Chemistry Reference
In-Depth Information
adsorb on the surfaces of pigment particle and ink droplets, causing them to become
very hydrophobic. Air is then bubbled through the slurry. As the bubbles rise
through the system, they become preferentially attached to the hydrophobic pig-
ment and ink particles, acting like lifejackets and causing the particles to rise to
the surface. At the surface they are skimmed off and separated from the cellulose
slurry.
1.3.7. Mining and Ore Flotation
As just mentioned, the addition of the proper surfactant to a dispersion can produce
a situation in which the solid particles, having a specific gravity much greater that
that of water, can be made to float to the top and be easily (relatively speaking)
separated from the aqueous phase. In the deinking mentioned above, there is no
particular interest in being selective with respect to what is removed. It is essen-
tially an ''all out'' proposition. In the mining industry the situation is quite
different.
The flotation process has been important in mining for much longer than has
deinking. In many instances, the desired mineral is present in small amounts that
would be difficult or impossible to isolate and process while still ''mixed'' with the
bulk of the mined rock. In that industry, therefore, it is necessary to have a more
selective flotation process in which the desired mineral can be separated from the
bulk of the ore in a continuous and relatively inexpensive process. Because different
minerals tend to have slightly different surface properties, especially with regard to
electrical charge characteristics, it is possible (with luck and perseverance) to
design or formulate a surfactant system that will preferentially ''float'' a specific
class of mineral while having little effect on other materials present. The selective
surfactant or ''collector'' formulation allows the desired mineral to be skimmed
from the top of the foaming slurry and thereby concentrated. The unwanted mate-
rial can then be further processed or disposed of as slag.
While the theory of the adsorption of surfactants onto solid surfaces is highly
developed and well understood in ideal systems, the reality of the universe is
that in such complex multicomponent systems as mining ores, theory soon runs
out of steam and success ultimately depends on hands-on laboratory and field trials,
intuition, and art (or perhaps black magic).
Surfactants are also becoming more important in the coal mining industry. Aside
from flotation processes, they are also employed as binders for the suppression of
coal dust, and as dispersal aids and antifreezes for coal slurries that are pumped
through pipelines.
1.3.8. Metal-Processing Industries
Surfactants are as important to the metal processing as to the mining industry. In
order to perform as needed, metal surfaces must be cleaned and freed from deposits
of oxides, oils, and other contaminants. Welding, painting, and other machining
and surface treatments require a well-prepared surface. Even before that stage of
