Byproduct Recovery From Copper-Nickel Bearing Duluth Gabbro Flotation Tailings

A loch-grade copper-nickel deposit, with an estimated 4.6 Gt (5 billion st) and average analyses of 0.6% copper, 0.2% nickel, occurs in northeastern Minnesota. In addition to copper, nickel, cobalt, and precious metals, the Duluth gabbro contains magnetite, ilmenite, olivine, plagioclase, and biotite. It u estimated that flotation tailings that would be produced by a concentrator of optimal size to sustain a smelter would amount to 20 Mt/a (22 million stpy). The flotation tailings, having already been ground, warrant a closer examination for recovery and use of potential byproducts. Residual sulfide minerals and fibrous minerals may also be isolated and treated separately for useful purposes or for disposal in an environmentally acceptable manner. Two flowsheets were developed; one involving preconcentration by low- and high-intensity magnetic separation and another involving preconcentration by gravity concentration. Concentration methods for recovering and purifying individual byproduct minerals were investigated. From their chemical, physical, and mineralogical characteristics, the potential areas of application and marketabilities of each product fraction were surveyed.