite mud was deposited over the natural sediments without significant mobilisation of the latter and without relevant geomorphic changes. The subsequent cleaning up of the pyrite mud with the help of heavy machinery resulted in the removal of most of the bushy and herbaceous vegetation as well as the reworking of bed sediments and the destruction of their natural armouring. Relatively small amounts of submerged pyrite mud that could not be removed from the main channel and that mixed with the shallow natural sediments during the cleaning works provides a long-term pollution element in the system. Pyrite mud remnants on floodplains are not being directly removed by fluvial activity in the mid-term because these sedimentation areas are susceptible to erosion only by the wandering of the main channel. However, these materials can be easily oxidised, therefore, plant uptake and underground water pollution should be monitored. On the other hand, the channel bed and banks are source areas of sediments and pyrite materials that can be easily eroded due to the destruction of the natural protection features (vegetation and armouring). Once eroded, the pyrite particles will be transported over longer distances than the coarser host natural alluvium, and deposited on floodplains or areas with low flow velocity.

Image analysis characterization of pyrite in fine coal flotation

The flotation behavior of a −28 mesh Pittsburgh No. 8 coal sample is investigated through the use of Scanning Electron Microscopy in conjunction with Image Analysis. Release analysis is used to generate the flotation products, which are then characterized to provide the particulate composition in terms of pyrite, mineral matter and carbonaceous material. The results of this investigation indicate that the material recovered in the first stage of release analysis tends to be well-liberated carbonaceous material. This is followed by an increase in the recovery of middlings and fines in the later stages of the process. Any free carbonaceous material remaining in the tailings from the release analysis test tends to be associated with the very fine sizes (−400 mesh). Pyrite recovery is attributed to the hydrophobicity provided by small inclusions of carbonaceous material, since the amount of truly liberated pyrite particles (i.e., 100% pyrite) present in the sample is found to be negligible.

Hydrogeologic and environmental impact of amjhore pyrite mines, India

Drainage from active and inactive pyrite mines has produced chemical and physical pollution of both ground- and surface water in Amjhore region. In the present case, chemical pollution is caused by exposing pyrite minerals to oxidation or leaching, resulting in undesirable concentrations of dissolved materials. Pyrite mining suddenly exposed large quantities of sulfides to direct contact with oxygen, and oxidation proceeds rapidly, resulting in acidity and release of metal (Fe) and sulfates to the water system, eventually resulting in water pollution in the region. The magnitude and impact of the problem is just being recognized and, as the present and the future projected demand for clean water is of top priority, the present studies were undertaken.Mine drainage includes water flowing from the surface and underground mines and runoff or seepage from the pyrite mines. This article describes the various hydrologic factors that control acid water formation and its transport. The mine drainage is obviously a continuing source of pollution and, therefore, remedial measures mainly consisting of a double-stage limestone-lime treatment technique have been suggested. The present results will be used to develop an alternative and more effective abatement technology to mitigate acid production at the source, namely, the technique of revegetation of the soil cover applied to the waste mine dump material.Water quality change is discussed in detail, with emphasis on acidity formed from exposed pyrite material and on increase in dissolved solids. Preventive and treatment measures are recommended.