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Abstract
This thesis is divided into three chapters:
Chapter one is an introduction. It points out the studied area (Abu-Rushied),
located 50 km southwest of Marsa Alam on the Red Sea coast between longitude
34o 46` to 34o 46` 35`` E and latitude 24o 37` 16`` to 24o 38` N, south Eastern
Desert, Egypt. The mineralogy of rock units of Abu Rushied area was studied,
where the main rock unit was found to be cataclastic group with lamprophyre
dykes cutting through it. This chapter also discussed the abundance of uranium in
this area, its milling and purification. Uranium extraction methods are listed as
well as a brief outline of the chemistry of ion-exchange and solvent extraction of
uranium and the importance of exchanger used. At the end of the chapter, there
was a literature review related to the present work and the aim of the work.
Chapter two describes the experimental work, the different materials employed,
their chemical purity and detailed description of the instruments used. This
chapter also gives an account of preparation methods of the working solutions as
well as methods of determination of iron and uranium.
Chapter three is divided into four main parts; namely,
1- Uranium leaching from its ore using sulfuric acid solution:
a- Extraction of uranium using anionic resin from sulfate medium.
b- Recovery and purification of uranium using solvent extraction technique.
2- Comparative chemical studies between extraction of uranium using Amberlite
ion exchange resin and a prepared OSC Organosilicate compound as a selective
resin for uranium.
3- Adjustment of an appropriate conditions for achievement of continuous
countercurrent ion exchange process using gas diffusion (gas bubbling).
In the first part, different parameters affecting the leaching of uranium from its
ore using sulphuric acid solution were studied. Parameters affecting the leaching
efficiency are grain size, sulphuric acid concentration, agitation time,
temperature, effect of adding oxidizing agents and liquid to solid ratio. It was
found that the leaching efficiency of uranium increased as the grain size of the
ore was decreased. Sulfuric acid conc., of 100 g/l (1M) was found to be the
optimum acid conc. used to give maximum leaching efficiency. The optimum
liquid to solid ratio (L/S) was 5:1. Agitating time of 8 hours is found to be
sufficient for reaching equilibrium. The effect of temperature was studied and the
data obtained indicated that the leaching process is temperature dependant. The
effect of adding oxidizing agent as MnO2 was tested and the obtained results
showed that the presence of oxidizing agent increase the leaching efficiency by
converting uranium from an insoluble tetravalent state into a soluble hexavlalent
state.
Different parameters affecting the extraction of uranium from sulfate leach liquor
using anion exchange resin (Amberlite IRA402 (Cl-)) were studied. Parameters
affecting uranium extraction are pH, agitating time, temperature, free sulfate ions
as well as liquid to solid ratio(L/S ratio). It was found that the extraction
efficiency of uranium reaches a maximum at pH ~ 1.5. Shaking time of 20 min.
was found to be sufficient for reaching equilibrium. The effect of temperature
was studied and the data obtained indicated that the sorption process increase
with increase temperature till reach 40 oC then decrease so the process is said to
be exothermic. L/S increase by increasing the volume of solution and the
extraction efficiency decreases.
Different parameters affecting the recovery and purification of uranium from
solution obtained from the previous process using solvent extraction technique
(TBP) was studied. Parameters affecting the extraction are nitric acid
concentration, TBP concentration, agitating time, temperature, as well as aqueous
to organic phase ratio (A/O ratio). It was found that the efficiency of recovery of
uranium reaches a maximum at nitric acid conc. ~ 4M. On the other hand, 20%
TBP concentration found sufficient to obtain maximum recovery. Agitating time
of 5 min. was found to be sufficient for reaching equilibrium. The effect of
temperature was studied and data obtained indicated that the extraction process is
temperature dependant. As the A/O phase ratio decrease the recovery efficiency
increased.
The optimum conditions for batch uptake experiments were carried out to
investigate the quantitative uptake of uranium by Amberlite IRA 402 and
Organosilicate compound. The parameters affecting the extraction such as pH,
time, temperature, L/S as well as uranium initial concentration have been studied
in detail. It was found that the extraction efficiency of uranium reaches a
maximum at pH ~ 1.5 for Amberlite while OSC can extract uranium at pH lower
than 1. Shaking time of 20 min. was found to be sufficient for reaching
equilibrium for both Amb.IRA402 & OSC. The effect of temperature was studied
and data obtained indicated that the uptake decreases with increasing temperature.
The effect of sorbent amount on uranium uptake shows the similarity of both
sorbents. The effect of initial uranium concentration for both sorbents presents
relatively low uptake at low initial uranium concentrations. Uranium uptake
increased with increasing uranium concentration in solution. The data show that
every 3 active sites of OSC react with one molecule of uranium, while 2 active
sites only react with one molecule of uranium in case of Amberlite IRA 402. The
interaction of uranium ions with the active sites of the studied OSC was found to
be higher than that of Amberlite IR 402.
After determination of optimum conditions for uranium extraction through
dynamic ion exchange using mechanical agitation, there was an idea to
investigate the possibility of using air bubbling instead of mechanical agitation
using turbines. Lowering of energy consumption is a great benefit of such
modification. At this stage, the effect of bubbling time was tested through time
intervals started from 1 minute up to 30 minutes. The other conditions were fixed
at liquid to solid (L/S) ratio 40:1, at room temperature. The obtained results refer
to that; 5 minutes represents the inversion point on the drawn curve with no
considerable increase in uranium extraction after this time. Therefore, air
bubbling agitation can be used instead of mechanical agitation to save energy and
to reduce the operation time.
Yellow cake was precipitated from solution with gaseous ammonia. The yellow
cake produced was investigated using EDX & XRF analysis which indicated that
uranium qualitatively is present as major constituent with trace amounts of Cu,
Zn. The quantitative analysis using spectrophotometer and atomic absorption was
done which indicate that the yellow cake produced contains 74.4% uranium and
Na, Ca, Fe, and S present as a traces.
References