INVESTIGATION OF URANIUM ADSORPTION BY USING COCONUT SHELL
Mahmoud A. A. ASLANI, Sema AKYIL, Şule AYTAS, Meral ERAL Ege University, Institute o f Nuclear Sciences, 35100, Bornova, Izmir -TURKEY
ABSTRACT
At the present study, we investigated the basic features of uranium uptake from dilute aqueous solution by using coconut shell and the effect of uranium on this adsorption phenomena. It has also been shown that the adsorption of uranium was affected with some factors such as pH, uranium concentration, and contact time.
INTRUDUCTION
Adsorption is an effective and convenient technique in the separation and isolation of elements. The greatest advantage of adsorption is the possibility to separate of small amounts of substances from a very large volume of solution. The accumulation of heavy metals, radionuclides and the sorption of uranium and thorium for recover or removal from aqueous systems using various micro-organisms and biological substances have been investigated by some workers. The uranium adsorbing abilities of various biopigments, microalgae and chitin, a most abundant organic resource, and its derivatives have been also studied by numerous scientists.1"4 In recent years, the use of biomaterials in the sorption process as adsorbents for the removal of heavy metals from polluted/waste water has come to the forefront. Biomaterials have been found to be useful and popular due to their low costs, and high efficiencies. Knowledge of the adsorptive properties of bio-materials has become of considerable importance in many fields.
EXPERIMENTAL Material and method
The imported Coconut was supplied from bazaar. After stripping the shell fraction, it was grounded and passed through a 0.250 mm sieve and homogenized to treatment.
All of the chemicals used were the analytical reagent (AR) grade. The pH of the solutions was adjusted using NaHC03 and H N03 solutions. A stock solution of uranium (VI) ion was prepared by dissolving of U0 2(N03)2 6H2O (Merck) in a few drops of concentrated HNO3 and diluted with deionized water.
Dibenzoylmethane (~k=395 nm in ethyl acetate, £=2.Ox 10^ L.m ol'l.cm 'l) method was applied for the determination of the uranyl ion concentration in aqueous solution.5 The optical density of the solution was measured by using Shimadzu UV-VIS 260 Model Recording
Spectrophotometer.
Determination o f uranium uptake capacity
0.125 g of the adsorbent and 0.01 M UO22+ aqueous solution were shaken at 30°C for 24 hours by batch technique. The uptake capacity of this adsorbent was determined by salicylic acid method.6 The amount of uranyl ion uptake (i.e. mmol UO22+/g of adsorbent) is calculated from the differences of the uranyl ion concentration in substrate before and after uptake. Uranyl ion uptake capacity of the adsorbent was found to be 0.392 mmol/g adsorbent.
Uptake experiments
The coconut shell (0.01 g) were suspended in 25 mL of solution at selected pH. The mixture was shaken at 25±2°C. The adsorbent was removed by filtration through a Whatman No. 42 filter paper. Amount of uranium taken up by the adsorbent was determined from the difference between the initial ([U+6]) and final ([U+6]f) concentrations of uranium in aqueous solution and calculated as uptake yield (%);
Uptake (%) =
RESULTS AND DISCUSSION
The uptake of uranium by the coconut shell was fairly rapid within the 30 minutes following the addition of uranium. The analysis of some factors effecting uranium uptake such as pH, initial uranium concentration, time and thorium concentrations are necessary for understanding the removal of uranium from aqueous system.
The effect of pH on the uptake of uranium was studied in varying range from pH 2 to pH 8 at 25°C. Below and above pH 5, the uptake of uranium fell off rapidly. As a result it was observed that the uptake yield increases reaching a maximum of 68.92%. For these reason pH 5 was
selected for further studies.
The uranium uptake on adsorbent as a function of varying uranium concentration from 10 pg/mL to 125 pg/mL was studied at 25°C while keeping constant to 25 mL of volume. It was observed that the percentage of the adsorbed UO22+ complex increases from 37.80% to 81.26% with increasing uranium concentration of the aqueous solutions from 10pg/mL to 50pg/mL. The yield of adsorption was slightly decreased after 50pg/mL UO22+ concentration and then remained constant.
The uptake of uranium on coconut shell at different time intervals (30-360 minutes) was studied at 50pg/mL uranyl ion concentration while keeping all other parameters constant. The equilibrium sorption of coconut shell was reached within a period of 30 minutes and the yield of uranium sorption is 95.25%.
From the obtained results, it is evident that the coconut shell has the ability to accumulate of uranium from aqueous solution.
[U+6], - [U +6]f
[U+6]i
x100 (1)
Acknowledgement
The authors are grateful to Ege University Research Foundation.
REFERENCES
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2. T. Sakaguchi, T. Horikoshi and A. Nakajima, J. Ferment. Technol. 56 (6) (1978) 561.
3. T. Sakaguchi, T. Horikoshi and A. Nakajima, Agric. Biol. Chem. 45 (10) (1989) 2191.
4. M. A. A. Aslani, and M. Eral, Investigation o f Uranium Recovery from Dilute Aqueous Solutions Using Silk Fibroin, J. Bio. Trace Ele. Res., 43-45, 737-743p, 1994.
5. J. Korkish, Modern Methods fo r the Seperation o f Rare Metal Ions, Pergamon Press, Oxford, 574-587, 1974.
6. Kabay, N.; Egawa, H., Sep . Sci. Tech., 28, 1985, 1993.
