Application of polymer-modified nanoporous silica to adsorbents of uranyl ions

The surface modification of nanoporous silicas (MSU-H) of submicron-scale particle size with polyethyleneimine (PEI), polyacrylic acid (PAA), and carboxymethylated polyethyleneimine (CMPEI) was carried out for the extraction of uranyl ions. Adsorption behaviors of uranyl ions onto the polymer-modified silicas, denoted as PEI/MSU-H, PAA/MSU-H and CMPEI/MSU-H, were examined in batch experiments. In 0.05 mM UO22+ solution, it was found that the nearly complete removal of uranyl ions can be achieved by the CMPEI-modified MSU-H (CMPEI/MSU-H). Especially, the CMPEI/MSU-H exhibited significantly high distribution coefficient value (Kd = 2.30 × 106). In concentrated UO22+ solution (ca. 1 mM), uranium-uptake capacities onto the three polymer-modified nanoporous silicas were in the following order: CMPEI/MSU-H > PAA/MSU-H > PEI/MSU-H. It is noteworthy that CMPEI/MSU-H showed excellent uranium-uptake capacity (124 mg-U/g-adsorbent), based on the total weight of polymer and silica. In addition, the loading stability of uranium on the adsorbent was examined with time. It was observed that about 15% of uranium was discharged from CMPEI/MSU-H in a day and additional 5% uranium was released with a relatively slow desorption rate in 12 days.