B. Maiti

Separation and preconcentration of U(VI) on XAD-4 modified with 8-hydroxy quinoline

Amberlite XAD-4 adsorber resin was modified with 8-hydroxy quinoline (Oxine) by equilibrating with methanol solution of the reagent and the modified resin was used as a support material for the solid phase extraction and preconcentration of UO(2)(2+) from aqueous solution at pH between 4 and 5.5. Ten micrograms of uranium from 300 ml of aqueous phase could be quantitatively extracted in to 1g of the modified resin giving an enrichment of 200. Uranium collected in the column could be eluted out with methanol-HCl mixture and determined spectrophotometrically using arsenazo(III) as the chromogenic reagent. The preconcentration could be made selective to uranium by using EDTA as a masking agent for transition metal ions and Th(IV).

Determination of iodate and sulphate in iodized common salt by ion chromatography with conductivity detection

A simple, rapid and accurate method for the determination of iodate in iodized common salts has been developed. The quantitative determination of iodate was accomplished by anion exchange chromatography with conductimetric detection. The method requires a sample pretreatment for the removal of large excess of chloride from the sample matrix. Onguard silver cartridges were found most suitable for this purpose. The sulphate content in the salt was simultaneously determined. The lower limits for the determination of iodate and sulphate in solution are 0.5 and 0.05 mug ml(-1), respectively. Quantitative recovery of the anions in synthetic samples has been obtained and the interferences from different cations and anions have been studied. The method has been successfully applied to the determination of iodate and sulphate in the commercially available salts. The concentrations of iodate measured by this method are in good agreement with those claimed by the manufacturer.

Transport of uranyl ion across a bulk liquid membrane using calixarene and synergistic agents as carriers

Transport of uranyl ion across a bulk liquid membrane using chloroform solutions of calixarenes (as carriers) has been studied. Various factors that affect the transport have been optimised in order to obtain maximum transport. It has been observed that the use of tri-n-octyl phosphine oxide (TOPO) as a synergistic reagent showed a marked enhancement of transport of uranyl ion. Crown ether 18 Crown 6 (18C6) also exhibited synergistic behaviour when used in combination with calixarenes. The use of these synergistic reagents resulted in high transport of uranyl ion with 0.1 M nitric acid as the receiving solution. The interference from different transition metal ions was found to be negligible. The serious interference from Th(IV) could be minimised by using EDTA as masking agent. A possible application of this carrier system and transport process to the pre concentration and recovery of uranium from seawater has also been examined.

Permeation of inorganic anions through Nafion ionomer membrane

Permeation of different inorganic anions, namely, F−, Cl−, Br−, NO2−, NO3− and SO42− through NafionTM 117 ionomer membrane has been studied as a function of pH and salt concentrations in feed solution. At low pH, fluoride and nitrite ions showed higher permeation than other anions. This has been attributed to a higher association of HF and HNO2 in the membrane phase. Easy diffusion of the undissociated acids and their subsequent permeation has been explained on the basis of the morphology of the ionomer. The lowering of anion transport in the presence of different cations has been attributed to the complex formation of the anions with these cations.

Selective permeation of Cu2+ and UO22+ through a Nafion ionomer membrane

Abstract The selective permeation of Cu 2+ and UO 2 2+ in the presence of common cations through a Nafion 117 ionomer membrane have been studied. EDTA served as a receiving agent for an effective permeation of Cu 2+ , whereas the same has been used as masking agent for Fe 3+ , Cu 2+ , Ni 2+ and Zn 2+ during the selective permeation of UO 2 2+ using Na 2 CO 3 or Tiron as a receiving solution. Selective permeation of Cu 2+ from a mixture of Fe 3+ and Cu 2+ after masking Fe 3+ with F − , SCN − and PO 4 3− was studied in detail. A lowering of permselectivity and the permeation of anions has been attributed to the simultaneous permeation of Fe 3+ through metal speciation.

SELECTIVE AND UPHILL TRANSPORT OF URANYL ION IN THE PRESENCE OF SOME BASE METALS AND THORIUM ACROSS BULK LIQUID MEMBRANE BY DI (2-ETHYLHEXYL) PHOSPHORIC ACID

Di (2-ethylhexyl) phosphoric acid has been successfully used as a selective carrier for the transport of uranyl ion across a bulk liquid membrane of chloroform. More than 98% uranium is selectively transported from a binary or a multi component mixture of cations in less than 3 hr. The pH of the feed solution was kept between 4.0 and 5.0 while 0.1 M hydrochloric acid served as a stripping agent in the receiving compartment. The co-transport of Zn2+ and Fe3+ was significantly small (<4%) but that of thorium was very high. However, the interference from Th(IV) and transition metal ions could be eliminated by the addition of EDTA (E. Merck (India) Ltd., Mumbai) to the feed solution. Different experimental parameters affecting the transport process were optimized and the membrane separation method was applied to the recovery and pre-concentration of uranium from synthetic seawater sample. It was concluded that approximately 98% of uranium could be recovered and a hundred fold pre-concentration of the metal could be accomplished in less than 3 hr.

FACILITATED TRANSPORT OF Th(IV) ACROSS BULK LIQUID MEMBRANE BY DI(2-ETHYLHEXYL)PHOSPHORIC ACID

Di(2-ethylhexyl) phosphoric acid (DEHPA) has been successfully used as a carrier for the selective and efficient transport of Th(IV) across a bulk liquid membrane (BLM) of chloroform. The feed comprised of a solution of pure Th(IV) or a binary mixture of Th(IV) and a cation, such as Na+, K+, Ca2+, Mg2+, Cu2+, Pb2+, La3+, Fe3+, or UO2+ 2, in water maintained at pH 2, while 0.1 mol/L hydrochloric acid served as a stripping agent in the receiving compartment of the permeation cell. Greater than 99% of Th4+ selectively permeated across the membrane in less than 3 h, while the transport of other cations present along with thorium was less than 3% during the same time. Selectivity of the transport of thorium was greatly affected by the presence of Fe3+ and UO2+ 2 in the feed solution. Fe3+ could be effectively masked by the addition of SCN− or citric acid to the feed solution but the cotransport of UO2+ 2 could only be partially reduced by the addition of carbonate or thiocyanate to the feed solution.

Determination of boron by flow injection analysis using a conductivity detector

A flow injection method for the determination of boron using a conductivity detector has been described. Boric acid injected into the flow system reacts with mannitol (0.3 M) in the mobile phase and an equivalent amount of H(+) is liberated in the stream. The increase in the conductance of the mobile phase due to the liberated H(+) has been equated to the boron concentration in the sample. A linear calibration for light- and heavy-water samples containing 0-20 μg/mL boron was obtained. Boron concentrations in the samples of light and heavy water and lithium pentaborate solution have been measured. The interferences due to various ions such as Na(+), Li(+), Cu(2+), Ni(2+), Co(2+), Fe(3+), Al(3+), SO(4)(2-), NO(3)(-), F(-), and Cl(-) could be eliminated by adopting a two-step sample pretreatment procedure. In the first step, all the anions were converted to Cl(-) by treating the sample solution with a strong anion-exchange resin. In the second step, the solution obtained from the first step was passed through a silver-guard cartridge to remove interfering cations and Cl(-). The relative standard deviation was ±0.25% for the determination of 1 μg of boron in light water, and the limit of detection was 0.01 μg present in an injection volume of 100 μL. The corresponding values for heavy water were ±0.38% and 0.1 μg, respectively.

Crown Ethers as Carriers for the Transport of Anionic Thiocyanate Complex of Uranyl Ion Across a Bulk Liquid Membrane

Transport of UO2+ 2 as its anionic thiocyanate complex [UO2(SCN)4]2− across a bulk liquid membrane using 18 Crown 6 (18C6) and Dibenzo 18 Crown 6 (DB18C6) as carriers in the membrane phase has been studied. The anionic complex is formed by the addition of KSCN to the feed solution at a pH of 1. A dilute acid (pH = 5) served as the stripping agent in the receiving compartment. The interference from Th(IV) and a few other cations could be eliminated by using EDTA as a masking agent in the feed solution. Various factors influencing the transport process have been studied and an uphill transport (>89%) of UO2+ 2 from the feed solution could be accomplished under optimum conditions.

Facilitated Transport of Alkali Metal Ions Across Bulk Liquid Membrane Containing Phenoxy Compounds as Carrier

The carrier activity of several phenoxy ethers toward the facilitated transport of alkali metal ions through a chloroform bulk liquid membrane has been studied. A brief description of the synthesis of carrier compounds has been given, and the mechanism of transport process has been discussed. The organic carriers are protonated on the receiving side of a permeation cell, and the protons are exchanged with the metal ions at the membrane interphase of the feed side. Protonation of carriers has been confirmed from electronic spectral studies. A high degree of selectivity for Na+ transport has been observed when 1,2-bis-(2-acetyl phenoxy) ethane is used as carrier whereas dibenzo-[a,e]-3,4-dihydroxy-3,4-dimethyl-7,10-dioxocyclodeca-1,5-dione facilitated selective transport of K+.