Cadmium adsorption on vermiculite, zeolite and pumice: Batch experimental studies Maria Rosaria Panuccio * , Agostino Sorgona `, Marcella Rizzo, Giovanni Cacco Dipartimento di Biotecnologie per il Monitoraggio Agroalimentare ed Ambientale (BIOMAA) Universita ` degli Studi ‘‘Mediterranea’’ di Reggio Calabria, Localita ` Feo di Vito, Reggio Calabria I-89133, Italia, Italy Received 30 January 2007; received in revised form 7 September 2007; accepted 12 October 2007 Available online 21 December 2007 Abstract Batch experiments were performed to evaluate the combined effects of ionic activity, pH, and contact time on the cadmium sorption in three different minerals, vermiculite, zeolite, and pumice, commonly employed as substrata in nurseries and recently considered for their potential use in remediation methods. The extent of cadmium sorption was vermiculite > zeolite > pumice, as shown by the Langmuir and Freundlich param- eters, and it was highly dependent on mineral characteristics. The percentage of cadmium sorption in zeolite and vermiculite did not depend on cadmium concentration, while in pumice this percentage was positively correlated to the initial cadmium concentration. At low cadmium concentrations (30e120 mM), the metal sorbed on zeolite was mainly present in the nonexchangeable form (70%) at levels much higher than those found for vermiculite and pumice. The primary variable responsible for determination of cadmium mobility in these minerals was confirmed to be pH. The ionic concentrations of Hoagland nutrient solution were significantly modified by both pH and mineral composition, while the presence of cadmium caused no changes. With vermiculite and zeolite, the time-course of cadmium sorption was related to mineral composition to a greater extent than to cadmium concentration. While with pumice, the percentage of cadmium sorbed after 6 weeks was lower than with the other two minerals, and it was inversely correlated to the initial cadmium concentration. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Minerals; Cation; Heavy metal; Sorption; Cadmium 1. Introduction The bioavailability of metals in soil is a dynamic process that depends on specific combinations of chemical, biological, and environmental parameters (Li and Thornton, 2001; Peijnenburg and Jager, 2003). Metals may be present in several different physicochemical phases that act as reservoirs of trace elements in the environment. The adsorptionedesorption reac- tions at the particle-solution interface are primarily involved in the control of metal bioavailability in soil systems, and the ac- cessible fractions may differ greatly, ranging from free metal ions in solution to completely solid metal. Soluble, exchange- able, and loosely adsorbed metal ions are quite labile and hence more available for uptake by microorganisms or plants. Therefore, to assess environmental risk and the availability of metals, efforts should be concentrated on collecting measurements of these avail- able fractions in soil (Kabata-Pendias, 1993; Wang et al., 2004). Cadmium belongs to the very hazardous heavy metal group. It is fairly mobile in soil and is primarily present as an organically bound, exchangeable, and water-soluble species (Holm et al., 1995; Chlopecka, 1996). On the basis of general adsorption mechanisms identified for cadmium, the surface complexation to calcite and oxides, such as aluminium, iron, and manganese oxides, may be the most prominent adsorption mechanism at low cadmium concentrations (<10 5 M). Meanwhile at higher concentrations (>10 5 M), a non-spe- cific adsorption process, such as cation exchange, is the likely controlling mechanism (Brummer et al., 1988). Several factors * Corresponding author. Dipartimento Biotecnologie per il Monitoraggio Agroalimentare ed Ambientale (BIOMAA), Universita ` degli Studi ‘‘Mediter- ranea’’, Feo di Vito, I-89061 Reggio Calabria, Italia, Italy. Tel.: þ39 0965324077; fax: þ39 0965311092. E-mail address: mpanuccio@unirc.it (M.R. Panuccio). 0301-4797/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2007.10.005 Journal of Environmental Management 90 (2009) 364e374 www.elsevier.com/locate/jenvman