SPECTROSCOPIC CHARACTERIZATION OF CADMIUM AND COPPER MODIFIED SMECTITES FOR SOIL REMEDIATION

The presence of heavy metals in the environment is a potential risk for the ecosystem due to their toxicity to plant, animals and human life. Lots of technologies and treatments have been developed to remove them from aqueous solutions, employing natural or synthetic sorbents. Among them, clay minerals have revealed interesting properties in soil remediation due to their natural occurrence, low toxicity, and low cost. Moreover, mechanochemical processes allow to activate chemical reactions by inducing different kinds of mechanical stress and without any other energy supply. In this study the effect of mechanochemical treatments on the ability of dioctahedral and trioctahedral smectites to “entrap” heavy metals is investigated. To this purpose a dioctahedral smectite “bentolite L” and a trioctahedral one “laponite RD” were ground with different distinct amounts of copper and cadmium chloride in dry conditions by means of zirconia planetary ball mill. Experimental tests were performed modifying the milling time and metal/clay minerals mass ratio, whereas grinding energy and ball to powder ratio were kept constant. The efficiency of the mechanochemical process to promote the interaction between smectites and heavy metals was evaluated by means of different analytical techniques: the immobilization degree was evaluated by ICP/OES analyses and expressed by the leachable fraction of metal ions. While the investigation on the main adsorption sites of the heavy metals on the ground surfaces was tested by means of solid-state measurements through the combined use of X-ray Fluorescence Spectroscopy, Fourier Transform Infrared Spectroscopy, X-ray Diffraction, Nuclear Magnetic Resonance and X-ray Photoelectron Spectroscopy.