Chemistry Reference
In-Depth Information
Liquid
Contact
Angle
Mineral
FIGure 5.14
Contact angle at a mineral particle and liquid interface.
Bubbles as needed for floatation are created by various methods. These may be by
Air injection
Electrolytic methods
Vacuum activation
In a laboratory experiment (Adamson and Gast, 1997), the following recipe may
be used. To a 1% sodium bicarbonate solution, add a few grams of sand. Further,
some acetic acid (or vinegar) will cause the bubbles of CO
2
produced to cling to the
sand particles and thus make these float to the surface. It must be mentioned that, in
wastewater treatment, the flotation method is one of the most important procedures.
When rocks in a crushed state are dispersed in water with suitable surfactants
(also called
collectors
in industry) to give stable bubbles an aeration, hydropho-
bic minerals will be floated to the surface by the attachment of bubbles, while the
hydrophilic mineral particles will settle to the bottom. The preferential adsorption of
the collector molecules on a mineral makes it hydrophobic.
Xanthates have been used for flotation of lead and copper. In these examples, it is
the adsorption of xanthane that dominates the flotation.
5.8.2 p
of l I S h I n g
of f
S
o l I d
S
u r f a c e S
The reflection of light from a smooth solid surface determines the degree of polish.
The industrial applications are many, considering the impact of design and appear-
ance on both sales and the product (cars, household appliances, furniture). A very
sensitive procedure for the determination of surface roughness has been to use atomic
force microscope (AFM; Birdi, 2003).
5.8.3
p
o W d e r S
(S
u r f a c e
T
e c h n o l o g y
)
The solid material when transformed into fine powder creates a new material
(regarding its surface properties and applications). The technology related to this
subject is very expansive (found in talcum powder, cement, the clay industry, etc.).
The Following areas of powder science are currently being investigated:
Formation and synthesis of particles by different procedures (e.g., grinding,
crushing, precipitation, etc.)
Modification of particles by agglomeration, coating, etc.
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