Selective extraction of thorium from uranium and rare earth elements using sulfonated covalent organic framework and its membrane derivate

Abstract

Thorium, as a nuclear-power replacement for the uranium-based nuclear reactors and an effective avenue to produce uranium source, has become a key element for the increasing energy demand. However, we now are seriously restricted to gain thorium from mineral, due to co-existence of thorium, uranium, and rare earth elements. Accordingly, there is an urgent need to develop solid extraction technique with both large thorium adsorption capacity and high adsorption selectivity. In this work, a COF (covalent organic framework) adsorbent, namely [NH4]+[COF-SO3−] was prepared for selective extraction of thorium from uranium, and rare earth elements. The selective adsorption towards Th(IV) is reflected on the large distribution coefficient (Kd) of 1.34 × 105 mL/g, the big difference up to two orders of magnitude in the adsorption capacity, and the high selectivity (more than nine). This ultrahigh Th(IV) capture up to 395 mg/g presents the largest value for Th(IV) adsorption by porous absorbents. Furthermore, the practical separation of Th(IV) from U(VI) and rare earth elements (Eu3+ and Ce3+) was for the first time executed by both the breakthrough experiment and membrane-based separation experiment. Most importantly, upon this breakthrough separation a Th(VI) solution with high purity up to 93.5% was obtained.