April 25, 2016

Nearing affordable extraction of uranium from seawater, which would unlock over 800 times current reserves and with breeder reactors provide resources for billion years of current world power

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.

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.

Best places in the oceans to intercept uranium

In marine science, current strength is sometimes measured in “Sverdrups”, a unit that corresponds to one million tons of water per second, or 30 trillion tons of water per year. The Strait of Gibraltar carries a current of about 1 Sverdrup.

Japan has proposed various scaling up plans for uranium from seawater. Japans look at the Black Current (42 Sverdrup) in the ocean off of Japan and how much materials it is moving.

The Agulhas Current is the Western Boundary Current of the southwest Indian Ocean. It flows down the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is even suggested that the Agulhas is the largest western boundary current in the world ocean, as comparable western boundary currents transport less, ranging from the Brazil Current, 16.2 Sverdrups), to the Kuroshio, 42 Sverdrups

The sources of the Agulhas Current are the East Madagascar Current (25 Sverdrups), the Mozambique Current (5 Sverdrups) and a reticulated part of the Agulhas Current itself (35 Sverdrups). The net transport of the Agulhas Current is estimated as 100 Sverdrups.

Uranium for more than current energy needs for 5 billion years - 4.5 billion tons of Uranium in the oceans, 4 billion tons of uranium on the seafloor and 32000 tons of uranium runoff from rivers

It now seems quite certain that uranium can be extracted from the ocean at well below $500 per pound and there is even some optimism that it can become competitive at current market prices ($30/lb). It is clear, then, that uranium from seawater must be considered as a completely acceptable fuel for breeder reactors, contributing less than 1% to the cost of electricity. In terms of fuel cost per million BTU, even at $400/lb the uranium cost is only 1.1 cents.

Seawater contains 3.3×10^–9 (3.3 parts per billion) of uranium. The 1.4×10**18 (1.4 million trillion) tonnes of water in the oceans contains 4.6×10**9 tonne of uranium. The energy content of uranium burned in a breeder reactor is 1 MW day/g, or 1000 GW day/tonne; at 37% efficiency, readily achievable in a breeder reactor, this is 1.0 GWe yr/tonne (GWe = GW of electricity). All of the world’s present electrical usage, 2325 GWe [372 GWe of nuclear make up 16% of world electrical supply] , could therefore be supplied by the uranium in seawater for (4.6×10**9/2325) = 1.98 million years.

At ten times the power level, it would last 198,000 years and at one hundred times it would be 19,800 years.

Rivers bring 32 trilloion tons per year of water into the oceans, and their uranium content averages one part per billion. 32,000 tons per year of uranium enter the oceans from this source.

We can withdraw 16 000 tonne/yr of uranium from seawater continuously for hundreds of millions of years. This is enough to produce 16 000 GWe or 480 quadrillion BTU per year, which is 6 times the world’s present electricity usage, and almost the world’s present total energy consumption.

SOURCES - Oak Ridge National Lab, Wikipedia

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