The effect of metal contaminants on the formation and properties of waste-based geopolymers

The stabilisation and solidification of waste materials by the technology o f geopolymerisation is receiving increasing attention from researchers; imm obilisation of metal contaminants in these structures seems to be a viable alternative to present stabilisation techniques. This paper presents some e xperimental evidence concerning the effect of the inclusion of mainly Cu an d Pb on the physical and chemical characteristics of geopolymers manufactur ed from fly ash. A variety of experimental and analytical techniques were u sed in this investigation, including compressive strength testing, specific surface area analyses, transmission electron microscopy, nuclear magnetic resonance, X-ray diffraction, and infrared spectroscopy. It was found that contaminants are being immobilised through a combination of chemical bondin g and physical encapsulation. The nature of the contaminant seems to have a fairly large effect on both the physical and chemical characteristics of t he final product, with subsequent long-term implications as far as durabili ty is concerned. It is therefore concluded that a definite interaction exis ts between matrix-forming components and the immobilisation of the contamin ant, where the amount of contaminant is a critical factor in the analysis. (C) 1999 Elsevier Science Ltd. All rights reserved.