Remediation of Hg-contaminated marine sediments by simultaneous application of enhancing agents and microwave heating (MWH)

The aim of this work was to investigate Hg removal ability of a novel microwave heating (MWH) treatment for marine sediment remediation enhanced by the application of several agents, biodegradable complexing agent (methylglycinediacetic acid, MGDA), surfactant (Tween (R) 80), and citric acid. Main results revealed that MWH allowed a very rapid heating (similar to 450 degrees C in 7 min) of the irradiated medium. However, without the addition of enhancing agents, a maximum Hg removal of similar to 72% can be achieved. The application of MGDA led to a higher contaminant removal of similar to 87% (residual concentration = 5.4 mg kg(-1)). For the treatment including the simultaneous addition of both chelating agent and surfactant, their synergetic action and stripping processes resulted in a very high Hg removal of similar to 99% for an irradiation time of 7 min, corresponding to a residual concentration of 0.56 mg kg(-1), which is lower than the Italian regulatory limit of 1 mg kg(-1). The use of citric acid resulted in a shortening of the removal kinetics, which allowed the successful application of a shorter remediation time of 5 min. The observed strong passive ability of sediments to convert a microwave irradiation energy into a rapid and large temperature increase undoubtedly represents a key factor in the whole remediation process, making the studied treatment an excellent choice. Kinetic data are suitable for a preliminarily assessment of the effectiveness of clean-up activities, and as basis for future scaling-up studies on MWH of Hg-contaminated sediments