AU2009259277A1

AU2009259277A1 - Method for leaching nickel matte in the presence of added copper

Info

Publication number: AU2009259277A1
Application number: AU2009259277A
Authority: AU
Inventors: Sergey Kotukhov; Marko Latva-Kokko; Esa Lindell
Original assignee: Norilsk Nickel Finland Oy
Current assignee: NORILSK NICKEL HARJAVALTA Oy
Priority date: 2008-06-19
Filing date: 2009-06-18
Publication date: 2009-12-23
Anticipated expiration: 2029-06-18
Also published as: CA2728519A1; FI20085627A; AU2009259277B2; ZA201100473B; CA2728519C; WO2009153409A4; WO2009153409A1; FI121380B; FI20085627A0

Description

WO 2009/153409 PCT/F12009/050540 1 METHOD FOR LEACHING NICKEL MATTE IN THE PRESENCE OF ADDED COPPER Field of the invention The present invention relates to a method for leaching pyrometallurgically pro 5 duced nickel mattes in a multistep hydrometallurgical process. Prior art A large portion of the world's nickel is produced hydrometallurgically from pyrome tallurgically produced nickel mattes. Generally, such a production process involves the leaching of nickel contained in the matte by a multistep process, followed by 10 purifying the nickel-bearing aqueous solution and reclaiming the nickel. The leach ing process is determined according to the composition and properties of em ployed nickel matte. These, on the other hand, are influenced by the grade of con centrate used as a raw nickel material and by its metallurgical smelting process. There is a prior known method described in US patent publication 6,039,790 for 15 recovering nickel in one and the same process from two pyrometallurgically pro duced nickel mattes, one of which contains a remarkable percentage of iron. In the method, leaching of the nickel matte that contains iron is carried out in one step by conducting solution from the leaching cycle of the less iron containing matte into the leaching of the iron containing matte at a stage where the iron of the less iron 20 containing matte is in soluble form. The iron contained in the mattes is advanta geously precipitated as jarosite and the solution created in the leaching of the iron containing matte is conducted back into the leaching cycle of the less iron contain ing matte. A similar method has been described in US patent publication 6,206,951, wherein 25 copper-rich sulfidic, and metallic nickel mattes are leached in a multi-stage process. Nickel is leached from sulfidic nickel matte by means of copper sulfate in a pressure leach process. The required copper sulfate is obtained from the leach ing of metallic nickel matte, as well as by leaching the copper-rich material in a separate copper leaching process. 30 GB patent publication 2,108,480 describes a process developed for sulfidic nickel mattes rich in copper, wherein nickel is first treated by a pressure leach under oxi dizing conditions with an anolyte obtained from copper electrolysis. Once at least WO 2009/153409 PCT/F12009/050540 2 70% of nickel values in the matte are extracted, the leaching is continued under non-oxidizing conditions. The solution from this stage is conducted to an atmos pheric purification leach, in which the solution is stripped of copper by means of finely powdered matte. Precipitate from the purification leach is conducted to a 5 nickel pressure leach, and the precipitate remaining after that is conducted to an oxidizing pressure-leaching process of copper. The residual precipitate mainly comprises iron previously contained in the matte. US patent publication 5,628,817 discloses still another multi-stage leaching process developed for nickel matte, wherein the leaching of nickel takes place in 10 at least two stages in conditions where free sulfuric acid is essentially absent. The method is of the same type as the one used in US publication 6,039,790 in the leaching of matte with a low iron content. The finely ground matte is first subjected to a two-step oxidizing atmospheric leach and thereafter to a two-step pressure leach, wherein the first step is carried out in non-oxidizing or mildly oxidizing condi 15 tions and the second step in oxidizing conditions. As opposed to the previously described method, the entire copper content is leached in the latter atmospheric leaching and the removal of iron takes places by precipitation from the solution downstream of the first pressure leaching step. The most severe limitation of prior known leaching processes, such as those de 20 scribed above, is the applicability thereof to certain types of nickel matte only. For example, the method disclosed in GB patent publication 2,108,480 is only applica ble to sulfidic nickel mattes with a remarkably high copper content (the weight ratio of nickel/copper less than 2,5, i.e. the weight ratio of copper/nickel more than 0,4). On the other hand, the processes described in US patent publications 6,039,790 25 and 6,206,951 are not suitable for metallic nickel mattes containing precious met als as the precious metals therein end up in the iron precipitate. Accordingly, there is still demand for a method with a versatility of adapting to a variety of nickel mattes, whose contents of copper, nickel, iron, sulfur, as well as precious metals may fluctuate without a major effect on the recovery of various 30 metals and on the quality of products recovered from the leaching process. Summary of the invention The present invention provides a method according to claim 1. A few preferred embodiments of the invention are presented in the dependent claims.

WO 2009/153409 PCT/F12009/050540 3 An essential feature of the invention is that the copper-nickel weight ratio of the delivered solid matter is raised, preferably to higher than about 1, by the addition of a copper-bearing solid substance. The copper-bearing solid substance is added preferably downstream of the atmospheric leaching step into leach residue. 5 Solid matter is preferably obtained by circulating the leach residue from a latter stage of the method. Another possibility is, for example, the use of synthetically produced copper sulfide, precipitated especially with hydrogen sulfide. The method comprises processing nickel mattes preferably in such a way that the nickel and iron contained in the mattes are converted into soluble form and the 10 copper and precious metals end up in leach residue. Sulfidic nickel matte is preferably leached first in an atmospheric step by means of sulfuric acid and air, such that soluble copper precipitates but iron remains in the solution. Following a solid-liquid separation, the solid matter is conducted to a pressure leach. The pressure leach is preferably a two-step process and of the 15 type in which the first step comprises leaching mostly copper and the second step leaches nickel and iron as copper is precipitating. After the pressure leach, the leach residue consists of copper sulfide precipitate quite pure in terms of iron and contains the precious metals (such as Au, Pt and Pd) of nickel mattes. Metallic nickel matte is processed preferably in a separate atmospheric step by 20 means of sulfuric acid and oxygen for leaching metallic components of the matte, i.e. most of the nickel and iron. The solution, as well as sulfidic components and precious metals remaining in the matte, are preferably conducted to the atmos pheric leaching step of sulfidic nickel matte. A benefit gained by the method according to the invention is its applicability for a 25 wide variety of nickel mattes, which may contain for example varying amounts of copper, iron, and precious metals, as well as may be sulfidic and/or metallic in terms of their composition. Another benefit gained by the method is that the leach residues of mattes end up in the same precipitate, which contains copper and pre cious metals coming along with nickel mattes. In addition, the discussed copper 30 sulfide precipitate is relatively pure and contains just a little iron. One of the advan tages is also the fact that the residence time for the first pressure leach step can be kept remarkably short, less than 45 minutes, thus providing a high leaching ca pacity considering the size of process equipment.

WO 2009/153409 PCT/F12009/050540 4 The invention will now be described in more detail with reference to the flowchart depicted as a figure. Description of the drawing Fig. 1 shows in a flowchart the leaching of pyrometallurgically produced nickel 5 mattes by a multistep hydrometallurgical process. In the figure, reference numer als designate unit processes as follows: 1 Atmospheric removal of copper In 2 Atmospheric leach A Sulfidic Ni-matte 10 3 I pressure leach B Metallic Ni-matte 4 Il pressure leach C Air (oxygen) 5 Removal of iron Out 6 Solution purification D Fe-precipitate 7 Nickel electrolysis E Cu-precipitate 15 F Ni-cathode Detailed description of a few embodiments of the invention As shown in the flowchart, finely ground sulfidic nickel matte is fed to an atmos pheric copper removal step 1. The term sulfidic nickel matte refers to pyrometal 20 lurgically produced smelter matte, in which most of the metal content is present in the form of sulfidic components, such as for example nickel sulfide Ni 3

S

2 , copper sulfide Cu 2 S, and nickel-iron sulfide (Ni,Fe) 9

S

8 . The sulfur concentration of sulfidic nickel matte is typically 15-25%, nor is it strongly magnetic. The concentrations of various metal and impurities may fluctuate even quite extensively, but the total 25 weight percentage of nickel, copper and iron is nevertheless typically more than 60%. In addition to sulfidic nickel matte, the atmospheric copper removal step 1 is also supplied with a copper- and iron-bearing solution from an atmospheric leach step 2 and from a second pressure leach step 4. In addition to these, the discussed 30 step is supplied with air. The removal of copper is performed in atmospheric condi tions and at a temperature of 80-100'C. The elemental nickel and nickel sulfide present in the matte precipitate copper existing in the solution as copper sulfate upon being themselves oxidized into nickel sulfate according to the following reac tion equations: WO 2009/153409 PCT/F12009/050540 5 Ni 0 + CuSO 4 -> NiSO 4 + Cu 0 (1) Ni 3

S

2 + 2 CuSO 4 --> Cu 2 S + NiS +2 NiSO 4 (2) Ni 3

S

2 + 2 CuSO 4 + % 02 --> 2 NiS + NiSO 4 + Cu 2 0 (3) In a continuously running operation, the reactors present a rising pH-profile in 5 which the precipitation of copper occurs, in response to the above reactions, in acidic conditions at the start of the process step as the solution has a pH of less than 4. The leaching of metals consumes oxygen and, as pH rises, copper precipi tates also as alkaline copper sulfate CuSO 4 *2Cu(OH) 2 . From the standpoint of the effective extraction of copper and iron, however, it is preferred that this zone be 10 kept as brief as possible in terms of its residence time in order to minimize the concurrent precipitation of iron. The precipitate, i.e. the leach residue from this step, is delivered after the liquid-solid separation to a first pressure leach step 3 and the solution is conducted to an iron removal 5. The finely ground metallic nickel matte is conducted to the atmospheric leach step 15 2. The term metallic nickel matte refers to pyrometallurgically produced smelter matte, in which most of the metal content is present in the form of metallic compo nents, such as for example elemental nickel Ni 0 , copper Cu 0 , and iron Fe 0 and/or in compositions (alloy) of these metals. The sulfur concentration of metallic nickel matte is typically less than 15% and it is highly magnetic. The concentrations of 20 various metals and impurities may fluctuate even quite extensively, but the total weight percentage of nickel, copper and iron is nevertheless typically more than 80%. The leaching of metallic nickel matte is performed in atmospheric conditions and at a temperature of 80-100'C. In addition to nickel matte, the atmospheric solution is 25 supplied with oxygen and sulfuric acid. Some of the sulfuric acid can be replaced by an acid-containing anolyte obtained from a nickel electrolysis 7. The principal leaching reactions are: Ni 0 + H 2

SO

4 + % 02 -- NiSO 4 + H 2 0 (4) Cu 0 + H 2

SO

4 + %/ 02 CuSO 4 + H 2 0 (5) 30 Fe 0 + H 2

SO

4 + % 02 -> FeSO 4 + H 2 0 (6) The formation of hydrogen during leaching is prevented by an abundant introduc tion of oxygen and the precipitation of iron by maintaining the solution at a low pH, lower than 2,0. The leach residue and the solution from this step are conducted to the atmospheric copper removal 1.

WO 2009/153409 PCT/F12009/050540 6 The first pressure leach step 3 is supplied with oxygen as well as with an acid containing anolyte from the nickel electrolysis 7. The copper concentration of a solid matter delivered to the pressure leach step is increased by circulating some copper-bearing solid substance from a liquid-solid separation downstream of the 5 second pressure leach step 4 into the precipitate coming from the atmospheric copper removal 1. The input solid substance has a preferred copper/nickel weight ratio of 1-2,5. The temperature in the first pressure leach step is higher than 100 C, preferably within the range of 110-120'C and the partial oxygen pressure is preferably higher than 200 kPa. The principal leaching reactions of the first 10 pressure leach step are: 5 Cu 1

.

8 S + 4 H 2 SO4 + 12 0 2 -+ 9 CuSO 4 + 4 H 2 0 (7) Ni 3

S

2 + H 2

SO

4 + 2 02 -> NiSO 4 + 2 NiS + H 2 0 (8) The step is mainly intended for leaching a sufficient amount of copper for the leaching of nickel effected in the second pressure leach step. This is enabled by 15 recycling, if necessary, a copper-bearing solid matter into an autoclave, which sol id matter in this case consists of precipitate containing copper-sulfide from a liquid solid separation downstream of the second pressure leach step 4. By virtue of re cycling the precipitate, the method according to the invention enables leaching al so nickel mattes of low copper contents. Besides, by virtue of a high copper/nickel 20 weight ratio of the solid matter, the first pressure leach step can be managed in a remarkably brief residence time, less than about 1 hour, even less than about 45 minutes, thus preventing nickel sulfide from reacting too far according to a reaction (9) presented below. This is of essential importance as regards the proper func tioning of the second pressure leach step. 25 4 NiS + H 2

SO

4 + % 02 -+ Ni 3

S

4 + NiSO 4 + H 2 0 (9) Leaching is manageable also in highly acidic conditions, but it is preferably carried out in such a way that some of the leached copper precipitates in the form of alka line copper sulfate, the solution having a pH of not lower than about 3 at the end of the step. 30 Alternatively, the copper/nickel weight ratio of a solid matter to be fed into the first pressure leach step 3 can be increased by supplementing the precipitate coming from the atmospheric copper removal 1 for example with synthetic copper sulfide precipitated with hydrogen sulfide or with some other copper-containing solid of the type that dissolves rapidly in the conditions of the first pressure leach step 3.

WO 2009/153409 PCT/F12009/050540 7 From the first pressure leach step, the slurry is passed in its existing state as the only feed to the second pressure leach step 4. The passage of slurry can be im plemented by pushing the flurry first to a normal air pressure and by pumping the refrom, by direct pumping, or without pumping by maintaining the first pressure 5 leach step at a pressure higher than the second pressure leach step. Temperature in the second pressure leach step is preferably higher than 140*C, and even more preferably within the range of 140-160", and nickel sulfides dissolve as nickel sul fate functions as the oxidizer: 8 Ni 3

S

2 + 27 CuSO 4 + 4 H 2 0 -+ 24 NiSO 4 + 15 Cu 1

.

8 S + 4 H 2

SO

4 (10) 10 6 NiS + 9 CuSO 4 + 4 H 2 0 -- > 6 NiSO4 + 5 Cu1.

8 S + 4 H 2

SO

4 (11) As the acid concentration rises in non-oxidizing conditions, the slurry leaches also iron and arsenic during the second pressure leach step. The liquid-solid separation downstream of the step is a source of relatively pure copper sulfide precipitate, having just a low iron concentration and containing the precious metals (such as 15 Au, Pt and Pd) received along with nickel mattes and practically non-leached in the above-defined conditions. A desired portion of the precipitate is returned the feed of the first pressure leach step 3. The copper sulfide precipitate separated from the process can be fed for example to a copper smelting facility or subjected to metallurgical further processing by some prior known method. The solution from 20 liquid-solid separation is conducted to the atmospheric copper removal 1. A leaching process product solution (PLS), subsequent to the atmospheric copper removal 1, is conducted, downstream of the liquid-solid separation, to the iron re moval 5. The iron removal is effected with some prior known method, such as by precipitating the iron with oxygen 02 and by neutralizing the acid evolved in the 25 precipitation process for example with lye NaOH. Following the iron removal, the precipitate is separated and the solution is conducted to a solution purification 6, wherein the solution is stripped of cobalt and other impurities detrimental to nickel production by some prior known method, for example by liquid-liquid extraction. The pure nickel sulfate solution is used for producing nickel products by known 30 methods, such as for example cathode by means of the nickel electrolysis 7. Nick el electrolysis provides a source of an acid-containing nickel solution or anolyte, the sulfuric acid contained therein being useful in the presently described leaching process. The invention will be described further by way of the accompanying non-limiting 35 examples: WO 2009/153409 PCT/F12009/050540 8 Example 1 Atmospheric copper removal step Ground sulfidic nickel matte with a composition of 67% Ni, 3,0% Cu, 2,0% Fe and 23% S was leached in laboratory into a copper-containing nickel sulfate solution. Leaching was conducted in a heated cover-equipped steel reactor provided with 5 agitation and aeration. The solution volume was two liters, air feed 50 L/h, temper ature 850C and leaching time one hour. Other conditions and results are shown in table 1. The results reveal that there is achieved a practically complete precipita tion of the parent solution copper while leaching nickel and iron. This indicates that the method of the invention enables an effective separation of copper and iron. 10 Table 1 Solution Solid V L pH Ni (QL Cu (l Fe (L) m (Q) Ni % Cu% Fe% Feed 2.0 1.2 109 2.1 2.6 164 67.3 3.0 2.0 End 2.0 4.3 119 0.004 3.2 156 60.8 5.5 1.8 Example 2 Two-step pressure leach The leach residue of nickel matte, treated as in example 1 and with a composition of 63% Ni, 6,2% Cu, 2,2% Fe and 23% S, was leached with a laboratory autoclave 15 in a two-step fashion. Prior to leaching, the solid matter had its copper/nickel weight ratio changed by having copper sulfide precipitate containing 66% Cu and 28% S admixed within the leach residue. In the series of tests, the solution volume was 1 liter and the pressure in autoclave was 8 bar. During the first pressure leach step, the temperature was 1120C and the autoclave was supplied with oxygen un 20 der the agitator. Leaching time was 45 minutes. After this, the supply of oxygen was shut off and the autoclave was heated for the second pressure leach step to the temperature of 1470C. Leaching time in the second pressure leach step was two hours and during this period the autoclave was not supplied with oxygen. Other conditions and the results of pressure leach tests are shown in table 2. 25 The results reveal that the leaching of nickel is also managed in highly acidic con ditions, but is preferably carried out in such a way that the solution pH at the end of the first pressure leach step is not lower than 3. Between tests 1 and 2 is also visible the effect of a copper/nickel weight ratio in the solid matter. At a higher copper/nickel weight ratio, substantially more copper becomes leached during the 30 first pressure leach step and thereby an improved recovery of nickel is achieved in the second pressure leach step. The results further reveal that the leaching of iron takes place at the latest during the second pressure leach step, such that the ob- WO 2009/153409 PCT/F12009/050540 9 tained leach residue comprises relatively pure copper sulfide precipitate which can be recycled into the feed of a two-step pressure leaching process. Table 2 Solution Solid H904(g/L) pH Ni(g/L) Cu(g/L) Fe(g/L) m (g) Ni % Cu% Fe% Cu/Ni ratio Test 1 Feed 52.0 73 1.0 1.0 140 26.9 40.5 1.0 156 End of step 1 1.1 88 20.2 1.6 19.3 45.4 0.2 End of step ll 0.9 112 0.3 1.9 85.6 2.4 67.1 0.05 Test 2 Feed 62.0 73 1.0 1.0 18S 20.9 46.2 0.7 22 End of step 1 1.2 O 29.3 1.6 10.7 54.8 0.1 End of step ll 0.6 111 7.8 1.7 103 0.8 70.4 0.04 Test 3 Feed 17.0 73 1.0 1.0 170 22.1 45.0 0.8 2fD End of step 1 3.9 88 24.3 0.06 10.1 49.8 1.6 End of step II 0.9 105 8.1 1.6 83.5 0.05 74.8 0.07 5 Example 3 Atmospheric leaching Ground metallic nickel matte with a composition of 48% Ni, 7,4% Cu, 30% Fe and 5,7% S was leached in laboratory into an acidified nickel sulfate solution. Leaching was conducted in a heated cover-equipped steel reactor provided with agitation and aeration. The solution volume was two liters, oxygen feed 50 L/h, temperature 10 850C and leaching time three hours. Other conditions and the results are shown in table 3. The results indicate that metallic nickel matte can be leached in atmos pheric conditions in such a way that practically all that remains in the leach residue are sulfidic -components. The test also demonstrates that iron remains in a dis solved state as long'as the solution is maintained at a low pH. 15 Table 3 Solution Solid H2-SO 4 (gAi) pH Ni (gAi) Cu (gi-) Fe (gL) m (g) Ni % Cu % Fe % S % Feed 72.0 60 0.1 - 124 48.1 7.4 30.3 5.7 End 1.8 85 0.002 16 27.5 27.1 29.6 9.6 25.8_

Claims

1. A method for leaching pyrometallurgically produced, copper-containing sulfid ic nickel matte, characterized in that - sulfidic nickel matte is fed to an atmospheric leach step from which is obtained a 5 nickel-bearing solution and a copper- and nickel-bearing leach residue, whereby a copper-bearing solid matter is added into the nickel matte before the leaching or to the leach residue after the leaching in such an amount that the weight ratio of cop per to nickel in the leach residue is more than about 1, and - the leach residue is conducted to pressure leaching. 10

2. A method as set forth in claim 1, characterized in that the solid matter has its source in a latter stage of the method.

3. A method as set forth in claim 1, characterized in that the solid matter con sists of synthetically produced copper sulfide. 15

4. A method as set forth in any of claims 1-3, characterized in that copper, but not iron, is precipitated from the solution in the atmospheric copper removal.

5. A method as set forth in any of claims 1-4, characterized in that the pres 20 sure leaching is a two-step process and that temperature in the first pressure leach step is within the range of 100-120*C.

6. A method as set forth in claim 5, characterized in that the residence time in the first pressure leach step is less than about 1 hour. 25

7. A method as set forth in claim 5 or 6, characterized in that temperature in the second pressure leach step is higher than about 140*C.

8. A method as set forth in any of claims 1-7, characterized in that the atmos 30 pheric leaching step of sulfidic nickel matte is also supplied with a solution and a leach reside obtained from the atmospheric leaching of metallic nickel matte.

9. A method as set forth in claim 8, characterized in that the atmospheric leaching of metallic nickel matte is conducted by means of sulfuric acid and oxy 35 gen at a pH sufficiently low for the dissolved iron not to precipitate. WO 2009/153409 PCT/F12009/050540 11

10. A method as set forth in any of claims 1-9, characterized in that the leach residues of nickel mattes end up in one and the same precipitate, which also con tains the copper and the precious metals that were possibly present in the nickel 5 mattes. AMENDED SHEET (ARTICLE 19)