An Efficient NTAamide( <i>n</i> -Oct) Extraction Resin for High-Purity Thorium Preparation

High-purity thorium is essential for producing key radioactive nuclides, such as ²³³U and ²²⁵Ac. Currently, the primary challenge in preparing high-purity thorium is separating trace amounts of uranium and rare earth impurities from crude thorium products. To address this, an efficient NTAamide(<i>n</i>-Oct)@CG71M extraction resin was developed for isolating high-purity thorium in a nitric acid medium containing uranium and rare earth elements. Batch adsorption studies exhibit high selectivity and strong adsorbability for thorium over a relatively wide acidity range of 0.10-8.0 mol/L HNO₃. The adsorption of thorium onto the resin conforms to pseudo-second-order kinetics and the Langmuir model, with a maximum Th(IV) adsorption capacity (<i>q</i>_max) of 79.9 mg/g. Thermodynamically, the process is exothermic and spontaneous, accompanied by an increase in the entropy. The NTAamide(<i>n</i>-Oct) extractant in the resin coordinates with Th(IV) via three oxygen atoms of the carbonyl groups and one tertiary amine nitrogen atom. Dynamic separation experiments confirmed that the NTAamide(<i>n</i>-Oct)@CG71M extraction resin can efficiently remove trace uranium impurities from commercial thorium nitrate reagents, yielding high-purity thorium nitrate (99.99%). Furthermore, the resin selectively separated thorium from simulated monazite HNO₃ leach liquor with a 99.4% recovery rate and high-purity thorium (99.99%) while demonstrating good reusability. Overall, this efficient extraction resin provides reliable technical support for high-purity thorium nitrate preparation and shows significant application potential.