Note: Descriptions are shown in the official language in which they were submitted.
PC-l 1060Z19
This invention relates to a l~ydromc~;lliur(Jic;l]
process for extracting metal values from manganiferous oxidc
ores containing a major amount of manganese and iron and a
minor amount of nonferrous metal values such as nickel, cobalt~
copper and molybdenum, and more particularly to a process for
selectively extracting and separating nickel, cobalt and
copper from such ores.
Althougll the process in accordance with the present
invention is applicable generally to manganiferous oxide ores
1~ that contain a major amount of manganese in the tetravalent
state and iron and a minor amount of nonferrous metals including
at least one of the metals nic]cel, cobalt or copper, it will
be described herein in conjunction with deep sea nodules. The
nodular deposits contain substantial amounts of manganese and
iron, and the nonferrous values can be present in a total
amount of up to 10%. The physical and chemical nature of these
deposits vary depending on their location. Typical deposits
can contain, for example, up to about 2% nick.el, up to about
2% copper, up to about l~ cobalt, up to about 25~ iron and up
to about 40~ manganese.
BACKGROUND OF THE INVENTION
The nodular deposits are found in large ~uantities on
the ocean floor and they are a potential source of metals.
However, since the components are tied in intimate and complex
association they are not amenable to separation by conventional
beneficiation procedures. For the same reason extraction of
the valuable metals is difficult.
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Numerous methods have been proposed for extracting
metal values from sea nodules. Among them are processes
which include the use of sulfur dioxide, mainly in neutra]
or acidic media. U.S. Patent No. 3,169,856, for example,
uses sulfur dioxide or nitrogen dioxide to preferentially
dissolve the values in the manganese phase leaving the iron
phase in the residue for subsequent treatment. Similarly,
German Patent No. 2,150,785 leaches the ores, preferably in
the presence of added MnSO4, with SO2 to preferentially
dissolve the manganese phase leaving the iron phase in the
residue for further acid treatment. In U.S. Patent No.
3,810,827, nodules are treated with SO2 in a fluid bed in
the absence of oxygen to preferentially sulfate the manganese
content of the nodules. Leaching the sulfated nodules
dissolves manganese leaving the remaining nonferrous values
in the residue for dissolution in a subsequent treatment.
In each of these processes, most of the manganese content of
the nodules is dissolved in a weakly acidic liquor containing
at least a portion of the copper, nickel, or cobalt present
in the nodules. Separation and recovery of the valuable
nonferrous metals and manganese from these solutions may be
complex and expensive.
Other processes are known to utilize leaching `in
ammoniacal solutions to extract the valuable nonferrous
metals leaving manganese and iron in the residue. Among
these are processes such as U.S. Patent No. 3,471,285 which
involve high temperature selective reduction of the nodules
prior to leaching in the ammoniacal medium. These processes
are becoming less attractive because of the large energy
requirement to dry and heat the nodules. Another process,
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.S. Patent No. 3,728,105, leaches the nodules in ammoniacal media at
temperatures between 100 and 300C. under atmospheres containing H2 and/or
CO at 300 to 1000 psig total pressure to reduce the Mn and selectively
extract the Cu, Ni, and Co. The cost of pressure vessels to withstand
such high temperatures and pressures in addition to the large energy require-
ment for heating a slurry makes this process unattractive.
It is an object of the present invention to provide an improved
method for treating manganese oxide ores, expecially manganiferous sea
nodules in which copper, nickel and cobalt are selectively separated from
manganese. Another object is to provide a method in which neither thermal
pretreatment nor drying of the ore is required. A further object is to
provide a hydrometallurgical method in which leaching of the ore is carried
out under essentially atmospheric pressures. It is a still further object
to provide a process for extracting metal values from manganese oxide ores
in which early separation of metals including copper, nickel and/or cobalt
from manganese is effected, thereby avoiding complex separation procedures.
It is a further object to provide a leach residue from which manganese
recovery can be achieved by a simple procedure.
These and other objects will become apparent from the following
20 description taken in conjunction with the accompanying drawing.
THE INVENTION -
The present invention may be generally defined as a process for
extracting metal values from a manganiferous ore containing a major amount
of manganese and iron, manganese being present in tetravalent form, and a
lesser amount of at least one of the nonferrous metals nickel, cobalt and
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copper. The novel process comprises leaching said ore in an aqueous ammonia-
cal medium maintained at a pH of not less than 8, in the presence of a re-
ducing agent which is a member of the group S02 and N02, at reaction conditions
to convert tetravalent manganese to the divalent state and in the presence
of a carbonate capable of forming substantially insoluble manganous carbonate
in the ammoniacal medium, whereby at least one of the nonferrous metal values
nickel, cobalt and copper is extracted into the leach solution and the
manganese and iron values are separated into the leach residue.
Suitable reducing agents are charac~erized in that they are capable
of reducing tetravalent manganese to the divalent state in an ammoniacal
medium under essentially atmospheric pressure or relatively low pressures,
and they permit extraction of desired metal values such as copper, nickel
and cobalt into the leach solution. Examples of the reducing agents are
S02, N02, H2S, elemental sulfur, and metallic iron. S02 is preferred
because it is efficient, commonly available, economical, and in its oxidized
form as SO4= can be disposed of with minimum environmental impact.
The ammoniacal medium contains in addition to the reducing agent
and NH4+, a carbonate which will precipitate the reduced manganese as
manganous carbonate. The carbonate precipitant is for example C02, (NH4)2C03,
or an alkali metal carbonate. C02 and ~NH4)2C03 are preferred reagents
Manganous carbonate is precipitated in a crystalline form which may be
recovered from the leach residue by well-known flotation technology. In
the absence of carbonate, non-crystalline manganous hydroxide is precipitated
which would require more complex techniques. Also, it is desirable to
obtain less than 50 ppm. manganese in the leach solution, and
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1060Zl~
it has been found that this low value is readily achieved in
ammoniacal media if carbonate is present. In the absence of
carbonate, manganese hydroxide is formed which precipitates
more slowly.
In the preferred embodiment in which SO2 is the
reducing agent and NH3 and CO2 are tne reagents, it is
believed that the follo~ing overall reaction occurs ~Jith
respect to the tetravalent manganese:
~5no2 + SO2 + (~IH4)2CO3 ~_ MnC03 + (NEl4)2SO4
The Ni, Co, Cu and ~lo values are extracted as ammine complexes.
The leaching conditions and reagent additions are
controlled to ensure that the residue is substantially free of
ammonia compounds so as to realize maximum economy of ammonia
consumption and minimum harmful environmental impact. In
general, the reducing agent is added in an amount substantially ,
stoichiometric to the amount of manganese, and it may be in-
troduce~d into the leaching medium at the start of the leach
or adcled in stages or continuously throughout the leaching
step. The plI of the leaching medium is maintained at not
less than about 8 and, preferably, the pH is maintained at
about 8.5 to about 9. At a pH below about 8, the nickel,
cobalt and copper tend to precipitate from the leach solution.
When too low, the pEI is suitably adjusted with NH3. ~t a p~i
above about 9, the solubility of manganese in the leach
sc)lution increases. ~'hen too high, the pH is suitably
adjusted with CO2.
In general, the leaching medium is provided with from
about 60 to about 200 grams per liter NH3 and about ~0 to about
150 grams per liter of CO2 (or its equivalent of CO3=) and in
suitable propor~ions to maintain the pl~ in the range of about
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~.5 to about 9. A sufficient amount of ~i3 is required to
complex all the nonferrous metal values to be extracted, such
as Cu, Ni, and Co. However, in the presence of the required
amount of CO3=, i.e. at least stoichiometric, and preferably
in excess of the amount required to precipitate all of the
manganese in the nodules as manganous carbonate, and at a pH
no lower than about 8.5, more than sufficient NH3 is present
to complex the nonferrous metals to be extracted.
The temperature of the leaching slurry is maintained
at about 25 to about 100C., preferably abou-t 50 to about
80C. The leaching step is carried out essentially at
atmospheric pressure. However, the pressure may range to
about 50 psig, depending on the partial pressure of the
gaseous components at the reaction temperature. Preferably,
the reaction is effected at atmospheric pressure.
Preferably, the slurry is maintained under reactin~ -
conditions until solubilization of the nonferrous metals such ~-
as Ni, Cu or Co and the precipitation of the manganese and
iron values are substantially maximized. Suitably, a slurry
containing SO2, NH3 and CO2 and/or (NH4)2CO3 is maintained
under reacting conditions for about 4 to 10 hours.
The leach residue can be treated to recover the
manganese and/or iron and the nonferrous metal can be recovered
from the leach solution by known methods.
TH~ DRAWING
The accompanying figure is a schematic flo~ sheet
showing the process for treating raw sea nodules according
to a preferred embodiment of this invention.
As illustrated in the Figure, raw sea nodules are
subjected directly to a reductive leach undcr rclatively mild
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conditions. Prior to the leaching step, it is advantageous
to reduce the particle size of the nodules. The nodules are
crushed, ground or otherwise reduced to a fine particle size,
e.g. 95% ~ 48 mesh (TSS), and preferably 95% lO0 mesh.
Although the nodules are porous and have a relatlvely large
surface area, the great tortuosity of the pores in the nodules
hinders diffusion of reactants and products. Therefore, it
is advantageous to reduce the size of the nodules, thereby
making the nodules receptive to complete and rapid reactions.
It will be noted that it is not necessary to dry the
nodules before they are subjected to reductive leaching. The
wet raw nodules are ground and fed directly to an aqueous
medium and reduction and precipitation of the manaanese is
achieved in the leaching medium.
Referring to the drawing, raw ocean nodules, ground
to about minus lO0 mesh (TSS), are mixed with water to provide
a slurry containing about lO~ to 30% solids. NH3 and CO2
are bubbled into the slurry to provide approximately 150 grams
per liter of N~13 and lO0 grams per liter of CO2. The tempera-
ture is maintained at about 50 to 80C. and the pH at about
8.5 to 9. SO2, the reducing agent is fed to the slurry to
provide an amount of about 30% to 50~ by weight, e.g. about
45~, based on the weight of the sea nodules. The atmosphere
is neutral or mildly reducing, air being excluded to prevent
the oxidation of SO2. The total leach time is approximately
4 to lO hours.
Using the above reagents and conditions up to 90%
of Cu, Co, and Ni can be extracted into virtually Mn and Fe
free solutions.
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After separating the leach solution from the residue,
the Ni, Co, and Cu values can be recovered from the leach
solution by known techniques. For example, free ~H3 can be
distilled from the solution to cause Cu, Ni, and Co to pre-
cipitate as basic carbonates. After solid/liquid separation
and washing, the basic carbonate precipitate can be redis- -
solved with H2SO4. This solution can then be treated to
separate and recover the Cu, Ni, and Co by several well-known
techniques including, for example, solvent extraction, ion
exchange, hydrolysis, sulfide precipitation, and electrolysis.
After separating the barren solution from the basic
carbonate precipitate, the SO~ in solution is precipitated as
gypsum with, for example, lime and the NH3 and CO2 are
recovered by distillation.
The leach residue can be treated, for example, to
recover a high grade manganous carbonate concentrate by well-
known flotation techniques. This concentrate could then be
treated to recover manganese by pyrometallurgical techniques
or by dissolving and electrowinning.
The following illustrative examples are given for the
purpose of enabling those skilled in the art to have a better
understanding of the invention.
E~LE 1
In a series of tests, raw sea nodules ground to
pass lO0 mesh (TSS) are added to an enclosed vessel containing
an aqueous ammoniacal medium to provide a pulp density of
about 15% solids. The nodules contain 1.22% Ni, 0.97~ Cu,
0.20% Co, 25.0% Mn and 5.35% Fe, the composition of the aqueous
ammoniacal medium for each of the tests is given in TABLE I.
After raising the temperature of the slurry to 60C., SO2 is
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1060Z19
bubbled into the baths at a rate of 300 milli]itcrs pcr minute
for l to 3 hours and the leach ~olution is analyæcd for Cu,
Ni, Co and Mn. The results of typical tests are tabulated
in TABLE I. Tests C and D are duplicate runs.
Comparison of the data in Tests A, s, C and D of
TABLE I shows that leaching with NH40H and SO2 in the presence
of (NH4)2SO4 or CO2 is more effective for extracting nickel
and copper than leaching with N114O1-I and SO2 alone. Further
comparison of Test B with Tests C and D show that CO2 is
more effective than (NH4)2SO4 for extracting nickel and
copper. In addition, very low manganese concentrations in
the leach solution are more readily attained in the presence
of a carbonate. Other advantages of a carbonate precipitate
were indicated previously.
~XAMPLF, 2
In a series of three tests, raw sea nodules qround
to pass l00 mesh (TSS) are added to an enclosed vessel
containing an aqueous ammonium medium at 75C. to provide a
pulp density of about 15% solids. The nodules contain l.22%
Ni, 0.97% Cu, 0.20% Co, 25.0% Mn, and 5.35% Ee. The aqueous
ammoniacal medium contains 150 y. NH3/l, l00g. CO2/l, and 30,
36, or 42% SO2 by weight of nodules added. The slurry`is
agitated and maintained at 75C. for 6 hours. After filtra-
tion and washing the residue and solution are analyzed. The
results are summarized in TABLE II.
The results of these tests show the variations in Cu,
Ni, and Co extractions with the amount of SO2 added. As the
S2 is increased from 30 to ~2% extraction of the Cu~ Ni, and
Co increased,
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Although the present invention has been de.scribed in
conjunction ~ith preferred embodiments, it is to be understood
that modifications and variations may be 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 appended claims.
