A preliminary investigation of the removal of heavy metal species from aqueous media using crushed concrete fines

Abstract

The crushing of reclaimed concrete 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 the primary aggregate. It is the coarse fraction which is of use in construction and the fine fraction which is destined for landfill. The application of ordinary Portland cement (OPC) based materials in the solidification and stabilisation of heavy metal-bearing wastes is well established. Accordingly, it is proposed that this fine, cement-rich fraction of OPC-based waste may be used to immobilise heavy metal species from aqueous media. The removal of heavy metal nitrates (Pb2+, Ba2+, Zn2+, Ni2+, Cr3+ and Cu2+) from aqueous solution by the addition of crushed OPC concrete waste (in the particle size range 1–2 mm) is reported herein. The extent of exclusion of the metal ions indicates that mechanisms other than pH-dependent precipitation are in operation. The fate of the heavy metal species has been determined by scanning electron microscopy.