White Pine reverberatory furnace slags contained economically recoverable amounts of copper for a variety of reasons. Among them:
- White Pine concentrates yield extremely high matte grades (65+% Cu) and viscous slags. The viscous slags hinder matte settling causing matte “prill” entrapment in the slag.
- White Pine’s total refined copper output is accomplished through fire refining requiring special techniques for impurity removal, especially small amounts of nickel introduced from purchased pyrite and chalcopyrite fluxes. These special techniques result in high-copper slags, refractory to smelting, being reintroduced into the reverberatory furnace.
- Furnace bottom build-ups resulting in mechanical matte entrapment through the formation of “dams” hindering matte flow.
The plant flowsheet utilized a dual-density heavy media drum and jigging to recover the chunk and “BB” sized prill matte following wet screen sizing for media preparation. Coarse slag, -1″ x 4 mesh, is treated in a 3-product Wemco heavy media system yielding a coarse final concentrate, a copper-enriched middling and a reject tailing. Screen undersize, -4 mesh x 0, is cycloned at approximately 100 mesh with the +100 mesh distributed to three 24″ x 36″ Denver Duplex mineral jigs. Jig concentrates are dewatered and join the heavy media concentrates.
The heart of the plant is the heavy media circuit with its control and media stabilization systems. Pilot testing demonstrated the absolute need for a media stabilizing agent to achieve direct smelting concentrate grades with maximum recovery. The high separation densities required dictated the use of coarse, semi-spherical media (ferrosilicon) which is inherently quite unstable. Commingling various sized media will achieve reasonable stability but at the price of higher viscosities, lower recovery, and difficulty in attaining and holding the high separation densities (3.4+). Plant feed was very clean, containing very little magnetite or natural slimes to help provide media stabilization.
The second factor enabling good metallurgical control and operation of the dual-density heavy media system was the plant instrumentation package. Under normal operation, the entire system is automatically monitored and controlled at operator selected separation densities and levels. Again, pilot testing had determined the need of extremely close density control. Compounding the problem was the need to develop close density control over quite large specific gravity ranges due to the density and copper content variability of the incoming slag feed.