37th Annual Meeting
of the American Clay Mineral Society 

            Recently I participated in the 37th Annual Meeting of the American Clay Mineral Society.  The conference took place in the Loyola University, Chicago on June 24-29, 2000. The conference was supported financially by Oil-Dri Corporation of America. My coauthor, Prof. J. Stucki was a program chair. The conference had several symposiums, including Nanocomposite Materials, Redox processes in Clays (where our paper was presented), Archaeology and Clays  and even Clays in the Human Future: Extra-terrestrial clays. It also included a poster session and students awards.

            I enjoyed the meeting, especially the plenary lecture given by Jillian F. Banfield, Recipient of the 2000 Marion and Chrystie M. Jacksom Midcareer Clay Scientist Award. This lady is really creative and a year ago she has been named MacArthur Fellow along with 31 other creative people, who will receive five years of unrestricted financial support.  Another lecture was given by the now retired 2000 Pioneer in Clay Science, William F. Moll: "Clays where you least expect them". Bill has spent his life in industry, and in his recollections he told us how clays were found application in paper industry, tooth paste, paints, etc. Bill has promised to send me his lecture on CD to use in our class of Colloid Chemistry.

            The highest honor of Clay Minerals Society (M&S. Bailey Distinguished Member Award) was given to professor from Moscow Boris Zvyagin. Before the meeting he visited me and my family in Urbana- Champaign and I was able to discuss his and our results, and also talk about the huge collection of records of classical music that Professor Zvyagin keeps in Moscow.  Boris gave a lecture entitled Current problems of the nomenclature of phyllosilicates".

            My  paper (co-author Prof. Stucki J., University of Illinois at Urbana-Chapaign)  described the use of an artificial membrane, where a thin layer of clay is immobilized between two porous supports (see figure 1). This three-layer membrane is formed by simple filtration of smectite clay and then drying it with air on a surface of a nitrocellulose filter. Another filter is placed on the upper side of the clay layer. The membrane is stable enough to be placed vertically in a special chamber where it separates air and water or two different aqueous solutions. In the latter case it is easily possible to characterize the barrier properties of the membrane by measurements such as transmembrane potential and transmembrane electrical resistance. Transport through the membrane and concentration changes in the aqueous solutions can be easily measured by standard analytical methods, such as HPLC and UV-visible spectroscopy.

            Results revealed that transport of water and ions into and through the clay membrane involves two kinetic steps (fast and slow). These steps can be described by reversible first order kinetics, and resemble the two-phase kinetics of sorption and transport of low molecular-weight substances, which are well known for the clays and soils. The membrane was used to characterize sorption, transport, degradation, and desorption of the herbicide, alachlor. With time, the herbicide disappeared from the donor solution and appeared in the acceptor phase. Kinetics of this process also had both fast and slow steps. Iron reduction by dithionite prior to the membrane formation changed the physico-chemical properties of the clay and, under anaerobic conditions, resulted in a chemical alteration of the herbicide. No such alteration occured when the oxidized smectite was used as the membrane. Degradation of the alachlor occurred as it diffused through the <1-mm thick reduced smectite membrane, and the extent of degradation increased with time. Experiments with the clay membrane are simple, fast, and can be used, for example, in environmental chemistry to predict the fate of herbicides and their dependence on the redox state of the soil or clay.  

Figure 1 : The clay membrane-based experimental set-up