Note: Descriptions are shown in the official language in which they were submitted.
1~557~
This invention relates to a method for enhancing the
atmospheric leaching of nickeliferous matte, such as nickel
sulfide and nickel-copper sulfide mattes.
By "atmospheric leaching" is meant the leaching of
nickeliferous matte in a hot acid solution at atmospheric pres-
sure as opposed to high pressure leaching.
State of the Art
Methods have been proposed for the selective leaching
of nickel from nickeliferous sulfide mattes, such as nickel
sulfide and nickel-copper sulfide mattes.
For example in U.S. Patent ~o. 940,292 (dated ~ovem-
ber 16, 1909), a method is disclosed for selectively leaching
nickel from nickel-copper matte containing about 40% nickelr
40'~ copper and the balance substantially sulfur. The matte is
lS pulverized and agitated with a hydrochloric acid solution at a
temperature of about 180F (83C). According to the patent, a
substantial amount of nickel is selectively dissolved from ~he
matte with the copper remaining in the residue.
In U.S. Patent ~o. 967,072 (August 9, 1910), a nickel-
copper matte is leached with hot sulfuric acld to dissolve
selectively ~he nickel, the process relying on the~formation ~
of H2S in situ to prevent the copper from being dissolved from
the matte. ~ ~
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~05571~
A method is disclosed in U.S. Patent No. 1,756,092
(April 29, 1930) for selectively extracting nickel from
nickel-copper sulfide matte. In order to increase the solution
rate of nickel into the acid, the matte is melted and then
rapidly cooled by granulation in water. The leaching i5 car-
ried out in sulfuric acid under atmospheric pressure and a
temperature of about 80C to lOO~C (176~F to 212F)
U.S. Patents No. 2,223,239 (November 16, 1940),
No. 2,239,626 (April 22, 1941) and ~o. 2,753,259 (July 3, 1956)
disclose the selective leaching of nickel from nickel-copper
matte with acid, such as HCl or H2S04. The patents point up
the importance of employing matte in which the sulfur content
is stoichiometrically less than the amount required to combine
with all the metal values present. The less the amount of com-
bined sulfur, the higher is the nickel recovery following leach-
ing.
However, a problem in the atmospheric leaching of
nickeliferous matte is that the leaching characteristics of
matte tend to vary from composition to composition, whether
in the as-cast state or in the conventionally produced granu-
i lated state. Such characteristics are generally reflected in
¦ prolonged leaching times which adversely affect the economics
I ~ of the process. It would be desirable to provide a method of
i pretreating a matta independent of its history 50 as to assurea consistent feed product having substantially uniform leaching
characteristics, particularly with respect to shorter leaching
times and higher extraction efficiencies.
l~SS7~1
Objects of the Invention
It is thus the object of the invention to provide a
nickeliferous sulfide matte in a form capable of being econo-
mically leached in hot acid at atmospheric pressure to extract
selectively therefrom a substantial portion of the contained
nickel.
Another object is to providé a method of pro~ucing
a nickeliferous matte having improved leaching characteristics
wherein a plurality of mattes of different histories are blen-
ded together, with or without the addition of metal scrap,
such as nickel, cobalt, copper-containing scrap and alloys
containing these metals.
These and other objects will more clearly appear
when taken in conjunction with the following disclosure and
the appended claims.
The Invention
According to the lnvention, a method is provlded for
the preparation of sulfide matte for atmospheric acid leachlng,
such as nickeliferous sulfide mattes containing by weight about
30~O to 75/O nickel (e.g. about 40% to 70~/O)~ up to about 50~O
copper (e.g. about 2% to 40%), up to about 10% Co, about 4% to
25% sulfur ~eOg~ about 5% to 20~/o) and up to about 5% iron, the
nickel, copper and sulfur content making up at least ab~ut 90~/O
by weight of the matte, the balance being gangue, other me~als,
;. : ~ .
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:
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--
~ 16~5S7~1
~, and the like. It is important that the amount of sul~ur con-
tained in the matte be less than that required stoichiometrical-
ly to combine with the metal values therein and not exceed that
amount required to combine with nickel as Ni3S2. In order to
provide a matte capable of being economically leached at at-
mospheric pressure and at temperatures ranging up to àbout 100C
to extract selectively a substantial portion of nickel there-
from, a method is employed which comprises establishing a bath
.
of molten matte of predetermined composition having the afore-
mentioned characteristics, the temperature of said molten matte
being at least about 100C higher than the li~uidus-solidus tem-
perature thereof, lowering the temperature of the molten matte
to a granulating temperature relative to said liquidus-solidus
temperature so that the granulating temperature falls within the
range of about 50C above to about 100C below said liquidus-
solidus temperature, granulating the matte and quenching it in
the presence of a quenching fluid, e.g. water or a cool gas,
from said granulating temperature, and then comminuting~sald~
granulated matte to produce a feed product characterized by im-
proved dissolution characterlstics with respect to the nickel
therein when subjected to atmospheric leaching in a hot acid
solution.
Tests have indicated that matte pretreated and pro-
duced in the foregoing manner exhibits superior d~issolutlon
2~ characteristics compared to mattes of similar composltion~in
either the as-cast state or in the conventionally produced granu-
lated state. Mattes produced in the as-cast state generally in-
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volve the slow cooling of a large molten mass of nickeliferous
sulfide which usually results in a segregated structure. Such
mattes in the comminuted state do not behave uniformly during
atmospheric leaching as such mattes generally have different
melting and cooling histories. convehtionally granulated mattes
are those mattes which are granulated by pouring said matte fr~m
a temperature substantially above the liquidus-solidus tempera-
ture of said matte, that is, more than 100F above said liquidus-
solidus temperature.
While conventionally granulated mattes in the commi-
nuted state generally exhibit superior leaching characteristics
over as-cast mattes, such mattes vary in characteristics from
lot to lot or composition to composition and do not always pro-
vide uniform leaching results.
Time is an important economic factor in atmospheric
leaching. Thus, by shortening the leaching time in the selec-
; tive dissolution of nickel from ~he matte, the residue remain-
ing can then be processed much sooner by high pressure leaching
to recover therefrom the remaining metal values, such as nickel
and copper.
We have found that we can obtain uniform and~markedly
improved leaching results by controlling the granulation tem-
_ perature within a range that does not exceed 50C~above the~
solidus-liquidus temperature of the matte composit~ n~ and whLch
. ~ .'
~55'7~L~
extends to about 100C below said solidus-liquidus temperature,
so long as a temperature is chosen within the range tnat en-
ables the molten matte to be easily poured and granulated in
a quenching medium, e.g. water, water`spray, cool gas, etc.
The thermal characteristics of a particular matte
composition are determined by heating the matte to a superheat
temperature above its solidus-liquidus temperature and then
allowing it to cool slowly to and through the solidus~ uidus
- temperature range using an immersion thermocouple to detect
the one or more thermal arrests indicative of the transitory
change of state of the matte during cooling. Haviny determined
that thermal arrest of the liquidus-solidus temperature for a
specified matte composition, this temperature is then utilized
to determine the correct granulation temperature defined herein-
above.
Details of the Invention
As stated hereinabove, matte grades of different his-~
tories can be treated in accordance with the invention to pro-
vide comminuted ma~te having the desired dissolution rate in
hot sulfuric acid. The amount of nickel of the total nickel pre-
sent available for leaching is dependent on the composition of
the matte. For example, the lower the amount of sulfur in the
matte, the higher is the amount of available leachable nicXel
(usually in the form of finely dispersed metal nickel), and as
the compound Ni3S2, the nickel combined as ~iS being not rea-
dily acid soluble within the time period of intsrest.
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~L0557~
As illustrative of the foregoing, analyses of var-
; ious~grades of mattes are given in both the as-cast condition
and the granulated condition (the invention) as follows:
_ ble 1 ~
.
Available Nickel
_ Percent Elemen t % of Total
Type Matte~i Cu S Fe Nickel in Matte*
lA (As-Cast) 40.039.6 16.4 0.23 61
. 2A (Granulated) 40.8 38.8 16.6 0.40 61
(Invention) -.
.
lB (As-Cast) 68.03.4 21~0 3.4 50
2B (Granulated) 68.0 6.8 18.6 2.88 50
(Invention)
.
lC (Granulated) 51.6 38.4 5.0 1.84 92**
(Low S)
2C (Low S) 52.0 38.8 5~4 1.28 95
(Granulated~
(Invention)
* - Calculated from ~i-Cu-S Ternary Diagram
** - Received as-granulated from
Outokumpu (Finland)
: :: : .,
Each of the mattes lA, lB and lC in the table is~ in
- 10 the as-received condition, mattes lA and lB being in the~:as~
cast state while matte lC was received from Finland in the con-
ventionally granulated state.
: The foregoing mattes were then converted to the
:
granulated mattes of the invention, to wit, 2A, 2B and 2C.
In the case of matte lA, a charge was produced:by
. ,
blending with the as-received:matte such materials as nickel
powder, copper shot and element sulfur in percentage amounts
.
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~05S71~
corresponding to the initial composition of matte lA. The
; ~ charge was melted in a 15KW induction furnace, and the melt
raised to 2500F (1371C). An immersion thermocouple was inser-
ted into the molten bath and the bath turned off. A cooling
curve was obtained which gave a rest point at the liquidus-
solidus temperature of about 1760F (960C).
Using the rest point temperature as a guide, the
foregoing charge was reheated to substantially above the liquidus-
solidus temperature (2500F or 1371C) and then tapped into a
preheated clay-graphite crucible (preheated to 2000F or 1093C)
and the charge allowed to cool to the desired granulating tem-
perature of about 1800F (982C) before being poured into a
preheated pouring basin having a quarter-inch opening or ori-
fice in the bottom thereof, the basin being disposed within a
granulating apparatus comprising a rotating disc having radially
disposed carbon vanes fixed thereto. A perforated copper ring
is located within the apparatus surrounding the pouring basin
through which water is sprayed as the stream of molten matte
is fed gravimetrically at about 1800F (982C) to impinge on
the surface of the rotatlng disc for deflection by the carbon vanes,
The temperature of the matta during the pouring step is substan-
tially at the liquidus-solldus temperature or may be slightly
above it, e.g. 20C to 50C above. Thus, as the molten matte
lS thrown by centrifugal force to the sides of the apparatus as
fin~ly divided globules, it is immediately quenched to form
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55711
frozen granules which drop to the bottom of the granulation
apparatus where they are collected.
After granulation, the product is ground to 50~/0 minus
400 mesh, with about 75% of the comminuted product passing
through 270 mesh.
Matte 2B was produced by granulating matte lB and
matte 2C produced by granulating matte lC, the granulated mattes
being thereafter ground as stated hereinabove.
Following production of the comminuted mattes of
the invention, each of the mattes was subjected to a leaching
program using a leaching solution containing 22 grams per liter
(gpl) o~ Cu+~ ions and 46 gpl of H2S04. The presence of copper
ions in the solution corresponds to recycle spent electrolyte
from copper electrolytic cells to be discussed later. Each of
the tests was conducted in 450 milliliters (ml) of solution into
which air is vigorously bubbled at a rate of 520 ml/min, the
solution being stirred at a rate of 420 RPM with the temperature
\ maintained at 75C (167~F). The solution with the foregoing acid
concentration has a starting pH of less than about 0.5 and gen-
erally a pH in the neighborhood of about 0.3.
The matte granulated according to the invention is
compared to the corresponding as-received matte by leaching
~ the respective mattes under the foregoing conditions until the
pregnant solution reaches a pH of about 5.3, the foregoing pH
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being taken as indicative of the completion of dissolution for
practical purposes. The time to reach the pH is measured and
used in comparing the leaching characteristics of the various
mattes.
The results obtained in leaching 164 grams each of
mattes lA and 2A in 450 ml of solution (about 27% solids by
weight) are given in Table 2 as follows:
Tabl,e_ ?
Type IMelting~Granulation ¦Time to pH ~ % Ni
Matte F ¦ F = 5.3 min. qpl Extraction ___
1A As-Cast 83 0.001 18.1
2A ¦ 2500 ¦ 1800 ~ 65 0.001 26.1
The solution following leaching of 164 grams reached
a pH of 5.3 much sooner with the granulated matte than with the
as-cast matte and larger amounts of soluble nickel were dis-~
solved. In both tests, the copper was cemented out of~solution
by the free nickel in the matte to the very low level of 0.001
gpl 1 part per million (ppm).
,
However, when a lower amount of 91 grams of the same
matte samples were leached in the same amount of solution (that
is, at a lower pulp density), approximately 80'~o of~the avail-
able nickel was extracted,;the-granulated matte (2A3 being lea-
ched 25 minutes sooner than the as-cast matte (lA), Su~s~an-
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5711
tially all of the copper was cemented from the leaching solu-
tion by the free nickel in both mattes as shown in Table 3.
Table 3
Type ~ on j Time to pH Cu~+ ¦ % Ni
Matte F ¦ F = 5.3 min. qpl Extraction
lA As-Cast 145 0 . 002 47 ~ 6 _
2A 2 5 0 0 ¦ 18 0 0 _12 0 0 . 0 02 _4 7 3 _ I
Similar tests were conducted on mattes lB and 2B.
These results are given as follows:
Table 4
Type Melting ¦Granulation Time to pH Cu ¦ % Ni
Matte _ F ¦ F = 5-3 min._ qpl Extrac-tion
lB As-Cast ~? 2 50 7 ~ 2 0 2 5 . 9
2B 2500 ¦ 1800 110 0.001 41~1
The leaching of granulated matte 2B was completed
after 110 minutes; about 41% of the nickel being extracted which
corresponds approximately to about 80~/o of the avallable sol~~ble
nickel. Substantially all of the copper was rejected from solu-
tion. The cast matte, on the other hand, leached very~poorly
and after more than 250 minutes, only 25~/o was dissolved. The
solution (lB) still contained relatively large amounts of copper
~ (7~2 gpl).
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1~55'7~1
Tests have indicated that the temperature of granu-
.
lation has an effect on the leaching activity of the material.
For example, matte 2A granulated from temperatures of 2300~F
~-, to 2500F (1260C to 1371C) tended'to be less reactive than
the matte granulated in the neighborhood of 1800F.
¦ ~o batches of low sulfur matte lC were melted at
J
2500F (1371C) and then granulated at 2100F tll50C) and
2300F (1260C), respectively. A cooling curve showed that
.
this matte had a solidus-liquidus temperature of about 2155F
'A 10 tll80C). Thus, one granulation temperature (1150C) was 30
below the solidus-liquidus temperature, while the other (1260C)
was 85 above this temperature.
In a leaching program involving 88 grams of each of
.
the two differently granulated mattes in 450 ml (about 16~5%
solids by weight) of the aforementioned solution, the following
results were obtained:
.
Table 5
Melting Granulation Time to pE Cu++ /O Ni
-.3 F Temp~ F _ = 5.3 min. qPl Extracted
j~ 2G 2500 _2300 185 _0 001 38.3
2500 2100 _ 165 _ 0.001 , 37O4~ __
~ As will be noted, while substantially the same amount
.~ .
of nickel was dissolved, the matte granulated at 2100F (1150C)
wasimore active in that the solution reached a pH of 5.3 about
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~557~1
20 minutes sooner. In other words, atmospheric leaching is
- completed sooner with the matte granulated in accordance with
the invention.
When 49 grams of the same matte were similarly leached
in ~he same amount of solution as in Table 5, the following re-
sults were obtained:
Table 6
Melting Granulation Total Leach Final Cu~+ I % ~i
F F _ Time PH qpl Extracted
2500 2300 460 4.5 4 0 ~9 2
. . .
2500 2100 380 4.~5_ -7 _ 51.8
Much faster leaching was obtained with the material
granulated at 2100F (1150C) as compared to a granulation tem-
perature of 2300E ~1260C). As will be noted, the matte quen-
ched at 2100F (1150C) leached 80 minutes sooner and, moreover,
rejected most of the copper from solution,
The atmospheric leaching in general is carried out for
a period of time until the pH increases to substantially over
4, e.t. 4.5 and above and, preferably, at least about 5.~ ~
It appears that nicXeliferous mattes granulated in
accordance with the invention produce a very fine grain struc-
- ture which is almost homogeneous when examined optically. In
contrast, the cast matte contains much larger grains with segre-
gated phases. In the cast matte, the area of contac~ among the
different phases is greatly reduced and, as a result, the rate
of galvanic type reactions due to the presence of free nickel
during leaching is also reduced. ~- ~
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~0~57~
The granulation temperature has a beneficial effect
on the leaching time. As stated above, the temperature may
range from about 50C above the solidus-liquidus temperature
to 100C below this temperature, with the granulation tempera-
ture preferably ranging to below the iiquidus-solidus tempera-
ture, for example, 15C to 75C below this temperature.
Generally speaking, for mattes having the same Ni/Cu
weight ratio, the liquidus-solidus temperature increases with
decreasing sulfur content. For example, in the case of low-
sulfur matte lC (51.6% Ni, 38.4% Cu, 5% S and 1.84% Fe), the
liquidus-solidus temperature determined ~rom the Ni-Cu-S ter-
nary diagram is about 2180~F (1200C). An experimental cool-
ing curve placed the temperature at approximately 2200F. The
foregoing matte corresponds to the mattes referred to in Tables
5 and 6.
As stated hereinbefore, the granulation treatment
of the invention is important in providing a eed product exhibit-
ing enhanced leaching rates. This is important as it enables
the setting up of a unit operation in which a plurality of pro~
cesses can be coordinated together to provide recovery of such
metal values as nickel, cobalt, copper, among others.
~ The granulation treatment may constitute the flrst
_step of the process. Thus, following granulation, the matte
is comminuted to provide a~finely divided feed product, such
:
as a feed product in which at least 50% by weight passes through
.,:
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270 mesh (U.S. Standard Screen). The matte may be a blend of
conventionally prepared matte compositions to which scrap metal
te.g. Ni, Co, Cu, etc.) may be optionally added together with
make-up sulfur.
A typical granulated matte is one having the follo~-
ing composition: 50.5% ~i, 28.1% Cu, 0.6% Co, 2% Fe and 18.8%
S.
Putting it succinctly, a typical unit operation
would comprise subjecting the gxanulated matte in the commi-
nuted state to acid leaching at a temperature of about 150F
to 185F (65C to 85C) while the leaching solution is strongly
aerated. Generally speaking, the pulp density may range from
about 10% to 40% by weight solids. The acid leaching solution
is preferably spent electrolyte recycled from copper electroly-
sis process carried out later on in the process. An example of
a spent electrolyte is one containing 55 gpl ~i, 20 gpl Cu,
0.85 gpl Co, 122 gpl of S04 ions and 43 gpl H2S04. Broadly
speaking, the spent electrolyte may comprise up to about~75 gpl
nickel combined as sulfate, 5 to-30 gpl copper combined as sul-
fate and ~ree sulfuric acid in an amount ranging ~rom about 20
to 100 gpl.
The copper is re~ected from solution by hydrolysis
_ and/or cementation during atmospheric leaching and a nickel-
~; rich solution obtained which is treated to remove iron and then
sent to nickel and cobalt recovery. The methods for recovering
nickel and cobalt are well known in the art and need not be
described here.
::
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~L~5S71~L
.Following atmospheric leaching, the residue is fil-
tered, washed and slurried in an acid solution to remove most
of the iron therefrom. The residue may contain at this stage
about 28% Ni, 48% Cu, 0.8% Co, 2.4% Fe and 22~/o S~ The residue
after washing is pulped (e.g. 20% to 50% solids) and high pres-
sure leached in an acid solution at a pressure of about 600 to
700 psig at a temperature of about 350F to 400F (177C to
204~C). This results in a pregnant liquor which, after filter~
ing, becomes the feed solution for copper electrowinning after
acidifying and dilution to contain about 40 to 50 gpl Ni, ~0 to
50 gpl Cu and about 100 gpl free sulfuric acid.
The foregoing solution is sent to copper electroly~
sis for copper recovery, the spent solution for recycle to
atmospheric containing about 55 gpl ~i, 20 gpl Cu, 0.85 gpl Co,
122 gpl S04 ions and 43 gpl H2SO4.
An important advantage of producing the desired feed
matte by blending together mattes of different grades and hls-
tories, with or without the addition of scrap metal (~i, Co,
Cu, alloys thereof, etc.), is that a feed product is obtained
following granulation which is independent of the pr1or hLstory
of the blended materials. Examples of blended compositlons for
; ` use in producing the granulated feed material of the invention
are as follows:
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Table 7
- r Blend
Material Wt. ~/~ 7i Co nposltion I % Fe % Otherc
_ . _ _
lA 45 4039.6 16.4 0.23 3 8
. ._.
lB 45 683.4 21.0 3.40 3~? _
Cu Scrap _ _ 10 _ 100 0 - _ ~ _
_ . .
Blend Com-
p~sition 100 48.629.5 16 9 1 1.6 3.4
Table 8
!
Blend Com ~osition _ % Other
Material Wt. % Ni % Cu % S % Fe (bal.)
lB 30 68.0 3.4 21.0 3.4 4.2
lC 40 51.6 38.4 5.0 ~1.8 3.2
Monel
Scra~ 13 67.0 30.0 ~ 1.5 1.5
Scrap 10 _ 100.0 _ _ _
Sulfur 7 _ _ 100.0 _ _ ~ _
Blend Com-
Position100~49~8 30.3 -15.3 1.9 2.7
. ~
~ As wlll be apparent, any desired blend can be produced
so long as the final composition is melted and granulated in
accordance with the invention. While cobalt is not listed~in
_ Tables 7 and 8, it is understood to be present in~small~amounts
in most nickeliferous sulfide mattes. Of course, cobalt scrap
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1~557~
in the form of the metal or alloys thereof may be employed in
producing blended compositions containing cobalt ranging up to
about 10% or higher.
Although the present invention has been described in
conjunction with preferred embodiments, it is to be understood
that modifications and variations may bè resorted to without
departing from the spirit and scope of the invention as those
skilled in the art will readily understand. Such modifications
and variations are considered to be within the purview and
scope of the invention and the appended claims.
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