Rationale of heavy metals immobilization by ball milling in synthetic soils and remediation of heavy metals contaminated tailings

In thiswork, the use of mechanical milling for the remediation of heavy metals in synthetic soils and tailings sampled fromthe mining area of “Barraxiutta”, SW of Sardinia, Italy is investigated. Specifically, Pb(II) contaminated synthetic soils of sandy, bentonitic and kaolinitic type are taken into account following the results obtained in previous works. Suitable sequential extraction procedures have been performed on both untreated and treated synthetic soils. It is found that mechanical loads which occur during collisions amongmillingmedia and soils are able to modify the distribution of Pb(II) onto the different solid fractions of contaminated synthetic soils. Such phenomena may contribute to Pb(II) immobilization efficiency since the heavy metal trans-speciation occurs in favor of fractions characterized by stronger bonds and lower solubility. As for the heavy metals contaminated tailings, their immobilization is obtained using both ball and attrition milling devices under specific ball to powder ratio values. The degree of metals immobilization is evaluated by analyzing the corresponding leachable fraction obtained through the Synthetic Precipitation Leaching Procedure (SPLP) proposed by EPA.