Removal of Cr(VI) in contaminated water of Stoppani S.p.a. site (Liguria, Italy) by surface active maghemite nanoparticles

The importance of the interface between geosphere and biosphere represents one of the most fascinating frontiers of mineral science.Heavy metal release, transport and dispersion into the biosphere have a direct impact on the environment and on human health.New technologies for water and soils remediation represent a main task, and magnetic nanoparticles emerge as one of the most promising mean in this field.Environmental applications and risk assessment of manufactured nanoparticles greatly depend on the understanding of their interactions with water and soils.Novel superparamagnetic nanoparticles (Surface Active Maghemite Nanoparticles, SAMNs) constituted of stoichiometric maghemite, characterized by specific surface chemical behavior without any coating or superficial modification, stable in water for months as colloidal suspensions, were used as adsorbent of chromium(VI) in water.SAMNs can be superficially modified by simple incubation in presence of K2Cr2O7, forming a hybrid nanomaterial, SAMN@Cr(VI), stable without any release of Cr(VI) in solution.The aim of this work is to test the efficiency of SAMNs for Cr(VI) removal from Stoppani Spa site, an extreme environmental polluted Cr(VI) site.Stoppani industry located in the Cogoleto and Arenzano Area (Genova, Italy), transformed Cr(III) from chromite mineral (FeCr2O4) (Piccardo et al., 1989) to Cr(VI).It ceased the activity at the beginning of 2003, and since 2001, the Stoppani S.p.A. has been included, with DM n.468, into the national program of environmental remediation and restoration.In the 1918-1982 period, it discharged up to 1 million tons of post-treatment mud on the neighbouring beaches, groundwater resulted heavily polluted by Cr(VI). The water samples object of this work are representative of 3 pumping wells distinguished on the basis on the Cr(VI)-content in: sample W1(527< Cr(VI) < 11700 g/lt); W6 (83800 < Cr(VI) < 146000 g/lt); W9 (10500 < Cr(VI) < 232000 g/lt).Water temperature, electrical conductivity, alkalinity by acidimetric titration, pH, and Eh were determined during sampling. In the laboratory, waters have been analyzed for: Mg, and Ca by AAS, Na and K by AES Cl, SO42-, and NO3- by ion-chromatography, Si, Fe, minor and trace elements by ICP-OES.The application of SAMNs (100 mg mL-1) of three water samples removed 75-80% of Cr(VI), while, if the same treatment was accomplished at pH 3.0, Cr(VI) removal was about 95% with respect the initial concentration.Temperature, in the 4-25 °C range, did not influence Cr(VI) removal by SAMNs.A second SAMN treatment on the same water samples increased Cr(VI) removal efficiency up to 98 %, leading to a final Cr(VI) concentration below the limits stated by Italian law.SAMNs represent efficient candidates for Cr(VI) removal from aqueous polluted environments.