Methods of recovering platinum-group metals from Stillwater Complex ore

Synopsis

As part of its strategic and critical minerals program, the U.S. Bureau of Mines investigated methods for beneficiating and recovering platinum-group metals (PGM) from ores found in the Stillwater Complex, the only primary resource of platinum-group metals located in the United States. Because the ore is sulfidic in nature, it was concentrated by froth flotation. A 45 kg/h process development unit (PDU) was constructed and 85 to 95% of the platinum and palladium were recovered from the ore by using mercaptobenzothiazole or sodium isobutyl xanthate as collectors. Bench-scale research showed that conventional matte smelting and leaching methods could be used to recover the precious metals from the flotation concentrate. More than 95% of the precious metals reported to the matte phase during smelting. Several leaching schemes were evaluated that selectively extracted the base metals from the matte and allowed recovery of high-grade PGM residues that were suitable as feed material for a precious metals refinery. Oxidative leaching of roasted flotation concentrate to selectively extract precious metal values was also investigated as an alternative to conventional matte smelting-leaching strategies.

Ongoing research is evaluating the effect of bioleaching using Thiobacillus ferrooxidans on sulfide oxidation and liberation of precious metals present in Stillwater Complex flotation concentrate.