An international Australian-led research team, including a core group of ANSTO scientists, has discovered that doping a promising material provides a simple and effective method for extracting uranium from seawater. The research, published in the journal Energy Advances and presented here, could help develop new materials that are highly selective for uranium, efficient and cost-effective.

Uranium is a very valuable mineral used as a fuel source in nuclear reactors around the world.

“There is a lot of uranium in the oceans, a thousand times more than in the depths, but it is really diluted, so it is very difficult to extract it. The main problem is that other substances in seawater, salts and minerals such as iron and calcium, are present in much larger quantities than uranium,” he explains principal investigator Dr. Jessica Welyszek Carolan.

Layered double hydroxides, materials noted for their ability to remove metals, are relatively easy to make and can be modified to improve their performance. Because these layers have positive and negative charges, they can be adapted to trap certain substances, such as uranium.

Alloying impurities of lanthanides were tested: neodymium, europium and terbium. Adding neodymium to layered double hydroxides (LDHs) improved their ability to selectively capture uranium from seawater, a highly complex process that scientists have long studied.

The synthesized materials were characterized using a variety of techniques, including scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM), at the ANSTO Microscope Laboratory under the supervision of Dr Daniel Oldfield and at UNSW under the supervision of Yuwei Yang.

When neodymium was added to SDG (MgAlNd), these materials favored uranium over ten other common elements found in real seawater. It is important to note that the experiments were carried out in conditions close to sea water. The most important discovery was that the alloying impurity neodymium changes the way uranium binds to LDH.

The research team also used X-ray absorption spectroscopy (XAS) and soft X-ray spectroscopy at Australia’s ANSTO synchrotron to elucidate the octahedral coordination environment, oxidation state and adsorption mechanism, respectively. Co-authors of the paper, instrument scientists Dr. Jessica Hamilton and Dr. Lars Thomsen helped them.

X-ray measurements showed that uranium removal in seawater conditions occurs through a process in which uranium atoms form complexes on the SDH surface, replacing nitrate ions in the SDH layers with uranyl carbonate anions from the seawater.

Due to the addition of neodymium and other lanthanide elements to the structure of LDH, the chemical bond between metal atoms and oxygen in LDH has become more ionic. This improved ionic bonding made these materials much better at selectively binding to uranium through ionic surface interactions.

The study demonstrates a way to regulate a material’s ability to capture uranium, which could lead to the creation of new materials that are better at separating uranium from other substances, the authors said. These materials are not only useful in extracting uranium from seawater, but can also be used to clean uranium from radioactive wastewater near nuclear power plants.

“Additional advantages are that these materials are simple and cheap to produce, making them a cost-effective choice for large-scale uranium mining,” said Dr Velyszek Karolan.