الفهرس 
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Abstract
Peaceful nuclear facilities and its application in diver’s activities led to inescapable generation of low and intermediate level liquid wastes. The discharge of these wastes into aquatic ecosystem causes detrimental contamination to human health and environment. In this respect, it’s mandatory to provide a proper radioactive waste management in order to safeguard human health and environment. Ion exchangers which can be naturally occurring or synthetic plays an important character in the treatment of such wastes.
The major focus of present study is to synthesis and characterize of poly(AM-AA)/FA as a nanocomposite ion exchanger by gamma radiation for the purpose of removal of Co2+ and Cs+ from aqueous solutions using batch and fixed-bed column techniques. Posteriorly, geopolymerization process was proceed by preparation and characterization of optimized geopolymer material. Leaching investigations of 60Co2+ and 134Cs+ radionuclides from geopolymer formulations as affected by single and binary component stabilization systems were studied. By this way we can attained wasteform safely to handled, stored and disposed.
This work was carried out in three substantial chapters.
Chapter (1): Introduction
This chapter gives insight overview on radioactive wastes, their sources, types, classification, treatment methods and general aspects on ion exchanger. Also the traditional and advanced solidification materials and processes were illustrated. Additionally this chapter involved the literature review covering the related studies done by the others.
Chapter (2): Experimental
The explication of essential chemicals and the description of instrumentation used in this study were viewed in this chapter. The experimental procedures used in the preparation of nano fly ash, polyacrylamide and poly(AM-AA)/FA nanocomposite were shown. Also, factors affected on the sorption phenomena of cesium and cobalt were clarified through bath and column investigations. Furthermore, this chapter involved solidification of waste, preparation and characterization of geopolymer specimens and study different parameters affected on the solidified of single and binary component stabilization systems.
Chapter (3): Results and discussion
This chapter was ordered into three main sections summarized as the subsequent:
Characterization of Prepared Materials
Characterization of Poly(Acrylamide- Acrylic acid)/Fly ash Nanocomposite
Poly(AM-AA)/FA nanocomposite was characterized by XRD, XRF, FTIR , DTA-TGA, SEM and TEM analyses, results inferred that:
The amorphous structure of poly(AM-AA)/FA nanocomposite was observed with traces of crystalline phases belonging to percent loaded of nano-FA.
The quantitative elemental analysis indicated that the major oxides in the synthetic nanocomposite was found to be SiO2, Al2O3, P2O5 and CaO. Additionally the kind of examined fly ash was inferred to belong C class.
FTIR analysis confirmed the presence of all expected characteristic function groups in synthesized poly(AM-AA)/FA nanocomposite material.
The TGA/DTA curves showed the thermal stability of the nano-FA sample while the poly(AM-AA)/FA nanocomposite was degraded in four steps till reaching the complete destroying of the main chain of polymeric backbone.
The surface seems homogeneous with a series of irregular cavities structure distributed over the surface of all composite material revealed the homogeneous incorporation of nano-FA into the polymer matrix
TEM inspection revealed that both fly ash particles and synthesized poly(AM-AA)/FA nanocomposite were found in nano-scale diameter (less than 100 nm).
Characterization of Optimized Geopolymer
Mk-based geopolymer loaded with 10% nanocomposite was supported using XRD, XRF, SEM and FTIR analyses, results concluded that:
XRD pattern showed that quartz was the predominant phase exhibited different degrees of 2Ө (20.8, 26.6, 36.6, 45.8, 50.28, 60, 68.4o) with varied intensities.
The elemental composition of Mk-based geopolymer formulation revealed that Al2O3, SiO2, Na2O and K2O are the major oxides while CaO, Fe2O3 and SO3 are the minor ones.
FT-IR analysis proofed the presence of characteristic band attributed to amorphous silica and this reflecting good geopolymer synthesis.
SEM micrographs clarified the good quality of the optimized Mk-based geopolymer with less amounts of un-reacted raw materials. Geopolymer surface seemed to be muli-layered structures with better homogeneity of nanocomposite.
Sorption Investigations
The batch and fixed-bed column approaches were implemented to assess the sorptivity of synthesized poly(AM-AA)/FA nanocomposite respect Co2+ and Cs+.
Batch Studies
There are different factors affected on the removal of Co2+ and Cs+ onto poly (AM-AA)/FA nanocomposite.
Effect of Solution pH
The effect of pH as a parametric factor was studied purposing to attain the optimum chemical conditions at which both Co2+ and Cs+ can be effectively sorbed onto the synthesized poly(AM-AA)/FA nanocomposite. It was observed that uptakes of both metal ions were gradually increased till pH of 7.0 ± 0.02 recording percentage uptakes of 93.2 and 88.5% for Co2+ and Cs+, respectively.
Effect of Nanocomposite Particle Size
A wide range of particle size (106–500 µm) were assessed and revealed that the smallest nanocomposite particle size (106–250 µm) recorded higher uptakes (93.18 and 88.64% for Co2+ and Cs+, respectively).
Effect of Contact Time and Temperature
The preliminary investigations exhibited that the sorption of both systems are temperature dependent. Sorption process represented as sharply increased with time at the initial stage till 15 min. of contact then gradually increased to reach an equilibrium value in approximately 60 min. The percentage uptake of sorbed metal ions were evaluated at different temperatures. The sorption nature is endothermic; this is point out by the proportional relation between the amounts sorbed with temperature.
Sorption Kinetic Modelling
Sorption rate constants were clarified by analysis of experimental data. Pseudo 1stand 2nd-order kinetic models were applied and the results suggested the applicability of the later model with chemisorption reaction mechanism.
Sorption Isotherm
At the steady state, all sorption isotherms were endothermic and the sorbed amounts were increased from 46.5 and 41.5 to 56.46 and 47.9 mg/g for Co2+ and Cs+, respectively.
Sorption Isotherm Modelling
Analysis of experimental data by different isotherm models such as Langmuir, Freundlich and Dubinin–Radushkevich D–R were constructed.
Langmuir results confirmed that:
The monolayer sorption capacity was increased by increasing temperature, suggesting more availability of active sites at high temperature.
High R^2 values were attained (0.988–0.993) confirming that the sorption of Co2+ and Cs+ onto poly(AM-AA)/FA nanocomposite is applicable with Langmuir model.
Freundlich results confirmed that:
Values of Freundlich constant (n) were greater than unity, all sorption systems were favorable.
D–R results confirmed that:
The magnitude of sorption mean free energy were lied in the range from 9.58 to 11.82 kJ/mole giving an impression of the ion exchange is the controlling reaction mechanism of all studied systems.
Thermodynamic Studies
Several thermodynamic parameters were determined and the –ve and +ve quantities of ∆G^° and ∆H^° confirms the spontaneous and endothermic natures of all studied sorption systems, respectively.
Fixed Bed Column Studies
Performance evaluation of fixed bed column was examined using 60Co and 134Cs spiked solutions as affected by bed depth, flow rate and initial metal ion concentration. The effect of essential column parameters on the performance of fixed bed column was studied as subsequent.
Effect of Bed Depth
The breakthrough curves of 60Co2+ and 134Cs+ radionuclides sorbed onto poly(AM-AA)/FA nanocomposite were studied at different bed depth ((1.5 and 3.0 cm). Results demonstrated that increasing bed depth led to enhancement the sorption performance (q_tot= 8.75 and 6.97 to 18.8 and 15.01 mg) for 60Co2+ and 134Cs+, respectively. This can be attributed to providing more available sorption sites and sufficient residence time.
Effect of Flow Rate
The breakthrough curves of 60Co2+ and 134Cs+ radionuclides sorbed onto poly(AM-AA)/FA nanocomposite were studied at different flow rate (1.0 and 2.0 mL/min). Results inferred that increasing flow rate led to decline in sorption performance (q_tot = 18.8 and 15.01 to 12.25 and 9.31 mg) for 60Co2+ and 134Cs+ radionuclides, respectively.
Effect of Initial Concentration
Breakthrough curves of different concentrations of 60Co2+ and 134Cs+ radionuclides (100-400 mg/L) sorbed onto poly(AM-AA)/FA nanocomposite were studied. Results demonstrated that at lower influent concentration, the breakthrough curves were dispersed and breakthrough occurred slower. As the influent concentration increased sharper breakthrough curves were observed. So, it can concluded that the diffusion process is a concentration dependent.
Fixed Bed Column Modelling
Thomas, Yoon–Nelson and Adams Bohart models have been applied to evaluate the fixed bed column sorption kinetics, time required for retaining 50% of the initial sorbate (τ, min) and the maximum sorption capacity per unit volume (N_0, mg/L), respectively.
Thomas results concluded that:
The predicted sorption capacities of Thomas (q_Th) of poly(AM-AA)/FA nanocomposite were very close to those obtained experimentally at all operating conditions. These findings reflected the applicability of Thomas model to describe the sorption processes.
Yoon–Nelson results concluded that:
By increasing fixed column bed depth (1.5–3 cm) the rate constant (K_YN) values were decreased (0.064 and 0.059 to 0.041 and 0.037 min-1), while the 50% breakthrough time τ was extended (89.05 and 68.55 to 177.2 and 149.3 min) for 60Co2+ and 134Cs+ radionuclides, respectively.
Adams Bohart results concluded that:
Values of maximum sorption capacity (N_0) were decreased with increase flow rate while the sorption rate constant values (K_AB) were influenced by flow rate and were increased with increase in flow rate. This indicated that external mass transfer dominated the overall system kinetics in the initial part of the sorption of the fixed bed.
Solidification of Radioactive Wastes
The unique properties of geopolymer, which mentioned in literature, were further investigated towards solidified organic-inorganic material loaded with radionuclides. Solidification of poly(AM-AA)/FA nanocomposite loaded with 60Co2+ and 134Cs+ radionuclides in hardened MK-based geopolymer matrices was applied. Several factors affecting the characteristics of the solidified waste product towards safe disposal such as compressive strength and leaching behavior of radionuclides were studied.
Compressive Strength Studies
Solid to liquid ratios, Si-modulus and nanocomposite additions percent (%) were evaluated to attain the optimum conditions for solidified geopolymer strengths.
Overall results showed that compressive strength increased with increased curing time.
Highest compressive strength (88.52 MPa at 90 days of ageing) was achieved at solid/liquid ratio of 0.85.
Increasing Na2SiO3/NaOH ratio up to 1.45 achieved maximum compressive strength (92.74 MPa) for geopolymer matrix.
Results revealed that formulations with lower nanocomposite loading percentages recorded higher compressive strengths.
Percent loading of 10 wt.% poly(AM-AA)/FA nanocomposite was selected for further investigations due to its high loading percent with a compressive strength more than twice the waste acceptance criteria.
Leaching Investigations
Leaching behaviors of Co2+ and Cs+ radionuclides from geopolymeric matrices were studied as affected by single and binary component stabilization systems.
The variation of CLF of 60Co2+ and 134Cs+ radionuclides incorporated in geopolymer formulations loaded with 10 wt.% loaded poly(AM-AA)/FA nanocomposite was detected.
Results indicated that all radionuclides were leached in greater fractions for the binary systems than for the single ones.
The leachability indexes for 60Co2+ and 134Cs+ radionuclides leached from Mk-based geopolymer matrices as affected by single and binary component stabilization systems were in the range of 9.17 to 11.16. It was clearly observed that these values exceeded the required value of 6, the minimum value for acceptance as a low level waste form.
Leaching mechanisms were determined to be wash-off controlled.