TECH NOLOGY
Chemical Process for Copper Gets Tryout Process uses sulfuric acid in leach step rather than ammonia and ammonium carbonate, as in other chemical methods A chemical method for producing oxygen-free copper powder will be used as the basic process at a new copper-refining plant at Bagdad, Ariz. The process is based on hydrogen reduction of copper sulfate solutions. The most significant difference between this process and other chemical copper-refining processes is that the Bagdad plant will use sulfuric acid in the leach step in place of ammoniaammonium carbonate. This will eliminate the formation of ammonia byproducts and reduce operating costs. The plant is the result of a joint venture between Chemetals Corp. (New York, N.Y.) and Bagdad Copper Corp. (Bagdad, Ariz.). A new firm, Arizona Chemcopper, jointly owned by Chemetals and Bagdad, will operate the plant, which will get its copper ore from Bagdad. The facility will produce 8250 tons of copper powder per year and will cost about $4 million. Foster Wheeler (New
York, N.Y.) will design and build the plant. In the process copper oxide ore is leached with sulfuric acid (about 2.5 grams per liter) forming a weak solution of copper sulfate. This is passed over scrap iron to replace the copper and to form iron sulfate. Copper precipitates on the scrap iron. The precipitate (cement copper) contains about 84% copper on a dry basis with iron the predominant impurity. The cement copper is then leached at 160° to 180° F. with sulfuric acid (about 150 grams per liter) and in the presence of air to make a strong copper sulfate solution at 2 pH. Under these conditions, iron reaches a solubility equilibrium of 10 grams per liter and then drops out of solution as hydrated ferric oxide. The copper sulfate in solution cycles to a titaniumclad autoclave, where it is reduced with hydrogen at 450 p.s.i.g. and 300° F.
Filter
Hydrogen Sulfuric acid leach
Reduction autoclave
Chemical Process Recovers Copper
Centrifuge
Sintering furnace
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C&EN
DEC.
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1964
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Copper powder
An acrylic acid-based dispersing agent is added in the autoclave to speed the reduction rate and to regulate the particle size of the copper. The more dispersing agent used, the finer the particle size. Ferrous State. In the sulfuric acid leaching, 90% of the iron is converted to the ferric state. In the following step, besides converting copper sulfate to a relatively pure copper, hydrogen reduction also changes lingering iron to the ferrous state. Since iron is the only impurity which is higher than copper in the electromotive series and since it is in the ferrous state, hydrogen replaces 95% of the copper, with iron as well as the remaining copper staying in solution. The copper, now at 99.9% or more purity, is then sintered in a furnace where trace amounts of sulfur, oxygen, and other impurities are removed. The copper is then ready for shipment or for further processing to tubing or strip. The complete refining process takes about eight hours. The final product exceeds 99.95% purity. The route which Arizona Chemcopper will use differs from the conventional electrolytic refining method to make high-purity copper powder. Electrolytic refining process uses blister copper which is made from cement copper and from copper sulfide ore, which has been concentrated by flotation. The cement copper and the concentrate are fire-refined first in a matting furnace, then in a reverberatory furnace. The blister copper contains 98.5% copper. The new route is an offshoot of a process used by Sherritt Gordon Mines of Toronto, Ont. However, the Canadian operation uses ammonia in the leaching step and is designed to produce nickel and cobalt. Chemetals holds patent rights on the sulfuric acid process and some of its variations. For example, it has licensed to Universal Minerals and Metals an ammonium carbonate system to refine copper.
