Determination of rhenium in igneous rock by X-ray fluorescence spectrometry with prior electrochemical concentration

Abstract

This paper describes a technique for determining rhenium in igneous rock. The technique involves electrochemical concentration of rhenium into solid phase followed by its determination by X-ray fluorescence spectrometry. Compounds of rhenium and other metals were converted into a solution as a result of processing of igneous rock samples with a mixture of nitric and chloric acids. After the resulting solutions had been neutralized, rhenium was electrochemically concentrated by electrodeposition on a cathode. Due to the presence of a considerable amount of iron group metals in the studied samples, it was possible to use induced electroreduction with regard to rhenium, molybdenum and tungsten compounds. As a result, the refractory metals converted into a cathode deposit and thus were effectively concentrated into solid phase. The detection limit for rhenium in the solution is ~2 mcg/L. Considering the complex chemical composition of the analyzed samples, spike test appears to be the best solution for quantitative determination of rhenium. The developed technique allows to determine the concentration of rhenium with the concentration of molybdenum being ten times in excess. The latter is typical of igneous rock samples. More than 100 samples taken from Kudryavy volcano were analyzed in the study: the concentration of rhenium in the samples was within 0.5 to 50 g/t. For the sake of verification, the obtained data were compared against the results of inductively coupled plasma mass spectrometry (ICP-MS). The comparison showed a good convergence. At the same time, lower values would be systematically obtained when using inductively coupled plasma atomic emission spectrometry (ICPAES). The developed technique can be used to determine rhenium and molybdenum in rock. The authors would like to thank O. A. Nabelkin, a research fellow at the Institute of Mineralogy, Geochemistry and the Crystal Chemistry of Rare Elements, for his help with the adoption of X-ray fluorescence spectrometry, and R. G. Chumakov, Candidate of Physical and Mathematical Sciences, a senior researcher at the National Research Centre Kurchatov University, for his help with the X-ray photoelectron spectroscopy studies.This research was carried out using the funds assigned to D. Mendeleev University of Chemical Technology of Russia (Х-2020-011).