ADSORPTION MECHANISMS OF MONOBUTYLTIN IN CLAY-MINERALS

Two phyllosilicates of high permanent charge and expandable (swelling) structure, montmorillonites, and two silicates of low permanent charg e and nonexpandable structure, kaolinite (phyllosilicate) and sepiolit e (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 particulate matte r. Adsorption kinetics and isotherms, desorption measurements, and stu dies of organotin-clay complexes by X-ray diffraction and FTIR spectro scopy indicated-that the MBT adsorption process is a cationic exchange on these clay minerals, besides an additional adsorption of neutral ( MBT)Cl3 attracted by the lipophilic moiety of the first MBT(n+) adsorb ed. The expandable (swelling) minerals showed much higher adsorption c apacity because MBT adsorbed in their interlayer spaces where MBT(n+) species, besides (MBT)Cl3, make ''aggregates'' or ''clusters'' that pr opelled some montmorillonite layers from 14 to 22 angstrom. The result s show the important role of clay minerals in the presence and dynamic s of MBT in sediments as bound residues. The use of montmorillonite as a filter for MBT-contaminated waters is also suggested.