Modified Red Muds and Slag Based Hydraulic Binders for Zn Removal: A Matrix-Spiking Approach Applied on Clayey Sediments

Abstract

Dredging sediments can be implemented as primary resources in several civil engineering applications, on the condition that the release of anthropogenic compounds meets environmental requirements. The remediation of sedimentary wastes constitutes therefore, a key step before valorization consideration in circular economy schemes. This study focused on Zn removal from clayey river sediments dredged in northern France (Lille, Saint-Omer and Aire-Sur-La Lys) using a Thermo-Evolved Red Mud (TERM) and a Slag Based Hydraulic Binder (SBHB). The first step consisted in investigating Zn-trapping mechanisms prior to TERM and SBHB application as Zn-stabilizers. Results underlined poorer metal retention within the most organic sediment (high fatty acids and polycyclic aromatic molecules concentrations), emphasizing the minor role of the organic fraction typology during Zn-trapping. The pollutant displayed its best binding yields within the sediment with the highest interstitial pH and specific areas, which stressed out the preponderant influence of alkalinization ability and particles size distribution. In a second step, the spiked sediments were treated with TERM and SBHB, which resulted in a substantial lowering of Zn release at 12% of stabilizer/sediment ratio. Even though the organic content role was not preeminent during the pollutant trapping, it appeared here influential as delays in removal efficiencies were observed for the most endowed sediment. Two preferential geochemical pathways were adopted during the remediation operations with significant promotive roles of basic background pH. Indeed, Zn removal with TERM consisted mainly in sorptive mechanisms involving exchanges with Ca and Mg ions, whereas binding onto SBHB was principally achieved through precipitation phenomena.

Flash-Calcined Sediments for Zinc Adsorption

“…The closeness of these two values suggested a buffering effect of FCS 750 instead of a significant influence of the initial pH on the uptake process. Contrary to this observation, several studies suggested an increase of Zn stabilization at pH = 7 as a response to growing alkalinity [51]. This was not observed here, probably due to the impact of FCS 750 on the acido-basic configuration of the medium during the blending steps.…”

“…To evaluate the stabilizing capacity of FCS 750 on polluted solid matrices, three different fluvial sediments (La Deule, Aa and La Lys) were spiked with Zn solutions before treatment. The mechanisms of Zn-trapping and its promoting factors are described in a previous study [51]. This study indicated that the Aa sediments had the best Zn retention properties because of a higher alkalizing capacity.…”