Download THE URANIUM CAPTURING BY Fe/Mn GLAEBULES OF SOME

X I X C O N G R E S S O F T H E C A R PAT H I A N B A L K A N G E O L O G I C A L A S S O C I AT I O N
Thessaloniki, Greece, on 23-26 September 2010
THE URANIUM CAPTURING BY Fe/Mn GLAEBULES OF SOME QUATERNARY PALEOSOLS OF ITALY
D. MAGALDI*, M. LAUBENSTEIN & D. RANALLI , ITALY
*DIPSA, University of Florence
Recently (2008)the concentration of naturally occurring radionuclides (238U, 232Th, Knat) was measured in some Red Mediterranean soils from carbonate
1. INTRODUCTION
rocks in Spain , Italy and Turkey using gamma-ray spectrometry at the Gran Sasso National Laboratory of INFN (Italy) . The Uranium content ranges 1 to 5 ppm,
Uranium frequency into lithosfere is:
Magmatic acid rocks: 4.8 ppm
Magmatic basic rocks: 0.6
Magmatic ultrabasic rocks: 0.003 ppm
the content for Thorium ranges 3 ppm up to 30 ppm, whereas for Potassium its content goes 0.13% up to 1.3%. The results indicated that soils characterised by
absence or scarcity of 2:1 clay minerals are poor in uranium whereas soils with illite––smectite as the dominant minerals in clay fraction are noticeably richer.
Knat/
232
Th vs. U/
232
Th
2000
Gran Sasso
The mean content of the Sedimentary Rocks is:
Shales = 3.2
Sandstone = 1.0 to 3.0
Limestone = 2.2
Sierra Espuña
1500
Turkey
K/Th
Apulia
1000
The carbonate rocks include U for Ca being
relative atomic Radius almost similar:
Ca2+ = 0.99, U 4+ =1.06
500
As an example , uranium coming also from
different sources is common in much caves world
wide: e.g. Antro del Corchia on the Apuane Alps,
Northern Tuscany
0
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
0,45
U/Th
Da Ford & Williams
2. METHODS
Uranium is assumed to move freely in the water of soil profile after the processes of dissolution from carbonate parent The calculation of Uranium content excluding Th and others alpha emitters was carried out for glaebules as follows :
2
material and others. It is claimed that its mobility is favoured by acid conditions, whereas in an alkaline pH the
Glaebule section area = G mm
adsorption of its oxide would be increased. Clay and Fe/Th glaebules are lively to capture Uranium.
P = alpha tracks on photo
Transparent plates of CR 39 poly carbonate were placed for exposition on polished sections during more than 360
S = CR 39 exposure in seconds
days. After a chemical etching (NaOH solution) of detectors to show alpha tracks damage, their location on thin section
Alpha density in thin section = P × 8 × 2 ×G / S = D
features by overlapping of CR 39 transparent plates and the corresponding density (proportional to % of U (and Th)
Alpha activity in Beq / kg = D / 0,0039
was performed by an image analysis software (Image J).
Uranium activity in ppm = D / 12,67
3. RESULTS
a)
b)
c)
The photographs carried out on sample coming from Tuscany (Campiglia Marittima, Livorno) and
Puglia (Conversano, Bari) revealed 3 typologies of images:
a) a random tracks distribution on the soil “red” clay matrix (“groundmass”);
b) some round cluster of tracks produced by Fe/Mn nodules and concretions;
c) some very compacted concentration of tracks produced by small radioactive minerals
included in greater not radioactive minerals of the soil parent material (e.g. vesuvianite).
Conversano: 0,0013 Beq/kg
b1)
b3)
b2)
Conversano: 0,06 Beq/kg
300 micron
150 micron
150 micron
4. CONCLUSIONS
Conversano: 0,22 Beq/kg
As is well know ,know, it is not surprising such a result because Fe/Mn nodules and concretions are formed by main minerals of both the elements as goethite, hematite,
lepidocrocite, ferrihidrite, maghemite ecc.for Fe, and birnessite, vernadite, psilomelano, lithiophorite ecc. , for Mn .Moreover the Fe/ Mn glaebules are commonly
including several elements as Al, Ca, Mg, Ba, Li , K, Na, Zn, Cu, Co, Pb, Ni, Cr, V and more rarely , Th and U (Short et al., 1989) . These elements are characterized by an
elevate coordination number (3-12), proximity in ionic potential diagram (radius 0.6 to 1.4; ionic charge +1 to +4).
The autoradiographyautoradiography method is not particularly relevant for assessing the total content of natural radioactivity as soils and its components but it
appears very promising and not expensive to individuate where U ( Ra, Th ?) can concentrate and eventually their movement along soil profile as a response to soil
process changing in relation to environmental or human influence.
We concluded that a detailed study of Uranium content of glaebules could be very interesting in order to asses both the potential Radon emission of soil and derived
material in air and water and the hazard of plant uptake of radionuclides as one of main vector for introduction of radioactive elements into the human food chain
(Morton et al., 2002).