Note: Descriptions are shown in the official language in which they were submitted.
3 FIELD OF THE INVENTION
. 7 The Eield of art -to which the invention pertains
includes the Eield of differential froth flotation, particularly
with the employment of preferential modifying agents. More
specifically, the field relates to the separation and recovery
of molybdenum sulfide from copper ore concentrate containing
both molybdenum sulfide and copper sulfide by froth flotation
in the presence of a depressant for copper sulfide to effect
~ recovery of a molybdenum concentrate in the flotation overflow
:~ and recovery of a copper concentrate in the flotation underflow.
1 .
¦ BACKGROUND AND 'SUMMARY OF THE IN~IENTION
Molybdenite ~MoS2) can be found in small amounts
with sulfidic copper ores such as those containing chalcopyrite.
Typically, copper ores of such nature are beneficiated by
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flotation to ob-tain an ore concentrate cont:aining about 25-30%
copper and abou-t 0.3-1% molybdenum. In obtalning the concen-
trate, reagents such as collectors and frot:hers are added during
treatment of the ore to facilitate separati.on from the gangue
materials, the molybdenite following -the copper sulEide in
the flotation circuit to obtain a concentrate as above des-
cribed. Thereafter, the molybdenite content of the copper
ore concentrate is separated by differential flotation to
obtain a molybdenum concentrate containing about 40% or more
Mo. In view of the fact tha-t sulfidic copper minerals and
molybdenite are floated by the same collectors, in order to
effect a differential flotation of the molybdenite it has .
been found.necessary to depress.the copper sulfide while
floating the molybdenite content of the concentrate. The
use of sulfides with or wi-thout a collector for the molyb- ~ .
denum sulfide has been known and used in the industry for
many years. However, in the last 25 years a process widely
used in industry for differential flotation of molybdenite
has included conditioning an aqueous pulp of the molybdenite- -
containing copper ore concentrate with a material known as
a "Nokes-type" reagent for depressing the copper sulfide
and with a conventional collector for molybdenum sulfide.
The conditioned pulp is then subjected to froth flotation
with a conventional fl.otation machine to obtain a molybdenum
concentrate as -the flotation overflow and a copper concentrate
tailing as the flotation underflow.
Nokes-type reagents are complex sulfur compounds
of phosphorus, arsenic or antimony and a caustic. See, in
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this regard, Nokes et al U.S~ Patent No. 2,492,936. They
are substantially more expensive than simpler sulfides, Eor
example, sodium hydrosulfide, cos-ting at present about 1.5
times as much as such simple sulfides, but their effective-
ness is such that substantially less Nokes-type reagent
need be used than the simple sulfide with the result that
the Nokes-type depressants have become a standard in the
industry.
Although Nokes-type depressants are used at lower
levels than the simple sulfides, their cost and constant
consumption adds significantly to the cost of the molybdenum
ultimately produced. An attempt to mitigate such costs can
be found in Delaney U.S. Patent No. 3,655,044 wherein a
process is described in which the amount of Nokes-type
reagent required as a depressant is reduced so that only
about one-fifth to one-half of the usual amount is needed.
The process requires the addition of a collector for the
molybdenum sulfide along with the use of an inert gas,
such as nitrogen, as the froth producing gas. While ordinary
collectors are not a major cost item, the use of
nitrogen is sufficiently costly so that the aforenoted
xeduction in the concentration of Nokes reagent cannot
readily justify nitrogen aeration, particularly when
one considers that an increased capital investment may
be required.
The present invention provides a process for
froth flotation of molybdenum sulfide which also employs
nitrogen as the aerating gas but which is economically
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l operational hecal1se it (a) uses a clepressant reagent for
2 the copper sulEide which is substanti.ally less costly than
3 the Nokes-type reagen-t, (b) surprisingly operates with an
4 amount of depressant reagent which can be as little as
51 l/20 or less of -the amount of depresc,ant usually required
6 in -the absence oE nitrogen aeration, and (c) can often
71 operate without the further addition of a collec-tor for
81 the molybdenite. r
91
lO¦ i~lore particularly, an aqueous pulp of copper
ll¦ ` concentrate containing both molybdenum sulfide and copper
l2¦ sulfide is conditioned with a depressant comprising, as
l3¦ its major constituent, a water-soluble ammonium, alkali
l4¦ metal or alkaline earth metal sulfide and the conditioned
l5¦ pulp is subjected to froth flotation in which an inert
~61 gas comprising nitrogen as its major component is employed
17¦ as the froth producing medium. A molybdenum concentrate
18 ¦ is recovered in the flota-tion overflow and a copper con-
l9 ¦ centrate i5 recovered in the flotation underflow wi-thout
20 ¦ the occurrence of substantial oxidation in the conditioned
21 ¦ aqueous pulp.
22 1
23 ¦ The present process is par-ticularly suitable
241 for continuous operation wherein the sulfide concentration
251 oE the copper ore concentrate pulp is measured on a con-
26 tinuous basis and the above sulfide depressant is added
27 in an amount suEficient to maintain the measured sulfide
28 concentration above a predetermined value sufficient to
29 effectively depress the copper sulfide. In accordance
with the present invention, a sulEide concentration as
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little as 0.1 pounds per ton of concentrate can he used
to e~fect satisfactory separation of the molybdenite.
The present in~entlon, therefore, provides a process (and
preferably a continuous process) for the separation and recovery of
molybdenum sulfide fr copper ore concentrate containing both
molybdenum sul~ide and copper sulfide which comprises
conditioning an aqueous pulp of the copper ore concentrate
with a depressant or said copper sulfide comprising as the
major depressa~t constituent 0~1 lb lb to 3.0 lbs. per ton of
said concentrate of a water-soluble am~tonium, alkali metal or
alkaline earth metal sulfide, and subjecting the conditioned
pulp to froth flotation in which an inert gas comprising
nitrogen as its major component is ~tployed as the froth
producing medium to effect recovery of a molybdenum con~entrate
ir.t the flotation overflow and recoYery of a copper con.centrate
i~ the flotation underflow with~ut the occurrence of su~stantial
oxidation in the conditioned aqueous pulp.
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BRIEF DESCRIPTION OF T~E DRAl~INGS
.FIGURE 1 is a graph showing the chanye in sulfide
concentrations at different initial levels, measured by
means of an electrode with respect to time when the pulp
is aerated with air and with nitxogen; and
FIGURE 2 is a.graph which illustrates the rela-
` tionship between the percentage o~ molybdenite recovered,
copper sulfide recovered and sul~id~ concentration, t~ith
respect to time when the pulp is.~erated with air in one
example and with nitr~gen ir.t another example.
3~
DETAILED_DESCRIPTION
As above-described, conventional ore benePiciation
operations on sul~idic copper ores, such as chalcopyrite r
can result in the preparation o~ a copper ore concentrate
that typically contalns up to about 30 plercen-t by weight
copper and up to about 1 percent by weight molybdenumO In
accordance with the present invention, molybdenite is,
separat~d from the coppex sulfide concantrate by the ~ddi-
tion of a s~lfide depressant for th~ copper sulfide and
froth flotation by aeration wi~h nitroyen. ~ ~ollect:or
or the moly~denite need not ~e added, but is not pr~cluded,and, for parti~ular ores, i~ may be desirable. In su~h
case, any conventional.colle~t~r can be usPd t such as
potassium xanthat~, fuel oil, or sodi~m di-sec-butyl~
thiophospha.te~ Add~tionally~ any ~on~en~ional froth~r
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can be added such as pine oil or methyl isobutyl carbinol
(MIBC) and a commercial form of MIBC as sold by -the Shell
Oil. Co. under ~he designation 1638, comprising 90% MIBC
and 10~ still bot-toms. As a resul-t of the copper circuit,
the pulp is at a pH level of about 11~12 03^ higher.
The copper sulfide depressan-t comprises as the
ma~or depressant constituent a water-solub~Le ammonium, alkali
metal or alkaline earth metal sulfide. The term sulfide is
meant to include monosulfides, polysulfides, hydrosulfides
and hydrated forms. Specific examples of the sulfide com-
pounds include ammonium sulfide, ammonium hydrosulfide, lithium
sulfide, lithium hydrosulfide, sodium monosulfide, sodi~lm
hydrosulfide, potassium monosulfide, potassium hydrosulfide,
rubidium monosulfide, cesium monosulfide, calcium hydro-
sulfide, strontium hydrosulfide, barium hydrosulfide, water-
soluble polysulfide forms thereof, hydrated forms thereof,
and mixtures thereof. It is an important and surprising
result of the present invention that the foregoing sulfides,
most of which are readily and economically available, can
be used in the present process in place of a Nokes reagent
at levels which are only a fraction of the amount normally
required of such suIfides. Thus, while the usual total
amount (rougher and cleaner operations) of sodium hydro-
sulfide required for effective molybdenite separation is
about 10-25 pounds per ton (PPT), a satisfactory separation
can be obtained with the present process by the typical use
of 0.5--1 PPT and as little as 0.1 PPT of the sulfide. A sat-
isfactory range, depending on the source of ore, is about 0.1-3
PPT. Accordingly, as little as 1/20 or less of the normal amount
of sulfide is required. Par-ticularly prefexred, enconornically
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optimal sulfides are sodium sulfide, sodium hydrosulfide~
ammonium sulfide, ammonium hydrosulfide ancl mi~tures
-thereof.
The froth flo-tation is carried out in conventional
agitator-equipped flotation cells which otherwise use air
as the froth producing gas. In the present inventionl
nitrogen is used in place of air; more broadly, an inert
gas is used which comprises nitrogen as its ma~or com-
ponent.
Electrode determination of the concentration
of sulfide in the pulp can be used as a measure of
whether copper sulfide is being effectively depressed.
Such electrodes are commercially available and can be
exemplified by the "Orion"* Research Model 9~-16 electrode
(Orion Research Incoporated~ Cambridge, ~assachusetts)
which is specific for silver ion and for sulfide ion
activity. The electrodes are periodically standardized
using 0.10 molar sodium sulfide solution. An amplified
millivolt signal is plo-tted automatically on a strip chart
and represents the sulfide concentration. Any abrupt
change in slope of the sulfide content, as measured on
the strip chartl indicates a drop-off in depressant
concentration. Referring to Figure 1, there is plotted
the concentration of sulfide as indicated by millivolt
reading from an "Orion" Research electrode in various pulp
slurries. When 6.0 PPT, of sodium hydrogen sulfide is
added to a copper sulfide concentrate pulp, and air is
used for the ~roth flota*ion, there is a rapid drop in
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1 sul:Eide concentration, as indicated by the line 10. After
2 3-~1 minutes, the amount o:E sul:Eide concen~ration :is so
3 low tha-t an inordina-te amount of copper sulfide floats
with the molybdenum sulfide. When ni-t:rogen is substituted
.~or air -there is virtually no drop in sul:Eide concentration
6 over the ~ull 10 minutes oE flota-tion, as indicated by the
7 line 12. ~s shown by the line 14, when the amount of sodium
8 hydrogen sulfide is reduced -to 1/10 o~ -the above amount,
9¦ i.e., 0.6 PPT, the initial concentra-tion of khe sulEide is,
10 ¦ of course, lower and there is some drop with time, but,
lI ¦ importantly, the level is main-tained at a sufficient con-
12 ¦ centra-tion to prevent inordinate copper floating.
13 I .
1~ I In a further embodiment, the present invention
15 ¦ is particularly suitable fo~ a continuous process in which
1~ ¦ concentrate pulp is fed on a continuous basis -to a bank
17 ¦ of serially disposed froth flotation cells. The floated
18 ¦ froth, i.e., the molybdenum rougher concen-trate,can be
19 reslurried for one or more successive operations and
sul~ide depressant is pre~erably added as needed to each
21 cleaner bank of cells. In accordance with this embodiment,
22 the quantity of reagent used is regulated by the concen-
23 tration of sulfide ion which is measured on a continuous
2~ basis as an amplified millivolt signal given by an elec-
trode,as above described. The phrase "continuous basis"
26 is meant to include measurements which are either contin-
27 uous without interrupti.on or are periodic. While it is
28 preferred ko measure the sulfide concentration without
29 interruption, periodic measurements are satisfactory i~
the intervals are short enough so that quality control can
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be maintained. By continuous moni-toring of -the sul~ide
con-tent and adjustment there-to to the leveL deslred, e.g.
0.1 PPT oE NaHS, a minimum amount of sul~ide can be used
to obtain a satisfactory depression of the copper sulEide.
Taken together with the lower sulfide addition permitted
by the us-e of nitrogen as the aerating gas, the total
savings are quite substantial.
In order that those skilled in -the art may
better understand how the present invention may be prac--
ticed, the following Examples are given by way of illus-
tration and without limitation.
EXAl~PLE I
A pulp charge of 1343 grams of copper sulfide
concentrate obtained from rougher and cleaning flo~tation
of Pima Arizona chalcopyrite, and containing 24.3% copper
and 1.0% molybdenum, was added to a standard laboratory
flotation machine, sold under the trade mark "Agitair",
and diluted with 4 liters of water. Sufficient sodium
hydrosulfide was added to obtain a concentration of 8
pounds of the sulfide per ton o~ the concentrate. The
sulfide ion concen-tration was monitored with an "Orion"
Research Sulfide Ion electrode. The pulp was allowed to
condition until stable sulfide ion readings were obtained
on a strip chart. At that point, air was injected and
flotation carried out for a period of 16 minutes. During
the flotation, the voltage output from the sulfide ion
electrode was continuously recorded on a strip chart
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recorder. The flotation ovexflow, i.e., the froth, was
collec-ted at 2 minutes intervals, the mineral con-tent
thereof was welghed and the copper and molybdenum con-
-tent were assayed. At the conclusion of the run, -the
flotation underflow was collected, the mineral content
thereof was weighed and -the copper and molybdenum con-
tent were assayed. The results are set forth in Table I.
TABLE I
Time,Wt. mineral Assay Cum. weight Recovered
Min Rec.% Cu % Mo Cu Mo % ~u % Mb
2 60.710.26 16.74 6.23 10.161.91 74.59
4 23.9 16.56 7.83 10.18 12.03 3.12 88.32
6 18.7 22.25 3.50 14.34 12.68 4.39 93.09
8 19.1 25.40 1.11 19.19 12.89 5.88 94.63
30.0 25.91 0.555 26.97 13.06 8.27 95.88
12 147.5 31.90 0.182 74.0 13.33 22.7 97.85
14 196.9 30.99 0.047 135 13.42 41.41 98.52
16 181.3 29.01 0.023 188 13.47 57.67 98.89
tails 665 20.73 0.023 326 13.62
:
EXAMPLE II
The procedure of Example I was fo]lowed in all
details except that sodium hydrosul~ide was used in a con-
centration ofl PPT and pure nitrogen was used in place of
air as the aeration gas. The pulp charge was 1353 grams of -
copper sulfide concentrate containing 25.0% copper and 0.97% ~
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molybdenum. Measurements, weighings and assays were conducted
as in Example I. The resulLs are set Eorth in Table II~
TABLE II
Time; Wt. mineral Assay ~lm. weight Recovered
Min. Rec. % Cu ~ MD Cu Mo % Cu %Mo
2 62.~ 27.94 16.47 17.~3 10.27 5.15 78O0
4 19.6 13.51 7.94 20.08 11.83 5.92 90.0
6 15.4 19.00 2.956 23.01 12.29 6.8 93.
8 14.5 23.52 2.120 26.41 12.59 7.8 95.5
15.4 26.11 1.229 30.43 12.78 9.0 97.0
12 14.8 26.62 0.792 34.38 12.90 10.1 98.5
14 10.4 26.62 0.582 37.15 12.96 10.8 98.6
16 11.3 26.62 0.419 40.15 13.01 11.8 98.8
tails 1189 25.10 0.014 338.5 13.18
A comparison of the results in Tables I and II reveals
that not only was a greater percentage of molybdenum recovered
in a shorter period oE -time but containing very much less
copper, all with the use of, in this case, 1/8 the amount of
sodium hydrosulfide.
Referring to Figure 2, the results listed in Tables
I and II are shown graphically along with the sulfide ion
concentration as represented ~y the millivolt reading from
an '!Orion" Research electrode in each case. The solid line
indicates the values pertinent to the first Example and -the
dashed line indicates the values pertinent to the second
Example. It can be seen that a slight benefit was obtained
in -terms of molybdenum recovery and that a tremendous benefit
-
was obtained with respect to the continued dep:ression of
copper sulfide.
E~AMPLES III-XIV
The procedure of Example II can he followed
except that in twelve separate runs, 1 PPT of ammonium
sulfide, ammonium hydrosulfide, lithium sul.-fide/ lithium
hydrosulfide, sodium monosulfide, potassium monosulfide,
potassium hydrosulfide, rubidium monosulfide, cesium
monosulfide, calcium hydrosulfide, strontium hydrosulfide
and barium hydrosulfide, respectively, are substituted :
for the sodium hydrosulfide.
It should be understood that while the present
invention has been described in considerable detail with
respect to certain specific embodiments thereof, it is
not to be considered limited to those embodiments, but
may be used in other ways which do not depart from the
spirit of the invention or the scope of the appended
claims.
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