[ RadSafe ] Re: uranium smoke is a teratogen
Dan W McCarn
hotgreenchile at gmail.com
Sun May 11 00:47:07 CDT 2008
Dan W. McCarn, Geologist; 3118 Pebble Lake Drive; Sugar Land, TX 77479; USA;
HotGreenChile at gmail.com UConcentrate at gmail.com
Ben or James or whomever is wrong!
Virtually all uranium in agricultural waters are in the +6 valent state as complexed uranyl ions, else they would not be present in detectable concentrations. The equilibrium solubility of uraninite [UO2], a reduced U(IV) species, is on the close order of 10^-12 Molar, whereas the equilibrium solubility of schoepite, an oxidized U(VI), uranyl hydroxide mineral species [UO2(OH)2:H2O] is about 10^-2.5 Molar. The oxidation of uraninite would typically yield shoepite. The equilibrium solubility of autunite [Ca(UO2)2(PO4)2], another oxidized U(VI) uranyl phosphate mineral species, is about 10^-3 Molar. (MINTEQ DB, 5/31/2001). See:
Field sampling in the San Luis Valley (McCarn, 2004, IAEA TECDOC 1396, Fig. 3, Page 295) revealed high concentrations of uranium in oxidizing conditions whereas reducing conditions typically resulted in <0.1 ug/L U, "non-detectable" concentrations. This sampling was conducted in a targeted area with coincident alteration, favorable depositional environments and redox features common to sandstone uranium deposits.
These quite high concentrations are not "leaching into" the groundwater, but are present typically in ore-forming processes common to many sandstone basins and source for "sandstone-type" uranium deposits. Interception of redox-controlled, roll-fronts by irrigation wells is not uncommon, but seldom recognized except by exploration geologists. High volume pumping of these wells causes oxidizing waters to be pulled across the redox front giving rise to quite high concentrations in groundwater. In the case of the San Luis Valley, roughly 10,000 wells are present. Some fraction, perhaps 5-10%, of these wells, intercept a clearly defined redox front. With targeted, confirmatory geochemical sampling, high concentrations of uranyl were detected along the redox / alteration front in the San Luis Valley.
Ditto for the Central Valley in California as well as hundreds of sandstone basin exploration targets throughout the world.
These clearly defined and understood geochemical features are used to mine uranium via In Situ Leach (ISL) or In Situ Recovery (ISR) methods.
However, the risk is not the uranium, it’s the remobilized and reconcentrated radium in soils!
As a final note, although most of the uranium in bottom ash is in the reduced form, quite a bit of the U(IV) is quite easily leachable if exposed to oxidizing waters; thus the consideration for byproduct uranium production from uraniferous lignites. Development of Fluidized Bed Reactors significantly drop the operating temperature to 1500-1700ºF for a low NOx - SOx emission profile and thus reduce the tendency of uranium to form ceramics at higher temperatures. By the way, 2100ºK is 3320ºF; 1500 degree Fahrenheit = 1089 kelvin.
Dan W McCarn
From: jsalsman at gmail.com [mailto:jsalsman at gmail.com] On Behalf Of Ben Fore
Sent: Saturday, May 10, 2008 10:41 PM
To: radsafelist; hotgreenchile at gmail.com
Subject: [ RadSafe ] Re: uranium smoke is a teratogen
Thank you for your estimates:
> So for agriculture in the USA, I would "guess" that there are on the order
> of 700 Tonnes U per year placed on agricultural soils and of that, 100
> Tonnes U per year redistributed as dusts. Now "apply" the years of
> agricultural use for the soils (e.g. 99 years - median - for the San Luis
> Valley), a source term, a "Leaching Coefficient" to calculate the U
> concentration in the upper soil zone, and transfer coefficients into plants,
> etc. and now uranyl becomes an issue in the food chain.
Less than one in ten thousand uranium atoms released
by irrigation are uranyl or other U(VI) compounds, in areas
where uranyl is not leaching into the water table. My source
on this is not peer-reviewed, so I would appreciate it if you
would please say whether this is right or wrong.
Irrigation is not a major source of U in the +6 oxidation state
entering the environment; that's coal (which actually burns at
2100K, contrary to my previous message -- which was still
correct in that under 10% of the uranium in coal fly ash is U(VI).
James Salsman, as Ben Fore
More information about the RadSafe