Rakesh Verma

Application of poly(aniline) as an ion exchanger for the separation of palladium, iridium, platinum and gold prior to their determination by neutron activation analysis

The distribution coefficients of PdIII, IrIV and AuIII on poly (aniline) in 0.1–10 mol l–1 HCI were determined. They are strongly adsorbed at low acidities and the extent of adsorption decreases with increase in acidity, except for AuIII. Palladium, Pt and Au are quantitatively eluted with 5% thiourea in 0.05 mol l–1 HCI whereas the recovery of lr is >90% with 1% ascorbic acid followed by 10 mol l–1 HCl. It was found that Cr, Fe, Co, Ni, Zn, Ga and Ge are not retained on poly(aniline) at low acidities. This separation procedure was applied prior to the determination of Pd, lr, Pt and Au in iron meteorite and PCC-1 standard rock by neutron activation analysis.

SORPTION OF PLATINUM, PALLADIUM, IRIDIUM, AND GOLD COMPLEXES ON POLYANILINE

ABSTRACT Sorption of Pt, Pd, Ir and Au on polyaniline, synthesised by chemical oxidation of aniline in HC1, from HC1, LiC1 and H2SO4 solutions in the concentration range 0.1 to 10 mol dm-3 has been studied. The as-prepared polyaniline (acid-PANI) and the one treated with 1 mol dm-3 NH4OH (base-PANl) have been used. Analysis of the data indicate that the AuC14 − species and negatively charged chloro-complexes of Pt and Pd are involved in the sorption process from HC1 solutions. Sorption of metal species from H2SO4 solutions is higher than that from HC1 solutions and negatively charged sulphate complexes of Pt and Pd are involved in the sorption

Sorption of As(III) and As(V) on chemically synthesized manganese dioxide

Sorption of As(III) and As(V) on manganese dioxide was studied by batch equilibration method using 76As radioactive tracer. Manganese dioxide was prepared by two different methods viz. reacting (a) KMnO4 solution with MnSO4 solution, and (b) KMnO4 solution with concentrated hydrochloric acid. Manganese dioxide was characterized by zeta potential measurement, surface area measurement, thermogravimetry (TG), differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Point of zero charge (PZC) for manganese dioxide was between pH 3 and 4. Radioactive tracer (76As) was prepared by neutron irradiation of arsenious oxide in self serve facility of CIRUS reactor followed by conversion to As(III) and As(V), by appropriate chemical methods. Sorption of As(III) and As(V) were studied separately, between pH 1 to 11, using (i) freshly prepared, (ii) air-dried and (iii) aged manganese dioxide. Sorption of As(III) and As(V) on freshly prepared as well as aged manganese dioxide, from both the methods was greater than 98% between pH 1 to 9 and decreased above pH 9. Percentage sorption was comparable for manganese dioxide prepared by both the methods in different batches. Sorption capacity was ∼2 mg g−1 for both As(III) and As(V). Arsenic was desorbed from the manganese dioxide by 0.1 M sodium hydroxide and oxidation state of desorbed arsenic was determined by solvent extraction method. It was found that the desorbed arsenic was present in As(V) oxidation state, independent of the initial oxidation states. This simple and direct chemical evidence, establishing that As(III) is converted to As(V) by manganese dioxide, is reported for the first time. Sorption of As(III) and As(V) on manganese dioxide did not cause an increase in manganese concentration above solubility limit confirming that Mn2+, formed during oxidation of As(III) to As(V), was re-adsorbed.

Studies on the Separation and Recovery of Thorium from Nitric Acid Medium using (2-ethyl hexyl) Phosphonic Acid, Mono (2-ethyl hexyl) Ester (PC88A)/N-Dodecane as Extractant System

This paper deals with the studies on the separation and recovery of thorium and 233-uranium from nitric acid medium using (2-ethyl hexyl) phosphonic acid, mono (2-ethyl hexyl) ester/n-dodecane as an extractant system. The different extraction parameters were investigated. The distribution ratio of thorium decreased with increase in nitric acid concentration. The optimum solvent concentration for quantitative separation of thorium from aqueous feed solution was 0.75 M of PC88A whereas dodecane was the most suitable of diluents with an organic to aqueous phase ratio of 1:1. Among the various strippants used, 2 M solution of (NH4)2CO3 was found to be the most suitable for back extraction of thorium. The developed method was used to recover thorium and 233U from radioanalytical waste generated during thorium analysis by ethylene diamine tetraacetic acid (EDTA) titremtric method and recoveries for both Th and U were more than 85%.

Evaluation of uncertainty in the energy dispersive X-ray fluorescence determination of platinum in alumina

Evaluation of uncertainty in the Energy Dispersive X-ray Fluorescence (EDXRF) spectrometric determination of platinum in alumina catalysts is discussed. Pressed pellets of the platinum standard and a catalyst sample were prepared by using microcrystalline cellulose powder as the base material. A linear calibration of the X-ray fluorescence spectrometer was obtained in the range of 0.1–3 mg g−1 of platinum using pellets of matrix matched synthetic standards. The calibration function was obtained through bivariate least squares fitting, in conjunction with weighted regression of the residuals. The EDXRF results were compared with those obtained by instrumental neutron activation analysis and inductively coupled plasma optical emission spectrometry. Analysis of variance established the statistical parity of the results obtained by all the three techniques. A comprehensive evaluation of the various sources of uncertainty in the complete measurement process was carried out using a bottom-up approach. The main source of uncertainty was identified as the calibration of the EDXRF spectrometer, in which the major share was attributed to the intercept of the calibration function.

Polyaniline as a base material for preparation of a mercury standard for use in neutron activation analysis

Polyaniline sorbed with microgram quantity of mercury was prepared and its homogeneity and stability with respect to mercury was evaluated over a period of time. The volatilisation loss of mercury during and after neutron irradiation was studied. It was found that polyaniline was homogeneous and stable with respect to mercury. No loss of mercury from polyaniline was observed during and after neutron irradiation. Thus polyaniline sorbed with mercury can serve as a good standard for neutron activation analysis of mercury.

Neutron activation analysis for chlorine in Zr-2.5 wt% Nb coolant tube material

Zr-2.5 wt% Nb has been found to be better compared to Zircaloy-2 as coolant tube material in Canadu-PHW reactors but has a stringent specification of less than 0.5 mg/kg of chlorine. Instrumental neutron activation analysis (INAA) for the determination of chlorine in Zr-2.5 wt% Nb is not possible because of the high activity produced due to the determination of the matrix. Hence a radiochemical neutron activation analysis (RNAA) procedure has been developed for the determination of chlorine in this material. For the first time the chlorine determination at less than a ppm level by NAA is being reported in this paper, in a number of Zr-2.5 wt% Nb samples ranging from 0.1 to 2 mg/kg.

ION-EXCHANGE SEPARATION OF 60Co AND 125Sb FROM ZIRCONIUM FOR RADIOACTIVE WASTE MANAGEMENT

Abstract The feasibility of using ion-exchange resins to separate cobalt and antimony from zirconium in acid solutions was investigated. The distribution coefficients of zirconium, cobalt, and antimony on strong cation and anion exchangers in HCl and oxalic acid media were determined. The mass effect of zirconium on the distribution coefficients of cobalt and antimony was studied. The isotherm for zirconium was obtained in HCl solution. The distribution coefficient and isotherm data were used to develop ion-exchange processes for separation of cobalt and antimony from zirconium in the linear and nonlinear regions of the isotherm. A decontamination factor of more than 103 was achieved in a single ion-exchange cycle with respect to both cobalt and antimony. Two cycles of ion exchange will bring down the activity to acceptable levels for processing of irradiated zirconium as well as achieve a significant reduction in the waste volume. This is the first paper on separation of 60Co and 125Sb from zirconium for radioactive waste management.

Comparison and statistical evaluation of neutron activation methodologies for the determination of gold in copper concentrate

Gold was determined in copper concentrate by an instrumental neutron activation analysis technique using the relative method. The determination was repeated by radiochemical and chemical neutron activation analysis with the aid of an anion exchange strategy for the chemical separation of gold from the matrix (Fe, Cu, and Zn). Irradiation of copper concentrate samples was carried out in APSARA reactor (BARC, India) with a thermal neutron flux of about 1012 cm−2 s−1. Analysis of variance established that the results obtained by instrumental, radiochemical and chemical methodologies were statistically indistinguishable. Among the three approaches, radiochemical activation showed superior detection limits, which was attributed to both the reduction in background and increase in sensitivity. The best measurement repeatability was observed in chemical activation methodology, compared to the other two. The rationale behind the improvement in measurement repeatability was the capability of chemical activation to process a larger mass of sample for each replicate, which resulted in improved counting statistics and reduction in sampling error with respect to gold. Combined uncertainty for all the three methodologies was evaluated through the bottom-up approach. Systematic evaluation of various uncertainty parameters showed that the major contributor to the combined standard uncertainty was the counting statistics during the instrumental approach and the chemical separation yield during radiochemical and chemical activation. The combined uncertainty for all the three approaches was less than the measurement repeatability indicating the inhomogeneous distribution of gold in copper concentrate. Calculations showed that the sampling constant for gold in copper concentrate was about 22 g.

Sorption of arsenic on manganese dioxide synthesized by solid state reaction

Arsenic in groundwater is a major concern in many parts of the world and suitable sorbents are required for removal of arsenic from ground water. Removal of arsenic from groundwater has been studied using manganese dioxide, synthesized by solid state reaction of manganese acetate with potassium permanganate. Manganese dioxide was characterized by X-ray diffraction (XRD), zeta potential, surface area, particle size measurements and thermal analysis. XRD measurement showed that the manganese dioxide had α-MnO2 structure. Sorption of As(III) and As(V) on manganese dioxide was studied by radiotracer technique using 76As radio isotope. Arsenic removal efficiency for both As(III) and As(V) at concentration of 2 mg L−1 was ∼99% in the pH range of 3–9. The sorption capacities for As(III) and As(V) were ∼60 mg g−1. Kinetic studies showed that the equilibrium was reached within 30 s. Arsenic sorbed on manganese dioxide was present as As(V) irrespective of initial oxidation state. The presence of Ca2+, Mg2+, Cl− and SO42− up to a concentration of 1000 mg L−1 had no significant effect on arsenic sorption. The sorption of arsenic decreased significantly in the presence of phosphate and bicarbonate anions above 10 mg L−1. Arsenic sorbed on manganese dioxide was desorbed by 0.1M NaOH. Arsenic was effectively removed by manganese dioxide from groundwater samples collected from arsenic contaminated areas of West Bengal, India.