scholarly journals Precipitant Effects on Aggregates Structure of Asphaltene and Their Implications for Groundwater Remediation

Water ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 2116
Author(s):  
Christian B. Hammond ◽  
Dengjun Wang ◽  
Lei Wu
Keyword(s):  
Groundwater Remediation ◽  
Aggregate Size ◽  
Fractal Dimensions ◽  
Limiting Factor ◽  
Heavy Oils ◽  
Compact Structure ◽  
Sand Surface ◽  
Onset Point ◽  
Aquifer Systems ◽  
Smoluchowski Model

Asphaltenes generally aggregate, then precipitate and deposit on the surfaces of environmental media (soil, sediment, aquifer, and aquitard). Previous studies have recognized the importance of asphaltene aggregates on the wettability of aquifer systems, which has long been regarded as a limiting factor that determines the feasibility and remediation efficiency of sites contaminated by heavy oils. However, the mechanisms/factors associated with precipitant effects on asphaltene aggregates structure, and how the precipitant effects influence the wettability of surfaces remain largely unknown. Here, we observe the particle-by-particle growth of asphaltene aggregates formed at different precipitant concentrations. Our results show that aggregates for all precipitant concentrations are highly polydisperse with self-similar structures. A higher precipitant concentration leads to a more compacted aggregates structure, while precipitant concentration near to onset point results in a less compact structure. The well-known Smoluchowski model is inadequate to describe the structural evolutions of asphaltene aggregates, even for aggregation scenarios induced by a precipitant concentration at the onset point where the Smoluchowski model is expected to explain the aggregate size distribution. It is suggested that aggregates with relative high fractal dimensions observed at high precipitant concentrations can be used to explain the relatively low Stokes settling velocities observed for large asphaltene aggregates. In addition, asphaltene aggregates with high fractal dimensions are likely to have high density of nanoscale roughness which could enhance the hydrophobicity of interfaces when they deposit on the sand surface. Findings obtained from this study advance our current understandings on the fate and transport of heavy oil contaminants in the subsurface environment, which will have important implications for designing and implementing more effective and efficient remediation technologies for contaminated sites.

Fractal Concepts And Aggregation Of Iron Oxides

1990 ◽  
Vol 180 ◽  
Author(s):  
R. Amal ◽  
J.A. Raper ◽  
T.D. Waite
Keyword(s):  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Iron Oxides ◽  
Aggregate Size ◽  
Fractal Dimensions ◽  
Aggregation Kinetics ◽  
Diffusion Limited ◽  
Scattering Measurements ◽  
The Relationship ◽  
Kinetics Of

ABSTRACTThe modelling of the aggregation kinetics of iron oxides has been succesful in predicting the increase in aggregate size as determined by dynamic light scattering measurements. The aggregates were found to exhibit fractal behaviour with fractal dimensions obtained from the scattering exponent in static light scattering studies dependent on the aggregation mechanism and ranging from 2.3 for rapid (diffusion limited) to 2.8 for slow (reaction limited) aggregation. Polydispersity and restructuring of aggregates were found not to affect the relationship between scattering exponent and aggregate fractal dimension. Excellent correspondence over a range of temperatures and ionic strengths has been obtained between results of sizing experiments using dynamic light scattering and sizes predicted using a modified Smoluchowski model incorporating fractal dimensions.

Transport and Reaction Processes in Bioremediation of Organic Contaminants. 2. Role of Aggregate Size in Soil Remediation in a Slurry Bioreactor

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Soheila Karimi Lotfabad ◽  
Murray R Gray
Keyword(s):  
Aqueous Phase ◽  
Diffusion Coefficients ◽  
Soil Aggregates ◽  
Aggregate Size ◽  
Transport Processes ◽  
Limiting Factor ◽  
Transfer Model ◽  
Soil Matrix ◽  
Significant Difference ◽  
Phase Liquid

Transport processes in the soil matrix can control the rates of bioremediation of low-solubility contaminants. In this study, experiments were designed to test the hypothesis that diffusion of contaminants within soil aggregates of diameter 40 - 1000 micron was the limiting factor in bioremediation of creosote-contaminated soil. The concentrations of 6 different PAHs (acenaphthene, anthracene, chrysene, fluoranthene, phenanthrene, and pyrene) were monitored during the course of bioremediation of sonicated and non-sonicated soil by an active mixed culture in slurry bioreactors. Sonication of the soil to disperse soil aggregates increased the rate of microbial degradation up to 5 fold, however, there was no significant difference in the final residual concentrations between the two soil treatments. The aggregate size distribution after three weeks of treatment in a slurry bioreactor was comparable in both the sonicated and non-sonicated soils, which was consistent with the independence of the residual concentrations of PAHs on sonication treatment. The soil aggregates were modelled as porous materials, with pores filled with non-aqueous phase liquid and with films of non-aqueous phase liquid on particle surfaces. As the soil aggregates were dispersed, either by sonication or mixing, then the fraction of contaminants in exposed films increased. A diffusion-controlled mass transfer model was developed to represent release of PAHs from the soil, based on this physical model. The estimated diffusion coefficients of four of the PAHs (acenaphthene, phenanthrene, fluoranthene and pyrene ) in the residual creosote phase were in the range 4.4-4.8 x 10-14 cm2/s, while the diffusion coefficients for anthracene and chrysene were lower by a factor of 2. The similar values of diffusion coefficient between the components was consistent with release by diffusion through a viscous residual creosote. The magnitude of the diffusion coefficients was intermediate between the transport properties in high-viscosity oils, and polymers.

Fractal Research on Cracks of Reinforced Concrete Beams with Different Aggregates Sizes

2011 ◽  
Vol 250-253 ◽  
pp. 1818-1822 ◽  
Author(s):  
Hong Quan Sun ◽  
Jun Ding ◽  
Jian Guo ◽  
Dong Liang Fu
Keyword(s):  
Fractal Dimension ◽  
Reinforced Concrete ◽  
Theoretical Basis ◽  
Concrete Beams ◽  
Fractal Theory ◽  
Aggregate Size ◽  
Fractal Dimensions ◽  
Reinforced Concrete Beams ◽  
Crack Evolution ◽  
Fractal Characteristics

Under the concentrated loads, the crack evolutions of reinforced concrete experimental beams (RCEB) with three different aggregate sizes are studied. Using fractal theory, the generation, development and distribution of the cracks on the RCEB are analyzed. The results show that the cracks on the RCEB have fractal characteristics obviously. By studying the fractal dimension of the cracks, the aggregate sizes have significant effect to the cracks on the RCEB. The relationships of the fractal dimensions of the crack evolution in loading processing and loads meet the power function laws. The researching results of this paper provide a new theoretical basis for selecting the appropriate aggregate size to improve the strength of reinforced concrete beams.

Utilizing Dark Field Electron Microscopy to Produce Lantern Slides

1974 ◽  
Vol 32 ◽  
pp. 116-117
Author(s):  
J. N. Meador ◽  
C. N. Sun ◽  
H. J. White
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Dark Field ◽  
Limiting Factor ◽  
Clinical Laboratories ◽  
Field Electron ◽  
Time Element ◽  
Field Electron Microscopy ◽  
Dark Field Electron ◽  
Dark Field Micrographs

The electron microscope is being utilized more and more in clinical laboratories for pathologic diagnosis. One of the major problems in the utilization of the electron microscope for diagnostic purposes is the time element involved. Recent experimentation with rapid embedding has shown that this long phase of the process can be greatly shortened. In rush cases the making of projection slides can be eliminated by taking dark field electron micrographs which show up as a positive ready for use. The major limiting factor for use of dark field micrographs is resolution. However, for conference purposes electron micrographs are usually taken at 2.500X to 8.000X. At these low magnifications the resolution obtained is quite acceptable.

Toward High-Resolution Low-Voltage SEM

1988 ◽  
Vol 46 ◽  
pp. 218-219
Author(s):  
Zhifeng Shao
Keyword(s):  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Limiting Factor ◽  
Operating Voltage ◽  
Probe Radius ◽  
Non Local ◽  
Electron Microscopes ◽  
Image Position ◽  
Scanning Electron Microscopes

Recently, low voltage (≤5kV) scanning electron microscopes have become popular because of their unprecedented advantages, such as minimized charging effects and smaller specimen damage, etc. Perhaps the most important advantage of LVSEM is that they may be able to provide ultrahigh resolution since the interaction volume decreases when electron energy is reduced. It is obvious that no matter how low the operating voltage is, the resolution is always poorer than the probe radius. To achieve 10Å resolution at 5kV (including non-local effects), we would require a probe radius of 5∽6 Å. At low voltages, we can no longer ignore the effects of chromatic aberration because of the increased ratio δV/V. The 3rd order spherical aberration is another major limiting factor. The optimized aperture should be calculated as

Computer averaging of lattice images of poly-4-methyl-pentene-1 (P4mp1): Noise created artifacts

1987 ◽  
Vol 45 ◽  
pp. 388-389
Author(s):  
P. Pradère ◽  
J.F. Revol ◽  
R. St. John Manley
Keyword(s):  
Low Dose ◽  
Polymer Concentration ◽  
Processing System ◽  
Limiting Factor ◽  
Dilute Solution ◽  
New Techniques ◽  
Dose Unit ◽  
Lattice Images ◽  
Dose Imaging ◽  
Imaging Conditions

Although radiation damage is the limiting factor in HREM of polymers, new techniques based on low dose imaging at low magnification have permitted lattice images to be obtained from very radiation sensitive polymers such as polyethylene (PE). This paper describes the computer averaging of P4MP1 lattice images. P4MP1 is even more sensitive than PE (total end point dose of 27 C m-2 as compared to 100 C m-2 for PE at 120 kV). It does, however, have the advantage of forming flat crystals from dilute solution and no change in d-spacings is observed during irradiation.Crystals of P4MP1 were grown at 60°C in xylene (polymer concentration 0.05%). Electron microscopy was performed with a Philips EM 400 T microscope equipped with a Low Dose Unit and operated at 120 kV. Imaging conditions were the same as already described elsewhere. Enlarged micrographs were digitized and processed with the Spider image processing system.

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