Energy From Thorium Discussion Forum

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PostPosted: Jan 14, 2007 5:24 pm 
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Since Th is a slightly lighter element than U, there is a bit more of it in the universe (and the earth).
But how much of Th is reasonably accessible ?
That may depend more on the peculiarities of geochemistry, and how much ends up in ore bodies or disolved in the seas....
Quote:
http://www.dae.gov.in/ni/nijul06/nijul06.pdf
Nuclear India, VOL. 40/NO.1-2/Jul.-Aug. 2006
Recovery of Uranium from Seawater by Harnessing Tidal Energy
A K Saxena
PICUS, Desalination Division Bhabha Atomic Research Centre, Mumbai

In the last century uranium has universally gained acceptance as primary energy source. Currently it caters to about 16% of the electricity generation globally. Uranium was projected as the main workhorse of future when the fossil energy reserves dwindle by the middle of this century.

The terrestrial distribution of uranium ore occurrence is grossly uneven.

With a large coastline, India, Japan, Korea and a few other nations have a larger stake in exploiting the 4.5 billion tones of uranium locked in seawater. The greatest of the scientific and technological challenges in extracting uranium from seawater are lying in finding a technology that gives a net positive energy balance in terms of electricity produced from the so recovered uranium and the other is the cost of production.

This article deals with the Indian efforts on both these issues.

Basic adsorption mechanism

During seventies and eighties the Initial investigations on the possibilities of recovery of uranium from seawater were done using inorganic adsorbents. The inorganic adsorbents suffer limitations of adsorption rate and insufficient mechanical stability. Since early nineties extensive investigations are being carried out on organic adsorbents. Poly Acrylamid Oxime (PAO) was picked up as the best bet for studies since July 1999. It preferentially extracts heavy metal ions by chelating mechanism. A polypropylene fibre substrate is irradiated with electron beam to create grafting sites on the polymer chain and then treated with acrylonitrile to graft cyano groups on those sites. Then the cyano groups are reacted with hydroxylamine to convert them into amidoxime groups.

These amidoxime groups trap the loosely bonded uranyl ion from the uranyl tricarbonate present in the ionic form i.e. UO2 (CO3)3 in seawater. For each pair of two molecules of PAO one uranium atom is captured. Stoichiometrically PAO should have an extraction capability of 3.6 kg U/kg PAO.

Lab-scale experiments

During lab-scale experiments, many types of fiber cross-sections and geometries were evaluated for establishing efficacy of grafting. Polypropylene fibre of 1.5 Denier cross-sections as stem material in nonwoven felt form was used. Electron Beam Radiation induced grafting of acrylonitrile was carried out with optimized parameters. The solution viscosity and temperature were also found to be important factors. Then the cyno group was converted to PAO.

The substrate was then reacted with alkaline solution to impart hydrophylicity and adsorption characteristics. The tokens of size 75x70x2 mm thick and 150x150x2mm thick were used.

Corrosion, bio fouling and their combined effect on the adsorption kinetics and mechanical properties of the materials used in the suspension assembly and the substrate were studied and their compatibilities with seawater and process chemicals were established.

Based on initial success of extracting about 800 μg of uranium by harnessing the tidal wave using PAO adsorbent, a process flow sheet for a facility to extract 100gU/year was developed.

Conclusion

The specially developed organic adsorbent PAO has shown promising results for recovery of uranium from seawater. Pumped circulation schemes are inherently riddled with negative electricity gain, which means that the electricity producing potential of the recovered uranium is less than the electricity spent in its recovery. Harnessing tidal waves has the advantage of positive electricity gain. [ I think they mean 'tides,' not 'tidal waves' ]
The extent of energy gain ratio will depend much on the site selection. Feasibility studies on various sizes of pilot scales will help in optimization of process design parameters of adsorbent synthesis and improving the yield of recovered uranium. Various configurations of contactor array designs are being developed to facilitate the operational flexibility for the offshore unit of the plant and utilization of tidal energy/waves more efficiently.


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PostPosted: Jan 14, 2007 8:10 pm 
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I think it has to do with the chemistry...there are water-soluble forms of uranium but I don't think there are water-soluble forms of thorium, at least not in normal water.

If there were, then they could have made an aqueous thorium blanket in the Aqueous Homogeneous Reactor project rather than having to rely on a slurry or suspension.

I found this in Chapter 3 of FFR, pages 98-99:

Thorium.
Thorium solutions having concentrations as high as 0.5 m would be useful for one-region breeder reactors. For the breeder blanket of a two-region reactor concentrations of about 6.0 m thorium appear to be optimal, although somewhat lower concentrations would be of interest. At the present time only thorium nitrate or phosphate solutions in the presence of excess acid have been demonstrated to have the required solubilities at elevated temperatures; both of these solutions have substantial disadvantages. Thorium chloride would be expected, by analogy, to show substantial solubility at elevated temperatures, but this system has not been investigated in detail. Complex organic salts, such as thorium acetylacetonate, have high solubilities at relatively low temperatures, but these have not been investigated for use in aqueous solutions at temperatures above 100°C. Data from the literature on the solubility of thorium sulfate at low temperatures both alone and in the presence of other solutes [20] indicate that such solutions will probably not be satisfactory at elevated temperatures.

Thorium phosphate (or thorium oxide) is very soluble in concentrated phosphoric acid . Solutions containing up to 1100 g Th/liter with PO4/Th ratios of 5 and 7 could be prepared and appeared to be thermally stable but had high viscosities . Solutions containing 400 g Th/liter at PO4/Th ratios of 10 were thermally stable at 250 to 300° C with viscosities little higher than that of concentrated phosphoric acid . Efforts to improve the properties of thorium phosphate-phosphoric acid systems by the inclusion of HF, HN03, H2SO4, SeO4= , SO4, Li+, or Mg++, alone or in combination, have not proved encouraging [21].

The thorium nitrate-water system has been reported [22] as having considerable solubility up to about 225°C, at which point hydrolytic precipitation occurs . Further investigation [23] revealed a maximal stability for the 80 w/o material (to around 255°C). Increasing the acidity of the solutions (increasing the NO3/Th ratio) suppresses hydrolysis and increases the stability of the solutions as indicated by Figure 3-16, which shows the precipitation temperatures for various solutions [24] . The intensity of vapor phase coloration at elevated temperatures (rapidly reversible) increased as the nitrate/thorium ratio was raised above 4.0.


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PostPosted: Apr 04, 2009 8:44 pm 
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I looked at this question independently, than searched for this post to reply to it (I knew someone else was thinking the same thing!). The answer is no.

http://www.agu.org/eos_elec/97025e-table.html

Presumably because of solubility differences, there's five orders of magnitude more uranium than thorium in the ocean - 3.2 ppb vs. 0.02 ppt (Extrapolating, ~30,000 tons Th in all). So unless we plan on strip-mining the earth's crust (I doubt it), we'll probably end up switching back to uranium from seawater, a couple of centuries out. Or fusion.


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PostPosted: Apr 05, 2009 12:01 am 
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Thorium is significantly less water soluble than uranium, therefore the Th content of sea water is much less.
There is about ~10^4 less Th in oceans than U, while there is ~3.8x more Th in the crust than there is U.

For more detailed discussion, see Nuclear Energy: Principles, Practices, and Prospects by David Bodansky, section 3.4.3 pg 70-74, Tab 3.4 pg 72:
http://books.google.com/books?id=fCWKCl ... s#PPA71,M1


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PostPosted: Apr 05, 2009 12:16 am 
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Thomas232 wrote:
So unless we plan on strip-mining the earth's crust (I doubt it), we'll probably end up switching back to uranium from seawater, a couple of centuries out. Or fusion.


True but I doubt than it would take centuries. First we are not going to abandon U cycle for Th cycle, both will be used. We have enough SNF and DU already mined up to run centuries on closed U cycle alone, then there is uranium in coal ashes, phosphates, and many deep mine locations which are not economic to mine or even prospect now. Similarly for Th, contemporary RAR numbers correspond to early estimates(, in times when Th is nearly worthless). This was recently demonstrated by nearly doubling of the global Th reserves after it's significant increase in the US.

Around 1910 it was though that there is only about 10 years of coal left.

So I agree than unless we come up with a new energy resource, we'll be eventually stuck with ocean uranium recovery, but I dont see that happening in the next thousand of years at the very least. Speculating about energy resources beyond thousands of years is entertaining, but not really an issue to worry about :)


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PostPosted: Apr 05, 2009 3:24 am 
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Thomas232 wrote:
So unless we plan on strip-mining the earth's crust (I doubt it), we'll probably end up switching back to uranium from seawater, a couple of centuries out. Or fusion.

Not bloody likely. Thorium is log normal distributed like uranium, meaning there are tens of thousands of years worth of ore at far higher concentrations than what you get from dirt. And even strip mining thorium out of ordinary granites is more economical than pulling uranium from the ocean. Thats not saying that uranium ocean recovery is expensive, just that the relative cost of thorium is so cheap.

Currently we extract uranium at Rossing with an ore concentration of less than 300 ppm. For ocean uranium recovery to be profitable it has to be some five to ten times the current price today, so then you'll be competing with hard rock mining of 30ppm. By the time we've exhasted all the thorium hard rock ores better grade than 30ppm, you're into the ten thousand year mark assuming you're burning all of industrial civilization at 10000 times the energy use today. It absolutely wont ever happen.

Uranium ocean recovery is an interesting, yet ultimately useless technology only for rhetorical purposes.


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PostPosted: Apr 05, 2009 10:36 am 
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This sea-water Uranium is just useful for rhetorical exercise. Something like a mathematician's tool to prove a point. It will never be mined (hopefully). We have far better resources (Depleted Uranium that has already been mined, Thorium sands, granites) that can be used for several thousands of years.

If you think human beings will not discover other sources of energy in the meanwhile, or more likely, escape from the terrestrial shackles of this planet, you are probably just kidding yourself.


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PostPosted: Feb 20, 2010 8:31 am 
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Yes, it's not likely we'll be doing large scale seawater uranium extraction anytime soon. However, what makes sea water absorbent uranium extraction interesting to me is:

1. the ocean's currents flow automatically. This makes uranium concentration much less important.
2. the absorbent technology appears to have a good learning curve. It improves reasonably quickly. Cost is directly proportional to absorber performance, so if a 4x improvement can be achieved at the same cost, that means 4x lower total cost for the extraction. Things start to get interesting then. (current estimates of large scale extraction with todays absorber are 100-300 USD/kg).
3. useful byproduct heavy metals such as vanadium are also extracted. (much vanadium production is a byproduct of oil refineries since the stuff corrodes engines. When oil production declines we'd like to have new sources of vanadium).
4. it is easy to see how this could be made sustainable: the absorber can be recycled and waste is of the organic type. The absorbers just sit there in the ocean, having very little impact on marine wildlife.


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PostPosted: Feb 20, 2010 10:45 am 
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I wouldn't cross uranium from seawater off the list just yet. The possibility exists of mining uranium from brine (from desalination). Unexplored territory is also the possibility bio-mining this brine using halophytes (salt-dwelling organisms) that concentrate uranium.


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PostPosted: Feb 20, 2010 6:36 pm 
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Burning once used uranium fuel and Depleted Uranium in breeder reactors are important sources of fuel which will last many decades or even a century. Thorium will last us a few more centuries. Uranium will also continue to be mined from less costly sources than the sea water. Sea water may be required as a uranium source only later, after a few centuries.
Harvesting uranium from sea water could be examined as a futuristic knowledge experiment now as also fast uranium or thorium fuel fueled thermal breeders.


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PostPosted: Feb 22, 2010 6:01 am 
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trkdirect wrote:
I wouldn't cross uranium from seawater off the list just yet. The possibility exists of mining uranium from brine (from desalination). Unexplored territory is also the possibility bio-mining this brine using halophytes (salt-dwelling organisms) that concentrate uranium.


The Nuclear Desalination Blog has references to recovery of various metals including uranium from brine rejection:

http://simon-nisan.com/blog/

The biomass option is also attractive, it is almost certainly not as efficient as dedicated absorbents, but if it can generate competitive bio-alkanes and bio-alcohols then that can be used for peaking in gas turbines and various transportation sources (ships, airplanes) then the uranium and other heavy metals could be a nice byproduct.


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PostPosted: Feb 22, 2010 6:12 am 
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Another interesting fact I'd like to discuss here is the equilibrium condition of the uranium in seawater. The 4.5 billion tons may sound like a lot but natural processes of erosion have brought orders of magnitude more uranium to the ocean than that. At current rates, rivers bring this quantity to the ocean every 140k years. Assuming a constant rate in the past that means over the last 140 million years (rough averaged estimate of one ocean tectonic cycle) about 4500 billion tons of uranium has been brought into the ocean by rivers. At least such a quantity is resting on and in the ocean floors as that's where it has precipitated out. So, when we remove a lot of uranium, we can expect a lot of re-leaching of uranium back into the water from the ocean floor, as the surface area of the ocean and seabeds is so huge. That would suggest that the sustainable rate of uranium extraction is absurdly high.


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PostPosted: Dec 27, 2010 10:37 am 
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Cyril R wrote:
about 4500 billion tons of uranium has been brought into the ocean by rivers. At least such a quantity is resting on and in the ocean floors as that's where it has precipitated out.


Hi,

My follow-up question:

Is the uranium on the ocean floor evenly distributed? I would not expect it to be. It should depend on the solubility of uranium in water. And isn’t the solubility of uranium in water dependent on the temperature? Does pressure have a role in the precipitation?

Maybe somewhere on the ocean floor there is a big depository of highly concentrated uranium ore, just where the conditions favor the precipitation?

What do you think?

Daddeldu


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PostPosted: Dec 27, 2010 2:36 pm 
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Daddeldu wrote:
Cyril R wrote:
about 4500 billion tons of uranium has been brought into the ocean by rivers. At least such a quantity is resting on and in the ocean floors as that's where it has precipitated out.


Hi,

My follow-up question:

Is the uranium on the ocean floor evenly distributed? I would not expect it to be. It should depend on the solubility of uranium in water. And isn’t the solubility of uranium in water dependent on the temperature? Does pressure have a role in the precipitation?

Maybe somewhere on the ocean floor there is a big depository of highly concentrated uranium ore, just where the conditions favor the precipitation?

What do you think?

Daddeldu


Perhaps you can look where rivers bring the stuff into the ocean. Estuaries from rivers with big sediment loads. Especially old, big rivers. Mississipi, Amazon. Places that have other precipitates on the ocean floor are always a good place to look as well. Manganese granules deposits might have many other valuable minerals nearby. There will likely be high concentrations to be found but scraping it from the ocean floor isn't as easy as floating some absorbents around. Sandstones, which are typically easier accesible, are available with high enough U concentrations. No surprise since sandstones are old sedimented deposits.


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PostPosted: Mar 23, 2011 3:12 pm 
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Thorium and Rare Earth Elements (REE) in ocean basins occur in (are scavenged by) manganese nodules on the ocean floor. If you google "manganese nodules + thorium" you can find book titles and articles on the subject.


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