P. S. Remya Devi

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.

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.

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.

Kinetic separation of cobalt from zirconium by cation exchange process

ABSTRACT Zirconium-tin alloys are used as pressure tubes in Indian pressurized heavy water reactors (PHWRs). Used pressure tubes contain neutron activation products of the constituent elements. 60Co is one of the long-lived radioisotopes of concern, for both radioactive waste management and recycling of pressure tubes. This article describes a facile cation exchange separation of Co(II) from Zr(IV) in HCl medium. Co(II) could be preferentially sorbed on the gel resin by utilizing its faster kinetics. Higher flow rates and shallow resin bed were the key steps, which prevented the loading of Zr(IV) on the resin phase.

Determination of impurities in graphite using synchrotron radiation based X-ray fluorescence spectrometry

Determination of impurities namely Ca, Mn, Fe, Ni, Zn, Sr and Pb in graphite by energy dispersive X-ray fluorescence spectrometry is described using microfocused synchrotron radiation. The internal standard and standard addition methodologies were adopted for quantification and the results were compared with tube-based X-ray fluorescence spectrometry. Analysis of the results by the F and t-tests revealed their statistical equivalence. Synchrotron measurements improved the detection limits by an order of magnitude compared to the tube based technique. Cr and Zr, which were below the quantification limit in tube based technique, were also quantified by synchrotron based technique.