Waste Stabilization/solidification (s/s) Using Fly Ash-based Geopolymers. Influence of Carbonation on the S/s of an Eaf Dust

The effect of the curing in a carbonated ambient of the solids obtained after the stabilization/solidification (S/S) of metallurgical waste using geopolymerization technology is described in this paper. The electric arc furnace (EAF) dust used to stabilize contains hazardous metals such as Pb, Cd, Cr or Zn. Different geopolymeric agents as potassium hydroxide, potassium silicate, metakaolin and blast furnace slag have been used. Mixtures of EAF waste with these kinds of geopolymeric materials and class F fly ash have been processed. Samples were submitted to an accelerated carbonation test. Compressive strength tests and different leaching tests for determining the efficiency of heavy metal immobilisation have been carried out. Comparison of fly ash-based geopolymer systems with classical Portland cement (OPC) stabilization methods has also been accomplished. Compressive strength values far better than those achieved by hydraulic S/S methods were easily obtained by geopolymer solids at 28 days. Carbonation produced a great increment of compressive strength in samples containing a higher K2O proportion. Regarding leachability, the geopolymer S/S solids also manifested better behaviour in general, showing very promising results. Carbonation effects on pH and on Zn and Pb leachabilities are more marked for OPC than for geopolymer S/S solids.