Hexavalent chromium reduction by sulfide in the presence of goethite was studied through several batch experiments. Under our specific experimental conditions including 20 μM of hexavalent chromium, 560-1117 μM of sulfide and 10.61-37.13 m2/L of goethite at pH of 8.45 controlled by 0.1 M borate buffer, the obtained hexavalent chromium disappearance rate was -d[Cr(VI)]/dt = k[surface area of goethite][Cr(VI)][S(-II)]T1.5 and the determined overall rate constant (k) was 31.9 ± 4.2 (min)-1(m2/L)-1(mol/L)-1.5. Among the potential major reducing agents in our comprehensive heterogeneous system such as aqueous phase sulfide, surface-associated sulfide, dissolved ferrous iron, ferrous iron on the goethite surface, as well as fresh ferrous sulfide in the solution, it was considered that the surface ferrous irons which could be produced following sulfide adsorption, played a leading role for Cr(VI) reduction as primary electron donors. In addition, no proof of the preliminary dissolution of ferrous iron from goethite to aqueous phase was observed in the experiments. Elemental sulfur was detected as the final stabilized product of sulfide and it took in charge for the promoted Cr(VI) disappearance for the successive addition of Cr(VI) at later stage.
In the determination of Re and platinum group elements in geological samples, various techniques have been employed for digesting samples, including Carius tube, high-pressure asher (HPA-S), alkali fusion and nickel sulfide fire assay. The normal Carius tube technique is able to digest relatively small amount of sample and has a possible safety problem caused by a high internal pressure. This paper reports a modified Carius tube method which utilizes a sealed stainless steel high-pressure autoclave filled with water to prevent explosion of the tube. During heating, the external and internal pressures of the Carius tube increase simultaneously, such that the possible explosion of Carius tube can be avoided. Consequently, this technique allows a higher temperature (up to 330°C), a greater volume of aqua regia (up to 2/3 of the total volume of the Carius tube) and thus larger sample mass (12 g) relative to the normal Carius tube technique. Fairly good agreement were obtained for PGE poor mafic rocks (IPGE < 0.03 ng/g). The efficiency to dissolve ultramafic rocks and chromites at different temperatures was investigated. We demonstrate that this technique is more effective than normal Carius tube technique for ultramafic rocks and chromites containing refractory minerals and the detection limits and precision can be improved for PGE poor mafic samples. The total procedural blanks are lower than 0.003 ng for Os, 0.03 ng for Re, Ir, Ru and Rh and 0.4 ng for Pd and Pt.
Twenty six sandstone samples from six wells penetrating the Miocene Surma Group in the Bengal Basin, Bangladesh, were analyzed by lithium metaborate/tetraborate fusion Inductively Coupled Plasma (ICP) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and by petrographic microscope. The framework grains of the Surma Group sandstones are rich in quartz followed by lithic grains, feldspar and mica (predominantly white mica). The sandstones are dominantly quartzolithic and quartzose one in composition with abundant low-grade metamorphic, sedimentary lithics, low feldspars and little volcanic detritus, indicating that the sands were derived from a quartzose recycled orogen province. The Surma Group sandstones have moderate to high SiO2 contents (64-85%; on average 77%), TiO2 concentrations averaging 0.5%, Al2O3 contents of about 8.4%, and Fe2O3 (total Fe as Fe2O3) + MgO content of around 4.5%. Compared to the average sandstone value, the Surma Group sandstones are depleted in CaO (2.36%) and enriched in Al2O3, Fe2O3 and Na2O. Geochemically, the sandstones are classified mainly as litharenites. The Chemical Index of Alteration (CIA) values for the Miocene Surma Group sandstones vary from 53 to 65 with an average of 59, indicating low to moderate weathering of the source areas. The average CIA value (59) is a little above than that (50) of the upper continental crust. The shales from the Miocene Surma Group show higher CIA (∼70-78) values, indicating significant weathering in the source. The geochemical characteristics suggest an active continental margin to passive margin setting for the Surma Group sandstones, and preserve the signatures of a recycled provenance. The Eu/Eu* (∼0.69), (La/Lu)cn (∼10.07), La/Sc (∼3.98), Th/Sc (∼1.44), La/Co (∼3.84), Th/Co (∼1.40), and Cr/Th (∼9.48) ratios as well as chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate derivation of the Surma Group sandstones from felsic rock sources.
Measurements of atmospheric CO2 were made continuously at a height of 34 m in Sapporo (lat 43.1°N, long 141.3°E), located in northern Japan, from November 2004 to December 2005. Air samples for measurements of atmospheric CO, CH4, and CO2 were also taken in Sapporo and Ishikari Hama (lat 43.3°N, long 141.4°E), facing the Japan Sea, at 10- to 14-day intervals during the same period. In Sapporo, the atmospheric CO2 data showed clear diurnal and seasonal variations. During the diurnal variation, the maximum CO2 concentration occurred in the morning and the broad minimum in the daytime. The daily mean value of atmospheric CO2 in the daytime (11-16 JST) was at a maximum in winter to spring and a minimum in summer. From December to February, the daytime atmospheric CO2 concentration was about 8-13 ppm higher than that in the background air at Ishikari Hama; from July to August, it was nearly equal to that of the background air. In winter, the atmospheric CO concentrations in Ishikari Hama and Sapporo showed a good correlation with atmospheric CO2 (10 ppb CO/ppm CO2, r = 0.82). However, atmospheric CH4 remained fairly constant against CO2 change. In summer, CO2 flux by the photosynthesis of terrestrial vegetation between 11 and 16 JST was nearly equal to that of area-averaged CO2 emission (between Ishikari Hama and Sapporo) due to human activities, which was estimated to be 11 μmol m-2s-1 in the catchment area.
In order to quantify H2O content and chemical composition of island arc low-K tholeiite magma that crystallized Ca-rich plagioclase, melt inclusions of a typical island arc tholeiite from Izu-Oshima volcano (34°N 44', 139°E 24') were analyzed. Composition of studied plagioclase ranges widely from An83 to An95. Composition of studied melt inclusions also shows wide variation, which suggests that the melt inclusions represent various stages of crystallization differentiation at Izu-Oshima volcano. Ca/Na ratios of plagioclase-hosted melt inclusions are comparable with compositions of aphyric lava, which preclude an exotic origin for the Ca-rich plagioclase. Analyzed H2O content of the melt inclusions ranges from 0.2 to 2.4 wt.% (0.2 to 1.4 wt.% for plagioclase-hosted melt inclusions and 0.8 to 2.4 wt.% for olivine-hosted melt inclusions). Ca/Na partition coefficient between plagioclase and hydrous basaltic melt, KD(Ca-Na)plag-melt, is empirically calibrated based on experimental data as ln KD(Ca-Na)plag-melt = 4100/T(K) -800* P(GPa)/T(K) + 2.2* ln (Al2O3melt(wt.%)/Sio2melt(wt.%)) + 0.33* √ H2Omelt(wt.%). Based on the equilibria between host plagioclase and melt inclusion and taking effect of overgrowth into consideration, 3 to 6 wt.% H2O in melt is required. The lower H2O content of the analyzed melt inclusions is probably due to the leakage of volatiles through the host crystal during decompression, eruption and quench. Variation in estimated H2O content in the melt at the time of crystallization of plagioclase (3 to 6 wt.%) can be due to polybaric crystallization from H2O-saturated melt.
In the early 1990's, the Neath Canal in South Wales, UK, received large amounts of drainage waters from nearby coal mines, which contributed to its contamination by heavy metals and arsenic. One sediment core and surface sediments were collected from the upstream section of the Neath Canal and characterized for their mineral composition and iron speciation using powder X-ray diffraction (XRD) and Mössbauer spectroscopy. The sediments show three distinctive layers that are defined by their physical properties including color, sediment components and dryness. The upper layer of the sediment (0-22 cm) is a reddish-brown wet precipitate dominated by iron oxides and hydroxides and a high content of arsenic. The middle layer (22-27 cm) is a soft wet deposit of yellow color which mainly contains calcite with sheet silicates (kaolinite) and goethite. Magnesium, calcium and manganese are enriched in this layer whereas iron is depleted compared to the upper layer. The lower part of the core (below 27 cm) is colored gray to dark gray and contains quartz, pyrite and clay minerals, similar to normal aquatic sediments. In addition, this layer also contains abundant coal particles. Silicon, aluminium, titanium, potassium, phosphorus and sodium concentrations are higher whereas iron, manganese, calcium and magnesium are lower in the lower portion of the core compared to the middle and upper layers. Mineral composition, major elements, and iron speciation indicate oxic conditions in the upper and middle layers whereas reducing conditions prevail in the lower layer, which likely control the distribution of hazardous elements. Given the variation of physico-chemical characteristics of the sediments with depth in the canal, different remediation treatments will likely be necessary for each layer of sediments.
Ubiquitous veins and stockworks of quartz traverse the ophiolitic emerald-hosting, carbonate-altered ultramafic rocks in the Swat Valley. Some of the emerald-bearing quartz veins contain chromian muscovite and tourmaline. In addition, veins and clusters consisting of chromian muscovite and/or tourmaline occur in zones of carbonate-altered rocks where the quartz veins are most abundant. The chromian muscovite is characterized by high Mg/Fe ratios (4-9) and contains variable and in some cases anomalously high concentration of Ni (ranging up to 9 wt% NiO). A detailed investigation reveals that the Ni and Mg entered the chromian muscovite structure as a part of a complex coupled substitution: (FeVI, MnVI, MgVI, NiVI)2+ + [SiIV]4+ ↔ (AlVI, CrVI)3+ + [AlIV]3+. The stable coexistence of quartz, chromian muscovite, tourmaline and emerald suggests that all these phases are cogenetic and precipitated from Si-rich, Al-, Be-, B- and K-bearing fluids related to a single episode of hydrothermal activity. The Mg, Cr and Ni contents in chromian muscovite were most probably extracted by the percolating hydrothermal solutions from the host carbonate-altered ultramafic rocks through wall rock reaction. The observed high variability in the Mg, Cr and Ni contents of chromian muscovite probably reflects low mobility of these elements during the hydrothermal process or a result of local equilibrium under relatively low T conditions.
A subsurface soil sample was studied for molecular composition and stable carbon isotopic ratios (δ13C) of fatty acids (FAs) using a capillary gas chromatography (GC) and GC/combustion/isotope ratio mass spectrometer, respectively. Compound specific radiocarbon analyses of FAs were also conducted using an off-line preparative capillary GC/accelerator mass spectrometer. Molecular distribution of FAs (C14-C32) is characterized by even carbon numbered predominance with two maxima at n-C16 and n-C28, being similar to that of plant leaf. However, branched chain C15 and C17 acids were abundant in soil, indicating bacterial degradation and modification of soil organic carbon. The δ13C of FAs (-35.2 to -23.0‰) are within the range of plant leaf δ13C (-36.4 to -31.2‰), except for heavy values (-23.0 to -28.1‰) of C14 to C18. The heavier δ13C values are most likely interpreted by microbial re-synthesis of shorter chain FAs in soil. We also report, for the first time, a significant diversity of Δ14C values (+17 to +127‰) in soil FAs, with higher values (+96 to +127‰) for saturated and unsaturated C18 and lower values (+16 to +19‰) for longer chain C28 and C30. The higher radiocarbon values can be explained by a combination of selective microbial decomposition of shorter chain FAs in subsurface soil, and the subsequent deposition and mixing of modern carbon with old carbon in soil. The modern carbon may be transported downward in the form of shorter chain FAs and other water-soluble organic compounds by meteoric water and/or tree roots, followed by microbial re-synthesis of lipids in soil. This study implies that microbial degradation and modification of soil organic matter play an important role in geochemical processes which control the carbon cycle on the Earth.
We developed an experimental method for precise determination of carbon stable isotope ratio (δ13C) of soil-respired CO2 under natural condition. We devised a flask sampling system optimized for collecting soil-respired CO2 to minimize the measurement artifacts related to pressure anomaly. The δ13C of soil-respired CO2 was estimated from relationship between change rates of the CO2 mole fraction and the δ13C of the CO2 in a closed chamber at the soil surface by using two end-member simple mixing model. We tested the influence of CO2 enrichment in the soil-chamber headspace on the estimates of the δ13C of soil respired CO2 by using high-precision measurements of CO2 mole fraction and δ13C. To our results, the estimates of the δ13C of soil respired CO2 was rather insusceptible to the influence of the CO2 enrichment in the chamber as compared with the soil CO2 efflux. Improvement of analytical precision of δ13C is preferred approach to reduce the error in the estimates of δ13C of soil respired CO2. On the other hand, extending the sampling range of CO2 mole fraction in the chamber can be cost-effective means for the error-reduction practically.