C. Harry Benedict Centennial David H. Kenny Michiean Technoloeical Universitv ~ o n ~ h t o~n i, c h i ~ 49931 an Nineteen seventv six. the American Bicentennial vear. is the one hundredthannkersary of the birth of a g r e a t ~ m i r ican industrial chemists, C. Harry Benedict (1876-1963). Mr. Benedict, whose first name was Centennial, was the inventor of the ammonia leaching process for the recovery of copper from its ores. A year after his 1897 graduation from Cornell University he was given the assignment by the then rich and famous Calumet and Hecla Copper Mining Company in Calumet, Michigan of finding a way of reducing the large amount of copper wasted in treating their ore, in which, unlike most copper ores, copper existed as the native metal. Over 25% of the copper mined had wound up in waste sand dumped in Torch Lake a few miles from the mine. Since the Calumet and Hecla mine had been worked since 1866, in 1915 the ground underneath Calumet was honeycombed with more than one hundred miles of mine tunnels and the lake contained an enormous amount, about thirty seven million tons, of this waste sand? he solution to this problem was the ammonia leaching process, patented by Mr. Benedict in 1915 and 1920. The waste sand. was dredged from the lake and treated in huge tanks with a cupric ammonium carbonate solution which dissolved the metallic copper that physical methods were not able t o remove. Steam distillation of the leach solution caused a mixture of the two copper oxides to precipitate.
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The mixed oxides were either sold as such or were reduced to metallic copper a t the refinery. The process was a financial and engineering success from its start in 1915. By the mid-nineteen fifties all the treatable sand had been dredged from the lake, t h e copper removed, and the spent sand returned to the lake. About half a billion pounds were recovered and the profit from its sale kept the mining company solvent during many lean years. The Calumet and Hecla process was used during World War I1 to recover the copper from scrap shells. Although Calumet and Hecla closed down for good after a strike in 1968, the process is still in use a t various places in the world and has been modified to treat zinc, cobalt, nickel, and copper sulfide ores. Further details of the process may be found in the two books written by Mr. Benedict after his ~etirement.~,~ In addition to Mr. Benedict's responsibilities with Calumet and Hecla, he was simultaneously a lecturer in hydrometallurgy a t Michigan Technological University for 25 years. In 1964 a new building housing the Institute of Mineral Research a t Michiean Technoloeical Universitv was named the Benedict ~ a c o r a t o r yin hisihonor.
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Thurner, A. W., "Calumet People and Copper," Privately Puhlished, 1974. Benedict, C. H., "Red Metal, the Calumet and Heda Story," The University of Michigan Press, Ann Arbor, Mich., 1952. Benedict, C. H., "Lake Superior Milling Practice," The Michigan College of Mining and Technology Press, Houghton, Mich., 1955.
