Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
Recovery of nickel and cobalt from laterites by sonic assisted sulfatation
FIELD OF THE INVENTION
[0001] The present invention relates to a method and a system for recovery of
nickel and cobalt from laterites.
More specifically, the present invention is concerned with a method and a
system for recovery of nickel and
cobalt from laterites by sonic assisted sulfatation.
BACKGROUND OF THE INVENTION
[0002] Laterites can be defined as a variety of sub-soil, much weathered in
tropical or subtropical climates, and
containing iron oxides, alumina, silicates and, in some instances, small
amounts, in percent range, of nickel
along with traces of cobalt. Weathering over ages of this type of materials
has created a segregation of metallic
content, high concentration of iron under the form of limonite being found
near the surface, while an intermediate
layer, i.e. saprolite, is found located on top of the original bed rock.
Nickel and cobalt distribution can vary very
significantly between these three levels.
[0003] The recovery of nickel and cobalt from laterites is currently practiced
in several countries all over the
world. The approaches used call upon hydrometallurgy, that is, the use of a
liquid leaching medium to collect the
desired nickel and cobalt values.
[0004] Two hydrometallurgical processes are currently used for the collection
of nickel and cobalt from
laterites: the Caron method, also referred to as the ammonia leaching method,
and the pressure acid leach, also
referred to as the PAL method.
[0005] The Caron method involves the roasting of the laterites under reducing
conditions followed by leaching
of Ni/Co with ammonia. This method, typically used in Cuba, Australia and
Brazil, is characterized by a very high
energy consumption, in particular due to the need of drying of laterite and of
reduction, and yields modest
recovery, typically 75-85 % for nickel and 45-55 `)/0 for cobalt.
[0006] The pressure acid leaching (PAL) method incorporates some variable
alternatives but essentially
consists in a digestion of the laterite with sulfuric acid in an autoclave at
2500C under 5 to 10 times the
atmospheric pressure. This method is currently planned or used in several
countries, such as Brazil,
Madagascar, Australia, New Caledonia and Cuba for example. This method leads
to higher recoveries of nickel
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and cobalt than the Caron method, with recovery rates above 90 %. But
operation of the method can be
rendered very difficult or even impossible if the starting ore is rich in
magnesium or free silica. Scaling problems
in the autoclave result from the presence of these substances that are of
frequent occurrence in laterites. Also,
the PAL method for Ni/Co extraction from laterites is very capital expensive
because of the high cost incurred by
material requirements, especially autoclave inert to sulfuric acid at high
temperatures.
[0007] Therefore, from the current practice worldwide, it appears that
sulfuric acid is the desirable reagent for
leaching nickel and cobalt from laterite but it is also obvious that the use
of this reagent calls for relatively
expensive equipment. Equally limitative is the adverse effect of the presence
of magnesium and free silica in the
laterites, a situation that precludes the use of laterites with high
magnesium/silica content but otherwise rich in
nickel and cobalt.
[0008] Thus, there is still a need in the art for a method and a system for
recovery of nickel and cobalt from
laterites.
SUMMARY OF THE INVENTION
[0009] More specifically, in accordance with the present invention, there is
provided a method for recovering
metallic values from laterites, comprising slurrying the laterites in sulfuric
acid; submitting the slurry to sonication;
and filtering the slurry.
[0010] There is provided a method for recovering nickel and cobalt from
laterites, comprising leaching the
nickel and cobalt from the laterites with sulfuric acid under sonication.
[0011] Other objects, advantages and features of the present invention will
become more apparent upon
reading of the following non-restrictive description of specific embodiments
thereof, given by way of example
only with reference to the accompanying drawings.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0012] The present invention is illustrated in further details by the
following non-limiting examples.
[0013] A laterite was slurried at the level of 40-50 weight % solid in a
sulfuric acid solution 25 weight %, and
submitted to sonication, at room temperature and under atmospheric pressure,
over a period of 30 minutes. As a
result of this sonication, the temperature of the slurry was raised from
ambient temperature to about 70 C. After
this treatment, the slurry was filtered and an elemental analysis indicated an
extraction of 96 % of the nickel, 88
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% of the cobalt, 81 % of the iron and 57 % of the magnesium, as sulfates of
these metals.
[0014] Standard procedures known to those of skill in the art, and including
for example selective precipitation,
separation on ion exchange resins and the like, allow the separation of these
dissolved species.
[0015] Thus, surprisingly, it was found that metallic values such as nickel,
cobalt, iron and magnesium, could
be extracted very efficiently from typical laterites with sulfuric acid at
near ambient temperature and under
atmospheric pressure, using sonication.
[0016] In an experiment, a slurry of 100 g of laterite from Cajalbana, Cuba,
which composition was, in weight
percent: Ni: 0.90%; Co: 0.05%; Fe: 23.9%; Mg: 8.26%, in 200 ml of 25 weight %
sulfuric acid was submitted to
sonication with stirring. The sonication was achieved with a Hielscher UP4005
equipment operating at 24 kHz
with an amplitude of 75%. The power consumption was 174 W, with a sonostrode
H22 (titanium, 22 mm wide X
100 mm length). The treatment lasted 30 minutes.
[0017] The reaction mass was filtered and the analysis of the filtrate showed
an extraction of 96% of the nickel,
88% of the cobalt, 81% of the iron and 57% of the magnesium, as sulfates.
[0018] In another experiment, a 100 g sample of R.F. (US) laterite was treated
as a slurry in 250 ml of 25
weight % sulfuric acid at room temperature for half an hour under sonication
as in the experiment described
hereinabove. The slurry was then filtered and the analysis indicated an
extraction of 95 % of the nickel, 87 % of
the cobalt, 74 % of the iron and 72 % of the magnesium. The composition of the
starting ore was: 1.48 % Ni;
0.156% Co, 20.7% Fe and 11.35% Mg, as sulfates.
[0019] In still another experiment using a different lateritic material from
Dominican Republic having the
following composition: 16.1% Mg, 6.1% Fe, 0.88% Ni and 0.011% Co, the same
sonication conditions were
applied, giving the following extractions: 54% for Mg, 45% for Fe, 96% for Ni
and 86% for Co, as sulfates.
[0020] In all cases, the initial temperature of the slurry, i. e. room
temperature, i.e. about 25 C, was found to
have risen to about 70 C at the end of the treatment, as the result of
sonication.
[0021] There is thus provided a method allowing the recovery of metallic
values from laterites by the action of
rather diluted sulfuric acid on nickel and cobalt-bearing laterites, at
atmospheric pressure and near ambient
temperature, assisted by ultrasonic treatment.
[0022] With an acid concentration in the range between about 10 and about 95
weight % of sulfuric acid, for
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example between about 25 and about 50 weight % of sulfuric acid, for example
between about 10 and about 40
weight % of sulfuric acid, under atmospheric pressure, sonication at
frequencies in the range between about 10
and about 50kHz, for example between 20 and 30 kHz, applied for a duration in
the range between about 5 and
about 60 minutes, extracting metallic values from the slurried laterites is
thus achieved, the temperature of the
slurry experiencing an increase from about 20 0C, i.e. room temperature, to
about 70 0C as a result the
sonication.
[0023] There is thus provided a method for the recovery of nickel and cobalt
from laterites, such as limonitic,
saprolitic or serpentinic laterites, comprising leaching the nickel and cobalt
with sulfuric acid with the assistance
of ultrasonic treatment. The laterites can present a magnesium content up to
20 A). The sulfuric acid can be
diluted to between 10 and 40 weight AL The leaching is conducted at
atmospheric pressure and at ambient
temperature.
[0024] The present method allows leaching of nickel and cobalt from the
laterite with sulfuric acid without
limitations resulting from high pressure and high temperature requirements,
and without restrictions imposed on
the selection of the laterites by the need to avoid high magnesium and free
silica content as it is presently the
case with the PAL method.
[0025] The scope of the claims should not be limited by the embodiments set
forth in the examples, but should
be given the broadest interpretation consistent with the description as a
whole.
