Some Observations on the Determination of Gold and the Platinum‐Group Elements in Black Shales

Abstract

This research compares various ways of applying oxidative chemical decomposition to the analysis of gold‐bearing black shale ores from the Russian Natalka and Sukhoj Log deposits. This study was conducted as part of the certification program for the Russian candidate black shale reference materials SLG‐1 and SCHS‐1 and also because of the paucity of data available on the determination of the platinum group elements (PGE) in analogous sample types. We report direct evidence of PGE volatilisation from black shale materials when processed in the presence of oxygen. We also developed a comprehensive analytical scheme for the quantitative determination of PGE in all phases (gaseous and ash) produced during slow combustion of carbonaceous materials in oxygen.This study has shown that during combustion in oxygen at 600 °C, PGE contained in the Natalka black shale ores are lost as gaseous reaction products. Thus, the volatilized PGE (recovered in traps) account for up to 14% Pt, 40% Pd, 40% Ru and 10 % Ir relative to their total concentrations in a carbonaceous concentrate. It was also established that in the process of combustion, Au quantitatively remains in the ash cake.In order to avoid the deleterious effects of oxygen on the volatility of the PGE, we propose a new comprehensive sample decomposition method based on the application of fluoroxidants such as BrF3and KBrF4. This method was validated using samples of black shale ores and their processing products by comparing our results with those obtained independently using sealed autoclave processing of the same materials. It was shown that PGE in black shale ores and their processing products not only exist in commercially exploitable quantities but that a small proportion of PGE compounds are soluble in alcohol. We propose that in gold‐bearing black shale ores, PGE are present as organometallic compounds.