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

Lime-activated pulverised fuel ash (PFA) has been leach tested under a rang e of pH conditions and the permeability of compacted samples determined usi ng distilled water and aqueous solutions of Ca2+, Zn2+, Cd2+ and Mg2+. Alth ough permeabilities were relatively high when tested with distilled water ( > 1x10(-7) mis), permeation with 0.05M metal solutions resulted in rapid re ductions in permeability to less than 1x10(10) m/s. Leachate and permeant s olution analysis shows that metal ion release from samples is low. The redu ction in permeability is believed to be due to pore sealing resulting prima rily from metal hydroxide precipitation and results in a metal concentratio n gradient across the sample thickness. Lime-activated PFA therefore acts a s both a chemical and physical barrier to metal ion migration and has the p otential to form low permeability barriers.