Note: Descriptions are shown in the official language in which they were submitted.
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_
PROCESS FOR R~COVERING ~INE~AL~ AND COMPO8ITION~
FOR U8B IN ~HI8
The invention relates to an improved composition of
dialkyl thionocarbamate collectors and use of this
composition in a process of beneficiation of mineral-
cont~;ni ng materials.
It is well known to beneficiate crude mineral ores and
o1_her mineral-containing materials by froth flotation
p]ocesses. These proce~e~ are used to separate a desired
mineral from unwanted minerals which are unavoidably
extracted in the mining operation with the desired mineral.
It i~; also possible to use froth flotation systems to
separate two or more desired minerals from a single crude
ore or other mineral-containing material.
In a froth flotation process the mineral-containing
material in particulate form is formed into an aqueous
pulp. If the mineral-containing material is a crude ore it
i~ generally ground to a particle size small enough that
discrete particles of the required minerals are present.
Some mineral-containing materials, such as coal, are
particulate when they reach the flotation stage of
processing.
The pulp is subjected to flotation to induce
preferential separation of the particles in the pulp to
form Reject and Accept fractions. Usually the Accept
fraction is the surface fraction formed during the
flotation process.
Dialkyl thionocarbamate collectors are often included
in the pulp, either by addition directly to the aqueous
pulp or by addition to the mineral-containing material
during grinding, if used, to enhance separation.
Other collector materials are known. Water-soluble
collectors are generally most conveniently added to the
aqueous pulp of ground ore in the form of a solution, at
around 5 to 10% concentration. Generally they are sold in
the solid form or, less commonly, as a concentrated
solut:ion, and diluted on site. It is also known to use
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some water-insoluble materials as collectors in the form of
an oil-in-water emulsion.
Dialkyl thionocarbamate collectors are normally water-
insoluble and are usually added neat, either singly or as
a blend with other collectors. This is accepted as t
generally convenient. In particular neat dialkyl
thionocarbamate collector can be added at the grinding
stage, although it is also known to add it to the aqueous
pulp. It is generally accepted within the industry that
this form of application gives adequate results, in
particular where neat collector is added at the grinding
stage.
Aqueous compositions containing certain types of
thionocarbamate collector have been described in the
literature. For instance in US 3,925,218 and US 4,040,950
it is stated that N-alkyl 0-alkyl thionocarbamate can be
caused to dissolve in an aqueous solution of a
dialkylthiophosphate salt. CA 1,105,156 describes
dissolution of N-alkyl 0-alkyl thionocarbamate in an
aqueous solution of dialkyldithiophosphinate. Such systems
provide an alternative method of dosing the water-insoluble
dialkylthionocarbamates. However the water-insoluble
dialkylthionocarbamate must be added in combination with
the water-soluble collector which allows it to be
solubilised in the aqueous solution.
In AU 8543817 a composition is described which
comprises a phosphorodithioic compound, a
dialkylthionocarbamate and optionally an alkyl xanthogen
alkyl formate. This mixture is descri~ed as being ~water-
emulsifiable~. However, the patent suggests that onlydispersion directly into water is used, and continuous
agitation of the storage facility is required to maintain
the water-insoluble mixture in dispersion. It is also
indicated that the presence of a phosphorodithioic compound
is essential to render the dialkylthionocarbamate
dispersible. Such a system requires rather long periods to
achieve efficient mixing, necessitates a make-up tank and
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.
agitation facilities and places restrictions on the point
of addition of the collector.
It is also known, for certain other water-insoluble
collectors, particularly those used in the coal industry,
to bl~nd these with emulsifiers before adding this blend to
the flotation stage. This is believed to assist in
distributing collector onto the surface of coarse
particles, rather than fine particles only.
A specific system of this general type for use in
proce~sing of metallic mineral ores is demonstrated in U.S.
4,211,644, in which mercaptan collector is mixed with an
emulsifying agent before addition to the pulp, in order to
impro~Je dispersion of the mercaptan into the pulp. The
mercaptan may be used together with other collectors which
include thionocarbamates, but these other collectors are
not included in the mixture of mercaptan and emulsifier.
A similar system is described in U.S. 4,526,696, in
which certain collectors are provided as a mixture with
~urfactant and cosurfactant. This mixture is said to
render the collector "microemulsifiable", that is it forms
a microemulsion on addition to the mineral pulp. The
collectors for which this system is said to be suitable are
mercaptans, thioethers and polysulphides. It is suggested
that handling can be facilitated by including water in the
ccmposition, although it is not indicated whether or not
the rlesulting aqueous composition is an emulsion of any
type.
The present invention is concerned with improvement of
the performance of thionocarbamate collectors specifically.
For instance it would be desirable to improve the recovery
and selectivity performance of these collectors.
~ccording to the invention we provide a process of
separating minerals from a mineral-containing material by
froth flotation comprising
i-orming an aqueous pulp of particles of the mineral-
containing material,
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subjecting the pulp to flotation in the presence of
one or more dialkyl thionocarbamate collectors,
allowing preferential separation of the particles in
the pulp to occur to form Reject and Accept fractions
and separating the Reject and Accept fractions,
characterised in that dialkyl thionocarbamate
collector is added to the mineral-containing material or
pulp in the form of an oil-in-water emulsion comprising
dialkyl thionocarbamate collector in an amount of 5 to
95wt~, emulsifier in an amount of 1 to 30wt% and water in
an amount of 5 to 95wt%, based on total emulsion.
The collector emulsion is also a novel product in
itself. Thus the invention also provides a collector
composition which is an emulsion of dialkyl thionocarbamate
collector in water and which comprises 5 to 95wt% dialkyl
thionocarbamate collector, 1 to 30wt% emulsifier and 5 to
95wt% water, based on total emulsion.
We find that the application of dialkyl
thionocarbamate collector in the emulsion form produces
surprising improvements in performance of these collectors.
Recovery of desired minerals can be improved, as can
selectivity for the desired mineral over undesired
minerals. We also believe that the efficiency of these
collectors can be improved. That is, lower doses of the
collector in emulsion form would produce equivalent or
better results than higher doses of the collector in neat
form.
In particular we find that the dialkyl thionocarbmate
emulsions of the invention give improved results in
comparison with mixtures of thionocarbamate and emulsifier,
and in comparison with neat dialkyl thionocarbamate added
simultaneously with a mixture of emulsifier and water.
We find additionally that the use of dialkyl
thionocarbamate collector in the emulsion form provides a
convenient method of diluting the collector and thus
provides for greater accuracy of dosage. Dosage can be at
any convenient point in the flotation process, including
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t]he flotation chamber. Emulsions of collector can be
stored and used without the need for specialised storage
facilities, which are required according to AU 8543817.
The process and product of the invention require a
dialkyl thionocarbamate collector. Any water-insoluble
dialkyl thionocarbamate collector may be used which is
appropriate for the beneficiation of the crude ore being
processed. Dialkylthionocarbamates have the formula
R20C ( S ) NHR1
lo R1 and R2 are alkyl groups of any suitable chain
length but are preferably C1 to C6 alkyl groups, more
preferably C1 to C4 alkyl groups. Ethyl and propyl,
especially isopropyl, groups are preferred. Particularly
preferred dialkylthionocarbamates have the above formula in
which one of R1 and R2 is isopropyl and the other is ethyl.
Especially preferred is isopropyl ethylthionocarbamate (R1
is ethyl and R2 is isopropyl). Mixtures of dialkyl
thionocarbamates may be used.
~ dialkyl thionocarbamate collector is normally water-
insoluble, that is it will generally have solubility in
water of 4g collector per lOOg deionised water or below,
often lg collector per lOOg deionised water or below.
The collector emulsion contains one or more dialkyl
thionocarbamates in a total amount in the range around 5 to
around 95%, preferably around 20 to around 80%, more
preferably around 35 to around 70, more preferably up to
55%, often around 45%, by weight of emulsion.
The emulsion contains emulsifier in amounts in the
range from around 1 to around 30~, preferably around 1 or
2 to around 20~, often around 10%, by weight of emulsion.
Standard surfactant emulsifiers may be used, for
insta]nce alkoxylated alcohols and fatty acids, ethoxylated
fatty amines and fatty diamines, quaternary fatty ammonium
compounds, alkyl benzenesulphonates and alkyl sulphates and
mixtures thereof. Preferred emulsifiers are ethoxy (20)sorbitan monolaurate and ethoxy (100) stearic acid, in
particular a 50:50 (weight) blend of these.
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.
The remainder of the emulsion is usually water. This
is generally present in an amount of from around 5 to 95%,
often around 20 to around 80%, preferably around 35 to
around 55%, often 45% or less by weight of the emulsion.
The ratio of dialkyl thionocarbamate to water in the
emulsion is preferably from 9:1 to 1:9, more preferably
from 3:1 to 1:3, most preferably from 2:1 to 1:2, often
around 1:1.
The ratio of dialkyl thionocarbamate to emulsifier in
the emulsion is preferably below 9:1, and can be below 8:1
or below 5:1.
In this specification we include within the term
"emulsion" systems in which the oily (collector) domains
are of any size, and in particular we include systems of
the type which are often referred to as microemulsions.
The dialkyl thionocarbamate emulsion of the invention
is preferably formulated so as to be stable, and in
particular it preferably remains stable (that is, the
emulsion does not break and separate3, without the need for
continuous agitation, for at least half an hour, preferably
at least 24 hours, more preferably at least one month and
even as long as 3 months or more, for instance at least 12
months.
Some instability can be tolerated however provided the
emulsion does not freeze on storage and provided it can be
agitated to form a new emulsion easily before addition to
the process.
The emulsion may contain components in addition to the
water, emulsifier and dialkyl thionocarbamate collector.
For instance it may contain water-soluble collector
materials in the aqueous phase. Preferably any such
materials are not such that they are cosolvents for the
water-insoluble collector or collectors. That is, they do
not induce solubility of the water-insoluble collector in
the aqueous phase. It may, alternatively or additionally,
contain other water-insoluble collector in minor amounts.
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Preferably however the emulsion consists essentially only
O:e water, emulsifier and dialkylthionocarbamate collector.
The dialkyl thionocarbamate emulsion can be prepared
using st~n~rd emulsion preparation techniques.
The dialkyl thionocarbamate emulsion, which can
comprise one or more additional types of collector, can be
used as the sole source of collector in the process.
Alternatively it may be used in combination with collector
provided in different forms. For instance it may be used
together with water-soluble collector in ac~eous solution
or water-insoluble collector added in the neat form.
Collector added in forms other than as an emulsion can be
added at any convenient stage of the separation process.
~mounts of dialkyl thionocarbamate emulsion and
collector in any other form if used are chosen to give a
total level of added collector which is in the range 2 to
3000 g/t, based on dry weight of the aqueous pulp of ground
ore, preferably 5 to 1500 g/t, often 10 to 200 g/t.
Preferably amounts of dialkyl thionocarbamate in these
ranges are used.
The collector emulsion itself is usually included in
a total amount of 2 to 4000 g/t, preferably 2 to 3000 g/t.
more preferably 5 to 1500 g/t, based on dry weight of the
pulp of ground ore.
~he mineral-containing material to be treated by the
froth flotation process is provided in particulate form.
Sc~me materials, such as crude mineral ores, are ground,
usual]Ly to a particle size small enough that discrete
particles of the individual minerals are produced. These
particles are usually of a size 80% below 150~m, often 80%
below 75~m. Grinding can be carried out by for instance
rod or ball milling.
~f desired, a portion of the collector emulsion can be
added to the ore at the grinding stage. Preferably however
substantially all of the collector emulsion is added to the
aqueous pulp. Crude ores are usually ground in the form of
a slurry of solids content around 40 to 70%.
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.
Materials such as coal are already in particulate form
when passing to flotation and do not require grinding.
Such materials passing to flotation usually have a particle
size of around 80% below about 750~m.
The particulate mineral material is formed into an
aqueous pulp. This requires adding water to materials such
as coal which do not re~uire grinding. For ground ores,
which are in the form of a slurry after grinding, further
water may be added if required. Solids content of the
aqueous pulp is usually from around 8 to 40~, often around
10 to 35%. Coal is usually subjected to flotation in the
form of an aqueous pulp of solids content around 10% and
ground mineral ores are often subjected to flotation in the
form of an aqueous pulp of solids content around 20 to
around 35%.
Collector emulsion can be added to the aqueous pulp.
It is also possible to include other collectors in other
forms, for instance in aqueous form, if these are required.
Other components which may be added to the pulp include
frothers, sulphidising agents, gangue depressants and pH
modifiers.
The aqueous pulp is then subjected to flotation,
usually by aeration and optionally agitation, in a
flotation ch;~ h-~r. As air bubbles travel through the
aqueous pulp to the surface the collector enhances the
natural tendency of selected minerals to adhere to the air
bubbles, usually by modifying the surface properties of the
particles of these selected minerals. The chosen minerals
then preferentially adhere to the air bubbles and are
carried to the surface of the pulp. If the selected
minerals are those which are required to be recovered, this
surface fraction is the Accept fraction, which can be
separated for further treatment if necessary. Alternatively
the selected minerals in the surface fraction may be those
which are not re~uired (the Reject fraction) and are
separated and dumped. Generally however it is the valuable
minerals which are floated and collected as the Accept
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_ . 9
fraction as a concentrate. Occasionally selectivity is
adequate after a single flotation. More commonly however
two or more sequential flotations are required before the
desired degree of ore refinement is obtained.
Two or more different collectors may be used in a
single process, either to improve selection of a single
mineral, or to allow separation from a single ore of two or
more different minerals.
The process of the invention may be used in the
beneficiation of any crude mineral ore, for instance those
of zinc, copper, lead and nickel (in the form of sulphides
or oxides), gold and silver and industrial minerals such as
apatite and fluorspar. It may be used for the extraction
o~ coal and graphite.
~5 The invention will now be illustrated with reference
to the following example.
~xample
A crude zinc-containing ore was air dried for two
days. It was then crushed and sieved at 500 ~m with the
oversize being returned to the jaw crusher. The below
500~m fraction was coned, quartered and riffled to produce
1 kg lots.
1 kg of ore, together with 540 cm of tap water, 250
gJtonne ZnS04 (10% wlv) and 7.5 g/tonne sodium isopropyl
xanthate (SIPX) (0.1% w/v), were added to a laboratory rod
mill and milled for 5.75 minutes to produce a particle size
of 63~ below 75~m. The milled sample was then transferred
to a 2.5 litre Denver flotation cell to await testing.
Initially a lead flotation procedure was carried out.
3 0 g/tonne SIPX (0.1% w/v) and 17.5 g/tonne (1 drop)
methyl isobutyl carbinol (MIBC) were added and conditioned
for 1 minute at 1,200 rpm. The air was turned on and the
froth produced was removed every alternate 10 second
interval over a 3 minute period to produce the first
concentrate. The air was turned off. 1.5 g/tonne SIPX
(0.1% w/v) and 17.5 g/tonne (1 drop) MIBC were added and
conditioned for 1 minute. Air was turned on and the froth
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~ .
produced was removed as before over a 3 minute period to
produce the second concentrate. Air was turned off . 1. 5
g/tonne SIPX (0.1% w/v) and 8.8 g/tonne (half a drop) MIBC
were added and conditioned for 1 minute. Air was turned on
and the froth produced was removed as above over a 4 minute
period to produce the third concentrate. Air was turned
off. Amounts of SIPX and MIBC the same as the last
addition were added and conditioned for 1 minute. Air was
turned on and the froth produced was removed as above over
a two minute period to produce a fourth concentrate. Air
was turned off. The same amounts of SIPX and MIBC as in
the last addition were added and conditioned for 1 minute.
Air was turned on and the froth produced was removed as
above over a two minute period to produce a fifth
concentrate. Air was turned off. The five concentrates
were individually filtered, dried and weighed for analysis.
The zinc flotation procedure was then carried out.
Pulp pH was adjusted to 10.5 with lime, Ca(OH)2. 375
g/tonne CUSO4 (10% W/v) was added and conditioned for 3
minutes. Air was turned on and the froth produced was
removed every alternate 10 second interval over a 2 minute
period to produce the first concentrate, Zn 1. Air was
turned off. Pulp pH was readjusted to 10.5 with lime.
20.1 to 20.2 g/tonne active potassium amyl xanthate (PAX)
in the form of a 1.0~ w/v aqueous solution and lO.0 to 10.1
g/tonne collector emulsion (product A, see below) and 17.5
g/t (1 drop) MIBC were added and conditioned for l minute.
Air was turned on and the froth produced was removed as
above over a 3 minute period to produce the second
concentrate, Zn 2. Air was turned off. Pulp pH was
readjusted to 10.5 with lime. Half the original addition
of product A (collector emulsion and PAX) was added
followed by 8.8g (half a drop) MIBC and then conditioned
for l minute. Air was turned on and the froth produced was
removed as above over a 3 minute period to produce the
third concentrate, Zn3. Air was turned off. Pulp pH was
readjusted to 10.5 with lime. Half the original addition
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- li
of product A (collector emulsion and PAX) was added
followed by 8.8 g (half a drop) MIBC and then conditioned
for 1 minute. Air was turned on and the froth removed as
above over a 3 minute period to produce the fourth
concentrate, Zn4. The four concentrates were lndividually
filtered, dried and weighed prior to analysis.
Concentrates Zn 1 and Zn 2 were analysed together.
I'he process was repeated with products B, C, D, E and
F, described below. The amounts specified refer to the
original addition between concentrates Zn 1 and Zn 2.
Product A: 20.1 to 20.2 g/tonne PAX + lO.o to
10.1 g/tonne of an emulsion containing
4 5 p a r t s b y w e i g h t
isopropylethylthionocarbamate, 45
parts by weight water and 10 parts by
weight emulsifier
Product B: 20.3 g/tonne PAX + 5.6 g/tonne of a
mixture of 45 parts by weight water
and 10 parts by weight emulsifier
Product C: 20.4 g/tonne PAX + 4.6 g/tonne neat
isopropylethylthionocarbamate
Product D: 20.1 to 20.2 g/tonne PAX + 4.5 to 4.6
g / t o n n e n e a t
isopropylethylthionocarbamate and,
added separately, 5.5 to 5.6 g/tonne
of a mixture of 45 parts by weight
water and 10 parts by weight
emulsifier.
Product E: 20.1 to 20.3 g/tonne PAX + 5.5 to 5.6
g/tonne of a mixture of 45 parts by
weight isopropylethylthionocarbamate
and 10 parts by weight emulsifier.
Product F: 20.1 to 20.2 g/tonne PAX.
The emulsifier system used was a 50/50 (wt/wt) blend
of ethoxy (20) sorbitan monolaurate and ethoxy (100)
stearic acid.
R~esults are shown in Tables 1 and 2 below.
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W O 97/25149 PCT/GB97/00071 - 12
o
~t
D ~ ~ ~ t
U~ ~ ~ t~ ~D tr~
~D t~ ~ c~ ~ t ~ t~
.
t~ ~
k IC~
t' ~ ~ O It~ o~
t:
~ ~ k '~
~ ~ -
~:: ~ + ~:
a
~ s
~t E~
o
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_ . 13
The above results show the surprising benefits of
using the invention (Product A). Product A shows excellent
zinc ~ecovery. In particular it shows excellent recovery
in the early stages of the flotation. In a commercial
s 5 flotal_ion process the speed with which acceptable
separation can be achieved i~ particularly important. The
S minute values (Zn 1 + Zn 2) are particularly illustrative
of this point. Product A shows excellent recovery and
selectivity (cumulative zinc recovery and cumulative zinc
10 gradel, respectively) at this stage and is superior in both
respects to all other products. In particular it is
superior to a simple blend of collector and emulsifier.
At the later 8 minute and 11 minute stages the product
of the invention shows recovery superior to all other
15 products. In addition, it does not undergo significant
reduct:ion in the selectivity achievable. Thus it can be
seen that the use of the invention allows achievement of
rapid recovery with high selectivity and, in the long term,
higher recovery combined with adequate selectivity. This
20 combination of features is not achieved with any of the
Products B to F.
]rt is particularly noticeable that the thionocarbamate
emulsiLon (in Product A) gives improved results in
comparison with Product E, which is a mixture of the
25 collector and emulsifier. This is particularly unexpected
in view of prior art suggestions to improve performance of
other types of collector by mixing them with emulsifier
alone. Addition of extra water together with the
thionocarbamate is again not as effective as the
30 thionocarbamate emulsion used in Product A. In particular,
Product D includes, simultaneously with but separately from
the thionocarbamate, amounts of water and emulsifier
equivalent to those included in Product A but gives
inferior results to those shown by Product A, in particular
35 in recovery values.
