Speaker
Description
Introduction
Due to the very promising properties of α-emitting radionuclides for cancer therapy, there is a high interest in α-emitters such as actinium-225. However, the poor availability of Ac-225 limits research, necessitating the development of new production routes. When using radium or thorium as target material, these new routes result in a highly active mixture of radionuclides from which the Ac-225 has to be separated. Currently, organic ion-exchange resins are applied for this separation, but they suffer from radiolytic degradation. As inorganic materials are generally much more radiation resistant, this research investigated the separation of radium and actinium using inorganic resins.
Methods
Four inorganic resin materials were examined, of which zirconium phosphate (ZrP) and titanium phosphate (TiP) were synthesized via the direct precipitation method, and zirconium oxide (ZrO2) and cerium oxide (CeO2) were purchased. Ra-223 and Ac-225 were used as target and product radionuclide tracers, with the chemically similar barium and lanthanum added to mimic more realistic concentrations. The sorption and reaction kinetics were determined in batch by contacting the resin material with stocks of different pH at different interaction times. Subsequent column experiments were performed using ZrP as resin material. The columns were run at a flow rate of 0.4 ml/min, loaded at neutral pH, after which the residual Ra-223 was washed off using a pH 3 HNO3 solution and the Ac-225 was eluted with 1 M HNO3.
Results
During the batch sorption experiments, it was found that neither Ac-225 nor Ra-223 were adsorbed at pH 1 for all four sorbents. The Ac-225 adsorption increased with pH, i.e. more than 97% of Ac-225 was adsorbed by ZrP, TiP and CeO2 at a neutral pH, while for ZrO2 only about half (55.7 ± 0.5%) of the Ac-225 was adsorbed. At this pH, the Ra-223 co-adsorption by CeO2 and ZrO2 was low, about 6 ± 1%, but relatively high (51 ± 5%) for the ZrP and TiP resin materials. Nevertheless, the kinetics experiments demonstrated that the Ac-225 adsorption by ZrP was much faster than that of Ra-223, making it still a viable option as resin material. Therefore, considering its exchange characteristics, synthesis and particle size, ZrP was selected as the most promising resin material.
Column experiments using ZrP as resin material demonstrated high loading efficiencies of Ac-225 (99.99 ± 0.02% ). Co-adsorption of Ra-223 was relatively high (40.9 ± 0.7%), but could mostly be washed off (33 ± 2%) using a pH 3 solution, with only very limited Ac-225 breakthrough (0.2± 0.4%). Near complete elution (99.2 ± 0.7%) of the Ac-225 was achieved using 1 M HNO3, accompanied by 7% of the Ra-223, demonstrating the separation capabilities of ZrP.
Concluding, different resin materials were tested of which ZrP seemed the most promising and column experiments demonstrated its potential for the separation of Ra-223 and Ac-225. Therefore, ZrP is a promising candidate to utilize in the production of Ac-225, overcoming radiolytic degradation issues of current organic alternatives.