Flash-Calcined Sediments for Zinc Adsorption

Heavy metal contamination of the environment could pose health risks to humans. Until recently, several geochemical routes were considered to address the issue of metallic leachates from sources such as e-waste deposal sites or mining areas. Following the adsorption pathway, this study focused on investigating the ability of calcination products as a low-cost option for the remediation of zinc contaminated effluents. Sediments dredged in northern France were calcined by flash calcination method, before testing the calcination products (FCS750 hereafter) as adsorbent for zinc removal. The calcination process performed at 750 °C resulted in a denser material with a higher specific surface area and lower organic matter content, suited for aqueous remediation. Kinetic and equilibrium assessment underlined a rapid adsorption better described with the Pseudo Second Order model than the Pseudo First Order or Bangham equations. Adsorption models (Langmuir, Freundlich and Temkin) implemented to describe the interaction under two pH conditions (pH = 2; pH = 7) resulted in a maximum adsorption capacity (qmax) of 89.61 mg g−1 under the most favourable configuration. The pH conditions had poor influence on the adsorbing capacity value, which suggested a good buffering property of the calcined sediment and a potential applicability on effluents with different chemistries. A qmax comparison based on 42 studies indicated that FCS750 was more beneficial than most raw organic adsorbents but remained less effective than grafted and composite materials. Nevertheless, the low number of steps necessary for FCS750 processing, the easy access of its precursor (harboring wastes) and its low energy cost suggested good economic competitiveness and pleaded in favor of field experimentations.