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Imad A.M. Ahmed Neil M.J. Crout Scott D. Young 《Geochimica et cosmochimica acta》2008,72(6):1498-1512
Time-dependent sorption and desorption of Cd on calcite was studied over 210 days utilizing 109Cd as a tracer to distinguish between ‘labile’ and ‘non-labile’ forms of sorbed Cd. Stabilizing the calcite suspensions for 12 months under atmospheric PCO2 and controlled temperature was necessary to reliably follow Cd dynamics following initial sorption. Results revealed time-dependant Cd sorption and marked desorption hysteresis by calcite under environmentally relevant conditions. Data obtained were fitted to a first-order kinetic model and a concentric shell diffusion model. Both models described the progressive transfer of Cd2+ to a less reactive form within calcite and subsequent desorption of Cd subject to different initial contact times. The kinetic model provided a better fit to the combined sorption and desorption data (R2 = 0.992). It differentiates between two ‘pools’ of sorbed Cd2+ on calcite, ‘labile’ and ‘non-labile’, in which labile sorbed Cd is in immediate equilibrium with the free Cd2+ ion activity in solution whereas non-labile Cd is kinetically restricted. For the diffusion model (R2 = 0.959), the rate constants describing Cd dynamics in calcite produced a half-life for Cd desorption of ∼175 d, for release to a ‘zero-sink’ solution. Results from this study allow comment on the likely mechanisms occurring at the calcite surface following long-term Cd sorption. 相似文献
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Imad Mahmood Ghafor Kamal Haji Karim Varrojan Sissakian 《Arabian Journal of Geosciences》2014,7(9):3599-3610
Oligocene and Lower Miocene sediments from High Folded Zone of Iraqi Zagros have been studied paleontologically at south of Sulaimaniyah, Kurdistan Region, NE Iraq. The identified fauna are consisted of (25) genera and species of benthonic and (16) species of planktonic foraminifera. The fauna comprises relatively abundant foraminiferal assemblages of moderate diversity. Based on the stratigraphic distribution of these species, two biozones have been recognized which are Nummulites—Rotalia and Globoquadrina dehiscens zones. These biozones indicate that the studied sections of Basara and Khewata are of Late Oligocene–Early Miocene age. Based on the microfossils, it has been found that the age of sediments is equivalent to or represents Anah and Serikagni Formations. Some previous studies described Oligocene rocks (Kirkuk Group) as interior sag basin. In the present study, the occurrence of the group inside High Folded Zone and its rich fauna content are used for the discussion of the sag basin versus normal marine water. 相似文献
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GeoJournal - The Shatt Al-Arab River region (SARR) in Iraq was an economically important area for food production. By the 1970s the environment of this region had begun to deteriorate, and since... 相似文献
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Ali Al Maliki Ahmed Kadhim Al-lami H. M. Hussain Nadhir Al-Ansari 《Environmental Earth Sciences》2017,76(12):433
Comparison of two conventional analytical techniques such as X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) for measuring Pb concentrations in soil samples was achieved using field and laboratory work. Seventy-three samples were collected from urban areas surrounding the large lead smelter at South Australia, as an indicator of the environment impact of smelter activity. Soil Pb concentrations were determined using hand-held XRF analyser under laboratory conditions. ICP-MS analysis on digested soils (using a microwave-assisted nitric acid digestion-extraction) was applied to validate p-XRF data. The analysis showed that Pb concentrations determined by XRF correlated with high linearity with Pb concentrations determined by ICP-MS measurements (R 2 = 0.89). Statistical test (t test) was applied to the data of both methods applied without any significant difference between the two techniques. These results indicated that ICP-MS corroborated XRF for Pb soil measurements and suggests that XRF was a reliable and quick alternative to traditional analytical methods in studies of environmental health risk assessment, allowing for much larger sampling regimes in relatively shorter times and could be applied in the field. 相似文献
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Polar plumes have been detected in X-rays with the Skylab S-054 experiment. Observations of one well observed plume are analyzed and the plasma pressure is determined. An isothermal model in hydrostatic equilibrium is found to require unacceptably low temperatures. A hydrodynamic model is proposed which is consistent with earlier white light and EUV observations. Calculations indicate that the total outward mass flux in polar plumes is comparable to that in high speed solar wind streams expected from a polar coronal hole. 相似文献
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Sorption, fixation and desorption kinetics of Cd2+ on calcium-exchanged zeolite-X were studied using an isotopic dilution technique utilizing 109Cd. The technique provided reliable measurements of time-dependent fixation of Cd and was validated using chabazite, which demonstrated wholly reversible Cd2+ ion exchange. A first-order kinetic model was developed to describe the progressive transfer of Cd2+ to a less reactive form in X-zeolite, following initial sorption, and subsequent desorption of Cd subject to different initial contact times. The kinetic model differentiates between two ‘pools’ of sorbed Cd2+ on zeolite-X, designated labile and non-labile sorbed Cd in which the labile sorbed Cd is in immediate equilibrium with the free Cd2+ ion activity in solution. Additionally, an intra-particle diffusion model was developed and compared with the kinetic model to determine whether time-dependent Cd sorption is controlled by reaction kinetics or diffusion within zeolite particles. The kinetic model provided a much better fit to the experimental data (R2 = 0.987) than the diffusion model. The rate constants describing Cd dynamics in CaX zeolite gave a half-time for Cd desorption of ∼77 d, for release to a ‘zero-sink’. 相似文献
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Imad Kadhim Abdulzahra Ayten Hadi Yoshihiro Asahara Hossein Azizi Koshi Yamamoto 《Chemie der Erde / Geochemistry》2018,78(2):215-227
The Shalair area, which is located in northeastern Iraq, is considered to be part of the northern Sanandaj-Sirjan Zone (SaSZ) and contains several granitoid bodies. One of these bodies, the Mishao porphyritic-granite (MG), was crystallized at 111.6?±?2.4 Ma, based on its zircon U-Pb age. Its geochemical characteristics suggest that the MG rocks are calc-alkaline, peraluminous, I-type granites with microgranular mafic enclaves. They are enriched in SiO2, Na2O, Al2O3 and Zr and depleted in MgO, Fe2O3, Nb and Ti; in contrast, the enclave sample records lower SiO2 content and higher contents of MgO and Fe2O3. These rocks show an enrichment of LREE relative to HREE, and pronounced negative Eu anomalies implying feldspar fractionation. The isotopic and geochemical characteristics of the MG samples suggest that these rocks are evolved through fractional crystallization. In the La/Nb-Nb diagram and Sm/Nd ratios, the MG rocks and the enclave samples exhibit strong evidence for crustal contamination. The MG rocks record high initial 87Sr/86Sr (0.70625–0.70740) and low 143Nd/144Nd(i) (0.51235–0.51274) ratios. These Sr-Nd isotopic data, combined with the presence of high Th/U and Rb/Sr ratios and significant depletions of Nb, Ta and Ti, show a relation of these bodies to an active continental margin regime. Based on the age and geochemical data of the MG, this study presents new information about the occurrence of Middle Cretaceous magmatic activities, which are related to the active continental margins in the SaSZ that run parallel to the Zagros Fold-Thrust Belt. 相似文献
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Kelly Kalvelage Michael C. Dorneich Christopher J. Seeger Gregory J. Welk Stephen Gilbert Jon Moon Imad Jafir Phyllis Brown 《GeoJournal》2018,83(3):477-488
Facilitated-voluntary geographic information (f-VGI) is a promising method to enable systematic collection of data from residents about their physical and social environment. The method capitalizes on ubiquitous mobile smartphones to empower collection of geospatially-referenced data. It is important to evaluate the validity of user-generated content for use in research or program planning. The purpose of this study was to test whether the aggregated environmental (“bikeability”) ratings from novice community residents converges with ratings from experts using a robust research-based, paper audit-tool (the established Pedestrian Environment Data Scan (PEDS) tool). Equivalence testing statistically showed overall agreement between the composite ratings of bikeability within the novice group. Agreement in categorical ratings between novices and experts were examined using the summary agreement index, which showed substantial agreement across the 10 locations rated by 11 novices using an f-VGI mobile application and four experts using PEDS; variability depended on the nature of the specific questions asked. Results reveal overall substantial agreement between novice and expert ratings for both composite scores and individual categorical ratings. However, additional research is needed to refine the methodology for use in formalized research applications. 相似文献
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Three polar plumes were studied using Skylab Mg x and O vi data. The plumes lie within the boundaries of a polar coronal hole. We find that the mean temperature of the plumes is about 1.1 × 106 K and that they have a small vertical temperature gradient. Densities are determined and found consistent with white light analyses. The variation of density with height in the plumes is compared with that expected for hydrostatic equilibrium. As is the case for other coronal features, polar plumes will be a source of solar wind if the magnetic field lines are open. On the basis of the derived plume model and estimates of the numbers of plumes in polar coronal holes, it appears that polar plumes contain about 15% of the mass in a typical polar hole and occupy about 10% of the volume.Skylab Solar Workshop post-doc appointee 1975–1976. The Skylab Solar Workshops are sponsored by NASA and NSF and managed by the High Altitude Observatory, National Center for Atmospheric Research. 相似文献