Comparative study for adsorptive removal of radioactive Cs⁺, Sr²⁺ and Co²⁺ ions from aqueous solution by acid-activated white clay

Raw white clay was acidified with H₂SO₄ (2 M) and then activated in a furnace for 2 h at 150^oC. The resulting acid-activated clay product was used as an adsorbent for the removal of radioactive substances such as Cs⁺, Sr²⁺ and Co²⁺ ions in aqueous solution. The specific surface area and the pore volume of acid-activated clay were three times higher compared to raw white clay. At 100 mg L^- of initial concentration and 1.0 g of dosage, removal efficiencies of Cs⁺, Sr²⁺ and Co²⁺ ions showed 60.0%, 27.3%, and 88.1%, respectively. It was found that the Langmuir isotherm was described well to the adsorption behavior of Cs⁺, Sr²⁺ and Co²⁺ ions on acid-activated clay rather than Freundlich isotherm. The Langmuir isotherm constant (Q) for Cs⁺, Sr²⁺ and Co²⁺ ions was found to be 8.81, 3.78 and 10.20 mg g^-1, respectively. Compared to the pseudo-first-order kinetic model, the pseudo-second-order kinetic model was more suitable for adsorption of Cs⁺, Sr²⁺ and Co²⁺ ions in water/acid-activated clay medium owing to the higher correlation coefficient (R²) and the more proximity value of the experimental value q_e,exp and the calculated value q_e,cal.