Phase Transition of Partially Miscible Solvents Induced by Heating Cycles: Application for the Remediation of Contaminated Sediments and Sludge

A novel process entitled “Sediments Remediation Phase Transition Extraction” (SR-PTE) is being developed for a simultaneous removal of both heavy metals and organic pollutants from contaminated sediments or sludge. The process uses partially miscible solvent mixtures, where one of the components is water. By heating the mixture above a certain temperature, a single phase is formed. This allows the organic solvent, containing an appropriate chelating agent, to penetrate the wetted sediment voids and efficiently extract simultaneously the organic and heavy metal pollutants. The phase separation, occurring during the cooling stage, is fast and allows the pollutants to propagate and concentrate in the lighter organic phase, leaving the sediments and the lower aqueous phase practically clean. The SR-PTE technology was tested on authentically polluted river sediments and on heavily contaminated sludge from a waste-water treatment plant. The extraction efficiency was found to improve by the phase transition cycle induced by temperature variation (about twice than that obtained when the extraction was carried out isothermally). Additionally, with the induced phase transition, the formation of stable emulsions is prevented albeit the presence of natural surfactants in the treated media. The process was tested on lab scale and bench-scale reactor. No significant effects of the process up-scaling from lab to bench scale were observed.