The flotation process by Rickard Thomas Arthur 1864-

Author:Rickard, Thomas Arthur, 1864- [from old catalog] ed
Language: eng
Format: epub
Tags: Ore-dressing
Publisher: San Francisco, Mining and scientific press
Published: 1916-03-25T05:00:00+00:00

Fig. 38.

This case, as well as the one illustrated in Fig. 36, would allow of the air bubbles becoming completely covered with oiled mineral.

Other phases are possible, but these are given to show how very feasible it is to get an explanation of flotation in terms of inter-facial tensions.

In an investigation conducted by the Minerals Separation, the 'contact angle' of various minerals with water was examined to find at what angle the mineral had to come in contact with a water surface before it was wetted and could sink.^ A glance at Clerk MaxweU's

8H. L. Sulman, Trans. Inst. M. & M., 1912.

famous paper on * Capillarity/ upon which Reinders' work is based, will suggest immediately the explanation of a contact angle, and that it is the result of a certain equilibrium of inter-facial tensions of air, water, and solid. Valentiner® has likewise investigated the contact angle and its hysteresis under certain conditions and has connected it very definitely with capillary phenomena. There can be no doubt that there is a close parallelism between the angle of hysteresis of the contact angle and the ability of a mineral to float. But if we go no further than to observe the parallelism we cannot designate the statement of the parallelism as a theory, although we might be able to predict by its means whether a mineral would float.

To go into this a little farther, and indeed along the line suggested by Mr. Durell, we ought to consider the properties of the surface layers of the substances involved. For example, the plane surface of water in contact with air is known to have considerably different properties from the inner bulk of the water. In Fig. 39 the film is

AIR

Fig. 39.

shown magnified in thickness. It acts like a tightly stretched elastic skin, due to what we have long called a 'surface tension' of 81 dynes per centimetre, as is usually given in text-books. (This means that for a strip of the surface film one centimetre wide, a longitudinal tension of 81 dynes has been measured at ordinary temperatures, and there is-a definite tension for each temperature.) This tension of the surface film is one of its most commonly known properties, but some other interesting points about it are given in the following:

Its thickness, varying with temperature and other conditions, has been estimated^^ to be all the way from 4 X 10 *^ to 10 ^ cm. Its density averages 2.14 as compared with 1 for bulk water, although it is doubtless more dense at the immediate surface next to the air and gradually

9'A Theory of Flotation/ Metall und Erz, 11:455, 1914. lophilosophical Magazine, 20:502, 1910.

i

shades off into that of bulk water. This consideration probably explains the wide variation in the results of the measurement of the thickness, as one method might be less delicate than another and hence not take account of some of the layers of the film that are nearly bulk water in their properties. This average density, however, is illustrative of

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