Isolation of gold from geological samples by microwave plasma from neutron activation analysis

Abstract

A method for the isolation of gold from geological samples in a microwave helium-oxygen plasma is proposed as a preliminary step prior to the determination of gold by neutron activation analysis and gamma spectrometry. The study of the degree of chemical sublimation of gold in the plasma was carried out with samples that had been irradiated with neutrons. The dependence on the composition of the plasma support gas and on the time of treatment with the plasma is discussed. For the complete isolation (⩾ 95%) of gold the following optimum conditions were established: plasma support gas, helium-oxygen (40 + 60); flow-rate, 0.25 l min −1; and time, 15 min. The isolated gold was transferred completely into tributyl phosphate as solid extractant, which was then analysed by neutron activation analysis and gamma spectrometry. The accuracy of the technique was checked using reference materials and the results agreed to within 10%.