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Extraction of Nickel and Cobalt from Sulfide Ores
Chapter 13
Extraction of Nickel and Cobalt from Sulfide Ores About half the global production of primary nickel is extracted from the sulfide ores. This chapter describes nickel sulfide ores and provides an overview of the methods used to extract nickel and cobalt from these ores. These extraction processes are described in detail in subsequent chapters in the following sequence: (a) the production of nickel-rich sulfide concentrates is discussed in Chapters 14 through 16; (b) the smelting and converting of the nickel concentrate to molten sulfide matte is discussed in Chapters 17 through 19; and, (c) the refining of the sulfide matte to high-purity nickel metal and other products is discussed in Chapters 21 through 27.
13.1. NICKEL SULFIDE ORES Nickel sulfide deposits occur as massive sulfides or as disseminated ores. Massive sulfides have a mineral sulfide content of 90%95%. Disseminated sulfides are a mixture of sulfides and siliceous gangue rock. The sulfide minerals found in nickel sulfide ores are given in Table 13.1. Virtually, all the nickel in nickel sulfide ores occurs in the mineral pentlandite [(Ni,Fe)9S8]. Only small amounts of nickel in the ore occur as millerite [NiS], violerite [Ni2FeS4] and nickeliferrous pyrrhotite [(Fe,Ni)8S9]. The proportion of nickel and iron in pentlandite is variable. Pentlandite typically contains approximately 36% Ni, 30% Fe and 33% S (plus about 1% Co). Pentlandite always occurs with other sulfide minerals, mostly pyrrhotite [Fe8S9] and chalcopyrite [CuFeS2]. These minerals are hosted by silicate and alumino-silicate minerals and their hydrated derivatives (Kerr, 2002). These silicate rock minerals are referred to as gangue rock.
Extractive Metallurgy of Nickel, Cobalt and Platinum-Group Metals. DOI: 10.1016/B978-0-08-096809-4.10013-9 Copyright Ó 2011 Elsevier Ltd. All rights reserved.
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TABLE 13.1 Minerals Found in Nickel Sulfide Ores* Mineral name
Chemical formula
Nickel content, %
Pentlandite
Ni4.5Fe4.5S8
34.2
Millerite
NiS
64.7
Heazlewoodite
Ni3S2
73.3
Polydymite
Ni3S4
57.9
Violarite
Ni2FeS4
38.9
Siegenite
(Co,Ni)3S4
28.9
Fletcherite
Ni2CuS4
75.9
Niccolite
NiAs
43.9
Maucherite
Ni11As8
51.9
Rammelsbergite
NiAs2
35.4
Breithauptite
NiSb
32.5
Annabergite
Ni3As2O8$8H2O
29.4
Pyrrhotite
(Ni,Fe)7S8
1-5
Chalcopyrite
CuFeS2
Magnetite
Fe3O4
Cubanite
CuFe2S3
Chromite
(Mg,Fe)Cr2O4
Galena
PbS
Sphalerite
ZnS
Bornite
Cu5FeS4
Mackinawite
(Fe,Ni,Co)S
Valleriite
Cu3Fe4S7
* Boldt & Queneau, 1967
The mineralogical compositions of five ores are given in Table 13.2, and their chemical compositions are given in Table 13.3. Besides nickel, pentlandite ores contain copper, cobalt, silver, gold and platinum-group elements (Pt, Pd, Rh, Ru, Ir) to a greater or lesser extent.
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Chapter | 13 Extraction of Nickel and Cobalt from Sulfide Ores
TABLE 13.2 Major Constituents of Five Nickel Sulfide Ores Ore composition, % Location
Pentlandite Chalcopyrite Pyrrhotite
Gangue rock
Kambalda, Australia
6
0.6
12 þ (2% pyrite 79 FeS2)
Raglan, Canada
8
2.4
11
79
Sudbury, Canada (A)
3.6
4.3
23
70
Sudbury, Canada (B)
3e6
2e5
20e30
Remainder
Thompson, Canada
7
0.4
22
70
TABLE 13.3 Chemical Composition of the Ores Given in Table 13.2, with Two Additional Ores from Russia. Note the large variation in copper content
Ore composition, % Location
Ni
Co
Cu
Kambalda, Australia
2.2
0.06
0.2
Raglan, Canada
2.8
0.08
0.8
Sudbury, Canada (A)
1.3
0.04
1.5
Sudbury, Canada (B)
1.6
0.04
1.2
2.5
0.07
0.1
Norilsk, Russia (average)
1.7
0.06
3.2
Pechenga, Russiaa
0.7
NA
0.3
Thompson, Canada a
a
Plus platinum-group metals and Au.
13.2. EXTRACTION OF NICKEL AND COBALT FROM SULFIDE ORES The main extraction process for treating nickel sulfide ores is shown in Figure 13.1. The process is broadly divided into three steps: (a) the production of a nickelcobalt concentrate; (b) the production of nickelcobalt converter matte; and, (c) the refining of this converter matte into pure metals or chemicals of nickel and cobalt.
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PART | I Extractive Metallurgy of Nickel and Cobalt
FIGURE 13.1 Main process steps for extracting nickel and cobalt from sulfide ores. Parallel lines indicate alternative processes. The dashed line indicates a developing process. The compositions are for ores from Sudbury, Canada.
Chapter | 13 Extraction of Nickel and Cobalt from Sulfide Ores
151
13.2.1. Concentrate Production Mined sulfide ores contain pentlandite, pyrrhotite, chalcopyrite and gangue rock. A high-grade nickel concentrate is produced from these ores by the following minerals-processing techniques: (a) crushing and grinding the ores to liberate the nickel- and cobalt-bearing minerals from the other minerals and gangue; (b) froth flotation to separate the nickel-, cobalt- and copper-bearing minerals from the gangue rock and pyrrhotite; and, (c) froth flotation to separate the nickel- and cobalt-bearing minerals from the copper-bearing minerals. These process steps result in a high-grade concentrate that is a suitable feed to a nickelcobalt smelter.
13.2.2. Smelting and Converting The nickel- and cobalt-rich concentrates are smelted and converted to form a converter matte that has a high nickelcobalt content and a low iron content. As shown in Figure 13.1, there are two options for smelting and converting: (i) flash smelting; and, (ii) electric furnace smelting. The smelting of nickelcobalt sulfides involves the following three processes: (a) the partial oxidation of the nickelcobalt sulfide to nickelcobalt oxide; (b) the oxidation of iron sulfide to iron oxide and the dissolution of the iron oxide in the silicate slag; and, (c) the melting of silicate gangue rock to form a silicate slag. In the electric furnace process, there is a separate roaster for the oxidation of nickel and iron sulfides. The melting of these roasted products then occurs in an electric furnace. Two products are separated in this electric furnace: the furnace matte, which is rich in nickelcobalt and lean in iron, and the silicate slag, which is rich in iron and lean in nickel and cobalt. In the flash furnace process, the oxidation and melting reactions both occur in the furnace. The advantage of this process is that the heat of reaction from roasting is used to power the furnace. The disadvantage of this type of operation is that the losses of nickel to the slag are higher than in the electric furnace. Both the flash furnace and the electric furnace produce a furnace matte that contains 40% Ni, 0.5% Co, and 25% Fe, with the remainder being sulfur. The furnace matte is converted, which is the oxidation of iron and sulfur to produce a converter matte that contains 50%60% Ni, 1% Co, 1% Fe, and 20%23% S. There are two flash furnace installations where strong oxidizing conditions are used. This results in a furnace matte that is similar to the converter matte, thus by-passing the need for a converter.
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PART | I Extractive Metallurgy of Nickel and Cobalt
The converter matte is refined, either using vapometallurgical or hydrometallurgical techniques.
13.2.3. Refining of Converter Mattes to Nickel and Cobalt Metal Converter mattes are refined to pure nickel and cobalt either in a vapometallurgical refinery (carbonyl process) or in a hydrometallurgical refinery. The basis for the carbonyl process is that carbon monoxide, CO, reacts preferentially with nickel to form nickel carbonyl, Ni(CO)4, which is a gas, at about 50 C. This gas, which contains only nickel, can be decomposed to nickel metal at much higher temperatures, such as 240 C. The carbonyl process has been used for over a hundred years, and the extractive metallurgy and conditions are well established. In contrast to the established nature of carbonyl refining, there is no standard flowsheet for the hydrometallurgical processing of converter mattes and nickel sulfides. Broadly, the hydrometallurgical refining of nickel sulfides occurs in the following steps: (i) leaching; (ii) solvent extraction and one of either; (iii) electrowinning; or, (iv) hydrogen reduction. These topics are examined in separate chapters, starting with Chapter 24 on leaching. However, since this part-by-part comparison of the refining steps oversimplifies the integrated nature of hydrometallurgical operations, a whole-by-whole comparison of these refining processes is given in Chapter 23. The product of the refining processes is high-purity nickel metal, suitable for applications.
13.3. HYDROMETALLURGICAL ALTERNATIVES TO MATTE SMELTING An alternative to the smelting of nickel concentrates to matte, which is then refined in a hydrometallurgical refinery, is to treat all of the concentrate hydrometallurgically. There are three different process chemistries that such a hydrometallurgical treatment facility can be based on: (i) ammoniacal; (ii) sulfate; and, (iii) chloride routes.
13.3.1. Ammoniacal Processes for Nickel Concentrates Nickel concentrates were pressure leached in ammonia solutions using air in Fort Saskatchewan, Alberta from 1954–1987 and at Kwinana, Western Australia from 1970–1987. Both operations used the Sherritt process. The mines supplying concentrate to the Fort Saskatchewan operation became depleted. This led to the processing of various feeds, such as nickelcopper mattes, and in 1987 exclusively to leaching of mixed
Chapter | 13 Extraction of Nickel and Cobalt from Sulfide Ores
153
nickelcobalt sulfide precipitates from Moa Bay, Cuba (Kofluk and Freeman, 2006). The Kwinana nickel refinery began processing concentrate in 1970. In 1974, low-iron matte from the Kalgoorlie nickel smelter was blended with concentrate feed. The proportion of matte was gradually increased until 1987 when the entire input became matte (Smith, 2004; Woodward & Bahri, 2007). Both refineries could still process concentrate; however, this would probably lead to lower production rates and increased amounts of residue. Both of these refineries are now in built-up communities making residue disposal more challenging.
13.3.2. Sulfate Processes for Nickel Concentrates Pentlandite concentrates can be processed in sulfate solutions, in a manner similar to the processing of mixed nickelcobalt precipitates and converter mattes. However, the concentration of nickel in the concentrate is about 15%, whereas it is about 50% in converter mattes. This means that the rate of processing must be about three or four times more efficient in the hydrometallurgical process that treats concentrates than in a similar process that treats converter matte if the same size of process plant were to be used. Because of the need to minimize capital investment, attention has focused on increasing the rate of leaching. The rate of leaching can be increased in two ways: (i) increase the intrinsic rate by adding a catalyst, such as chloride ions or increasing the temperature; and, (ii) decrease the particle size (Crundwell, 2005). Both of these strategies have been proposed for the leaching of nickel concentrates. Vale plans to add hydrochloric acid to the leaching liquor in order to accelerate the rate of leaching for their Voisey’s Bay operation (Stevens, Bishop, Singhal, Love, & Mihaylov, 2009). The pentlandite is leached from the gangue in sulfuric acid using oxygen. The construction of the Voisey’s Bay operation at Long Harbour, Newfoundland, is well advanced. This process is described in more detail in the next section. CESL have proposed the same strategy for their process (Jones, Mayhew, & O’Connor, 2009; Jones, Mayhew, Mean, & Neef, 2010). The addition of hydrochloric acid complicates the processes, particularly the choice of the materials of construction. This may explain why industrial adoption has been slow. Another process using sulfate solutions is Activox (Norilsk). This process adopts the second strategy mentioned above for increasing the rate of leaching, which is, decreasing the particle size. The process was demonstrated at Tati Nickel, in Botswana, but the full-scale operation was not built. The concentrate was ground very fine, to about 10 mm (Palmer & Johnson, 2005).
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PART | I Extractive Metallurgy of Nickel and Cobalt
13.3.3. Chloride Processes for Nickel Concentrates Outotec has developed an ambient pressure Cl2-HCl-O2 leaching step, called the HydroNic process, for pentlandite concentrate (Karonen, Tiihonen & Haavanlammi, 2009). It, too, has not yet been adopted industrially.
13.3.4. Disadvantages of Hydrometallurgical Processes for Concentrates The most important disadvantage of hydrometallurgical options for processing nickel concentrates is the difficulty of recovering both the precious metals and the base metals. Smelting and converting are able to remove gangue, sulfur and iron from the concentrate while leaving all the base and precious metals in the matte. This simplifies the hydrometallurgical recovery of the nickel, copper, cobalt and precious metals from the matte.
13.4. VOISEY’S BAY PROCESS FOR LEACHING NICKEL CONCENTRATES A schematic flowsheet for the Voisey’s Bay process is shown in Figure 13.2 (Stevens et al., 2009). The feed to this process is ground concentrate, which is contacted with a mixture of oxygen and chlorine gases from the nickel tankhouse in a series of stirred tank reactors. The step is called the chlorine preleach. The slurry is pumped into the pressure-leaching autoclave where the concentrate is dissolved using nickel spent electrolyte (sometimes called nickel anolyte). The anolyte is acidic and provides the acid required for leaching. The discharge slurry from the autoclave goes through the counter-current decantation section, where undissolved and precipitated solids are separated from the solution. The solids are neutralized and transferred to disposal. The solution goes to impurity removal where iron and other contaminants are removed. After impurity removal, the solution is transferred to copper solvent extraction. Copper is removed from the solution by solvent extraction using LIX 84. The stripped solution from solvent extraction is the feed to copper electrowinning, where high-purity copper is produced. Cobalt is extracted from the solution by solvent extraction using CYANEX 272. Cobalt is electrowon from the strip solution from solvent extraction as cobalt rounds. The raffinate from cobalt extraction is the feed to nickel electrowinning. The nickel electrowinning occurs in a divided cell, with anode bags for the collection of chlorine and oxygen gases. These gases are used in the leaching section of the process. The nickel spent, or anolyte, is recycled to leaching.
Chapter | 13 Extraction of Nickel and Cobalt from Sulfide Ores
155
FIGURE 13.2 Schematic diagram of the Voisey’s Bay process. The raffinate from the copper solvent extraction is passed through further purification steps, such as cadmium removal by sulfide precipitation, and a second iron-removal step. Then, the solution goes on to impurity solvent extraction were D2EPHA is used to remove calcium, copper, lead, iron, manganese and zinc. The purified solution is transferred to cobalt solvent extraction.
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PART | I Extractive Metallurgy of Nickel and Cobalt
The Voisey’s Bay process has been extensively piloted. The demonstration plant showed that both magnesium and silica built up in the circuit. Effective controls measures were implemented. It is anticipated that this process will be commissioned during 2013. The advantage of this process is that the capital-intensive steps of smelting and converting are avoided. The process cannot, however, recover precious metals.
13.5. HEAP LEACHING OF NICKEL SULFIDE ORE An alternative to intensifying the rate of leaching of concentrates is to heap leach the whole ore. This has the significant advantage of eliminating the concentration of the sulfides, which is the step that has the lowest recovery on route from ore to metal. Nickel sulfide ores are processed by heap leaching in Sotkama, eastern Finland (Talvivaara, 2011). The process entails the following: (a) (b) (c) (d) (e)
open-pit mining of 0.2% Ni, 0.5% Zn, 0.1% Cu, and 0.02% Co sulfide ore; four-stage crushing; rotary kiln agglomeration with sulfuric acid; stacking the agglomerate in 8 m high heaps; leaching nickel and other metals from the agglomerate by sprinkling metal-depleted, purified, recycle solution on the heaps; and, (f) maintaining adequate temperature and conditions to promote bacterial activity.
Copper, zinc and nickel are recovered from the pregnant leach solution by sequential hydrogen sulfide precipitation of separate metal sulfide precipitates. The heaps are typically leached for 1.5 years. The planned production of nickel in the sulfide precipitate is approximately 50 000 tonnes per year. Recent production has been considerably lower (Talvivaara, 2010).
13.6. SUMMARY Nickel sulfide ores occur as disseminated or massive orebodies. The nickel sulfide is separated from the host rock by flotation. The flotation concentrate is smelted to produce a converter matte, which is then refined either by carbonyl refining or in a hydrometallurgical refinery. This route is by far the most dominant. Alternatives to smelting and converting include various hydrometallurgical processes that treat concentrates, which have been demonstrated in the past, but are not currently practiced. Heap leaching of the sulfide ore is practiced at only one location.
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REFERENCES Boldt, J. R., & Queneau, P. (1967). The winning of nickel. Longmans. Crundwell, F. K. (2005). The leaching number: Its definition and use in determining the performance of leaching reactors and autoclaves. Minerals Engineering, 18, 1315– 1324. Jones, D. L., Mayhew, K., Mean, R., & Neef, M. (2010). Unlocking disseminated nickel sulphides using the CESL nickel process. In A. Taylor (Ed.), ALTA 2010 Nickel-Cobalt Conference. ALTA Metallurgical Services. Jones, D. L., Mayhew, K., & O’Connor, L. (2009). Nickel and cobalt recovery from a bulk coppernickel concentrate using the CESL process. In J. J. Budac, R. Fraser & I. Mihaylov, et al. (Eds.), Hydrometallurgy of nickel and cobalt 2009 (pp. 45–57). CIM. Karonen, J., Tiihonen, M., & Haavanlammi, L. (2009). Hydronic – a novel nickel refining method for nickel concentrates. In J. J. Budac, R. Fraser & I. Mihaylov, et al. (Eds.), Hydrometallurgy of nickel and cobalt 2009 (pp. 17–26). CIM. Kofluk, R. P., & Freeman, G. K. W. (2006). Iron control in the Moa Bay operation. In J. E. Dutrizac & P. A. Riveros (Eds.), Iron control technologies (pp. 573–589). CIM. Palmer, C. M., & Johnson, G. D. (2005). The Activox process: Growing significance in the nickel industry. Journal of Metals, 57, 40–47. Smith, R. (2004). Kwinana nickel refinery. October 28, 2004. Stevens, D., Bishop, G., Singhal, A., Love, B., & Mihaylov, I. (2009). Operation of the pressure oxidative leach process for Voisey’s Bay nickel concentrate at Vale Inco’s hydromet demonstration plant. In J. J. Budac, R. Fraser & I. Mihaylov, et al. (Eds.), Hydrometallurgy of nickel and cobalt 2009 (pp. 3–16). CIM. Talvivarra. (2010). Talvivaara falls after hydrogen sulphide leak. The Guardian (UK). May 6, 2010. Talvivaara. (2011). Talvivaara operations.. Accessed 25.05.2011. Woodward, T. M., & Bahri, P. A. (2007). Steady-state optimisation of the leaching process at Kwinana nickel refinery. In V. Plesu & P. S. Agachi (Eds.), 17th European symposium on computer aided process engineering – ESCAPE17 (pp. 1–6). Elsevier.
SUGGESTED READING Budac, J. J., Fraser, R., Mihaylov, I., et al. (2009). Hydrometallurgy of nickel and cobalt 2009. Metallurgical Society of CIM. Burkin, A. R. (1987). Extractive metallurgy of nickel. Society of (British) Chemical Industry. Donald, J. & Schonewille, R. (Eds.). (2005). Nickel and cobalt 2005, challenges in extraction and production. Metallurgical Society of CIM. Habashi, F. (2009). A history of nickel. In J. Liu, J. Peacey & M. Barati, et al. (Eds.), Pyrometallurgy of nickel and cobalt 2009, proceedings of the international symposium(Taylor, A., ed.) (pp. 77–98). Metallurgical Society of CIM. Jones, R. T. (2004). JOM world nonferrous smelter survey, part II: Platinum group metals. Journal of Metals, 56, 59–63. Jones, R. T. (2006). Southern African pyrometallurgy 2006 international conference. The South African Institute of Mining and Metallurgy. Liu, J., Peacey, J., Barati, M., et al. (2009). Pyrometallurgy of nickel and cobalt 2009. Metallurgical Society of CIM.
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Kerr, A. (2002). An overview of recent developments in flotation technology and plant practice for nickel ores. In A. L. Mular, D. N. Halbe & D. J. Barratt (Eds.), Mineral processing, plant design, practice and control proceedings, Volume 1 (pp. 1142–1158). SME. Warner, A. E. M., Diaz, C. M., Dalvi, A. D., et al. (2006). JOM world nonferrous smelter survey, part III: Laterite. Journal of Metals, 58, 11–20. Warner, A. E. M., Diaz, C. M., Dalvi, A. D., et al. (2007). JOM world nonferrous smelter survey, part IV: Nickel sulfide. Journal of Metals, 59, 58–72.
Extraction of Nickel and Cobalt from Sulfide Ores About half the global production of primary nickel is extracted from the sulfide ores. This chapter describes nickel sulfide ores and provides an overview of the methods used to extract nickel and cobalt from these ores. These extraction processes are described in detail in subsequent chapters in the following sequence: (a) the production of nickel-rich sulfide concentrates is discussed in Chapters 14 through 16; (b) the smelting and converting of the nickel concentrate to molten sulfide matte is discussed in Chapters 17 through 19; and, (c) the refining of the sulfide matte to high-purity nickel metal and other products is discussed in Chapters 21 through 27.
13.1. NICKEL SULFIDE ORES Nickel sulfide deposits occur as massive sulfides or as disseminated ores. Massive sulfides have a mineral sulfide content of 90%95%. Disseminated sulfides are a mixture of sulfides and siliceous gangue rock. The sulfide minerals found in nickel sulfide ores are given in Table 13.1. Virtually, all the nickel in nickel sulfide ores occurs in the mineral pentlandite [(Ni,Fe)9S8]. Only small amounts of nickel in the ore occur as millerite [NiS], violerite [Ni2FeS4] and nickeliferrous pyrrhotite [(Fe,Ni)8S9]. The proportion of nickel and iron in pentlandite is variable. Pentlandite typically contains approximately 36% Ni, 30% Fe and 33% S (plus about 1% Co). Pentlandite always occurs with other sulfide minerals, mostly pyrrhotite [Fe8S9] and chalcopyrite [CuFeS2]. These minerals are hosted by silicate and alumino-silicate minerals and their hydrated derivatives (Kerr, 2002). These silicate rock minerals are referred to as gangue rock.
Extractive Metallurgy of Nickel, Cobalt and Platinum-Group Metals. DOI: 10.1016/B978-0-08-096809-4.10013-9 Copyright Ó 2011 Elsevier Ltd. All rights reserved.
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PART | I Extractive Metallurgy of Nickel and Cobalt
TABLE 13.1 Minerals Found in Nickel Sulfide Ores* Mineral name
Chemical formula
Nickel content, %
Pentlandite
Ni4.5Fe4.5S8
34.2
Millerite
NiS
64.7
Heazlewoodite
Ni3S2
73.3
Polydymite
Ni3S4
57.9
Violarite
Ni2FeS4
38.9
Siegenite
(Co,Ni)3S4
28.9
Fletcherite
Ni2CuS4
75.9
Niccolite
NiAs
43.9
Maucherite
Ni11As8
51.9
Rammelsbergite
NiAs2
35.4
Breithauptite
NiSb
32.5
Annabergite
Ni3As2O8$8H2O
29.4
Pyrrhotite
(Ni,Fe)7S8
1-5
Chalcopyrite
CuFeS2
Magnetite
Fe3O4
Cubanite
CuFe2S3
Chromite
(Mg,Fe)Cr2O4
Galena
PbS
Sphalerite
ZnS
Bornite
Cu5FeS4
Mackinawite
(Fe,Ni,Co)S
Valleriite
Cu3Fe4S7
* Boldt & Queneau, 1967
The mineralogical compositions of five ores are given in Table 13.2, and their chemical compositions are given in Table 13.3. Besides nickel, pentlandite ores contain copper, cobalt, silver, gold and platinum-group elements (Pt, Pd, Rh, Ru, Ir) to a greater or lesser extent.
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Chapter | 13 Extraction of Nickel and Cobalt from Sulfide Ores
TABLE 13.2 Major Constituents of Five Nickel Sulfide Ores Ore composition, % Location
Pentlandite Chalcopyrite Pyrrhotite
Gangue rock
Kambalda, Australia
6
0.6
12 þ (2% pyrite 79 FeS2)
Raglan, Canada
8
2.4
11
79
Sudbury, Canada (A)
3.6
4.3
23
70
Sudbury, Canada (B)
3e6
2e5
20e30
Remainder
Thompson, Canada
7
0.4
22
70
TABLE 13.3 Chemical Composition of the Ores Given in Table 13.2, with Two Additional Ores from Russia. Note the large variation in copper content
Ore composition, % Location
Ni
Co
Cu
Kambalda, Australia
2.2
0.06
0.2
Raglan, Canada
2.8
0.08
0.8
Sudbury, Canada (A)
1.3
0.04
1.5
Sudbury, Canada (B)
1.6
0.04
1.2
2.5
0.07
0.1
Norilsk, Russia (average)
1.7
0.06
3.2
Pechenga, Russiaa
0.7
NA
0.3
Thompson, Canada a
a
Plus platinum-group metals and Au.
13.2. EXTRACTION OF NICKEL AND COBALT FROM SULFIDE ORES The main extraction process for treating nickel sulfide ores is shown in Figure 13.1. The process is broadly divided into three steps: (a) the production of a nickelcobalt concentrate; (b) the production of nickelcobalt converter matte; and, (c) the refining of this converter matte into pure metals or chemicals of nickel and cobalt.
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PART | I Extractive Metallurgy of Nickel and Cobalt
FIGURE 13.1 Main process steps for extracting nickel and cobalt from sulfide ores. Parallel lines indicate alternative processes. The dashed line indicates a developing process. The compositions are for ores from Sudbury, Canada.
Chapter | 13 Extraction of Nickel and Cobalt from Sulfide Ores
151
13.2.1. Concentrate Production Mined sulfide ores contain pentlandite, pyrrhotite, chalcopyrite and gangue rock. A high-grade nickel concentrate is produced from these ores by the following minerals-processing techniques: (a) crushing and grinding the ores to liberate the nickel- and cobalt-bearing minerals from the other minerals and gangue; (b) froth flotation to separate the nickel-, cobalt- and copper-bearing minerals from the gangue rock and pyrrhotite; and, (c) froth flotation to separate the nickel- and cobalt-bearing minerals from the copper-bearing minerals. These process steps result in a high-grade concentrate that is a suitable feed to a nickelcobalt smelter.
13.2.2. Smelting and Converting The nickel- and cobalt-rich concentrates are smelted and converted to form a converter matte that has a high nickelcobalt content and a low iron content. As shown in Figure 13.1, there are two options for smelting and converting: (i) flash smelting; and, (ii) electric furnace smelting. The smelting of nickelcobalt sulfides involves the following three processes: (a) the partial oxidation of the nickelcobalt sulfide to nickelcobalt oxide; (b) the oxidation of iron sulfide to iron oxide and the dissolution of the iron oxide in the silicate slag; and, (c) the melting of silicate gangue rock to form a silicate slag. In the electric furnace process, there is a separate roaster for the oxidation of nickel and iron sulfides. The melting of these roasted products then occurs in an electric furnace. Two products are separated in this electric furnace: the furnace matte, which is rich in nickelcobalt and lean in iron, and the silicate slag, which is rich in iron and lean in nickel and cobalt. In the flash furnace process, the oxidation and melting reactions both occur in the furnace. The advantage of this process is that the heat of reaction from roasting is used to power the furnace. The disadvantage of this type of operation is that the losses of nickel to the slag are higher than in the electric furnace. Both the flash furnace and the electric furnace produce a furnace matte that contains 40% Ni, 0.5% Co, and 25% Fe, with the remainder being sulfur. The furnace matte is converted, which is the oxidation of iron and sulfur to produce a converter matte that contains 50%60% Ni, 1% Co, 1% Fe, and 20%23% S. There are two flash furnace installations where strong oxidizing conditions are used. This results in a furnace matte that is similar to the converter matte, thus by-passing the need for a converter.
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The converter matte is refined, either using vapometallurgical or hydrometallurgical techniques.
13.2.3. Refining of Converter Mattes to Nickel and Cobalt Metal Converter mattes are refined to pure nickel and cobalt either in a vapometallurgical refinery (carbonyl process) or in a hydrometallurgical refinery. The basis for the carbonyl process is that carbon monoxide, CO, reacts preferentially with nickel to form nickel carbonyl, Ni(CO)4, which is a gas, at about 50 C. This gas, which contains only nickel, can be decomposed to nickel metal at much higher temperatures, such as 240 C. The carbonyl process has been used for over a hundred years, and the extractive metallurgy and conditions are well established. In contrast to the established nature of carbonyl refining, there is no standard flowsheet for the hydrometallurgical processing of converter mattes and nickel sulfides. Broadly, the hydrometallurgical refining of nickel sulfides occurs in the following steps: (i) leaching; (ii) solvent extraction and one of either; (iii) electrowinning; or, (iv) hydrogen reduction. These topics are examined in separate chapters, starting with Chapter 24 on leaching. However, since this part-by-part comparison of the refining steps oversimplifies the integrated nature of hydrometallurgical operations, a whole-by-whole comparison of these refining processes is given in Chapter 23. The product of the refining processes is high-purity nickel metal, suitable for applications.
13.3. HYDROMETALLURGICAL ALTERNATIVES TO MATTE SMELTING An alternative to the smelting of nickel concentrates to matte, which is then refined in a hydrometallurgical refinery, is to treat all of the concentrate hydrometallurgically. There are three different process chemistries that such a hydrometallurgical treatment facility can be based on: (i) ammoniacal; (ii) sulfate; and, (iii) chloride routes.
13.3.1. Ammoniacal Processes for Nickel Concentrates Nickel concentrates were pressure leached in ammonia solutions using air in Fort Saskatchewan, Alberta from 1954–1987 and at Kwinana, Western Australia from 1970–1987. Both operations used the Sherritt process. The mines supplying concentrate to the Fort Saskatchewan operation became depleted. This led to the processing of various feeds, such as nickelcopper mattes, and in 1987 exclusively to leaching of mixed
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nickelcobalt sulfide precipitates from Moa Bay, Cuba (Kofluk and Freeman, 2006). The Kwinana nickel refinery began processing concentrate in 1970. In 1974, low-iron matte from the Kalgoorlie nickel smelter was blended with concentrate feed. The proportion of matte was gradually increased until 1987 when the entire input became matte (Smith, 2004; Woodward & Bahri, 2007). Both refineries could still process concentrate; however, this would probably lead to lower production rates and increased amounts of residue. Both of these refineries are now in built-up communities making residue disposal more challenging.
13.3.2. Sulfate Processes for Nickel Concentrates Pentlandite concentrates can be processed in sulfate solutions, in a manner similar to the processing of mixed nickelcobalt precipitates and converter mattes. However, the concentration of nickel in the concentrate is about 15%, whereas it is about 50% in converter mattes. This means that the rate of processing must be about three or four times more efficient in the hydrometallurgical process that treats concentrates than in a similar process that treats converter matte if the same size of process plant were to be used. Because of the need to minimize capital investment, attention has focused on increasing the rate of leaching. The rate of leaching can be increased in two ways: (i) increase the intrinsic rate by adding a catalyst, such as chloride ions or increasing the temperature; and, (ii) decrease the particle size (Crundwell, 2005). Both of these strategies have been proposed for the leaching of nickel concentrates. Vale plans to add hydrochloric acid to the leaching liquor in order to accelerate the rate of leaching for their Voisey’s Bay operation (Stevens, Bishop, Singhal, Love, & Mihaylov, 2009). The pentlandite is leached from the gangue in sulfuric acid using oxygen. The construction of the Voisey’s Bay operation at Long Harbour, Newfoundland, is well advanced. This process is described in more detail in the next section. CESL have proposed the same strategy for their process (Jones, Mayhew, & O’Connor, 2009; Jones, Mayhew, Mean, & Neef, 2010). The addition of hydrochloric acid complicates the processes, particularly the choice of the materials of construction. This may explain why industrial adoption has been slow. Another process using sulfate solutions is Activox (Norilsk). This process adopts the second strategy mentioned above for increasing the rate of leaching, which is, decreasing the particle size. The process was demonstrated at Tati Nickel, in Botswana, but the full-scale operation was not built. The concentrate was ground very fine, to about 10 mm (Palmer & Johnson, 2005).
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13.3.3. Chloride Processes for Nickel Concentrates Outotec has developed an ambient pressure Cl2-HCl-O2 leaching step, called the HydroNic process, for pentlandite concentrate (Karonen, Tiihonen & Haavanlammi, 2009). It, too, has not yet been adopted industrially.
13.3.4. Disadvantages of Hydrometallurgical Processes for Concentrates The most important disadvantage of hydrometallurgical options for processing nickel concentrates is the difficulty of recovering both the precious metals and the base metals. Smelting and converting are able to remove gangue, sulfur and iron from the concentrate while leaving all the base and precious metals in the matte. This simplifies the hydrometallurgical recovery of the nickel, copper, cobalt and precious metals from the matte.
13.4. VOISEY’S BAY PROCESS FOR LEACHING NICKEL CONCENTRATES A schematic flowsheet for the Voisey’s Bay process is shown in Figure 13.2 (Stevens et al., 2009). The feed to this process is ground concentrate, which is contacted with a mixture of oxygen and chlorine gases from the nickel tankhouse in a series of stirred tank reactors. The step is called the chlorine preleach. The slurry is pumped into the pressure-leaching autoclave where the concentrate is dissolved using nickel spent electrolyte (sometimes called nickel anolyte). The anolyte is acidic and provides the acid required for leaching. The discharge slurry from the autoclave goes through the counter-current decantation section, where undissolved and precipitated solids are separated from the solution. The solids are neutralized and transferred to disposal. The solution goes to impurity removal where iron and other contaminants are removed. After impurity removal, the solution is transferred to copper solvent extraction. Copper is removed from the solution by solvent extraction using LIX 84. The stripped solution from solvent extraction is the feed to copper electrowinning, where high-purity copper is produced. Cobalt is extracted from the solution by solvent extraction using CYANEX 272. Cobalt is electrowon from the strip solution from solvent extraction as cobalt rounds. The raffinate from cobalt extraction is the feed to nickel electrowinning. The nickel electrowinning occurs in a divided cell, with anode bags for the collection of chlorine and oxygen gases. These gases are used in the leaching section of the process. The nickel spent, or anolyte, is recycled to leaching.
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FIGURE 13.2 Schematic diagram of the Voisey’s Bay process. The raffinate from the copper solvent extraction is passed through further purification steps, such as cadmium removal by sulfide precipitation, and a second iron-removal step. Then, the solution goes on to impurity solvent extraction were D2EPHA is used to remove calcium, copper, lead, iron, manganese and zinc. The purified solution is transferred to cobalt solvent extraction.
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The Voisey’s Bay process has been extensively piloted. The demonstration plant showed that both magnesium and silica built up in the circuit. Effective controls measures were implemented. It is anticipated that this process will be commissioned during 2013. The advantage of this process is that the capital-intensive steps of smelting and converting are avoided. The process cannot, however, recover precious metals.
13.5. HEAP LEACHING OF NICKEL SULFIDE ORE An alternative to intensifying the rate of leaching of concentrates is to heap leach the whole ore. This has the significant advantage of eliminating the concentration of the sulfides, which is the step that has the lowest recovery on route from ore to metal. Nickel sulfide ores are processed by heap leaching in Sotkama, eastern Finland (Talvivaara, 2011). The process entails the following: (a) (b) (c) (d) (e)
open-pit mining of 0.2% Ni, 0.5% Zn, 0.1% Cu, and 0.02% Co sulfide ore; four-stage crushing; rotary kiln agglomeration with sulfuric acid; stacking the agglomerate in 8 m high heaps; leaching nickel and other metals from the agglomerate by sprinkling metal-depleted, purified, recycle solution on the heaps; and, (f) maintaining adequate temperature and conditions to promote bacterial activity.
Copper, zinc and nickel are recovered from the pregnant leach solution by sequential hydrogen sulfide precipitation of separate metal sulfide precipitates. The heaps are typically leached for 1.5 years. The planned production of nickel in the sulfide precipitate is approximately 50 000 tonnes per year. Recent production has been considerably lower (Talvivaara, 2010).
13.6. SUMMARY Nickel sulfide ores occur as disseminated or massive orebodies. The nickel sulfide is separated from the host rock by flotation. The flotation concentrate is smelted to produce a converter matte, which is then refined either by carbonyl refining or in a hydrometallurgical refinery. This route is by far the most dominant. Alternatives to smelting and converting include various hydrometallurgical processes that treat concentrates, which have been demonstrated in the past, but are not currently practiced. Heap leaching of the sulfide ore is practiced at only one location.
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REFERENCES Boldt, J. R., & Queneau, P. (1967). The winning of nickel. Longmans. Crundwell, F. K. (2005). The leaching number: Its definition and use in determining the performance of leaching reactors and autoclaves. Minerals Engineering, 18, 1315– 1324. Jones, D. L., Mayhew, K., Mean, R., & Neef, M. (2010). Unlocking disseminated nickel sulphides using the CESL nickel process. In A. Taylor (Ed.), ALTA 2010 Nickel-Cobalt Conference. ALTA Metallurgical Services. Jones, D. L., Mayhew, K., & O’Connor, L. (2009). Nickel and cobalt recovery from a bulk coppernickel concentrate using the CESL process. In J. J. Budac, R. Fraser & I. Mihaylov, et al. (Eds.), Hydrometallurgy of nickel and cobalt 2009 (pp. 45–57). CIM. Karonen, J., Tiihonen, M., & Haavanlammi, L. (2009). Hydronic – a novel nickel refining method for nickel concentrates. In J. J. Budac, R. Fraser & I. Mihaylov, et al. (Eds.), Hydrometallurgy of nickel and cobalt 2009 (pp. 17–26). CIM. Kofluk, R. P., & Freeman, G. K. W. (2006). Iron control in the Moa Bay operation. In J. E. Dutrizac & P. A. Riveros (Eds.), Iron control technologies (pp. 573–589). CIM. Palmer, C. M., & Johnson, G. D. (2005). The Activox process: Growing significance in the nickel industry. Journal of Metals, 57, 40–47. Smith, R. (2004). Kwinana nickel refinery. October 28, 2004. Stevens, D., Bishop, G., Singhal, A., Love, B., & Mihaylov, I. (2009). Operation of the pressure oxidative leach process for Voisey’s Bay nickel concentrate at Vale Inco’s hydromet demonstration plant. In J. J. Budac, R. Fraser & I. Mihaylov, et al. (Eds.), Hydrometallurgy of nickel and cobalt 2009 (pp. 3–16). CIM. Talvivarra. (2010). Talvivaara falls after hydrogen sulphide leak. The Guardian (UK). May 6, 2010. Talvivaara. (2011). Talvivaara operations.
SUGGESTED READING Budac, J. J., Fraser, R., Mihaylov, I., et al. (2009). Hydrometallurgy of nickel and cobalt 2009. Metallurgical Society of CIM. Burkin, A. R. (1987). Extractive metallurgy of nickel. Society of (British) Chemical Industry. Donald, J. & Schonewille, R. (Eds.). (2005). Nickel and cobalt 2005, challenges in extraction and production. Metallurgical Society of CIM. Habashi, F. (2009). A history of nickel. In J. Liu, J. Peacey & M. Barati, et al. (Eds.), Pyrometallurgy of nickel and cobalt 2009, proceedings of the international symposium(Taylor, A., ed.) (pp. 77–98). Metallurgical Society of CIM. Jones, R. T. (2004). JOM world nonferrous smelter survey, part II: Platinum group metals. Journal of Metals, 56, 59–63. Jones, R. T. (2006). Southern African pyrometallurgy 2006 international conference. The South African Institute of Mining and Metallurgy. Liu, J., Peacey, J., Barati, M., et al. (2009). Pyrometallurgy of nickel and cobalt 2009. Metallurgical Society of CIM.
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Kerr, A. (2002). An overview of recent developments in flotation technology and plant practice for nickel ores. In A. L. Mular, D. N. Halbe & D. J. Barratt (Eds.), Mineral processing, plant design, practice and control proceedings, Volume 1 (pp. 1142–1158). SME. Warner, A. E. M., Diaz, C. M., Dalvi, A. D., et al. (2006). JOM world nonferrous smelter survey, part III: Laterite. Journal of Metals, 58, 11–20. Warner, A. E. M., Diaz, C. M., Dalvi, A. D., et al. (2007). JOM world nonferrous smelter survey, part IV: Nickel sulfide. Journal of Metals, 59, 58–72.