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Flotation's earliest patent was issued in 1860. However, the process was first applied commercially in Australia until 1904, and in Montana in 1911. Major advances followed both in reagent treatment and in cell design, with resulting process improvements. Mechanical cells have seen the widest use and with the major increases in plant capacities (Fig. 1) their volumes have also increased (Fig. 2).
In 1991, the principal use for the process was to produce copper concentrates for smelting. It was applied to 243 Mt (268 million st) of copper ore. The total of all ores floated that year was 426 Mt (470 million st). In 1997, US mines produced 257 Mt (284 million st) of copper ores for flotation, yielding 1.75 Mt (1.94 million st) of copper.
Nine decades of flotation
The first five decades (19111960). Early developments: Hoover's History of Flotation summarized the first production of flotation concentrates from zinc gravity tailings. This began in 1904 in Australia with 46.8 kt (51,602 st) and reached a maximum of 472.2 kt (520,518 st) in 1912. The Hyde patent described the first cleaner circuit for upgrading rougher concentrates obtained by floating zinc gravity tailings. This was applied to the tailings at Butte and Superior Copper's flotation mill in Montana. The result was a smelter-acceptable zinc concentrate, assaying 50.1% and recovering 94.6% of the zinc (Photo 1).
Another important advance was made in the Inspiration Mill (Photo 2). This operation first applied flotation directly to an ore instead of to gravity tailings. The 13.6 kt/d (15,000 stpd) mill started up in June 1915. By using flotation first and followed by gravity, the Inspiration Mill obtained copper recoveries of 79.95%. Miami Copper treated ore from the same ore body by gravity only. Copper recoveries were 64.54%.
Taggart's 1927 handbook described 15 plants floating copper ores. The largest plant capacity was 22.6 kt/d (25,000 stpd), while the smallest was 91 t/d (100 stpd). Total flotation plant capacity was 95.7 kt/d (105,500 stpd).
Taggart's 1945 handbook reviewed 23 operations that floated a total of 228 kt/d (251,546 stpd) of copper ores. Three of them had capacities greater than 18 kt/d (20,000 stpd). Eight had capacities of between 4.5 and 18 kt/d (5,000 and 20,000 stpd). And 12 had capacities of less...