Theoretical Insight Towards Uranium Extraction from Seawater
Uranium’s economical consumption is based on the industrial nuclear fuel cycle. Today there remains 4-6 million tons of terrestrial uranium in Earth’s ores. However, as the projected population is estimated to double by 2040, current uranium reserves are only estimated to provide nuclear fuel for the next century. Unconventional methods for acquiring uranium are, therefore, required to maintain longevity and sustainability for future economic nuclear energy demands.
One unconventional alternative for mining uranium is diving from land and into the open seas. Although uranium resides uniformly in the oceans at very low concentrations of 3.3 ppb, in a vast body of Earths water, there exists an untapped reserve of uranium at an astounding 4.5 billion ton. Uranium exists in aqueous environment as the stable oxo-cation, in the hexavalent (VI) state called uranyl, UO22+, and as the neutral ternary-uranyl-carbonato, Ca2UO2(CO3)3, in seawater.
After six generations of research and development, current extraction methods rely on a polymer grafter amidoxime-based (poly(AO)) material for uranium recovery from seawater. One chemical advancement in adsorption capacity is from the inclusion the hydrophilic group carboxylate (Ac). However, displacing coordinating carbonates with poly(amidoxime) from uranyl, which is both at low concentrations and existing in soup of various metal-ions in a seawater matrix, still remains a formidable challenge. One of the multifaceted efforts involved with increasing adsorption selectivity is by the theoretical insight into uranium’s coordination chemistry with interacting ligands in seawater-related environments.
Herein we utilize current state-of-the-art, advanced computing technology to investigate coordinating uranium species in a completely explicit model. First, we employ a pure quantum mechanical (QM) simulations to pry into the chemistry of surrounding water molecules’ influence on the dominant Ca2[UO2(CO3)3] specie. Furthermore, large scale classical molecular dynamics (CMD) simulations are assisted with umbrella sampling to develop computational techniques for investigating coordinating uranyl-AO from calculating binding free-energies (Gbind). Furthermore, we investigate the influence of capacity by inspecting the interactions of mix-ligand containing AO/Ac. Additionally, employing umbrella sampling method coupled with WHAM, we investigate the sodium ion solvation environment of one of the most competing vanadium-containing species, HVO42-.