The adsorption efficiency of Sr2+ and Ba2+ from aqueous solutions by zeolite 4A was investigated. Adsorption studies were carried out both in single and binary component systems. The single ion equilibrium adsorption data were fitted to three isotherm models: Langmuir, Freundlich and Dubinin–Radushkevich. The Langmuir model represents the equilibrium data better than the Freundlich model in the studied initial metal concentration (0.3–25 mmol L−1) in both the single and binary component systems. The obtained RL (separation factor or Langmuir parameter) values were in the range of 0–1 indicating that Sr2+ and Ba2+ sorption were favorable. The obtained mean free energy value for adsorption of Ba2+ and Sr2+ was 8.45 kJ mol−1 and 9.12 kJ mol−1, respectively, indicating that both ions were uptaken through an ion exchange process. The maximum adsorption capacities (Qmax) were 2.25 mmol g−1 and 2.34 mmol g−1 for Ba2+ and Sr2+ ions, respectively. Also, the study of the competitive sorption of ions in the binary system showed that zeolite 4A preferentially adsorbs cations in the following order: Ba2+ < Sr2+.

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