22 August 2012
Fuelling nuclear reactors with uranium harvested from the ocean could become more feasible with a material developed by a team led by the US Department of Energy’s Oak Ridge National Laboratory (ORNL).
According to a statement, the combination of ORNL’s high-capacity reusable adsorbents and a Florida company’s high-surface-area polyethylene fibres creates a material that can rapidly, selectively and economically extract valuable and precious dissolved metals from water.
Dubbed HiCap, the material is said to vastly outperform today’s best adsorbents, which perform surface retention of solid or gas molecules, atoms or ions. HiCap also effectively removes toxic metals from water, according to results verified by researchers at Pacific Northwest National Laboratory.
‘We have shown that our adsorbents can extract five to seven times more uranium at uptake rates seven times faster than the world’s best adsorbents,’ said Chris Janke, one of the inventors and a member of ORNL’s Materials Science and Technology Division.
HiCap is claimed to effectively narrow the fiscal gap between what exists today and what is needed to economically extract some of the ocean’s estimated 4.5 billion tons of uranium.
Although dissolved uranium exists in concentrations of 3.2 parts per billion, the sheer volume means there would be enough to fuel the world’s nuclear reactors for centuries.
Research and development projects
The goal of extracting uranium from the oceans began with research and development projects in the 1960s, with Japan conducting the majority of the work.
Many adsorbent materials have been developed and evaluated, but none have emerged as being economically viable.
What sets the ORNL material apart is that the adsorbents are made from small-diameter, round or non-round fibres with high surface areas and excellent mechanical properties.
By tailoring the diameter and shape of the fibres, researchers can increase surface area and adsorption capacity.
This and ORNL’s patent-pending technology to manufacture the adsorbent fibres results in a material able to selectively recover metals more quickly and with increased adsorption capacity, thereby dramatically increasing efficiency.
‘Our HiCap adsorbents are made by subjecting high-surface-area polyethylene fibres to ionising radiation, then reacting these pre-irradiated fibres with chemical compounds that have a high affinity for selected metals,’ Janke said.
After the processing, scientists can place HiCap adsorbents in water containing the targeted material, which is quickly and preferentially trapped. Scientists then remove the adsorbents from the water and the metals are readily extracted using an acid elution method. The adsorbent can then be regenerated and reused after being conditioned with potassium hydroxide.
HiCap’s adsorption capacity is reportedly seven times higher (146g versus 22g of uranium per kilogram of adsorbent) in spiked solutions containing six parts per million of uranium at 20°C.
In seawater, HiCap’s adsorption capacity of 3.94g of uranium per kilogram of adsorbent was more than five times higher than the world’s best at 0.74g of uranium per kilogram of adsorbent. The numbers for selectivity showed HiCap to be seven times higher.