On the Kaolinite Floc Size at the Steady State of Flocculation in a Turbulent Flow

Abstract

The flocculation of cohesive fine-grained sediment plays an important role in the transport characteristics of pollutants and nutrients absorbed on the surface of sediment in estuarine and coastal waters through the complex processes of sediment transport, deposition, resuspension and consolidation. Many laboratory experiments have been carried out to investigate the influence of different flow shear conditions on the floc size at the steady state of flocculation in the shear flow. Most of these experiments reported that the floc size decreases with increasing shear stresses and used a power law to express this dependence. In this study, we performed a Couette-flow experiment to measure the size of the kaolinite floc through sampling observation and an image analysis system at the steady state of flocculation under six flow shear conditions. The results show that the negative correlation of the floc size on the flow shear occurs only at high shear conditions, whereas at low shear conditions, the floc size increases with increasing turbulent shear stresses regardless of electrolyte conditions. Increasing electrolyte conditions and the initial particle concentration could lead to a larger steady-state floc size.

Dynamics of fluvial hydro-sedimentological, nutrient, particulate organic matter and effective particle size responses during the U.K. extreme wet winter of 2019–2020

“…Here, entrainment of less cohesive deposited fine sediment during the rising limb of hydrographs may be responsible for the finest floc sizes at peak flows ( Sander et al, 2011 ). Additionally, orthokinetic flocculation processes can decrease floc size during progressively rising Q since shear flow may disaggregate fragile and loose flocs into smaller flocs/primary particles in highly turbulent river systems ( Jarvis et al, 2005 ; Zhu et al, 2016 ; Byun and Son, 2020 ). The increased silt size (<64 μm) floc volume with Q ( Fig.…”

“…Understanding the size characteristics of flocs is particularly important for elucidating the fate of sediment and associated contaminants and nutrients in rivers, lakes and reservoirs, since flocculation has important implications for hydraulic behaviour i.e., the deposition in and dispersal through, fluvial systems ( Grangeon et al, 2014 ; Hoffmann et al, 2020 ). In these cases, floc size distribution is a crucial factor potentially leading to differing deposition rates in water than the rates for individual particles alone ( Zhu et al, 2016 ; Lamb et al, 2020 ) with significant impacts on light penetration, contaminant and nutrient concentrations and likelihood of retention on, or in, the river bed ( Ahn, 2012 ; River and Richardson, 2018 ). Therefore, local floc-size distributions determine the dynamics of suspended sediment fluxes in aquatic systems and associated transport of carbon (C), nutrients and contaminants ( Lamb et al, 2020 ).…”

Physical and hydrodynamic properties of deep sea mining-generated, abyssal sediment plumes in the Clarion Clipperton Fracture Zone (eastern-central Pacific)

“…The calculation of the mean shear rate G (s -1 ) produced in the chamber followed Van Duuren's (1968) method. The Couette flow reactor was used instead of other mixing devices, such as an oscillating grid or paddle mixer, because of the uniformity of the produced turbulent shear flow and the absence of mixing mechanisms that prevent aggregate breakup during mixing (Coufort et al, 2005;Serra et al, 2008;Zhu et al, 2016). Each experimental approach has limitations but as Serra et al (2008) concluded, the Couette reactor is still the most suitable method for aggregating particles without interference.…”

Chemometric Optimisation of a Copper Sulphide Tailings Flocculation Process in the Presence of Clays

“…The mean shear rate as a descriptor of mixing was characterised using the average velocity gradient (G) in turbulent regime and the circulation time (t c related with the frequency of exposure of the aggregates to the impeller zone), as described by Spicer et al [19] and Zhu et al [23]. The parameter G is described by:…”