Morpho-granular approach to characterize harbour sediments and their agglomeration/dispersion behaviour

• Physicochemical and granular characterization of solid fractions of sediments
• Study of agglomeration/dispersion/aggregation phenomena by granulometry and SEM
• Proposition of a method using laser granulometry to classify different sediments
• Optimization of particle size selection for sieving method

An exhaustive physico-chemical and morpho-granular characterization of sediments collected in Port-Camargue harbour was investigated to improve marine sediment knowledge and to study inter-particle phenomena (granular properties and agglomeration/dispersion state). In the context of dredging framework, these phenomena could lead to disperse pollution in water column through chemical mobilization (dissolution or sorption phenomena) and/or physical mobilization (dispersion/agglomeration phenomena). Moreover they could disturb sedimentation behaviour which may lead to take pollution away from harbour. This work was focused on particle solid phase of sediment. Granular aspects were jointly studied with laser granulometry, electrophoresis measurements and Scanning Electron Microscopy (SEM). Chemical and mineralogical properties were mainly characterized with X-ray Diffraction (XRD) and Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM–EDX). These analyses were performed on bulk sediments and size fractioned sediments (< 20 μm; 20–40 μm; 40–63 μm; 63–80 μm; > 80 μm). Results showed that sediments can be differentiated by their granular properties (different in size distribution, shape and inter-particle interactions). A classification was proposed in function of their particle size distribution and silt percentage (very low proportion of clay is neglected): silty, silty sand and sand sediments. Furthermore, due to the presence of agglomeration/aggregation and dispersion behaviours, a morpho-granular approach was used to identify different types of agglomerates/aggregates. To minimize the impact of these phenomena on separation process of size fraction, often needed to investigate these systems, an optimized method was developed for sieving with a mechanical agitation and rinsing.This experimental work could therefore supplement and enrich the chemical and biological approaches of marine sediments observed in the more conventional pollution mobilization studies.

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