Calcination of dredged sediments: Investigation of the behaviour of heavy metals and the organic compounds

Abstract

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 investigation of the behaviour of the heavy metals and organic compounds during calcination of the phosphated dredged sediment. Afterwards, the structural change of the sediment during thermal treatment was investigated: particle size, specific surface area, density and the porosity changes of the treated sediment in relation with the vaporization of heavy metals.