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131.
Pyrite (FeS2) oxidation: A sub-micron synchrotron investigation of the initial steps 总被引:1,自引:0,他引:1
Anand P. Chandra 《Geochimica et cosmochimica acta》2011,75(20):6239-6254
Pyrite is an environmentally significant mineral being the major contributor to acid rock drainage. Synchrotron based SPEM (scanning photoelectron microscopy) and micro-XPS (X-ray photoelectron spectroscopy) have been used to characterise fresh and oxidised pyrite (FeS2) with a view to understanding the initial oxidation steps that take place during natural weathering processes. Localised regions of the pyrite surface containing Fe species of reduced coordination have been found to play a critical role. Such sites not only initiate the oxidation process but also facilitate the formation of highly reactive hydroxyl radical species, which then lead the S oxidation process.Four different S species are found to be present on fresh fractured pyrite surfaces: S22−(bulk) (4-fold coordination), S22−(surface) (3-fold coordination), S2− and S0/Sn2− (metal deficient sulfide and polysulfide respectively). These species were found to be heterogeneously distributed on the fractured pyrite surface. Both O2 and H2O gases are needed for effective oxidation of the pyrite surface. The process is initiated when O2 dissociatively and H2O molecularly adsorb onto the surface Fe sites where high dangling bond densities exist. H2O may then dissociate to produce OH radicals. The adsorption of these species leads to the formation of Fe-oxy species prior to the formation of sulfoxy species. Evidence suggests that Fe-O bonds form prior to Fe-OH bonds. S oxidation occurs through interactions of OH radicals formed at the Fe sites, with formation of SO42− occurring via S2O32−/SO32− intermediates. The pyrite oxidation process is electrochemical in nature and was found to occur in patches, where site specific adsorption of O2 and H2O has occurred. Fe and S oxidation was found to occur within the same area of oxidation probably in atomic scale proximity. Furthermore, the O in SO42− arises largely from H2O; however, depending on the surface history, SO42− formed early in the oxidation process may also contain O from O2. 相似文献
132.
The present investigation evaluates the adsorption effectiveness of Cd(II) ions on Ficus religiosa leaf powder (FRL). The experimental parameters chosen included time, pH, particle size, temperature, adsorbate, anion, and Pb(II) concentrations. The time data followed pseudo‐second‐order kinetics. Cd(II) adsorption increased from 1.38 to 75.17% with the increase in pH from 2 to 4 and further increase in pH to 5.5 resulted in its marginal increase to 77.52%. Based on regression coefficient values, the isothermic data fitted the various models in the order Langmuir > Redlich–Peterson > Temkin > Freundlich model. The maximum loading capacity of FRL was estimated to be 27.14 mg g?1. The presence of Cl?, , or Pb2+ exhibited adverse effect on Cd(II) uptake. The thermodynamic parameters of enthalpy (ΔH0) and entropy (ΔS0) were estimated to be 8.31 kJ mol?1 and 38.22 J mol?1 K?1, respectively. SEM‐EPMA of the loaded FRL showed Cd(II) distribution at specific sites. The XRD patterns of Cd(II) loaded FRL sample showed disappearance of some peaks corresponding to β‐Ca(PO3)2; shifting of peaks and decrease in %RI corresponding to γ‐CaSO4 phase. Positive shift of IR bands for the Cd(II) loaded sample was observed. 相似文献
133.
Didier G. Leibovici Lucy Bastin Suchith Anand Gobe Hobona Mike Jackson 《Transactions in GIS》2011,15(3):347-364
Overlaying maps using a desktop GIS is often the first step of a multivariate spatial analysis. The potential of this operation has increased considerably as data sources and Web services to manipulate them are becoming widely available via the Internet. Standards from the OGC enable such geospatial ‘mashups’ to be seamless and user driven, involving discovery of thematic data. The user is naturally inclined to look for spatial clusters and ‘correlation’ of outcomes. Using classical cluster detection scan methods to identify multivariate associations can be problematic in this context, because of a lack of control on or knowledge about background populations. For public health and epidemiological mapping, this limiting factor can be critical but often the focus is on spatial identification of risk factors associated with health or clinical status. In this article we point out that this association itself can ensure some control on underlying populations, and develop an exploratory scan statistic framework for multivariate associations. Inference using statistical map methodologies can be used to test the clustered associations. The approach is illustrated with a hypothetical data example and an epidemiological study on community MRSA. Scenarios of potential use for online mashups are introduced but full implementation is left for further research. 相似文献
134.
Aryavart Anand Anuj Kumar Singh Klaus Mezger Jayanta Kumar Pati 《Meteoritics & planetary science》2023,58(5):722-736
The Dhala structure in north-central India is a confirmed complex impact structure of Paleoproterozoic age. The presence of an extraterrestrial component in impactites from the Dhala structure was recognized by geochemical analyses of highly siderophile elements and Os isotopic compositions; however, the impactor type has remained unidentified. This study uses Cr isotope systematics to identify the type of projectile involved in the formation of the Dhala structure. Unlike the composition of siderophile elements (e.g., Ni, Cr, Co, and platinum group elements) and their inter-element ratios that may get compromised due to the extreme energy generated during an impact, Cr isotopes retain the distinct composition of the impactor. The distinct ε54Cr value of −0.31 ± 0.09 for a Dhala impact melt breccia sample (D6-57) indicates inheritance from an impactor originating within the non-carbonaceous reservoir, that is, the inner Solar System. Based on the Ni/Cr ratio, Os abundance, and Cr isotopic composition of the samples, the impactor is constrained to be of ureilite type. Binary mixing calculations also indicate contamination of the target rock by 0.1–0.3 wt% of material from a ureilite-like impactor. Together with the previously identified impactors that formed El'gygytgyn, Zhamanshin, and Lonar impact structures, the Cr isotopic compositions of the Dhala impactites argue for a much more diverse source of the objects that collided with the Earth over its geological history than has been supposed previously. 相似文献
135.
L. Palanikumar A. K. Kumaraguru C. M. Ramakritinan M. Anand 《International Journal of Environmental Science and Technology》2014,11(3):765-774
Carbendazim and Chlorpyrifos are some of the most widespread environmental contaminants of major concern to human and animal reproductive health. Acute toxicity test results for pesticides were evaluated by the Probit analysis method and 96 h LC50 values for C. chanos exposed to chlorpyrifos was 3.73 and 11.5 μg l?1 for carbendazim. Chlorpyrifos and carbendazim significantly decreased total protein, catalase, glutathione S-transferase and acetyl choline esterase and induced lipid peroxidation. Maximum effects of protein, catalase, lipid peroxidation, acetyl choline esterase and glutathione s-transferase were obtained in response to 23.68 μg l?1 of chlorpyrifos and 43.68 μg l?1 of carbendazim. Micronuclei assay results have shown increased abnormality with increasing doses of chlorpyrifos and carbendazim. Maximum increasing in micronuclei was observed in chlorpyrifos exposed C. chanos. This study showed that chlorpyrifos and carbendazim induced alterations in the activity of antioxidant enzymes and could induce clastogenicity. 相似文献
136.
High resolution surveys of the galactic centre suggest the existence of an extended nonthermal source (Bulge) with an intensity much larger than the total background radiation in that direction. In this paper, we have first evaluated the physical conditions existing in this restricted region of space from an analysis of the radio spectrum and shown that if the distribution of matter, magnetic fieldB(r) and cosmic ray densityk(r) in the plane of the Galaxy is of gaussian type then at the centreB
(0)=25–30 G andk(0)=25–35 times that in the near interstellar space. It is also found that most of the absorption in the Sagittarius A spectrum at low frequencies takes place in the Bulge and one requires a small additional absorption to take place in the line of sight corresponding to n
e
210 cm–6 pc at a temperature typically of clouds 100 K. The gamma ray spectra from the Bulge arising from interactions of cosmic rays with matter and radiation are then calculated in detail. A comparison made with the estimated background gamma ray spectra from the disk reveals that a detector with angular resolution 6° having a threshold of a few times 10–6 photons cm–2 s–1 can detect this source; this bulge is not found to be a good X-ray source for detection. From a comparison of these calculations with the observed flux above 100 MeV, the following inferences have been deduced: (i) the lower limit to the magnetic field strength at the centre is 12 G, (ii) the observed gamma ray flux towards the Anti-centre can be well explained as due to interactions of cosmic rays with matter alone and a similar explanation towards the center reveals that cloud complexes could be more in the inner parts of the Galaxy than in the outer parts, and (iii) the observed flux values are found to be inconsistent with the existence of submillimeter radiation in the galactic scale. 相似文献
137.
Andreas Morlok Chiyoe Koike Kazushige Tomeoka Andrew Mason Carey Lisse Mahesh Anand Monica Grady 《Icarus》2012,219(1):48-56
Mid-infrared (5–25 μm) transmission/absorption spectra of differentiated meteorites (achondrites) were measured to permit comparison with astronomical observations of dust in different stages of evolution of young stellar objects. In contrast to primitive chondrites, achondrites underwent heavy metamorphism and/or extensive melting and represent more advanced stages of planetesimal evolution. Spectra were obtained from primitive achondrites (acapulcoite, winonaite, ureilite, and brachinite) and differentiated achondrites (eucrite, diogenite, aubrite, and mesosiderite silicates). The ureilite and brachinite show spectra dominated by olivine features, and the diogenite and aubrite by pyroxene features. The acapulcoite, winonaite, eucrite, and mesosiderite silicates exhibit more complex spectra, reflecting their multi-phase bulk mineralogy.Mixtures of spectra of the primitive achondrites and differentiated achondrites in various proportions show good similarities to the spectra of the few Myr old protoplanetary disks HD104237A and V410 Anon 13. A spectrum of the differentiated mesosiderite silicates is similar to the spectra of the mature debris disks HD172555 and HD165014. A mixture of spectra of the primitive ureilite and brachinite is similar to the spectrum of the debris disk HD113766. The results raise the possibility that materials produced in the early stage of planetesimal differentiation occur in the protoplanetary and debris disks. 相似文献
138.
139.
Sanjeev Anand Sahu Soniya Chaudhary Pradeep Kumar Saroj Amares Chattopadhyay 《Arabian Journal of Geosciences》2017,10(5):120
The study of surface waves (Rayleigh wave) finds their virtuous applications in a numerous geological and geophysical fields including water, oil, gas, and other subsurface geological probing and exploration. The present paper efforts to investigate the influence of initial stress, Earth magnetism, and gravity on propagation of Rayleigh waves. Considered model is consist of a liquid layer lying over a magnetoelastic orthotropic half-space under self-weight and initial stress. Method of separation of variable is used to solve the equation of motion. Solutions of governing equations are obtained in terms of displacement. Frequency relation for Rayleigh wave has been obtained and matched with classical Rayleigh wave equation. In addition to classical case, some existing results have been deduced as particular case of the present study. Obtained results have been shown through numerical illustrations. It is found that the considered parameters (initial stress, Earth magnetism, and gravity) have prominent effect on phase velocity of Rayleigh wave. Graphical representations have been made to exhibit the velocity profile of Rayleigh waves for different cases with the help of MATHEMATICA. The present study may be useful for seismologists and engineers who are concern with applications of wave propagation in magnetoelastic orthotropic medium. 相似文献
140.
N. V. Chalapathi Rao M. Anand A. Dongre I. Osborne 《International Journal of Earth Sciences》2010,99(8):1791-1804
A number of limestone and metasomatised carbonate xenoliths occur in the 1,090 Ma Siddanpalli kimberlite cluster, Raichur
kimberlite Field, Eastern Dharwar craton, southern India. These xenoliths are inferred to have been derived from the carbonate
horizons of the Kurnool (Palnad) and Bhima Proterozoic basins and provide evidence for a connection between these basins in
the geological past. A revised Mesoproterozoic age is proposed for the Bhima and Kurnool (Palnad) basins based on this kimberlite
association and is in agreement with similar proposals made recently for the Chattisgarh and Upper Vindhyan sediments in Central
India. The observed Bhima–Kurnool interbasinal uplift may have been caused by: (1) extension- or plume-related mafic alkaline
magmatism that included the emplacement of the southern Indian kimberlites at ~1.1 Ga, (2) mantle plume-related doming of
the peninsular India during the Cretaceous, or (3) Quaternary differential uplift in this region. It is not possible, with
the currently available geological information to constrain the exact timing of this uplift. The deep erosion of primary diamond
sources in the Raichur kimberlite Field in the upper reaches of the Krishna River caused by this uplift could be the elusive
source of the alluvial diamonds of the Krishna valley. Mesoproterozoic sedimentary basins can host world class unconformity-type
uranium deposits. In light of its inferred Mesoproterozoic age, a more detailed stratigraphic and metallogenic analysis of
the Kurnool basin is suggested for uranium exploration. 相似文献