الفهرس 
Geological and Radiometric StudiesOnly 14 pages are availabe for public view
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Abstract
The potential applications of biotechnology like bioleaching,
biosorption and bioaccumulation processes in the field of metal
extraction from its ores, looks very promising, have an important
echo in the world, especially for uranium. Whereas, recent research
showed the importance of using microorganisms in the operations of
leahing and extracting valuable elements.
This study aimed to investigate the effect of radionuclides
on the microorganisms, which found naturally in the uraniferous
rock samples. Moreover, study the effect of these microorganisms
upon the uranium leaching process from its ores, which collected
from Um Bogma Formation, southwestern Sinai, Egypt. Therefore,
the present study was concerned with the mechanisms of
biotransformation of radionuclides and toxic metals were briefly
discussed with the view of using such a knowledge-base for
developing novel biometallurgy strategies.
Microorganisms, in the environment, are needed for a
complete life cycle, which many species may be under appropriate
circumstances from multicellular structure, sometimes with
morphological and metabolic differentiations between the various
cells making up a bio-structure. Growth by cell division is the most
common way of microorganism propagation. They are characterized
by their almost infinite ability to biodegradation and biosynthesis
naturally occurring compound in the environment. Microorganism
reactions control, partly or fully, the chemical composition of many,
very different environments such as sediments, soil, lakes and
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ground water. Furthermore, they have the ability to adapt to extreme
environments such as alkaline and acidic ground water.
Modern methods and techniques were used to achieve the
aim of this study; after the bioleaching process of uranium by the
chemical methods and radiometrically using High purity germanium
detector (HPGeD) - Analysis by X-ray Diffraction (XRD) to
determine the mineral change of the rock samples through the stages
of study – Environmental scanning Electron Microscopy (ESEM)
and the Energy Dispersive Analytical X-ray unit (EDAX), also
optical and spectral methods were used. The sediment was analyzed
by bio-polarized microscope to differentiate between the
crystallization and amorphous structures. The identification of the
chemical composition was occurred by using ESEM.
Moorganisms play an important and a major role in the
mobilization and immobilization of radionuclides and toxic metals
by direct enzymatic or indirect non-enzymatic actions. They could
affect the chemical nature of the radionuclides by altering the
speciation, solubility and sorption properties and thus could increase
or decrease the concentrations of radionuclides in solution.
Nine grapped samples were collected, two samples from the
lower member, four samples from the middle member, and three
samples from the upper member of lower Carboniferous Um Bogma
Formation, southwestern Sinai, Egypt. After isolation and
purification processes of microorganisms from the tested samples,
nine fungal species were identified according to their
morphological features. The fungal strains are belonged to three
species and known as
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xxi
- Aspergillus species, contains five genera were identified,
Aspergillus niger, A. fumigatus, A. flavus, A. terreus and
A. oryzae.
- Penicillium species, contains three genera were
Penicillium steckii, P. Italicum, P. diversum
- Mucor species, contains one type.
In this work, all the fungal strains investigated were found
to exhibit lower leaching efficiency except A. niger and
A. terreus were achieved high leaching efficiency 57% and 42%
respectively.
The optimum conditions influencing uranium bioleaching
process by both fungi were 7days as the incubation period, 30 ºC
as incubation temperature, initial pH value equal 3 and 3% pulp
density of the ore material. In these conditions, the uranium
leaching efficiency using A. niger and A. terreus reached 80%
and 60% respectively.
The recovery of uranium using A. niger reached up to
71.4 % of the lowest uranium grade sample. The recovery of
uranium has been performed by proper precipitation to obtain a
concentrate with high quality containing 98% pure uranium.
from the recovery process, the obtained bioprecipitate
analyzed by polarized light microscope, which could differentiate
between the crystallized and amorphous forms. The chemical
composition of each is identified by environmental scanning
electron microscope. Examination of the produced bioprecipitate
by X-Ray Diffraction (XRD) technique identified as uranyl
acetate hydrate (C4H4O6U.2H2O) well, its formation ascribed to
the bio-dissolution of uranium from the original sample
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(dolomite). Furthermore, the formation of some complexes with
acetic acid that secreted from the A. niger and creating the uranyl
acetate hydrate. Consequently, the rest of the dolomite complex
with the iron (in the original sample) forming ankerite mineral
[Ca (MgO.67 FeO.33) (CO3)2]. Under bioleaching condition
uranium complexed with organic ligand (acetic acid) are reduced
to uranium (IV)-acetate.
Distribution of the different radionuclides (i.e. 238U, 226Ra,
232Th, 235U and 40K) under the previous optimum conditions were
studied in this work, the bioleaching efficiency was bound to
increase with the decreasing uranium concentration. One of the
important results is the bioleaching of some radionuclides as
226Ra, 214Bi and 214Pb which did not achieve by the traditional
acid leaching technique.
Through the bioleaching process, selective leaching for
several radionuclides are exhibited; whereas, A. niger able to
leach 70-80% 238U, 40-60% 226Ra and 70-78% 235U. on the other
hand, A. terreus specified for 232Th, which achieved 32-74%
leachability of the studied samples.
It appears from our study of uranium bioleaching process,
that a reduction in the final pH was occurring from 6.5 to 3. This
reduction was accompanied by the production of high quantities
of organic acids as a secondary metabolite in the growth media of
tested fungal strains, which have an appreciable and effective role
in uranium solubility. These organic acids identified as:
- Formic; acetic; citric and oxalic acids in the case of
A. niger.
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- Citric, oxalic, galic, malonic and ascorbic acids by using
A. terreus.
The obtained results proved that: (1) The acetic acid has an
important role in bioleaching process by using A. niger strain,
whereas it increased by increasing the pulp density and could
form organo-complex with uranium (uranyl acetate) appeared in
XRD of the product. (2) The formic acid decreased by increasing
the ore concentrations with A. niger strain. (3) The common agent
between the two fungal strains A. niger and A. terreus secretion
was oxalic acid, which has slight changes with an increase the ore
concentrations for A. terreus strain, on the contrary, for A. niger
strain.
Moreover, all secreted organic acids decreased except
acetic acid has an appreciable increase to 18 mg/ml in case of
A. niger. On the other hand, secretions of oxalic acid by
A. terreus in the growth media are increased to 19 mg/ml at 1%
ore concentration and decreased to 16 mg/ml by increasing the
ore concentration to 5%. Furthermore, citric and aascorbic are
secreted only at control value which are found to be 6.96 and 7.9
mg/ml, respectively, and disappeared with increasing the ore
concentration in the growth media.
The adaptation of A. terreus strain with the surrounding
medium are achieved by secreting malonic and galic acids, where
malonic acid was found with 12.69 mg/ml at 1% sample
concentration and decreased to 7.92 mg/ml at 5% sample
concentration, while galic acid was secreted with 5.67 mg/ml
only at 5% sample concentration.
During the bioleaching process, the biosorption take place.
from the measuring of the biosorption controlling factors, the
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optimum conditions occurred at 5% ore concentration, 9 days
incubation period, 35 ºC and pH 9 were achieved the maximum
biosorption efficiency for A. niger and A. terreus.
The morphological investigations, in this study, showed
several changes of A. niger during their development accordingly
in the primary stegmata, it became shorter in their length than the
control, while the secondary stegmata are disappeared by
increasing the ore concentrations in the growth media.
Furthermore, the changes in conidial diameters exhibited to be
increased when the fungus grown at 1% and 5% sample (A-3)
concentrations, and its number is decreased with increasing ore
concentration in the growth media.
By using the transmission electron microscope for A. niger
is grown upon Dox agar medium containing different ore
concentrations (control, 3%, 5%, 7% and 9%); the substantial
changes upon the cell membrane permeability for the different
metal ions in the surrounding medium occurred. The obtained
result showed that:
- The ultrastructure changes of the cell wall increase with
increasing ore concentration.
- High accumulation and precipitation of various
elements are displayed in black dense areas around the
cell wall
- Large vacuoles and partial distortions like inner cell
wall irregularity are formed at 3%, 5% and 7%.
- The shrinkage of cellular structures is clearly appeared
with increasing the ore concentration.
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xxv - Finally, at 9% ore concentration, the ability of an
organism to tolerate more concentration of toxic metals
is decreased and succeeds to diffuse inside the cell
causing highly deformation of cellular structure causing
their degradation and disappearance.
from the obtained results of this work mention that using
the microorganisms in the uranium leaching considered as one of
the most promising technology to extract the valuable elements
from its rich ores than the traditional methods. Consequently;
recommended for use the bioleaching process, in addition to
increasing the studies in the direction of the effect of
microorganisms to dissolve the precious radionuclides.