CA1057063A

CA1057063A - Recovery of base metals from manganese-containing ores

Info

Publication number: CA1057063A
Application number: CA228,735A
Authority: CA
Inventors: Herbert E. Barner; Roger N. Kust; Robert P. Cox
Original assignee: Kennecott Copper Corp
Current assignee: Kennecott Corp
Priority date: 1974-06-13
Filing date: 1975-06-06
Publication date: 1979-06-26
Also published as: FR2274697B1; FR2274697A1; JPS5110123A; AU499333B2; GB1516161A; DE2526388A1; AU8202875A

Abstract

A B S T R A C T

This invention is for a process for the recovery of base metals such as copper, nickel, cobalt and molybdenum that are present in manganese containing ores and in which the ore is brought into contact with cuprous ions in a vessel thus reducing the oxides in the ore and enabling the metal values to be solubilized. At the same time regeneration of cuprous ions is accomplished by carbon monoxide reducing gas which is introduced to the reacting mixture under pressure.

Description

~7~63 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 ~ - 2 -' .
. . . - . ~ - -1057~63 ~.
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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~LOS7~63 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.

7~63 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 i -4-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 ~ . , .- - . .
. ~

1~57~63 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 ; - 6 -11~57~63 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 .. .

1~57~63 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 ~7~63 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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57~3 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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~C~5~63 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) - 11 - :-1C~57~63 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 ~ 7~63 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

, . . . , . - :

~057~63 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 ~ - 14 -.

~ ID~7~63 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 . I
~ - 14a -,~ . . . . . . .

1~7~63 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 - 14b -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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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the recovery of base metals such as copper, nickel, cobalt and molybdenum present in a manganese containing ore, which 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 said cuprous ions to enable the metal values to be solubilized while continuously regen-erating 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.

2. A process according to claim 1, which comprises flowing the reducing gas through the reaction vessel so that the flow thereof through the vessel is in the same direction as the flow of the reaction product from the vessel.

3. A process according to claim 1, which comprises maintaining the temperature of the reaction vessel at about 35°C. through 55°C.

4. A process according to claim 1, which comprises employing a plurality of reaction vessels in series and the reaction product from one vessel flows into the next vessel in the series.

5. A process according to claim 1, which comprises employing plurality of reaction vessels which are connected in series by gravity overflow.

6. A process according to claim 3, 4 or 5, which comprises maintaining the desired amount of cuprous ion by introducing streams of manganese containing ore simultaneously into the plurality of reaction vessels.

7. A process according to claim 1, 2 or 3 which comprises maintaining the temperature of the reaction vessel or vessels by removing heat from the reaction product as said product enters a reaction vessel.

8. A process according to claim 1, 2 or 3, which comprises removing heat through a shell and tube exchanger.

9. A process according to claim 1, 2 or 3 which comprises including the additional step of delivering the reaction product from a reaction vessel to a recovery zone recovering solubilized base metals therefrom.

10. A process according to claim 1, 2 or 3, which comprises delivering the reaction product to at least one other reaction vessel containing cuprous ions and to which only manganese containing ore from another reaction vessel is delivered.