Resource utilization of mercury and safe disposal of iodine in iodine-containing mercury–bismuth co-modified silica gel

A low-cost mercury‑bismuth co-modified silica gel has been previously reported as an alternative to expensive silver-loaded silica gel for adsorbing radioactive gaseous iodine. This study proposed a two-step treatment strategy for iodine-containing secondary waste, enabling simultaneous resource utilization of mercury and safe immobilization of iodine. First, Na 2 S was employed as the eluent, and the resulting mercury‑bismuth‑sulfur composite (HBS@SiO 2 ) was reused as an iodine adsorbent. Second, iodine was preliminarily immobilized into iodosodalite, followed by mixing with glass powder and sintering for secondary immobilization. The results demonstrated that Na 2 S elution efficiencies for HgI 2 @SiO 2 -I 2 and HgI 2 @SiO 2 -CH 3 I were 99.02% and 99.19%, respectively. For mercury reuse, the adsorption capacities of HBS@SiO 2 for I 2 and CH 3 I were 298.3 ± 6.9 mg/g and 160.1 ± 21.6 mg/g, respectively, and no significant performance decrease was observed after three cycles. Both experimental and theoretical calculations indicate that the capture of CH 3 I was attributed to the synergism of the chemisorption of Bi 2 S 3 and the surface electrostatic adsorption of HgS. For iodine disposal, the iodine derived from the liquid after I 2 adsorption was confined within the cage structure of sodalite in the forms of I − and IO 3 − , whereas only I − was present in the sample obtained after CH 3 I adsorption. The iodosodalite solidified by 20 wt% borosilicate glass exhibited a better chemical stability. PCT leaching tests indicated that the iodine leaching rate was 8.8 × 10 −5  g·m −2 ·d −1 . Overall, it presented a treatment strategy for iodine-containing secondary waste, achieving the resource recovery of active metals and the stable solidification of radioactive iodine.