Remediation of heavy metals contaminated soils by ball milling Selena Montinaro a , Alessandro Concas b , Massimo Pisu b , Giacomo Cao a,b,c, * a Dipartimento di Ingegneria Chimica e Materiali, Universita ` degli Studi di Cagliari and Unita ` di Ricerca del Consorzio Interuniversitario Nazionale ‘‘La Chimica per l‘Ambiente’’ (INCA), Piazza d’Armi, 09123 Cagliari, Italy b CRS4, Center for Advanced Studies, Research and Development in Sardinia Parco Scientifico e Tecnologico, Polaris, Edificio 1, 09010 Pula, CA, Italy c Centro Interdipartimentale di Ingegneria e Scienze Ambientali (CINSA) and Cagliari Laboratory of Consorzio Interuniversitario Nazionale ‘‘La Chimica per l’Ambiente’’ (INCA), Via San Giorgio 12, 09123 Cagliari, Italy Received 20 June 2006; received in revised form 2 November 2006; accepted 3 November 2006 Available online 22 December 2006 Abstract In the present work, the use of ball milling reactors for the remediation of lead contaminated soils was investigated. Lead immobi- lization was achieved without the use of additional reactants but only through the exploitation of weak transformations induced on the treated soil by mechanical loads taking place during collisions among milling media. The degree of metal immobilization was evaluated by analyzing the leachable fraction of Pb(II) obtained through the ‘‘synthetic precipitation leaching procedure’’. The reduction of leach- able Pb(II) from certain synthetic soils, i.e., bentonitic, sandy and kaolinitc ones, was obtained under specific milling regimes. For exam- ple, for the case of bentonitic soils characterized by a Pb(II) concentration in the solid phase equal to 954.4 mg kg 1 , leachable Pb(II) was reduced, after 7 h of mechanical treatment, from 1.3 mg l 1 to a concentration lower than the USEPA regulatory threshold (i.e., 0.015 mg l 1 for drinkable water). Similar results were obtained for sandy and kaolinitic soils. X-ray diffraction, scanning electron microscopy, electron dispersive spectroscopy and granulometric analyses revealed no significant alterations of the intrinsic character of sandy and bentonitic soils after milling except for a relatively small increase of particles size and a partial amorphization of the treated soil. On the other hand, the mechanical treatment caused the total amorphization of kaolinitic soil. The increase of immobilization efficiency can be probably ascribed to specific phenomena induced by mechanical treatment such as entrapment of Pb(II) into aggregates due to aggregation, solid diffusion of Pb(II) into crystalline reticulum of soil particles as well as the formation of new fresh surfaces (through particle breakage) onto which Pb(II) may be irreversibly adsorbed. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Ball milling; Soil remediation; Heavy metals; Immobilization 1. Introduction Heavy metals such as Pb(II) are widespread in urban and industrial areas as a consequence of lead dispersion due to the production and recycling of lead batteries, metal mining, smelting and refining, gasoline processing, storage, distribution and production of painting materials and their use (Paff and Bosilovich, 1995). Since inhalation and inges- tion of Pb(II) may cause various health diseases such as anemia, neuropsychological effects and teratogenic impli- cations (Needleman and Bellinger, 1991) remediation tech- niques of lead contaminated soils are of great interest (Nedwed and Clifford, 1997). Remediation of heavy metal contaminated soils is recognized to be one of the most dif- ficult problem to be solved by taking advantage of suitable technologies (Sheppard and Thibault, 1992; Abramovitch et al., 2003). Typical remediation techniques are consti- tuted by extraction and immobilization processes. The aim of extractive processes is to remove Pb(II) from the soil 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.11.009 * Corresponding author. Address: Dipartimento di Ingegneria Chimica e Materiali, Universita ` degli Studi di Cagliari and Unita ` di Ricerca del Consorzio Interuniversitario Nazionale ‘‘La Chimica per l‘Ambiente’’ (INCA), Piazza d’Armi, 09123 Cagliari, Italy. Tel.: +39 070 675 50 58; fax: +39 070 675 50 57. E-mail address: cao@visnu.dicm.unica.it (G. Cao). www.elsevier.com/locate/chemosphere Chemosphere 67 (2007) 631–639