الفهرس 
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Abstract
The objective of this work is to aid in obtaining a uranium concentrate
with high recovery rates and low costs of production of a uranium
concentrate of reasonable quality.
Both laboratory and pilot-scale leaching tests of mineralized granite
ore deposits were carried out to optimize various process parameters
for maximizing the recovery of uranium. Samples of mineralized
granite were collected from Jabal El-Erediya occurrence, central
eastern desert, Egypt. It considered as one of the most important
uranium occurrences in Egypt. The collected ore samples morphology
and chemical analysis showed high uranium content in the studied
area. It is bounded by latitudes 26º18`30`` - 26º23`30``N and
longitudes 33º27`23``- 33º29`45``E.
Such laboratory studies help to figure out technical and economic
feasibility for the constructed continuous leaching apparatus and to
calculate the expected results on future up-scaled models. Laboratory
experiments make it possible to analyze process dynamics, evaluate
the volume and mass of ores and rock to be leached and to predict
expected uranium recovery as an indication of the overall efficiency of
the leaching process.
Collected ore samples were crushed to size -3 cm using adequate lab
scale jaw crusher. Samples were subjected to full chemical analysis
prior leaching studies. The concentration of uranium in pregnant leach
liquor was determined volumetrically by Modified Davies and Gray
technique.
Lab scale leaching tests were conducted on crushed ore samples
containing nearly 1.13% U3O8. Samples were crushed to -3 cm using a
laboratory jaw crusher. The particle size-fraction ranging from +2mm
SUMMARY II
to - 3cm was separated and considered useful for most of the study as
the invented apparatus was designed to deal with solid particles of
such size range.
Laboratory leaching experiments are usually confined to batch
techniques. Although batch tests do not properly simulate the real
conditions of the designed leaching apparatus, yet they can help to
great extent to determine preliminary uranium dissolution data and
recovery improvements.
The present work provides a detailed account on the optimization of
various process parameters. Leaching studies were carried out to
develop a suitable method for the recovery of uranium and to eliminate
non-desired oxides. A detailed study of Counter-current acid leaching
tests of uranium ore using H2SO4 was conducted on the studied
mineralized granite ore to establish high extraction efficiency of
uranium.
A simple bench scale composite was found to be useful for such
tests. It consists of a plastic 2L container fitted with a suitable
laboratory mechanical agitator with stainless steel impeller to
withstand stirring of hard ore particles. The used beaker is from plastic
material to withstand the vigorous mixing of hard ore particles against
the walls of the container. Such system made it possible to perform
laboratory tests using ore particles of the same physical properties
used in the real pilot scale apparatus.
The effect of the following variables was assessed to determine
optimum leaching conditions:
- Ore particle-size.
- Solid : aqueous phase ratio.
- Leaching agent concentration.
- Temperature.
SUMMARY III
- Oxidation potential
- Contact time.
- pH value of leaching solution.
- Strong acid-pugging step.
All the factors affecting uranium leachability from uraniferous ores
by sulfuric acid have been comprehensively studied. Results were
organized, tabulated and mathematically analyzed in order to be
helpful in understanding the leaching process and to aid in design
and implementation of a pilot scale model for a continuous
countercurrent leaching process. The concept of the designed system
was to provide a novel, unobvious, rapid, high recovery, low capital
processing leaching facility means.
Increasing the temperature causes an increase in the rate of
leaching of uranium. The extraction of uranium increases
significantly as a function of temperature in the range of 30 –90°C.
It is clear also that the uranium extraction increases with increasing
leaching time. The first 30 minutes were sufficient to extract nearly
four times the total quantity of uranium leached during the next 30
minutes at all the studied temperatures.
Increasing the initial acid concentration influences the overall
leaching efficiency. The decrease in particle size enhanced uranium
dissolution; the smaller the particle size the faster the reaction rate.
It was observed that when an ore is ground to a maximum particle
size of 3 cm and when the concentration of sulfuric acid used is
about 1M, the mixing ratio of lixiviant to ore necessary to attain
uniform mixing was optimum at phase ratio 1(solid):4(aqueous).
If the pulp-density is lower than 2000 L/ton production of more
concentrated leaching solution becomes possible, yet mixing
becomes harder and can be very exhaustive to most mixing machines
SUMMARY IV
A characteristic feature of the designed leaching system is that even if
the mixing ratio is as low as 1:1, uniform mixing is still possible.
Leaching efficiency is enhanced by a higher liquid to solid ratio. At
any given mixing time, the leaching efficiency with a phase ratio of
6:1 will yield about 6 folds that yielded by a phase ratio of 1:1, the
leaching efficiency with a phase ratio of 5:1 yield about 5 folds that
by the ratio of 1:1, and so on.
The application of Shrinking Core Model (SCM) to the
dissolution of uranium in sulfuric acid solution was
invest igated. The apparent activation energy (Ea) was calculated to
be 8.6938 kJ/mol. The low value of activation energy reflects the
least energy requirements of the chemical reaction. This leads to a
faster rate of a spontaneous chemical reaction. Hence, the rate
determining step is a diffusion step and the overall process is said to
be diffusion-controlled process.
Adding an acid-pugging step before the ordinary leaching tests at
solid : aqueous phase ratio 1:4, 1M acid concentration, 4 cycles of
counter current leaching and a contact time 60 minutes at room
temperature showed 65.41 % leaching efficiency, which is nearly
double efficiency without performing acid pugging. Strong acid
pugging technique is said to be advantageous economically and
technically than ordinary leaching process and without further
process complexity. In fact, it can not be considered a separate
process rather than a step added prior to the ordinary leaching
process.