A comparison between Fe0/pumice and Fe0/lapillus mixtures in permeable reactive barriers

Recent experimental studies have shown that it is possible to improve the hydraulic and reactive behaviour of permeable reactive barriers (PRBs) composed of zero-valent iron (ZVI) by admixing this reactive medium with volcanic materials such as lapillus or pumice. In this study, the adsorption behaviour of lapillus and pumice was evaluated through batch tests carried out using nickel- and zinc-contaminated solutions at three different initial concentrations (5, 10 and 50 mg/l). It was observed that the lapillus sorption capacity is four and eight times higher than that of pumice for nickel and zinc, respectively. The comparison of column tests results, carried out using mixtures of ZVI/pumice and ZVI/lapillus with two different contaminated solutions (nickel and zinc at initial concentration of 50 mg/l), has shown that the best performance is by the ZVI/lapillus mixtures. In fact, thanks to the contribution of lapillus to contaminant removal, the use of ZVI/lapillus mixtures would allow reducing PRB thickness compared to the use of ZVI/pumice mixtures when the same mass of ZVI is considered. A column test carried out with lapillus only has also shown that it is possible to use the latter as a reactive medium in PRBs in the presence of low concentrations of contaminants.