Production and purification of no-carrier-added ⁸⁹Zr at the Leipzig cyclotron for extraction studies with a calix[4]arene

Zirconium is one of the main contaminants in important lanthanide ores. To study the separation of tetravalent zirconium from the trivalent lanthanides by means of calixarene liquid-liquid extraction, the radiotracer technique was used [⁸⁹Zr (T_1/2=78.4 h, E_γ=909 keV, 99%)]. The production of this radionuclide was performed at the Leipzig cyclotron CYCLONE 18/9^® by using the nuclear reaction ⁸⁹Y(p,n)⁸⁹Zr. An yttrium foil (natural abundance 100% ⁸⁹Y; 80 mg) was irradiated with 14 MeV protons at a current of 22 µA for one hour. The irradiated target was stored for one hour for the decay of the short-lived ^89mZr (T_1/2=4.2 min) and was then dissolved in conc. HNO₃. After dissolution of the residue with 9 M HNO₃, UTEVA-Spec^® was used to adsorb ⁸⁹Zr and elute Y³⁺ with 9 M HNO₃ from the resin. ⁸⁹Zr was washed from the resin by complexation with 0.1 M oxalic acid. The oxalic acid complex was decomposed by fuming with conc. H₂SO₄. The no-carrier-added ⁸⁹Zr was dissolved in 1 M H₂SO₄ with a radiochemical yield of 101% ± 8%. An activity of ~400 MBq was achieved 5 hours after end of bombardment with a detection limit of 7 fM (0.6 pg/L) for no-carrier-added ⁸⁹Zr.
Liquid-liquid extraction was performed with a calixarene/chloroform system from acidic aqueous solutions with pH values from 1 to 5. A calix[4]arene, exhibiting phosphonate ester and carboxylic groups, was used. A solution containing ~5 MBq/L ⁸⁹Zr and 10 µM non-radioactive zirconium carrier was shaken with a tenfold excess of the calixarene at the desired pH for one hour. After separation of the organic and the aqueous phases, the content of ⁸⁹Zr was measured by γ-counting in both phases. An extraction yield of >95% was reached for zirconium at pH 4. In previous studies with ¹⁵²Eu, less than 5% of this lanthanide were extracted at pH 4, while >98% of the ¹⁵²Eu were extracted at pH 8.
In future studies, ⁸⁹Zr could be used for radiolabelling ZrO₂-nanoparticles in environmental sciences as a surrogate for long-lived ThO₂-nanoparticles.