Distribution Coefficients of 46 Elements in Phosphoric Acid аnd Phosphoric–Nitric Acid Solutions on a Strong-Acid Cation-Exchange Resin (DOWEX 50WX8)

Phosphoric acid provides a chemically active medium for the dissolution, treatment and separation of metal ions, making it relevant to a number of analytical and radiochemical tasks. It influences the speciation and sorption behavior of metal ions, which is critical for understanding their interaction with ion-exchange resins. For such applications, separation of metal impurities is required, and ion exchange remains one of the most effective techniques. In this work, the distribution coefficients of 46 elements were determined on a strong-acid cation-exchange resin (DOWEX 50WX8, 100–200 mesh) in phosphoric acid solutions containing 1–85 wt% H₃PO₄, as well as in mixed phosphoric–nitric acid media containing 0.3 or 1.0 mol/L HNO₃. Measurements were performed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) following the equilibrium between phases. This study provides the first multi-element dataset of their sorption behavior on cation exchange resin in phosphoric acid and H₃PO₄-HNO₃ media. The observed distribution patterns demonstrate the potential of DOWEX 50WX8 for selective separation of several groups of elements, including gallium from iron, thorium from uranium, and magnesium from the heavier alkaline-earth metals. Systematic differences in the retention of light lanthanides in phosphoric acid also indicate the potential for their fractionation. The difference in the distribution coefficients of thorium and uranium, together with the characteristic retention behavior of lanthanides, may be relevant to the separation of actinium from thorium and uranium-containing matrices in processes related to 225Ac production. In mixed phosphoric–nitric acid systems, increasing nitric acid concentration generally reduced element retention and separation selectivity.