Permeability of lime-activated pulverised fuel ash to metal-containing permeants.

Lime-activated pulverised fuel ash (PFA) has been leach tested under a range of pH conditions and the permeability of compacted samples determined using distilled water and aqueous solutions of Ca2+, Zn2+, Cd2+ and Mg2+. Although permeabilities were relatively high when tested with distilled water (> 1x10(-7) m/s), permeation with 0.05M metal solutions resulted in rapid reductions in permeability to less than 1x10(-10) m/s. Leachate and permeant solution analysis shows that metal ion release from samples is low. The reduction in permeability is believed to be due to pore sealing resulting primarily from metal hydroxide precipitation and results in a metal concentration gradient across the sample thickness. Lime-activated PFA therefore acts as both a chemical and physical barrier to metal ion migration and has the potential to form low permeability barriers.