Cement copper production in the United States has increased during the past few years, principally because more submill-grade material from open-pit operations is being leached in waste dumps. Since 1960, the cement copper annual growth rate has been about twice the rate for primary copper. If this trend continues, annual production of copper from cement copper precipitates will be 550,000 tons by 1975.
In commercial cementation plants, shredded detined cans are the chief source of iron used as the copper precipitant. The cement copper produced contains from 60 to 90 percent copper. Oxygen is the principal impurity owing to partial oxidation of the moist, fine copper particles during drying. Copper precipitates also are contaminated with silica, unreacted iron, and extraneous debris associated with tin cans. Standard practice is to smelt this impure cement copper in the reverberatory furnace along with copper sulfide flotation concentrates. Because of the increasing production of cement copper and absence of excess capacity at existing smelters, alternative processing routes to present smelting practice should be considered.
The direct smelting and fire refining of cement copper in an electric furnace was investigated by the Bureau of Mines in the early sixties. This approach has not been commercially adopted. Other