Decomposition Of Pyrite Research Articles

Pyrite alteration and neoformed magnetic minerals in the fault zone of the Chi‐Chi earthquake (Mw7.6, 1999): Evidence for frictional heating and co‐seismic fluids

During an earthquake, physical and chemical transformations lead to alteration and formation of minerals in the gouge layer. Altered and neoformed minerals can be used as tracers of some earthquake processes. In this study, we investigate pyrite and magnetic minerals within the host Chinshui siltstone and the 16‐cm‐thick gouge. This gouge hosts the principal slip zone of Chi‐Chi earthquake (Mw7.6, 1999). In the Chinshui siltstone, pyrite framboids of various sizes and euhedral pyrite are observed. The magnetic mineral assemblage comprises stoichiometric magnetite, greigite, and fine‐grained pyrrhotite. The pyrite content is generally reduced in the gouge compared to the wall rock. The magnetic mineral assemblage in the gouge consists of goethite, pyrrhotite, and partially oxidized magnetite. The pyrrhotite, goethite and some magnetite are neoformed. Pyrrhotite likely formed from high temperature decomposition of pyrite (>500°C) generated during co‐seismic slip of repeated earthquakes. Goethite is inferred to have formed from hot aqueous co‐seismic fluid (>350°C) in association with the 1999 Chi‐Chi event. Elevated fluid temperatures can also explain the partial alteration of magnetite and the retrograde alteration of some pyrrhotite to pyrite. We suggest that characterization of neoformed magnetic minerals can provide important information for studying earthquake slip zones in sediment‐derived fault gouge.

Calcium-promoted catalytic activity of potassium carbonate for steam gasification of coal char: Transformations of sulfur

K2CO3-catalyzed char gasification with steam was carried out on a laboratory fix-bed reactor and it featured in the preparation of char from a high-sulfur coal by the prior addition of Ca(OH)2 to the coal. This work was focused on the clarification of sulfur transformations during the coal pyrolysis and the char gasification. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy was employed to determine quantitatively the forms of sulfur in coal and their changes in process. Results showed that the addition of Ca(OH)2 to coal promoted the decomposition of both pyrite and organic sulfur during the charring. In the K2CO3-catalyzed char gasification, the calcium additive enabled more sulfur to be retained eventually as K2SO4 rather than CaSO4. The formation of K2SO4 would be conducive to the recycled use of potassium catalyst.

Sulfur isotopic trends and iron speciation from the c. 2.0 Ga Pilgujärvi Sedimentary Formation, NW Russia

Sulfide sulfur isotope values and iron speciation data are reported here for sediments from the 2.0 Ga old Pilgujärvi Sedimentary Formation, Pechenga Greenstone Belt, NW Russia. Sulfides are abundant throughout the c. 1400m thick turbiditic sandstone-siltstone-shale succession and present as pyrite and pyrrhotite. A stratigraphic trend is discernible with respect to sulfide mineralogy and sulfur isotopic compositions, changing up-section from highly to less variable and positive δ34S values. The occurrence of pyrrhotite, particularly high in the upper part of the section, is thought to be the result of decomposition of pyrite during low-grade metamorphism. This is evidenced by the crystallographic habit and sulfur isotopic composition of the different sulfide minerals. The δ34S of both sulfur species is quite variable in the lower part of the formation (−9.5% to 18.7%) while the upper part displays a smaller fluctuation in δ34S (4.4%–13.3%). The pyrrhotite is generally depleted in 34S by approximately 3.6% (average isotopic difference between pyrrhotite and pyrite) compared to the pyrite; this shift in the sulfur isotopic composition results from thermal decomposition of pyrite.The overall spread in δ34S is indicative for the microbial reduction of sulfate, but δ34S values suggest a sulfate limited environment in the upper part of the formation. We note, however, that the sulfate limitation is restricted to the pore water realm, caused by high sedimentation rates that inhibited a sufficiently high sulfate flux from the overlying water column into the sediment.Based on iron speciation data, a previous characterization of the depositional environment as non-euxinic can be specified more precisely. We note that the siliciclastic succession of the Pilgujärvi Sedimentary Formation was deposited under anoxic and ferruginous water column conditions derived from high ratios of FeHR/FeT and low ratios of Fepy/FeHR.

Thermal transformations of organic and inorganic sulfur in Type II kerogen quantified by S-XANES

Sulfur X-ray Absorption Near Edge Structure Spectroscopy (S-XANES) was used to quantify the thermal transformations of organic and inorganic sulfur forms in pyrite-containing Type II kerogens and kerogen chars after open system pyrolysis for a series of well-defined times and temperatures. These results are compared to identical experiments conducted on the same kerogens treated to be pyrite-free. No significant differences were found in the thermal transformations of organic sulfur between the pyrite-containing and pyrite-free kerogen. The loss of aliphatic sulfur forms occurs early (equivalent Ro<1.5%) while there is a relative increase in thiophenic sulfur over aromatic sulfide at higher maturity (Ro>1.5%). In pyrite-containing kerogens, the complete conversion of pyrite (FeS2) into pyrrhotite (Fe1−xS) occurs by a laboratory equivalent Ro=1.5%, followed by the conversion of pyrrhotite into troilite (FeS) at higher maturity. The availability of hydrogen from hydrocarbons generated from kerogen accelerates the initial decomposition of pyrite resulting in pyrrhotite and H2S evolution. H2S evolution up to Ro=2.4% corresponds to the sulfur loss associated with pyrrhotite and troilite formation and aliphatic sulfur loss, indicating that sulfur from pyrite results almost exclusively in H2S evolution with no significant incorporation and retention of sulfur into the organic matter of the kerogen chars under the current set of open system pyrolysis conditions.

Derivation of S and Pb in Phanerozoic Intrusion-Related Metal Deposits from Neoproterozoic Sedimentary Pyrite, Great Basin, United States

The thick (≤8 km), regionally extensive section of Neoproterozoic siliciclastic strata (terrigenous detrital succession, TDS) in the central and eastern Great Basin contains sedimentary pyrite characterized by mostly high δ 34 S values (−11.6 to 40.8‰, >70% exceed 10‰; 51 analyses) derived from reduction of seawater sulfate, and by markedly radiogenic Pb isotopes ( 207 Pb/ 204 Pb >19.2; 15 analyses) acquired from clastic detritus eroded from Precambrian cratonal rocks to the east-southeast. In the overlying Paleozoic section, Pb-Zn-Cu-Ag-Au deposits associated with Jurassic, Cretaceous, and Tertiary granitic intrusions (intrusion-related metal deposits) contain galena and other sulfide minerals with S and Pb isotope compositions similar to those of TDS sedimentary pyrite, consistent with derivation of deposit S and Pb from TDS pyrite. Minor element abundances in TDS pyrite (e.g., Pb, Zn, Cu, Ag, and Au) compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated, implying that enrichment in source minerals is not a precondition for intrusion-related metal deposits. Three mechanisms for transferring components of TDS sedimentary pyrite to intrusion-related metal deposits are qualitatively evaluated. One mechanism involves (1) decomposition of TDS pyrite in thermal aureoles of intruding magmas, and (2) aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy S, radiogenic Pb, and possibly other sedimentary pyrite and detrital mineral components, as sulfide minerals in intrusion-related metal deposits. A second mechanism invokes mixing and S isotope exchange in thermal aureoles of Pb and S exsolved from magma and derived from decomposition of sedimentary pyrite. A third mechanism entails melting of TDS strata or assimilation of TDS strata by crustal or mantle magmas. TDS-derived or assimilated magmas ascend, decompress, and exsolve a mixture of TDS volatiles, including isotopically heavy S and radiogenic Pb from sedimentary pyrite, and volatiles acquired from deeper crustal or mantle sources. In the central and eastern Great Basin, the wide distribution and high density of small to mid-sized vein, replacement, and skarn intrusion-related metal deposits in lower Paleozoic rocks that contain TDS sedimentary pyrite S and Pb reflect (1) prolific Jurassic, Cretaceous, and Tertiary magmatism, (2) a regional, substrate reservoir of S and Pb in permeable and homogeneous siliciclastic strata, and (3) relatively small scale concentration of substrate and magmatic components. Large intrusion-related metal deposits in the central and eastern Great Basin acquired S and most Pb from thicker lithospheric sections.

Experimental investigation of the combustion of bituminous coal in air and O2/CO2 mixtures: 2. Variation of the transformation behaviour of mineral matter with bulk gas composition

Combustion of a Chinese bituminous coal was carried out in a laboratory-scale drop tube furnace (DTF) to clarify the variation of ash properties with bulk gas composition. The combustion conditions tested include three bulk gases, air, 21% O2/79% CO2 and 27% O2/73% CO2, two furnace/gas temperatures close to the fluidized bed reactor temperature range, 1073K and 1273K, and three particle residence times. Apart from bulk properties analysis, individual ash particles and the original mineral species in coal were characterized using Computer – Controlled Scanning Electron Microscopy (CCSEM). The results indicate that, under the given experimental conditions, shifting bulk gas from air to O2/CO2 mixtures is insignificant in terms of the elemental composition of bulk ash, in agreement with the literature. However, changes in the properties of individual species/metals are noticeable, including the extent of the vaporization of volatile elements, ash particle-size distribution (PSD), crystallization extent of K alumino-silicate associate, pyrite decomposition and oxidation rate and formation propensity of liquidus in ash. These changes were mostly considered to be caused by the evolution of included mineral grains in the distinct char particles in the O2/CO2 environment. Reduction in char particle temperature with bulk gas shifting from air to O2/CO2 mixtures was primarily crucial, which, however, could be overweighed by the existence of a fairly strong local reducing condition on the char surface in O2/CO2. Consequently, vaporization of the volatile elements such as Na and P was promoted; formation of the crystalline leucite in air was in contrast inhibited. Furthermore, the extent of coalescence of included minerals and oxidation rate of pyrite (or its derivative, pyrrhotite) were also influenced by char consumption rate, i.e. the receding extent of char surface. These parameters exerted a combined effect on ash formation, requiring detailed mathematical modeling to describe the dynamics of the formation of oxy-fuel ash. This study also indicated that the differences of ash properties formed between air and O2/CO2 mixtures can be greatly reduced and eventually eliminated by increasing furnace temperature. Increase in the turbulence of gas flow should also benefit the elimination of the side effects of local reducing gases on char surface.

Thermal Decomposition of Pyrite FeS&lt;sub&gt;2&lt;/sub&gt; under Reducing Conditions

The thermal decomposition of pyrite was investigated under reducing atmosphere, e.g. p(O2)~10-6 bar. Thermogravimetric measurements were coupled with differential scanning calorimetry and mass spectrometry. Multi-scan method was used to calculate the values of the activation energy of the reaction of thermal decomposition of the pyrite. It was shown that the value of the activation energy of the decomposition of pyrite into pyrrhotite varies with the reaction progress. The values of activation energy vary from 250 to 350 kJ.mol-1.

Matrix composition and community structure analysis of a novel bacterial pyrite leaching community

Here we describe a novel bacterial community that is embedded in a matrix of carbohydrates and bio/geochemical products of pyrite (FeS(2)) oxidation. This community grows in stalactite-like structures--snottites--on the ceiling of an abandoned pyrite mine at pH values of 2.2-2.6. The aqueous phase in the matrix contains 200 mM of sulfate and total iron concentrations of 60 mM. Micro-X-ray diffraction analysis showed that jarosite [(K,Na,H(3)O)Fe(3)(SO(4))(2)(OH)(6)] is the major mineral embedded in the snottites. X-ray absorption near-edge structure experiments revealed three different sulfur species. The major signal can be ascribed to sulfate, and the other two features may correspond to thiols and sulfoxides. Arabinose was detected as the major sugar component in the extracellular polymeric substance. Via restriction fragment length polymorphism analysis, a community was found that mainly consists of iron oxidizing Leptospirillum and Ferrovum species but also of bacteria that could be involved in dissimilatory sulfate and dissimilatory iron reduction. Each snottite can be regarded as a complex, self-contained consortium of bacterial species fuelled by the decomposition of pyrite.

Transformations of pyrite during formation of metallurgical coke

The desulfurization of pyrite during the coking process leads to the formation of phases of varying size, shape and composition. The phases are represented mostly by Fe and S-bearing associations, which can be divided into two categories: those represented only by of Fe–S phases (three varieties), and aggregates containing both sulfides and almost pure iron. There are also Fe–O and Fe–S–O phases, which were probably formed after the coke was pushed from the coke oven. It is suggested that the formation of Fe and S-bearing associations can cause the appearance of cracks and cavities in the coke matrix, which, together with the pressure of the released SO 2 gas, will detract from the strength of the coke. Large grains of pyrite can create weaker spots than do smaller ones, and the incomplete decomposition of pyrite will cause migration of the remaining part of the sulfur to the blast furnace, affecting the reactions there. This may be more common in cokes of relatively low porosity and small pore size and in those made from coals with large pyrite grains.

The progressive formation of submicron particulate matter in a quasi one-dimensional pulverized coal combustor

In this work, we aim to investigate the formation mechanisms of submicron particulate matter (PM 1) by observing progressive changes of collected samples at different combustion stages. A 25 kW quasi one-dimensional down-fired pulverized coal combustor was used, where PM 1 was collected from the furnace centerline through the desired sampling ports by using a nitrogen-aspirated, water-cooling isokinetic sampling probe followed a 13-stage electric low pressure impactor. First, the mass concentration particle-size-distributions (PSD) of PM 1 sampled at coal flame zone clearly exhibit two distinct modes separated by a fraction of 0.173–0.267 μm, ultrafine mode and intermediate mode. However, the ultrafine peak around 63 nm greatly decreases and becomes flat as coal combustion further progresses along axial length. Then, the contributions of either organically bounded minerals or inherent minerals to these two modes at different stages are analyzed. Finally, the evolution of sulfur-concentration PSD reveals the effects of pyrite decomposition and the sulfation reaction on PM 1 formation in the combustion system.

PERTLIKITE, A NEW TETRAGONAL Mg-RICH MEMBER OF THE VOLTAITE GROUP FROM MADENI ZAKH, IRAN

Pertlikite, a new member of the voltaite group, is the tetragonal Mg-dominant analogue of the isometric phases voltaite and zincovoltaite. At its type locality, Madeni Zakh, Iran, the mineral occurs in a pyrite-bearing trachytic eruptive rock, and probably formed after the decomposition of pyrite. Pertlikite forms single crystals up to 1 cm; the phase is associated with metavoltine, botryogen, pyrite and alunite. In contrast to voltaite and zincovoltaite, the optical properties and the single-crystal study of the structure ( R 1 = 0.022) confirm the tetragonal symmetry, ω = 1.590(2), e = 1.586(2), space group I 4 1 / acd , a 19.2080(3), c 27.2158(7) A, V 10041.2(6) A 3 , and Z = 8. The results of the chemical analysis, in combination with the Mossbauer data and the crystal-structure refinement, give the formula (K 1.98 Na 0.01 ) ∑1.99 M 2 (Fe 2+ 1.13 Mg 0.49 Mn 2+ 0.27 Fe 3+ 0.10 Zn 0.01 ) ∑2.00 M 3 (Mg 2.52 Fe 3+ 1.49 ) ∑4.01 M 1 Fe 3+ 2.00 Al 1.00 (SO 4 ) 12.00 ·18 H 2 O, which can be simplified to an ideal formula: K 2 M 2 (Fe 2+ ,Mg) 2 M 3 (Mg,Fe 3+ ) 4 M 1 Fe 3+ 2 Al (SO 4 ) 12 ·18 H 2 O. The strongest eight lines of the powder pattern [ d in A( I )( hkl )] are: 5.543(28)(132), 3.396(100)(440), 3.136(21) (345), 3.038(39)(444), 2.848(31)(361), 2.534(21)(273), 2.078(29)(567) and 1.601(21)(6104). The unit-cell parameters refined from the powder data (Cu K α radiation) are a 19.2167(2), c 27.1976(4) A. The tetragonal structure of pertlikite results from Mg,Fe order at the Fe 2 site. Relative to the isometric voltaite and zincovoltaite, the Fe 2 site splits to create a site that is predominantly Mg ( Mg 3) and another that is dominantly Fe ( Fe 2) in pertlikite. For the three metal sites, the results of the refinement are Fe 1: . Fe; Fe 2: Fe >> Mg; Mg 3: Mg >> Fe. The H 2 O molecules that bond to the Al atom are extensively disordered, as has been observed in the isometric phases. The measured density is 2.59(3) g/cm 3 (by pycnometer), and the calculated density is 2.56(1) g/cm 3 . The name honors Franz Pertlik, Professor of Mineralogy and Crystallography, University of Vienna, Austria, in recognition of his extensive work on the crystal chemistry of minerals.

High magnetic susceptibility produced by thermal decomposition of core samples from the Chelungpu fault in Taiwan

We carried out thermomagnetic susceptibility analyses of fault rocks from core samples from Hole B of the Taiwan Chelungpu Fault Drilling Project (TCDP) to investigate the cause of high magnetic susceptibilities in the fault core. Test samples were thermally and mechanically treated by heating to different maximum temperatures of up to 900 °C and by high-velocity frictional tests before magnetic analyses. Thermomagnetic susceptibility analyses of natural fault rocks revealed that magnetization increased at maximum heating temperatures above 400 °C in the heating cycle, and showed three step increases, at 600 to 550 °C and at 300 °C during the cooling cycle. These behaviors are consistent with the presence of pyrite, siderite and chlorite, suggesting that TCDP gouge originally included these minerals, which contributed to the generation the magnetic susceptibility by thermomechanical reactions. The change in magnetic susceptibility due to heating of siderite was 20 times that obtained by heating pyrite and chlorite, so that only a small fraction of siderite decomposition is enough to cause the slight increase of the susceptibility observed in the fault core. Color measurement results indicate that thermal decomposition by frictional heating took place under low-oxygen conditions at depth, which prevented the minerals from oxidizing to reddish hematite. This finding supports the inference that a mechanically driven chemical reaction partly accounts for the high magnetic susceptibility. A kinetic model analysis confirmed that frictional heating can cause thermal decomposition of siderite and pyrite. Our results show that decomposition of pyrite to pyrrhotite, siderite and, to some extent, chlorite to magnetite is the probable mechanism explaining the magnetic anomaly within the Chelungpu fault zone.

A study on the thermal decomposition of coal-derived pyrite

The thermal behavior of coal-derived pyrite as well as ferrous sulfide compound during heat treatments was investigated by temperature-programmed decomposition–mass spectrometer analysis (TPD–MS) and X-ray diffraction (XRD) measurements. An influence of atmosphere on pyrite and FeS decomposition and the interaction between pyrite and a coal-like environment were examined. The results showed that pyrite decomposition under inert atmosphere occurred in steps and the different transition states with Fe/S value were formed during heat treatments. The final solid state under helium contained only Fe (1− x) S phase. The presence of carbon support and hydrogen could promote pyrite transfer and change the sulfur evolution behavior during decomposition process. However, hydrogen was the principal factor which could determine the presence of iron phase in the final products.

Evaluation of Environmental Pollution Caused by Heavy Metal Elements in Natural Ground

The pollution of ground water caused by the inflow of drainage water from mudstone excavation sites is a serious issue. It has been recognized that the problem results from the discharge of sulfate generated by the decomposition of pyrite contained in the mudstone. Urban natural ground commonly contains mud sediments, and when the underground environment is altered by underground openings, pollution by acid water originating from these mud sediments may occur. The prediction of pollution is therefore important in constructing underground openings. We used numerical simulation to attempt prediction of the spatial extent of pollution caused by the drainage of acid water with heavy metals from mud sediment.

ARSENOPYRITE MELTING DURING METAMORPHISM OF SULFIDE ORE DEPOSITS

Arsenopyrite is present as a minor phase in many different types of ore deposits. Here we investigate a number of ore deposits metamorphosed to mid-amphibolite facies and above to show that in some environments, arsenopyrite is likely to melt during metamorphism, but in others it will persist until it is converted to lollingite + pyrrhotite. The fate of arsenopyrite is governed by the sulfur fugacity imposed by the surrounding mineralogy during metamorphism. At the Hemlo gold deposit, Canada, which contains a range of disseminated sulfi des, the breakdown of barite promoted conditions of high f(S2) and melting of arsenopyrite during prograde metamorphism. On the other hand, at several massive sulfi de deposits including Osborne Lake, Montauban and Geco in Canada, high f(S2) conditions were instead generated through pyrite breakdown on the pyrite–pyrrhotite buffer, also causing arsenopyrite to melt in favorable parts of the deposits. In contrast, metamorphic processes that inhibit high f(S2) through consumption of sulfur promote the solid-state conversion of arsenopyrite to lollingite and pyrrhotite rather than melting. In most mineral deposits, the strongest infl uence on sulfur fugacity is the pyrite-to-pyrrhotite reaction, which buffers f(S2) to increasingly elevated values as temperature increases. Once pyrite is consumed, however, f(S2) no longer is maintained at elevated values. If rocks hosting arsenopyrite are able to conserve pyrite to middle-amphibolite-facies conditions (beyond 491°C at 1 bar, or ~560°C at 5 kbar), arsenopyrite melting will occur. If not, arsenopyrite melting is unlikely, though still possible. Of the mechanisms that promote pyrite decomposition at metamorphic conditions below arsenopyrite melting, sequestration of sulfur by iron silicates or oxides (or both) to form pyrrhotite may be the most effective in many types of deposit. At the Calumet deposit and in some parts of the Geco deposit, this process was found to be effective in converting pyrite to pyrrhotite in magnetite-rich rocks. Pyrite consumption and low-f(S2) conditions are also promoted to a small extent by incorporation of sulfur in hydrothermal fl uids, such as an introduced fl uid or those generated by dehydration reactions, this effect becoming more signifi cant as temperature rises. Deposits where arsenopyrite is likely to melt during metamorphism include pyrite-rich massive sulfi de deposits as well as disseminated deposits lacking abundant iron silicates and oxides. The As-rich melts that result are highly effective in incorporating and mobilizing other metals, particularly gold and silver, as demonstrated at the Challenger deposit (Australia) and at Hemlo, Ontario.

Mapping Fe-bearing hydrated sulphate minerals with short wave infrared (SWIR) spectral analysis at San Miguel mine environment, Iberian Pyrite Belt (SW Spain)

Short-wave infrared reflectance (SWIR) spectra obtained from a Portable Infrared Mineral Analyser (PIMA) were applied to map acidic mine soils at San Miguel massive sulphide deposit, Iberian Pyrite Belt, Spain. Field spectral measurements and laboratory analysis were performed on samples from 58 stations from two very polluted grounds. These analyses identified secondary and tertiary Fe-rich sulphate–hydrate minerals associated with the alteration of sulphide-bearing mine wastes and other associated infrared active minerals. The spectral absorption features for the pure salt types found in these areas allowed the preparation of a specific reference library for automatic mineral identification. Using this approach three separate zones around the sources of contamination have been discriminated: a “proximal” zone dominated by rozenite + hexahydrite, a “transitional” zone dominated by copiapite + coquimbite and a “distal” zone of hydronium–jarosite. An additional zone of “gypsum” was also recognized locally at the areas, where, last decade the neutralization of the acid soils with limestones was attempted. In addition to discriminating distinct mineralogical zones quantitative spectral data allowed contoured mineral maps to be produced that are comparable with the estimated mineralogical data obtained from conventional methods, such as XRD and field observations. These maps demonstrate that sulphate minerals were firstly formed by oxidation of the pyrite-rich ores followed by dissolution and precipitation involving a combination of oxidation, dehydration, and neutralization reactions. The study shows the potential of SWIR spectral analysis to identify and understand the distribution of efflorescent salts and other products of pyrite decomposition and provides a methodology to assist the research and monitoring of sources of environmental contamination.

Dependence of pyrite concentration on kinetics and thermodynamics of coal pyrolysis in non-isothermal systems

Thermogravimetric investigation has been undertaken to evaluate the kinetic and thermodynamic parameters and the influence of pyrite concentration on coal pyrolysis in inert atmosphere. Weight loss up to 150 °C are 4.3 wt.%, 5.5 wt.% and 7.0 wt.% in 1%, 5% and 10% pyrite blended coals, respectively, and in the raw coal (8.2 wt.%) suggests that the presence of pyrite can influence loss of moisture and volatile matter characteristics. The essential weight loss is restricted in the temperature range of 220–650 °C for all the samples. DTA shows two peaks in that region; the first one is related with the primary carbonisation of coal and the second, which appears at a relatively higher temperature, is attributed to the decomposition of pyrite, both shifting to higher temperature with increasing pyrite concentration. Further presence of pyrite in substantial amount decreases the reactivity of coal for pyrolysis; however, its negligible amount has no significant impact on carbonisation. Kinetic study reveals that, with increase in temperature, the rate constants continuously increase; however, the trend is irregular for activation energy (range: 20.42–36.17 kJ mol −1 from Arrhenius equation and 28.72–38.29 kJ mol −1 from Coats and Redfern equation) and frequency factor (range: 1.35–2.11×10 −4 s −1) for all the samples. It has been inferred that decomposed products of pyrite rather than pyrite itself were the real catalyst for enhancing coal pyrolysis; non-stoichiometric pyrrhotite accelerates carbonisation and/or elemental sulphur stabilises free radicals through cross linking. The pyrolytic reaction in all the systems proceeds with the absorption of heat, decrease in randomness and non-spontaneous in nature. It is suggested that the carbonisation process is a diffusion controlled reaction rather than thermodynamically controlled.

A model for calcium, magnesium and sulfate in seawater over Phanerozoic time

A theoretical model has been constructed for calculating the concentrations of dissolved calcium, magnesium and sulfate in seawater over the past 550 million years (Phanerozoic time). It is demonstrated that the weathering of Ca carbonates and silicates by carbonic acid can be generally ignored in the modeling. A previous model of the carbon cycle is used to guide input to the oceans of Mg from carbonate and silicate weathering by H 2 CO 3 . Similarly a previous model of the sulfur cycle is used to guide input fluxes to the ocean by calcium sulfate weathering and the weathering of Ca and Mg carbonates and silicates by sulfuric acid. The sulfuric acid is derived from the oxidation of pyrite during weathering plus the oxidation of sulfur gases derived from the metamorphic/volcanic decomposition of pyrite and CaSO 4 . Calcium is removed from seawater as sedimentary carbonates and sulfates, SO 4 is removed as sedimentary pyrite and CaSO 4 , and Mg is removed by exchange for Ca via basalt-seawater reaction and/or dolomitization (plus minor burial in sediments with pyrite as anoxic dolomite). By adjusting starting conditions modeling results can be found that agree well with results of studies of salt fluid inclusions for variations of Ca and SO 4 . This is especially true of the timing when Ca was more abundant in seawater than SO 4 and vice versa. General agreement was also found with fluid inclusion results for changes in the Mg/Ca ratio thereby distinguishing calcite seas from aragonite seas. Because of this overall agreement the modeling offers a new perspective on why oceanic Ca, Mg and SO 4 have varied over Phanerozoic time.

Effect of mineral on sulfur behavior during pressurized coal pyrolysis

Chinese Yima coal and its HCl/HF and HCl/HF/HNO 3 treated samples were pyrolyzed in a fixed bed reactor under a pressure of 2 MPa. The effect of mineral on organic and pyrite sulfur transformation was investigated along with the effect of decomposition of pyrite on organic sulfur removal during pyrolysis. The results showed that the inherent mineral in coal has little effect on the decomposition of pyrite. The problems to hinder sulfur removal from coal during pyrolysis mainly include following three aspects: (I) large proportion of sulfide was produced from alkaline mineral matter in coal reacting with sulfur containing gas; (II) pyrite sulfur transformed into organic sulfur; (III) iron sulfide produced by decomposition of pyrite, which is more difficult to decompose at low temperature.

Thermal decomposition of pyrite in the nitrogen atmosphere

The effects of gas flow rate, reaction temperature, particle size, and time on thermal decomposition of pyrite have been investigated between 673 and 1073 K in a nitrogen gas environment in which the gas–solid contact is effective. The decomposition reaction is well represented by the “shrinking core” model and can be divided into two regions with different rate controlling step. The rate-controlling step was found to be the heat transfer through the gas film for low conversion, but the mass transfer through product ash layer for high conversion. The activation energies for the heat transfer through the gas film and mass transfer through product ash layer-controlled cases were calculated as 113 and 96 kJ mol −1, respectively.