FACTORS AFFECTING THE IMMOBILIZATION OF METALS IN GEOPOLYMERIZED FLY-ASH

Geopolymerization, a fairly new technology based on a very old princip le, has emerged during the last few years as a possible solution to so me waste stabilization and solidification problems. Some commercial su ccesses have been achieved, although the technique remains fairly unkn own as well as seemingly unpopular. It has been shown that most waste materials containing sources of silica and alumina should be capable o f taking part in a geopolymerization reaction. In this article, flyash was used as a reactant in creating a geopolymeric matrix for the immo bilization of process water containing 25,000 ppm of Cu or Pb cations. By means of X-ray diffraction, scanning electron microscopy (SEM), in frared spectroscopy, Brunauer-Emmett-Teller (BET), compressive strengt h, as well as kinetic leaching analyses, the main factors influencing matrix stability, immobilization efficiency, and therefore leaching be havior were investigated and discussed qualitatively. It was found tha t relatively high strengths could be obtained using low Ca flyash. The environment and coordination number of source aluminum and silica see med to play a major role in the eventual matrix stability. Other facto rs influencing matrix stability include the alkali metal cation used a s well as the type of metal being immobilized. The kinetics of leachin g of immobilized metals from the geopolymerized flyash were qualitativ ely found to proceed along a combination of pore diffusion and boundar y diffusion control mechanisms. It is finally concluded that immobiliz ation of metals in geopolymerized flyash proceeds by a combination of physical encapsulation and chemical bonding, with adsorption also thou ght to play a role.