1918.] 
The N.Z. Journal of Science and Technology. 
39 
The Concentration of Ores by Flotation. 
By D. M. Deane, Superintendent, Talisman Battery, Karangahake. 
(Paper read before the Karangahake School of Mines, 22nd May, 1917.) 
Prior to the advent of the flotation process all mechanical ore-concentrat¬ 
ing machines were built with the object of taking advantage of the differences 
in the specific gravity between the various mineral contents of an ore, 
and so separating the minerals of a higher specific gravity from those 
of a lower. The higher the specific gravity of a mineral the more easily 
and completely was concentration effected. 
Flotation is a process of separating not by specific gravity, but by 
making use of the well-known selective adhesiveness of oils and gases for 
mineral particles possessing metallic lustre. Separation is possible because, 
while there is mutual adhesion between oil or gas and lustrous metallic 
particles, quartz and other gangue minerals which do not possess a metallic 
lustre are only feebly adhesive to oil and gas, but strongly adhesive to 
water. In other words, in the presence of oil and water the lustrous metallic 
particles are not easily wetted, whereas the gangue particles are easily 
wetted. Just why this should be is not known. 
In the flotation processes many forces are brought into play; but the 
principles governing the whole why and wherefore of flotation are so little 
understood, and so little experimental work has been done to bring light 
to the subject, that at the present time no satisfactory reason can be given 
to clear up the many questions of doubt that exist. Inventors have 
been engaged in perfecting a workable process, but the theoretical part of 
it has been allowed to stand aside. But now that the practical side of 
flotation is a success the theoretical side will be attacked, and ere long 
we shall have conclusive and acceptable evidence as to the physical laws 
governing the process. 
When ore crushed to the proper degree of fineness is violently agitated 
with water and oil in the presence of air a froth is formed. This froth, 
rising to the surface of the liquid, carries with it the sulphides and other 
metallic particles, while the gangue sinks to the bottom. Flotation in 
its latest meaning is therefore a process for the concentration of ores by 
froth-formation. Ore, water, oil, and gas are mixed so that they form an 
emulsion, and are all that is required for the success of the process. The 
ore is crushed to the necessary fineness in order to liberate the mineral 
from the gangue. It is then mixed with water in the proportion of from 
1 to 1, to 7 or 8 to 1, and violently agitated with from Jib. to Jib. of oil 
per ton of ore in the presence of air. This agitation produces the froth, 
which carries with it the sulphides ; and all that is necessary is a suitable 
means of removing the froth as it forms at the surface. The froth may 
be from 1 in. to 1 ft. thick. The amount of oil used has been reduced to a 
fraction of a pound per ton, and the use of acid in latter-day work has 
been entirely done away with. 
Short History of the Process. 
In 1860 Haynes first discovered the selective action of oils for lustrous 
minerals, and in 1885 Carrie Everson showed that acid increased this so- 
called selective action. Bulk-oil flotation was patented by Elmore in 
1894, but was discarded in favour of his vacuum process in 1904. In 
1902 Potter and Delprat, acting independently, patented their processes. 
