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URANIUM(VI) ADSORPTION FROM AQUEOUS SOLUTION ONTO VOLCANIC CLINKER

URANIUM(VI) ADSORPTION FROM AQUEOUS SOLUTION ONTO VOLCANIC CLINKER HİÇSÖNMEZ, Ü. 1 , ERAL, M. 2 , KAYNAR, Ü. 3 AYCAN, Ş. 4. 1 Celal Bayar University, Faculty of Sciences-Arts, Chemistry Department, MANISA-TURKEY 2 Ege University, Enstitute of Nuclear Science, IZMIR-TURKEY

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URANIUM(VI) ADSORPTION FROM AQUEOUS SOLUTION ONTO VOLCANIC CLINKER

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  1. URANIUM(VI) ADSORPTION FROM AQUEOUS SOLUTION ONTO VOLCANIC CLINKER HİÇSÖNMEZ, Ü.1, ERAL, M.2, KAYNAR, Ü.3 AYCAN, Ş.4 1 Celal Bayar University, Faculty ofSciences-Arts, Chemistry Department, MANISA-TURKEY 2 Ege University, Enstitute of Nuclear Science, IZMIR-TURKEY 3 Celal Bayar University,Faculty of Education, Demirci, MANISA-TURKEY 4 Mugla University, Faculty of Education MUGLA-TURKEY

  2. Uranium is a toxic heavy metal arising from the nuclear industry. Various techniques are employed for the removal of uranium from wastewaters and radioactive wastes. Adsorption is one of the techniques, which is comparatively more useful and economical in waste water treatment.Various substances, such as silk fibroin (Aslani et al., 1998), zeolite (Erdem et al., 2004), active carbon (Mellah et al., 2006), zeolitic tuff (Krestou etal., 2003), PAN/Zeolite (Kaygun and Akyıl, 2007), Na-Kanemite (Guerra et al., 2008), have been investigated as adsorbents for the removal radioactive elements from radioactive and industrial wastes.

  3. The aim of this work is to study the possibility of the useful of volcanic clinker for adsorption of uranium(VI) from aqueous solution. It was investigated under various experimental conditions particle size pH initial concentration contact time temperature

  4. MATERIAL and METHODS The volcanic clinker used as adsorbent for uranium adsorption was taken from around Demirköprü Dam (Kula-Manisa) which is a volcanic region in the West Anatolia Region of Turkey. Kula which has a number of interesting volcanological aspects, is a small town on Izmir-Ankara highway (Fig. 1).

  5. Fig. 1. a) Location of study area b) Generalized geological map of the Kula area(Tokçaer et al., 2005)

  6. The volcanism in Kula is associated with an extensional regime in western Anatolia that was developed during Late Miocene-Piocene. This volcanic field provides a good example ofQuaternary alkaline volcanism andis the youngest volcanics of western Anatolia (Alıcı et al., 2002).

  7. The Kula volcanics are alkaline and dominantly sodic in character. Chemically, they contain SiO2 in the range of 45.6 and 50.8%), and have higher Al2O3 (>20%) and K2O (>3%) contents (Tokçaer et al., 2005). Table 1. Chemical Analyses of the Natural Kula Volcanics (Alıcı et al., 2002).

  8. These samples were crushed and sieved through the mesh screens • (100, 200 and 400 mesh). • The pH of volcanic clinker was measured with the AOAC Official Method 994.16. • Stoc solution: (UO2(NO3)2.6H2O) (2000 mg/L) • the Arsenazo III spectrophotometric (Jasco V-530 model UV-VIS spectrophotometer) method (Leib, 1984) • Experiments were carried out in Erlenmeyer flasks. • The clinker samples were mixed with 10 mL uranyl solutions • by a magnetic stirrer at room temperature. • After stirring for 1 h, the mixture was filtered. • The uranium uptake was calculated according to Eq. (1); • Adsorption (%)= [(mo-ms) / mo]x100 (1) • mo is the amount of the uranium in the initial (mg) and • msis the amount of the uranium in the final solutions (mg)

  9. RESULTS AND DISCUSSION The pH was found as 7.18-7.35. As it was seen it is an alkaline basic . The cation exchange capacity (CEC) determination for this material was performed by the Metylene Blue (Rytwo et al., 1991) and titrimetric method (Cunniff, 1999). The mean CEC value was found as 5 meq/100 g. Its CEC value is lower than other natural materials (Data Handbook for Clay, 1979). The results of the first experiments showed that uranium adsorption is low onto volcanic clinker. The samples were activatedfor two different temperatures (600 and 800 °C) for 2 hours according to the references (Koçak and Aycan, 2000; Kaynar and Aycan 2000),.

  10. Parameters; Effect of particle size The particle size effect was examined for untreated and treated samples. Fig 2. Effect of particle size on uranium adsorption onto volcanic clinker (adsorbent amount= 0.1 g, CU= 40 mg/L, pH= 3.83, contact time 1 h, temperature 25 °C).

  11. Effect of pH The effect of pH on uranium adsorption was studied over the pH range 2-8. As shown in Fig. 3., adsorption strongly depended on variations of the pH. Fig 3. Effect of pH on uranium adsorption onto volcanic clinker (adsorbent amount= 0.1 g, CU= 40 mg/L, contact time 1 h, temperature 25 °C).

  12. This case may be explained by influences of both the chemistry of uranium in aqueous solution and surface of structure clinker. In the our study, it was found that the pH of the solution increases after adsorption process. The initial and final pH values after adsorption is shown in Fig. 4. Fig. 4. Initial and final solution pH for volcanic clinker.

  13. The oxo groups present on the surface react with the water molecule as follow (Mor et al., 2007); MxO + 2H2O → MxOH22+ + OH- Thus, hydroxyl ions released into solution raise the equilibrium pH. In high acidic solutions (pH< 3), the volcanic clinker was ineffective for the adsorption of uranium. The broken Si0 bonds and Al-OH bonds along the surfaces of the clay crystals results in hydrolysis (Tahir and Rauf, 2006). At low pH the reaction might be; SiOH + H+→ SiOH2+ The surface is protonated and uptake of uranium is reduced.

  14. After, adsorption increases with increasing pH. Because U (VI) exists as UO22+ in acid region, ion-exchange occurs between it and water molecules on surface of adsorbent (Parab et al., 2005). Maximum uraniumyields were obtained at pH 3 fortreated samples, while for the untreated onesit was pH 4. At higher pH values, uranium hydrolysis products occur (UO2(OH)+, (UO2)2(OH)22+, (UO2)3(OH)52+) (Psareva et al., 2005; Woayang et al., 2007). Therefore, adsorption slightly is decreasing both for untreated and treated at 800 °C clinker. Treated at 600 °C sample presents a different status. Increasing adsorption yield at pH 5 treated at 600 °C was also thought to change in structure by activation. Weller and Peri (1965) reported that water molecules dissociatively adsorb onto aluminium oxide.

  15. Kawasaki and co-workers (2008) have been reported that the specific surface area reached a maximum at the calcination temperature of 400 °C, and then decreased as the calcination temperature rose for aluminum oxide. The concentration of surface hydroxyl groups was the highest when the calcination temperature was 400 °C and above 400 °C it decreased with increasing calcination temperature. Because of excess surface hydroxyl groups, the clinker surface can exist as negative according to following reaction (Tahir and Rauf, 2006); At high pH the reaction is: SiOH + OH-→ SiO- + H2O We suggested thathydrolysis products of uranium attributed this negative sites.

  16. Above the pH 6.0, uranium occurs in the solution only in the form of carbonate-complex ions that are highly negative charged. Therefore, adsorption is decreasing. All further experiments were performed with treated at 600 °C clinker showing high adsorption at pH=5 since it realizes nearly in neutral media. Effect of initial concentration The effect of uranium concentration was studied by using different uranium solutionsvarying from 10 mg/L to 140 mg/L. The results are shown in Fig.5.

  17. Fig. 5. Effect of the uranium concentration on adsorption onto volcanic clinker (activation 600 °C and 100 mesh adsorbent amount= 0.1 g, initial pH= 5.00±05, contact time 1 h, temperature 25 °C). • The adsorption percentage of U increases with increasing uranium concentration • up to 60 mg/L and then starts to decrease. • The maximum adsorption is between 40 and 60 mg/L

  18. Effect of contact time The adsorption tests were done at different contact times. The experimental results are indicated in Figure 6. Fig. 6. Effect of the contact time on uranium adsorption onto volcanic clinker (activation 600 °C and 100 mesh adsorbent amount= 0.1 g, CU= 60 mg/L, initial pH= 5.00±05, temperature 25 °C). • It was seen that adsorption kinetic is quite fast • At 30 min contact time was chosen as the optimum contact time

  19. Effect of temperature Fig. 7. Effect of temperature on uranium adsorption onto volcanic clinker (activation 600 °C and 100 mesh adsorbent amount= 0.1 g, CU= 60 mg/L,initial pH= 5.00±0.05, contact time= 30 mim). It is seen that the adsorption decreases with increasing temperature. The adsorption of uranium is favored at low temperatures.

  20. The distribution coefficients (Kd) were calculated by: Kd = (Co – Ce)/ Ce (V/m) Co is the initial concentration of uranium in the solution mg/L Ce equilibrium concentration of uranium in the solution mg/L V is the solution volume (mL) and m is the mass of adsorbent (g).

  21. Adsorption entalpy was measured using the method based on the Van’t Hoff plot. The values of ∆H° and ∆S° was calculated from the slopes andintercept of the lineer variation of lnKd with reciprocal temperature, 1/T, Fig.8. Fig. 8. The Van’t Hoff plots for the adsorption of uranium onto volcanic clinker

  22. Table 2. Thermodynamic Parameters for Uranium Adsorption onto Volcanic Clinker lnKd = ∆S° / R - ∆H° / RT ∆G° = ∆H° - T ∆S°

  23. SEM images Fig. 9. a) SEM image before adsorption (treated 600 clinker) b) SEM image after adsorption (treated 600 clinker)

  24. Fig. 10. a) SEM b) EDX analyses after adsorption(treated 600 clinker)

  25. CONCLUSION • Particule size and activation temperature greatly affected uranium adsorption. • The pH is the most important factor for U adsorption onto volcanic clinker. • It is seen that useful of untreated clinker was unsuitable for uranium adsorption at all pH values. • Maximum adsorption was provided at low temperature. • Amount of adsorbent : 0.1 gram • Particule size : 100 mesh • Activation temperature : 600 °C • Solution of pH : 5 • U concentration : 60 ppm (10mL solution) • Contact time : 30 minutes • Temperature : 20 °C • Adsorption yield of uranium was determined to be as 80.69±4.61 % • Various thermodynamic parameters, such as ∆H°, ∆S°, and ∆G°, • were calculatedfrom theexperimental data • The thermodynamic data indicate exothermicand spontaneous nature of the process

  26. This study is still being carried out for further experiments ; • To see changes in the structure, to make X-Ray diffraction analyses. • To measure the specific surface area and pore volume of samples. • This study is funded by the Research Fund of Celal Bayar University (Project numbers: FEF 2005-067). • Also we would like to thank the Turkish Çekmece Nuclear Research and Traninig Center for SEM images. THANKS FORYOUR ATTENTIONS

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