The flotation process . d higher-grade concentrates. Consequently, it may bedesirable to collect enough froth from a series of tests to be re-treatedin a cleaning test. Of course, this is provided for in the Callowtest set, where only cleaned concentrate is discharged from themachine. It is further found desirable to weigh and analyze someof the successive fractions of the froth being discharged from aflotation machine, as the tailing becomes leaner, and determine atwhat point it may be desirable to re-treat such froth. Many reports of flotation test-work with mechanical-agitationmachines give
The flotation process . d higher-grade concentrates. Consequently, it may bedesirable to collect enough froth from a series of tests to be re-treatedin a cleaning test. Of course, this is provided for in the Callowtest set, where only cleaned concentrate is discharged from themachine. It is further found desirable to weigh and analyze someof the successive fractions of the froth being discharged from aflotation machine, as the tailing becomes leaner, and determine atwhat point it may be desirable to re-treat such froth. Many reports of flotation test-work with mechanical-agitationmachines give the speed of the rotation of the agitating-blades. Wehave found that it was possible to get much the same work donewith quite a variation of speeds, the only effect being to lengthenor shorten the time of treatment. We feel that the importance ofthis matter has been much exaggerated. Some means of speed-control is necessary and the speed can be adjusted in each case until TESTING ORES FOR THE FLOTATION PROCESS—II 305. Fig. 75. the case machine. the froth presents the proper appearance as to depth, size of bubbles,color, etc. Speeding toward the end of a test in order to give adeeper froth with a faint line of concentrate on the very top is often 306 THE FLOTATION PROCESS advisable. We recommend adjusting the speed in each test to suitthe other conditions, rather than running a series of tests withdifferent speeds. Only in the slide machine, where operation ofthe impeller must be suspended in order to allow froth to collect,is the speed of much importance. Here we recommend agitation fora definite length of time, and then a period of settling. The effectof variation of speed during a definite length of time may be aconsiderable variation in the amount of froth collected during thequiet period. Hence we are prejudiced against the use of the slidemachine except for oil-testing. When a good set of conditions has been found for the flotationtreatment of an ore, it is best to reco
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