Dredging of sediments is necessary in order to maintain maritime activities and for flood prevention. However the increased industrial activities are causing accumulation of pollutants in the sediments. The main contaminants are heavy metals and organic compounds. Because of the cost of storage, treatment and valorization can be economically sound. This study focuses on the technology to treat heavy metals from dredged sediments using phosphoric acid (H3PO4) (the Novosol® process developed by Solvay company) with a goal to stabilize heavy metals by capturing them in calcium phosphate matrix and to destroy organic matter by calcination at 650°C. Several studies have been conducted in this field. The stabilized materials obtained have been used in civil engineering. However these studies have never assessed the effect of the composition of the phosphoric acid on the treatment. In this paper the effect of two types of phosphoric acids with various composition and origins were compared. The investigation focuses on the effect of the phosphoric acids on the environmental behavior of metals and on the geotechnical properties of the dredged sediment.

a b s t r a c tDredging operations produce considerable quantities of materials, to be managed and this opens an opportunity for valorization in civil engineering. However, the contamination of the dredged sediments has become a major problem to solve. The major contaminants are heavy metals and organic compounds. This study focuses on the use of phosphoric acid (H 3 PO 4 ) to stabilize heavy metals from sediments and destroy organic matter by calcination at 650 °C with a goal of using sediments in roadworks. Several studies have been conducted in this field. The stabilized materials obtained have been used in civil engineering. The main purpose of this work is to discuss the environmental behavior of marine sediment treated by phosphatation and calcination. Two types of phosphoric acids were used. The pH dependence leaching test has been used as the basic characterization to evaluate the effect of the type of phosphoric acid on the metals behavior in a valorization scenario. The standard leaching test and the Toxicity Characteristic Leaching Procedure (TCLP) were conducted as compliance tests. In regards of the obtained results, the environmental assessment has also shown a reduction in the availability of targeted heavy metals in alkaline environment whatever the type of acid used for treatment. This opens opportunities for co-valorization.

Sediment deposits cause 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. Other problems then appear, such as an increased risk of flooding, a reduced capacity for biological purification, and an associated loss of biodiversity. The presence of toxic compounds in the sediments (of industrial, household, or agricultural origin) worsens the situation, and measures must be taken to restore the natural environmental conditions and processes. This study assesses the technology of treating heavy metals from dredged sediments using phosphoric acid (the NOVOSOL process, which was developed by SOLVAY), which aims to convert metals, mainly Pb, Cd, Zn, and Cu, into insoluble metallic phosphates, and (by calcination) to engineer the properties of the final residues for beneficial use. The effectiveness of this treatment was evaluated by creating the chemical reaction, followed by convective drying and maturation of the treated sediment at ambient temperature, and finally by calcination (400−1000°C). This paper focuses on the study of the decomposition of organics and structural change in the sediment during thermal treatment in a rotary kiln. The results showed that the specific surface, the particle size, and the total organic of the sediment are dependent on the calcination parameters such as the residence time, the calcination temperature, and the flow rate. The degradation of the organic compounds is effective at 600°C. An increase in specific surface is observed until 600°C, followed by a significant reduction accompanied by a densification and growth of particles. This increase in specific surface area observed attributed to the formation of pores due mainly to the decomposition of organics and the gas evolve (CO 2 , H 2 O, ...) from 600°C to 900°C.