الفهرس | Only 14 pages are availabe for public view |
Abstract The interesting demand of radioactive elements in nuclear energy program require a suitable method for their separation, preconcentration and determination in various types of samples e.g. rocks, waste effluents, water samples and etc. Actually, these heavy elements have been present virtually everywhere in the earth’s crust. The great interest for their accurate determination at low concentrations arises from their toxicity and the possibility to reach human beings through different pathways. They are known to cause acute toxicological effects for human and their compounds are potential occupational carcinogens. Modern analytical chemistry is characterized by hyphenated analytical methods which involve a combination of a separation and/or sensitive detection technique with a preconcentration step. The latter operation is a consequence of the problems encountered in the chemical analysis of real analytical samples such as low analyte concentrations (in many cases incompatible with quantification limits of instrumental methods) and high concentrations of matrix interference species present in these complex samples, especially those of environmental origin. Consequently, there is an ongoing need for the development of separation and preconcentration procedures prior to their determination which should be safe, rapid, convenient, and accurate.Several enrichment and separation techniques including solvent extraction, coprecipitation, ion exchange, electrodeposition, cloud point extraction and solid phase extraction have been used for separation of most analytes before their determination. In the last decades, cloud point extraction and solid phase extraction procedures have been extensively applied to trace metal ions before their determination in several matrices. These techniques offer several advantages including experimental convenience, low cost and environmental safety. The use of micellar systems such as CPE has attracted considerable attention in the last few years mainly because it is in agreement with the “green chemistry” principles, because low amounts of low toxicity surfactants replace the usual toxic organic solvents. In addition, surfactants are non-flammable and present low volatility, minimizing risks in the extraction process. Cloud point extraction procedure is based on the following phenomenon: When a non-ionic surfactant solution is heated over a critical temperature, namely cloud point (CP), the solution easily separates into two distinct phases. The first one is a surfactant phase, which consists a large hydrated micelles (surfactant-rich phase) of the small volume and the second one (aqueous phase) is an aqueous solution in which the concentration of the surfactant is approximately equal to the critical micelle concentration. Any organic or inorganic species interacts with the aggregates of micelles formed, and at and above cloud point it will be extracted into small surfactant-rich phase. Solid phase extraction is another approach that offers a number of important benefits. It reduces solvent usage and exposure, disposal costs and extraction time for sample preparation. In recent years SPE has been successfully used for the separation and sensitive determination of metal ions. The present work is concerned with the preconcentration and separation of thorium(IV) by cloud point extraction from aqueous solutions using Triton X-114 as a nonionic surfactant and 5-Br-PADAP as a complexing agent. The effect of parameters affecting the cloud point extraction of thorium ions is investigated. Also, the factors controlling the determination and preconcentration of uranium after the adsorption of (NH4 +) (TPB-) ion pair complex on naphthalene are examined. The present thesis comprises into three main chapters. The first chapter It includes the information about occurrence, the main uses of uranium and thorium and their hazard effects. It also contains the literature survey related to the methods of separation and preconcentration (cloud point extraction and solid phase extraction) for the two interested elements.Additionally, it highlights on the principles and theoretical aspects for the two procedures. The second chapter It involves the specification of chemicals, standards and reagent solutions with detailed explanation of their preparations as well as instruments used throughout this work. It also contains the procedure that used for adsorbent preparation. Moreover, the method that used for samples preparation and the recommended procedures for the cloud point extraction of thorium ions and solid phase extraction of uranium ions are discussed in details. The third chapter This chapter encloses the results and discussion of the obtained data. It divides into two main parts. The first part Cloud point extraction method has been proposed for the preconcentration of thorium species as a prior step using 5-Br-PADAP as ligand. For that, the formed complex is extracted by Triton X-114 and subsequently detected spectrophotometrically at 531 nm. The operating conditions affecting on CPE procedure of thorium ions from aqueous solution e.g. pH, buffer type, surfactant concentration, dye concentration, salt type and concentration, equilibration temperature and time, centrifugation rate and time, diluting agent type and foreign ions are studied. It is induced at the optimized conditions: λ 531nm, pH 3.4, 1.0 ml of 0.05% 5-Br PADAP and 2.0 ml of 0.5% Triton X-114 in the presence of 0.6 M NaCl as salting out with equilibration temperature and time 55°C, 15 min and centrifuge rate of 5000 rpm in 20 min. Calibration curve is linear in range (0.125-2.5) μg/ml of Th(IV) with molar absorptivity of 1.63 ×105 l/mol cm. The proposed method is applied on different water samples and some geological silicate samples collected from Wadi Sikait area that located in the South Eastern Desert of Egypt. The second part This part explains the preconcentration of uranium ions by solid phase extraction technique using (5-Br-PADAP) as chelating reagent in addition to the (NH4+) (TPB-) ion pair supported on naphthalene as adsorbent. The reveling factors effect on the determination of uranium ions such as absorption spectra, pH, buffer type, reagents concentration, shaking time, solvent type, influence of foreign ions and validity of the method are examined and treated. Uranium species are found to be enriched quantitatively from aqueous solution at pH 8.0, 2.0 ml of 0.05% 5-Br-PADAP, 1.5% TPB and 20% naphthalene. The linearity is maintained in the concentration range (0.05- 1.0) μg/ml of uranium ions with molar absorptivity 2.63 ×105 l/mol cm. FTIR spectra for ligand and its complex with uranium ions are carried out and the surface of adsorbent is examined using SEM before and after loading of uranium that confirms its adsorption on the surface of naphthalene–NH4– TPB adsorbent.The investigated procedure is assessed by standard addition method using fresh water samples and some reference certified rock samples then applied for analytical uranium determination in liquid waste and some collected silicate samples. Finally, we conclude that the procedures of cloud point extraction and solid phase for the determination of thorium and uranium ions, receptively using the suggested dye reagent are simple, highly sensitive and accurate. It can detect very low concentration levels. |