الفهرس 
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Abstract
Title: Liquid Waste Treatment and Immobilization Using Local
Geomedia
In this study it is intended to benefit from the using of low cost clay
minerals supplied from Egyptian mine. These clay minerals can be used as a
selective adsorbent without any physical or chemical modification to
represent one of the most effective possibilities for removal of some
radionuclides that may be released from nuclear reactors waste. Also these
clays as cheap and plentiful materials can be used for retarding the migration
of radionuclides that being arise from the nuclear waste disposal sites to the
ground water flow path. The thesis was subdivided into four main chapters
including: the introduction in chapter 1, experimental in chapter 2, results
and discussion part in chapter 3 and 4.
Chapter-1:
The introduction includes radioactive waste identification, radioactive
waste categories according to the international atomic energy authority and
some brief notes related to the environmental impact of this radioactive
waste. Descriptions of natural geomedia as low cost adsorbents include
bentonite with its types of (sodium, calcium and potassium bentonite) and
kaolin. This part also includes adsorption process definition and its types of
chemisorptions and physisorptions.
This chapter also contains the literature review about the
environmental behavior of six radionuclides including barium, nickel,
cobalt, cesium, europium and strontium as well as the general objective of
the current work is stated.
Chapter-2:
The experimental part, defines the chemicals and standards used, as
well as clay samples preparation and the different methods applied for its
physical and chemical characterization. These procedures include measuring
clays cation-exchange capacity, specific surface area and surface digestion
analysis. Also, the batch adsorption technique includes the effect of pH,
contact time and the concentration of both inactive (cobalt, nickel) and
radioactive (cesium, strontium, barium and europium).
This chapter also contains a brief description for ICP-OES instrument
that used to determine metal ions concentration. Sodium iodide gamma
measurements and the liquid scintillation counting system (LSC) used for
measuring the radioactivity levels of radionuclide (strontium) are also
described.
Chapter-3:
This chapter includes results and related discussion of physical and
chemical characteristics of clay samples collected from Egyptian geological
sites used for treatment or disposing low-level radioactive waste.
The scan electron microscope showed that A-Bent and W-Bent were
mainly composed of flakes or layers, while kaolinite (S-Kaol) particles
appear as pseudo-hexagonal platelets. The X-ray diffraction pattern (XRD)
of W-Bent and A- Bent showed that, the main component of the two clay
minerals is montmorillonite and the presence of some quartz as impurities.
Also, the XRD analysis of kaolin indicates that the mineral constituent is
kaolinite and the presence of some quartz and illite as impurities. The XRF
data indicated that the percent of silicon to aluminum for each clay mineral
was similar to the theoretical formula of these kinds of clays, 2:1 for
montmorillonite and 1:1 for kaolinite. Chemical analysis of all types of clay
revealed a relatively high Ca, Mg, Na and K percent, in which these ions can
be exchanged easily with other ions without affecting the clay mineral
structure. CEC was found to be (26.76, 67.3 and 11.58 meq/100g) for A -
Bent, W-Bent and S-Kaol, respectively. The PZC (point of zero charge) for
A-Bent and W-Bent is approximately the same and is ranged, 6.5-7, while
for kaolin was found to be ranged, 5 -5.5, using 0.01M NaCL. The surface
area for A-Bent and W-Bent was found to be 11.8 and 18.5 m2/g,
respectively which is greater than the value of S-Kaol (0.24 m2/g).
Chapter-4:
This chapter includes results and discussion related to study the
different parameters affecting on radionuclides adsorption. This chapter
includes also the results of applying different empirical fitting models, which
allow the systematic description of the influence of different conditions on
radionuclides behavior. These models include empirical adsorption isotherms
such as Langmuir, Freundlich, D-R and Temkin
The pH experimental results of all clay minerals generally showed that
the increase of clay uptake attributed to the immobilization of trace elements
by making existing sites more reactive towards metal binding due to decrease
of proton competition. For all metal ions, montmorillonite (W-Bent and ABent)
had a higher uptake percent than kaolinite at any pH. The optimum pH
condition was found to be 6 for a maximum uptake of all metal ions on WBent,
S-Kaol and A-Bent.
The results of the kinetic experiments for uptake of 10 ppm of Cs+,
Ba2+, Sr2+, Co2+, Ni2+ and Eu3+ from aqueous solutions mixture at pH 6 onto
A-Bent, W-Bent and S-Kaol as a function of contact time showed that, the
adsorption of Cs +, Ba2+, Ni2+ and Co2+ on A-Bent and W-Bent is
heterogeneous with an initial rapid adsorption rate followed by a slower
uptake. A homogeneous adsorption process is observed for Sr2+ and Eu3+
where the uptake is fast and did not change within the whole time range. In
case of S-Kaol sample the adsorption is heterogeneous for Ba2+, Ni2+ and
Co2+ and homogenous for Cs+, Sr2+ and Eu3+.
The maximum uptake was recorded within 40 min for A-Bent, WBent,
and S-kaol and equilibrium reached within 60 min. It was observed
that in case of S-Kaol, Cs+ ion gives zero uptake during all range of shaking
time (180 min.), it need more time, so the overnight agitation of metals ions
with all types of clay is chosen to be the optimum agitation time condition
for more solid/liquid stabilization and maximum uptake .
According to the kinetic modeling, it was found that pseudo second -
order model fits more than pseudo-first order model with correlation
coefficient not lower than r2= 0.995 for all metal ions under investigation.
Pseudo second-order model describes the chemical sorption reaction, so that
some types of chemical reactions is considered to take place, which include
valence forces with the exchange of ions or the formation of covalent bonds.
The sorption isotherm results for different radionuclides were studied
using batch experiments. Also, four isotherm models including Freundlich,
Langmuir, Temkin and Dubinin-Radushkevich (D-R) were compared against
experimental data. The distribution coefficient Kd decreases with increase
134Cs, 133Ba , 90Sr , 152Eu and inactive Co2+ , Ni2+ concentration for all types
of clay minerals. It is clear that the distribution coefficient for 152Eu in case
of (A-Bent) is higher than 134Cs up to 150 mgL-1, after that the Kd values of
134Cs became higher than 152Eu. This trend indicates that the number of sites
selective for 134Cs is significantly higher than that is selective for 152Eu. Na-
Bent is preferred rather than A-Bent for uptake of 90Sr over all range of
concentrations, while 134Cs is up to 150 mgL-1 and Co2+ at 50 mgL-1. In
comparison with A-Bent, S-Kaol and Na-Bent which have the lowest values
of Kd for 133Ba than all other metal ions, W-Bent has a higher value for 133Ba
than Co2+ at low concentration of 50 mgL-1 and Ni2+ up to 150 mgL-1.
According to the isothem models, the uptake of radionuclides
increases with increasing the initial concentration. The correlation coefficient
(r2) for A-Bent showed that, 134Cs (0.990) fits well to the Langmuir model,
suggesting a monolayer sorption, mainly due to ion exchange, while Co2+ is
more fitted to Freundlich model with r2 = 0.981. Sorption of Co(II) at high
concentration is less stronger than that at low solution concentration, in
which at low surface coverage, the sorption of Co(II) from solution occurs
through outer-sphere complex formation via electrostatic interaction between
the first hydrolytic complex CoOH+ and the surface of bentonite. Temkin
isotherm model, provides a close fit to the radioactive tracer 152Eu and 90 Sr
and the metal cation Ni2+ with correlation coefficient r2 = 0.970, 0.980, and
0.970, respectively. 133Ba follows D-R model with r2 =0.990.
The adsorption isotherm model for Na-Bent showed that 134Cs, 133Ba,
Co2+and Ni2 fit well to the Langmuir model with correlation coefficient r2 =
0.910, 0.960, 0.980 and 0.990, respectively. While 152Eu and 90Sr is more
fitted to Temkin model with correlation coefficient of 0.892 and 0.987,
respectively. 90Sr is the only radioactive metal cation that have a higher value
of Langmuir monolayer capacity, qm (0.27 mol/Kg) on the monolayer surface
of Na-Bent than A-Bent (0.22 mol/Kg).
Examination of W-Bent isotherm data showed that the Temkin
isotherm model provides a close fit to the radioactive tracer 133Ba with a
correlation coefficient r2 =0.939 and Langmuir model fits to 134 Cs, 152Eu
and Ni2+ with correlation coefficient r2 = 0.998, 0.965, and 0.915,
respectively. While 90Sr and Co2+ follow D-R model with r2 = 0.966 and
0.968, respectively.
Examination of S-Kaol isotherm data revealed that, both 152Eu and
Co2+ fit well to the Langmuir isotherm model with correlation coefficient r2
= 0.938 and 0.921, respectively. At the same time 134Cs, 133Ba and Ni2+
follow Temkine model with r2 = 0.947, 0.969 and 0.910, respectively, while
90Sr fits well to the D-R model with r2 = 0.995. The values of E calculated
using D-R equation are (12.9, 12.9, 10, 7.9, 8.5 and 6.7 kJ mol−1) for cesium,
europium, strontium, barium, cobalt and nickel, respectively. The typical
range of bonding energy for ion-exchange mechanisms is 8–16 kJ mol−1,
indicating that chemisorptions may play a significant role in the adsorption
process for all metal cations adsorbed on S-Kaol surface, except for Ni2+
which have E value < 8, indicating that nickel undergo a physical adsorption
process. from the isotherm modeling it is clear shown that montmorillonite
has a much higher adsorption capacity rather than kaolinite, with comparable
maximum sorption capacity (qm) for 134Cs adsorption on A-Bent, Na-Bent
and W-Bent for 50 mgL-1, according to Langmuir isotherm model it is found
to be (0.28, 0.224, and 0.251 mol/Kg) respectively, while for kaolinite it was
(0.048 mol/Kg).
Finally montmorillonite, which has high capacity for cations can be
used as a barrier material for landfills and final repositories of hazardous
waste. Kaolinite can also be used for the purpose of selective cation
adsorption because of its porous properties.
Conclusion
1- Generally, the physical and chemical characterization of bentonite
samples (A-Bent and W-bent), show that the Egyptian bentonite
has a very good characterization and excellent sorption capacity not
only for liquid waste treatment but also can be used as a buffer
material in the low level disposal system for different disposal
nuclear waste level.
2- According to kinetic data and pH experiments, the affinity of clay
samples for Cs+ is low compared with other metal cations at pH 5-6
3- The adsorption of the investigated metal cation on the surface of ABent,
W-Bent and S-kaol follow the pseudo-second order model,
which describes the chemical adsorption and thus some types of
chemical reaction is considered.
4- The adsorption capacity varies from metal to metal and also
depends on the type of clay used. When a comparison is made with
other low cost adsorbent, bentonite either better or equivalent in
adsorption capacity.
5- Although kaolin has a lower activity in comparison with bentonite
but it can be used in the purpose of selective cations adsorption
because of its porous properties.
6- Na –Bent does not increase the number of adsorption sites to a large
extent if compared with A-Bent, but it was found that Na –Bent is
more preferred than A-Bent in the uptake of 90Sr over all the range
of concentrations, while for 134Cs and Co2+ at low concentration
only.