Characterization and kinetics of surface area reduction during the calcination of dredged sediments

The deposit of sediment causes the silting of channels, rivers and lakes. This completely natural phenomenon is exacerbated by the introduction of industrial and urban wastes into the erosion and sedimentation process. Consecutively, other problems appear, such as flooding risks, decrease of biological purification capacity and associated loss of the biodiversity. The presence of toxic compounds (from industrial, household or agricultural origins) in the sediments worsens the situation, and requires curing to restore the natural environment and its function. This study assesses the technology to treat heavy metals from dredged sediments using phosphoric acid (The Novosol® Process, developed by Solvay) with the goal of converting metals, mainly Pb, Cd, Zn and Cu to insoluble metallic phosphates, and engineering properties (by calcination) of the final residues for the beneficial use. The effectiveness of the treatment was evaluated by performing the chemical reaction, followed by convective drying and maturation of the treated sediment at ambient temperature and finally calcination (400 °C–1000 °C). This paper is focused on the calcination of the phosphated dredged sediment that destroys the organics and generates the particle size, specific surface area and the porosity changes of the treated sediment.

This study assesses the technology to treat heavy metals from dredged sediments using phosphoric acid (The Novosol® process, developed by Solvay) with the goal of converting heavy metals to insoluble metallic phosphates, and to destroy the organics by calcination. Our objective is to understand the physicochemical behaviour of the sediment during calcination. The understanding of the evolution on these properties will help for the beneficial reuse of the treated sediment in various industries such as civil engineering. The results show a significant structural change of the sediment during thermal treatment. An increase in specific surface is observed until 400°C followed by a significant reduction accompanied by a densification and growing of the particles that is explained by the sintering that occurs during thermal treatment.Figure options