Adsorption of Sr from Synthetic Waste Effluents Using Taiwan Zhi-Shin Bentonite.

This study investigated strontium (Sr) adsorption by Taiwan Zhi-Shin bentonite (cation exchange capacity (CEC): 80-86 meq 100 g) using Sr(NO)-simulated nuclear waste. Kinetic analysis revealed pseudo-second-order adsorption kinetics, achieving 95% Sr removal within 5 min at pH 9. Isothermal studies showed a maximum capacity of 0.28 mmol g (56 meq 100 g) at 15 mmol L Sr, accounting for 65-70% CEC and fitting the Freundlich model. Cation exchange was the dominant mechanism (84% contribution), driven by Sr displacing interlayer Ca. Alkaline conditions (pH > 9) enhanced adsorption through improved surface charge and electrostatic attraction. Thermodynamic studies demonstrated temperature-dependent behavior: increasing temperature reduced adsorption at 0.01 mM Sr but increased efficiency at 10 mM. Na addition suppressed adsorption, aligning with cation exchange mechanisms. Molecular dynamics simulations identified hydrated Ca-Sr water bridges interacting with bentonite via hydrogen-bonding networks. The material exhibits rapid kinetics (5 min equilibrium), alkaline pH optimization, and resistance to ion interference, making it suitable for emergency Sr treatment. It shows promise as a cost-effective and good performing adsorbent for radioactive waste solutions.