Evaluation of Fe-doped calcium phosphate for ⁶⁵Zn sorption

⁶⁵Zn, a fission product found in cooling water reactors, poses significant environmental risks due to its toxicity. This study explores the use of Ca–Fe²⁺ phosphate (SB1) and Ca–Fe³⁺ phosphate (SB2) as sorbents for Zn(II), prepared via the wet chemical method. The Zn(II) solution, spiked with ⁶⁵Zn radionuclides, was analyzed radiometrically. Optimal sorption conditions were determined to be pH 4.5, a contact time of 24 h, and a sorbate volume to sorbent mass ratio of 1:10 at 20 °C. The Langmuir isotherm model best fit the adsorption data, indicating monolayer adsorption capacities of 0.574 mmol g⁻¹ for SB1 and 0.621 mmol g⁻¹ for SB2. Sorption kinetics followed a quasi-n^th-order model. Furthermore, 0.1 M FeCl₃ effectively desorbed 99% of Zn(II) from both sorbents. The sorption process was found to be spontaneous and endothermic. These findings suggest that SB1 and SB2 have potential applications in recycling Zn(II) from the black mass of expired batteries.