2
QUARTZ SURFACE PROPERTIES
Two surface properties that are important when consid-
ering dust suppression are the hydrophobicity/ hydro-
philicity of the particle surfaces and the surface charge.
Hydrophobicity is a measure of the wettability of a surface
and is often measured using contact angle techniques. In
the sessile drop technique, a drop of water or surfactant or
other chemical solution is placed on the surface of a pol-
ished piece of material. If the droplet spreads, it gives a low
value for contact angle and indicates the ease of wetting the
surface, which is a requirement for the application of dust
suppressants. An alternative technique, the captive bubble
technique, places the specimen in the liquid and an air bub-
ble is applied to the surface with the angle of contact being
measured. Contact angle values for quartz can be found in
the literature as shown in Table 2. Compared to values for
known hydrophobic materials, like high rank coal, these
values are low and would represent surfaces that are hydro-
philic or wettable.
Another surface property that is important is the zeta
potential or surface charge. This affects the interaction
between particles in a slurry, with highly charged parti-
cles (either negative or positive) repelling each other and
oppositely charged particles being attracted to each other.
Another phenomenon that can be investigated using the
zeta potential technique is spontaneous flocculation when
the surface charge becomes close to zero. This is rapid when
the surface charge is 0 to ±5 mV and can be considered
strong even at ±25 mV. This change in surface charge can
occur in the presence of different ions in solution, meaning
that it is critical to assess surface charge, as well as hydro-
phobicity, using water from the site that is being evaluated.
Some examples of zeta potential measurements for quartz
from the literature are given in Figure 1 (20, 21, 22). The
quartz surface charge is generally negative across the entire
pH range shown. This will affect the type of chemical that
can be used as a surfactant as some of these chemicals also
have ions that carry a charge (cationic being positively
charged, anionic being negatively charged, etc.).
HOW SURFACTANTS WORK
Surfactants are “surface active agents.” They reduce the sur-
face tension of water, allowing it to spread over the surface
of a particle more easily, wetting the particle. Finer droplets
of water can be produced to increase the likelihood of par-
ticle-droplet contact in a spray or foam application. The use
of surfactants allows for a residual dust suppression effect
as water has no additional effect once it is evaporated (23).
Studies estimate a 50 percent reduction in water require-
ments with the improved efficiency associated with the use
Table 1. Silica as an accessory phase in common
commodities (1)
Commodity Type of Silica
Antimony Quartz
Bauxite Quartz
Beryllium Quartz
Cadmium Quartz, jasper, opal, chalcedony
Concrete Quartz
Clay Quartz
Copper Quartz
Crushed stone Quartz
Diatomite Quartz
Dimension stone Quartz
Feldspar Quartz
Fluorite Quartz
Garnet Quartz
Germanium Quartz
Gold Quartz
Gypsum Quartz
Industrial sand Quartz
Iron ore Chert, quartz
Iron oxide pigment Chert, quartz, opal
Lithium Quartz
Magnesite Quartz
Mercury Quartz
Mica Quartz
Perlite Opal, quartz
Phosphate rock Quartz, chert
Pumice Obsidian
Pyrophyllite Quartz
Sand and gravel Quartz
Selenium Quartz
Silicon Quartz
Silver Quartz, chert
Talc Quartz
Tellurium Quartz
Thallium Quartz, chert, chalcedony, opal
Titanium Quartz
Tungsten Quartz
Vanadium Quartz, opal
Zinc Quartz, chert, chalcedony, opal
Zircon Quartz
Table 2. Contact angle values of quartz from various sources
(15, 16, 17, 18)
Contact Angle Source
27.8–50.3 Deng et al. (15)
35 Szyszka (16)
43 ± 2 Kowalczyk (17)
26.8 Janczuk and Zdziennicka (18)
26.15 Xie et al. (19)
QUARTZ SURFACE PROPERTIES
Two surface properties that are important when consid-
ering dust suppression are the hydrophobicity/ hydro-
philicity of the particle surfaces and the surface charge.
Hydrophobicity is a measure of the wettability of a surface
and is often measured using contact angle techniques. In
the sessile drop technique, a drop of water or surfactant or
other chemical solution is placed on the surface of a pol-
ished piece of material. If the droplet spreads, it gives a low
value for contact angle and indicates the ease of wetting the
surface, which is a requirement for the application of dust
suppressants. An alternative technique, the captive bubble
technique, places the specimen in the liquid and an air bub-
ble is applied to the surface with the angle of contact being
measured. Contact angle values for quartz can be found in
the literature as shown in Table 2. Compared to values for
known hydrophobic materials, like high rank coal, these
values are low and would represent surfaces that are hydro-
philic or wettable.
Another surface property that is important is the zeta
potential or surface charge. This affects the interaction
between particles in a slurry, with highly charged parti-
cles (either negative or positive) repelling each other and
oppositely charged particles being attracted to each other.
Another phenomenon that can be investigated using the
zeta potential technique is spontaneous flocculation when
the surface charge becomes close to zero. This is rapid when
the surface charge is 0 to ±5 mV and can be considered
strong even at ±25 mV. This change in surface charge can
occur in the presence of different ions in solution, meaning
that it is critical to assess surface charge, as well as hydro-
phobicity, using water from the site that is being evaluated.
Some examples of zeta potential measurements for quartz
from the literature are given in Figure 1 (20, 21, 22). The
quartz surface charge is generally negative across the entire
pH range shown. This will affect the type of chemical that
can be used as a surfactant as some of these chemicals also
have ions that carry a charge (cationic being positively
charged, anionic being negatively charged, etc.).
HOW SURFACTANTS WORK
Surfactants are “surface active agents.” They reduce the sur-
face tension of water, allowing it to spread over the surface
of a particle more easily, wetting the particle. Finer droplets
of water can be produced to increase the likelihood of par-
ticle-droplet contact in a spray or foam application. The use
of surfactants allows for a residual dust suppression effect
as water has no additional effect once it is evaporated (23).
Studies estimate a 50 percent reduction in water require-
ments with the improved efficiency associated with the use
Table 1. Silica as an accessory phase in common
commodities (1)
Commodity Type of Silica
Antimony Quartz
Bauxite Quartz
Beryllium Quartz
Cadmium Quartz, jasper, opal, chalcedony
Concrete Quartz
Clay Quartz
Copper Quartz
Crushed stone Quartz
Diatomite Quartz
Dimension stone Quartz
Feldspar Quartz
Fluorite Quartz
Garnet Quartz
Germanium Quartz
Gold Quartz
Gypsum Quartz
Industrial sand Quartz
Iron ore Chert, quartz
Iron oxide pigment Chert, quartz, opal
Lithium Quartz
Magnesite Quartz
Mercury Quartz
Mica Quartz
Perlite Opal, quartz
Phosphate rock Quartz, chert
Pumice Obsidian
Pyrophyllite Quartz
Sand and gravel Quartz
Selenium Quartz
Silicon Quartz
Silver Quartz, chert
Talc Quartz
Tellurium Quartz
Thallium Quartz, chert, chalcedony, opal
Titanium Quartz
Tungsten Quartz
Vanadium Quartz, opal
Zinc Quartz, chert, chalcedony, opal
Zircon Quartz
Table 2. Contact angle values of quartz from various sources
(15, 16, 17, 18)
Contact Angle Source
27.8–50.3 Deng et al. (15)
35 Szyszka (16)
43 ± 2 Kowalczyk (17)
26.8 Janczuk and Zdziennicka (18)
26.15 Xie et al. (19)