This paper presents a study of metal adsorption by a Brazilian vermiculite, and a critical analysis of some aspects of the adsorption test procedure. Current or potential geo-environmental uses of vermiculite associated to its high ion exchange capacity include treatment of wastewaters, immobilisation of heavy metals in hazardous wastes, and enhancement of sealing properties of clay liners. The suitability of these applications depends on the capacity to adsorb pollutant cations or molecules. Adsorption tests were carried out to study vermiculite retention of Cu, Cd, Cr, Pb, Ni, Zn and Hg. Freundlich and Langmuir adsorption isotherms equations, applied to test results, described fairly well vermiculite adsorption of the studied metals. As batch-type adsorption tests are not yet normalized in Brazil, some test variables, i.e. time, solution pH and mass ratio, were researched and analyzed. Test duration of 4 hours was enough to reach equilibrium for all metals. Adsorption was strongly dependent on pH for all metals, except for chromium. For practical applications, tests should be carried out at specific limited concentration ranges, in order to obtain more precise parameters, due to the non-linear relation of adsorbed mass in soil with equilibrium concentration.
Commercial utilization of vermiculite in Brazil, concentrated mainly in the fabrication of thermalacoustic insulators, has been expanding to other applications as a consequence of exploration amplification. Current and potential geo-environmental uses, related to its high ion exchange capacity, include treatment of wastewaters as a cations concentrator, immobilization of heavy metals in hazardous wastes, and enhancement of sealing properties of soil liners in waste disposal sites. The suitability of these applications is strongly dependent on vermiculite capacity to adsorb pollutant cations or molecules. Clay minerals adsorb heavy metal ions through an exchange process and specific bonding (Grim, 1968).
