Cleaning up environments contaminated with uranium
Uranium is dissolved during the extraction process to allow concentration and transportation. But it is hazardous. Luckily Australia abounds in minerals that can capture uranium. Daniel Boland is investigating the use of iron oxides, particularly goethite, to clean up uranium in contaminated environments.
Robyn Williams: And our PhD this week is Daniel Boland from the University of New South Wales, whose work on making uranium safe even goes back to how they made ancient art in caves.
Daniel Boland: Australia is one of the world's largest producers of uranium. During the extraction process, uranium ore is dissolved, either above the ground in process plants or sometimes even while the ore is still in the ground. This is done so that the uranium can be concentrated into compounds that are easily exported, mostly for use in nuclear power plants. The trouble is, dissolving the uranium like this causes an environmental hazard.
Soluble uranium can readily be transported by both surface and subsurface water flow, putting land and water surrounding mining and processing activities at risk of contamination. Uranium in spent nuclear waste could also contaminate surrounding areas in the same way, so it is a very important that we have a way of controlling or stopping the movement of uranium in the environment.
The answer to this challenge may already be in the ground in the form of iron oxide minerals. Australia abounds in iron oxides. They exist not only in the familiar iron ore deposits that underpin the mining sector, but also in small but important quantities widespread throughout the environment. There are numerous types of iron oxides, each with quite different properties. For example, the varied shades of red, orange, brown and yellow, so iconic in Australian landscapes, are each caused by different iron oxide minerals.
Iron oxides may transform from one type into another. It has been observed recently that if dissolved uranium is present when this transformation takes place, it can become trapped inside the new iron oxide, making the uranium immobile, stopping it from moving around in the subsurface and groundwater. The aim of my research is to find out how this trapping occurs and how we could induce it to occur in a natural setting in order to clean up uranium contamination.
My research involves adding uranium to a range of different iron oxide minerals, simulating varying geochemical conditions and observing what happens. I use a synchrotron to look into the structure of the iron oxides. Using a synchrotron is like giving a molecule, crystal or mineral an X-ray. It reveals which elements are present and how they are arranged. In my research it tells me which iron oxides exist and where the uranium exists within them.
I found that the best iron oxide at trapping uranium is a yellow one called goethite. Goethite has been used in art for over 30,000 years, most notably as a pigment in European cave paintings. It is formed from another iron oxide, ferrihydrite, and if uranium is present when this happens it can get sucked into and immobilised inside the goethite.
I've also found that this transformation will only take place under a delicate set of geochemical conditions and may be inhibited by other things found in the environment such as silica from sand or organic matter. If conditions which promote the formation of goethite can be achieved in the field, this process has the potential to provide an effective means to stabilise uranium contaminated environments.
Robyn Williams: Daniel Boland at the University of New South Wales, doing subtle work, even taking X-rays of minerals. And that should have immense practical value.
- Daniel Boland
- PhD Candidate
Water Research Centre