Combining trace elements micro-analysis in deposited dredged sediments: EPMA and μ-XRF analysis

Abstract

Since deposited dredged sediments are rich in metallic contaminants, they present a risk for environment. This work aims to study dredged sediments chemical composition, identify metal-carrier minerals and understand their mobility. Combining chemical and spectroscopic techniques at multi-scale for an integrative approach of trace elements (zinc, lead, iron) behaviour is therefore necessary. The global mineralogy and the chemistry of the sediment were determined by X-ray diffraction and fluorescence (XRF), respectively. Zn and Pb enriched fractions were separated using a sequential chemical extraction procedure and measured by inductively coupled plasma atomic emission and mass spectroscopy. Microanalyses using scanning electron microscopy (SEM), electron microprobe microanalysis (EPMA), combined with synchrotron radiation X-ray fluorescence (μ-XRF) were carried out to characterize mineralogical phases and identify Zn and Pb carrier minerals. Iron oxyhydroxides and iron sulphides were consistently identify as Zn and Pb carriers. The assumption that carbonate fraction was the major Zn carried phase, as demonstrated by chemical extraction results, was not verified by EPMA or μ-XRF.