Light expanded clay aggregates are described that are prepared by firing and expanding a clay- based material, wherein metals such as palladium, copper or nickel are added to the clay together with iron prior to expansion and firing. The expanded clay aggregates can be used for cleaning of water contaminated with halogenated organic compounds. The latter are chemically degraded to harmless compounds in proximity of the added metals. The aggregates can be used as a reactive medium for treatment of contaminated groundwater, wastewater and landfill leachate.
