Keshav Chander

Complexes of lanthanides with trioctylphosphine oxide and tributylphosphine oxide

Abstract Several complexes of lanthanide nitrates, chlorides and thiocyanates with trioctylphosphine oxide and tributylphosphine oxide were prepared by solvent extraction method. An attempt was made to characterize them by IR and thermoanalytical studies. Nitrate groups in these complexes were found to be covalently bonded. These complexes were found to be converted to their corresponding metaphosphates on heating to 1000°C.

Studies on the nature of the reactions and species involved in potentiometric titrimetric determination of uranium.

The species and reactions involved in the determination of uranium by the Davies and Gray method have been investigated through the behaviour of the various species when present alone or in various combinations in the reaction medium. The studies indicate the formation of Fe(II) and V(III) in the titration system. These two species appear easily prone to oxidation by the titration medium. Probable reasons for the negative bias found when the titration is not completed in the stipulated time period, and for the sharpening of the end-point by the presence of vanadium(IV), are discussed.

Alpha-liquid scintillation counting for the determination of plutonium

Liquid scintillation counting is useful and extensively employed for α-activity measurement. However, quenching is observed and erroneous results are obtained when the size of the solution aliquot and its acidity exceed certain limits. A simple procedure has been developed to overcome the quenching effect of volume and acidity on α-counting.

Complexometric determination of thorium in ThO2−PuO2

A method based on the complexometric titration of thorium using ethylene diaminetetra-acetic acid (EDTA) as complexant has been developed for the determination of thorium in thorium-plutonium solution without resorting to prior separation of plutonium. Plutonium in the form of Pu(VI) does not affect the thorium determination when present up to 10% in thorium—plutonium solution. For oxidation of plutonium to Pu(VI), HClO4 or AgO was used. HClO4 is preferred. The thorium values obtained without prior separation of plutonium are compared with those obtained after separating plutonium by anion exchange technique. A precision of ±0.5% has been obtained for 5–10 mg of thorium in the aliquot.

DETERMINATION OF PLUTONIUM AND URANIUM IN THE SAME ALIQUOT BY POTENTIOMETRIC TITRATION

A potentiometric titration method was developed for the determination of plutonium and uranium in the same aliquot in nitric acid medium. Plutonium was first determined by oxidation to Pu/VI/ by fuming with conc. HClO4. Pu/VI/ formed was reduced to Pu/IV/ with known excess of Fe/II/ and the excess Fe/II/ was titrated with standard K2Cr2O7 to a potentiometric end point. Uranium in the same solution was determined by reduction to U/IV/ with Fe/II/ in conc. H3PO4 medium and titrating U/IV/ formed with standard K2Cr2O7 using the potentiometric end point detection technique. For the quantity of plutonium and uranium each in the range of 3–5 mg per aliquot a precision of ±0.2% and ±0.4%, respectively, was obtained.

Stability constants of complexes of plutonium(III) and americium(III) with 5-sulphosalicylic acid

Abstract The stability constants of the complexes formed by plutonium(III) and americium(III) with 5-sulphosalicylic acid were determined by the Bjerrum-Calvin pH titration technique in 1 M NaClO 4 at 25°C. The corresponding values for samarium(III) and europium(III) complexes were obtained under identical conditions for comparison. The values were calculated by a weighted least-squares method (incorporating a correction for the hydrolysis of the metal ion) using a high speed computer. The results show that the 5f electrons influence the stability of the actinide complexes more than the 4f electrons influence the stability of the lanthanide complexes.

Studies on the solubility of Pu(III) oxalate

Studies have been carried out on the solubility of Pu(III) oxalate by precipitation of Pu(III) oxalate from varying concentrations of HNO3/HCl (0.5–2.0M) solutions and also by equilibrating freshly prepared Pu(III) oxalate with solutions containing varying concentrations of HNO3/HCl, oxalic acid and ascorbic acid. Pu(III) solutions in HNO3 and HCl media were prepared by reduction of Pu(IV) with ascorbic acid. 0.01–0.10M ascorbic acid concentration in the aqueous solution was maintained as holding reductant. The solubility of Pu(III) oxalate was found to be a minimum in 0.5M–1M HNO3/HCl solutions containing 0.05M ascorbic acid and 0.2M excess oxalic acid in the supernatant.

Effect of excess AgO and EDTA on the redox titration involved in potentiometric determination of plutonium

Attempts to carry out potentiometric determination of plutonium (by AgO-oxidation method) following the determination of thorium (by complexometric EDTA titration) gave positively biased irreproducible values of plutonium. In order to understand the factors leading to the erroneous values of plutonium, the effect of varying amounts of AgO and EDTA on redox [Fe(II)/K2Cr2O7] titration in the medium consisting of 1M H2SO4 and 0,4M HNO3 was studied. When AgO (up to 200 mg) was added in the titration medium and destroyed by sulfamic acid prior to the redox titration, the dichromate tittre value (amount of standard K2Cr2O7 solution equivalent to 1 g of Fe(II) solution) showed negative bias. The bias was found to decrease with increase in time interval between AgO destruction and the redox titration. The presence of EDTA (up to 15 mg) gave positive bias in the titre value. Results on the titre values obtained under different conditions of the aqueous medium indicated the possibility of formation of unstable Ag(II)-sulfamic acid compled, which is probably responsible for the irreproducible values of plutonium.

A titrimetric method for the sequential determination of thorium and plutonium

A method for the sequential determination of thorium and plutonium has been developed. In the sample solution containing thorium and plutonium, thorium is first determined by complexometric titration with EDTA and then in the same solution plutonium is determined by redox titration employing potentiometry. Prior to the determination of plutonium, EDTA is destroyed by fuming with concentrated HClO4. Thorium is determined at 10 mg level and plutonium at 1 mg level with precision and accuracy of better than ±0.5%.

Effect of plutonium on the potentiometric determination of uranium

Effect of the presence of plutonium on the determination of uranium by potentiometric method has been studied. The presence of large quantities of plutonium does not appear to affect the determination of uranium present at 5 mg as well as 250 mg levels.