5328669 Extraction of precious metals from ores and other precious metal containing materials using halogen salts

Abstract

In this work, a novel method was reported for the determination of ultra-trace Au, Ir, Pd, Pt and Rh in rocks and minerals. Purified basic lead carbonate instead of commercial lead oxide (PbO) was used as fire assay collector in order to greatly reduce the reagent blank. Au, Ir, Pd, Pt and Rh were enriched in about 5 mg of composite granule of lead fire assay. After the granule was fully dissolved in HNO3, HCl was added to form aqua regia so as to completely digest Au, Ir, Pd, Pt and Rh, then the sample solution were determined by high resolution continuum source graphite furnace atomic absorption spectrometry (HRCS-GFAAS). The decomposition method of chromite was investigated as well as the pyrolysis/atomization temperatures, atomization reading time and effective pixels of CCD detector for the determination of Au, Ir, Pd, Pt and Rh were optimized. Besides, the influence of spectral interference of co-existing elements and the residual amount of lead were discussed. Under the optimal conditions, excellent curve fitting of Au, Ir, Pd, Pt and Rh were obtained between 0.05 and 50 ng mL−1, with the correlation coefficients exceeding 0.9996. The experimental characteristic mass of Au, Ir, Pd, Pt and Rh were 0.0068, 0.052, 0.013, 0.060 and 0.011 ng, respectively. The established method was successfully applied to analyze Au, Ir, Pd, Pt and Rh in Chinese Certified Reference Materials (CRMs), and the determined values were in good agreement with the certified values. The relative standard deviations (RSDs, n = 5) of Au, Ir, Pd, Pt and Rh were between 5.5% and 13% for the determination of GBW07291. The proposed method was sensitive and accurate which could meet the analysis requirement of ultra-trace Au, Ir, Pd, Pt and Rh in rocks and minerals.