Chemical pore closure of zeolite A using tetraethyl orthosilicate: A potential method for enhancing the use of zeolites as part of a long-term waste immobilization strategy

Abstract

The use of zeolites as an integral part of long-term toxic waste storage strategies are hindered by the very ion-exchange properties which make them so useful in cleaning waste water of toxic contaminants. Previous literature shows that a range of surface modifications have been proposed for changing the catalytic properties of zeolites, this study examines one of these techniques, the control of pore opening size by coating the zeolite surface with silica using tetraethyl orthosilicate (TEOS), as a means of reducing ion-exchange. After initial removal of waste material from solution, pores are sealed using liquid TEOS at 80 °C, and the ion exchange is remeasured in comparison to a sample of untreated zeolite. Sealing the surface with a silica deposit has yielded up to 95% reduction in waste leached from the zeolite without significant reduction in the overall crystallinity of the material. The stability of the coating against physical abrasion has also been studied and been shown to be resistant to simple attrition forces.