The flotation process . m $100 to $ least 1000 grams of ore is required for a test and about 30 minutesto 1 hour is spent. It can be seen that nothing but a finished concen-trate and a tailing are obtained or a middling product may be left inthe cleaner cell. This middling may be assayed as such and calculatedinto the concentrate and tailing or its sulphides may be panned outand added to the concentrate. The machine is said to give resultsclosely paralleling those obtained with larger-scale apparatus. A TESTING ORES FOR THE FLOTATION PROCESS—II 299 source of supply of compressed air at 3
The flotation process . m $100 to $ least 1000 grams of ore is required for a test and about 30 minutesto 1 hour is spent. It can be seen that nothing but a finished concen-trate and a tailing are obtained or a middling product may be left inthe cleaner cell. This middling may be assayed as such and calculatedinto the concentrate and tailing or its sulphides may be panned outand added to the concentrate. The machine is said to give resultsclosely paralleling those obtained with larger-scale apparatus. A TESTING ORES FOR THE FLOTATION PROCESS—II 299 source of supply of compressed air at 3 to 5 lb. per sq. in. is necessaryand the main valves on the air-pipe leading to each machine shouldbe some type of needle-valve in order to ensure exact control. In testing practice, the air-lift type of middling-return has beenfound more satisfactory than the centrifugal pump shown in Fig. 71. Laboratory Manipulations. Turning from the description of themachines used to the operations on the ore before and after the. Fig. 72. test-machixe with pachuca mixer. A. Pachuca mixer. B. Pulp-feed to air-blanket. C. Needle-valve air-control. D. Blanket-clamps for quickly removing blanket for cleaning. E. Wind-boxes. flotation operation, we have in general the problems of crushingthe ore and of drying the froth-concentrate. As a rule laboratory machinery for the pulverization of ore isof the dry-grinding type, with the exception of small ball-mills thatcan crush from 1 to 100 lb. charges in the wet. Consequently, most 300 THE FLOTATION PROCESS people start with weighed charges of finely-ground dry ore, a knownquantity of water, of oil, and of acid or alkali. Our experience hasbeen that most dry-ground ore must be treated in an acidified pulpto get good flotation. Doubtless the surfaces of sulphide particlesbecome somewhat oxidized in, or shortly after, dry grinding andthe function of the acid would be to clean the slightly oxidizedsurfaces. Wet grinding usually does not call
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