Froth flotation characterization and processing plant design for the platiniferous and auriferous marine sediments of Southwestern Alaska

Abstract

The purpose of this study was to characterize, and investigate the beneficiation of, the platiniferous and auriferous marine sediments of Southwestern Alaska, located near Platinum, Alaska. The majority of placer gold particles are contained in the 50 x 150 mesh size fraction, while the platinum is finer, residing in the 100 x 200 mesh size fraction. Liberated placer gold and placer platinum group metals (PGM) particles are visible to the naked eye and readily observed under a binocular microscope. Preliminary, qualitative microprobe analysis of PGM grains from the flotation concentrate showed grains of nearly pure iridium, isoferroplatinum and Pt-Rh-Ir-Fe-S-As mineralogy. Froth flotation showed that placer gold responded very well to all the collectors used, with gold recoveries of 82.7-99.8%. Flotation of platinum responded well to only potassium amyl xanthate, with a recovery of 80.4%. Results of low intensity magnetic separation showed that virtually all the liberated gold and platinum reported to the non magnetic product. A flowsheet, with estimated capital and operating costs, was developed to process 1500 tph of marine placer feed. Annualized costs per ton to process marine sediments were estimated to be $2.40 to $3.72 depending upon plant availability, 90% to 50%, respectively.