The oceans hold more than four billion tons of uranium—enough to meet global energy needs for the next 10,000 years if only we could capture the element from seawater to fuel nuclear power plants.
For half a century, researchers worldwide have tried to mine uranium from the oceans with limited success. In the 1990s, Japan Atomic Energy Agency (JAEA) scientists pioneered materials that hold uranium as it is stuck or adsorbed onto surfaces of the material submerged in seawater. In 2011, the U.S. Department of Energy (DOE) initiated a program involving a multidisciplinary team from U.S. national laboratories, universities and research institutes to address the fundamental challenges of economically extracting uranium from seawater. Within five years this team has developed new adsorbents that reduce the cost of extracting uranium from seawater by three to four times.
- Uranium from seawater would unlock access to over 4 billion tons of uranium and more uranium goes into the ocean from rivers eroding land (all land has about 3 parts uranium per billion)
- Switching to advanced breeder reactors or extensive reprocessing can increase the efficiency of uranium usage by 60 times.
- New material would absorb one kilogram of uranium per ton of membranes every two months. This is dozens of times more efficient than than a peak uranium doomer assumed a few years ago. Ugo Bardi assumed recovering one kilogram of uranium would require processing at least 3 tons of membranes per year.
Oak Ridge National Laboratory researchers developed a fiber to adsorb uranium from seawater. Researchers at Pacific Northwest National Laboratory exposed the fibers to Pseudomonas fluorescens and used the Advanced Photon Source at Argonne National Laboratory to create a 3-D X-ray microtomograph to determine that the fiber structure was not damaged by the organism. Image credit: Pacific Northwest National Laboratory, U.S. Dept. of Energy
“Understanding how the adsorbents perform under natural seawater conditions is critical to reliably assessing how well the uranium adsorbent materials work,” Gill said. “In addition to marine testing, we assessed how well the adsorbent attracted uranium versus other elements, adsorbent durability, whether buildup of marine organisms might impact adsorbent capacity, and we demonstrated that most of the adsorbent materials are not toxic. PNNL also performed experiments to optimize release of uranium from the adsorbents and adsorbent re-use using acid and bicarbonate solutions.”
American Chemical Society - The Uranium from Seawater Program at the Pacific Northwest National Laboratory: Overview of Marine Testing, Adsorbent Characterization, Adsorbent Durability, Adsorbent Toxicity, and Deployment Studies
Marine testing at PNNL showed an ORNL adsorbent material had the capacity to hold 5.2 grams of uranium per kilogram of adsorbent in 49 days of natural seawater exposure—the crowning result presented in the special issue. The Uranium from Seawater program continues to make significant advancements, producing adsorbents with even higher capacities for grabbing uranium. Recent testing exceeded 6 grams of uranium per kilogram of adsorbent after 56 days in natural seawater – an adsorbent capacity that is 15 percent higher than the results highlighted in the special edition.
The Pacific Northwest National Laboratory (PNNL) is evaluating the performance of adsorption materials to extract uranium from natural seawater. Testing consists of measurements of the adsorption of uranium and other elements from seawater as a function of time using flow-through columns and a recirculating flume to determine adsorbent capacity and adsorption kinetics. The amidoxime-based polymer adsorbent AF1, produced by Oak Ridge National Laboratory (ORNL), had a 56-day adsorption capacity of 3.9 ± 0.2 g U/kg adsorbent material, a saturation capacity of 5.4 ± 0.2 g U/kg adsorbent material, and a half-saturation time of 23 ± 2 days. The ORNL AF1 adsorbent has a very high affinity for uranium, as evidenced by a 56-day distribution coefficient between adsorbent and solution of log KD,56day = 6.08. Calcium and magnesium account for a majority of the cations adsorbed by the ORNL amidoxime-based adsorbents (61% by mass and 74% by molar percent), uranium is the fourth most abundant element adsorbed by mass and seventh most abundant by molar percentage.
Marine testing at Woods Hole Oceanographic Institution with the ORNL AF1 adsorbent produced adsorption capacities 15% and 55% higher than those observed at PNNL for column and flume testing, respectively. Variations in competing ions may be the explanation for the regional differences. Hydrodynamic modeling predicts that a farm of adsorbent materials will likely have minimal effect on ocean currents and removal of uranium and other elements from seawater when farm densities are less than 1800 braids per square kilometer. A decrease in uranium adsorption capacity of up to 30% was observed after 42 days of exposure because of biofouling when the ORNL braided adsorbent AI8 was exposed to raw seawater in a flume in the presence of light.
No toxicity was observed with flow-through column effluents of any absorbent materials tested to date. Toxicity could be induced with some non-amidoxime based absorbents only when the ratio of solid absorbent to test media was increased to part per thousand levels. Thermodynamic modeling of the seawater−amidoxime adsorbent was performed using the geochemical modeling program PHREEQC. Modeling of the binding of Ca, Mg, Fe, Ni, Cu, U, and V reveal that when binding sites are limited (1 × 10^–8 binding sites/kg seawater), vanadium heavily outcompetes other ions for the amidoxime sites. In contrast, when binding sites are abundant, Mg and Ca dominate the total percentage of metals bound to the sorbent.
- Uranium coordination and computer-aided ligand design (ORNL)
- Thermodynamic, kinetic and structural characterization of the adsorbent (Lawrence Berkeley National Laboratory, ORNL, PNNL)
- Adsorbent synthesis using radiation to graft more polymer onto the polyethylene (ORNL, Brookhaven National Laboratory, University of Maryland)
- Adsorbent synthesis using a chemical method (ORNL, University of Tennessee)
- Adsorbent nanosynthesis (ORNL, PNNL, Hunter College, University of Chicago, University of South Florida, SLAC National Accelerator Laboratory, University of California–Berkeley)
- Laboratory testing and modeling of adsorbent performance (ORNL, Georgia Tech)
- Marine testing and performance assessment of the adsorbent (PNNL, Woods Hole Oceanographic Institution, University of Miami)
- Adsorbent durability and reusability (PNNL, University of Idaho)
- Adsorbent characterization, toxicity and biofouling studies (ORNL, PNNL, UI)
- Technology cost analyses and modeling (University of Texas–Austin)
- Green chemistry: Adsorbents prepared using marine shellfish waste (University of Alabama)
- Adsorbent deployment (PNNL, ORNL, MIT)
Uranium from terrestrial sources can last for approximately 100 years, according to Erich Schneider of the University of Texas–Austin. As terrestrial uranium becomes depleted, prices are likely to rise. “If we have technology to capture uranium from seawater, we can ensure that an essentially unlimited supply of the element becomes available if uranium prices go up in the future,” Schneider said.
Read more »
Reposted via Next Big Future
No comments:
Post a Comment