Simulated spent adsorbent with Sr adsorbed on granular potassium dititanate was prepared and its leaching behavior was evaluated. Since Sr was adsorbed on the granular potassium dititanate by ion-exchange, Sr was leached into acidic solutions or solutions with high cation concentration. The influence of the cationic species in the solution on Sr leachability was larger for Ca than for Na. It can be seen the ion selectivity of potassium dititanate is higher for alkaline earth metals such as Ca and Sr than for alkali metals such as Na and K. Heat treatment was effective in reducing Sr leaching from the simulated spent adsorbent. The heat treatment at 500°C was not effective enough to reduce the Sr leaching, but the heat treatment above 900°C showed a significant reduction in the Sr leaching ratio. This might be related to the stabilization of Sr as Sr₂Ti₆O₁₃ crystal and the reduction of specific surface area of the simulated spent adsorbent. At the heat treatment temperature of 1100°C, there was no significant difference in the crystal phase formed from that at 900°C. However, the specific surface area of the simulated spent adsorbent was reduced, therefore the effect of reducing Sr leaching was even larger.

Alkali conversion of paper sludge ash into cation exchanger via acid leaching was examined. The extraction behaviors of major elements (Si, Al, Ca and Mg) from the ash into hydrochloric acid (1 mol/L HCl) and sulfuric acid (0.5 mol/L H₂SO₄) aqueous solutions were almost same except Ca due to the formation of gypsum in the H₂SO₄ solution. The ashes leached with 1 mol/L HCl and 0.5 mol/L H₂SO₄ aqueous solutions were converted into zeolite-P and tobermorite, respectively, while the raw ash was converted into hydroxysodalite. The cation exchange capacities of the converted products from the ashes leached with HCl and H₂SO₄ were 1.30 and 0.75 mmol/g, respectively, which were higher than that of the product from the raw ash (0.60 mmol/g). These results indicated that paper sludge ash could be converted into different types of cation exchanger via acid leaching.

In this study, a hydrochloric acid-stable 2D covalent organic framework (TpPa-1) was prepared. And its adsorption behaviors in the recovery of palladium (Pd(II)) from hydrochloric acid solution was systematically investigated under the effect of contact time, hydrochloric acid concentration, chloride ions concentration, and adsorption capacity. The adsorbed species on TpPa-1 was clarified as chloridated Pd(II) by X-ray photoelectron spectroscopy.