U.S. patent application number 09/433110 was filed with the patent office on 2002-01-17 for method for leaching nickeliferous laterite ores.
Invention is credited to ARROYO, J. CARLOS, GILLASPIE, JAMES D., NEUDORF, DAVID A., WEENINK, ERIK M..
Application Number | 20020006370 09/433110 |
Document ID | / |
Family ID | 23718891 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020006370 |
Kind Code |
A1 |
ARROYO, J. CARLOS ; et
al. |
January 17, 2002 |
METHOD FOR LEACHING NICKELIFEROUS LATERITE ORES
Abstract
A process is provided for the leaching of both the "limonite"
(Fe approx. .gtoreq.25% and Mg approx. .ltoreq.6%) and "saprolite"
(Fe approx. <20% and Mg approx. .gtoreq.10%) fractions of
typical nickel and cobalt bearing laterite ore. The low magnesium
fraction of the laterite ore is leached with sulfuric acid at high
pressure and temperature to solubilize the metal values while
precipitating most of the solubilized iron as hematite or other
iron compounds and a portion of the dissolved aluminum as alunite
or other aluminum compounds. After reducing the pressure of the
leach slurry to approximately atmospheric pressure, the pregnant
leach slurry or solution is contacted with the high magnesium
fraction of the ore to solubilize most of the nickel contained in
the high-magnesium ore fraction while dissolving only a small
portion of the iron content of the high magnesium ore fraction.
Further neutralization of the leach slurry in the presence of an
alkali metal or ammonium ion will allow the precipitation of
iron-bearing jarosite at ambient pressure. This process for
incorporating the leaching of saprolite in the high pressure
leaching process for limonite ores requires neither high
temperature and pressure, nor special treatment of the saprolite
ore fraction, nor the addition of special reagents, e.g. reducing
reagents.
Inventors: |
ARROYO, J. CARLOS; (SPARKS,
NV) ; GILLASPIE, JAMES D.; (RENO, NV) ;
NEUDORF, DAVID A.; (RENO, NV) ; WEENINK, ERIK M.;
(SPARKS, NV) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Family ID: |
23718891 |
Appl. No.: |
09/433110 |
Filed: |
November 3, 1999 |
Current U.S.
Class: |
423/150.1 ;
423/150.4 |
Current CPC
Class: |
C22B 23/043 20130101;
C22B 23/0461 20130101 |
Class at
Publication: |
423/150.1 ;
423/150.4 |
International
Class: |
C01G 053/00 |
Claims
What is claimed:
1. A hydrometallurgical sulfuric acid leaching process for the
extraction of nickel and cobalt from nickeliferous laterite oxide
ore that comprises: a. providing an aqueous pulp of nickeliferous
oxide ore at a low magnesium content; b. leaching the aqueous pulp
at an elevated temperature (at least 200.degree. C.) and pressure
with an addition of sulfuric acid at least sufficient
stoichiometrically to effect the leaching of contained nickel and
cobalt and thereby provide a pregnant solution of nickel sulfate,
cobalt sulfate and a leach residue; and c. atmospheric pressure
leaching of high magnesium containing nickeliferous oxide ore with
the pregnant solution from step (b) by adding controlled quantities
of raw, untreated high magnesium ore to the pregnant solution at
temperatures of from 80.degree. C. up to the normal boiling point
of the solution and providing sufficient agitation and time to
effect the extraction of nickel and cobalt from the high magnesium
ore and form a final leach slurry.
2. The process of claim 1 wherein the pregnant solution and leach
residue of step (b) are not separated before atmospheric pressure
leaching of the high magnesium containing nickeliferous oxide
ore.
3. The process of claim 1 further comprising leaching a portion of
the high magnesium laterite ore at atmospheric pressure with
sulfuric acid before adding it to the pregnant solution from step
(b).
4. The process of claim 1 further comprising neutralizing the
pregnant solution from step (b) with a portion of the high
magnesium laterite ore.
5. The process of claim 3 further comprising neutalizing the
pregnant solution from step (b) with a portion of the high
magnesium laterite ore.
6. The process of claim 1 further comprising neutralizing the final
leach slurry by the adding a neutralization agent selected from the
group consisting of alkali and alkaline earth oxides, hydroxides,
carbonates, or mixtures thereof.
7. The process of claim 5 further comprising neutralizing the leach
slurry by adding a neutralization agent selected from the group
consisting of alkali and alkaline earth oxides, hydroxides,
carbonates, or mixtures thereof.
8. The process of claim 1 further comprising neutralizing the final
leach slurry by adding high magnesium laterite ore.
9. The process of claim 5 further comprising neutralizing the leach
slurry by adding high magnesium laterite ore.
10. The process of claim 6 further comprising providing a
sufficient amount of a precipitating agent selected from the group
consisting of alkali metal ions, ammonium ions, and mixtures
thereof, to precipitate ferric iron as jarosite.
11. The process of claim 7 further comprising providing a
sufficient amount of a precipitating agent selected from the group
consisting of alkali metal ions, ammonium ions, and mixtures
thereof, to precipitate ferric iron as jarosite.
12. The process of claim 8 further comprising providing a
sufficient amount of a precipitating agent selected from the group
consisting of alkali metal ions, ammonium ions, and mixtures
thereof, to precipitate ferric iron as jarosite.
13. The process of claim 9 further comprising providing a
sufficient amount of a precipitating agent selected from the group
consisting of alkali metal ions, ammonium ions, and mixtures
thereof, to precipitate ferric iron as jarosite.
14. The process of claim 1 further comprising subjecting the leach
slurry to a solid/liquid separation step to produce a final
pregnant leach liquor suitable for recovery of nickel and cobalt
and a final leach residue.
15. The process of claim 6 further comprising subjecting the leach
slurry to a solid/liquid separation step to produce a final
pregnant leach liquor suitable for recovery of nickel and cobalt
and a final leach residue.
16. The process of claim 7 further comprising subjecting the leach
slurry to a solid/liquid separation step to produce a final
pregnant leach liquor suitable for recovery of nickel and cobalt
and a final leach residue.
17. The process of claim 8 further comprising subjecting the leach
slurry to a solid/liquid separation step to produce a final
pregnant leach liquor suitable for recovery of nickel and cobalt
and a final leach residue.
18. The process of claim 9 further comprising subjecting the leach
slurry to a solid/liquid separation step to produce a final
pregnant leach liquor suitable for recovery of nickel and cobalt
and a final leach residue.
19. The process of claim 1 further comprising grinding the high
magnesium containing nickeliferous ore before adding it to the
pregnant solution from the pressure leaching step.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the hydrometallurgical
processing of nickeliferous ores and, in particular, to an improved
method for leaching nickel values from the high-magnesium or
saprolite fraction of such ores in combination with high pressure
and temperature leaching of the limonite fraction of the ore.
BACKGROUND OF THE INVENTION
[0002] The high pressure and temperature leaching of the limonite
portion of nickeliferous laterite ores with sulfuric acid is well
known, having been practiced commercially at Moa Bay in Cuba since
1959 (Boldt and Queneau, "The Winning of Nickel," Longmans Canada
Ltd., Toronto, pp. 437-449). The quantity of sulfuric acid required
to leach the major portion (approx. .gtoreq.90%) of the contained
nickel and cobalt and variable portions of several impurity
elements in the ore, e.g. magnesium, manganese, iron, aluminum,
chromium, is in excess of that required to form the corresponding
water-soluble metal sulfate compounds. This is because sulfuric
acid only dissociates to the single proton (H.sup.+) and the
bisulfate (HSO.sub.4.sup.-) ion at the high temperature used in
this leaching step, typically .gtoreq.200.degree. C. The bisulfate
ion dissociates on cooling of the leach slurry to sulfate
(SO.sub.4.sup.2) ion, releasing an additional proton. Thus, the
cooled leach slurry inevitably contains excess sulfuric acid in
addition to the dissolved metal values and impurity elements. This
excess acid must be neutralized before recovery of the dissolved
nickel and cobalt values, as would be apparent to anyone skilled in
the art. The cost of the excess sulfuric acid that must be added to
the leaching step and the cost of neutralizing agents required to
neutralize excess sulfuric acid in the final leach liquor are
significant disadvantages of this process.
[0003] Furthermore, the efficient recovery of nickel and cobalt in
substantially pure form from the high pressure leach liquor often
requires the prior removal of impurities such as ferric iron,
aluminum, and chromium, which dissolve to a greater or lesser
extent during pressure leaching. These impurities may interfere in
downstream nickel and cobalt recovery processes if not removed from
the solution. The removal can be effected by raising the pH of the
leach liquor to effect the hydrolysis and precipitation of these
impurities as hydroxide or hydroxysulfate compounds. Unfortunately,
when carried out at atmospheric pressure and temperatures below the
solution boiling point, this hydrolysis often produces voluminous
precipitates that are difficult to separate from the pregnant
liquor by conventional settling and filtration techniques. A
further disadvantage is the co-precipitation and subsequent loss of
significant quantities of the nickel and cobalt values during this
hydrolysis step.
[0004] A variety of methods have been developed to deal with the
above-mentioned disadvantages and problems of the high pressure
leaching process.
[0005] Taylor et al. (U.S. Pat. No. 3,720,749) teach the
precipitation and removal of iron and aluminum by the addition of a
soluble neutralizing agent, e.g. magnesia, to the leach liquor at a
temperature in excess of 130.degree. C. thereby precipitating the
iron and aluminum in an easy to separate form.
[0006] An improvement of the neutralization process was patented by
Lowenhaupt et al. (U.S. Pat. No. 4,548,794). This patent teaches
the recovery of nickel and cobalt from laterite ore by using a
low-pressure leach of high magnesium ore, after high pressure
leaching of low magnesium ore, to precipitate aluminum and iron. A
size separation of the laterite ore feed is made to produce low and
high magnesium ore fractions for the process. The finer, low
magnesium fraction is leached at high temperature and pressure and,
after separating the pressure leach liquor form the leach residue,
contacting the liquor with the coarser, high magnesium fraction of
the ore at greater than atmospheric pressure and high temperature
such that iron and aluminum precipitate in crystalline forms, e.g.
hematite, alunite. This aids the subsequent settling and filtration
of the precipitated iron and aluminum, while also dissolving
additional nickel units from the high magnesium fraction of the
ore. The preferred temperature for the neutralization step ranges
from 140.degree. to 200.degree. C. and requires the use of
autoclaves to maintain the elevated temperature and pressure. The
patent also describes a method where high magnesium ore is
contacted at atmospheric pressure and temperatures less than the
boiling point, with the leach solution from the pressure leach
step, before the low-pressure leach step. Nickel extraction is very
low in the atmospheric leach step (only 33-44%) and the
low-pressure leach is still required to achieve adequate nickel
extraction and to precipitate iron and aluminum in an easy to
settle and filter form.
[0007] Other methods for using the high magnesium fraction of the
ore to neutralize the high-pressure leach liquor have been
patented. U.S. Pat. No. 3,991,159 teaches the use of high magnesium
ore to neutralize acid resulting from the high-pressure acid leach
of a low magnesium ore. This is accomplished by coordinating the
leaching of the low magnesium fraction with the leaching of the
high magnesium fraction at high temperature and pressure. In this
method, leaching of the high magnesium fraction is carried out at
high temperature (150.degree.-250.degree. C.) and pressure for
effective iron and aluminum rejection, but with relatively low
nickel extraction from the high magnesium ore. Again, this process
has the disadvantage of requiring relatively high temperature and
pressure for the neutralization step.
[0008] In U.S. Pat. No. 3,804,613, a method to conduct
high-pressure acid leaching of high magnesium ore at relatively low
acid/ore ratios is disclosed. This is accomplished by
preconditioning the high magnesium ore with leach liquor from the
high-pressure leach step, before a high-pressure leach of the
conditioned high magnesium ore. The high magnesium ore must still
be submitted to a high pressure leaching step following the
atmospheric pressure conditioning step.
[0009] U.S. Pat. No. 4,097,575 teaches the use of high magnesium
ore that has been previously roasted to neutralize acid present in
a leach slurry resulting from the high-pressure acid leach of a low
magnesium ore. The high magnesium ore is thermally treated at
500.degree.-750.degree. C. under oxidizing conditions prior to the
neutralization step to increase the neutralization capacity of the
ore. The pH of the final liquor is taken above 2, but the
neutralization residue containing unleached high magnesium ore is
recycled to the autoclave to obtain higher nickel recovery.
Furthermore, rejected iron and aluminum are in the form of
hydroxides, which are difficult to deal with. This process suffers
from the high capital cost needed for roasting facilities and
disadvantages associated with injection of high magnesium ore
atmospheric leach slurry into the high pressure autoclave.
[0010] U.S. Pat. No. 4,410,498 teaches a method to leach high
magnesium laterite ore with sulfuric acid at a controlled pH of 1.5
to 3.0 while adding a reducing agent to maintain the redox
potential between 200 and 400 mV (vs. saturated calomel reference
electrode). The addition of a reducing agent increases the
reactivity of the serpentine in the ore and results in maximum
extraction of nickel consistent with minimum extraction of iron and
magnesia and minimum acid consumption. The process has the
disadvantages of the additional cost of the reducing agent, the
need for electrochemical potential control, and the need for
equipment to control the leaching atmosphere and prevent external
discharges in the case of toxic, gaseous reductants such as sulfur
dioxide.
[0011] The above methods are aimed at utilizing both the high and
low magnesium fractions of the nickeliferous laterite ore in order
to fully utilize the ore body, maximize the nickel and cobalt
extraction and minimize the iron and/or aluminum content of the
final leach liquor. All of these methods require the use of one of
the following to leach the high magnesium ore effectively: a)
elevated temperature and pressure; b) pretreatment by calcination
or roasting, or; c) addition of a reducing agent with controlled
pH.
[0012] It is an object of the current invention to combine the
leaching of the high magnesium fraction of the ore with the high
pressure leaching of the low magnesium portion of the ore, without
the use of elevated temperature and pressure, calcination
pretreatment, or addition of reducing agents, and still achieve
high nickel and cobalt recoveries, relatively short leaching time,
low iron extraction to solution and good solid/liquid separation
properties.
[0013] In most practices, pH adjustment of the leach slurry causes
the precipitation of metal hydroxides, including the hydroxides of
ferric iron, chromium and aluminum, which are separated from the
leach solution in the subsequent liquid/solid separation. During
this process, nickel and cobalt co-precipitate with the metal
hydroxides and reduce the metals recovery. Another important
consideration is the efficiency of the liquid/solid separation
process. In general, hydroxides produced at atmospheric pressure
are colloidal and difficult to filter or settle, thus requiring
very large equipment for effective separation. On the other hand,
alkali metal or ammonium jarosite is crystalline, which makes it
easier to filter and settle. In the presence of an alkali metal or
ammonium ion and in a certain range of pH, ferric iron will form
jarosite, a basic sulfate compound of the formula
M[Fe.sub.3(SO.sub.4).su- b.2(OH).sub.6] where M is sodium, lithium,
potassium or ammonium.
[0014] It is a further object of this invention to provide a
solution that is very low in iron by the formation of jarosite at
atmospheric pressure in the presence of alkali metal or ammonium
ions. The loss of nickel and cobalt by precipitation as metal
hydroxides is minimized, resulting in maximum metals recovery,
while an easier to settle iron compound is formed.
SUMMARY OF THE INVENTION
[0015] The present invention provides a process for the efficient
leaching of both the low magnesium and high magnesium fractions of
nickel laterite ore. The low magnesium fraction of the ore is
leached at high temperature and pressure, as in other processes
previously described. No special reductants, pretreatment steps or
high pressure steps are required to leach the high magnesium
fraction of the ore, representing substantial simplification over
the prior art. The current invention also provides for the removal
of iron by the formation of alkali metal jarosite, e.g. sodium
jarosite, to produce a low iron solution suitable for nickel and
cobalt recovery.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a flow sheet of one embodiment of the process of
the present invention.
[0017] FIG. 2 shows another embodiment of the process of the
present invention.
[0018] FIG. 3 is a graph showing the rate of nickel extraction from
high magnesium containing ore, or saprolite, as a function of
sulfuric acid concentration.
[0019] FIG. 4 is a graph showing the rate of nickel extraction as a
function of time during atmospheric leaching of saprolite ore with
sulfuric acid at 90.degree. C.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention provides a novel method for combining
the leaching of the high magnesium fraction of nickeliferous
laterite ore with the high pressure leaching of the low magnesium
fraction of the ore, while maximizing the extraction of nickel and
cobalt.
[0021] Referring to FIG. 1, laterite ore is separated into two
fractions 10. This separation can be based on selective mining or
on size classification by, for example, screening. One fraction is
finer than the other and has a lower magnesium content. This low
magnesium laterite, or so-called limonite, is mixed with water to
provide an aqueous pulp. This pulp is leached with sulfuric acid at
elevated temperature (at least about 200.degree. C.) and pressure.
During this leaching process 20, most metals in the ore are
completely or partially solubilized.
[0022] Upon completion of the leaching reaction, typically within
30 to 45 minutes, the pressure leach slurry is discharged to
atmospheric pressure and cooled to a temperature at or near the
normal boiling point of the leach solution. Steam is "flashed" off
during this step. The leach slurry, or leach liquor after
solid/liquid separation to remove the pressure leaching residue, is
now contacted 30 at atmospheric pressure with the other laterite
fraction. The high magnesium laterite or saprolite is used to
neutralize the free acid in the leach liquor at a temperature of
80.degree. to 98.degree. C., preferably above 90.degree. C. This
temperature is conveniently the temperature of the low magnesium
ore leach slurry after flashing to atmospheric pressure. The free
sulfuric acid concentration in the pressure leach solution is
typically 20 to 100 g/L H.sub.2SO.sub.4. The quantity of high
magnesium ore or saprolite added is calculated based on the
pre-determined acid consumption properties of the saprolite and the
quantity of free acid in the pressure leach solution. It is not
necessary to control the pH of the leach slurry, unlike the
teaching of U.S. Pat. No. 4,410,498. In fact, the relatively low
pH, typically <1.0, or high acidity of the pressure leach
solution is advantageous in that the rate of saprolite leaching is
higher at lower pH. Surprisingly, it is also unnecessary to add a
reducing agent to control the oxidation/reduction potential (see
FIG. 3 in U.S. Pat. No. 4,410,498) of the slurry in order to effect
rapid leaching of the saprolite at the higher acid concentration
prevailing in the pressure leach slurry or solution.
[0023] A high nickel extraction from the high magnesium ore is
possible in this process, without the need of ore pretreatment or
the use of any other reagents to increase the reactivity of the
ore.
[0024] Referring to FIG. 2, in another embodiment of this
invention, the high magnesium fraction of the laterite ore is first
leached 60 with additional sulfuric acid. The quantity of acid to
be added is calculated from the pre-determined acid consumption
properties of the saprolite ore, the quantity of free acid in the
pressure leach solution and the desired limonite to saprolite
processing ratio. In this process, nickel and other metals will be
solubilized. This embodiment of the invention allows the ratio of
limonite to saprolite ore to be varied while maintaining high
overall nickel and cobalt extractions and minimal iron extraction.
Addition of the additional sulfuric acid directly to the hot,
pressure leach slurry prior to the addition of saprolite causes
redissolution of iron compounds that were precipitated during the
pressure leaching step. The iron redissolution is largely avoided
by mixing the additional acid with all or a portion of the
saprolite ore prior to mixing with the pressure leach slurry.
[0025] The terminal acidity of the slurry after neutralization with
saprolite is advantageously 5-10 g/L free sulfuric acid. If the
free acid to saprolite ratio in the overall feed to the saprolite
neutralization step is too low, the leach extraction will be
lowered. On the other hand, if the free acid to saprolite ratio is
too high, there will be excess acid in the final neutralization
slurry that requires neutralization prior to iron
precipitation.
[0026] In another embodiment of the process, the saprolite
neutralization step is carried out continuously in a series of
agitated tanks. The number and size of the tanks is chosen to
maximize the rate of leaching and minimize the overall retention
time required to achieve the desired nickel extraction from the
saprolite. Multiple tanks are used in order to carry out the
leaching process at the highest average acidity possible. This
increases the rate of reaction because the leaching rate increases
as the sulfuric acid concentration increases.
[0027] During any step prior to the jarosite formation 40, a
precipitating agent selected from the group consisting of alkali
metal ions, ammonium ions or mixtures thereof can be added to the
process. Preferably, the precipitating agent is a source of sodium
ions. One method is to recycle sodium sulfate solution from the
downstream recovery process. This is the filtration product in the
formation of a metal carbonate precipitate. The formation of iron
jarosite is advantageously carried out at temperatures of about
90.degree. C. to 100.degree. C. under atmospheric pressure for at
least two hours and at a pH of 1.6 to 2.0 (preferably at 1.8). The
acid that is produced from the iron hydrolysis can be neutralized
with any neutralizing agent to maintain the desired pH. Examples of
the neutralizing agent include but are not limited to limestone,
lime or magnesia. Alternatively, more high magnesium laterite can
be added to neutralize the acid that is produced by the formation
of jarosite. Jarosite precipitation occurs at much lower pH values
than iron hydroxide precipitation and virtually eliminates the
problem of co-precipitation of nickel and cobalt and their
subsequent loss.
[0028] After the formation of jarosite, the leach slurry proceeds
to the liquid/solid separation process 50. This is preferably a
counter current decantation circuit, which produces a solids
residue virtually void of nickel and cobalt, and a clear leach
liquor to proceed to the metals recovery.
[0029] The following examples illustrate, but do not limit, the
present invention. Unless otherwise indicated, all parts and
percentages are by weight.
EXAMPLE 1
[0030] This example illustrates the atmospheric leaching of
saprolite ore with sulfuric acid solutions at constant acid
concentration and at temperatures between 80.degree. and 90.degree.
C. Saprolite ore was pulped at 15% solids in deionized water and
agitated in a well-sealed kettle with sulfuric acid at either
80.degree. or 90.degree. C. The concentration of sulfuric acid was
kept constant during the tests. Samples of liquid were taken at
different times during the test for analysis. The solids at the end
of the tests were filtered, washed, dried and split for chemical
analysis. Table 1 shows the final leaching results for each
test.
1TABLE 1 Results of saprolite atmospheric leach tests conducted at
constant sulfuric acid concentration Acid (Acid consumption) conc.
Temp. Sample Wt Composition Extraction (%) Kg/tonne Kg/Kg (g/L)
(.degree. C.) ID (g) Ni Fe Mg Ni Fe Mg ore Ni 100 80 Ore 50 1.92
8.01 14.10 94 84.2 79.7 599 32.26 Residue 30.2 0.192 2.1 4.75 50 80
Ore 50 1.87 7.14 13.59 89.7 66.2 77.7 -- -- Residue 31.1 0.309 3.89
4.87 25 80 Ore 50 1.87 7.35 13.91 77.6 38.7 66.4 529.6 34.89
Residue 34.6 0.606 6.51 6.77 10 90 Ore 233.5 1.91 7.31 16.07 70.1
31.6 71.8 625.0 45.50 Residue 192.6 0.693 6.06 5.49
[0031] These results show that saprolite ore is effectively leached
with sulfuric acid at temperatures close to the boiling point at
atmospheric pressure without the need of any ore pre-treatment or
additional reagents during leaching. The data also show that at
lower acid concentrations the kinetics of iron dissolution lag
behind those of nickel and magnesium dissolution resulting in a
high nickel extraction and low iron extraction. This is an
important criterion since iron poses a problem in the downstream
recovery of nickel by means known to those skilled in the art. A
process in which high nickel and low iron dissolution from
saprolite ore can thus be devised by leaching the ore with acid
concentrations below about 50 g/L The nickel extraction as a
function of time is illustrated in FIG. 3, which shows that the
rate of nickel extraction is a strong function of the sulfuric acid
concentration.
EXAMPLE 2
[0032] This example illustrates the atmospheric leaching of
saprolite ore with a fixed amount sulfuric acid solution at
90.degree. C. Saprolite ore was pulped at 15% solids in deionized
water and agitated in a well-sealed kettle with sulfuric acid at
90.degree. C. for 3 hours. The initial sulfuric concentration
varied from 106 to 114 g/L in the 4 tests described. Samples of
liquid taken at different times during the test for analysis. The
solids at the end of the tests filtered, washed, dried and split
for chemical analysis. Table 2 shows the final leaching results for
each test and FIG. 4 shows the kinetics of nickel dissolution from
saprolite ore.
2TABLE 2 Results of saprolite atmospheric leach with sulfuric acid
at 90.degree. C. Initial Acid consumption Test [H.sub.2SO.sub.4]
Sample Wt Composition Extraction (%) Kg/Kg No. (g/L) ID (g) Ni Fe
Mg Ni Fe Mg Kg/ton Ni 1 106 Ore 107.8 1.91 7.45 15.90 86.7 28.7
86.6 559 33.6 Residue 71.8 0.38 7.98 3.19 2 106 Ore 165.9 1.11 9.10
14.60 76.2 36.4 65.6 512 60.5 Residue 103.5 0.42 9.28 8.07 3 114
Ore 167 2.04 8.54 15.30 84.1 46.3 76.3 565 32.9 Residue 104.7 0.51
7.27 5.73 4 101 Ore 164 1.28 11.40 16.10 73.7 33.3 69.6 507 53.8
Residue 112.4 0.50 11.20 7.21
[0033] The variation of final nickel extraction between the various
tests is due mostly to the different amount of acid used in each
test and to the variation of composition of the samples. Metal and
free acid concentrations in solution as a function of time are
shown in Table 3. Approximate metal extractions were calculated
from the solution assays over time. These data show that most of
the nickel dissolves within the first 15 minutes of leaching when
the acid concentration is higher. After this time, saprolite
continues to react at much slower rates until most of the acid is
consumed. Since saprolite ore was leached at acid concentrations
under 50 g/l for most of the test period, the final iron
dissolution was relatively low.
3TABLE 3 Solution composition as a function of time during the
atmospheric leaching of saprolite ore at 90.degree. C. (Test 3)
Time Solution concentration (g/L) Extraction % (min) Ni Fe Mg
H.sub.2SO.sub.4 Ni Fe Mg 0 0 0 0 114 0 0 0 5 2.37 4.4 11.4 34.4
65.9 29.4 42.2 15 2.82 5.4 14.9 21.6 79.3 36.5 55.7 30 2.91 5.6
16.1 16.7 82.6 38.1 61.0 45 2.72 5.4 15.5 13.7 78.6 37.4 59.5 60
2.80 5.6 16.4 12.3 81.7 39.1 63.6 90 2.67 5.2 15.5 9.3 79.1 36.9
61.1 120 2.69 5.1 15.9 7.8 80.5 36.9 63.2 150 2.68 5.4 16.6 6.9
81.3 38.7 66.4 180 2.85 5.5 17.4 6.9 86.9 40.3 70.3
EXAMPLE 3
[0034] This example illustrates the atmospheric leaching of
saprolite ore with the product leach slurry from pressure leaching
of low magnesium, or limonite, ore. Limonite ore was first leached
in a titanium autoclave for 30 minutes at an acid to ore ratio of
0.38, 270.degree. C. and 40 wt % solids. After leaching and
pressure letdown, saprolite ore was added as a 50 wt % slurry to
neutralize the remaining free acid in the autoclave discharge that
results from the bisulfate shift at low temperatures. The saprolite
to limonite ratio, when leaching saprolite in this manner, was
about 0.17 (tests 1 and 2). In some cases, concentrated sulfuric
acid was added to the leach slurry in order to leach more saprolite
ore and increase the saprolite to limonite ratio (tests 3-5).
Saprolite leaching was carried out in an agitated tank at
90.degree. C. for 3 hours. The results from each test are shown in
Table 4.
4TABLE 4 Results of saprolite atmospheric leaching with autoclave
discharge at 90.degree. C. Additional sulfuric acid was added to
tests 3-5. Test Sample Wt Composition (%) Extraction (%) No. ID (g)
Ni Fe Mg from Ni Mg 1 Limonite 738 1.95 37.5 3.55 ore HPAL 650 0.13
43.7 0.9 Limonite 94.2 76.5 residue Saprolite 110 1.91 7.6 15.6
Saprolite 70.8 66.0 ore Final 722 0.20 40.1 1.7 Overall 91.2 72.3
residue 2 Liminite 721 1.89 36.4 3.35 ore HPAL 634 0.09 44.1 0.9
Limonite 95.8 77.5 residue Saprolite 120 1.91 7.6 15.6 Saprolite
66.1 64.4 ore Final 724 0.19 40.1 1.7 Overall 91.5 71.8 residue 3
Liminite 802 1.97 37.9 3.44 ore HPAL 705 0.11 41.0 1.0 Limonite
95.3 75.6 residue Saprolite 335 1.91 7.6 15.6 Saprolite 80.4 66.0
ore Final 897 0.22 33.8 2.7 Overall 91.0 69.3 residue 4 Liminite
658 1.88 36.5 3.46 ore HPAL 579 0.13 41.7 0.9 Limonite 93.7 76.0
residue Saprolite 245 1.91 7.6 15.6 Saprolite 76.1 67.2 ore Final
741 0.26 34.6 2.4 Overall 88.9 70.5 residue 5 Liminite 790 2 36.9
3.66 ore HPAL 695 0.14 41.60 0.96 Limonite 94.0 76.8 residue
Saprolite 315 1.91 8.25 15.00 Saprolite 74.9 73.2 ore Final 927
0.27 32.90 2.09 Overall 88.7 74.6 residue
[0035] These results demonstrate that saprolite ore can be used to
neutralize the free acid in the autoclave discharge from a
high-pressure acid leach of limonite ore, while obtaining high
nickel extractions from this high magnesium ore fraction. The
results also show that it is possible to vary the saprolite to
limonite ratio by adding extra sulfuric acid to the autoclave
discharge.
EXAMPLE 4
[0036] This example shows a method of iron control by precipitation
of jarosite after leaching of limonite ore at high pressure and
temperature and neutralization of the remaining acid with saprolite
ore at 90.degree. C. Limonite ore was first leached in a titanium
autoclave for 30 minutes at an acid to ore ratio of 0.38,
270.degree. C. and 40 wt % solids. After leaching and pressure
letdown, saprolite ore was added as a 50 wt % slurry to neutralize
the remaining free acid in the autoclave discharge slurry (ACD) at
atmospheric pressure and 90.degree. C. Concentrated sulfuric acid
was also added to the ACD to be able to leach more saprolite ore
and increase the saprolite to limonite ratio to 0.4. Sodium sulfate
was added to the saprolite slurry before addition to the ACD to
provide a source of alkali ions for jarosite formation. The final
step, after saprolite leaching, consisted of precipitating the iron
in solution as natro-jarosite. This was achieved by maintaining the
free acid concentration at around 5 g/l H.sub.2SO.sub.4
(pH.about.1.5) and the temperature at about 95.degree. C. for an
additional 3 hours. The free acid concentration was kept at the
mentioned level by periodic additions of CaCO.sub.3 slurry after
200 minutes of leaching. Results from this test are shown in Tables
5 and 6.
5TABLE 5 Results of saprolite atmospheric leaching with autoclave
discharge at 90.degree. C. followed by jarosite precipitation. Test
Sample Wt Composition (%) Extraction (%) No. ID (g) Ni Fe Mg from
Ni Mg 6 Limonite 355 1.92 35.7 4.9 ore HPAL 312 0.13 40.7 1.4
Limonite 94.1 73.9 residue Saprolite 140 1.91 7.3 16.1 Saprolite
75.3 69.7 ore Final 448 0.24 32.6 2.5 Overall 88.8 71.5 residue
[0037]
6TABLE 6 Kinetics of saprolite atmospheric leaching with autoclave
discharge at 90.degree. C. followed by jarosite precipitation. Time
Solution concentration (g/L) Extraction (%) (min) H.sub.2SO.sub.4
Ni Fe Mg Na Ni Mg 0 76 0 0 0 4.2 0 0 20 46.6 7.42 3.66 15.9 4.15
33.5 24.6 60 15.7 7.96 4.82 21.4 3.87 63.5 56.9 120 10.3 7.75 4.52
22.1 3.97 57.9 62.0 180 10.1 7.48 3.70 22.1 4.03 49.6 63.5 230 3.0
7.78 1.00 22.8 3.93 68.0 69.1 280 5.2 7.81 0.92 23.4 3.81 73.5 73.8
330 4.4 7.83 0.56 22.6 3.78 76.5 70.8
[0038] These results, once again, show that saprolite was
effectively used to neutralize the acid in the autoclave discharge
and to leach a high proportion of the nickel contained within the
saprolite ore. At the end of the atmospheric leach step, iron in
solution decreased from a maximum of about 5 g/l by the formation
of jarosite until the iron concentration in solution reached about
0.5 g/l. The low nickel assay of the final residue after jarosite
precipitation was achieved despite the precipitation of approx. 5
g/L iron as jarosite.
EXAMPLE 5
[0039] This example illustrates the continuous processing of
limonite ore under high-pressure acid leach (HPAL) conditions
followed by the processing of saprolite ore under atmospheric leach
(AL) conditions.
[0040] A limonite ore slurry at 38.5 wt. % solids was leached at
high pressure and temperature (270.degree. C. and 820 psi) at an
acid to ore ratio of 0.4 tonnes acid/tonne ore in a continuous
autoclave. Limonite was processed at a rate of 0.8 dry tonnes/day
yielding an autoclave retention time of 30 minutes. The discharge
from the autoclave consisted of HPAL residue and leach solution
containing metals and free sulfuric acid (92 g/L). The compositions
of the ore fed to the autoclave and the discharge residue, as well
as the calculated metal extractions, are shown in Table 7.
7TABLE 7 High pressure acid leaching (HPAL) results. Al Co Cr Fe Mg
Mn Ni (%) (%) (%) (%) (%) (%) (%) Limonite 2.82 0.125 1.47 34.4
3.72 0.71 1.63 feed HPAL 2.62 0.000 1.54 39.5 0.93 0.17 0.075
residue Extraction 20.0% 100.0% 9.5% 1.1% 78.4% 79.7% 96.0%
[0041] The autoclave discharge slurry was mixed with saprolite ore
(at 46 wt. % solids) in the proportion of 0.3 tonnes
saprolite/tonne limonite. Sodium was added as sodium sulfate to the
water used to prepare the saprolite ore slurry. Sulfuric acid was
added to the mixture in the proportion of 0.46 tonnes concentrated
acid/tonne saprolite. The concentrated acid combined with the
residual acid from the HPAL yielded an acid to saprolite ratio of
0.96 tonnes acid/tonne saprolite. The overall concentrated acid to
ore ratio was 0.41 tonnes acid/tonne ore (limonite plus
saprolite).
[0042] The atmospheric leach circuit (AL) consisted of 3 tanks in
series with an overall retention time of 4.2 hours (1.4
hours/tank). This circuit was followed by a jarosite precipitation
circuit (JP) consisting of 2 tanks in series with an overall
retention time of 5.9 hours (first tank 1.4 hours, second tank 4.5
hours). Limestone slurry was added to the jarosite precipitation
tanks to control the slurry pH. Average conditions of these tanks
over the test duration of approximately 70 hours are presented in
Table 8:
8TABLE 8 Atmospheric Leach and Iron Precipitation Conditions Tank
pH Free Acid (g/L) Temperature (.degree. C.) AL1 37.7 97 AL2 33.5
92 AL3 27.1 94 JP1 1.5 10.5 94 JP2 1.9 5.9 92
[0043] The compositions of the residues resulting from the
consecutive operations and the calculated metal extractions from
saprolite in atmospheric leaching and the overall extractions from
HPAL followed by atmospheric leaching are given in Table 9.
9TABLE 9 Ore and Leach Residue Compositions and Metal Extractions
for Each Stage Al (%) Co (%) Cr (%) Fe (%) Mg (%) Mn (%) Ni (%)
Limonite ore 2.82 0.125 1.47 34.4 3.72 0.71 1.63 Saprolite ore 1.58
0.085 0.85 11.4 14.83 0.48 1.31 HPAL residue 2.62 0.000 1.54 39.5
0.93 0.17 0.075 AL residue 2.45 0.027 1.38 32.9 2.00 0.23 0.13 JP
residue 2.04 0.007 1.19 29.2 1.53 0.18 0.092 Extraction from 17.6%
82.6% 13.9% -5.4% 73.3% 38.8% 85.6% saprolite Extraction from 20.0%
97.5% 10.3% 0.6% 75.6% 72.8% 94.1% limonite and saprolite
[0044] The solutions resulting from the leaching and precipitation
stages show the increase in nickel and cobalt content as well as
the decrease in free acidity. The Fe content initially increased
during the atmospheric leaching stage, but subsequently decreased
during jarosite precipitation, as shown in Table 10.
10TABLE 10 Solution Compositions after Each Stage Al Co Cr Fe Mg Mn
Ni Free (mg/ (mg/ (mg/ (mg/ (mg/ (mg/ (mg/ Acid L) L) L) L) L) L)
L) (g/L) HPAL 2741 695 491 2463 16847 3791 9826 92 solution AL 3728
825 768 13715 33066 4472 12084 27 solution JP 2819 820 587 1417
35663 4500 12591 5.9 solution
EXAMPLE 6
[0045] This example illustrates the continuous processing of
limonite ore under high pressure acid leach (HPAL) conditions
followed by the processing of saprolite ore under atmospheric leach
(AL) conditions.
[0046] A limonite ore slurry at 35 wt. % solids was leached at high
pressure and temperature (270.degree. C. and 820 psi) at an acid to
ore ratio of 0.34 tonnes acid/tonne limonite in a continuous
autoclave. Limonite was processed at a rate of 0.8 dry tonnes/day
yielding an autoclave retention time of 30 minutes. The discharge
from the autoclave consisted of HPAL residue and leach solution
containing metals and free acid (102 g/L). The compositions of the
ore fed to the autoclave and the discharge residue, as well as the
calculated metal extractions, are shown in Table 11.
11TABLE 11 High pressure acid leaching (HPAL) results Co (%) Fe (%)
Mg (%) Ni (%) Limonite feed 0.11 40.33 2.79 1.66 HPAL residue 0.004
43.8 0.82 0.091 Extraction 96.1% 1.2% 70.5% 94.8%
[0047] The autoclave discharge slurry was mixed with saprolite ore
(at 51 wt. % solids) in the proportion of 0.38 tonnes
saprolite/tonne limonite. Sodium was added as sodium sulfate to the
water used to prepare the saprolite ore slurry. Sulfuric acid was
added to the mixture in the proportion of 0.23 tonnes concentrated
acid/tonne saprolite. The concentrated acid combined with the
residual acid from the HPAL yielded an acid to saprolite ratio of
0.59 tonnes acid/tonne saprolite. The overall concentrated acid to
ore ratio was 0.31 tonnes acid/tonne ore (limonite plus
saprolite).
[0048] The atmospheric leach circuit (AL) consisted of 4 tanks.
Half the saprolite was added to the first tank (1 hour retention)
along with the concentrated sulfuric acid, while the other half was
added to the second tank (1.4 hour retention) along with the
autoclave discharge slurry. The first tank overflowed into the
second tank, which then overflowed into 2 tanks in series (1.4 hour
retention each). This circuit was followed by a jarosite
precipitation circuit (JP) consisting of 2 tanks in series with an
overall retention time of 5.9 hours (first tank 1.4 hours, second
tank 4.5 hours). Limestone slurry was added to the jarosite
precipitation tanks to control the slurry pH. Average conditions of
these tanks over the test duration of approximately 82 hours are
presented in Table 12:
12TABLE 12 Atmospheric Leach and Iron Precipitation Conditions Tank
pH Free Acid (g/L) Temperature (.degree. C.) AL1 54.4 71 AL2 21.5
92 AL3 20.3 91 AL4 14.7 91 JP1 1.7 7.6 94 JP2 2.1 6.5 93
[0049] The compositions of the residues resulting from the
consecutive operations and the calculated metal extractions from
saprolite in atmospheric leaching and the overall extractions from
HPAL followed by atmospheric leaching are given in Table 13.
13TABLE 13 Ore and Leach Residue Compositions and Metal Extractions
for Each Stage Co (%) Fe (%) Mg (%) Ni (%) Limonite feed 0.11 40.33
2.79 1.66 Saprolite ore 0.088 11.4 14.2 1.30 HPAL residue 0.004
43.8 0.82 0.091 AL residue 0.016 36.7 1.83 0.147 JP residue 0.018
33.0 1.83 0.132 Extraction from saprolite 42.9% -4.7% 62.7% 76.5%
Extraction from limonite and 83.6% 0.6% 69.9% 91.8% saprolite
[0050] The solutions resulting from the leaching and precipitation
stages show the increase in metals content as well as the decrease
in free acidity. The Fe content initially increased during the
atmospheric leaching stage, but subsequently decreased during
jarosite precipitation, as shown in Table 14.
14TABLE 14 Solution Compositions after Each Stage Al Co Cr Fe Mg Mn
Ni Free (mg/ (mg/ (mg/ (mg/ (mg/ (mg/ (mg/ Acid L) L) L) L) L) L)
L) (g/L) HPAL 4391 764 719 3820 17220 4264 12030 102 solution AL
3261 698 640 6618 32628 3982 11228 14.7 solution JP 3343 757 547
1568 35399 4279 12185 6.5 solution
[0051] While there have been described what are presently believed
to be the preferred embodiments of the invention, those skilled in
the art will realize that changes and modifications may be made
thereto without departing from the spirit of the invention. It is
intended to claim all such changes and modifications that fall
within the true scope of the invention.
* * * * *