Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to improvements in a process
for the recovery of base metals, such as copper, nickel, cobalt
and molybdenum, which are present in manganese-containing
ores, such as are found on the bottoms of oceans and lakes.
The process of the invention comprises introducing
the ore into a reaction vessel containing an aqueous ammoniacal-
ammonium carbonate solution and cuprous ions, the amount of
said cuprous ions being greater than 2 grams per liter, and
reducing the manganese oxides in the ore by saic cuprous
ions to enable the metal values to be solubilized while con-
tinuously regenerating cuprous ions by a carbon monoxide reducing
gas while maintaining the pressure of said reducing gas at
50 - 100 lbs. per square inch (18-36 Kg/cm2) and increasing the
rate of cuprous ion regeneration. In this vessel, manganese
oxide in the ore is reduced to form a reduced ore reaction
product, and the base metals are solubilized, the cuprous ions
forming cupric ions as a result of the reduction. Thereafter,
the cuprous ions are regenerated from the cupric ions by passing
a reducing gas, such as carbon monoxide, into the reaction
vessel. The thus-solubilized base metals are then recovered
from the reaction vessel.
In the present invention, the rate of solubilization of
the base metals is increased without depleting the cuprous ions
by maintaining the amount of cuprous ions in the reaction
veqsel greater than 2 grams per liter. The temperature of the
reaction vessel is preferably maintained at about 35-55C.
The rate of regeneration of the cuprous ions with
the reducing gas is increased in the process by maintaining the
pressure of the reducing gas at 50-100 lbs. per sq. in. The
rate is also improved by flowing the reducing gas through the
reaction vessel so that the gas flows through the vessel in the
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~.
same direction as the flow of the reaction product there-
from.
In another feature of the process of the invention,
a plurality of reaction vessels are connected in series so.
that ;
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the reaction product from one vessel flows into the next ~essel
in the series, preferably by gra~ity overflow.
In still another feature of the invention, the desired
amount of cuprous ions is maint~ined by introducing streams of
the ore into a plurality of the reaction vessels simultaneously.
In another featuxe of the invention, the reaction
vessel is m~intained at the desired temperature by remo~in~ heat
from the reaction product which enters the nex~ reaction ~essel,
preferably with a shell and tube exchanger.
A further feature of the invention i8 the additional
step Or delivering the reaction product from the react~on ~essel
to a recovery zone for recovering solubilized base metals
therefrom.
The improYed process Or this in~ention
begins with mangane~e-containing ores found as ocean floor
deposit~, generally ha~ing the following compo~ition:
METAL CONTENT ANALYSIS RA~GE
Copper O.B ~ %
Nickel 1.0 - 2.0%
Cobalt 0.1 - 0.5%
Molybdenum 0.03 - 0.1%
Manganese 10.0 - 40.0%
Iron 4.0 - 25.0%
The remainder of the ore consist~of oxygen as oxides,
clay minerals with les~er amounts of quartz, apat~te, biotite,
sodium and potas~ium feldspars and water of hydration. Of the
many ingredients making up the manganese ore, copper and nickel
are emphasized becau~e, from an economic ~tandpoint, they are
the most significant metals in most of the ocean floor ores.
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The ore then i~ reduced wqth cuprous ions in a
reaction vessel in an aqueous ammoniacal ammonium carbonate t
solution. The cuprous ion~ reduce the manganese dioxide in
; the ore, and solubilize the copper, nickel, cobalt and
molybdenum, to a dissolved state, from whence it can be easily
recovered, while leaving undesirable metals, such as iron, in
the ~olid residue. In the reduction process, the manganese
dioxide in the ore i~ reduced by cuprous ion to manganese
carbonate according to the following equation (1), in which
cupric ions are formed:
MnO2 + 2 Cu(NH3)2 ~ 4 NH3 1 C2 ~ H20
~1) ',
MnC03 + 2 Cu (NH3)~ + 2 OH-
In the process, the necessary cuprous ions are re-
generated from cupric lon~, formed in the reduction step, by
reaction with a reducing ga~, such as carbon monoxide, according
to the following equation (2): :
2 Cu (NH3)4 ~ CO + 2 0~
: (2)
2 C~(NH3)2 + 4 N~3 + C02 2
Cuprous ion i9 consumed in reaction (1) and is re-
~enerated by reaction (2). Therefore, the net overall reaction
for the reduction proces~ is the sum of equations (1) and (2),
or equation (3):
MnO2 ~ CO - ~MnC03
Concurrently with the reductlon step, the base metals
are transformed from the solid form in the ore to a solubilized
form for recovery thereafter from the reaction vessel.
To increase the overall efficiency Or the
process, it is necessary to increase the rate of regeneration
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iC~57~)63
of the cuprous ions and/or increase the rate of solubilization
of the base metals without depleting the cuprous ions. It has
been discovered that the rate of regeneration is increased by
maintaining the pressure of the reducing gas at 50-100 lbs per
sq. in. (1~-36 kg./cm.2), and/or flowing the gas through the
reaction vecsel in the same direction as the flow of the reaction
product therefram, and that the rate of solubilization ~s increased
by maintaining the amount of cuprous ions greater than 2 grams per
liter, and/or maintaining the temperature Or the reaction vessel
at about 35-55C.
Another advantage which derives from increasing the
pressure in accordance with the present invention is that the
pH of the system can be lowered. By increasing the pressure
of the reduction ~tep from atmospheric pressure to about 50-100
lbs./~q. in. (1~-36 kg./cm.2), it i8 possible to operate at a
pH o~ about ~0 with rates eoual to those obtained at a pH of
10.6. Operating at this lower pH enables the reduced nodules
to be washed more efficiently. The reduction step also operates
more efficiently at this pressure and pH,
In accordance with the present invention it has been
discovered that there is an optimum temperature range for
equation~ (1) and (2) which take place in the reaction vessels.
That temperature range is 35-55C The preferred operating
temperature for each reaction vessel is approximately 55C. To
maintain the temperature within the foregoing range, heat is
removed from the reaction product whlch leave~ each reaction
vessel. In one important embodiment of the present invention,
heat is removed from the reaction product leaving each ve~el
in sufficient quantities so that the tem~erature in each reaction
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vessel is substantially identical. In another embodiment,
heat is removed from the reaction product in sufficient ;
quantities so that the temperature in each reaction vessel
is between the range of 35-55C.
In another embodiment of the invention, the cuprous
ion concentration is maintained at a fairly high level
because the reduction of cupric ions to cuprous ions is
controlled by the actual amount of cuprous ions. The
level of cuprous ions preferably is above about 2 grams
per liter (at atmospheric pressure, pH's below 10.0 and
temperatures below approximately 40C). If the pH is
increased above 10.0, or the CO pressure is increased,
then it would be possible to allow the level of cuprous
ions to drop below 2 grams per liter.
Fig. 1 is a flow sheet illustrating the process of the
present invention,
Fig. 2 is a flow sheet of an alternate embodiment of
the invention in which a single stream of reducing gas
flows through a series of reduction reactors in a con-
current manner with the manganese ore.
The process of the invention can be broken down in thefollowing sections, as shown in Flgure l; Ore preparatlon,
reduction-leach, oxidation and wash-leach, liquid ion-
exchange separation of the metals, electrowinning.
The process of the invention begins by processing the
manganese-containing ores. Accordingly, the ores are
crushed and milled into fine particles and wetted into a
stream with synthetic sea water to about a 40~ moisture
content. Then the stream is introduced into a reaction
vessel having cuprous ions therein in a strong, aqueous
ammoniacal ammonium carbonate so~ution which converts the
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manganese dioxide in the ore to a manganese carbonate
reduced ore reaction product, and solubilizes the base
metals in the ore. Usually a plurality of reaction
vessels connected in series are employed for this purpose.
The next step is regeneration of cuprous ions produced
in the reduction step by reaction with carbon monoxide
reducing gas. The carbon monoxide gas is introduced from
the bottom of the reaction vessel as a mixture of 95
percent carbon monoxide and 5 percent hydrogen, the latter
being used only because it is part of a commercially
available carbon monoxide.
In operation of the process according to one
embodiment of the invention, each of the first several
reaction vessels is fed an equal amount of a stream of
ore, called "multipoint injection". The ore stream can be
injected into two, three, five or more vessels and the
amount of stream going into any given vessel need not be
equal to the amount going into the others. It has been
found advantageous, however, that there be no stream
injection into at least the last vessel. That is, each
portion of the stream should pass through two stages in
progression; therefore, there should be no stream injec-
tion in the last stage.
While the streams are fed to the first four vessels,
carbon monoxide is introduced into the bottom of each
vessel as required. Preferably the carbon monoxide is
introduced into each vessel under pressure so that the
pressure in each vessel is about 50-100 lbs/sq/in/(18-36
kg~/cm ). The stream slurry in the fifth and sixth
reaction vessels is approximately 3.S percent solids and
the average residence time in the system is twenty minutes
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per stage. The stream slurry overflowing the last reactor
is flocculated to enhance settling before entering a
clarifier, The clarifier is used to separate the liquid
from the solids.
The present invention also is directed toward a
continuous process in which ore is continuously treated to
produce various desirable metals. In order to reach a
continuous steady state, the reaction vessels are loaded
with start-up materials. Thus, each of the reactors is
filled with an ammonia-ammonium carbonate solution con-
taining approximately 100 grams per liter total ammonia
and approximately 15 grams per liter total carbon dioxide.
After the reactors are filled with the ammonia-ammonium
carbonate solution, copper metal is added and is partially
oxidized. The metal is added as a copper powder and is -
oxidized to convert some of the copper to cuprous ions.
Hydroxyl ions are also produced with the cuprous ions.
Enough copper metal is added so that greater than 2 grams
per liter results, for example, 10 grams per liter copper
in solution results.
The first reaction vessels have pH loops which consist
of a finger pump which pumps the solution to a housing
which contains a pH electrode. The pH is then measured in
a readout on a control panel. The pH is a valuable
control device and can be used to indicate whether or not
the carbon dioxide, ammonia or cuprous ions are being
maintained within the desired concentration limits.
After the reaction vessels have been loaded for start-
up as set forth above, the manganese-ores are added to the
30 first four vessels. The total rate of feed to the four
reaction vessels is about 30 pounds (66 kg.) per hour of
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ore. As the stream of ores are fed into the reaction
vessels, carbon monoxide is passed through the bottom of
the vessels under a pressure of about 50 lbs/sq.in. (18
kg/cm.2) at a total rate of about 70 standard cubic foot
(2.0 cubic meters) per hour. At this point it should be
noted that the amount of carbon monoxide that is fed into
each stage of the reaction vessel is controlled by the
cuprous ion concentration of the contents of any given
reaction vessel.
Following the reduction step, approximately 120
gallons per hour (454 liters) of reduction product slurry
enters the clarifier. The solids leave the bottom of the
clarifier in the form of a slurry with approximately a 40
per cent solids content. The overflow from the clarifier
is clear liquid which constitutes the recycle reduction
liquor. However, after leaving the clarifier, the recycle
reduction liquor enters a surge tank whereupon it is
passed into an ammonia makeup unit. Gaseous ammonia and
carbon dioxide are sparged into the ammonia makeup unit in
order to keep the ammonia and carbon dioxide content of
;~ the liquid at a prescribed level. At steady state, that
level is approximately 100 grams per liter ammonia and the
C2 content about approximately 25 grams per liter.
After leaving the makeup unit, the liquid is pumped by a
metering pump through a heat exchanger into the first
reactor and the grinding mill. The heat exchanger removes
heat that was generated in process.
In accordance with the present invention, heat
exchangers 28, 30, 32, 34, 36 and 38 are positioned in the
flow path of the slurry leaving reactors 10, 18, 20, 22,
24 and 26 respectively. These heat exchangers are shell
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and tube heat exchangers. In this type of heat exchanger,
the slurry passes through a tube and a water coolant flows
through the shell surrounding the tube counter to the flow
of the slurry.
In one embodiment of the present invention, the -
recycled liquor 12 entering reaction vessel lO is at a
temperature of about 51C. As a result of the reactions
which take place in vessel lO, the temperature therein is
increased to 55C. A sufficient amount of heat is removed
from the slurry leaving reaction vessel lO by heat
exchanger 28 so that the temperature in reaction vessel 18
will not exceed 55C. The same heat extraction is con-
tinued for reaction vessels 20 through 26. It should be
noted that the temperature of the slurry increases about
3C in reactors 10-22. Thus, in order to maintain the
temperature within reactors 10-22 at a temperature of
55C, heat exchangers 28, 30 and 32 lower the temperature
of the slurry to about 51C. The temperature does not
increase greatly in reaction vessels 24 and 26. This is
due to the fact that the reaction between the nodules and
the cuprous ions is the reaction that generates the most
significant amount of heat. However, in reactors 24 and
26 no fresh nodules are introduced; thecefore, the temper-
ature in these reactors does not increase significantly.
In an alternative embodiment of the invention, heat is
removed from the slurry so that the temperature in any
reaction vessel is between the range of 35-55C. In this
embodiment of the invention it is not necessary to remove
heat from each stage. For example, the slurry leaving
3n reactor 10 may be allowed to enter reaction vessel 18
without any heat removal. If the temperature of the
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slurry in reaction vessel 10 is 51C it will attain a tem-
perature of about 54C in reaction vessel 18. Heat can
then be extracted from the slurry leaving reaction vessel
18 by heat exchanger 30. This heat exchanger may lower the
temperature of the slurry to 51C so that the temperature
in reaction vessel 20 reaches a value of 55C. Of course
the details of how to maintain the temperature within each
reactor 10-26, at either a constant range or a constant
single temperature, is well within the skill of those in
this art.
It should be noted that the slurry leaving the reac-
tion vessel 26 passes through a heat exchanger 38. If
heat is extracted by a heat exchanger located at this -~
position in the circuit then it need not be extracted by
heat exchanger 16. In another embodiment of the invention
one-half of the heat to be removed may be extracted by
heat exchanger 38 and the other half may be extracted by
heat exchanger 16.
One advantage of operating the reduction reactor
within the range of 35-55C is an improved nickel and
cobalt solubilization. For example, a test showed that
for reactors operated at 65C, a pH of 10.8, 120 g/l NH3
and a CO2/NH3 ratio of 1:5, nickel solubilization was
minus (-) 19.3% and cobalt solubilization was minus (-)
121%. The minus value indicates that nickel and cobalt in
the recycle liquor goes into the solids phase. When the
temperature was decreased to 50C with other parameters
held constant, the nickel solubility was increased to 88%
and the CO solubility was increasefl to 77.8%. The lower
temperature did not greatly affect copper solubilization.
; A small stream of basic metal carbonate (aMC)
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containing primarily copper and nickel carbonates can also
be recycled to the first stage if required to maintain the
total copper in the reduction system at an acceptable
level. This stream of basis metal carbonate compensates
for unsolubilized copper leaving the reduction loop in the
clarifier underflow. Details of the BMC recycle are
amplified below.
In the oxidation and wash-leach circuit, the clarifier ;
underflow is combined with the second stage wash liquor
and the resulting slurry is oxidized with air to convert
the cuprous ion in the clarifier underflow to cupric ion
to facilitate future processing. The oxidized slurry is
then pumped to a countercurrent decantation system (CCD)
consisting of seven stages of countercurrent washing
units. The wash-leach steps are carried out on a batch
basis in nine tanks. It should be noted that in the pilot
plant nine stages are used to simulate a countercurrent
wash system. Although this system is not truly a counter-
current, it has been able to demonstrate that a seven
reactor countercurrent system i5 advantageous. The two
extra units used in the pilot plant are necessary because
one unit is either being filled or is being emptied. In
the wash-leach system, the metal solubilization is
; completed as the displacement wash process is carried
out. Fresh wash liquor is added to the seventh stage of
the system as a solution containing 100 grams per liter
ammonia and 100 grams per liter carbon dioxide. Liquor is
transferred from one tank of the settled slurry every
twelve hours to another appropriate tank in the system to
affect the countercurrent washing. The carbon dioxide
concentration varies throughout the washing system and
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exits in the pregnant liquor which contains approximately
65 grams per liter CO2. This decrease in CO
concentration is due to the fact that the slurry entering
the oxidation and wash-leach circuit has a liquor phase
which contains only 25 grams per liter CO2. Pregnant
liquor, containing the metal to be recovered, is decanted
from the first wash stage and pumped to a surge tank.
Fresh ammonia solution without metals is added to the last
solids wash stage. The metal values in solution range
from approximately 0 in the fresh wash liquor to between
4-8 grams per liter copper and 5-10 grams per liter nickel
in the pregnant liquor. Of course, other metal values are
also present in the pregnant liquor but nickel and copper
are the major metal values of interest.
After the wash-leach step, the pregnant metal bearing
liquor is piped off for further processing as is explained
below. The second stage wash is recycled back to the
oxidation reactor. The tailings, which are nothing more
than reduced nodules washed of most of their non-ferrous
metal values and with the manganese converted to manganese
carbonate, are sent to a surge tank ~not shown). From the
surge tank, they are then pumped to a steam stripping
operation where the ammonia and CO2 are driven off. The
tailings are then drummed. The ammonia and CO2 obtained
in the steam stripper may be recycled.
A portion of the pregnant liquor from the oxidation
and wash-leach circuit is steam stripped on a batch basis
to remove ammonia and carbon dioxide and to precipitate
the basic metal carbonates. The precipitated basis metal
carbonates are dissolved in an aqueous solution containing
approximately 60 9/1 NH3 and 60 9/1 CO2. This BMC
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feed is pumped to the first stage of the reduction circuit.
The pregnant liquor contains various metal values -
including copper, nickel, cobalt and molybdenum. In the
liquid ion exchange separation circuit, the object is to ~-
separate the copper, nickel cobalt and molybdenum from
each other and from the pregnant liquor. Initially, the
copper and nickel are co-extracted by an organic
extractant in a series of mixer/settler units.
The organic extractant is a kerosene base.
The copper and nickel free liquor ~raffinate) is sent
to a storage tank before it is steam stripped. -
The organic extractant which contains copper and
nickel values is washed with an NH4 HCO3 solution
followed by an ammonium sulfate solution to remove ammonia
picked up during extraction. This scrubbing operation is
carried out in another series of mixer settlers. The
organic extractant is then stripped with a weak H2SO4
solution (p~ about 3) to preferentially remove nickel.
Thereafter, the copper is stripped, which is accomplished
by using a stronger (160 9/1) H2SO4 solution. The
copper and nickel free organic extractant is recycled to
the metal extraction circuit of the LIX process.
The raffinate which contains only cobalt, molybdenum
and some trace impurities that were not extracted into the
organic phase is sent into a surqe tank for future pro-
cessing to recover cobalt and molybdenum. In the cobalt
and molybdenum recovery circuit, the ammonia and CO2 are
stripped from the raffinate thereby precipitating cobalt.
The ammonia and CO2 are condensed and sent back to the
process for recycling. The cobalt precipitate is
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separated from the liquor and the liquor is subsequently
treated with hydrated lime to precipitate the molybdenum.
The resulting slurry is agitated and then allowed to
settle. The solution which no longer contains cobalt and
molybdenum is recycled back to the process as fresh wash
liquor. Ammonia and C02 are added to the solution to
bring it up to the prescribed concentration.
Copper and nickel are recovered from the solution
prepared in the liquid ion exchange plant as described
above by electro-refining which is performed on a batch
basis for the copper recovery and on a continuous basis
for the nickel recovery in separate plants.
An alternative embodiment of the present invention is
shown schematically in Fig. 2. In this embodiment of the
invention, the reducing gas flows in a co-current manner
; with the flow of the stream of the oee into the reaction
vessels. As is shown in Fig. 2, the system includes six
stages, that is a first stage, second stage and so forth,
represented by reference numerals 51-56, respectively. In
20 this system, the streams are introduced into the first
five reactors as is shown by arrows 60 through 64. Carbon
monoxide reducing gas is introduced through the bottom of
the first reactor 51 in the series, is sparged there-
through; collected at the top; and flowed through each
stage until it reaches the last reactor 56; whereupon it
is removed and treated to recover any ammonia dissolved
therein. The flow of carbon monoxide through the reactors
is as follows: Carbon monoxide enters reactor 51, as is
; shown by arrow 70, exits from the top thereof and enters
reactor 52 through the bottom, as is shown by the arrow
72. The gas leaving reactor 52 through the top thereof is
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conducted to the bottom of reactor 53, as is shown by the
arrow 74. The flow pattern continues, as is shown by
arrows 76, 78 and 80. Of course slurry flows from the
first through the last reactor as is indicated by lines
81, 82, 83, 84 and 85. Slurry exits the last reactor and
enters the clarifier 86 as is shown by arrow 87. At this
point it should be noted that one of the major advantages
of a co-current flow of the ores and reducing gases is
that a
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lC~57063
large amount of reducing gas is available at the first stage
where the need for cuprous ion regeneration is greatest.
As is shown in Fig. 2, heat exchangers 90, 91, 92, 93
and 94 are positioned between stages to enable the slurry to
be cooled to a desired temperature which is preferably between
the range of 35-55C.
With the arran~ement shown in Fig. 2, the carbon mon-
oxide pressure is greatest in the first reactor and is diminishèd
after passing through each subsequent reactor. The major reason
~hy the pressure decreases as the gas is fed through the series
of reactors i5 that the carbon monoxide i~ consu~ed in each
reactor. Therefore le~s csrbon monoxide enters each successive
reactor.
AQ i8 also shown in Fig. 2, additional carbon
monoxide may be sent through reactors 52 through 56 along lines
100, 101, 102, 103 and 10~. The ability to bypas~ some fresh
carbon monoxide directly into any given stage is desirable and
is an additional control feature to maintain the proper cuprous
ion conoentration.
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