Adsorption mechanisms of monobutyltin in clay minerals

Abstract

Two phyllosilicates of high permanent charge and expandable (swelling) structure, montmorillonites, and two silicates of low permanent charge and nonexpandable structure, kaolinite (phyllosilicate) and sepiolite (fibrous silicate), were used as sorbents to elucidate the capacity and mechanism of adsorption of monobutyltin (MBT) species, as related to the presence and dynamics of MBT in sediments and participate matter. Adsorption kinetics and isotherms, desorption measurements, and studies of organotin-clay complexes by X-ray diffraction and FTIR spectroscopy indicated that the MBT adsorption process is a cationic exchange on these clay minerals, besides an additional adsorption of neutral (MBT)C13 attracted by the lipophilic moiety of the first MBTn+ adsorbed. The expandable (swelling) minerals showed much higher adsorption capacity because MBT adsorbed in their interlayer spaces where MBTn+ species, besides (MBT)Cl3, make >aggregates> or >clusters> that propelled some montmorillonite layers from 14 to 22 A. The results show the important role of clay minerals in the presence and dynamics of MBT in sediments as bound residues. The use of montmorillonite as a filter for MBT-contaminated waters is also suggested.