Highly Efficient Adsorption of Sr and Co Ions by Ambient Prepared Alkali Activated Metakaolin.

This study aimed to explore a low cost and sustainable adsorbent to remove Sr and Co ions, which are major radioactive ions in nuclear wastewater. The material properties of the alkali-activated metakaoline as a function of soaking time at ambient temperature from 1 day to 7 days were examined by XRD, XRF, SEM, and solid-state NMR. Adsorption isotherms were used to evaluate the appropriate soaking time for the optimal sorption performance for both Sr and Co ions. The alkali-activated metakaolin soaked for 3 days (BK3) presented the maximum adsorption capacities of 3.81 meq/g (167.5 mg/g) and 4.02 meq/g (118.5 mg/g) for Sr and Co, respectively. The sorption mechanisms for Sr and Co in the BK3 sample were investigated, and the experimental results indicated that adsorption for Sr was achieved via ion exchange. By contrast, surface complexation in combination with ion exchange contributed to the sorption mechanisms for the removal of Co. Competitive adsorption experiments revealed that the alkali-activated metakaolin favored the adsorption for divalent ions (i.e., Sr and Co), and it was less effective for Cs. Finally, the used adsorbent could be directly mineralized and vitrified by heat treatment to immobilize the Sr and Co ions.