Innovative Reuse of Fly Ashes for Treatment of a Contaminated River Sediment: Synthesis of Layered Double Hydroxides (LDH) and Chemical Performance Assessments

Purpose This investigation presents a new valorization route of fly ash, based on the synthesis of layered double hydroxide (LDH) used as efficient and cost-effective adsorbent for the stabilization of contaminants in sediments. Methods LDH were synthesized through an acid leaching method at constant pH followed by precipitation, applied on waste paper fly ash (WPFA) and biomass fly ash (BFA), obtained from industries of the Hauts de France region. The synthesized LDH (LDH WPFA and LDH BFA ) were calcinated at 450 °C, their physico-chemical and adsorption properties were then compared before and after calcination, with a commercial hydrotalcite (HT). Results The XRD diffractograms of synthesized LDH showed characteristic bands of hydrocalumite Ca 4 Al 2 (OH) 12 (Cl,CO 3 ,OH) 2 ·4H 2 O and paraalumohydrocalcite (CaAl 2 (CO 3 )(OH) 4 .6H 2 O) for LDH WPFA and LDH BFA , respectively. The FTIR spectra showed similar patterns to LDH containing interlamellar anions (CO 3 2− and OH − ) in the vicinity of 1360 cm −1 and 3600 cm −1 . The LDH morphology presented platelets and hexagonal block shapes with some octahedral forms. The batch and column adsorption results showed that more than 98% of Sb, Zn and SO 4 2− were stabilized when the sediment matrix was amended with 5% of calcinated LDH WPFA , compared to untreated sediment, due to the negative charge of the surface. Conclusion Synthesized LDH were able to stabilize both cationic species (by adsorption and electrostatic attraction), and anionic species (by anion exchange) inside the sediment matrix. Graphical Abstract