2011 World of Coal Ash Conference, Mayıs 9-12, 2011, Denver, Colorado

The immobilization of chromium (III) and (VI) in geopolymeric matrices are studied in this paper. The geopolymers were prepared using coal combustion fly ash as the main aluminosilicate source. The influence of the activating solution has been studied using different solutions such as potassium silicate, sodium silicate, potassium hydroxide and sodium hydroxide. In addition, some samples containing Ordinary Portland Cement (OPC) and the same activating solutions were prepared for comparative purposes. Mixtures were cured at ambient temperatures and in an oven at 60 ºC. After curing, samples were subjected to different leaching tests such as UNE-EN 12457-4 and USEPA TCLP tests to assess the efficiency of the immobilization of Cr in both oxidation states. The total chromium leached was generally less than 0.05 % of the total Cr (III) added, in spite of the fact that a partial oxidation of Cr (III) to Cr (VI) was observed in most Cr (III) samples. With regard to Cr (VI), the immobilization was more problematic. Thus, the total chromium leached was between 2.4 – 4.8% of the total Cr (VI) added, the immobilization achieved with potassium hydroxide being better than that achieved with sodium hydroxide. Moreover, the use of OPC alone as a binder showed better leaching results than coal fly ash. No significant differences were found regarding Cr immobilization between the two curing conditions used.