فهرست مطالب زهرا شیری یکتا

Heavy metal ions have increased wastewater production with the development of various nuclear activities. One of the most significant metal ions that harm the environment and living organisms, especially humans, is the uranyl ion. There are many methods to remove metal ions, and biological adsorption is the cheapest and most efficient method. In this research, the absorption of uranyl ions from aqueous solutions from tea waste has been studied. Due to the presence of various functional groups such as carboxyl, hydroxyl, amine, etc, tea wastes have good cations adsorption ability. The effective parameters in adsorption including pH, adsorbent dose, temperature, initial uranyl concentration, and contact time parameters were investigated. Response surface methodology (RSM) was used to conduct experiments and analyze the results. The optimum conditions for uranyl adsorption by tea waste adsorbent were pH = 3.9, temperature 25°C, adsorbent dose 0.275 g, initial concentration of uranyl 10 mg/L, and contact time 90 minutes. Using Freundlich's isothermal and pseudo-second-order models, we fitted the most accurate isothermal and kinetic models. Results showed that tea waste was a good bio adsorbent for uranyl adsorption from real wastewater with a 93.50% adsorption rate.

One of the most important persistent and non-degradable pollutants are heavy metals, which are among the most toxic pollutants in the environment. Therefore, removing these pollutants is of particular importance. Uranium, as one of the heavy metals, is a natural radionuclide that has harmful effects on human health and the environment due to its serious toxicity and radiation properties. In this research, Amberlite XAD-4 resin impregnated with bis-2-hydroxybenzaldehyde 1,2-diaminoethane (H2L) Schiff base ligand was used for the adsorption of uranium from aqueous solution. The effect of effective parameters such as aqueous phase pH, contact time, amount of adsorbent and temperature dependence of the process were investigated. The results showed that 98% of uranium ions in the optimal conditions of pH5.5, adsorbent amount 0.1 g, contact time 60 min. and temperature 25˚C, uranium ion with an initial concentration of 20 mg/L was quantitatively removed from 20 mL of the aqueous solution. A comparing the adsorption percentage of non-impregnated resin with impregnated resin with Schiff base ligand shows a shift for uptake of the uranium ions vs. pH curves towards lower pH the values (about ΔpH0.51) and the adsorption behavior of the resin at pH5.5 improves with increasing adsorption from 52% to 98%. Kinetic and adsorption data correspond well with pseudo-second-order equation and Freundlich isotherm, respectively. Thermodynamic investigation also showed that the studied ion adsorption process is based on entropy.

Due to the importance of removing strontium ions in nuclear wastes, in the present work, while synthesizing hydroxybenzaldehyde propyltriethoxysilane ((EtO)3Si-HL) and pyridylmethylidene propyltriethoxysilane ((EtO)3Si-L) ligands, we investigated the properties of silica nanoparticles modified with these ligands as solid adsorbents in The removal of strontium ion from the aqueous solution was investigated and parameters such as pH, time, the mass of adsorbent, temperature, and interfering ions were tested. The adsorption behavior of the adsorbents showed that by modifying the surface of the nano adsorbent, the ability of the adsorbents to adsorb strontium ion at pH=6 increased from 6.31% to 86% and 22.11% using the (EtO)3Si-HL and (EtO)3Si-L ligands, respectively. The results of isotherms and adsorption kinetics indicate that the adsorption process follows the Longmuir isotherm and the pseudo-second-order model, respectively. Also, thermodynamic parameters show that strontium removal from the aqueous solution is an endothermic process. The positive entropy values are the driving force behind the adsorption process.

Uranium, as one of the heavy metals, is a natural radionuclide that has harmful effects on human health and the environment due to its serious toxicity and radiation properties. Biosorption is a simple and cost-effective technique that can be used for remove of heavy metals and Radionuclides from waste waters. In this study, Micrococcus luteus biomass pretreated with autoclave heat was used. Then, physicochemical factor affecting the biosorption including biosorbent dose, initial uranium concentration, temperature and pH were investigated by Response Surface Methodology. The results showed that the factor of initial uranium concentration, sorbent dose and pH statistically (p-value‹ 0.05) affect the uranium biosorption process. In contrast, temperature factor (p-value› 0.05) statistically have no effect on uranium removal by M. luteus. Discussion and The results indicated that the pre-treated biomass under the conditions suggested by Design Expert software (19.75 g/liter of biomass, temperature 32.14 OC and pH 3.33) is able to remove approximately 99.98 percent of uranium from the contaminated area is 26.11 mg/liter of uranium, which shows its valuable potential in bioremediation applications of uranium from acidic wastewaters contaminated with low concentrations of uranium.

Toxic heavy metal contamination of industrial water is a significant universal problem. They accumulate in living tissues throughout the food chain which has humans at its top. These toxic metals can cause accumulative poisoning, cancer, and brain damage. Uranium is one of the most serious heavy metals because of its high toxicity and radioactivity. Excessive amounts of uranium have found their way into the environment through the activities associated with the nuclear industry (1). Conventional methods for removing uranium from wastewater include precipitation, evaporation, ion exchange, membrane processing, and adsorption. Nevertheless, these methods have several disadvantages, such as high installation and operating costs, the requirement of preliminary treatment steps, the difficulty of treating the subsequently generated solid waste, and low efficiency at low metal concentration (2,3). Owing to an increase in environmental awareness, there has been an emphasis on the development of new environmentally friendly ways to decontaminate waters using low-cost methods and materials. In this study, microbial biomass has emerged as a complementary, economic, and eco-friendly device for controlling the mobility and bioavailability of metal ions (2,4). The present work evaluates the performance of the Citrobacter freundii biomass to remove uranium ions from aqueous solutions. The effect of pH, temperature, initial concentration, and sorbent dose on biosorption capacity is also studied.

Materials: Citrobacter freundii bacteria used in this research with PTCC No. 1772 was purchased from the Scientific and Industrial Research Organization of Iran. Uranyl nitrate salt (UO2(NO3)2.6H2O) was obtained from the Research Institute of Nuclear Sciences and Technologies. Nutrient Broth culture medium, sulfuric acid, and sodium hydroxide and other materials used in this research were supplied from the Merck Company.Preparation of uranium solutions and biomass: A stock solution containing 1000 mg L-1 of U(VI) was prepared of UO2(NO3)4.6H2O. The working solutions were prepared daily from stock solutions. In this study, the biomass of Citrobacter freundii bacteria was heat treated in an autoclave at a temperature of 121°C for 15 minutes at a pressure of 1.5 atmospheres. Experimental design and batch biosorption studies: The design of the experiment was done using the response surface method by Design Expert software. Four variables, including initial uranium concentration (mg/l), temperature (°C), pH, and biosorbent dose (g/l), in five levels α-, -1, 0, +1, α+, 1 were used to design the experiment (Table 1). Therefore, 27 experiments were presented using a central composite design. The values of the variables and the obtained answers are shown in Table 2. Uranium biosorption experiments were performed by adding specified amounts of bacterial biomass in 20 ml Erlenmeyer flasks containing uranium solution with the concentration and pH corresponding to each experiment, with the specified temperature in the Shaker. After 90 minutes, each sample was centrifuged at 4500 rpm for 15 minutes at 4°C. Then, the remaining uranium in the solution was measured by ICP (Perkin Elmer/Optima 7300DV). The percentage of uranium removal (R) was calculated by equation 1:  Where C0 and Cf are the initial and the final concentrations of the metal ion solutions (mg/l), respectively.Table 1- Variables and Levels of the Central Composite Design Method

By using the RSM-CCD method, the optimization of the biosorption process was carried out. Table 2 shows the experimental results based on each point of the experimental design. Then, using analysis of variance (ANOVA), the obtained results were evaluated.The equation obtained for the biosorption efficiency of uranium by Citrobacter freundii is expressed as follows:Removal= +68.97045-1.43160 * C (ppm)+12.81296 * pH+1.08935 * T (0C)+2.89856 * M (g/l)+0.55737 * C (ppm) * pH+0.011459* C (ppm)* T (0C)+0.014961* C (ppm)* M (g/l)-0.32111 * pH * T (0C)-0.62783 * pH * M (g/l)-0.037633* T (0C) * M (g/l)-6.93488E-003* C (ppm)2-4.06361 * pH2Table 2- Values of Variables and Experimental Responses in the Response Surface Method.

The F-value and p-value of the proposed model are equal to 5.03 and 0.0027, respectively, reflecting the accuracy of the proposed model. This model with R2 equal to 0.81 shows that the proposed model can well predict the experimental values. The results showed that the factor of initial uranium concentration and pH statistically affect (p-value‹ 0.05) the uranium biosorption process. In contrast, temperature and sorbent dose factor (p-value› 0.05) have no statistically effect on uranium removal by Citrobacter freundii. With increasing uranium concentration from 10 mg/l to 77.5 mg/l, the removal increases from %66.5 to %99/92. Then, with increasing uranium concentration from 77.5 mg/l to 100 mg/l, the removal decreases to %97.34. On the other hand, one of the most important effective parameters in biosorption is the pH of the solution. With increasing the pH from 2 to 5, the removal decreased from %96.82 to %79.01 due to the formation of uranyl complexes (5). In this research, the results indicated that the pre-treated biomass under the conditions suggested by Design Expert software (19.84 g/l of biomass, temperature 28.92 OC, pH 2.89 and initial uranium concentration 53.71 mg/l) is able to remove approximately 99.99 percent of uranium from the contaminated area, which shows valuable potential Citrobacter freundii in bioremediation applications of uranium from contaminated wastewaters.

The safety assessment of Anarak site as the only center for the disposal of radioactive waste is of particular importance in order to maintain human health and the environment. Distribution coefficients of radioactive materials in the soils of the area under study is one of the influential parameters in the safety assessment calculations. Therefore, in this study, the distribution coefficient of cobalt in the alluvial soil of Anarak waste was determined by the batch method and two parameters of concentration and soil to solution ratio were studied. Linear adsorption isotherms, Friendlich and Langmuir were also analyzed to determine the adsorption behavior of cobalt in Anarak soil. The average value of cobalt distribution coefficient in the mentioned soil was calculated equal to 247.18 mL / g. The adsorption behavior of cobalt in Anarak soil followed the Langmuir adsorption isotherm with a positive and significant correlation. The maximum amount of cobalt uptake was determined as 0.029 mg / g soil. The results of the distribution coefficient obtained in this study are lower than the most of the values ​​presented in the other previous researches, which can be related to the soil texture (sandy loam) and the other soil characteristics.

Calculation of distribution coefficients is one of the essential provisions in the safety assessment of radioactive waste repository and safe management of radioactive waste. Due to the importance and characteristics of thorium radionuclide in radioactive waste inventory, the distribution coefficient of thorium in the alluvium soil of Anarak Radioactive Waste Repository was determined by the Batch method two parameters of thorium concentration and soil granulation were studied. Also, the Flow-Through method studied the adsorption behavior of thorium has investigated the effect of thorium concentration and soil height. The average value of thorium distribution coefficient in Anarak soil was calculated 110960 L/kg using the Batch method. The study of adsorption behavior by the Flow-Through method demonstrated high uptake of thorium in the soil due to the strong bond created between the ion and the adsorbent. The results showed that the distribution coefficient increases with the decrease of soil particle size. Regarding the effect of concentration on the thorium distribution coefficient, first, an increasing trend and a decreasing trend were observed in the test range. The results obtained in this study were compared with the results of other studies on thorium radionuclide, which showed a good agreement with other studies.

The separation of thorium and uranium ions in radioactive waste is one of the important and complex processes in the management and storage of radioactive waste in the nuclear industry. One way of removing radioactive materials from nuclear waste is by means of natural adsorbents. In this study, natural zeolites of Firoozkooh and Tabrizhave been prepared and identified with the FT-IR, XRD, BET, and XRF methods. The results showed the Clinoptilolite and Ferrocarpholite structure with an average particle size of 30, 38.7 nanometer, and a specific surface area of 28.51 and 4.78 m2/g for Firoozkooh and Tabriz zeolites, respectively. The effects of different variables such as pH, time of contact between the exchanger and solution, initial concentration of ions and the amount of adsorbent were investigated and optimum conditions for separation of these ions were determined. The maximum adsorption of thorium ions on both adsorbents under optimum experimental conditions was observed at 25 mg/L, pH=4, 240 min. and weight of 0.1 g, 96.93% and 96.77%, and for uranium ion, the maximum adsorption was at 25 mg/L, pH=4 for Firouzkohe zeolite and  pH=5 for Tabriz zeolite, 240 min. contact time, 0.1 g weight, 93.01% and 52.68% respectively by zeolites of Firouzkooh and Tabriz, which increased the mass of zeolite in Tabriz up to 0.3 g, the highest uranium uptake reached 83.65%.

One of the most important safety problems and challenges of the countries having the nuclear technology is to find the methods for the treatment of the radioactive materials in the nuclear wastes. Thorium ion is one of the elements required to manage in the nuclear wastes. In this study, the modified nano-silica adsorbents with Schiff base ligands salicylaldimine propyl triethoxysilane (L1) and pyridylmethyl idenepropyl triethoxysilane (L2) were used for improvement of the thorium ions adsorption. Besides the influence of the used ligand structure, the effects of different variables such as the pH, contact time and adsorbent were investigated, and the optimum conditions were determined. The results showed that the modified adsorbent with ligand L1 provides better performance in this regard.