A CRITICAL EVALUATION OF WASHING METHODS FOR HEAVY METAL REMEDIATION OF DREDGED SEDIMENTS

Today marine sediments dredged from coastal areas must be considered a resource of materials to be reused. For this purpose, innovative, effective and sustainable technological processes are needed in order to guarantee the possibility of reusing materials in various application sectors. Heavy metals are some of the pollutants with particular toxicity, persistence and bioaccumulation. In the sediments, metals are present in various chemical forms (speciation), the determination of which is fundamental for optimization of remediation process by washing. For this purpose in recent years, different techniques that use washes with chelating solutions have been tested for metals removal from contaminated marine sediments. This work critically illustrates the applications of washing method for metal remove from marine sediments, taking as a case study experiments conducted on sediments of the coastal area of Taranto. The aim of the study is to discuss the efficacy of selected chelating agents (EDDS, EDTA, citric acid, etc.) for sediment remediation. The effects of different operating parameters such as the type of washing solution, the reaction time, the concentration of the chelating solution, pH and the solution / sediment ratio are illustrated. The speciation of metals on treated and untreated sediments, performed with Tessier's sequential extraction method, proved to be a useful tool for assessing the mobility of heavy metals and changes in their distribution in the different phases after washing treatments. The kinetics of the extraction process for various metals and for the various chelating compounds are also presented. The final results show that the use of EDDS (ethylenediamine N, N'-disuccinic acid) as a chelant provided good extraction efficiencies unlike the lower removal rates found with the use of citric acid.