Use of perlite in combination with clays for the production of low environmental impact filter for heavy metals polluted aqueous solution

The aim of this work is to prepare a relatively cheap mixture ofperlite (a volcanic rock with intermediate composition betweenrhyolite and dacite) and clays, effective in the retention of heavymetals even after treatments at relatively high temperatures. Theobtained product could be possibly reused and therefore notdisposed of as toxic waste. The perlite used in this study comesfrom Greek quarries and is provided by the company "PerliteItaliana”. Three different types of clay materials were used: 1) aclay material coming from the Argille Varicolori formation; 2) acommercial bentonite (supplied by Laviosa, Italy; 3) a standardmontmorillonite (STx-1, from the County of Gonzales, Texas,USA), to be used as reference materials.Column and batch tests were carried out on several differentmixtures of the previously described materials in order toevaluate the effective adsorption of Cd, Pb, and Zn fromaqueous solution. Pb, Zn, and Cd contents of the “polluted”mixtures were thus measured via inductively coupled plasmaoptical emission spectroscopy (ICP-OES) after acid digestion.The obtained results indicate that the mixture consisting ofVaricolori clay and perlite can be profitably used as adsorbentof metals in solution. Adsorption data are consistent with thoseexpected from theoretical calculations.The method chosen for the permanent inertization ofpolluted samples is thermal treatment, which, as evidenced bynumerous literature data, can lead to a chemically inert product,eventually suitable for reuse in construction. Before being fired,each mixture was added from opportune amount of kaoliniteand feldspar. Release tests were, thus, carried out on firedproducts using weakly acid solution (pH values between 5.5.and 6) as leaching media. Results, which are very encouraging,are reported in the Table 1.