Identification of refractory ores containing Au, Pd and Rh in northeastern Iran and determination of the elements using two Fire Assay methods

In this article, we address two important issues: the identification of refractory ores containing gold and PGEs, and the investigation of the optimal determination methods using pyrometallurgical techniques. We selected two types of rock samples (Olivine-Pyroxene and Plagioclase-Pyroxene) from mines in northeastern Iran, determined their mineral composition using XRF and XRD, and confirmed the presence of gold, palladium, and rhodium through microscopic study with SEM-EDS. We then conducted Sn-fire assay with a new recipe for the rock samples and compared the results with the classic NiS-fire assay method. Our analysis showed that the Sn-FA method produced better results for gold and palladium, while the Ni-FA method was slightly superior for rhodium. Compared with NiS-FA and Pb-FA, the reagent blank of tin powder was relatively low and can directly use in Sn-FA to collect Au, Pd and Rh without purification. Digestion time of nickel sulfide button is very long (overnight) while the digestion of Sn bead in HCl solution accursed easily and in very little time. Lower melting temperature and convenience of this method are among the advantages of this method. The established method applied to determining of the PGEs in Australian certified reference materials (CRMs) and the results were in good agreement with the values listed in the CRM certificate. The sample solutions determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Over ۱۰ analytical runs mean instrumental detection limits for a ۲۰-g sample ۰.۵ ppb for Au, ۱ ppb for Pd and ۲.۰ ppb for Rh obtained. Analyses of the CRMs: OREAS ۶۸۰, OREAS ۶۸۲ and OREAS ۶۸۴ indicate that recoveries of PGEs by NiS-FA were ۸۸.۲-۹۵.۶%, ۹۱.۳-۹۴.۴% and ۸۴.۲-۸۸.۶% for Au, Pd and Rh respectively, and recoveries of PGEs by Sn-FA were ۹۱.۹-۹۶.۹%, ۹۲.۲-۹۶.۲% and ۸۱.۷-۹۱.۱% for Au, Pd and Rh respectively.

کلیدواژه ها:

Refractory Gold Ores ، PGEs ، Australian certified reference materials ، New Sn-FA ، NiS-FA