Determination of Au in High Grade Gold Deposits by Flame Atomic Absorption Spectrometry

The conventional fire assay method to determine high grade gold has a long chemical procedure with many factors influencing the analysis result. Moreover, the ash blowing process for the Pb button volatilizes a large amount of Pb, causing serious pollution to the environment. In this paper, a method is described whereby the 20.0-100.0 g sample was split into small amounts and calcinated. The products of calcination were dissolved by 50% aqua regia and the residues were filtered. All the clean filtrates were loaded into a volumetric flask. An appropriate volume of solution was selected to extract Au with foam enrichment. After ashing the Au bearing foams, the Au was dissolved again by concentrated aqua regia. Then, the Au was measured by Flame Atomic Absorption Spectrometry (FAAS). The detection limit was 0.101 μg/g. Through verifications for a few national first grade standard materials and the analysis samples, the accuracy and precision met the relevant requirements. The sampling weight was from 20.0 g to 100.0 g which effectively improved the sample representativeness and extended the analysis content range for Au by FAAS. This method is also suitable for samples with Au contents from 50.0 μg/g to 550.0 μg/g.