Adsorption of Sr from waste effluents using Taiwan Zhi-Shin bentonite

Strontium (Sr²⁺), a hazardous radionuclide in nuclear waste, requires efficient adsorption for pollution control. Taiwan’s Zhangyuan bentonite, with high cation exchange capacity (CEC: 80–86 meq/100 g), offers potential for Sr²⁺ removal. This study systematically investigated its adsorption performance and mechanisms under diverse conditions, aiming to develop an eco-friendly and cost-effective solution for radioactive wastewater treatment.

Batch adsorption experiments evaluated the effects of time, Sr²⁺ concentration, temperature, pH, and Na⁺ levels. Adsorption kinetics and isotherms were modeled using pseudo-second-order and Freundlich equations. XRD analyzed interlayer spacing (d001) to track Sr²⁺ intercalation. Cation desorption quantified exchange mechanisms, while ab initio molecular dynamics (AIMD) simulations elucidated Sr²⁺-Ca²⁺ interactions via water bridge networks.

Taiwan bentonite achieved 95% Sr²⁺ removal within 5 minutes, with a maximum capacity of 0.28 mmol/g (56 meq/100 g, 65% of CEC). Cation exchange dominated (84% contribution), primarily displacing Ca²⁺ (60.4% desorbed ions). XRD confirmed Sr²⁺ intercalation, expanding d001 from 14.71 Å to 15.6 Å. Alkaline conditions (pH >9) enhanced adsorption by strengthening electrostatic attraction and suppressing Ca²⁺ competition. Na⁺ reduced capacity, validating exchange priority. AIMD revealed Sr²⁺ formed hydrogen bonds with bentonite oxygen via bilayer hydration (adsorption energy: -15.3 eV), while water bridges between Sr²⁺ and Ca²⁺ stabilized adsorption sites.

Taiwan bentonite emerges as a promising material for emergency Sr²⁺ treatment in nuclear wastewater, offering rapid kinetics (5-minute equilibrium), high capacity, and pH adaptability (optimized at pH >9). Its natural abundance, low cost, and resistance to ion interference (e.g., 65% CEC utilization under Na⁺ competition) surpass synthetic alternatives. The dual mechanism—cation exchange and surface complexation—provides a theoretical basis for enhancing bentonite’s swelling properties and long-term stability. This study advances the application of natural minerals in nuclear waste disposal, highlighting their practicality in large-scale environmental remediation.