Itrax μ-XRF core scanning for rapid tephrostratigraphic analysis: a case study from the Auckland Volcanic Field maar lakes     

Leonie Peti  Patricia S. Gadd  Jenni L. Hopkins  Paul C. Augustinus 《第四纪科学杂志》2020,35(1-2):54-65

Itrax micro X-ray fluorescence (μ-XRF) core scanning is a non-destructive, rapid approach to measuring elemental concentrations and their variability in sediment cores. As such, it records elemental signatures of tephra layers, which serve as correlation tie points and chronological markers for these sedimentary archives of past climatic changes. The traditional tephra identification approach using electron microprobe-based geochemical fingerprinting of glass shards is a slow and invasive process, whilst μ-XRF scanning of rhyolite tephra in sediment cores from Auckland (New Zealand) could provide a faster, non-invasive approach to aid the recognition of tephra layers. This study highlights the potential and pitfalls in this novel approach: changes in most scanning parameters, and the use of two different Itrax core scanners, still led to similar chemical characterizations of the tephra layers. Changes in other scanning parameters have a biasing influence on the chemical characterization of the tephra, which would lead to misidentification of unknown layers. We demonstrate that μ-XRF core scanning provides a faster and non-invasive approach to correlation of sediment sequences using chemically distinct, visually pure tephra layers if a strict scanning protocol is followed. Nevertheless, an extensive database of μ-XRF-scanned rhyolite tephra is required for recognition of unknown tephra units using this approach.  相似文献   

A comparative evaluation of minerals and trace elements in the ashes from lignite, coal refuse, and biomass fired power plants     

Smriti SinghLal C. Ram  Reginald E. MastoSantosh K. Verma 《International Journal of Coal Geology》2011,87(2):112-120

Coal being a limited source of energy, extraction of energy from other sources like lignite, coal-refuse, and biomass is being attempted worldwide. The minerals and inorganic elements present in fuel feeds pose different technological and environmental concerns. Lignite ash, refuse ash, and biomass ash collected from Indian power plants burning lignite, coal-refuse, and mustard stalk, respectively, were analyzed for physico-chemical characteristics and trace elements. The lignite ash has high SiO₂, CaO, MgO, Al₂O_3, and SO₃; the refuse ash has high SiO₂ and Fe₂O₃, but low SO₃; the biomass ash has high SiO₂ (but low Al₂O₃), and high CaO, MgO, K₂O, Na₂O, SO₃, and P₂O₅. A substantial presence of chloride (2.1%) was observed in the biomass ash. Quartz is the most abundant mineral species. Other minerals are mullite, hematite, gehlenite, anhydrite, and calcite in the lignite ash; orthoclase in the refuse ash; albite, sanidine, gehlenite, anhydrite, and calcite in the biomass ash. Ashes with high concentrations (> 100 mg/kg) of trace elements are: lignite ash (V < La < Mn < Cr < Ni < Nd < Ba < Ce, Zn < Sr); refuse ash (Cr < Ce < V < Rb < Mn < Sr, Zn < Ba); biomass ash (Cu < Zn < Ba, Sr). Based on Earth crust normalization, Co, Ni, As, Se, Mo, Zn, Pb, U, and REEs (except Pr and Er) are enriched in the lignite ash; molybdenum, Zn, Cs, Pb, Th, U, La, Ce, and Lu in the refuse ash; and Mo, Zn, Sr, Cs, Pb, and Lu in the biomass ash. Elements As, Zn, Mo, Ni, Pb, Rb, Cr, V, Ba, Sr, and REEs are correlated with Al, indicating the possibilities of their association with aluminum silicates minerals. Similarly, barium, Cs, Th, and U are correlated with iron oxides; molybdenum and Sr may also be associated with sulfates and chlorides. Due to the alkaline nature of these ashes, the high concentrations of As and Se in the lignite ash; molybdenum in the biomass ash; and Se in the refuse ash may pose environmental concerns.  相似文献   

重庆地区上三叠统须家河组煤质特征规律初探     

蒙丽  程军  任世聪  李长林  陈威  袁为真 《中国煤炭地质》2011,(8):73-77

重庆地区须家河组为一套砂岩、泥岩、砂质泥岩、粉砂岩和煤层组成的湖滨-三角洲型沉积,煤质分级主要为中灰（特低灰-高灰）、低硫（特低硫-中高硫）、高热值（低热值-特高热值）煤;灰分与硫分等值线分布较为相似,总趋势为北东-南西向展布,呈不规则条带状和团块状分布;原煤灰分值与发热量值呈负相关性,浮煤灰分值与发热量值呈正相关性,初步得出同一采集点原煤和浮煤的灰分与发热量的相关性正好相反,煤类分布与挥发分等值线展布相似的结论。  相似文献   

燃煤固体产物的矿物组成研究   总被引：12，自引：1，他引：12  

孙俊民 《矿物学报》2001,21(1):14-18

利用X射线衍射、穆斯堡尔谱与扫描电子显微镜等方法研究中国典型燃煤煤种的燃烧产物的矿物学特征，揭示出不同化学成分以及不同类型产物中矿物组成的差异性。根据化学成分，可将燃煤固体产物分为硅铝质、铁质和钙质三组，硅铝质产物结晶相主要为莫来石和石英，而结渣中基本为莫来石；铁质产物中主要矿物包括α-Fe2O3、γ-Fe2O3与Fe3O4，其含量随锅炉燃烧湿度的变化而变化；钙质产物中矿物种类复杂，飞灰石检出石灰、石膏和石英，沾污中检出石膏、赤铁矿和石类，而结渣中还发现钙的硅酸盐矿物。上述矿物分布特征是由不同成分的硅酸盐熔体在不同热力学条件下的结晶行为所决定的。  相似文献   

花椒果实膨大生长与品质的气象条件   总被引：8，自引：0，他引：8  

余优森  任三学 《气象》1994,20(7):50-54

研究了花椒果实膨大生长与品质的气象条件，得出果实膨大生长和着色成熟期温度，降水，相对湿度，是影响花椒单株产量和品质的主要气象因子，揭示了我国花椒气候资源和优质气候区。  相似文献   

Retention of fly ash-derived copper in sediments of the Pandu River near Kanpur,India     

D. V. Ravi Chander  C. Venkobachar  B. C. Raymahashay 《Environmental Geology》1994,24(2):133-139

A coal-based thermal power plant is situated on the bank of the Pandu River, which is a tributary to the Ganges near Kanpur. River sediments downstream from the ash pond outfall are contaminated by fly ash. In order to establish the role of soils and sediments in retaining fly ash-derived heavy metals, copper was investigated as a model metal. A maximum concentration of 70 ppm Cu could be leached from the fly ash, confirming that it is a major source of this metal. Soil samples and river sediments were examined for Cu adsorption in the natural state as well as after treatment with H₂O₂, EDTA, and H₂O₂ followed by EDTA. The organic fraction of the samples was determined, and it had a major control on removal of Cu from a solution with 10^–4 M initial concentration. Further characterization of organic matter indicated that with reference to natural samples, the humic acid fraction had a copper enrichment factor in the range 9.1–15.1. The factor for fulvic acids, in contrast, was between 3.5 and 5.5. This leads to the conclusion that river deposits rich in humic acids would withstand relatively high metal loads. Only when the metal input exceeds the maximum retention potential, would the metal be fractionated into the aqueous phase and act as a potential biocide.  相似文献   

Sustainable Construction Case History: Fly Ash Stabilization of Recycled Asphalt Pavement Material     

Lin Li  Craig H. Benson  Tuncer B. Edil  Bulent Hatipoglu 《Geotechnical and Geological Engineering》2008,26(2):177-187

A case history is described where Class C fly ash was used to stabilize recycled pavement material (RPM) during construction of a flexible pavement in Waseca, MN, USA. The project consisted of pulverizing the existing hot-mix asphalt (HMA), base, and subgrade to a depth of 300 mm to form RPM, blending the RPM with fly ash (10% by dry weight) and water, compacting the RPM, and placement of a new HMA surface. California bearing ratio (CBR), resilient modulus (M_r), and unconfined compression (q_u) tests were conducted on the RPM alone and the fly ash stabilized RPM (SRPM) prepared in the field and laboratory to evaluate how addition of fly ash improved the strength and stiffness. After 7 days of curing, SRPM prepared in the laboratory had CBR ranging between 70 and 94, M_r between 78 and 119 MPa, and q_u between 284 and 454 kPa, whereas the RPM alone had CBR between 3 and 17 and M_r between 46 and 50 MPa. Lower CBR, M_r, and q_u were obtained for SRPM mixed in the field relative to the SRPM mixed in the laboratory (64% lower for CBR, 25% lower for M_r, and 50% lower for q_u). In situ falling weight deflectometer testing conducted 1 year after construction showed no degradation in the modulus of the SRPM, even though the SRPM underwent a freeze–thaw cycle. Analysis of leachate collected in the lysimeter showed that concentrations of all trace elements were below USEPA maximum contaminant levels.  相似文献   

Efficacy of Cement-stabilized Fly Ash Cushion in Arresting Heave of Expansive Soils     

M. Rama Rao  A. Sreerama Rao  R. Dayakara Babu 《Geotechnical and Geological Engineering》2008,26(2):189-197

Expansive clays swell and shrink seasonally when subjected to changes in the moisture regime causing substantial distress to the structures built in them. Techniques like sand cushion and cohesive non-swelling soil (CNS) layer have been tried to arrest heave and consequent damages to structures. Sand cushion has been proved to be counter-productive. Studies have indicated that even though CNS layer was effective initially, it became less effective after the first cycle of swelling and shrinkage. Research carried out by the authors, using cement-stabilized fly ash as a cushioning material, has shown that it was quite effective in arresting heave. Fly ash cushion, stabilized with 10% cement with thickness equal to that of the expansive soil bed reduces heave by about 75% in the first instance. With subsequent swell-shrink cycles, the performance further improves, unlike in the case of a black cotton soil provided with a CNS cushion. At the end of fourth cycle of swelling, the reduction in the amount of heave is as high as 99.1%.  相似文献   

A field,laboratory, and literature review evaluation of the water retention curve of volcanic ash soils: How well do standard laboratory methods reflect field conditions?     

Giovanny M. Mosquera  Marín Franklin  Feyen Jan  Célleri Rolando  Breuer Lutz  Windhorst David  Crespo Patricio 《水文研究》2021,35(1):e14011

Accurate determination of the water retention curve (WRC) of a soil is essential for the understanding and modelling of the subsurface hydrological, ecological, and biogeochemical processes. Volcanic ash soils with andic properties (Andosols) are recognized as important providers of ecological and hydrological services in mountainous regions worldwide due to their large fraction of small size particles (clay, silt, and organic matter) that gives them an outstanding water holding capacity. Previous comparative analyses of in situ (field) and standard laboratory methods for the determination of the WRC of Andosols showed contrasting results. Based on an extensive analysis of laboratory, experimental, and field measured WRCs of Andosols in combination with data extracted from the published literature we show that standard laboratory methods using small soil sample volumes (≤300 cm³) mimic the WRC of these soils only partially. The results obtained by the latter resemble only a small portion of the wet range of the Andosols' WRC (from saturation up to −5 kPa, or pF 1.7), but overestimate substantially their water content for higher matric potentials. This discrepancy occurs irrespective of site-specific land use and cover, soil properties, and applied method. The disagreement limits our capacity to infer correctly subsurface hydrological behaviour, as illustrated through the analysis of long-term soil moisture and matric potential data from an experimental site in the tropical Andes. These findings imply that results reported in past research should be used with caution and that future research should focus on determining laboratory methods that allow obtaining a correct characterization of the WRC of Andosols. For the latter, a set of recommendations and future directions to solve the identified methodological issues is proposed.  相似文献   

Coupled consolidation model for negative skin friction on piles in clay layers     

《Geomechanics and Geoengineering》2013,8(2):141-149

Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content was varied as 0%, 2%, 4%?and 6%?and fly ash content as 0%, 10%?and 20%. A fly ash content of 20%?showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell potential and swelling pressure decreased with increase in lime content also. Further, consolidation characteristics improved. Compaction characteristics and unconfined compression strength improved at 4%?lime and reduced at 6%?lime.  相似文献