The amorphous, nonequilibrium, iron-depleted layer (NL) produced by the leaching amounted to half of the residue mass and was composed of predominantly low-spin ferrous iron and polysulfide anions. Problem RO1.1. The XPS sulfur (S2p) spectrum shows sulfate and a form of elemental sulfur on the reacted surface. X-ray Fe Lα,β emission spectra showed the formation of intermediate, high-spin Fe(II) within the NL oxidized in the humid environment, but not in the dry air. Problem RO1.7. Similarly, Kappler and Newman observed formation of the poorly crystalline Fe(III) (hydr) oxide ferrihydrite from anaerobic FeS oxidation by an anoxygenic, Fe(II)-oxidizing phototrophic bacterium, but goethite and lepidocrocite from oxidation of Fe(II) sol by the same organism. The primary iron(III) ions are supplied by the bacterial extracellular polymeric substances, where they are complexed to glucuronic acid residues. The induction period is best described as a period of inhibited dissolution, before the onset of H2S production and increased rate of iron release of at least 2 orders of magnitude. why 100ml of a gas at 10°c will not occupy 200 ml at 20°c, pressure and mass remaining constant? Geobiotropy, Oxidative dissolution of iron monosulfide (FeS) in acidic conditions: The effect of solid pretreatment, An electrochemical study of the oxidative dissolution of iron monosulfide (FeS) in air-equilibrated solutions, The relationship between the electrochemical, mineralogical and flotation characteristics of pyrrhotite samples from different Ni Ores, Iron monosulfide (FeS) oxidation by dissolved oxygen: Characteristics of the product layer, Development of Novel Phosphate Based Inhibitors Effective For Oxygen Corrosion, Estimating activation energy from a sulfide self-heating test, A new screening test to evaluate the presence of oxidizable sulphide minerals in coarse aggregates, Aqueous Oxidation of Iron Monosulfide (FeS) by Molecular Oxygen, Avaliação das Alterações em Propriedades Físicas de Solos Brasileiros após Oxidação Química por Persulfato, Development of Novel Phosphate Based Inhibitors Effective for Oxygen Corrosion. Reaction half-lives ranged from 1.50+/-0.09 h for Al to 8.15+/-0.36 h for Zn. In FeS? Monosulphide of the sulphur-rich underlayer is oxidized to disulphide and polysulphides primarily. The acid-insoluble metal sulfides FeS2, MoS2, and WS2 are chemically attacked by iron(III) hexahydrate ions, generating thiosulfate, which is oxidized to sulfuric acid. All free elements have an oxidation state of 0. oxygen has an oxidation number −2 in most of its compounds except peroxides where it has an oxidation number −1. The length of the induction period is controlled by the amount of surface oxidation products on the mineral surface, acid strength, and temperature. Problem RO1.10. Neutralization by carbonate of acidification generated by pyrite (FeS2) oxidation was investigated by both solution (iron and sulfur speciation, pH and Eh) and solid (FT-IR) characterizations. Elemental sulfur and goethite were the only crystalline products of the NL decomposition. The experimental results demonstrate the importance of temperature and initial pH for the FeS oxidative dissolution. `FeS_2 + O_2 -> Fe_2O_3 + SO_2` Oxidation number it is the number assigned to a compound which represent the number of electrons lost or gained. The amounts of dissolved iron strongly increase with temperature and [H(+)], whereas an increase of H(2)O(2) concentration seems to reduce the troilite oxidation. No unpaired electron spins were detected by EPR; lines of paramagnetic Fe3+ appeared after the samples were aged in the dry air for 49 d and even later in the humid atmosphere. After a short period, R = [S]tot/[Fe]tot stabilized from 1.25 at pH = 1.5 to 1.6 at pH = 3. Unlike the surfaces of simple oxides (e.g. Quantification of depth profiles utilizing the sequential layer sputtering model (SLS) indicate alteration trends correspond compositionally to FeO1.5, FeS2, Fe2S3 and Fe7S8.Compositional zones develop by electron and iron migration towards the oxidized surface. Although Fe diffuses from the interior to the surface, sulphur species do not migrate appreciably from the subsurface giving rise to the sulphur-rich zone. It is possible to demonstrate a heterogeneous reaction mechanism for both pyrite oxidation and reduction using a molecular orbital theory approach. Reactions. A t1/2 rate law describes dissolution in air saturated solutions and supports diffusion controlled dissolution under these conditions. Rates measured in sealed-tube experiments at 25°C, for H2O2 concentration of 2 × 10−3 M are 8.8 × 10−9 M/m2/sec, which are higher than previous estimates. Oxidation state of O is -2 in all its compounds exceptions: a. The experimental observations suggest a mechanism based on the protonation of FeS surface (Chirita and Descostes, 2006) followed by oxidation of FeS by dissolved oxygen to produce Fe2+, S0 and Sn2-. Oxidation of pyrite in aqueous solutions in contact with air (oxygen 20%) was studied at 25°C using short-term batch experiments. Further knowledge as to the nature of the structure of a terrestrial sample of troilite, FeS [stoichiometric iron(II) sulfide] is revealed by a combination of XPS studies and dissolution studies in acid. concentrations. The results of an initial study of the electrochemical behavior of pyrrothite before alteration suggest that its alteration involves the formation of 3 surface layers (in agreement with previous reports): (1) in immediate contact with pyrrhotite corresponding to a metal-deficient sulfide; (2) an intermediate layer corresponding to elemental S, and; (3) the most external layer, consisting of precipitates of Fe oxy-hydroxides, like goethite. The chemical forms of Fe and S in the surface layers are discussed in detail with changes in the proportion of the oxidised and iron-deficient sulfide products. This explains leaching of metal sulfides by Thiobacillus thiooxidans. The oxidation of FeS powders in flowing dry air was investigated over the temperature range of 648 to 923 K. Thermodynamic calculations and experimental observations showed that the initial stages of oxidation are characterized by the formation of FeS 2 and Fe 3 O 4 or Fe 2 O 3.Sub-sequently, the oxidation process goes through a formation and eventual oxidation of Fe 2 (SO 4) 3 to Fe 2 O 3. followed by and finally possibly in several stepsThe overall reaction is Thus, carbonate pH buffer properties seem to be limited and effective for moderated carbonate Problem RO1.8. Immediately below the O-rich layer exists an Fe-deficient, S-rich layer that displays a continuous, gradual decrease in from the O-rich zone to that of the unaltered pyrrhotite. How Biden's plans could affect retirement finances. Typically, in acidic conditions, an initial period of slow dissolution involving no release of H2S can suddenly change to nonoxidative dissolution, with release of H2S and greatly increased rates of release of both iron and sulfur species. Thus, these metal sulfides are degradable by all bacteria able to oxidize sulfur compounds (like T. thiooxidans, etc.). Monoclinic and hexagonal pyrrhotites leached in 1 mol/L HCl and exposed to the air at 100% and ∼10% relative humidity for up to 5 months were studied using X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy, Mössbauer spectroscopy, and electron paramagnetic resonance (EPR). The reaction orders with respect to [H(+)] are variable, pointing out notable modifications of reaction mechanism with experimental conditions. Underlying this sulphur-rich zone is bulk pyrrhotite.Auger compositional depth profiles confirm that the outer most iron-oxyhydroxide layer is approximately 5 Å thick. Sulfate green rust was identified as the primary iron corrosion product, which is shown to be the result of elevated [SO(4)(2-)]/[HCO(3)(-)] ratios in solution. Since is in column of the periodic table, it will share electrons and use an oxidation state of . The anoxic dissolution of troilite (FeS) in acidic medium has been investigated at 50 degrees C using batch dissolution experiments. Continued adsorption onto or co-precipitation with iron corrosion products are secondary metal uptake processes. Sulfate concentrations increased rapidly to 1.0 ppm within the first few minutes of reaction, then remained unchanged over the duration of the experiment These results demonstrate that sulfate release was a rapid one-time event in the earliest stages of pyrrhotite dissolution. With the removal of iron from the pyrrhotite structure, polysulfide replaced monosulfide as the dominant sulfur species. The same negative charge shift is measured for all C, Fe, and S chemical states implying a crystal-wide space-charge surface region. The second reaction is the oxidation of pyrite by dissolved O2 to generate Fe²⁺ and SO4²⁻: FeS2+7/2O2+H2O⇒Fe²⁺+2SO4²⁻+2H⁺ The third is the reaction to produce ferric hydroxide and SO4²⁻: FeS2+15/4O2+7/2H2O⇒Fe(OH)3(s)+2SO4²⁻+4H⁺Reactions (1) and (2) appear to be first-order with respect to [O2] as suggested by Manaka (1998). The kinetics of these processes are dependent on the concentration of the iron(III) ions and, in the latter case, on the solubility product of the metal sulfide. The accumulation of this surface charge during dissolution appears to result in the reduction of oxidised disulfide and polysulfide species back to sulfide, thus inducing nonoxidative dissolution. Intermediate sulfoxy anions were observed only at high stirring rates. +2: What is the oxidation number for C in C 60? The pH dependency of the reaction rates was not determined in this study. consistent with R = 1.6. During the induction period there is slow release of iron but little or no production of H2S. Leached pyrrhotite surfaces are initially featureless (T1 texture). To find the oxidation state of , set up an equation of each oxidation state found earlier and set it equal to . The mechanism and chemistry of the degradation is determined by the mineral structure.The disulfides pyrite (FeS2), molybdenite (MoS2), and tungstenite (WS2) are degraded via the main intermediate thiosulfate. Fe2+ is unstable in oxidative conditions (Descostes et al., 2002) and transforms into Fe(OH)3(s) and goethite after approximately 30 h of reaction. The analysis of the basic properties of the films was carried out by standard optical and electrical characterization techniques. Cr2+). (3) Rapid, acid-consuming reaction of mono-sulfide species under nonoxidative or reductive conditions with production of H2S. INTRODUCTION Pyrite (FeS 2) is the most abundant and widespread sulfide mineral on the Earth’s surface, and it plays an important role in geochemistry, biology, and environmental processes. Only the first two stages of dissolution occur. Iron sulfide reacts with hydrochloric acid, releasing hydrogen sulfide: FeS + 2 HCl → FeCl 2 + H 2 S FeS + H 2 SO 4 → FeSO 4 + H 2 S Results show that it is possible to establish a reliable maximal limit for corrosion forms containing goethite and magnetite in oxidising conditions. Five different contact duration were selected : 6 hours, 1, 3, 8 and 30 days. The oxidation state of sulphur is -1 in FeS2, just as oxygen is in peroxides like H2O2 and BaO2. Geochemical model results indicate that metal removal is most effective in solutions that are highly undersaturated with respect to pure-metal hydroxides suggesting that adsorption is the initial and most rapid metal uptake mechanism. In FeS2, iron is in +2 state. The experimental data suggest a mechanism based on the protonation of FeS surfaces followed by oxidation of FeS by dissolved oxygen to produce Fe 2+, S 0, and S 2− n. Fe 2+ is unstable under oxidative conditions and transforms into Fe(OH) 3(s), goethite and lepidocrocite. The intermediate species cannot be detected, and it is consistent with calculated concentrations being below the detection limits. Reduction also occurs with synthetic pyrrhotite that, before dissolution in acid, has undergone only limited oxidation. Small, higher oxidation state sulfur contributions, including a disulfide-like state are also present, which suggest the presence of defects due to some nonstoichiometry. At higher temperatures (35 and 45oC) and pH 3.00, nH:nFe<2 and is quasi-invariant over the reaction time. Cations and anions have an oxidation number equal to their charge, for example in Fe2+, Fe hasan oxidation number of +2 and in S2- S has an oxidation number of -2. The proposal of this mechanism is also supported by theoretical considerations regarding the low probability of a direct reaction between paramagnetic molecular oxygen and diamagnetic pyrite. Fe3+) or the reductant (e.g. FTIR spectroscopy indicated the presence of several sulfur species (S0, Sn2-, S2O32-, SO32- and SO42-) and ferric hydroxides or oxyhydroxide (Fe(OH)3 and goethite) on residual FeS surface. Two distinct activation energies are associated with the two regimes. In contrast, sulfate interacts strongly with FeIII. The same conversion probably occurs in the sulphur-rich zone of pyrrhotite, where diffusion of Fe to the oxidized surface results in formation of marcasite-like composition and structure in the sulphur-rich layer of oxidized pyrrhotite. The purpose of this experimental study was to ascertain the relative roles of Fe(III) and DO in pyrite oxidation at circumneutral pH. The charge. sulfate incorporating sulfite and thiosulfate, and then lepidocrocite. The changes with time in these variables of the experimental solutions suggest that pyrite decomposition proceeds through three major overall reactions. The kinetics and mechanism of troilite oxidation by H(2)O(2) was studied at temperatures of 25 and 45 degrees C. Solutions within the range 0.1-0.85 mol L(-1) H(2)O(2) in HClO(4) (0.01-0.1 mol L(-1)) were used as dissolution media. Details of reactions between pyrite and water initially equilibrated with the atmosphere (pO2 = 0.2 atm and pCO2 = 10−3.5 atm) were investigated in a closed-system, batch reactor at 25°C and 37°C. Pyrrhotite (Fe7S8) fractured under high vacuum (10−7 Pa) and reacted with air for 6.5 and fifty hours was analyzed using X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). (1) The immediate dissolution of an outermost layer of oxidised iron hydroxide/oxyhydroxide species and oxy-sulfur species. Whereas pyrite has S 2 subunits, arsenopyrite has [AsS] units, formally derived from deprotonation of arsenothiol (H 2 AsSH). Pyrrhotite leaching in acid solutions proceeded via the diffusion of iron to the mineral surface. (4) Inhibited dissolution due to reoxidation of the sulfide surface by oxidising solution species (i.e., Fe3+, residual oxygen) to produce polysulfide, elemental sulfur, and oxy-sulfur species.Dissolving synthetic pyrrhotite in similar, but aerated, acidic conditions, results in inhibited dissolution characterised by a lower rate of Fe release, minimal release of SO42− and no release of H2S . ZnS and PbS, by contrast, are quite stable and retain S in the -2 state. Hematite was detected only in solid residue produced during high temperature experiments. geek..... Lv 7. Molecular oxygen initially taken onto the surface is reduced to O2− probably by electron transfer from the pyrrhotite interior and is facilitated by rapid electron exchange between Fe(III) and Fe(II) of the bulk solid. 2) Ca + Cl 2 → CaCl 2 The pristine troilite S2p spectrum comprises mainly monosulfide 161.1 eV, within the reported range of monosulfide, together with evidence of an unsatisfied monosulfide surface state arising from S–Fe bond rupture. Pyrrhotite (Fe7S8) grains were reacted in solutions of H2SO4 (pH 3.0) for eight hours and analyzed using secondary electron microscopy (SEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Short-circuit currents of 8.9 and 22 mA/cm2, open-circuit voltages of 0.489 V and 0.324 V, fill factors of 0.29 and 0.42 and conversion efficiencies of 1.26 and 3.12% were obtained for SnO2/Zn0.9Cd0.1/CdTe and SnO2/ZnS/CdTe, respectively, under normalized 100 mW/cm2 illumination (AM1). 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