[ RadSafe ] RE: UO{2,3} dissolved: which increases?

[Dan W McCarn]

Dan W. McCarn, Geologist; 3118 Pebble Lake Drive; Sugar Land, TX 77479; USA
HotGreenChile at gmail.com           UConcentrate at gmail.com

1) May I also suggest Stumm and Morgan, "Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters" ISBN: 0-471-51185-4.  They have a long section on carbonate speciation in waters as does Langmuir.  Amazon offers both Langmuir's and Stumm & Morgan's books together for a discount.

http://www.amazon.com/Aquatic-Chemistry-Werner-Stumm/dp/0471511854

2) Typically groundwater contains CO2 from 10^-2.5 to 10^-2 atmospheres pressure. Normal air is about 10^-3.5 atm CO2.  See Freeze & Cherry, Groundwater:

http://www.amazon.com/Groundwater-Alan-R-Freeze/dp/0133653129/

3) Carbonate does not "oxidize" uranium, but does provide a complexing ion to form an aqueous species. Uranium (IV) will rapidly convert to uranium (VI) in the presence of oxidants such as free oxygen and be transported until a reducing environment is encountered.  There, it will promptly precipitate.  This natural mechanism gives rise to redox-controlled sandstone deposits and several other interesting uranium-concentrating mechanisms.

4) I would say that virtually all irrigation and other natural waters used for domestic and livestock purposes contains concentrations of bicarbonate (HCO3-) suitable to transport mg/L concentrations of uranium if available and depending on the availability of oxygen.  These concentrations of bicarbonate range from 10-100 mg/L.

5) Much depends on the availability of uranium.  Uranium can be "weathered" from uranium-enriched granites. Oxidizing meteoric waters infiltrating and recharging a basin from such a source can, in geologic time, produce uranium deposits such as is the case for the Wyoming Basins uranium and many other sandstone uranium deposits. Is uranium in GW or fertilizer being directly placed on crops? Or is it somewhere sequestered with the "bottom ash" of a power plant?  The fate and distribution of uranium in these cases depends on local mechanisms in soils and geologic media as well as the chemical characteristics of water passing through uranium-bearing materials.

6) As has been previously pointed-out, someone 100 m from a "uranium fire" is more likely to receive injuries from shrapnel, and are directly being targeted. These fires are probably better characterized as Gaussian "Puffs" which rapidly dissipate.  

So, beyond several hundred meters:

Smoke: 
   1) is not persistent, 
   2) exposure times are brief, 
   3) concentrations are low and 
   4) natural sources of uranyl complexes dominate exposure in the long run.

-----Original Message-----
From: jsalsman at gmail.com [mailto:jsalsman at gmail.com] On Behalf Of Ben Fore
Sent: Monday, May 12, 2008 4:12 AM
To: hotgreenchile at gmail.com; radsafelist
Subject: UO{2,3} dissolved: which increases?

Dan,

You are absolutely correct at a neutral pH when carbonate is present.
In that case the fraction of uranyl increases, and is soluble.  Does
most irrigation water contain substantial enough amounts of dissolved
carbonate to allow UO2 to oxidize?

In that case coal fly ash contains nowhere near the volume of soluble
uranyl compounds as irrigation water.  But those are both background
sources, unless there is a locally rich concentration of U(VI) or (IV)
leachate, or very close proximity to an unscrubbed coal smokestack.

Nether has the potential in a lifetime to exceed the possible soluble
uranyl dose from being 100 m downwind of a 5 kg uranium fire.

James Salsman, as Ben Fore