Adsorption Behavior of Sr and Ba Using TDS-Impregnated Microporous Silica-Based Adsorbents in Nitric Acid Solution

Abstract

Silica-based adsorbents impregnated tetra-n-butyl thiuram disulfide (TBTDS) or tetrakis (2-ethylhexyl) thiuram disulfide (T(2EH)TDS) as extractants on a macroporous silica/polymer composite support (SiO₂-P) were prepared to separate barium (Ba) ions from strontium (Sr) ions present in mixed solutions. The Ba and Sr ion adsorption behaviors of each adsorbent were investigating by varying acid concentration, contact time, temperature, and metal concentrations in solution using the batch method. The Ba and Sr adsorption affinities depended on nitric acid concentration, and the difference in distribution coefficient (K_d) between the two ions was maximum in 1 M HNO₃. Furthermore, results indicated that the adsorption reaction starts several hours after the initial solution–adsorbent contact and reaches equilibrium within 4–10 hours. The dependence for thermal for adsorption indicated to be spontaneous processes. The adsorption mechanisms were investigated by applying two isotherm models. The shapes of the isotherms were different between the TBTDS adsorbent and the T(2EH)TDS adsorbents. The isotherm for the two T(2EH)TDS adsorbents were well fitted by the Langmuir model, but that for TBTDS was S-shaped and more metal ions were adsorbed than the other adsorbents. These results suggest that the Ba and Sr ions could be separated from each other via the batch method using these adsorbents.