Some breakage characteristics of ultra-fine wet grinding with a centrifugal mill     

Heechan Cho  Hoon LeeYeongwoo Lee 《International Journal of Mineral Processing》2006

A centrifugal mill is a high-power intensity media mill that can be used for ultra-fine grinding, employing centrifugal forces generated by gyration of the axis of the mill tube in a circle. The mill charge motion is quite different depending on the ratio of the gyration diameter to the mill diameter (G / D ratio), varying from a motion similar to that of a conventional tumbling media mill to that of a vibration mill. In this study, a centrifugal mill was constructed with an arrangement where the gyration diameter could be readily adjusted. The batch grinding characteristics of three different minerals (limestone, talc and illite) in water with dispersing agent were investigated at various G / D ratios. It was found that the optimum G / D ratio in terms of the specific energy consumption to give a desired fineness of product was different for the three minerals. This was due to their different reactions to the breakage mechanisms provided by the mill charge motion at varying G / D ratios. The size distributions became progressively narrower at increased grinding times, and particles finer than about 0.1 μm were not detected even for prolonged grinding times. Measurement of specific surface areas indicated that this was not due to an artifact of the size measurements by laser diffractometry. This implies that there is a limitation in which particles finer than 0.1 μm are not produced under the conditions tested in this type of mill, but further investigation is needed for experimental verification of this limit of comminution.  相似文献   

Carbon, sulfur and O₂ across the Permian–Triassic boundary     

Robert A. Berner   《Journal of Geochemical Exploration》2006,88(1-3):416

A model for the carbon and sulfur cycles across the Permian–Triassic boundary has been constructed from carbon and sulfur isotopic data. Results indicate a drop in global organic matter burial, the formation of an anoxic deep ocean, and a large drop in atmospheric oxygen over the time span 270 to 240 Ma. Much of these changes were probably due to a drop in terrestrial productivity and preservation and an increase in global aridity.  相似文献   

Forests, climate, and silicate rock weathering     

K. Caldeira   《Journal of Geochemical Exploration》2006,88(1-3):419

Over time periods of 10⁶ years and longer, atmospheric carbon dioxide content is largely controlled by a balance between silicate rock weathering and CO₂ sources (degassing from the Earth plus net organic carbon oxidation). Vegetation cover can affect silicate rock weathering rates by increasing soil CO₂ content, stabilizing soil cover, and producing organic acids. Forests absorb more solar radiation than most other ecosystems; this tends to warm Earth's climate, especially outside of the tropics; this warmth would tend to increase silicate rock weathering rates. Here, we develop preliminary parameterizations of this effect that could be incorporated into carbonate–silicate cycle models, based on the results of general circulation model simulations.  相似文献   

Measurement of the total nitrogen in lake sediments： Comparison and its environmental significance     

Wei JIANG Xinqing LEE 《中国地球化学学报》2006,25(B08):12-12

Nitrogen cycle is an important bio-geochemical process in the environment. Measurement of the total nitrogen （TN） is a routine experiment in agriculture, biology and environmental sciences. The Kjeldahl method （KM） and elemental analyzer method （EA） are both commonly used to determine TN. Total nitrogen by EA is the sum of nitrate （NO3）, nitrite （NO2）, organic nitrogen and ammonia. Total nitrogen by KM （TKN） is made up of both organic nitrogen and ammonia. A comparative study focused on the two methods is conducted by analysis of TN in 97 samples from the sediment sequence of Gouchi, a salt lake in North China. KM presents a higher degree of accuracy than EA with a standard deviation of 0.007 vs. 0.024. With the presence of nitrate and/or nitrite nitrogen, however, measurement by KM is considerably lower than that by EA. Therefore, for samples from lake sediment sequences or soils in North China, KM is inapplicable to determining TN because of usually high contents of nitrous salt. Despite the inconsistency, use of both methods to the same samples makes sense in reconstructions of climatic and environmental changes from lake sediments. In Lake Gouchi, the contents of nitrate and nitrite nitrogen vary from 1.40% in the lower part of the sequence to 14.77% in the uppermost part, suggesting a gradual evolution process from a fresh water lake to the present-day salt lake.  相似文献   

High-resolution sedimentary record of lead in the coastal mud of the East China Sea in the past one hundred and fifty years     

Yunchao HAO Zhigang GUO Dejiang FAN 《中国地球化学学报》2006,25(B08):13-13

In the East China Sea （ECS）, there are some mud areas, including the south coastal mud area, the north coastal mud area, and the mud area to the southwest of Cheju Island. X-ray fluorescence （XRF） techniques and Thermal Ionization Mass Spectrometry （TIMS） were used to study the high-resolution sedimentary record of Pb concentrations and Pb stable isotopic compositions in the past one hundred and fifty years in the coastal mud of the ECS. Pb concentrations of a ^210Pb dating S5 core in the study area have increased rapidly since 1980, and reached the maximal value with 65.08 μg/g in 2000, corresponding to the fast economic development of China since the implementation of the ＂Reform and Open Policy＂ in 1978; ^206Pb/^207Pb ratios generally had stabilized at 1.195 from 1860 to 1966, and decreased gradually from 1966 to 2000, indicating that the anthropogenic source Pb contribution to the ECS has increased gradually since 1966, especially since 1980. Pb concentrations decreased distinctly from 2000 to 2003 and ^206Pb/^207Pb ratios increased from 2001 to 2003, corresponding closely to the ban of lead gasoline from 2000 in China. From 1950 to 2003, there occurred four distinct decrease events of ^206Pb/^207Pb, possibly responding to the Changjiang River （Yangtze River） catastrophic floods in 1998, 1991, 1981 and 1954; from 1860 to 1966, there were two decrease periods of ^206Pb/^207Pb, which may respond to the catastrophic floods of Changjiang River in 1931 and 1935, and 1870. As a result of the erosion and drowning by the catastrophic floods, the anthropogenic lead accumulated in soil and water environments over a long period of time was brought into the Changjiang River, then part of them was finally transported into the ECS, which leads to changes in Pb stable isotopic composition.  相似文献   

Effects of dynamic shear strength and time-histories stress analysis on newmark sliding block analyses     

LI Hong-jun  CHI Shi-chun  LIN Gao 《岩土力学》2006,27(Z1):1063-1068

A simplified procedure for evaluating aseismic stability of slope subjected to earthquake shaking, in which the effect of dynamic shear strength and time-history stress on the yielding angular acceleration of sliding block is taken into account, is presented. The fundamental feature of this procedure is the dynamic shear strength. The numerical computations are performed by using the proposed method. It is shown that the computed sliding displacement for a given core dam, with either method of dynamic shear strength properly considered, is more rational compared with the conventional computational results based on static shear strength.  相似文献   

Periodic accumulation and destruction of aeolian erg sequences in the Permian Cedar Mesa Sandstone, White Canyon, southern Utah, USA     

NIGEL P. MOUNTNEY 《Sedimentology》2006,53(4):789-823

The Permian Cedar Mesa Sandstone represents the product of at least 12 separate aeolian erg sequences, each bounded by regionally extensive deflationary supersurfaces. Facies analysis of strata in the White Canyon area of southern Utah indicates that the preserved sequences represent erg‐centre accumulations of mostly dry, though occasionally water table‐influenced aeolian systems. Each sequence records a systematic sedimentary evolution, enabling phases of aeolian sand sea construction, accumulation, deflation and destruction to be discerned and related to a series of underlying controls. Sand sea construction is signalled by a transition from damp sandsheet, ephemeral lake and palaeosol deposition, through a phase of dry sandsheet deposition, to the development of thin, chaotically arranged aeolian dune sets. The onset of the main phase of sand sea accumulation is reflected by an upward transition to larger‐scale, ordered sets which represent the preserved product of climbing trains of sinuous‐crested transverse dunes with original downwind wavelengths of 300–400 m. Regularly spaced reactivation surfaces indicate periodic shifts in wind direction, which probably occurred seasonally. Compound co‐sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger, slipfaceless draa. Each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity. Aeolian sequence generation is considered to be directly attributable to cyclical changes in climate and related changes in sea level of probable glacio‐eustatic origin that characterize many Permo‐Carboniferous age successions. Sand sea construction and accumulation occurred during phases of increased aridity and lowered sea level, the main sand supply being former shallow marine shelf sediments that lay to the north‐west. Sand sea deflation and destruction would have commenced at, or shortly after, the time of maximum aridity as the available sand supply became exhausted. Restricted episodes of non‐aeolian accumulation would have occurred during humid (interglacial) phases, accumulation and preservation being enabled by slow rises in the relative water table. Subsidence analysis within the Paradox Basin, together with comparisons to other similar age successions suggests that the climatic cycles responsible for generating the Cedar Mesa erg sequences could be the product of 413 000 years so‐called long eccentricity cycles. By contrast, annual advance cycles within the aeolian dune sets indicate that the sequences themselves could have accumulated in just a few hundred years and therefore imply that the vast majority of time represented by the Cedar Mesa succession was reserved for supersurface development.  相似文献   

Structural architecture of a highly oblique divergent plate boundary segment   总被引：1，自引：0，他引：1  

Amy E. Clifton  Simon A. Kattenhorn 《Tectonophysics》2006,419(1-4):27-40

The Reykjanes Peninsula in southwest Iceland is a highly oblique spreading segment of the Mid-Atlantic Ridge oriented about 30° from the direction of absolute plate motion. We present a complete and spatially accurate map of fractures for the Reykjanes Peninsula with a level of detail previously unattained. Our map reveals a variability in the pattern of normal, oblique- and strike-slip faults and open fractures which reflects both temporal and spatial strain partitioning within the plate boundary zone. Fracture density varies across the length and width of the peninsula, with density maxima at the ends and at the northern margin of the zone of volcanic activity. Fractures with similar strike cluster into distinct structural domains which can be related to patterns of faulting predicted for oblique extension and to their spatial distribution with respect to volcanic fissure swarms. Additional structural complexity on the Reykjanes Peninsula can be reconciled with magmatic periodicity and associated temporal strain partitioning implied by GPS data, as well as locally perturbed stress fields. Individual faults show variable slip histories, indicating that they may be active during both magmatic and amagmatic periods associated with different strain fields.  相似文献   

Up-temperature flow of surface-derived fluids in the mid-crust: the role of pre-orogenic burial of hydrated fault rocks   总被引：1，自引：0，他引：1  

C. CLARK  M.  HAND  K.  FAURE  A. SCHMIDT MUMM 《Journal of Metamorphic Geology》2006,24(5):367-387

The Walter‐Outalpa shear zone in the southern Curnamona Province of NE South Australia is an example of a shear zone that has undergone intensely focused fluid flow and alteration at mid‐crustal depths. Results from this study have demonstrated that the intense deformation and ductile shear zone reactivation, at amphibolite facies conditions of 534 ± 20 °C and 500 ± 82 MPa, that overprint the Proterozoic Willyama Supergroup occurred during the Delamerian Orogeny (c. 500 Ma) (EPMA monazite ages of 501 ± 16 and 491 ± 19 Ma). This is in contrast to the general belief that the majority of basement deformation and alteration in the southern Curnamona Province occurred during the waning stages of the Olarian Orogeny (c. 1610–1580 Ma). These shear zones contain hydrous mineral assemblages that cut wall rocks that have experienced amphibolite facies metamorphism during the Olarian Orogeny. The shear zone rock volumes have much lower δ¹⁸O values (as low as 1‰) than their unsheared counterparts (7–9‰), and calculated fluid δ¹⁸O values (5–8‰) consistent with a surface‐derived fluid source. Hydrous minerals show a decrease in δD_(H2O) from ?14 to ?22‰, for minerals outside the shear zones, to ?28 to ?40‰, for minerals within the shear zones consistent with a contribution from a meteoric source. It is unclear how near‐surface fluids initially under hydrostatic pressure penetrate into the middle crust where fluid pressures approach lithostatic, and where fluid flow is expected to be dominantly upward because of pressure gradients. We propose a mechanism whereby faulting during basin formation associated with the Adelaidean Rift Complex (c. 700 Ma) created broad hydrous zones containing mineral assemblages in equilibrium with surface waters. These panels of fault rock were subsequently buried to depths where the onset of metamorphism begins to dehydrate the fault rock volumes evolving a low δ¹⁸O fluid that is channelled through shear zones related to Delamerian Orogenic activity.  相似文献   

GGR Critical Review of Analytical Developments in 2004–2005     

Janet M. Hergt  L. Paul Bédard  Etienne Deloule  Klaus Peter Jochum  Kathryn L. Linge  Paul J. Sylvester  Matthias Willbold  Jon D. Woodhead 《Geostandards and Geoanalytical Research》2006,30(3):141-142

In 2005 Geostandards and Geoanalytical Research embarked upon a new initiative for its readers. Key researchers in various fields of geoanalytical technique development and their application were identified and invited to provide reviews pertinent to their expertise. As noted in the first of these publications "…instead of revisiting the historical context or decades of development in each analytical technique, the goal here has been to capture a snapshot of "hot topics" across a range of fields as represented in the… literature" (Hergt et al . 2005). Rather than prepare an annual review, a decision was taken earlier this year to provide a biennial summary of progress and accomplishments, in this case for the years 2004–2005. The principal techniques employed in Earth and environmental sciences are covered here, and include laser ablation and multicollector ICP-MS, ICP-AES, thermal ionisation and secondary ion mass spectrometry, as well as neutron activation analysis, X-ray fluorescence and atomic absorption spectrometry. A comprehensive review of the development of reference materials, often essential to these techniques, is also provided. The contributions assembled serve both to keep readers informed of advances they may be unfamiliar with, but also as a means of showcasing examples of the breadth and depth of work being conducted in these fields.  相似文献