Effect of alkali activation on coal fly ash and its role in microwave-sintered ceramic for radionuclide immobilization

Considerable amounts of coal fly ash (CFA) are produced annually without adequate resource utilization. Given the abundance of silica and alumina in CFA, as well as its established reactivity when subjected to an alkali medium, alkali-activated CFA was introduced to prepare ceramics for treating neodymium-contaminated soil. The effect of alkali activation on the phase, microstructure, and elemental distribution of the CFA particles and microwave-sintered ceramics was systematically investigated, and crude CFA was used for comparison. The results indicated that the alkali activation of CFA led to a desilication reaction, and new phases rich in sodium were generated. Additionally, the alkali-activation of CFA was conducive to enhancing the mechanical properties of the ceramics. The alkali-activated CFA bearing 30 w t% Nd 2 O 3 , which was microwave sintered at 1200 °C, exhibited the highest bulk density (2.79 g/cm 3 ), while that of untreated CFA was only 2.57 g/cm 3 . Moreover, the Nd ions were homogeneously distributed in the Ca 2 Nd 8 (SiO 4 ) 6 O 2 matrix.