Highly efficient diluent-free solvent extraction of uranium using mixtures of protonated trioctylamine and quaternary ammonium salts. Comparative Life Cycle Assessment with the conventional extractant

A more environmentally friendly solvent extraction process was formulated for uranium extraction using diluent-free extractants based on trialkylammonium compounds. The effect of ammonium cations and anions toward extraction efficiency, viscosity and phase separation was also evaluated. These systems were shown to be highly efficient and simple to implement as they rely on the same chemical components as those applied in the actual industrial process. It has also been demonstrated that using such alternatives allows not only to prevent third phase formation and subsequent extractant degradation, but also reduces the evaporation loss of solvent by a factor of 20. Among the systems investigated, the pure [TOAH](2)[SO4] was selected as the simplest and most efficient. A comparative Life Cycle Assessment (LCA) was also conducted between this system and the conventional solvent to compare more objectively their sustainability. Results based on four environmental indicators show that the new system is 18 times less impactful. Contrary to expectations, this study also showed that the pure (diluent-free) extractant system needs to be at least 2 times more efficient in terms of metal extraction to become significantly more sustainable. Other main effects contributing to the LCA are derived from: (i) the production of chemicals, which is much more harmful for extractants than for aliphatic diluents, (ii) the loss of Volatile Organic Compounds (VOC) to the environment, and (iii) to a lesser extent, the additional centrifugation step that may be required to separate more viscous systems.