Eu (III) sorption from an aqueous solution onto SrTiO3 and surface complex behavior

• Eu (III) sorption on SrTiO3 occurs when the solid surface is positively charged.
• Eu (III) sorption occurs through an interaction between two surface sites with EuNO32+ in solution.
• Eu (III) sorption occurs through bidentate surface complex formation.
• The Eu (III) sorption process on SrTiO3 is exothermic and spontaneous.

The present work considers the interaction between Eu (III) in liquid phase and a sorbent solid material (SrTiO3). Certain materials are known strong complexion agents, including titanate; strontium titanate can be easily synthesized as a single-phase compound at a low temperature. Thus, the sorbent material SrTiO3 in the perovskite form was tested using 1 × 10−4 M Eu3+(NO3)2 solutions in a KNO3 0.5 M salt background. Both structural and thermodynamic studies were performed using the batch method. The sorption edge for Eu (III) on SrTiO3 was modeled using FITEQL 4.0v code and experimental sorption curves to calculate the europium surface complexation constants. The sorption edge was fitted with mono- and bidentate Eu3+(NO3)2+ surface complexes formed on the SrTiO3 surface. Below pH 6, bidentate surface complex was formed through two types of interactions (TiOH)2EuNO32+ (log K = 9.08 ± 0.02). However, at a pH values greater than 6, the immobilization process is associated with chemical precipitation due to surface europium hydroxyl and the carbonate species. The sorption thermodynamic parameters were thermodynamically quantified as a function of different system temperatures through applying the van’t Hoff modified equation; ΔH° = −31.30 kJ mol−1, ΔS° = −6.53 × 10−2 kJ mol−1 K−1, and ΔG° = −11.99 kJ mol−1. These results suggest that the Eu (III) sorption process onto SrTiO3 is exothermic and spontaneous.

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