Evolved gas analysis of coal-derived pyrite/marcasite

The products evolved during the thermal decomposition of the coal-derived pyrite/marcasite were studied using simultaneous thermogravimetry coupled with Fourier-transform infrared spectroscopy and mass spectrometry (TG-FTIR–MS) technique. The main gases and volatile products released during the thermal decomposition of the coal-derived pyrite/marcasite are water (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2). The results showed that the evolved products obtained were mainly divided into two processes: (1) the main evolved product H2O is mainly released at below 300 °C; (2) under the temperature of 450–650 °C, the main evolved products are SO2 and small amount of CO2. It is worth mentioning that SO3 was not observed as a product as no peak was observed in the m/z = 80 curve. The chemical substance SO2 is present as the main gaseous product in the thermal decomposition for the sample. The coal-derived pyrite/marcasite is different from mineral pyrite in thermal decomposition temperature. The mass spectrometric analysis results are in good agreement with the infrared spectroscopic analysis of the evolved gases. These results give the evidence on the thermal decomposition products and make all explanations have the sufficient evidence. Therefore, TG–MS–IR is a powerful tool for the investigation of gas evolution from the thermal decomposition of materials.

Oxidation of isochemical FeS2 (marcasite-pyrite) by Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans

A research-grade mineral sample that contained marcasite and pyrite (FeS2) was subjected to the oxidation by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Oxidation of FeS2 by A. ferrooxidans produced acid, and the redox potential increased with sulfide dissolution and the oxidation of Fe2+. jarosite was detected in solids from spent cultures. Preferential oxidation of either mineral was not consistently observed across all treatments. Neither iron sulfide was oxidized by A. thiooxidans. (C) 2006 Elsevier Ltd. All rights reserved.

Raman spectroscopy of pyrite in marble from Chillagoe, Queensland

Samples of marble from Chillagoe, North Queensland have been analysed using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. Different types of marble were studied including soft white marble, hard white marble and a black marble. In this work, we try to ascertain why the black marble has this colour. Chemical analyses provide evidence for the presence of minerals other calcite in the marble, including the pyrite mineral. Some of these chemical analyses correspond to pyrite minerals in the black marble. The Raman spectra of these crystals were obtained and the Raman spectrum corresponds to that of pyrite from the RRUFF data base. The combination of SEM with EDS and Raman spectroscopy enables the characterisation of the mineral pyrite in Chillagoe black marble.

Crystal structures and elastic properties of superhard IrN2 and IrN3 from first principles

First principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c. Our calculation indicates that the P2(1)/c phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of 1.414 A. These characters are consistent with the experimental facts that IrN2 is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of IrN2 is monoclinic P2(1)/c. The calculated bulk modulus of 373 GPa is also the highest among the considered space groups. It matches the recent theoretical values of 357 GPa within 4.3% and of 402 GPa within 7.8%, but smaller than the experimental value of 428 GPa by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for IrN2. For IrN3, cubic skutterudite structure (Im-3) was assumed.

内陆湖沼相和近海沼泽相沉积环境煤中微量元素和矿物的对比研究—以辽宁北票、江西建新和桥头煤研究为例

Using knowledge of geology, geochemistry, coal petrology, mineralogy, by means of a variety of advanced measuring methods such as inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled atomic emission spectrometry (ICP-AES), X-ray powder diffraction (XRD), scanning electron microscopy with energy-dispersive spectrometer(SEM-EDS), sequential chemical extract and density fractions, the characteristics of trace elements and minerals in Jurassic Beipiao coal mine under inland limnetic sedimentary environment and in late Permian Jianxin and Qiaotou coal mines under paralic swamp sedimentary environment were studied. Compared with the average concentration in the world bituminous coals, the Beipiao coal was characterized by relatively high contents of Sc, Ti, Cr, Co, Ni, Zn, Se, Sr, Zr, Y, Ba, REE and Th, and lower contents of V, Rb, Cd, Sn, Pb, Bi and U; while the Jianxin coal was relatively enriched in Li, Sc, Ga, Sr, Y, Nb, Sb, Th and U, with low concentration of Be, Co, Ni, Cu, Ge, Zr, Mo, Cd, Cs, Ba, Pb and Bi; and the Qiaotou coal was enriched in Li, Sc, Sr, Nb, Ta, Zr, REE, Hf, Th and U, with low concentration of Be, V, Co, Ni, Cu, Ge, Mo, Cd, Cs, Ba, Tl, Pb and Bi. The concentrations of Ca, Mg and K in Beipiao coal are higher than those in Jianxin coal and Qiaotou coal, while Fe, S and Ti in Beipiao coal are lower than those in Jianxin coal and Qiaotou coal. The proximate analysis of coal samples was carried out, which indicated that Beipiao coal was medium- to high- ash (5.92-60.68%) with low sulphur coal, and Jianxin coal and Qiaotou coal was medium to high ash (8.85-46.33%) with high sulphur. The reflectivity was measured, which explained that Beipiao coal belonged to high volatile bituminous coal, Jianxin coal was low volatile bituminous coal and Qiaotou coal was low volatile anthracite. Quantitative maceral analyses were studied. The characteristics of rare earth elements (REE) were investigated, which showed that the total contents of REE were higher than that of the world's average content. With the increase of coal's metamorphic grade, the total contents of REE decreased from 98.5 X 10"6 of Beipiao coal to 94.2 X 10"6 of Jianxin coal, and to 75.9 X 10"6 of Qiaotou coal, and 5Eu reduced which indicated that the element Eu depleted. The characteristics of REE was controlled by the metamorphic grade of coal. And REE were mainly absorbed in clay minerals in Beipiao coal samples, while in Jianxin and Qiaotou coal mines, REE were primarily related to clay mineral and pyrite. The variation of trace elements in vertical direction of coal seams was studied, and the results showed that different trace elements differed greatly. The correlation between trace elements and ash were determined. Four major trace elements (aluminium-silicates, sulphide, carbonate and phosphate) accounted for the occurrence and distribution of most elements studied were determined. Coal samples were separated by density fraction, which showed that Cr, Cu, Mo and Pb were closely related to inorganic matters mainly distributed in P >2.6 and dropped remarkably in the density fractions P <2.3 . The occurrences of Co, Cr, Ni, As, Se, Mo, U were studied directly and quantitatively using sequential chemical extract with six steps, which showed that Co. Ni, Mo and U were mainly in the form of mineral, and As, Se chiefly in the form of organic state, while Cr mostly in the form of organic state and mineral. Major mineral phases presented in the Beipiao coal were Kaolinite, illite, quartz, calcite, and small amount of siderite, barite. While major mineral phases in Jianxin and Qiaotou coal were pyrite, kaolinite, and small amount of marcasite, rutile, sphalerite. This is the first time that the chromite in the coal was discovered in China, which indicates that Cr occurrence appeared in the form of chromite. The ratio of Sr/Ba, Sr/Ca and V/Ni in Beipiao coal mine under inland limnetic is smaller than that of in Jianxin and Qiaotou coal mines under paralic swamp. The ratio of K/Na and Th/U of Beipiao coal mine is higher than that of Jianxin and Qiaotou coal mine, which proved that Beipiao coal was not affected by sea water and Jianxin and Qiaotou coal were affected by sea water. Trace elements such as Cr, Ni, Mo in minerals were analyzed by SEM-EDS. The factors controlling the enrichment of trace elements can be divided into syngenetic stage factors and epigenetic stage factors.

Genesis and distribution of Mississippi Valley-type ore assemblages in Middle Silurian strata, Niagara Peninsula, Ontario /

Presently non-commercial occurrences of Mississippi Valley-type ore assemblages in the Middle Silurian strata of the Niagara Peninsula have been studied. Based on this detailed study, a new poly-stage genetic model is proposed which relates ore mineralization in carbonate environments to the evolution of the sedimentary basin. Sulphide ore mineralization occurred during two episodes: 1. During the late diagenesis stage, which is characterized by compaction-maturation of the sediments, the initial mineralization took place by upward and outward movement of connate waters. Metals were probably supplied from all the sediments regardless of their specific lithologies. However, clay minerals were possibly the main contributors. The possible source of sulphur was from petroleum-type hydrocarbons presently mixed with the sediments at the site of ore deposition. Evidence for this is the fact that the greatest abundance of ore minerals is in petroliferous carbonates. The hydrocarbons probably represent liquids remaining after upward migration to the overlying Guelph-Salina reservoirs. The majority of sphalerite and galena formed during this period, as well as accessory pyrite, marcasite, chalcopyrite, chalcocite, arsenopyrite, and pyrrhotite; and secondary dolomite, calcite, celestite, and gypsum. 2. During the presently ongoing surface erosion and weathering phase, which is marked by the downward movement of groundwater, preexisting sulphides were probably remobilized, and trace amounts of lead and zinc were leached from the host material, by groundwaters. Metal sulphides precipitated at, or below, the water table, or where atmospheric oxygen could raise the Eh of groundwaters to the point where soluble metal complexes are unstable and native sulphur co-precipitates with sphalerite and galena. This process, which can be observed today, also results in the transport and deposition of the host rock material. Breakdown of pre-existing sulphide and sulphate, as well as hydrocarbon present in the host rock, provided sulphur necessary for sulphide precipitation. The galena and sphalerite are accompanied by dolomite, calcite, gypsum, anglesite, native sulphur and possibly zincite.

Paragenetic history of the Ordovician Trenton Group carbonates, Southwestern Ontario

Geochemical examination of the rock matrix and cements from core material extracted from four oil wells within southwestern Ontario suggest various stages of diagenetic alteration and preservation of the Trenton Group carbonates. The geochemical compositions of Middle Ordovician (LMC) brachiopods reflect the physicochemical water conditions of the ambient depositional environment. The sediments appear to have been altered in the presence of mixed waters during burial in a relatively open diagenetic microenvironment. Conodont CAl determination suggests that the maturation levels of the Trenton Group carbonates are low and proceeded at temperatures of about 30 - 50°C within the shallow burial environment. The Trenton Group carbonates are characterized by two distinct stages of dolomitization which proceeded at elevated temperatures. Preexisting fracture patterns, and block faulting controlled the initial dolomitization of the precursor carbonate matrix. Dolomitization progressed In the presence of warm fluids (60 75°C) with physicochemical conditions characteristic of a progressively depleted basinal water. The matrix is mostly Idiotopic-S and Idiotopic-E dolomite, with Xenotopic-A dolomite dominating the matrix where fractures occur. The second stage of dolomitization involved hydrothermal basinal fluid(s) with temperatures of about 60 - 70°C. These are the postulated source for the saddle dolomite and blocky calcite cements occurring in pore space and fractures. Rock porosity was partly occluded by Idiotopic-E type dolomite. Late stage saddle dolomite, calcite, anhydrite, pyrite, marcasite and minor sphalerite and celestite cements effectively fill any remaining porosity within specific horizons. Based on cathode luminescence, precipitation of the different diagenetic phases probably proceeded in open diagenetic systems from chemically homogeneous fluids. Ultraviolet fluorescence of 11 the matrix and cements demonstrated that hydrocarbons were present during the earliest formation of saddle dolomite. Oxygen isotope values of -7.6 to -8.5 %0 (PDB), and carbon isotope values of - 0.5 and -3.0 %0 (PDB) from the latest stage dog-tooth calcite cement suggest that meteoric water was introduced into the system during their formation. This is estimated to have occurred at temperatures of about 25 - 40°C. Specific facies associations within the Trenton Group carbonates exhibit good hydrocarbon generating potential based on organic carbon preservation (1-3.5%). Thermal maturation and Lopatin burial-history evaluations suggest that hydrocarbons were generated within the Trenton Group carbonates some time after 300 Ma . Progressively depleted vanadium trends measured from hydrocarbon samples within southwestern Ontario suggests its potential use as a hydrocarbon migration indicator on local (within an oilfield) and on regional scales.

Synthesis and characterisation of the anion-ordered tellurides MGeTe (M = Co, Rh)

The synthesis and structural characterisation, carried out using a combination of single-crystal and powder X-ray diffraction, of the materials MGeTe (M = Co, Rh) are described. These phases adopt an ordered α-NiAs2 structure, which can be considered intermediate between those of pyrite and marcasite. Electrical resistivity and Seebeck coefficient measurements, carried out over the temperature range 77 ≤ T/K ≤ 325, indicate that these materials are n-type semiconductors.