Seyyed Hossein Hosseini; Ahmad Hosseini; Ahmad Allah abadi; Abolfazl Rahmani sani; Zakiyeh Mojarrad
Volume 22, Issue 5 , November and December 2015, , Pages 879-892
Abstract
Background & Objectives: Despite the great importance of determination of radioactive elements in the environmental samples, most of analytical instruments have not the necessary sensivity for this purpose. Pre-concentration and separation of elements from the sample matrixes is the best and often ...
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Background & Objectives: Despite the great importance of determination of radioactive elements in the environmental samples, most of analytical instruments have not the necessary sensivity for this purpose. Pre-concentration and separation of elements from the sample matrixes is the best and often the only practical method for solving this problem and the purpose of the present research is solidphase extraction of uranium and thorium, using a selective and suitable sorbent, and precise determination of their ultra-trace concentrations in the environmental samples.
Materials & Methods: In this experimental study, Amberlite XAD-7 resin was impregnated with Clayton yellow and used for pre-concentration and determination of uranium and thorium in the environmental samples and, after investigating the optimum conditions of pH and ionic strength and studding equilibrium aspects of sorption process, determination of uranium and thorium was performed, using arsenazo III procedure, after their pre-concentration by the column method. In the column method, some variables such as sample flow rate, eluent type, eluent concentration, elution rate, eluent volume and tolerable concentration of interference ions were also optimized precisely.
Results: Optimization of pH and ionic strength showed that uranium and thorium can be simultaneously sorbed at pH 5. The equilibrium data obtained from the sorption experiments were adjusted to the Langmuir isotherm model (R2=0.9999)better than Freundlich (R2≤0.8979) and Tempkin (R2≤0.9705) models and the calculated maximum sorption capacities in terms of monolayer sorption were 0.609 and 0.571 mmol g-1 for uranium and thorium, respectively. The flow rates in both sorption and elution processes was desirable.The studies showed that, after simultaneous adsorption, the analyte ions can be separated by sequential elution with 0.5% (w/v) Na2CO3 for uranium and 2.0 mol L-1 HCl for thorium. The limits of detection for U(VI) and Th(IV) were as low as 50 and 25ng L-1, respectively. Relative standard deviations (RSDs, n=7) for U(VI) and Th(IV) were 3.1% and 2.9%, respectively. The interference effects of foreign ions on the retention of the analyte ions were ignorable. The method was successfully applied to determination of ultra trace amounts of U(VI) and Th(IV) in different real matrices including industrial wastewater samples and environmental waters.
Conclusion: According to the obtained results, it is proposed that CY/XAD-7is very desirable for pre-concentration and determination of ultra-trace amounts of U(VI) and Th(IV) in the environmental samples.