Objective
Develop new technolgies and techniques which enable recovery of strategic and critical minerals such as cobalt from domestic resources, thereby easing the U.S. dependence upon foreign producers for these valuable commodities.
Approach
The Bureau of Mines, through research, developed a process which uses mineral beneficiation techniques to recover cobalt-rich products from Missouri lead ores. Before development of this process, cobalt was lost as an impurity in the copper, lead, and zinc concentrates and in the mill tailings because the technology to recover it with minimum impact on present production did not exist.
Recovering Valuable Cobalt from Domestic Sources
Over 2.7 million lbs of cobalt, equivalent to about 15 pct of the Nation’s annual consumption, are lost each year due to a lack of technology permitting its, recovery from Missouri lead ores. These ores are now being mined for lead, copper, and zinc. The Bureau of Mines developed a process which fills this technology gap and allows for an alternative domestic source in the event that foreign supplies are suddenly cut-off. Currently cobalt is used in the manufacture of jet engines. At present the United States must rely upon Africa for sufficient quantities of this important metal.
The new cobalt recovery technique is a beneficiation process which uses a combination of fine grinding and froth flotation. The new process enables recovery of about 60 pct of the cobalt that winds up in copper concentrates made from the lead ores. The concentrates are first ground to an average size of 10 µm. After grinding, the slurry is scrubbed to polish the mineral surfaces and a flotation collector is added. The collector adsorbs on the fresh mineral surfaces, causing the copper mineral to float away from the cobalt mineral. As flotation proceeds, additional collectors are added to enhance the process. Separation occurs in a stagewise fashion, with about 98 pct of the cell feed floated away as a copper concentrate and the combined tailings becoming an enriched cobalt product. The floated material goes to the next stage and is refloated with the same product as the previous stage. Six stages of flotation will recover 60 plus pct of the cobalt and increase the grade of the cobalt by 4 to 6 times to a range of 2.5 to 4.0 pct. The recovered grade is comparable to the cobalt concentrates produced in Africa. Recovery could be increased by adding additional stages.
The recovery method can be incorporated as an add-on to existing plants and will not interfere with in-place processes. Costs are incremental since the feed material for this process is an existing product. Removing cobalt as a separate product also enhances the original copper concentrate by removing not only the cobalt but by reducing the magnesium oxide and iron contents.
Test Results
The cobalt recovery process has been tested at an operating Missouri lead mine using a continuous flotation unit with very good results. Tests have resulted in development of a flow-sheet that allows for the recovery of 70 pct or more of the cobalt in Missouri lead ore copper concentrates, at grades greater than 3 pct Co or 7 pct combined Ni-Co. This was accomplished on feeds grading as low as 0.25 pct Co. In addition, the flowsheet, which involves stage-wise separations, has proven to be much more flexible than the classic rough, scavenge, and clean configuration.
Patent Status
The U.S. Department of the Interior has not applied for any patents on the Bureau’s cobalt recovery process.