The efficiency of vermiculite as natural sorbent for heavy metals. Application to a contaminated soil

Vermiculite is a natural clay that has many applications as acoustic and thermal insulator, additive in concrete and plaster, fertilizer carrier and adsorbent. Moreover, clay minerals have been studied as adsorbent materials to remove heavy metals from industrial and/or municipal waste waters. In this work we have investigated the possibility to apply vermiculite for the clean-up of extracts resulting from the application of soil washing to a metal-contaminated soil collected from a polluted site in Italy. The soil was initially characterized for its total metal content; we also studied the availability of the pollutants by leaching at pH 5.0 and by Tessier's sequential extraction procedure. We tested a possible clean-up strategy, in which metals were extracted with hydroxylammonium chloride and vermiculite was used as natural sorbent for the decontamination of the extracting solutions. The possibility of recovering the metals by elution with acid and of reusing the clay was also demonstrated.