Smelting at Stillwater
Concentrates from the Nye and East Boulder Mines are transported to the smelter as a filter cake and are sampled, dried, and pneumatically conveyed to a concentrate bin. The concentrates are then metered into the electric furnace.
The furnace feed system consists of a fine feed system and a course feed system. Fine feed includes dry concentrate mixed with spent auto and petroleum catalysts, limestone, and dust. The coarse feed consists of granulated converter slag and crushed reverts. The fine feed is fed via bins above the furnace along an airslide and distributed to feed ports on the furnace roof. The coarse feed is feed directly into one or two feed ports via screw conveyors or double dump valves.
The electric furnace is rectangular with 3 in-line prebaked graphite electrodes. The furnace lining consists of magnesia-chrome oxide refractory bricks, with copper plate coolers installed in the slag zone.
Furnace matte is tapped approximately every 4-8 hours into ladles and granulated in preparation for converting. Furnace slag is tapped several times a day into a pit for air-cooling, and is shipped back to the Stillwater and East Boulder concentrators for PGM recovery.
Granulated furnace matte is converted in TBRC’s (Top Blown Rotary Converters). Converter matte is poured into ladles, granulated, dried and transported to the Refinery. Converter Slag is skimmed into ladles, granulated, dried and returned to the electric furnace.
Process off-gases first pass through a baghouse for dust removal before being cleaned of S02 in a Dynawave scrubber using a caustic solution. Secondary off-gases are also passed through a baghouse before being scrubbed of S02 in a second Dynawave scrubber. A state-of-the-art sodium regeneration circuit provides caustic for the scrubbing system. Gypsum produced in the regeneration process is pressure filtered into a low moisture filter cake and is sold as a soil amendment to farmers, ranchers, and the coal bed methane industry.
