In situ immobilization properties and mechanism of geopolymer microspheres after adsorbing Sr2+ and Cs+ (Sr/Cs@GPMs)

Herein, in situ immobilization properties and mechanism of the pre-prepared geopolymer microspheres after adsorption of Sr2+/Cs+ (Sr/Cs@GPMs) were studied. The Sr2+ and Cs+ were solidified via calcination and a GP slurry coating strategies. The conditions for leaching experiments were H2O, 0.1 mol/L (NaCl, NaOH, and HCl). The calcination results showed that the pore volume of the two adsorbents gradually decreased with increasing temperature and the order of leaching rate of Sr2+/Cs+ in calcination of Sr/Cs@GPMs was: HCl > NaCl > NaOH > H2O, while the leaching rate decreased with increasing temperature and met the national standards. The in situ immobilization mechanism revealed that the pores of the adsorbent disappeared after high-temperature calcination or ceramic reaction. The results of the GP slurry coating experiment showed that the leaching rates of Sr2+/Cs+ decreased with leaching cycles. The solidified slag-based GP with Sr/Cs@GPMs (12%) adsorbent in 0.1 mol/L HCl leaching environment had the 28-day leaching rate (R28) and cumulative leaching fractions (P28) for Sr2+ of 1.26 × 10-3 cm/d and 0.057 cm, respectively, and 1.51 × 10-3 cm/d and 0.127 cm for Cs+, respectively. These metrics met the requirements of the national standard, thus indicating that slag-based GP has value in treating radionuclides.