Efficient adsorptive removal of potassium from potassium perrhenate solution using a cationic ion exchange resin

Potassium is a harmful impurity in the rhenium sinter, which adversely affects its mechanical properties by significantly reducing the density of sintered rhenium. Cationic resin is a promising material for potassium removal. In this study, the strong acid cationic exchange resin C160H was pretreated with an HNO₃ solution to enhance its performance in potassium removal. The pretreated C160H resin was characterized using BET, SEM and point of zero charge (PZC) measurements to understand its physicochemical properties. It was verified that the lower PZC value of C160H than that of pristine C160 resin resulted in increased potassium adsorption efficiency. Moreover, the pretreated C160H resin exhibited a maximum potassium adsorption efficiency of 99.28% for 2.00 g L^-1 KReO₄ at 25 °C and pH 7.0 for 6 h, with a solid-to-liquid ratio of 1 : 20. The cation sequence affecting potassium adsorption efficiency was found to be Na⁺ < Ca²⁺ < Fe³⁺ < NH₄ ⁺. Isothermal adsorption thermodynamics showed that potassium adsorption by C160H resin followed a heterogeneous and exothermic process. The pseudo-second-order kinetics model best fitted the data, suggesting that potassium adsorption was primarily chemical in nature. DFT calculations confirmed that the adsorption mechanism was based on ion exchange between H⁺ and K⁺, with electrostatic interactions serving as the primary driving force for adsorption. The C160H resin demonstrated outstanding regeneration performance, maintaining an adsorption efficiency above 99% after ten cycles. These findings could contribute to improve the potassium adsorption capacity of the resin, thereby reducing both resin dosage and cost in the purification of perrhenate salts.