Fresh Pyrite Research Articles

Effect of oxidized pyrite activating persulfate on the degradation of aniline aerofloat: Mechanism and degradation pathway

Aniline aerofloat (dianilinodithiophosphoric acid, DDA) is a common flotation collector for sulfide minerals, but it is also toxic and difficult to be degraded. In this study, oxidized pyrite was used to degrade DDA through activating persulfate (PS). It was found that oxidized pyrite was far more effective than fresh pyrite at removing DDA from a PS system over a wide pH range. The effect of the pyrite oxidation time, initial pH, PS concentration, pyrite dosage and pyrite particle size on DDA degradation in the pyrite-PS system were studied and optimal conditions determined. Through analysis of the total Fe ions concentration, radical species identification and XPS analysis of the change of surface species Fe and S, the DDA degradation mechanism in the oxidized pyrite-PS system was determined. The degradation products were measured by gas chromatography-mass spectrometry (GC–MS) and a potential DDA degradation pathway was hypothesized. The results in this study suggest a template for the utilization of oxidized pyrite in gangue minerals to remove DDA from the wastewater in mineral processing plants.

Analysis of the Selective Flotation of Elemental Gold from Pyrite Using Diisobutyl Monothiophosphate

The gold contained in copper ores is an important resource for the gold industry. In some cases, elemental gold is present and can be recovered by selective flotation. It has been reported that the gold grade and recovery can be increased, without sacrificing the copper recovery, by replacing AERO 3477 (diisobutyl dithiophosphate (DTP)) with AERO 7249 (mixture of diisobutyl monothiophosphate (MTP) and diisobutyl dithiophosphate (DTP)) as the main collector. The fundamental understanding of the improvement in selectivity with the addition of MTP in the flotation of elemental gold from pyrite is limited and is the subject of this paper. In this regard, the hydrophobicity and selectivity of DTP and MTP in the flotation of pyrite and gold are compared and discussed. Density functional theory (DFT) was used to examine the electron density, reactivity, highest occupied molecular orbital (HOMO), and lowest unoccupied molecular orbital (LUMO) of the MTP and DTP collectors. The interaction energies for the adsorption of MTP and DTP from fresh pyrite, oxidized pyrite and gold surfaces were calculated and discussed with respect to the experimental results reported in the literature. Molecular dynamics simulation (MDS) was used to examine the adsorption state of MTP and DTP on the pyrite (100) and Au (111) surfaces.

Mercury forms and their transformation in pyrite under weathering

Pyrite is considered to be the major carrier of mercury in coal. Here, the chemical characteristics of two natural pyrite samples of different weathering degrees were characterized by time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). Thermal stability of Hg was also analyzed via temperature programmed desorption experiment (TPD). Characteristic ions such as S−, Fe+, FeS−, and FeS2−were detected on the surface of fresh pyrite. The release temperature of Hg ranged between 180°C and 300°C, and the characteristic peak of black HgS was recorded. In addition, abundant Fe2O3−, FeSO−, SO4−, and HSO4−were detected on the surface of weathered pyrite, and the release temperature of Hg therein was mainly distributed at 260°C to 380°C and 520°C to 600°C, corresponding to the characteristic peaks of red HgS and HgSO4, respectively. The results show that pyrite is acidified during weathering and that Hg forms in pyrite are transformed from the original state (HgS) to HgSO4.

A reaction rate model for pyrite oxidation considering the influence of water content and temperature

Natural oxidation of pyrite in refractory gold bearing rock stockpiles may facilitate the recovery of gold contained in mined low-grade material that was originally sub-economic due to the cost of pre-treatment to oxidise fresh pyrite. The evaluation of this potential requires the oxidation level of pyrite under various conditions. This paper proposes a reaction rate model for prolonged natural oxidation of pyrite under various water saturation conditions and temperatures and a circum-neutral to alkaline pH. The application is to a natural pre-treatment process for refractory gold ore to liberate the gold content encapsulated in pyrite crystals and allow effective cyanidation for gold extraction. The proposed model is based on the shrinking core model with half-order surface reaction on the pyrite surface. It assumes that, in unsaturated water conditions and at circum-neutral to alkaline pH, a diffusion barrier forms on the fresh pyrite surface during the reaction, which prohibits the diffusion of oxygen to the reacting sites and lowers the reaction rate over time. The diffusion barrier may consist of a thin solution film, some precipitations of soluble oxidation products and/or insoluble oxidation products depending on the water saturation and pH. The diffusivity of this diffusion barrier for oxygen is determined as a function of water saturation and temperature. In this model, the concept of effective oxygen concentration is also proposed to represent the change in oxygen concentration at the particle surface due to water; an exponential relationship is found to be appropriate. Based on the reaction rate data reported in the literature, the reaction rate constant in the model for the surface reaction is determined as 5 × 10−8 mol0.5·m−0.5·s−1 while the diffusion coefficient is 1.2 × 10−15 m2·s−1 for water saturation of 25% and above and 4.7 × 10−19 m2·s−1 for 0.1% water saturation. This rate model can be used for predicting and modelling the level of pyrite oxidation in rock piles or mine tailings where various unsaturated water conditions and circum-neutral to alkaline pH apply.

Attachment, Coalescence, and Spreading of Carbon Dioxide Nanobubbles at Pyrite Surfaces.

Recently, it was reported that using CO2 as a flotation gas increases the flotation of auriferous pyrite from high carbonate gold ores of the Carlin Trend. In this regard, the influence of CO2 on bubble attachment at fresh pyrite surfaces was measured in the absence of collector using an induction timer, and it was found that nitrogen bubble attachment time was significantly reduced from 30 ms to less than 10 ms in CO2 saturated solutions. Details of CO2 bubble attachment at a fresh pyrite surface have been examined by atomic force microscopy (AFM) measurements and molecular dynamics (MD) simulations, and the results used to describe the subsequent attachment of a N2 bubble. As found from MD simulations, unlike the attached N2 bubble, which is stable and has a contact angle of about 90°, the CO2 bubble attaches, and spreads, wetting the fresh pyrite surface and forming a multilayer of CO2 molecules, corresponding to a contact angle of almost 180°. These MDS results are complemented by in situ AFM images, which show that, after attachment, CO2 nano-/microbubbles spread to form pancake bubbles at the fresh pyrite surface. In summary, it seems that CO2 bubbles have a propensity to spread, and whether CO2 exists as layers of CO2 molecules (gas pancakes) or as nano-/microbubbles, their presence at the fresh pyrite surface subsequently facilitates film rupture and attachment of millimeter N2 bubbles and, in this way, improves the flotation of pyrite.

Mineralogy and spectral signature of reactive gossans, Victoria Island, NT, Canada

Gossans resulting from the oxidation of sulphide-rich bedrock occur sporadically across Canada, and these features are routinely indicated on geological maps published by the Geological Survey of Canada (GSC). In the Canadian Arctic Islands, some gossans display reactive zones in permafrost characterized by specific textures and mineralogical facies. In poorly-vegetated areas of the High Arctic, gossans can easily be detected on high-resolution satellite imagery. However, the mechanisms leading to their formation are poorly known. For this study, two reactive gossans located in the early Neoproterozoic Minto Inlier of Victoria Island, Northwest Territories, were investigated to determine if the deposits constitute (1) analogues of mine waste in permafrost and (2) vectors to economic resources. Mineralogy was determined in situ using a portable spectroradiometer, with follow-up laboratory measurements. Site 1, Gossan Hill, is a 75-m topographic high capped by a poorly consolidated, rust-coloured layer overlying pyrite-rich sands, and resembles a classic gossan. Site 2, Gossan Sill, underlies a mineralized gabbroic sill consisting of sulphide-rich veins and pods but appears to be inverted morphologically. Visible–Near Infrared–Short Wave Infrared spectral analyses of surficial materials at Gossan Hill indicate gypsum, goethite and jarosite, and X-ray diffraction (XRD) confirms their presence as well as quartz, illite and feldspar. At Sill Gossan, spectral analyses show gypsum and jarosite; XRD indicates variable amounts of goethite, hematite, pyrite, chlorite, calcite and feldspar. The positive relief and presence of concentric alteration zones at Gossan Hill suggest that cryogenic processes, typical of Arctic regions, are active. Water becomes expelled during the freezing cycle forcing material outwards and along with oxidation of the sulphides, forms variably coloured zones in gossanous material. The inverted stratigraphy at Sill Gossan is more problematic. Constant weathering and mass wasting from the overlying sill and pyrite-rich breccia provide fresh pyrite to the gossan on a regular (seasonal) basis.

Risk assessment of particle dispersion and trace element contamination from mine-waste dumps.

In this study, a model to delimit risk zones influenced by atmospheric particle dispersion from mine-waste dumps is developed to assess their influence on the soil and the population according to the concentration of trace elements in the waste. The model is applied to the Riotinto Mine (in SW Spain), which has a long history of mining and heavy land contamination. The waste materials are separated into three clusters according to the mapping, mineralogy, and geochemical classification using cluster analysis. Two of the clusters are composed of slag, fresh pyrite, and roasted pyrite ashes, which may contain high concentrations of trace elements (e.g., >1 % As or >4 % Pb). The average pollution load index (PLI) calculated for As, Cd, Co, Cu, Pb, Tl, and Zn versus the baseline of the regional soil is 19. The other cluster is primarily composed of sterile rocks and ochreous tailings, and the average PLI is 3. The combination of particle dispersion calculated by a Gaussian model, the PLI, the surface area of each waste and the wind direction is used to develop a risk-assessment model with Geographic Information System GIS software. The zone of high risk can affect the agricultural soil and the population in the study area, particularly if mining activity is restarted in the near future. This model can be applied to spatial planning and environmental protection if the information is complemented with atmospheric particulate matter studies.

Activation flotation and mechanism of lime-depressed pyrite with oxalic acid

Flotation tests, contact angle measurements, infrared spectrum analyses, X-ray analyses and computer simulation were carried out in order to study the activation mechanism of lime-depressed pyrite with oxalic acid. The results show that the oxalic acid effectively eliminated the hydrophilic calcium film from the surface of pyrite. Therefore, the efficiency of pyrite flotation was also activated. The results indicate that after reacting with hydrophobic insoluble remainders on the surface of pyrite, oxalic acid can produce hydrophilic compounds, such as CaCO3, Ca(OH)2 and Fe(OH)3. As a consequence, a fresh pyrite layer was exposed and its flotation activated.

Till geochemistry in the ribbed moraine area of Peräpohjola, Finland

The characteristics of ribbed moraines, with an emphasis on till geochemical prospecting, were studied in the area of Peräpohjola, southern Finnish Lapland. Percussion drilling, test pits and trenches were used for till sampling. The samples were partially extracted and then analysed using ICP-AES or GFAAS methods in the geolaboratory of the Geological Survey of Finland. The distribution of Au and Cu in fine fraction (<0.06 mm) of till in both horizontal and vertical dimensions showed that the uppermost part of the moraine ridges contained the highest metal contents. In the coarser fractions of till (0.06–0.5 and >2 mm), the anomalies were located on the distal side of the ribbed moraine ridges, down-ice from mineralized bedrock. Geochemical patterns together with fresh pyrite grains in till heavy mineral concentrates indicate a short glacial transport distance of the mineralized debris. This conclusion is also supported by the presence of a large proportion of local rock fragments and boulders in the uppermost till unit and at the surface, which is a result of glacial quarrying during the ribbed moraine formation.

The interaction of iron species with pyrite surfaces

The development of iron oxide films on pyrite has been investigated using linear potential sweep voltammetry. Voltammograms for a fresh pyrite surface indicated the presence of an iron(II) hydroxyoxide. After brief exposure to air, the surface layer oxidized to iron(III) hydroxy-oxide. Immersion in iron(II) solutions containing small amounts of iron(III) resulted in an increase in the thickness of the oxide layer to a limiting value; the oxide was present mainly in the iron(III) state. An iron hydroxy-oxide also developed on gold during immersion in iron(II) solution. A pyrite surface abraded on iron powder in deoxygenated water also became coated with iron hydroxy-oxide. Immersion of pyrite in cyanide solution resulted in a decrease in the quantity of oxide on the surface.

Catalytic activity of various iron sulphides in coal liquefaction

Iron sulphides with various S-Fe atomic ratios, such as pyrite, iron(III) sulphide, pyrrhotite and troilite, were used as catalysts for coal liquefaction. Catalytic activities were compared on the basis of the temperature of the exothermic peak due to coal hydrogenolysis. Effects of hydrogen sulphide on catalytic activity of iron sulphides were also investigated. It is concluded that: 1. 1. The catalytic activity of iron sulphides increases with increasing S-Fe ratio; 2. 2. pyrite, with the highest catalytic activity, is converted to pyrrhotite before the onset of exothermic reactions from coal hydrogenolysis, this evidently being the reason for the high catalytic activity; 3. 3. the catalytic activity of iron sulphides depends on the coal type; 4. 4. the high catalytic activity of pyrite may be due to the creation of fresh pyrite surface during the reaction rather than to the presence of high concentrations of hydrogen sulphide.