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Cornelius H. Keller​
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In 1925, Cornelius H. Keller’s first patent—the xanthate patent—began a revolution in sulfide minerals flotation that is still apparent in flotation plants throughout the world. The key virtue of the xanthate collectors was, and is, solubility in water, producing a solution that is both inexpensive and easy to feed into a flotation circuit. By 1985, 3.5 million pounds of xanthate collectors were being used annually in sulfide ore flotation plants in the United States, according to USBM statistics, accounting for well over half the total of flotation collectors sold in the United States during that year.​

The importance of Cornelius Keller’s contributions is widely recognized among minerals processors. In 1952, The Froth Flotation 50th Anniversary Volume described his xanthate patent as “A discovery of great magnitude.” In 1995, Professor D.W. Fuerstenau, in his plenary lecture at the XIX International Mineral Processing Congress, said, “Perhaps Keller’s discovery . . . ranks as the chemical discovery that had the greatest impact in flotation.”​

The last of Cornelius Keller’s 24 patents, issued in 1946, was on the flotation use of aroyl thionocarbamates and led to the production by Dow Chemical of Benzamate, Z-105, a flotation collector that was superior to anything on the market at that time. Z-105 then led to the discovery by Harris et al. of the dialkylthionocarbamates, Z-200, which displaced Z-105.​

Cornelius H. Keller was born in Zurich, Switzerland and was fluent in six languages. He studied at Heidelberg University in Germany, came to North America at the turn of the century, and settled at Parral, Chihuahua, Mexico, in rich mining country. There, Keller set up a lab with an English colleague, James Wilding, and met and married Adela Rios. During the Pancho Villa revolution in Mexico, Keller and his wife followed Wilding to Minerals Separation NA Co. in San Francisco, California, where he worked until his formal “retirement.” Subsequently, Cornelius Keller joined Dow Chemical, where he served as a consultant until his death in 1949.​