Heavy metals extraction with the SRPTE process from two matrices – Industrial sludge and river sediments

• A process for simultaneous removal of heavy metals and organic pollutants is presented.
• High efficiencies and short treatment times are demonstrated for both river sediments and sludge.
• The process is not sensitive to the presence of surfactants and emulsion formation is not encountered.
• Scale-up effects from lab to bench scale are insignificant.

A study on the treatment of authentically polluted river sediments and heavily contaminated sludge from waste-water treatment plant was conducted. It employs the process entitled “Sediments Remediation Phase Transition Extraction” (SR-PTE), which is being developed for a simultaneous removal of both heavy metals and organic pollutants. The process involves, in addition to chelating agents, use of partially miscible solvent mixtures, where one of the components is water, and therefore is beneficial for treating wet media. The extraction of the contaminants is carried out in the single phase state of the solvent–water system, avoiding the mass transfer resistance of interfacial barriers and improving the penetration to the wetted matrix voids. Therefore, efficient simultaneous extraction of the organic and heavy metal pollutants is achievable. The stage of phase separation occurs while cooling the mixture to room temperature. It is fast, with no emulsion formation. The chelating agent used in the present study is ammonium diethyldithiocarbamate, as its metal chelates are soluble in organic solvents. Thus, the extracted organic pollutants and metal ions concentrate in the lighter (mainly) organic phase, while the treated solids settle into the relatively clean (mainly) aqueous phase. Fast process with high removal efficiency was obtained mainly for Cu, Cd, Ni, and to some lower extent for Pb, while essential metals such as Fe, Mg and Ca are retained in the treated media. The effect of various operational conditions on the process efficiency was studied. The up-scaling from lab scale to a bench-scale reactor was also examined indicating no significant effect on the process efficiency.