Note: Descriptions are shown in the official language in which they were submitted.
1
"A Method for Improving Selectivity and Recovery in the Flotation of Nickel
Sulphide Ores that Contain Pyrrhotite by Exploiting the Synergy of Multiple
Depressants"
This application claims priority from U.S. Patent Application No.
61/623,459, titled "A Method for Improving Selectivity and Recovery in the
Flotation of Nickel Sulphide Ores that Contain Pyrrhotite by Exploiting the
Synergy
of Multiple Depressants," filed on Apr. 12, 2012.
FIELD OF INVENTION
The present disclosure relates to a method of selective froth flotation of
sulphide minerals using a combination of depressant reagents.
BACKGROUND
Sulphide mineral flotation has been practiced since the early 20th century.
Its industrial importance is well recognized as the concentrates from
flotation can
be more economically smelted and refined to provide primary metals. Froth
flotation is a process to selectively separate value minerals from waste
gangue
materials through utilizing the differences in surface hydrophobicity. In
general, the
flotation process involves the grinding of crushed ore in a dense slurry to
liberation
size. followed by its conditioning with different reagents in a suitable
dilute pulp.
The reagents include collectors, depressants, frothers, modifiers, etc.
Collectors
CA 2873696 2019-07-19
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
2
render the surface of desired minerals hydrophobic by physical/chemical
adsorption, which facilitates the attachment of air bubbles that cause the
mineral
particles to float to the surface of the slurries and form a stabilized froth
which is
collected for further treatment. Depressants have the reverse action to
collectors,
causing the surface of undesired mineral particles to become hydrophilic by
adsorbing hydrophilic components or by removing the active sites for the
collector's
adsorption, thus allowing the particles to remain in the tailings fraction.
Frothers
help to stabilize air bubbles of suitable sizes in the slurry in order to
capture and
transfer particles to the froth zone. Modifiers are usually used for pH
control. The
various schemes of froth flotation that are employed are generally quite
complex in
order to maximize grade and recovery of the valuable minerals present and to
maximize rejection of rock and sulphide minerals of little commercial value.
In the processing of sulphide ores for the recovery of non-ferrous pay
metals, the common value minerals treated include pentlandite and millerite,
chalcopyrite and chalcocite and bornite, galena, and sphalerite for the metals
Ni,
Cu, Pb and Zn respectively. However, these value minerals are naturally
associated with iron sulphides, namely pyrrhotite, pyrite, and marcasite,
which
have no commercial value and are considered as sulphide gangues. Selective
rejection of iron sulphides in flotation can significantly improve the
economic value
of the concentrate and also reduce the SO2 emissions at smelters where the
iron
sulphides are significant contributors to these gaseous emissions. However,
pyrrhotite rejection is challenging. It not only relates to the abundance of
pyrrhotite
in the ore, but also to the crystal structure of pyrrhotite (i.e. monoclinic,
hexagonal
or troilite). Furthermore, pyrrhotite is intimately associated with other
minerals,
primarily with pentlandite. Selective depression of pyrrhotite without
compromising
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
3
the recoveries of Cu and Ni during flotation is a key to building commercial
value in
an industrial mineral processing plant.
U.S. Patent No. 5,074,993 describes a method of flotation of sulphides
wherein pyrrhotite is depressed by use of a water-soluble polyamine in an
amount
>50 g/mt of the ground mineral mixture. The water-soluble polyamine is
preferably
diethylenetriamine (DETA), and can also be selected from a list that includes
triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 2-
[(2aminoethyl)amino] ethanol, Tris-(2-aminoethyl)amine, N-methyl
ethylenediamine
and 1,2 diamino 2 methylpropane.
U.S. Patent No. 5,411,148 describes a process for the improved separation
of mono- or multi-metallic sulphide minerals from iron sulphides. The process
comprises a conditioning stage before flotation with at least one water-
soluble
sulphur-containing inorganic compound as a prerequisite step before further
conditioning with a nitrogen-containing organic chelating agent which is
described
in US 5,074,993. The water-soluble sulphur-containing inorganic compound is
preferably sodium sulphite (Na2S03), and can also be selected from the group
consisting of sulphides, dithionates, tetrathionates, and sulphur dioxide, in
an
amount varying from 50 to 600 g/mt of dry solids processed. The nitrogen-
containing organic chelating agent is preferably a polyethylenepolyamine such
as
diethylenetriamine (DETA) used at an adequate dosage for a particular
flotation
feed. The pyrrhotite is depressed as a result of the combined effects of the
sulphur-containing compound and the nitrogen-containing organic compound,
added in a particular order.
The aforementioned processes are very effective at increasing Ni and Cu
concentrate grade and recovery with selective pyrrhotite depression. However,
the
use of DETA can complicate the operation of the wastewater treatment regarding
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
4
the total (soluble and insoluble) Cu and Ni discharged in the effluent. DETA
is a
strong chemical chelating agent that forms stable complexes with heavy metal
ions, such as Cu and Ni. These complexes cannot be precipitated out by raising
the pH above 11, as is typically done in the wastewater treatment plants.
Instead,
a polyamine precipitating agent such as NALMETO 8702 (available from the Nalco
Company, Naperville, IL) is added to the wastewater to react with the DETA-
metal
complexes and form a precipitate. However, the precipitates are very fine
particles
which do not settle in the clarifier, making it difficult to effectively
remove the Cu
and Ni from the wastewater. In order to avoid a high level of Cu and Ni in the
wastewater when using DETA, efforts are being made to identify alternative
iron
sulphide depressants to reduce or eliminate the use of DETA.
A recent patent from LignoTech (U.S. Patent No. 8,221,709) describes a
method of using hardwood lignosulphonates for separating gangue materials from
metallic sulphide ore. The patent specifies three hardwood lignosulphonates
obtained from Eucalyptus, Maple, and Birch trees with different sulphur or
sulphonate contents and molecular weights, and compared their performances at
dosages of ¨250-500 g/mt with NaCN additions in the flotation of a ground ore
slurry which comprised copper sulphide, zinc sulphide, or lead sulphide with
iron
sulphides. The lignosulphonates can be added before or after other reagents
and
pH adjustments. However, the selectivity between Cu/Ni sulphides and
pyrrhotite
is not improved with the addition of lignosulphonate alone in the industrial
process.
In this sense, the state of the art lacks a method for a) improving the
selectivity and recovery in the flotation of Cu/Ni sulphide minerals which are
associated with iron sulphides, and b) reducing or eliminating the use of
problematic polyamine chemicals (such as DETA) to minimize the negative impact
on the environment.
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
SUMMARY OF THE INVENTION
In light of the problems and unmet needs described above, the present
5 .. invention discloses a method of using the synergy of multiple depressants
to
improve the depression of iron sulphide without compromising the recovery of
the
valuable sulphide minerals in the flotation of non-ferrous metal sulphides,
while
reducing or eliminating the use of environmentally problematic chemicals such
as
polyamines. The method has significant economic and environmental benefits.
Included are examples of the flotation of Cu/Ni sulphide ore with pyrrhotite,
either
as freshly ground slurry or as a pre-treated and finely ground process
intermediate
during a flotation process.
The essence of the process involves the use of multiple depressants, taking
advantage of the individual depression effect of each chemical, and generating
a
synergistic effect to improve selectivity and recovery and reduce polyamine
usage
by at least 50%, or eliminate it whenever possible. The three chemicals used
include: 1) A polyamine, such as DETA; 2) A water-soluble sulphur-containing
inorganic compound, such as sodium sulphite; and 3) A hardwood lignosulphonate
product, preferably a calcium lignosulphonate with a 6 kDa molecular weight,
5%
sulphonate, and 2% sugar, and specifically the D-912 product from LignoTech.
Used individually, the chemicals either a) do not generate sufficient
pyrrhotite
depression, or b) decrease the Cu/Ni recovery, or c) cause environmental
discharge problems at the wastewater treatment plant due to potentially high
levels
of heavy metals.
The three chemicals can be added separately at the same time, or added
sequentially with no preferred order, or premixed into a single solution with
a
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
6
preferred ratio. Similarly, two components can be premixed into a single
solution
with a preferred ratio and added to the third one separately with varying
amounts.
The depressants can be added before or after other flotation reagents.
Aspects of the present invention promote the improvement of the selective
recovery of the non-ferrous pay metals which are associated with iron
sulphides.
Aspects of the present invention promote synergy between the depressants
and the collector allowing for a reduction of the polyamine (i.e. DETA) dosage
by at
least 50% over that typically used with the DETA/Na2S03 combination, without
compromising the selectivity and recoveries during flotation.
Aspects of the current invention help avoid discharges of heavy metals and
DETA at the wastewater treatment plant exceeding the mandated limits that can
occur due to the formation of DETA-metal complexes.
Additional advantages and novel features of these aspects of the invention
will be set forth in part in the description that follows, and in part will
become more
apparent to those skilled in the art upon examination of the following or upon
learning by practicing the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Various exemplary aspects of the systems and methods will be described in
detail, with reference to the following figures but not limited to, wherein:
FIG. 1 is a plot graph illustrating ineffective pyrrhotite depression with D-
912 alone
in rougher flotation;
FIG. 2 is a plot graph illustrating effective pyrrhotite depression with D-912
and
Na2S03 in rougher flotation;
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
7
FIGS. 3A and 3B are plot graphs illustrating lower recoveries with D-912 and
Na2S03 for an intermediate stream;
FIGS. 4A and 4B are plot graphs illustrating the synergy of pyrrhotite
depression
with D-912, Na2S03, DETA, and PAX for an intermediate stream ¨ effect of
dosages and the order of addition;
FIG. 5 is a plot graph illustrating the synergy of pyrrhotite depression with
0-912,
Na2S03, DETA, and PAX for an intermediate stream ¨ optimal dosages from
factorial design tests;
FIGS. 6A and 6B are plot graphs illustrating the synergy of pyrrhotite
depression
with 0-912, Na2S03, and DETA for an intermediate stream ¨ synergy studies from
optimization and duplicate tests;
FIG. 7 is a plot graph illustrating pyrrhotite depression with 0-912, Na2S03,
and
DETA ¨ effect of the order/method of adding reagents;
FIGS. 8A and 8B are plot graphs illustrating the synergy of pyrrhotite
depression
with D-912, Na2S03, and DETA in a middling stream; and
FIG. 9 is a bar graph illustrating pyrrhotite depression with 0-912, Na2S03,
and
DETA ¨ decreasing the residual DETA, Cu, and Ni concentrations in concentrate
and tailings waters
.. DETAILED DESCRIPTION
The following detailed description does not intend, in any way, to limit the
scope, applicability or configuration of the invention. More
specifically, the
following description provides the necessary understanding for implementing
the
exemplary features of the invention. When using the teachings provided herein,
CA 02873696 2014-11-14
W02013/152412 PC1713R2013/000121
8
those skilled in the art will recognize suitable alternatives that can be
used, without
extrapolating the scope of the present invention.
The present invention describes a method of using the synergistic effect of
multiple depressants to selectively float sulphide minerals which contain at
least
one or more non-ferrous pay metals and which are associated with iron
sulphides
consisting mainly of pyrrhotite to obtain an excellent grade and recovery of
the
non-ferrous pay metal values. By taking advantage of the synergistic effect
obtained by using multiple depressants, the dosage of one of the key chemicals
(i.e. DETA) can be significantly reduced, thereby alleviating a potential
negative
impact to the environment. The method comprising:
i) Treating a sulphide ore, either freshly ground slurry or a pre-treated and
finely ground process intermediate, which contains at least one or more non-
ferrous pay metal sulphide minerals (Cu/Ni) with iron sulphides (pyrrhotite),
in an
aqueous alkaline slurry in the presence of a collector, a frother, a pH
modifier, and
a carrier gas distributed through the slurry, and the multiple depressants.
= The slurry to be treated contains up to ¨80% iron sulphide. The non-
ferrous pay metals sulphides can be pentlandite and millerite,
chalcopyrite and chalcocite and bornite, galena, and sphalerite which
are the valuable minerals for Ni, Cu, Pb and Zn respectively. The iron
sulphides can be pyrrhotite, pyrite and marcasite.
= The collector can be selected from at least one of xanthate,
dithiophosPhate, thionoca rba mate, dithiocarbamate,
dithiophosphinate, xanthogen formates, xanthic esters or a mixture
thereof. Potassium amyl xanthate is used as an example. The
dosage of the collector is adjusted according to the dosage of
depressants for good recovery of the pay metals.
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
9
= The frother tested is a polyglycolether (F160-13, Flottec), but can
also be selected from at least one of natural oils, alkoxy paraffins,
aliphatic alcohol, polyglycol ethers, polypropylene glycols. The frother
is not a dominant factor in the current invention.
= The pH modifier tested is lime at pH 9.5, but can also be soda ash or
sodium hydroxide. The pH can range from 8 to 12.
= The carrier gas used is air. It can also be nitrogen, nitrogen-enriched
air or oxygen-enriched air, or carbon dioxide (enriched air).
= Conditioning steps are required after making additions of the collector
or depressants.
= The flotation machine can be a standard Denver flotation machine
with either a 2.2 L cell and a motor speed of 1200 rpm, or a 1.1 L cell
and a motor speed of 900 rpm.
ii) The multiple depressants contain at least one organic polymer (calcium
lignosulphonates from hardwood), at least one sulphur-containing compound, and
at least one nitrogen-containing organic compound (polyamine), the latter
being
present at lesser amounts in the mixture than would be needed if it was being
used
alone or in combination with one sulphur-containing compound.
= The said "organic polymer" is at least one water-soluble organic
negatively charged polymer selected from the group consisting of one
or more of lignosulphonate, dextrin, guar gum, tapioca, starch, or
cellulose. The preferable one is a calcium lignosulphonate from
hardwood with 6 kDa molecular weight, 5% sulphonate and 2%
sugar. One such product is "D-912" from LignoTech, as identified in
the LignoTech patent.
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
= The said "sulphur-containing compound" is at least one water-soluble
inorganic sulphur-containing compound selected from the group
consisting of one or more sulphides, sulphites, hydrosulphites, meta-
bisulphates, dithionates, tetrathionates, and sulphur dioxide. The
5 preferable one is sodium sulphite (Na2S03).
= The said "nitrogen-containing organic compound" is at least one
nitrogen-containing organic compound having a configuration
selected from the group consisting one of or more polyethylene-
polyamines with OCNCCCNCNC and NCCN structures, including
10 diethylenetriamine, triethylenetetramine, tetraethylenepentamine,
pentaethylenehexamine, hydroxyethyl-DETA, diethanolamine, and
aminoethylethanolamine. The preferable one is diethylenetriamine
(DETA).
iii) The addition of multiple depressants has the following options with some
conditioning time allowed:
= They can be added separately at the same time; or
= They can be added sequentially without any preferred order, with or
without conditioning between each other; or
= They can be premixed into a single solution with a determined
preferential ratio; or
= Two of the components can be premixed into a single solution with a
determined preferred ratio, with the third component added
separately in varying amounts as needed.
= The depressants can be added before or after the collector, with
some conditioning.
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
Ii
iv) The dosages of the depressants for the synergistic effect and reduced
polyamine usage will depend on the ore type, grade and its mineralogical
composition and should therefore be determined experimentally. For the tested
ore samples, 0-912 dosages ranged from 50 to 150 g/t, Na2S03 ?. 100 g/t, and
DETA from 0 to 50 g/t. The quoted dosages refer back to the ground ore, even
for
intermediate streams. The DETA dosage is kept as low as possible without
compromising the overall selectivity and recovery, to avoid the high levels of
heavy
metals in the wastewater.
v) The collector dosage will be adjusted accordingly for the optimal
metallurgy as there is competition between collectors and depressants.
In the preferred embodiments, the invention refers to a method of using the
synergistic effect of multiple depressants to selectively float at least one
or more
sulphide minerals which contain at least one or more non-ferrous pay metals
and
which is/are associated with iron sulphide in a sulphide ore, the process
comprising:
i) Treating a sulphide ore, either freshly ground slurry or a pre-treated and
finely ground process intermediate, which contains at least one of said
valuable
sulphide minerals associated with at least one iron sulphide mineral, in an
aqueous
alkaline slurry in the presence of a collector, a frother, a pH modifier, a
carrier gas
distributed through said slurry, and multiple depressants selected to include
at
least one organic polymer, at least one sulphur-containing compound, and/or at
least one nitrogen-containing organic compound; and
ii) Carrying out froth flotation to depress the iron sulphides, while allowing
the flotation of the valuable non-ferrous sulphides.
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
12
In another preferred embodiment, the invention refers to a method of using
the synergistic effect of multiple depressants to selectively float at least
Ni/Cu/Co
sulphide minerals which contain at least Ni, Cu, Co, Pt, Pd, Au, and Ag pay
metals
and which is/are associated with iron sulphide minerals including at least
pyrrhotite
in a sulphide ore, the process comprising:
i) Treating a Ni/Cu/Co sulphide ore, either freshly ground slurry or a pre-
treated and finely ground process intermediate, which contains at least the
minerals pentlandite and chalcocite associated with at least pyrrhotite, in an
.. aqueous alkaline slurry in the presence of a collector, a frother, a pH
modifier, a
carrier gas distributed through said slurry, and multiple depressants
including a
calcium-lignosulphonate product (preferably a product such as D-912), a sodium
sulphite (Na2S03) and/or DETA; and
ii) Carrying out froth flotation to depress the pyrrhotite, while allowing the
flotation of the valuable pentlandite and chalcocite.
Alternatively, the method of adding the three depressants may comprise 1)
separately, but all at the same time; and 2) sequentially with individual
conditioning.
Additionally, the depressants solution can be added before or after the
.. collector.
The dosages of the depressants for the synergistic effect and reduced
polyamine usage were found to depend on the ore type, grade and its
mineralogical composition and should therefore be determined experimentally.
For
the tested ore samples, D-912 dosages ranged from 50 to 150 g/t, Na2S03 100
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
13
g/t, and DETA from 0 to 50 g/t. The quoted dosages refer back to the ground
ore,
even for intermediate streams.
The synergistic pyrrhotite depression obtained when using multiple
depressants (i.e. by combining DETA, Na2S03 and 0-912) is obtained by
maximizing the pyrrhotite depression obtained with each depressant at a
minimum
dosage. More specifically, DETA, Na2S03 and 0-912 have their own unique
functions in iron sulphide depression. Pyrrhotite flotation has three proposed
mechanisms; 1) Cu activation to promote collector (xanthate) adsorption; 2)
Formation of poly-sulfur to produce some hydrophobic sites on the pyrrhotite
surface for the air bubble to attach to; and 3) Formation of dixanthogen for
hydrophobic sites. DETA can remove or mask the Cu2+ activation sites on the
iron
sulphides to inhibit collector adsorption on the surface. Na2S03 can prevent
iron
sulphide flotation by removing the adsorbed collector or the poly-sulfur
formed on
the iron sulphide surface. D-912 is a negatively charged hydrophilic polymer
which
can adsorb onto the iron sulphide surface through active sites (such as
Fe(OH)2 ,
Ca2+ or Cu2+) to render its surface hydrophilic, thus depressing the iron
sulphide.
With any one of the depressants used singly, no effective pyrrhotite
depression is obtained without compromising pay metal recovery or causing high
levels of heavy metals in the wastewater. By using three different depressants
simultaneously, a synergistic effect is created. An advantage can be obtained
from
each of the three reagents, resulting in maximizing the iron sulphide
depression
while minimizing decreases in the recovery of the valuable minerals.
EXAMPLES
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
14
The following examples are meant to illustrate, and not in any way to limit
the scope, applicability, or configuration of the claimed invention.
In the figures, it should be noted that short forms have been used in the axis
titles for the minerals. Included are
the notations: Pn (pentlandite), Cp
(chalcopyrite), and Po (pyrrhotite).
Example 1
Ineffective Pyrrhotite Depression with D-912 Alone
Figure 1 presents results for the cumulative recovery of pentlandite and
pyrrhotite in the rougher flotation of a nickel-copper ore containing about
1.5% Ni
(3.7% pentlandite), 1.5% Cu (4.3% chalcopyrite) and 21% Fe (19.7% pyrrhotite)
and 72.3% rock (other silicates), which was treated according to the procedure
in
U.S. Pat. No. 8,221,709 (LignoTech), using the hardwood lignosulphonate
product
D-912 alone as a pyrrhotite depressant. In this test, 1 kg of the ore was
ground in
a rod mill to reach P80 ¨ 106 pm, with the addition of 5 g/t of collector (PAX
-
potassium amyl xanthate) and 400 g/t of lime. The incremental rougher tests
were
performed at pH 9.5 with lime as the modifier. There were 2 minutes of
conditioning after the addition of depressants and collector respectively and
15
ppm frother (F160-13) is in the process water. A 2.2 L Denver flotation cell
was
used with a 1200 rpm rotation shaft and 3 Umin of air was applied in
flotation. The
concentrates were collected after 0.5, 1, 2, 5, 8 and 12 minutes. The
additions of
the chemicals added into the rougher are summarized in Table 1.
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
The test with the collector (PAX) alone showed no pyrrhotite depression.
The test with DETA/Na2S03 represented an acceptable pyrrhotite depression and
pay metal recovery.
Using the hardwood lignosulphonate product 0-912 as a pyrrhotite
5 depressant at a dosage of 25 to 50 g/t did not improve the pyrrhotite
depression in
comparison to the use of the combination of DETA and Na2S03 (i.e. the
"Baseline"
chemicals). At a high 0-912 dosage of 250 g/t, pentlandite was significantly
depressed without improving the selectivity of pentlandite/pyrrhotite in
comparison
to the combination of DETA and Na2S03.
Example 2
Effective Pyrrhotite Depression with D-912 and Na2S03for One Ore Feed
Figure 2 presents results for the cumulative recovery of pentlandite and
pyrrhotite in the rougher flotation of the same nickel-copper ore as used in
Example 1, in which Na2S03 was added with D-912 into the rougher. The ore was
ground in the same manner as in Example 1, including the 5 g/t addition of the
collector (PAX) and the 400 g/t addition of lime. Pyrrhotite depression was
observed when the Na2S03 dosage was a 200 g/t. The additions of the chemicals
into the rougher flotation are summarized in Table 2.
The test with the collector (PAX) alone showed no pyrrhotite depression.
The test with DETA/Na2S03 represented an acceptable pyrrhotite depression and
pay metal recovery.
It was demonstrated that using a dosage of 200 g/t Na2S03 by itself had
some effect on pyrrhotite depression, but the results were not as good as
those
obtained using the baseline chemicals DETA and Na2S03. In the tests with D-912
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
16
and Na2S03, some indications of pyrrhotite depression were observed when the
Na2S03 dosage was > 100 g/t. When the Na2S03 dosage was 2 200 g/t and the
0-912 dosage was 2 50 g/t, similar pentlandite/pyrrhotite selectivity curves
were
obtained with D912/Na2S03 as the baseline DETA/Na2S03. Increasing the dosage
of D-912 from 25 to 100 g/t and the dosage of Na2S03 from 200 to 400 g/t did
not
significantly change the shape of the pentlandite/pyrrhotite selectivity
curves (i.e.
the pentlandite recovery dropped with a decrease in the pyrrhotite recovery).
For this feed, there was no need to add DETA, which is preferable for
environmental concern.
Example 3
Lower Recoveries with D-912 and Na2S03 for an Intermediate Stream
Figures 3A and 3B present results for the cumulative pentlandite/pyrrhotite
and chalcopyrite/pyrrhotite selectivities respectively in the cleaner
flotation of an
intermediate stream containing 7.6% Cu (21.9% chalcopyrite), 6.4% Ni (17.3%
pentlandite), 37% Fe (39.8% pyrrhotite), and 21% Rock, in which Na2S03 was
added with 0-912 into the cleaner. This study involved rougher and cleaner
flotation tests and the depressants were added into the cleaner stage. A total
of 10
g/t of collector (PAX) was added into the rougher flotation and the rougher
concentrate was collected for 6 min. The rougher concentrates were treated in
the
cleaner stage at pH 9.5 with lime as the modifier. There were 2 minutes of
conditioning after the addition of depressants and collector respectively and
15
ppm frother (F160-13) is in the process water. A 1.1 L Denver flotation cell
was
used with a 900 rpm rotation shaft and 1 Umin of air was applied in cleaner
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
17
flotation. The cleaner concentrates were collected after 1.5, 3, 5 and 16
minutes.
The additions of the chemicals into the cleaner flotation are summarized in
Table 3.
It was observed that the selectivity was improved and even better than the
DETA/Na2S03 baseline when the D-912 dosage was .? 50 g/t with 200 g/t of
Na2S03. However, the recovery of chalcopyrite decreased by ¨15%. If the dosage
of D-912 is further decreased (5 25 g/t) or the dosage of PAX is increased,
the
selectivity will be compromised. This is not acceptable for industrial
production.
Example 4
The Synergy of Pyrrhotite Depression with D-912, DETA, Na2S03, and PAX for an
Intermediate Stream
Figures 4A and 48 present results for the cumulative pentlandite/pyrrhotite
and chalcopyrite/pyrrhotite selectivities respectively from the cleaner
flotation of the
same intermediate stream as used in Example 3. In this example, DETA was
added with Na2S03 and D-912 into the cleaner, but at reduced dosage compared
to when DETA and Na2S03 were used together as part of the "Baseline"
conditions. This study
involved rougher and cleaner flotation tests as described
in Example 3. The additions of the chemicals into the cleaner flotation are
summarized in Table 4.
In tests in which the dosages of each chemical were fixed (T18309, T18310,
T18311), the order of adding the chemicals was varied. No significant
differences
in the results were seen.
In tests in which the dosages of the depressants and collector were varied,
either the selectivity was very good but the recoveries of pentlandite and
chalcopyrite were far below target (T18309, 118310, T18311), or the recoveries
of
CA 02873696 2014-11-14
WO 2013/152412
PCTa3R2013/000121
18
pentlandite and chalcopyrite were acceptable but the selectivity was
significantly
reduced (T18358, 118360).
The selectivity and recovery approached the "Baseline" results only when a
balance between the collector and depressants was reached (118359). At the
proper dosages of 0-912, DETA, and Na2S03 and the collector (PAX), good
selectivity and recoveries are obtained.
Example 5
Factorial Design Tests to Find the Optimal Dosages of D-912, DETA, and Na2S03,
and PAX for the Synergy of Pyrrhotite Depression for an Intermediate Stream
Figure 5 presents results of a 23 factorial design study of the interaction
between D-912, DETA, and the collector (PAX) while keeping the dosage of
Na2S03 fixed. The results from Example 4 indicated that the combination of the
three chemicals as depressants generated synergy, which allowed the DETA
dosage to be reduced while maintaining good selectivity and pay metal
recovery.
At the same time, the dosage of the collector was found to play a very
important
role. In order to further confirm the synergy and determine the optimum range
of
dosages for each chemical, a three factor - two level (23) factorial design
study on
the dosages of PAX, DETA and D-912 was carried out, with the chemicals added
to the cleaner stage. The feed was the same as that described in Example 3.
The
rougher-cleaner flotation procedure was the same as described in Example 3. In
all these tests, Na2S03 was added at a fixed dosage of 200 g/t. The dosages of
DETA, D-912, and PAX and the test conditions are specified in Table 5.
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
19
In the test design, the criteria for selecting the dosages included: a) The
DETA dosage should be less than the level that was used in the DETA/Na2S03
combination (i.e. usually 50 g/t); b) As previous results showed that D-912
dosages
< 50 g/t did not work, and the upper limit was not known, the dosages were
extended to higher levels; and c) Since the results in Example 5 showed that
the
recoveries of pentlandite and chalcopyrite were adequate at FAX dosages of 10
to
g/t, there was no need to go to much higher dosages than normal (i.e. 5 git).
In one group with high dosages of D-912 (FD2, FD3, FD5 and FD7), a high
concentrate grade with a very low pentlandite recovery (20-50%) was obtained,
10 indicating that a
D-912 level of 150 g/t was too high. In another group with high
dosages of PAX and low dosages of D-912 (FD8 and FD9), the
pentlandite/pyrrhotite selectivity was reduced, resulting in a concentrate
grade
below the target. Using the dosages at the middle points of the ranges (FD1)
produced results between these limits. It can be seen that at 10 g/t PAX, 50
g/t D-
15 912, and 15 g/t
DETA (FD6), good pentlandite/pyrrhotite selectivity was obtained
with results approaching those of the DETA/Na203 baseline. Chalcopyrite
recovery
at these dosages was also very good (¨ 90%).
Example 6
Optimization and Duplication Tests Using D-912, DETA, and Na2S03 for the
Synergy of Pyrrhotite Depression for an Intermediate Stream
Figure 6 presents results of optimization tests and baseline tests carried out
to validate the repeatable synergy that was demonstrated in Example 5 when D-
912, DETA, and Na2S03 were used together and to optimize the dosages of the
chemicals. The rougher-cleaner flotation procedure was the same as described
in
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
Example 3. The intermediate stream was the same as that described in Example
3. The dosages of the chemicals added to the cleaner are specified in Table 6.
Starting from the conditions which gave good results (FD6: with 15 g/t DETA,
50 g/t
D-912, and 10 g/t PAX), when either 0-912 (T18558) or DETA (118560) or Na2S03
5 (T18612) was excluded, the pentlandite/pyrrhotite selectivity was not as
good as
when all chemicals were used together.
The other repeated and optimized results were all in the same
pentlandite/pyrrhotite selectivity range, indicating a stable performance. It
can be
seen that: a) Increasing the 0-912 dosage to 75 g/t decreased pentlandite and
10 chalcopyrite recoveries by a few percentage points; b) Changing the DETA
dosages from 15 to 25 and then to 35 g/t did not affect the recoveries and
selectivity, so that the lower DETA dosage (15 g/t) was preferred; and c)
Decreasing the PAX dosage slightly (i.e. from 10 to 7.5 g/t) did not have a
significant impact on the results.
Example 7
The Effect of the Order and Method of Adding D-912, DETA, and Na2S03
Figure 7 presents results on the evaluation of the order and method of adding
the chemicals. The intermediate stream was the same as that described in
Example 3. The rougher-cleaner flotation procedure was the same as in Example
3, with the following conditions: 1) Adding the three chemicals (D-912, DETA
and
Na2S03) at the same time with conditioning; 2) Adding Na2S03, DETA, and D-912
sequentially with a conditioning time for each addition; 3) Premixing DETA and
0-
912 into one solution and adding this as a single reagent with Na2S03 into the
pulp
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
21
with conditioning; and 4) Premixing DETA, D-912 and Na2S03 into one solution
and adding this as a single reagent into the pulp with conditioning.
The additions of the chemicals and the conditions of the addition method to
the
cleaner are summarized in Table 7.
The differences in the results obtained with the various methods of adding the
chemicals were not significant, as all the results showed good selectivity.
Adding
the three chemicals separately has the advantage of being able to adjust each
dosage individually. Using a premixed solution gives a simpler solution for
the
arrangement of chemical storage tanks and delivery lines, which is good when
the
conditions have been fully established.
Example 8
The Synergy of Pyrrhotite Depression with D-912, DETA, and Na2S03 for Another
Middling Streams
Figures 8A and 86 present results showing the effect of additions of D-912,
Na2S03, and DETA on the depression of pyrrhotite in middling streams. Two-
stage
rougher-cleaner flotation tests were carried out, using a middling feed
containing
1.0% Cu (2.7% chalcopyrite), 2.0% Ni (4.3% pentlandite), 44.6% Fe (65.7%
pyrrhotite) and 27.3% rock. The additions of the chemicals into the rougher
and
cleaner stages are summarized in Table 8.
Figure 8A presents results obtained by adding the depressants into the rougher
stages only. As compared with the case with PAX only (T20013), the addition of
0-912 resulted in a significantly reduced pyrrhotite recovery. The effect on
pyrrhotite depression of combining D-912 and Na2S03 (T20027) was not as good
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
22
as when 0-912, Na2S03, and DETA were used together (T20030). The results
from the test with the three chemicals were closer to the DETA/Na2S03 Baseline
(T20016), but with a much lower DETA addition (- 40% of DETA).
Figure 8B presents results obtained by adding the depressants into both the
.. rougher and cleaner stages. When using a combination of the three chemicals
(D-
912, DETA, and Na2S03), adding an adequate amount of D-912 into the rougher
stage is most critical. If this dosage is not high enough (i.e. <75 g/t of 0-
912) in the
rougher stage, little pyrrhotite depression occurs. With a high dosage of D-
912 in
the rougher stage, adding more D-912 to the cleaner stage can further improve
the
.. pentlandite/pyrrhotite selectivity. In summary, adequate dosages of D-912,
DETA,
Na2S03, and PAX are required to achieve good pentlandite/pyrrhotite
selectivity in
the flotation of high pyrrhotite middling streams.
Example 9
Decreasing the Residual Amounts of DETA, Cu, and Ni in the Process Water By
Using the D-912, DETA, and Na2S03 Combination
Figures 9A and 9B illustrate the effect of using the new depressant mixture
.. identified in Examples 5 and 6 on the quality of the concentrate and
tailings waters
respectively. Two rougher-cleaner flotation tests were carried out using the
procedure described in Example 3 on the same nickel-copper ore as used in
Example 1. The first test was carried out using the "Baseline" conditions,
with 50
g/t DETA, 200 g/t Na2S03. The second test was carried out using the new
conditions, with 50 g/t D-912, 15 g/t DETA and 200 g/t Na2S03. Both sets of
CA 02873696 2014-11-14
WO 2013/152412
PCT/BR2013/000121
23
conditions were shown previously to result in similar flotation metallurgy.
After
flotation, the concentrate and tailings waters from each test were collected
and
analyzed for residual DETA, Cu and Ni. The results of the analyses are
summarized in Table 9. The decreased residual levels of DETA, Cu and Ni
obtained with the use of the new mixture of D-912, DETA and Na2S03 can clearly
be seen.
It is known that the different tailings solids each have specific capacities
for
stably adsorbing DETA. The results given in Table 9 verified that by using the
combination of D-912, DETA and Na2S03 with a reduced DETA dosage, the
residual amount of DETA in the process water could be significantly decreased.
This amount of DETA can be adsorbed on the tailings solids without any
negative
impact on the wastewater treatment plant.
