Interactions of aqueous Cu 2+, Zn 2+ and Pb 2+ ions with crushed concrete fines

Abstract

The crushing of reclaimed concrete-based demolition waste to produce recycled aggregate gives rise to a large volume of cement-rich fine material for which market development would be beneficial. It was envisaged that this fine fraction may prove to be an effective sorbent for aqueous heavy metal species by virtue of its ion exchangeable phases and high pH. A batch sorption study confirmed that crushed concrete, in the particle size range 1–2 mm, successfully excluded Cu 2+ (35 mg g −1), Zn 2+ (33 mg g −1) and Pb 2+ (37 mg g −1) from aqueous media. Subsequent distilled water leaching of the metal-laden concrete particles indicated that 1.9, 0.9 and 0.2% of the bound metals, Cu 2+, Zn 2+ and Pb 2+, respectively, were readily soluble. Scanning electron microscopy revealed that the removal of Cu 2+ and Zn 2+ arose from surface precipitation reactions, whereas, the principal mechanism of uptake of Pb 2+ was found to be by diffusion into the cement matrix. The metal ion removal efficiency of crushed concrete fines is compared with those of other low cost sorbents and potential applications which may exploit this sorptive property are also discussed.