الفهرس 
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Abstract
Radioactive waste is produced from the various applications of radionuclides in research, medicine, industry as well as the nuclear fuel cycle used for power generation and military uses and from radiological accidents. Removal of hazardous elements from radioactive and industrial wastes has environmental and economic importance. Several methods are available for treatment processes, including chemical precipitation, sorption and ion exchange. A wide range of materials is available for the ion exchange treatment of liquid radioactive waste e.g., natural ion exchangers clays and clay minerals. This thesis is focused on evaluating the use of natural ball clay and its different modified forms to remove cobalt, strontium, cerium and gadolinium ions from aqueous solutions. A comparison was made between the materials resulting from the modification and the optimum material was selected to be used in the removal process. The result from the comparison indicated that the optimum ball clay was modified with acrylic acid and phosphoric acid using gamma irradiation polymerization technique (BC-AA-PA). The work executed in this thesis is presented in three main chapters, namely; Introduction; Experimental and Methods and Results and Discussion.
I. Introduction
This chapter includes the definition of radioactive waste, its sources, classifications and management. Also, it reviews different methods as well as different materials for treating radioactive wastes including clay and clay minerals as sorbent materials. This section also reviews the nomenclature, mineralogy, types and properties of clay and clay minerals. The chemical nature and pore structure of clay materials and their effect on their ability to absorb was also included. The possible chemical and physical modifications in the pore structure of the clay materials in order to increase their sorption capacities are discussed. It also includes some aspects of studied elements (cobalt, strontium, cerium and gadolinium) ions. Finally, a literature survey of removal and separation of lanthanides and heavy metals within the last decade using different methods is also covered.
II. Experimental and Methods
This chapter contains a detailed description of all chemicals and reagents, used in the preparation process. The purity degree of these materials and the type of used devicesin all experimental investigations were also discussed. It concludes the preparation of sorbent materials, metal ion solutions, batch investigation, determination of capacity and desorption investigations. It also contains an explanation of a simulation model of waste to show the sorptive capacity of a substance in a multi-ion medium as an application of the study.
III. Results and discussions
This chapter includes all the obtained experimental results from the sorption of metal ions onto the sorbent materials under investigation. This chapter is divided into four main parts as follows:
The first one is the characterization of the BC, BC-AA-PA and BC-AA-PA/Mn+ using different techniques including FTIR, SEM, XRD, XRF, TGA and DTA analyses.
- The FT-IR spectra are used to define the functional groups and bonds within the molecules of a material. It showed the characteristic peaks of the ball clay, which can be easily observed in the prepared material BC-AA-PA as evidence of clay interference inside the composite matrix. Additional appeared sorption bands indicated the presence of crosslinker, phosphoric acid and carboxylate group. The variance of relative strength of these peaks in BC-AA-PA/Mn+ spectra indicate variations in the degree of ionization of carboxylic groups on their surfaces. These variations may be due to the uptake of metal ions onto the prepared BC-AA-PA.
- SEM was used to investigate the morphology of (BC), (BC-AA-PA) composite and (BC-AA-PA/Mn+). The three obtained SEM images showed that the used particle size was in the range of micron which agrees with the used particle size through the analytical methods. The images also show that BC has a relatively homogeneous surface, while BC-AA-PA shows different morphology and irregular shape of aggregate grains confirming the interaction of BC with AA and PA. For BC-AA-PA/Mn+, a distinct morphological surface is observed that proves the metal sorption onto the prepared composite.
- XRF analysis indicated that the main constituents of BC are silicon and aluminium oxides. There was also a low content of titanium oxide and very low oxides of iron, calcium, copper and phosphorous. For BC-AA-PA material, the percent of SiO2 and Al2O3 was reduced while the phosphorus percent was increased which confirms the contribution of phosphoric acid in the modification process of BC. For BC-AA-PA/Mn+, the percent of SiO2, Al2O3 and P2O5 was reduced while Mn+ percent was increased indicating the uptake of metal ions onto the sorbent material.
- The XRD patterns showed that BC is mainly comprised of kaolinite, illite, quartz and anatase. For BC-AA-PA, it was found that the increase in the amorphous phase may be due to the formation of composite material with a slight shift of quartz peak from 25o to 26o which is proof of the presence of clay mineral in the composite matrix.
- The thermal analysis (TGA&DTA) showed that the prepared BC-AA-PA material is thermally stable at high temperatures.
- The maximum repeating capacities of BC and BC-AA-PA were found to be (0.013, 0.0212, 0.028 and 0.039) mmol/g and (0.222, 0.771, 0.862 and 0.927) mmol/g for (Co2+, Ce3+, Gd3+ and Sr2+) ions, respectively.
- The second part is the sorption experimental investigations of ball clay washed with water and those treated with different acids of different molarities and comparing these modified forms for the removal of cobalt, strontium, cerium and gadolinium ions. The results indicated that the removal efficiencies take the order of BC ˂ (BC-1M HCl) ˂ (BC-1M H3PO4). These results indicate that phosphoric acid was the best for the modification process.
- The acidity effect of phosphoric acid on the (BC) modification process and the efficiency of its removal towards the concerned ions (Co2+, Sr2+, Ce3+ and Gd3+) take the following order: (BC-1M H3PO4) ˂ (BC-1.5M H3PO4) ˂ (BC-2M H3PO4). (BC-1.5M H3PO4) was taken as an average value to ensure that the solubility of the substance at high acidity was avoided.
- A comparison between (BC-AA) (BC-AA-PA) with respect to (BC) take the order BC ˂ (BC-AA) ˂ (BC-AA-PA).
• The third part is experimental investigations for the sorption of cobalt, strontium, cerium and gadolinium ions onto BC-AA-PA and studying the effect of some factors such as pH, contact time, initial metal ion concentration and temperatureon the process. This sorption process was analyzed by applying different isotherm and kinetic models in order to determine the type, rate and mechanism of the sorption reaction.
• Effect of pH and speciation
- Sorption was studied at different pH values ranging from 2 to 7 for the four studied metal ions.
- The results indicated that by increasing pH value, the distribution coefficients of the studied metal ions increased.
- The removal percentage increased with increasing the pH value and the optimum pH value is 5 for all the four studied elements.
- As the pH value increased, the hydrolysis increased resulting in the formation of various hydro complexes in an aqueous solution.
- At (pH 5), both gadolinium and cerium are presented as either a free trivalent cation (Ln3+) or a divalent complex, Ln(OH)2+.
- Cobalt and strontium are likely to be removed as divalent cations.
- By measuring the final pH after metal sorption by (BC-AA-PA), it was found that the final pH was reduced after removal of Mn+ starting from the initial pH value of 3 which may be caused by the ion exchange between the hydrogen ions presented on the sorbent surface and the concerned ions.
• Determination of zero of point charge
- The pHPZC was studied using various pH values (pH range of 2.0–7.0) and plotting of pHinitial vs ΔpH (pHinitial–pHfinal).
- The pHPZC was determined as 6.2 and 3.2 for BC and BC-AA-PA, respectively.
- This indicates that BC modification reduced the pHPZC value, hence, the surface charge of (BC-AA-PA) becomes negative at pH values >3.2.
• Effect of particle size
- The effect of particle sizes was studied at four different sizes ranges (106-75) µm, (75-63) µm, (63-53) µm and (˂53) µm.
- As the BC-AA-PA particle size reduced, the removal percent of the studied ions increased. The smallest particle size was selected as the optimum size <53µm.
• Effect of V/m ratio
- The V/m ratio was studied from 0.01 to 0.1 L/g. V/m ratio was calculated by changing the amount of an adsorbent.
- By increasing the V/m ratio, the removal percent increases and it is deduced that the optimum V/m ratio was 0.1 L/g.
- This examination concluded that a low amount of (BC-AA-PA) can be sufficient to achieve high removal efficiency which makes it a very promising material in a wide range of applications.
• Effect of contact time
- The effect of contact time was studied from 3 to 120 minutes; at concentration 1 mmol/L, initial pH 5, particle size (<53µm) and V/m 0.1 L/g at room temperature.
- The sorption increased with increasing time till reaching equilibrium within 60 min.
- The values of amount sorbed at room temperature were found to be 0.076, 0.927, 0.088 and 0.091 mmol/g for cobalt, strontium, cerium and gadolinium ions, respectively.
• Sorption kinetic modelling
- Pseudo-first order, Pseudo-second order, intra-particle diffusion and Helfferich models were used to determine the rate and mechanism of the adsorption process.
- from the obtained data, it is found that the pseudo-second-order model is more applicable and thus the sorption process is controlled by a chemisorption process.
- Both intra-particle diffusion and film diffusion have a significant contribution in the rate determination but the sorption process is governed by intra-particle diffusion (the slowest step).
- The Helfferich model confirmed that the intra-particle diffusion mechanism controls the sorption process. The Di values were in the order of 10−14 m2/s for all the studied metal ions which means that the sorption process is chemisorption.
• Effect of initial metal ion concentration and temperature
- The effect of initial metal ion concentration (in the range from 0.1 to 30 mmol/L) on the sorption of cobalt, strontium, cerium and gadolinium ions at temperature range from298 to323 K was studied.
- The amount of sorbed quantity of the studied ionsincreased with increasing both the initial metal ion concentration and temperature.
- This confirms that the diffusion of ions onto the sorbent has an endothermic nature.
• Isotherm models
- Langmuir, Freundlich and Dubinin–Radushkviech (D–R) isotherm models were applied to the experimental data to obtain a model that sufficiently describes the equilibrium data.
- Langmuir was more appropriate than the Freundlich model and the ions are sorbed by ion-exchange mechanism.
- The maximum monolayer capacity of BC-AA-PA was 0.45, 1.22, 0.907 and 1.085 mmol/g for Co2+, Sr2+, Ce3+ and Gd3+, respectively.
- The value of mean sorption energy (E) estimated from the D-R model ranges between 8 and 16 kJ/ mol which indicates that the sorption occurs via a chemical reaction.
• Thermodynamic studies
- The thermodynamic parameters ∆Go, ∆Ho and ∆So for the sorption of the studied ions onto BC-AA-PA were estimated.
- It is found that ∆Gᵒ has a negative value indicating the feasibility of the process and its value decrease with increasing temperature due to the spontaneous nature of the sorption process.
- ∆Hᵒ has a positive value indicating the endothermic nature of the sorption process and confirms that the sorption capacity of the sorbent rises with increasing the temperature. ∆Sᵒ has a positive value which means the increase in the randomness at the solid/liquid interface.
• Desorption and reusability
- The ability to desorb cobalt, strontium, cerium and gadolinium ions from BC-AA-PA sorbent and reuse it was inspected using different eluents such as distilled water, 0.1 mol/L of NaOH, HCl and HNO3.
- The results confirmed that the four studied metal ions can be easily desorbed from BC-AA-PA sorbent using 0.1 mol/L HNO3 for cobalt, cerium and gadolinium ions and 0.1 M EDTA for strontium ions.
- BC-AA-PA sorbent can be reused for further sorption-desorption processes even 5 cycles.
• Effect of Competing ions
- The effect of competing ions was tested by using a solution containing equimolar concentrations of Co2+, Sr2+, Ce3+ and Gd3+ with an initial concentration of 1 mmol/L and at optimum conditions
- The results confirmed that the four studied metal ions acted as competing ions to each other taking the same order as in their single-component system Co2+ < Ce3+ < Gd3+ < Sr2+.
• Comparison Studies with Different Sorbents
- The sorption capacity and production cost of BC-AA-PA for the removal of the four studied ions was compared with other sorbents in the literature. The results revealed that BC-AA-PA has a comparatively high sorption capacity than many other sorbents.
- The data demonstrates that BC-AA-PA material is considered as a low-cost sorbent compared to other materials.
The fourth part is the application of using BC-AA-PA in the sorption-desorption process of a simulated waste solution.
- The efficiency of BC-AA-PA composite in waste treatment was performed by the removal of different ions from a waste solution containing multicomponent ions.
- The results denote that the BC-AA-PA has been effectively applied to capture the concerned ions from the multicomponent solution with high removal percentages.
- The removed ions can be easily desorbed using 0.1 M and 0.5 M nitric acid in a high percentage.