Concept of subaqueous capping of contaminated sediments with active barrier systems (ABS) using natural and modified zeolites

In this study the concept of subaqueous capping of contaminated sediments of lakes, rivers and coastal waters with active barrier systems (ABS) in order to minimise the contaminant release into the surface water is developed. This concept is supposed to provide a low-cost alternative to conventional methods in water protection. Active barrier systems, i.e. reactive geochemical barriers on the basis of low-cost materials, shall actively inhibit contaminant release from the sediment into the surface water, without the hydraulic contact between sediment and surface water being disturbed. Theoretical considerations and first experimental results regarding the retention of Pb2+ by four different zeolitic rocks suggest that natural zeolite as a reactive material in sediment capping meets all the economical and technical requirements posed by the active barrier concept. Natural zeolites are capable of demobilising large amounts of cationic pollutants by sorption, as shown for Pb2+, and, furthermore, they are capable of demobilising non-polar organics and anionic contaminants, when the zeolite surface is pre-treated with cationic surfactants. Active barrier systems on the basis of natural zeolites thus can be applied to nearly any type of contaminated sediment. Additionally, the physical characteristics of zeolitic rocks, as grain size and density, facilitate their use in subaqueous applications.