الفهرس 
Radioactive Waste and its SourcesOnly 14 pages are availabe for public view
 |  | from | 16 |  |  |
| | | from | 16 | | |
Abstract
This work deals with the economic utilization of local available
agricultural by-product that is coconut shells, and converting this raw
material (coconut shells) to produce a modified surface activated carbon
(MSAC) with high ability for adsorption (or removal) of some
radionuclides that may be released from nuclear reactors waste.
The coconut shells are chosen as a raw material for two reasons:
i) They are highly abundant renewable by-product.
ii) They have high mechanical strength.
The sorption behavior of the element Eu3+, Ce3+, Sr2+ and Cs+ from
their chloride solutions on MSAC prepared from coconut shells as
agricultural by-product, has been studied.
The introduction part of this thesis focuses on the following
points:
i) Radioactive waste identification and radioactive waste categories
according to the international atomic energy agency.
ii) Classification of activated carbon (AC) materials: their sources
and the different types of its modification.
iii) The essential schemes used for the production of MSAC through
one-activation step with H3PO4 acid followed by carbonization in
muffle furnace at 500oC and through chemical modification with
H2O2 followed by HNO3 acid.
iv) The objectives of carrying out this work.The experimental part includes the procedure and methods
followed for the preparation and characterization of the used MSAC. It
includes also performing of the adsorption process of the considered
metal ions on MSAC and investigating its selectivity and sorption
efficiency for these ions as a function of pH and initial metal concentration as well as other factors such as contact time, temperature
and the presence of competing ions. Determination of the thermodynamic
parameters (ΔH, ΔS & ΔG), sorption isotherms and kinetics studies have
been also reported.
The third part deals with the obtained results and the scientific
discussion of these data:
i) The prepared MSAC shows a high chemical stability in water and
in acid solutions of HNO3 and HCL acids up to 5M.
ii) FTIR analysis indicated the presence of different surface
functional groups such as CH-CH2, -OH of hydroxyl
functional group, alcohol and carboxylic groups in the MSAC.
iii) The SEM photographs show a high surface – area structure of the
prepared MSAC and many active sites for sorption of the
metal ions.
The determined optimum conditions for the most efficient
sorption process are found to be contact time : 180min, sorbent
dosage:0.05gm, initial metal ions concentration in 800ppm and pH of the
solution is 5.56 for Eu3+, Ce3+, pH 6.5 for Sr2+ and pH 6 for Cs+ .
In general, the removal efficiency of MSAC for the used metal
ions increases with increasing temp. specially in the case of Sr2+ and Cs+.
The presence of either competing ions, such as Na+, or
complexing agent, such as EDTA, greatly affect the sorption process negatively.
The distribution studies indicate that the distribution coefficient
(Kd) of the studied metal ions are pH - and temperature (T) - dependent. It
increases with increasing both pH and T.
The thermodynamic parameters ΔH, ΔS and ΔG are calculated
from the plots relating ln Kd and 1/T. The obtained data indicate an
endothermic nature of a spontaneous adsorption process and an increased
randomness of the solid – solution interface during the process It is to be concluded that, under the same experimental conditions,
the removal efficiency and saturation capacity of MSAC for the four
considered elements is increasing according to the following order:
Eu3+>Ce3+> Sr2+> Cs+
The adsorption models (Langmuir, Freundlich and D-R models)
allow predicting the type of the adsorption process and providing
information on the strength and values of the adsorption capacity.
Applying the three adsorption models to the present work show
that the obtained data are better fitted Freundlich than Langmuire model
and that the adsorption is endothermic and probably physicochemical
process.
In the kinetic studies, the pseudo first, pseudo second order and
intraparticle diffusion kinetic models are applied. It is found that the
adsorption of the investigated metal ions follows the second order
equation indicating the chemisorption control
As an application of this study, the adsorption of the considered
metal ions is carried out using the fixed column operation and compared
with the data obtained applying the batch operation.