The Stabalization of Aqueous Heavy Metal Species Using Recycled Concrete Fines

The crushing of reclaimed concrete-based demolition waste in the production of recycled aggregate produces a large volume of fine material which is rich in hydrated cement paste phases, the coarser fraction being predominantly composed of aggregate. It is the coarse fraction which is of use in construction and the fine fraction which is destined for landfill. Heavy metal-bearing wastewater and sludge arise from a number of industrial processes including electroplating, galvanizing, metal finishing and battery production. Treatment procedures for aqueous heavy metal-contaminated waste streams include precipitation, adsorption, ion exchange, membrane filtration and solidification/stabilization using cement or lime-based materials. The removal of heavy metal species from aqueous media by the cement-rich fraction of ordinary portland cement-based waste concrete is demonstrated herein. Crushed concrete waste in the particle size range 1 - 2 mm is shown to be effective in the exclusion of a range of heavy metal nitrates from solution. The leaching characteristics of the metal-impregnated cement matrices are also reported.