*Article* **Rapid Immobilization of Simulated Radioactive Soil Waste Using Self-Propagating Synthesized Gd2Ti2O7 Pyrochlore Matrix**

**Jiali Xue 1, Kuibao Zhang 1,2,\*, Zongsheng He 1, Wenwen Zhao 1, Weiwei Li 1, Dayan Xie 1, Baozhu Luo 1, Kai Xu <sup>3</sup> and Haibin Zhang 4,\***


Received: 22 February 2019; Accepted: 8 April 2019; Published: 10 April 2019

**Abstract:** A rapid and effective method is necessary in the disposal of severely radioactive contaminated soil waste. Simulated Ce-bearing radioactive soil waste was immobilized by self-propagating high-temperature synthesis (SHS) within 5 min in this study. The main work includes the rapid synthesis of soil waste forms, the analysis of phase composition, microstructure and chemical durability. These results show that the simulated nuclide Ce was successfully immobilized into the pyrochlore-rich waste matrice, whose main phases are SiO2, pyrochlore (Gd2Ti2O7) and Cu. The normalized leaching rates of Si and Na on the 42nd day are 1.86 × <sup>10</sup>−<sup>3</sup> and 1.63 × <sup>10</sup>−<sup>2</sup> <sup>g</sup>·m−2·d−1, respectively. And the normalized leaching rate of Ce also remains at low level (10<sup>−</sup>5–10−<sup>6</sup> <sup>g</sup>·m−2·d<sup>−</sup>1) within 42 days.

**Keywords:** Radioactive soil waste; Gd2Ti2O7 pyrochlore; SHS; CeO2; Immobilization
