Removal of Cesium and Strontium Ions from Aqueous Solutions by Thermally Treated Natural Zeolite

The radionuclides of cesium (Cs) and strontium (Sr) are dangerous products of nuclear fission that can be accidentally released into wastewater. In the present work, the capacity of thermally treated natural zeolite (NZ) from Macicasu (Romania) to remove Cs⁺ and Sr²⁺ ions from aqueous solutions in batch mode was investigated by contacting different zeolite quantities (0.5, 1, and 2 g) of 0.5-1.25 mm (NZ1) and 0.1-0.5 mm (NZ2) particle size fractions with 50 mL working solutions of Cs⁺ and Sr²⁺ (10, 50, and 100 mg L^-1 initial concentrations) for 180 min. The concentration of Cs in the aqueous solutions was determined by inductively coupled plasma mass spectrometry (ICP-MS), whereas the Sr concentration was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The removal efficiency of Cs⁺ varied between 62.8 and 99.3%, whereas Sr²⁺ ranged between 51.3 and 94.5%, depending on the initial concentrations, the contact time, the amount, and particle size of the adsorbent material. The sorption of Cs⁺ and Sr²⁺ was analyzed using the nonlinear form of Langmuir and Freundlich isotherm models and pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. The results indicated that the sorption kinetics of Cs⁺ and Sr²⁺ on thermally treated natural zeolite was described by the PSO kinetic model. Chemisorption dominates the retention of both Cs⁺ and Sr²⁺ by strong coordinate bonds with an aluminosilicate zeolite skeleton.