**4. Conclusions**

In summary, a series of Gd2Ti2O7-based waste forms containing 5–25 wt.% simulated radioactive contaminated soil have been successfully synthesized by SHS in 5 min. The obtained products are multiphase composite materials composed of SiO2, Gd2Ti2O7, and Cu. Furthermore, the simulated nuclide Ce exists in pyrochlore and soil phases simultaneously, which indicates that Ce migrates partly from soil to pyrochlore phase during the SHS reaction. The solidified body of Cu-20 sample exhibits high stability. The 42 days *NR*Si and *NR*Na are as low as 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 1–42 days *NR*Ce values also remain at a low level (10<sup>−</sup>5–10−<sup>6</sup> <sup>g</sup>·m−2·d<sup>−</sup>1). Based on the analysis of phase composition, microstructure, and chemical durability, the application potential of SHS technology in the rapid disposal of radioactive soil wastes is revealed.

**Author Contributions:** Conceptualization, K.Z., B.L. and H.Z.; Methodology, K.Z. and J.X.; Formal Analysis, J.X., K.X., Z.H. and W.Z.; Investigation, J.X., W.L., D.X. and Z.H.; Writing—Original Draft Preparation, J.X.; Writing—Review & Editing, K.Z. and B.L.

**Funding:** This research was funded by the National Natural Science Foundation of China (No. 51672228), the Project of State Key Laboratory of Environment-friendly Energy Materials (Southwest University of Science and Technology, No. 16kffk05 and 17FKSY0104) and Science Development Foundation of China Academy of Engineering Physics.

**Conflicts of Interest:** The authors declare no conflict of interest.
