Separation and Preconcentration of Trace Uranium(VI) by Solid Phase Extraction with 2,3-Dihydroxynaphthalene and Cetyltrimethylammonium Bromide on Molten Naphthalene and Its LED Fluorimetric Determination in Water Samples

A simple and rapid solid phase extraction (SPE) procedure has been developed for the extraction and determination of uranium in water samples. The method is based upon the adsorption of uranium(VI)-2,3-dihydroxynaphthalene complex on microcrystalline naphthalene at the pH range 10 - 12 in the presence of a counter cation cetyltrimethylammonium ion. The solid mass consisting of uranium-2,3-dihydroxynaphthalene-CTA complex and naphthalene is ignited in the furnace at a temperature of 700°C for 1 h and then digested in dil. HNO3 solution. Uranium is then determined by LED fluorimetry using fluorescence enhancing pyrophosphate buffer. The effects of different variables like pH of the solution, reagent concentrations, counter cations, stirring time, interfering ions etc. have been investigated thoroughly for the quantitative recovery of uranium. The accuracy of the developed method has been ascertained by standard addition method as well as conventional pellet fluorimetry method involving co-precipitation of uranium using aluminum phosphate as a carrier.

Removal of uranyl ions in aquatic mediums by using a new material: gallocyanine grafted hydrogel

A new material containing gallocyanine (GC) grafted polyacyril amide (PAA) was synthesized and its adsorption ability was examined for the removal of uranyl ions from aqueous media. The new developed adsorbent was characterized by FTIR, SEM, and PZC analysis. Adsorption of UO₂(2+) ions from aqueous solution as a function of ion concentration, pH, ionic strength, temperature, and reusability of adsorbent was investigated in detail. The adsorption data were analyzed by using the Langmuir, Freundlich and Dubinin-Radushkevich (DR) models. The adsorption of UO₂(2+) increased with pH and reached a plateau value in the pH range 5-6. The adsorption of UO₂(2+) ions were not affected by increasing ionic strength. The adsorption mechanism followed an endothermic and spontaneous process with increased disorderliness at adsorbate/adsorbent interface. The adsorption process followed a pseudo-second-order kinetics. The new developed material is a potential adsorbent for effective removal of uranyl ions from aquatic solutions.

Flow injection online spectrophotometric determination of uranium after preconcentration on XAD-4 resin impregnated with nalidixic acid

In this work, spectrophotometer was used as a detector for the determination of uranium from water, biological, and ore samples with a flow injection system coupled with solid phase extraction. In order to promote the online preconcentration of uranium, a minicolumn packed with XAD-4 resin impregnated with nalidixic acid was utilized. The system operation was based on U(VI) ion retention at pH 6 in the minicolumn at flow rate of 15.2 mL min(-1). The uranium complex was removed from the resin by 0.1 mol dm(-3) HCl at flow rate of 3.2 mL min(-1) and was mixed with arsenazo III solution (0.05 % solution in 0.1 mol dm(-3) HCl, 3.2 mL min(-1)) and driven to flow through cell of spectrophotometer where its absorbance was measured at 651 nm. The influence of chemical (pH and HCl (as eluent and reagent medium) concentration) and flow (sample and eluent flow rate and preconcentration time) parameters that could affect the performance of the system as well as the possible interferents was investigated. At the optimum conditions for 60 s preconcentration time (15.2 mL of sample volume), the method presented a detection limit of 1.1 μg L(-1), a relative standard deviation (RSD) of 0.8 % at 100 μg L(-1), enrichment factor of 30, and a sample throughput of 42 h(-1), whereas for 300 s of the preconcentration time (76 mL of sample volume), a detection limit of 0.22 μg L(-1), a RSD of 1.32 % at 10 μg L(-1), enrichment factor of 150, and a sampling frequency of 11 h(-1) were reported.

Spectrophotometric determination of uranium with arsenazo-III in perchloric acid

A short, sensitive and reliable spectrophotometric method, which has advantages over all known "wet chemistry" methods for uranium determination with regard to tolerance to common interferences, has been developed for the determination of uranium. Selectivity, molar absorptivity and the determination range of uranium have been enhanced by using 0.07% arsenazo-III as a chromogenic reagent. The use of 3 mol dm(-3) perchloric acid as a medium of determination was found to be excellent in terms of good solvent compatibility on dilution, destruction of organic contamination and simplicity of operation. The uranium-arsenazo-III complex formed instantly, and was found to be stable for more than 3 weeks with constant absorbance. Beer's law was obeyed up to a uranium concentration of 16 microg g(-1), with a molar absorptivity at 651 nm of 1.45x10(5) mol(-1) dm(3) cm(-1) at 24+/-2 degrees C. Only phosphate and citrate at 70-fold excess over uranium interfere seriously, whereas other anions studied could be tolerated up to a 70-fold excess over uranium. Of the cations studied, only Mn(II), Co(II), Ni(II), Cu(II) and Cr(III) decreased the normal absorbance of the complex. Iron(III), Ce(III) and Y(III) enhanced the absorbance. Other cations studied did not affect the absorbance up to a 50-fold excess. The accuracy was checked by determining uranium from standard solutions in the range 10-50 microg g(-1). It was found to be accurate with a 96.0-98.6% recovery rate. The method has been successfully applied to standard reference materials and ore samples at microg g(-1) levels.