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Columbus Metallurgical Complex

Sibanye-Stillwater’s Columbus Metallurgical Complex includes smelter facilities together with a base metal refinery, which are all located adjacent to each other in Columbus, Montana. The end product produced at the complex is a PGM-rich filter cake that is despatched for additional processing by a third-party precious metal refinery.

During the eight months in 2017, The Columbus Metallurgical Complex processed a record of 860,711oz (mined: 383,142oz and recycled: 477,569oz, including ounces tolled).

Operations in Montana - USA

Smelter

This facility consists of a concentrate drying plant, two electric furnaces, two top blown rotary converters (TBRCs), a matte granulator, and gas handling and solution regeneration systems. Construction of a new primary 150 ton-per-day smelter furnace was completed in 2009. This larger furnace allows room for growth in future processing volumes, partially mitigates potential operational risk by providing some redundancy (virtually all of Sibanye-Stillwater’s metal production is dependent on the availability of the smelting facility), and enables continued processing during periodic scheduled maintenance shutdowns. After stripping out the old refractory material from the original furnace during 2010, the furnace structure was re-bricked during 2011 and reconfigured during 2012 as a “slag cleaning” furnace. In this configuration, slag tapped from the primary furnace is transferred into the original furnace, providing additional residence time for PGM matte to separate from the slag material, with the intent of increasing metal recoveries. Reconfigured as such, the slag cleaning furnace also serves as a backup for the primary furnace if needed.

Concentrates from mine sites are transported by truck to the smelter, dried, and fed into the electric furnace. In the furnace, the concentrates are combined with spent catalyst materials collected by the recycling business segment. The combined feed is melted in the furnace, where the lighter silica-rich slag separates out into a distinct layer that floats on top of the heavier nickel-copper PGM-rich matte. The matte is tapped from the furnace periodically and granulated. This granulated furnace matte is then re-melted and processed (in a TBRC) to extract iron from the converter matte. The converter matte is poured from the TBRC, granulated and transferred to the base metal refinery for further processing. The granulated converter matte, approximately 6% of the original smelter feed by weight, consists principally of copper and nickel sulphides containing approximately 1.5% to 2.5% PGMs.

The TBRC slag is also granulated and returned to the electric furnace for recovery of any contained PGMs. Any residual slag from the slag cleaning furnace is periodically tapped from the furnace, cooled and returned to the Stillwater Mine concentrator for reprocessing.

The gases released from the smelting operations are routed through a gas/liquid scrubbing system, which removes approximately 99.8% of the contained sulphur dioxide. Spent scrubbing solution is treated in a process that converts the sulphur dioxide into gypsum, or calcium sulphate, and regenerates clean scrubbing solution. The gypsum is used by farmers as fertiliser.

Base metal refinery

The base metal refinery implements the patented Sherritt Process, whereby a sulphuric acid solution dissolves out the nickel, copper, cobalt and any residual iron from the PGM-bearing converter matte. The copper and nickel are marketed as by-products. A nickel crystallizer circuit produces a crystalline nickel sulphate by-product containing minor amounts of cobalt, which is marketed under sales contracts with various companies. A copper electro-winning circuit removes copper from the solution as cathode copper that is marketed to copper refiners for upgrading to commercial grade material. The removal of these metals upgrades the PGM fraction of the converter matte product from approximately 2% to approximately 50%.

The base metal refinery produces a palladium, platinum and rhodium-rich filter cake, which also contains minor amounts of gold and silver. This filter cake is shipped to Johnson Matthey under a toll-processing agreement. The palladium and platinum metals are returned to the Company’s account as 99.95% purity palladium and platinum sponge; refined rhodium, gold and silver are returned separate. The refined metals from mine production are sold to Johnson Matthey and Tiffany & Co.; refined metals from the recycling segment are normally delivered to the counterparties. The refiner is paid a per-ounce refining charge for toll processing of the refined filter cake, and the refiner also retains a small percentage of the contained metals.