MECHANOCHEMICAL IMMOBILIZATION OF COPPER BY DIOCTAHEDRAL AND TRIOCTAHEDRAL SMECTITES

Clay minerals have revealed highly potential in soil remediation due to their low cost, availability, and low toxicity. Mechanochemical processes allow to activate chemical reactions by inducing different kinds of mechanical stress and without any other energy supply. This study investigated the effect of dry milling on the ability of dioctahedral and trioctahedral smectites to immobilize heavy metals cations. To this purpose a dioctahedral smectite “bentolite L” and a trioctahedral one “laponite RD” were ground with different amount of copper(II) chloride in dry conditions into a zirconia planetary ball mill (mechanochemical treatment). Increasing milling time and Cu/clay minerals mass ratio were selected for experimental tests. From the ground mixtures two different kinds of samples were extracted using the following procedures: 1) with deionised water; 2) with 1 M MgCl2 solution. Copper immobilization degree was evaluated by ICP/OES analysis of exstracts as difference between the amount of Cu(II) spiked in the mixture and the amount of Cu(II) ions present in the extracted fraction. The analyses showed an increased Cu retention as time increases for both bentolite L and laponite RD. Mechanochemical treatments, depending on time and different mass ratio, induced the increase of retention efficiency. The solid phases were also characterized by means of solid-state NMR and spectroscopic techniques such as FTIR and XPS, to investigate the mechanisms of the “mechanochemical retention” of copper by both the clay minerals