Factors affecting the immobilization of metals in geopolymerized flyash |
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Authors: | J G S Van Jaarsveld J S J Van Deventer L Lorenzen |
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Affiliation: | (1) the Department of Chemical Engineering, The University of Melbourne, 3052 Parkville, Victoria, Australia;(2) the Department of Chemical Engineering, University of Stellenbosch, 7600 Stellenbosch, South Africa |
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Abstract: | Geopolymerization, a fairly new technology based on a very old principle, has emerged during the last few years as a possible
solution to some waste stabilization and solidification problems. Some commercial successes have been achieved, although the
technique remains fairly unknown as well as seemingly unpopular. It has been shown that most waste materials containing sources
of silica and alumina should be capable of taking part in a geopolymerization reaction. In this article, flyash was used as
a reactant in creating a geopolymeric matrix for the immobilization of process water containing 25,000 ppm of Cu or Pb cations.
By means of X-ray diffraction, scanning electron microscopy (SEM), infrared spectroscopy, Brunauer-Emmett-Teller (BET), compressive
strength, as well as kinetic leaching analyses, the main factors influencing matrix stability, immobilization efficiency,
and therefore leaching behavior were investigated and discussed qualitatively. It was found that relatively high strengths
could be obtained using low Ca flyash. The environment and coordination number of source aluminum and silica seemed to play
a major role in the eventual matrix stability. Other factors influencing matrix stability include the alkali metal cation
used as well as the type of metal being immobilized. The kinetics of leaching of immobilized metals from the geopolymerized
flyash were qualitatively found to proceed along a combination of pore diffusion and boundary diffusion control mechanisms.
It is finally concluded that immobilization of metals in geopolymerized flyash proceeds by a combination of physical encapsulation
and chemical bonding, with adsorption also thought to play a role. |
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