Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Dust Suppression and Reduction of Surface Oxidation for Mineral Agglomerates
The present invention relates to a composition consisting essentially of a
mineral substrate
and a dust suppressant, which is adhered to the surface of the mineral
substrate, and to
methods of reducing dust generation of a mineral substrate by applying a dust
suppressant
to the surface of the mineral substrate.
WO 03/052149 Al describes iron ore pellets having incorporated saturated
hydrocarbons
such as paraffin oils or synthetic oils in order to make the iron ore pellets
resistant to
abrasion, sticking, degradation and emission of dust. The saturated
hydrocarbons are
incorporated into the iron ore pellet at 250 C.
WO 2004/099452 Al describes iron ore pellets, wherein the surface layer of the
pellets is
coated with polymer or synthetic oils. The amount of polymer or synthetic oil
is 0.14 to 1% by
weight per weight pellet. The polymer or oil is applied to the pellets at 250
to 300 C. The
addition of the polymer or oil is best accomplished through the preparation of
the polymer or
oil diluted in 50 to 80% water.
The disadvantages of dust suppressants described in WO 03/052149 Al and
WO 2004/099452 Al are they are saturated hydrocarbons or synthetic oils that
are not very
convenient to work with. They can be toxic and flammable and thus represent a
health risk
and they are usually not biodegradable and thus can cause environmental
problems when
spilt or lost due to wind carry.
Therefore, it is an object of this invention to provide a composition
consisting essentially of a
mineral substrate and a dust suppressant, which is adhered to the surface of
the mineral
substrate, wherein the dust suppressant is biodegradable and does not
constitute a health
risk.
This object is solved by the composition according to claim I and the method
according to
claim 7.
The dust suppressant of WO 2004/099452 Al has the additional disadvantage that
it is
applied to the iron ore pellets as a preparation diluted in 50 to 80% water.
This aqueous dust
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suppressant preparation causes spitting problems when applied to the hot iron
ore pellets as
it instantenously boils.
Therefore, it is a further object of this invention to provide a more
convenient method of
applying dust suppressants.
This object is solved by the method according to claim 9.
The composition of the present invention consists essentially of a mineral
substrate and a
dust suppressant, which is adhered to the surFace of the mineral substrate,
wherein the dust
suppressant is a natural or synthetic triglyceride or a mixture comprising
triglycerides.
Triglycerides are esters of glycerine and fatty acids. In a preferred
embodiment the
triglycerides are natural such as soybean oil, sunflower oil, coconut oil,
paimitic oil,
cottonseed oil, castor oil etc. Further triglycerides are described e.g. in
Fbmpp Lexikon
Chemie, 10th edition, p. 1320 f., Georg Thieme Verlag. In a particular
preferred embodiment
the triglyceride is selected from the group consisting of soyabean oil,
sunflower oil, coconut
oil, paimitic oil, cottonseed oil, and castor oil and mixtures thereof.
The inventive method can be applied to all mineral substrates, which can be a
source of
dust. In particular, all known ore pellets can be used, preferably iron-ore
pellets are used.
The amount of dust suppressant usually can be chosen in the range of from 0.05
to 2.5% by
weight per weight of the mineral substrate. Preferably it is chosen in the
range of from 0.1 to
1.5% by weight per weight of the mineral substrate.
The dust suppressant can be adhered to at least 50% of the surface of the
mineral substrate.
Preferably it is adhered to at least 80% of the surface of the mineral
substrate and more
preferably to at least 90%.
The flrst method of the present invention of reducing dust generation of
mineral substrates
comprises applying a dust suppressant to the surface of a mineral substrate
having a
temperature in the range of from 150 to 250'C in an amount in the range of
0.05 to 2.5 % by
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weight per weight of mineral substrate, wherein the dust suppressant is a
natural or synthetic
triglyceride or a mixture comprising triglycerides.
Preferably, the mineral substrate is an ore pellet, preferably an iron-ore
pellet.
Generally, the dust suppressant is of ambient temperature when applied to the
hot pellets,
but, if desired, the dust suppressant may also be of a temperature as high as
the
temperature of the hot pellets.
The dust suppressant may be applied by well-known methods in the art such as
spraying or
dipping etc., spraying being preferred.
The process can be carried out batch-wise or continuously, e.g. using a
conveyor belt on
which the mineral substrates or pellets are sprayed and then further cooled
down or
transported to its storage site.
Usually the thus treated pellets are cooled down to ambient temperature and
then can be
stored, transported or further treated as desired.
Also part of the invention is the use of triglycerides as dust-suppressants.
The second method of the present invention of reducing dust generation of
mineral
substrates comprises applying a dust suppressant to the surface of a mineral
substrate
having a temperature in the range of from 100 to 250 C in an amount in the
range of 0.05 to
2.5% by weight per weight of mineral substrate, wherein the dust suppressant
is applied in
the form of a nonaqueous foam.
The dust suppressant can be a liquid nonvolatile hydrocarbon, a nonvolatile
polyol, a
synthetic oil or a natural or synthetic triglyceride or mixtures comprising
liquid nonvolatile
hydrocarbons, nonvolatile polyol, synthetic oils or triglycerides. Exampes of
liquid nonvolatile
hydrocarbons are petroleum oil and petroleum oil products such as mineral oil.
Examples of
mineral oils are fuel oils, e.g. gasoline, diesel fuel, heating oil and
kerosene, and lubricating
oils. Examples of nonvolatile polyols are glycol and polyethyleneglycol. An
example of a
synthetic oil is silica oil.
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Preferably, the dust suppressant is a natural or synthetic triglyceride or a
mixture comprising
triglycerides. More preferably, the dust suppressant is a natural triglyceride
or a mixture
comprising a natural triglyceride. Examples of natural triglycerides are given
above. Most
preferably, the dust suppressant is selected from the group consisting of
soyabean oil,
sunflower oil, coconut oil, paimitic oil, cottonseed oil and castor oil or
mixtures thereof.
Preferably, the mineral substrate has a temperature in the range of from 150
to 250 C.
The dust suppressant is preferably applied in the presence of a surfactant.
Examples of
suitables surfactants are HCF-740, which is a mixture of fluorosurfactants and
hydrocarbon
solvent, HCF-730, which is a nonionic mixture of silane surfactants, HCF-720,
which is a
nonionic mixtuture of silane surfactants and fluorosurfactants and HCF-710,
which is a
nonionic mixture of silane surfactants and sulfonic acids, all sold by
Clearwater.
The surfactant can be used in amounts of 0.2 to 5% by weight per weight of
dust
suppressant. Preferably, it is used in amounts of 0.5 to 2.5% w/w and more
preferably in
amounts of 1 to 2% w/w.
The dust suppressant nonaqueous foam cah, be applied to the mineral substrate
by dipping
the mineral substrate onto the surface of the foam or by passing it through
the foam, which
can be either a static or moving mass. Alternatively, the foam can be applied
to a moving
mass of mineral substrate, e.g. at a transfer point on a conveyor belt.
Generally, the dust suppressant nonaqueous foam is of ambient temperature when
applied
to the hot pellets, but, if desired, the dust suppressant may also be of a
temperature as high
as the temperature of the hot pellets.
Preferably, the mineral substrate is an ore pellet, preferably an iron-ore
pellet.
Also part of the invention are dust suppressants in the form of a nonaqueous
oil. Dust
suppressant is as defined for the second method of reducing dust generation of
mineral
substrates.
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The dust suppressant nonaqueous foam of the present invention has the
advantage that it
does not cause spitting when applied to hot mineral substrates. In addition,
it avoids the
enhalation risks connected with spraying a dust suppressant and also allows an
enhanced
control of the amount of adhered dust suppressant and a better distribution of
the dust
suppressant on the pellets, when very low amounts of adhered dust suppressant
are desired.
Examples
Example 1:
1.1. Preparation of a composition of iron ore pellets and soyabean oil using
sprayed oil
40 plant-fired spherical iron ore pellets, (diameter from 10 to 14 mm; total
weight 133.92 g)
are heated to 200 C for 1 hour (in order to simulate the temperature after
leaving the
furnace). The hot pellets are transferred to a wire basket and sprayed with
soyabean oil,
which is at ambient temperature, six times, the total amount of sprayed oil
being 1.59 g or
1.19% by weight per total weight of the pellets. The contents of the wire
basket are then
gently agitated, by hand, for a few seconds to increase transfer of the oil
fiom surface to
surface. Thereafter the pellets are further cooled down to ambient temperature
without
further agitation.
1.2. Dust measurement
35 of the thus treated pellets are then selected, weighed (111.94 g) and
afterwards
transferred to a sealable metal tube (6.5 cm diameter by 17.5 cm length). In
order to simulate
handling of the pellets the tube and its contents are then tumbled, end-to-
end, in a Roaches
"Dye Bath" for 2 hours at ambient temperature. Thereafter, the contents of the
tube are
transferred on a 500E..rn sieve, where the fine material is separated from the
remaining pellets.
The final weight of these 35 pellets is 110.41 g, and the fine material
(<500[xn), is 1.53 g or
(1.53/111.94)x100 = 1.37% by weight per weight of the untumbled pellets.
1.3. Pellet Surface Observation
A colour change from grey (plant fired pellet) to red (rustic) is an
indication of surface
oxidation. This change is quantifiable from a visual perspective (% surface
coverage). The
treatments noted here infer that surface oxidation is reduced when soyabean
oil is used
instead of water.
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Example 2:
2.1. Preparation of a composition of iron ore pellets and sunflower oil using
sprayed oil
Example 1.1 is repeated, except that sunflower oil is used instead of soybean
oil, the number
of pellets is 35, the total weight of the pellets is 130.79 g and the amount
of oil is 0.21 % by
weight per weight of pellets.
2.2. Dust measurement
Example 1.2. is repeated. The total weight of fine material is 0.98% by weight
per weight of
the untumbled pellets.
2.3. Pellet Surface Observation
A colour change from grey (plant fired pellet) to red (rustic) is an
indication of surface
oxidation also infer that surface oxidation is reduced when sunflower oil is
used instead of
water.
Comparative example 1:
Example 1 is repeated, however the 35 pellets employed (total weight 129.70 g)
are not
treated with a dust suppressant. The percentage of fine material is 5.56% by
weight per
weight of untumbled pellets.
Example 3:
3.1. Preparation of a composition of iron ore pellets and soybean oil using
foamed oil
Nitrogen is bubbled in a mixture of 100 mL soyabean oil and 2 mL HCF-740, a
mixture of
fluorosurfactants and hydrocarbon solvent, which is sold by Clearwater in
order to generate a
stable foam. 35 plant fired spherical iron ore pellets (6.5 cm diameter by
17.5 cm length) are
heated to 200 C for 1 hour (in order to simulate the temperature after leaving
the furnace).
The hot pellets are transferred to a wire basket and dipped onto the surface
of the foamed
oil, which has ambient temperature. The total amount of oil being adhered to
the pellets is
measured and the percentage (weight adhered oil/weight pellets)x100 is
calculated. The
contents of the wire basket are then gently agitated, by hand, for a few
seconds to increase
transfer of the oil from surface to surface. Thereafter the pellets are
further cooled down to
ambient temperature without further agitation.
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3.2. Dust measurement
The thus treated pellets are weighed and transferred to a sealable metal tube
(6.5 cm
diameter by 17.5 cm length). In order to simulate handling of the pellets the
tube and its
contents are then tumbled, end-to-end, in a Roaches "Dye Bath" for 2 hours at
ambient
temperature. Thereafter, the contents of the tube are transferred on a 4 mm
sieve, where the
fine material (<4 mm) is separated from the remaining pellets. The weight of
the fine material
is measured and the percentage (weight fine material/weight untumbled
pellets)x100 is
calculated.
Example 4:
Preparation of a composition of iron ore pellets and paraffin oil using foamed
oil
Example 3 is repeated except that SN 150, a paraffin oil, is used instead of
soyabean oil, and
I mL HCF-740 instead of 2 mL.
Comparative example 2:
Example 3 is repeated, however the 35 pellets employed are not treated with a
dust
suppressant.
Example Adhered oil Fine material Pellet surface
[%(w oil/w pellet)] [%(w fine material/w observation
untumbled pellet)]
Comparative example 2 0 5.72 Red surface
Example 3 0.22 1.54 Gray surface
Example 3 0.26 1.10 Gray surface
Example 3 0.29 0.77 Gray surface
Example 4 0.29 1.4 Gray surface
Example 4 0.30 1.71 Gray surface
Example 4 0.31 1.56 Gray surface
Example 4 0.37 1.47 Gray surface
Example 4 0.46 1.27 Gray surface
Example 4 0.49 1.47 Gray surface
Example 4 0.58 0.90 Gray surface
Example 4 1.04 0.91 Gray surface
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Table 1: Dust measurement and pellet surface observation of iron ore pellets
treated with
foamed oils.
The results show that oils can be successfully applied as a foam to reduce
dust generation
and surface oxidation of iron ore pellets. Soyabean oil was more effective
than paraffin oil at
equivalent dosages.
