•Flocculation can be studied applying logistic growth models.•These models reduce to well-known linear interpolations at onset of flocculation.•Studies of flocculation kinetics can be performed over ...long periods of time.•The dependence on relevant parameters is discussed.
The model based on logistic growth theory, that was introduced in Chassagne, Claire, and Zeinab Safar. “Modelling flocculation: Towards an integration in large-scale sediment transport models.” Marine Geology 430 (2020): 106361, can be used to model the time evolution of either the particle (floc) size or the concentration of particles of a given size. In the present article, we show how this model can easily be linked to the many studies performed over the years about the flocculation kinetics at the onset of flocculation experiments. Flocculation experiments done on kaolinite suspensions destabilized by addition of salt are used as examples. Both perikinetic and orthokinetic flocculation are considered. By fitting the experimental data over the whole experiment period, it is shown that the floc size L(t) time evolution follows the relation dL/dt=L/tb−L2/(Leqtb) where tb is a characteristic time and Leq a characteristic size, which are obtained from the fits.
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GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We previously proposed ( Gourdin-Bertin, S. ; Chassagne, C. J. Chem. Phys. 2016, 144 (24) ) a simple theoretical model to account for the evolution of conductivity with dielectric permittivity in ...nonpolar media. In this article, we validate the theory experimentally for the case of an ionogenic species kept at a constant chemical potential (i.e., in equilibrium with a nondissolved salt, in contrast to previously published conductivity measurements carried out as a function of various fully dissolved salt concentrations). To our knowledge, it is the first time that this type of experiment has been performed explicitly.
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IJS, KILJ, NUK, PNG, UL, UM
We derived the so-called standard set of electrokinetic equations in prolate spheroidal coordinates for all ionic strengths, zeta potentials, and applied electric field frequencies, with the ...assumption, however, that the particle’s electrophoretic mobility is small. We subsequently solved these equations using finite differences methods. We show that the dipolar coefficient of a prolate spheroid reduces to that of a sphere in the corresponding limit, but deviates strongly from it when the eccentricity of the spheroid is large, for the same particle volume. We also verified that a previously published analytical theory (Chassagne and Bedeaux, J. Colloid Interface Sci., 326:240,
2008
) is in good agreement with the numerical results for a large range of zeta potentials, ionic strengths, and frequencies.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Purpose
Sediment organic matter (SOM) influences settling and thus the rheological behavior of suspended particles by enhancing flocculation or reducing surface charges by forming organo-mineral ...complexes that facilitate particle–particle interactions in consolidating sediments. It was, therefore, assumed that the microbial degradation of SOM and its spatio-temporal variability would affect sediment rheological properties and enhance port maintenance dredging and navigability of ports and waterways.
Methods
To investigate this effect, samples were taken at six locations along a transect of 30 river kilometers through the Port of Hamburg, Germany, during nine sampling campaigns within two years. The collected samples were divided into different layers based on the differences in visual consistency and strength. For analysis of SOM degradability, the samples were incubated in the laboratory for 250 days in glass bottles under aerobic and anaerobic conditions following the evolution of gas composition (CH4, CO2) and pressure in the bottle headspace over time. Yield stress was analyzed before and after the dissolved organic matter (DOM) decay using a rheometer with Couette geometry. Standard properties of solids and pore water were also analyzed.
Results
Shear strength decreased upon SOM decay under both anaerobic and aerobic conditions. Under anaerobic conditions, organic matter decay reduced static and fluidic yield stresses to an average of 74% and 79% of the fresh sample values. Consolidated layers at lower depths showed the highest absolute decrease in fluidic yield stress of up to –110 Pa due to a larger absolute amount of degradable organic matter in these layers in connection to higher bulk density. Pronounced spatial trends with higher changes in yield stress at upstream locations and lower yield stress changes at downstream locations coincided with a decreasing gradient of SOM degradability from upstream to downstream. Seasonal trends indicated that the investigation area is impacted by temporally changing factors.
Conclusion
The availability of easily degradable organic matter significantly affects sediment strength, especially under the anaerobic conditions, even when the mass loss of organic matter mass loss is small. Seasonal variability in yield stress changes upon SOM decay indicate that the site-specific responses were modulated by overarching seasonal effects impacting the entire investigation area. It was assumed that during an anaerobic decay, the formation of gas bubbles added an additional physical component to the effect of biological SOM decay.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Influence of pH and ionic strength on shear-induced kaolinite flocculation behavior.
The relation between the electrokinetic charge of kaolinite particles and their flocculation behavior has been ...investigated over a wide range of pH and added salt (for
MgCl
2
and NaCl salts). All flocculation experiments have been done with a mixing jar (sediment volume concentration
φ
=
3.84
×
10
-
5
). The electrokinetic charge of particles in different suspensions has been assessed by electrophoresis while laser diffraction has been used to measure the floc size distribution. Mixing jar experiments can be successfully used to investigate the flocculation behavior of kaolinite at shear rates higher than or equal to
G
=
35
s
-
1
, which is the shear rate used in the experiments. At lower shear rates, the floc size distribution is affected by particle settling. The electrophoretic mobility of kaolinite decreases in absolute value when the pH of the suspension decreases. This is reflected in an increase of both floc size and flocculation rate: the floc size at pH 4 is three times larger than at pH 7 and the flocculation time is one order of magnitude smaller (from 1000 to 100
min). When the ionic strength of the suspension is increased, the electrophoretic mobility and the mean floc size display the same variations. On addition of NaCl (pH 9) both the electrophoretic mobility and the floc size display an optimum around 1
mM of added salt, a feature that has been observed by other authors as well. The equilibrium floc size for a suspension (A) at 1
M of added NaCl and pH 9 is the same as for a suspension (B) at pH 2 with no added salt. However, the time needed to reach the equilibrium for suspension (A) is one order of magnitude larger than for suspension (B). This is due to edge-face Coulombic attraction in suspension (B). The equilibrium floc size obtained by addition of
MgCl
2
or sea salt at pH 9 is similar to the size obtained by addition of NaCl. The flocculation rate for a suspension with added
MgCl
2
is higher than for suspensions with other added salts.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The hydrodynamic size and electrophoretic mobility of sulfate latex nanospheres are given as a function of ionic strength for KCl and MgCl2 and at different volume fractions. The results were ...obtained from Doppler velocimetry and Dynamic Light Scattering using a Malvern ZetaSizer Nano (ZetaNano) at 173 degree scattering angle and a Malvern ZetaSizer 3000HSA (Zeta3000) at 90 degree scattering angle. Although the instrumentation is similar, we observed differences in the hydrodynamic radii. The reason for these discrepancies are most probably due to the conversion of the detected light intensity into particle radius since the particles have a diameter of about 530 nm (measured by TEM) quite close to the lasers' wavelength (633 nm). From the study, we found in particular that the hydrodynamic radius decreases upon addition of monovalent or divalent salt. This behavior is generally attributed to the presence of a hairy layer on the particle's surface. We also found that the electrophoretic mobility decreases logarithmically with increasing particle concentration, as predicted for nearly salt-free conditions. The change in viscosity at higher ionic strength and the shift in the shear plane position are shown to play a role in the aggregation behavior.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Context:
Bone giant cell tumors (GCTs) are among the most common benign bone tumors and affect mostly young patients. They represent a rare etiology of head and neck cancer.
Objective:
We report the ...case of a 38-yr-old male with a GCT of the thyroid cartilage, initially treated as a thyroid cancer.
Case Illustration:
The patient had incomplete initial surgery, and a substantial tumor residue was observed at postoperative morphological evaluation. Given the potential risks associated with complete definitive surgery and recent data supporting the use of the receptor activator of nuclear factor κB ligand inhibitor, we proposed treatment with denosumab. Three months after initiating denosumab, computed tomography scan imaging showed a significant modification of the lesion with several calcifications. The patient underwent partial laryngectomy, and examination of the surgical specimen revealed a complete histological response.
Results:
A review of the literature was conducted to identify previous studies pertaining to GCTs, focusing on reports related to their management.
Conclusion:
Denosumab emerges as a new treatment for patients with GCTs. Additional clinical trial data are needed to establish the real efficacy and long-term safety of this treatment for the management of GCT.
Flocculation between inorganic sediment, salt ions and microscopic organic matter present in the marine environment might play an important role in the dynamics of turbidity currents. The ability to ...predict, understand, and potentially leverage the effect of flocculation on turbidity currents will help to minimize the impact of human interventions such as dredging, trenching, and deep-sea mining. To better characterize the effect of flocculation on the benthic turbidity currents generated by these activities, a series of laboratory experiments were performed. Turbidity currents were created by means of lock exchange experiments. The present work focuses on the flocculation of clays that are representative for abyssal regions where deep-sea mining is performed, but most of the conclusions of this work are generic and can be applied to other types of benthic flows, occuring in harbours and channels. The effect of salt and organic material as flocculant agent was investigated. Various concentrations of clay and organic flocculant were tested. Video analysis was used to determine the head velocity of the plume. Samples at different run-out lengths were collected at the end of the lock exchange experiments for particle size and settling velocity measurements. The velocities of the turbidity currents in fresh and saline water (when no organic matter was present) were found to be similar, which was expected considering the timescales of salt-induced flocculation (about 30 min or more compared to the duration of lock exchange experiment <60 s). It was however demonstrated that, in presence of organic matter, flocculation occurred during the short time (30–60 s) of the experiment, leading to a reduced current propagation and a significant change in floc sizes (from 20 to 1,000 µm) and settling velocities (from 1 to 60 mm s
−1
). Salt ions contributed to flocculation in the sense that flocculation with organic matter was improved in the presence of salt.
Electrophoretic mobility of a kaolinite suspension expressed as a zeta potential using the Smoluchowsky formula. The dashed curve represents the prediction according to the standard theory.
In this ...article a new formula for the electrophoretic mobility of a spheroidal colloid is given. This formula and the formula presented in Chassagne and Bedeaux C. Chassagne, D. Bedeaux, J. Colloid Interface Sci. 326 (2008) 240–253 for the dipolar coefficient of a spheroidal colloid are intertwined. The combination of electrophoresis and complex conductivity measurements (from which the dipolar coefficient can be derived) allows to assess both the zeta potential and the Stern layer conductance. We will in particular show that the values found for the zeta potential from both techniques are similar in the case of the kaolinite suspension studied. Electrophoretic mobility data are also presented and discussed for a wide range of ionic strengths, different types of salt and various pH. This data has been used in flocculation studies on the same kaolinite samples F. Mietta, C. Chassagne, J.C. Winterwerp, J. Colloid Interface Sci., accepted for publication,
doi:10.1016/j.jcis.2009.03.044.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Despite recent advancement in the field of sediment transport, the integration of cohesive sediment properties in large-scale transport models remain a challenging task. In order to model adequately ...the change in particle size that occurs in different environmental conditions, flocculation models based on the so-called Population Balance Equations (PBE) are often used. These models have to be efficient enough to be implemented in numerical transport models, and as full PBE's are time-expensive to run and depend on a huge amount of a-priori unknown parameters, simplifications have to be made. These simplifications comes unavoidably at the cost of properly accounting for the complex particle-particle and particle-fluid interactions. In order to stay as close as possible to the physical processes, we propose a different approach based on a logistic growth model that mimics the Particle Size Distribution (PSD) measured over time for all size classes. The parameters of the model can easily be found from laboratory measurements. In contrast to most models, the particle classes we propose are not defined by particle size, but in terms of mineral sediment composition. One class is composed of (unflocculated) mineral sediment particles, another of flocculated sediment particles and a third one of organic particles. The mass balance between classes and the way to obtain their corresponding average settling velocity are given. Mass balance and settling velocities are the required input parameters for all sediment transport models. The simplicity of the derived expressions, and their link with measurable variables, makes them good candidates for future implementation in such models.
•Population Balance Equations are not suitable for implementation in transport model.•Logistic growth models can be an alternative to Population Balance Equations.•Logistic growth models can be parametrized thanks to laboratory experiments.•Logistic growth models can be implemented in transport models.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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