Three zirconium phosphate products A, B and C, made through different synthesis routes, were investigated for their europium and americium ion exchange properties utilizing radiotracers ¹⁵²Eu³⁺ and ²⁴¹Am³⁺. Aim of this investigation was to see how material properties change based on different synthesis, and how does the changes effect on trivalent Eu and Am uptake and affinities on the materials. Ultimate goal of an ongoing research is to create inorganic exchanger suitable for separation of trivalent actinides and lanthanides. Powder X-ray diffraction showed that all three products had same α-zirconium phosphate crystal structure. The P:Zr ratio determined by microscope X-ray microanalysis was also the same for all products: 2.43±0.05. However, infrared absorbance, material acidity, particle morphology, and Eu and Am distribution coefficients differed significantly between products. The intensities of the strong IR absorption at approximately 960 cm⁻¹, attributed to vibrations of the orthophosphate group, were in descending order B>C>A. Material acidity showed the same descending order B>C>A. First acidity constants pK _a1 were 2.3 for product B, 3.1 for C and 3.5 for A. Unit cell volumes increased in the reverse order: BB for both Eu and Am. Separation factors, defined as K _D(Eu): K _D(Am), were from 4 to 41 for product A, from 5 to 15 for B, and from 3 to 7 for C. Selectivity coefficients (k _M/H, M=Eu, Am) and sorption strength decreased along with increasing ZrP product acidity. Metal binding coefficients (k _M) had high values, up to 10⁹, especially in ZrP C and A, while the selectivity coefficients were low, 10⁻⁵ to 10⁻¹, because they relate to the third power of the low pK _a1. It was observed that for ZrPs there are strong interdependencies between acidity of the product, unit cell volume, IR absorption, K _D, k _M/H and k _M. Finally, it can be concluded that the ion exchange properties of α-ZrP products can be modified considerably by varying their synthesis conditions, perhaps to tailor specific actinide/lanthanide separations.

The trivalent lanthanide-actinide separations are a major challenge in reprocessing of nuclear fuels. To achieve this, commonly organic extractants and solvents are utilized in elaborate processes. Here we report a simple new method that can perform a supportive or alternative role. A nanocrystalline α-zirconium phosphate ion exchanger was utilized for Eu(III)/Am(III) column separation. Comprehensive preliminary studies were done using batch experiments to optimize the final separation conditions. The distribution coefficients for Eu were determined as a function of pH (from 0 to 3) and salinity (Na, Sr). The distribution coefficients for Am were determined as a function of pH, and Eu concentration, from 1:40 to 10,000:1 Eu:Am molar ratio. The exchanger always preferred Eu over Am in our experimental conditions. Separation factors (Eu:Am) of up to 400 were achieved in binary Eu-Am solution in pH 1. The breakthrough capacity was determined in dynamic column conditions using Eu: 0.3 meq∙g⁻¹, which is approximately 4% of the theoretical maximum capacity. Two types of hot column separation tests were conducted: (i) binary load (selective Am elution), and (ii) continuous equimolar binary feed. In both cases separation was achieved. In (i), the majority (82% of the recovered 93%) of Am could be purified from Eu with extremely high 99.999% molar purity, while alternatively even more (95% of the recovered 93%) at a lower purity of 99.7 mol %. In (ii), up to 330 L∙kg⁻¹ of the equimolar solution per mass of the exchanger could be treated with Am purity above 99.5 mol % in the total eluate. Alternatively, up to 630 L∙kg⁻¹ above 95 mol %, or up to 800 L∙kg⁻¹ above 90 mol % purities.