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1.
The purpose of this research is to propose a laboratory method based on attrition and sieving for the treatment of runoff water sediments in the aim of developing a pilot unit. The attrition process serves to remove fine particles and pollutants from the surface of coarse stormwater sediment particles. In all cases, the efficiency of pollutant removal is dependent upon various parameters, including cutoff threshold, residence time, solid density, temperature and impeller speed. This article presents the optimization of these various parameters along with method efficiency; for this work, several sediments have been tested. The results indicate that an attrition scrubber may be effectively used to remediate contaminated sediment and that reuse is definitely possible. A model of the method will also be proposed to study the behavior of fine particles and pollutants. 相似文献
2.
S.W. Ihle B.B. Johnson T.A. Raven G.J. Sparrow 《International Journal of Mineral Processing》1983,11(4):239-253
Previous laboratory work indicated that the dewatering of suspensions of kaolin and fine quartz on a sand bed could be described by a simple two-term equation with one term for the drainage component and one for the evaporation component.Field tests have been carried out at three sand-washing operations in Victoria to determine if the equation is applicable in practice.The thickened suspensions were dewatered to a solid when they were ponded in shallow depths onto a sand bed. The changes in solids content during the dewatering confirmed that the dewatering equation could be used in practice.The dewatering equation is potentially very useful since it can be used to calculate optimum ponding depths, and therefore the area required to dewater a given production of tailing. 相似文献
3.
Eri Hirakawa Akiko Murakami-Kitase Takamoto Okudaira Jun Inoue Hideo Yamazaki Shusaku Yoshikawa 《Environmental Earth Sciences》2011,64(3):833-840
Spheroidal carbonaceous particles (SCPs) are produced by the high-temperature combustion of fossil fuels and emitted in to
the atmosphere. The distribution and concentration of SCPs in sediments have been used as a proxy for the distribution of
pollutants emitted to the atmosphere. However, the effect on the distribution of SCPs due to industrial activity at nearby
industrial cities is yet to be quantified. To clarify the origin of SCPs of ~20 μm in size that are preserved in sediments,
we evaluated the abundance, surface morphology, and chemical composition of SCPs in sediment core samples recovered from industrial
cities in Japan (Tokyo, Osaka, and Nagasaki) and China (Beijing), with the cities being located at least ~500 km away from
each other. Vertical profiles of SCP concentration in sediment cores from the Japanese cities and Beijing are different, reflecting
the contrasting industrial histories of the two countries. The SCPs from different cities show contrasting morphological and
chemical characteristics, suggesting that ~20 μm SCPs in sediments from the industrial cities could represent the local combustion
history in detail, as the influx of local SCPs is dominant at such sites. 相似文献
4.
应用了静态沉降实验方法中的移液管法,初步研究了水中常见阳离子对河流中细颗粒泥沙沉速的影响,这些阳离子包括Na+、Ca2+、Mg2+和Al3+等。实验结果表明,阳离子浓度对泥沙沉速的影响可以分为两个阶段:①随着阳离子浓度的增加泥沙沉速也增大;②当离子浓度大于某值时,离子浓度对泥沙沉速的影响不大。在同样离子浓度条件下,离子价态高者影响较大。同时分析了长江和黄河干流中下游河段的水化学特性;分析结果表明,在一般的河水水质的情况下,有必要考虑水中阳离子(主要是Ca2+、Mg2+)对细颗粒泥沙沉速的影响。 相似文献
5.
PAUL D. KOMAR 《Sedimentology》1985,32(3):395-407
Previous attempts to deduce the flow parameters of turbidity currents from their deposited sediments have focused on applications of criteria for the suspension or autosuspension of the grains and on hydrodynamic interpretations of the characteristic Bouma sequence of sedimentary structures. There has been a considerable diversity of opinion, however, as to how the transport criteria relate to the observed deposited grain-size distribution, and no attempt has been made to determine whether the separate analyses of deposited sediments and sedimentary structures agree as to the magnitudes of the evaluated flow parameters. Such analyses are performed on a turbidite from the Capistrano Formation (Miocene-Pliocene) of California. This turbidite is normally graded from medium sand at its base to very fine sand and silt at the top, and has the complete sequence of Bouma structures. Only a small degree of cementation has occurred so that samples from the layer could be disaggregated and grain sizes determined both by sieving and sedimentation balance analyses. It was decided to employ the grain-suspension criterion for the calculation of the flow conditions at the time of deposition, published experiments on the pipe-flow of suspensions having demonstrated that this criterion is one of deposition versus non-deposition of grains according to their settling velocities. The published work relating types of sedimentary structures to the sediment grain size and either the flow power or Shield's dimensionless stress is used to evaluate the flow parameters from the observed Bouma sequence. All methods employed yield estimates of the mean flow velocity and bed stress (force per unit bottom area). The evaluated flow parameters for the transition from a flat bed to ripples (Bouma B to C divisions) are nearly an order of magnitude greater than obtained from the grain-suspension criterion where the calculations are based on the median grain size of the deposited sediments. Agreement results only if the calculations utilizing the suspension criterion are based on nearly the coarsest grains deposited at any instant, a procedure that is difficult to justify with the expected sediment deposition from a waning current. Inclusion of other factors, such as possible lags in sediment deposition or ripple formation beneath the decelerating flow, provide no firm explanation as to the cause of the discrepancy between the results based on the two approaches, and in nearly all cases their inclusion would increase the difference. Something is amiss with our procedures for the hydraulic interpretation of sediments which can be resolved only by further study. 相似文献
6.
为实现疏浚淤泥高效快速脱水减容,选取化学絮凝和真空预压相结合的脱水技术,利用自制真空预压抽滤装置对5种类型絮凝剂调理淤泥进行系列室内脱水试验,通过上清液高度、泥水分界面高度、沉降速率、底泥含水率等指标,综合评价疏浚淤泥沉降过程与深度脱水效果。结果表明：5种絮凝剂对应最优添加量分别为Ca(OH)2(1 500 mg/L)、PAFSI(200 mg/L)、PAC(200 mg/L)、HCA(50 mg/L)、APAM(500 mg/L);与原始淤泥自然沉降过程相比（底泥高度17.14 cm、含水率96.8%）,真空预压可实现絮凝调理淤泥脱水减容、底泥平均含水率降至53.5%,使底泥体积进一步压缩20.48%～36.99%;真空预压作用下,絮凝调理淤泥在50 min内达到沉降速率峰值,前120 min内淤泥絮凝效果明显、泥水分离程度占据主导;与原始淤泥真空预压对比,絮凝?真空预压大幅提升淤泥沉降速率、有效缩短峰值对应沉降时间,最优絮凝剂（APAM）底泥沉降速率峰值、淤泥总高度沉降速率峰值对应时间点缩短87.5%和83.33%,峰值速率分别增加3.56倍、5.18倍;添加适量絮凝剂能有效改善淤泥脱水性能,增大泥粒尺寸、防堵促排,加速疏浚淤泥沉降与泥水分离效率。化学絮凝?真空抽滤技术有利于实现疏浚淤泥减量化,显著缩短工期、加快施工进度、减少堆积占地,具有显著的工程应用价值。 相似文献
7.
Conventional and non-conventional flotation for mineral processing and for water (and wastewaters) treatment and reuse (or recycling) is rapidly broadening their applications in the mining field. Conventional flotation assisted with microbubbles (30–100 μm) finds application in the recovery of fine mineral particles (< 13 μm) and flotation with these fine bubbles is being used as a solid/liquid separation to remove pollutants. The injection of small bubbles to conventional coarse bubbles flotation cells usually leads to general improvements of the separation parameters, especially for the ultrafines (< 5 μm) ore particles. Results obtained are believed to occur by enhancing the capture of particles by bubbles, one of the main drawbacks in fine ore flotation. It is believed that by decreasing the bubble size distribution (through the injection of small bubbles), increases the bubble surface flux and the fines capture. DAF or dissolved air flotation with microbubbles, treating water, wastewater and domestic sewage is known for a number of years and is now gradually entering in the mining environmental area. This technology offers, in most cases, advantages over settling, filtration, precipitation, or adsorption onto natural and synthetic adsorbents. The targets are the removal of oils (emulsified or not), ions (heavy metals and anions) and the reuse or recirculation of the process waters. Advantages include better treated water quality, rapid start up, high rate operation, and a thicker sludge. New applications are found in the mining vehicles washing water treatment and reuse, AMD (acid mining drainage) neutralization and high rate solids/water separation by flotation with microbubbles. This work reviews some recent applications of the use of microbubbles to assist the recovery of very small mineral particles and for the removal of pollutants from mining wastewaters. Emphasis is given to the design features of innovative devices showing the potential of conventional and unconventional DAF flotation. 相似文献
8.
Spatial distribution of heavy metals in surficial sediments from Guanabara Bay: Rio de Janeiro, Brazil 总被引：1，自引：0，他引：1
José Antônio Baptista Neto Franz Xaver Gingele Thomas Leipe Isa Brehme 《Environmental Geology》2006,49(7):1051-1063
Ninety-two surface sediment samples were collected in Guanabara Bay, one of the most prominent urban bays in SE Brazil, to
investigate the spatial distribution of anthropogenic pollutants. The concentrations of heavy metals, organic carbon and particle
size were examined in all samples. Large spatial variations of heavy metals and particle size were observed. The highest concentrations
of heavy metals were found in the muddy sediments from the north western region of the bay near the main outlets of the most
polluted rivers, municipal waste drainage systems and one of the major oil refineries. Another anomalous concentration of
metals was found adjacent to Rio de Janeiro Harbour. The heavy metal concentrations decrease to the northeast, due to intact
rivers and the mangrove systems in this area, and to the south where the sand fraction and open-marine processes dominate.
The geochemical normalization of metal data to Li or Al has also demonstrated that the anthropogenic input of heavy metals
have altered the natural sediment heavy metal distribution. 相似文献
9.
利用室内外实验和数学模型对波浪和湖流共同作用下太湖水体悬浮物输运过程进行了研究.结果表明:当太湖日平均风速在2~8m/s时,水体悬浮物再悬浮通量与平均风速符合正相关关系;太湖悬浮物沉降属于絮凝沉降.悬浮物浓度较低时,其沉降速率与浓度无明显的相关关系;而浓度较高时,沉降速率随浓度升高而增大.悬浮物浓度和沉降速率符合Logistic函数;将太湖湖流模型和波浪模型耦合,有效地反映了太湖的水动力过程;在太湖悬浮物模型中,引入底泥起悬条件,将底泥的起悬量与沉降量分开处理,有效地模拟了太湖悬浮物的输运过程.模拟结果表明太湖悬浮物沿岸区域受湖流的影响较大,湖心区域受波浪影响较大. 相似文献
10.
In order to explain why the magnetic directions of naturally and artificially deposited fine silts show deviations from the direction of the ambient field a theoretical model has been postulated of the process of deposition.
The deviations have been explained satisfactorily on the assumption that the sediment consists of quasi-spherical, non-cohesive particles which roll into hollows in the existing bed. A model of this kind provides a theoretical basis for the quantitative study of certain sedimentological questions which may be applied to the study of such problems as the apparent anomalous resistance to erosion of very fine grained sediments, their mechanism of compaction and the determination of current direction and velocity.
Since it does not depend on direct observation either visual or mechanical the magnetic method may be particularly fruitful for sediments of fine silt grade where such observation is very difficult. 相似文献
The deviations have been explained satisfactorily on the assumption that the sediment consists of quasi-spherical, non-cohesive particles which roll into hollows in the existing bed. A model of this kind provides a theoretical basis for the quantitative study of certain sedimentological questions which may be applied to the study of such problems as the apparent anomalous resistance to erosion of very fine grained sediments, their mechanism of compaction and the determination of current direction and velocity.
Since it does not depend on direct observation either visual or mechanical the magnetic method may be particularly fruitful for sediments of fine silt grade where such observation is very difficult. 相似文献
11.
长江与黄河河口沉积物磁性特征对比的初步研究 总被引：11，自引：1，他引：10
根据2001年8月和9月分别采自黄河与长江河口沉积物样品的磁性测量和粒度分析,探讨长江和黄河河口沉积物的磁性特征及其差异。长江河口沉积物中亚铁磁性物质的含量高于黄河口,但长江口与黄河口沉积物中都是亚铁磁性矿物主导了样品磁性特征,亚铁磁性矿物晶粒都以假单畴-多畴为主。相比黄河口沉积物,长江口沉积物不完整反铁磁性物质对磁性特征的的贡献较小。长江与黄河河口的这种磁性特征主要反映了不同的沉积物来源的控制影响。此外,无论是长江口还是黄河口沉积物,磁性参数χARM、χfd%与沉积物细粒级组分存在显著的相关性,表明这两个参数作为粒度的代用指标具有普遍性。 相似文献
12.
Entrainment of planktonic foraminifera: effect of bulk density 总被引：1，自引：0，他引：1
REINHARD OEHMIG 《Sedimentology》1993,40(5):869-877
Depositional hydrodynamics have been studied using settling rate distributions of Norwegian deep sea sediments (between Jan Mayen Island and the Vøring Plateau), together with Shields’ critical shear stress velocities. Planktonic foraminifera are the dominant sand sized component of these sediments. The bulk density of the foraminifera was calculated from their settling velocity, sieve size and shape. Density decreases from 2·39 g cm?3 at 0·05 mm diameter to 1·37 g cm?3 at 0·35 mm diameter. These density and size data were used to construct a threshold sediment movement curve. From the similarity in their Shield's critical shear-stress velocities and the observed correlation of foraminifera size with decreasing percentage of fine fraction, it is concluded that the two components, the sand size foraminifera and the quartz and carbonate silt, are transport-equivalent. 相似文献
13.
14.
Along a 2 km NW-SE transect along the energy gradient of an intertidal sand body of the back-barrier tidal flats of Spiekeroog island (German Wadden Sea, southern North Sea), three sets of closely spaced surface sediment samples were taken at different times to investigate whether the effects of progressive size sorting could be identified in the textural parameters and size-frequency curves of the sediments. Grain-sizes analyses were carried out with a high-resolution settling tube having an internal resolution of 1/50-psi intervals. The settling velocity data were subsequently transformed numerically into equivalent settling diameters on the basis of a quartz sphere standard. At this high resolution, it was possible to visualize subtle changes in textural parameters which would not have been resolved by standard 0.25-phi sieve analyses. The first two sample sets of 1992 and 1994 show similar trends of progressive fining in the sediment, combined with a slight decrease in skewness and sorting in the direction of decreasing energy. Ten years later, in 2003, the sediments were slightly coarser but still reflected the hydrodynamic energy gradient by a distinct fining trend along the transect. However, in contrast to the former data sets, the skewness values now remained constant, whereas the sorting values revealed the existence of two overlapping hydrodynamic energy regimes on the tidal flat. The better sorting in the coarser size fractions and the general coarsening trend in the central part of the tidal flat are interpreted to reflect an increase in the hydrodynamic energy level since the first two sample sets were collected. This observation suggests that some of the finer particles in the grain-size spectrum on the tidal flat were winnowed out by wave action without, however, completely obliterating the former trend. This interpretation is supported by an increase in the frequency and duration of strong winds as recorded by the national weather bureau since the early 1990s. The results of the study demonstrate that the intertidal sediments of the Wadden Sea respond rapidly and sensitively to gradual changes in the hydrodynamic energy regime. 相似文献
15.
Threshold of motion and settling velocities of mollusc shell debris: Influence of faunal composition
Alissia Rieux Pierre Weill Dominique Mouaze Clement Poirier Farid Nechenache Laurent Perez Bernadette Tessier 《Sedimentology》2019,66(3):895-916
Bioclastic particles derived from mollusc shell debris can represent a significant fraction of sandy to gravelly sediments in temperate and cool‐water regions with high carbonate productivity. Their reworking and subsequent transport and deposition by waves and currents is highly dependent on the shape and density of the particles. In this study, the hydrodynamic behaviour of shell debris produced by eight mollusc species is investigated for several grain sizes in terms of settling velocity (measurements in a settling tube) and threshold of motion under unidirectional current (flume experiments using an acoustic profiler). Consistent interspecific differences in settling velocity and critical bed shear stress are found, related to differences in shell density, shell structure imaged by scanning electron microscopy and grain shape. Drag coefficients are proposed for each mollusc species, based on an interpolation of settling velocity data. Depending on the shell species, the critical bed shear stress values obtained for bioclastic particles fall within or slightly below empirical envelopes established for siliciclastic particles, despite very low settling velocity values. The results suggest that settling velocity, often used to describe the entrainment of sediment particles through the equivalent diameter, is not a suitable parameter to predict the initiation of motion of shell debris. The influence of the flat shape of bioclastic particles on the initiation of motion under oscillatory flows and during bedload and saltation transport is yet to be elucidated. 相似文献
16.
In muddy sediments, the distinction between sortable silt and aggregated silty clay is important for the understanding of fine particle dynamics because both have different hydraulic properties. The Wadden Sea of the southern North Sea is severely depleted in fine-grained sediments mainly due to high energy levels along the diked coastline. As a result, muddy sediments are restricted to a narrow belt along the diked mainland shore. In the present study, the mechanism by which this mud is deposited and how floc deposition and break-up are reflected in the size distribution, has been investigated. For this purpose, surficial sediments from four intertidal nearshore transects were monitored and repeatedly sampled in the course of two years. High-resolution grain-size analyses were performed by an automated settling tube and a Sedigraph particle analyser for the sand and mud fractions, respectively.The grain size frequency distributions of the fine fractions demonstrate that the Wadden Sea muds are composed of two subpopulations, a well-sorted coarse silt and an unsorted silty clay population. A depletion of grain size around 8 μm (7 phi) demarcates the grain-size boundary between the two populations, suggesting that the finer mud population (< 8 μm) is deposited in the form of flocs and aggregates which are hydraulically equivalent to the local sands and coarser silts. Floc break-up and reconstitution in response to seasonally changing energy regimes lead to apparent seasonal sedimentation patterns in the back-barrier tidal basins. Furthermore, in the course of sample preparation, the flocs and aggregates are broken down into their constituent particles. This mechanical artefact in the size distributions produces an artificial seasonal fining/coarsening pattern. It was found that the comparison of clay/silt and < 8 μm/63 − 8 μm particle ratios are good indicators of floc behaviour. Higher ratios are found in mixed flats which are relatively protected from wave action, thereby promoting deposition of flocs. In addition, progressive size sorting and mixing processes along the transects are recognized in the frequency distributions of sands. The skewness pattern shows a landward decrease in positive values, which is exactly opposite to previously reported patterns, suggesting progressive winnowing of fine particles caused by increased wave action over the last decade. This effect of climate change further promotes depletion of fine-grained sediments in the basin. 相似文献
17.
钙质碳酸盐碎屑是热带海滩沉积物的重要组成部分,其物理特性与海滩中的石英颗粒差异明显。对海南岛东部文昌铜鼓角两侧海湾海滩砂样采用除钙和不除钙两种预处理方法,使用Mastersizer 2000激光粒度仪和筛析法进行粒度分析,结果表明:除钙以后粒度频率曲线主体朝细偏,但在粒度频率曲线细尾(4~9)会新增一小峰;去钙前后粒度参数存在明显的线性相关,平均粒径、分选系数和偏态的相关系数依次降低;粒度参数的组合变化以“平均粒径变细、分选系数变好、偏态朝细偏”为主,但仍存在其他的组合变化;在对类似于铜鼓岭周边环境的海滩进行沉积物粒度分析及动力环境研究时,需要了解钙质碎屑含量和颗粒组成。 相似文献
18.
Allison M. Colden Kelsey A. Fall Grace M. Cartwright Carl T. Friedrichs 《Estuaries and Coasts》2016,39(5):1435-1448
The eastern oyster, Crassostrea virginica, is a prominent ecosystem engineer, whose reefs exhibit strikingly consistent morphologies at multiple spatial scales throughout its North American range. These distinct morphologies are thought to form by interactions of nascent reef structures with hydrodynamics. We carried out two field studies to determine if historical reef configurations applied in a restoration context would improve reef persistence and restoration outcomes. We collected seabed and water column observations across constructed reefs of three orientations representative of those found historically throughout the oyster’s range: parallel or perpendicular to tidal currents or circular. Areas adjacent to reefs were sites of fine sediment trapping, with lower flow velocities, evidence of particle settling, and more fine sediments on the seabed relative to off-reef reference sites. The water column above the reef crest exhibited higher acoustic backscatter, higher flow velocities, and larger particles in suspension, consistent with local erosion of flocculated fine sediment from the reef crest. Perpendicular reefs produced conditions that were more conducive to reef persistence and improved oyster performance, including high flow velocities and enhanced resuspension of sediments from the reef, compared to parallel or circular reefs. Particle trapping in areas between reefs has the potential to inhibit reef growth between existing reef structures, providing support for hypotheses of landscape-scale reef pattern formation. Oyster reef restoration efforts can benefit from this improved understanding of biophysical interactions arising from reef orientation that contribute to sediment dynamics on constructed oyster reefs. 相似文献
19.
南京长江隧道盾构接收井地处江心洲上,开挖地层以粉细砂层和砾砂层为主,降水施工中成功地克服了强透水地层分布厚、受承压水影响大、基坑开挖深度深、民房离基坑边沿距离近、降水技术复杂、地表沉降控制难等一系列技术难题。本文对基坑降水方案设计、施工工艺及地表沉降控制等方面进行了研究和总结。 相似文献
20.
Rita M. F. Fonseca Fernando J. A. S. Barriga Patrícia I. S. T. Conceição 《International Journal of Earth Sciences》2010,99(8):1899-1916
The Southern region of Portugal is subjected to several forms of over-erosion. Most leached products, mainly composed of fine
particles containing nutrients, metals or pesticides, are easily transported by river flows. When these are hindered by a
physical barrier such as a dam, the particulate load accumulates on the bottom of the reservoirs, often leading to a pronounced
decrease of water quality. Bottom sediments from three reservoirs were subjected to grain-size analysis and a study of clay
minerals by X-ray diffraction. Most sediments contain a diverse set of clay minerals, mostly illites, smectites, chlorites
and kaolinites. The nature of the clay minerals reflects the nature of the parent rocks. During the cycles of transport and
temporary deposition, they may undergo significant chemical and physical transformations, which lead to an increase of expandable
properties and therefore, to a higher cationic exchange capacity, determining its important role as vehicles of environmental
pollutants. 相似文献