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Slow Cooling and Solidification of Converter Matte
Chapter 21
Slow Cooling and Solidification of Converter Matte The molten converter matte, discussed in Chapter 19, contains nickel, sulfur and a small amount of iron. It also contains copper, cobalt, silver, gold and platinum-group elements to a greater or lesser extent. These elements cannot be separated while the matte is molten. They are separated by solidifying the matte and treating it by two different techniques as follows: (a) vapometallurgical refining (Chapter 22); and, (b) hydrometallurgical refining (Chapters 23 through 27). However, about half of the global production of converter matte from sulfide smelting undergoes a preliminary treatment before these processes (Warner et al., 2007). The following steps are used: (a) between 12 and 25 tonnes of molten matte are poured into large molds; (b) this matte is slowly solidified and cooled in covered molds, which results in the formation of large individual grains of heazlewoodite (Ni3S2), chalcocite (Cu2S) and metallic alloy (see Figures 21.1 and 21.2); (c) the solid matte is crushed and ground, which liberates the grains of the different minerals from each other; and, (d) the ground ore is separated into alloy, copper–sulphide and nickel–sulphide concentrates by magnetic separation and froth flotation. A schematic diagram of the process is shown in Figure 21.3. Operating details are given in Tables 21.1 and 21.2. The advantages of this preliminary separation are that it simplifies the subsequent metal extraction and minimizes the in-plant residence times.
21.1. SOLIDIFICATION AND SLOW COOLING PROCESS The equilibrium phase diagram for the Ni–Cu–S system is shown in Figure 21.2. This phase diagram indicates that the products of solidifying the molten matte, then cooling it to ambient temperature, are nearly pure Ni3S2 and Cu2S. Extractive Metallurgy of Nickel, Cobalt and Platinum-Group Metals. DOI: 10.1016/B978-0-08-096809-4.10021-8 Copyright Ó 2011 Elsevier Ltd. All rights reserved.
259
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PART | I Extractive Metallurgy of Nickel and Cobalt
(a)
(b)
FIGURE 21.1 Photomicrograph (100) of (a) quenched and (b) slowly cooled nickel-copper converter matte, showing that the quenched matte is much more finely grained than the slowcooled matte. The grain size of the quenched matte is about 10 mm while that of the slow-cooled matte is about 100 mm. The dark grey grains are Cu2S; the light grey grains are Ni-Cu alloy. The matrix is Ni3S2. Grinding the solidified matte to a mean particle size of 70 mm liberates the three phases so that they can be separated from one another by magnetic and froth flotation processing. Source: Boldt and Queneau, 1967, courtesy of Vale.
The equilibrium conditions are closely approximated industrially by solidification and slow cooling of the converter matte. Slow cooling encourages the precipitated grains of Ni3S2 and Cu2S to grow to a size of approximately 100 mm in size, as shown in Figure 21.1. 1100 Liquid
Temperature, °C
1000
L+α
900 800
α
L+β 720°C
700
535°C 500 Cu2S
β
β+α
600
β + β’
β’ + α 20
40 60 Percent Ni3S2
β’ 80
Ni3S2
FIGURE 21.2 Equilibrium Cu2S–Ni3S2 phase diagram. The complete miscibility of Cu2S and Ni3S2 above the Cu2S melting point (~1130 C) and the almost complete immiscibility of Cu2S and Ni3S2 below 450 C are notable. The latter causes molten matte to separate into two individual phases during slow cooling.
magnetic separator
broken/crushed slowly frozen/cooled converter matte, 35% Ni, 41% Cu
ball mill
magnetic
Cu, Ni, Au, Ag, Pt group alloy
fraction
65% Ni, 17% Cu
to carbonyl nickel refinery
non-magnetic fraction: Cu2S and Ni3S2
pH = 12 –70 m diameter
Cu2S concentrate
to company's Cu smelter
4% Ni, 74% Cu
diphenyl guanidine collector-frother
froth
Cu2S flotation
underflow
Ni3S2 concentrate 71% Cu, 0.9% Cu
to roasting then to market or refining
261
FIGURE 21.3 Simplified flowsheet for separating slowly solidified and cooled converter matte into (i) magnetic alloy concentrate; (ii) copper-rich sulphide concentrate; and, (iii) nickel-rich sulphide concentrate (Tables 21.1 and 21.2). Concentrate cleaning circuits are not shown. Donald and Scholey (2005) and Dorigo, Yalcin, Duncan, & Montgomery, (2009) give more details. Wet magnetic separation is done with a magnetic drum, which rotates and lifts magnetic particles up and out of a slurry bath. The magnetic particles overflow, and the non-magnetic particles underflow.
Chapter | 21 Slow Cooling and Solidification of Converter Matte
water + CaO
262
PART | I Extractive Metallurgy of Nickel and Cobalt
TABLE 21.1 Details of the Sudbury Matte Separation Plant (Vale) for Making Magnetic Alloy, Copper Sulphide and Nickel Sulphide Concentrates from Solidified Low Sulfur (21% S) Converter Matte Location
Sudbury, Canada
Startup date
1948
Nickel production all products
~140 000 tonnes per year
Casting and slow solidification/cooling Source of matte
Peirce-Smith converters
Matte casting temperature
980 C
Molds Number
220
Material
Castable fire clay, coated with lime wash (imbedded in floor)
Size
4 2.4 0.6 m deep with 45 walls
Matte mass per mold
23 tonnes
Cover
Refractory-lined steel
Casting method
Molten matte poured from ladle via overhead crane
Cooling duration
Three days with cover on to ~480 C followed by 1 day with cover off to 200 C
Breaking, crushing and grinding Ingot transport
Via overhead crane using ‘scissor’ tongs.
Ingot breaking
With overhead chisel-tipped hammers (pile drivers)
Crushing
Jaw crusher (to ~1 m) then two open-circuit gyratory crushers in series to ~0.01 m
Grinding
Rod mill (open circuit) then ball mills (closed circuit)
Size control
Cyclone classifiers
Final matte Particle size
99% < 70 mm diameter
Destination
Magnetic and froth flotation separation of alloy, Cu sulphide, and Ni sulphide concentrates (Table 21.2)
This table gives matte casting, slow cooling, crushing and grinding details (Donald & Scholey, 2005). Similar procedures are followed at the Waterval Smelter, South Africa (Anglo American Platinum) but with round molds (Jacobs, 2006).
Chapter | 21 Slow Cooling and Solidification of Converter Matte
TABLE 21.2 Details of Magnetic and Flotation Separations at Vale’s Sudbury Matte Separation Plant* Location
Sudbury, Canada
Startup date
1948
Nickel production all products
~140 000 tonnes per year
Particle separations Isolation of magnetic metallic concentrate
Magnetic separation, consisting of the following steps: (a) magnetic separation of magnetic metal particles from non-magnetic sulphide particles; (b) ball mill regrind; and, (c) second magnetic separation (cleaning)
Product
Alloy concentrate: 65% Ni: 17% Cu with high concentrations of Ag, Au and Pt-group elements
Destination
To top blown rotary converting (Appendix G) and carbonyl refining (Chapter 22)
Isolation of Ni3S2 concentrate, low in Cu2S
Cu2S is floated from non-magnetic matte fraction by froth flotation using CaO for pH control (pH > 12) and diphenyl guanidine collector/frother Underflow Ni3S2 slurry is reground and has (i) Cu2S removed in a column flotation cell; and, (ii) alloy removed in a drum magnetic separator
Product
Ni3S2 concentrate: 71% Ni and 0.9% Cu
Destination
To NiO production by oxidation roasting. The NiO is sold or sent to Clydach, Wales for reduction, sulfur activation and ambient pressure carbonyl nickel refining (Chapter 22)
Isolation of Cu2S concentrate Product
Cu2S concentrate: 4% Ni and 74% Cu
Destination
Company’s copper smelter
Middlings concentrate
Underflow from grinding and cleaning Cu2S concentrate
Product
Ni3S2 middlings concentrate: 66% Ni and 6.6% Cu (not shown in Figure. 21.3)
Destination
Roasted then sent to Sudbury nickel refinery for high-pressure carbonyl nickel refining
The Anglo American Platinum (South Africa) Magnetic Concentrator Plant uses only magnetic separation (that is, no flotation) to produce a magnetic concentrate rich in platinum-group elements (~30% platinum-group metals) and a non-magnetic bulk sulphide concentrate (Jacobs, 2006). *Donald & Scholey, 2005
263
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PART | I Extractive Metallurgy of Nickel and Cobalt
The driving force for the grain growth is the minimization of the interfacial energy. The nickel converter matte purposely contains slightly less sulfur than is required to form stoichiometric Ni3S2 and Cu2S (Donald & Scholey, 2005). The low sulfur content is achieved by converting at a high temperature. This deficiency of sulfur causes a third phase to form during solidification and slow cooling. This third phase is a magnetic alloy that contains nickel, copper and most of the silver, gold and platinum-group elements in the feed matte.
21.2. INDUSTRIAL MATTE CASTING, SOLIDIFICATION AND SLOW COOLING Between 12 and 25 tonnes of molten converter matte, at about 1000 C, are cast into large refractory-lined steel depressions, or molds, at floor level. This is shown in Figure 21.4. A steel loop is placed into the solidifying matte, and the mold is covered with a steel lid. The matte is allowed to cool for 3 days. After 3 days, the lid is removed, and the matte is cooled for another day. The solid casting is lifted out of the mold using the steel loop and then sent to breaking, crushing, grinding and mineral separation.
21.2.1. Matte Structure The solidified matte contains grains of three major components: (i) a magnetic nickel–copper alloy (containing most of the silver, gold and platinum-group elements); (ii) chalcocite (Cu2S); and, (iii) heazlewoodite (Ni3S2). A small amount of other minerals, for example, bornite (Cu5FeS4) may also be present. As mentioned earlier, the grains are quite large, approximately 100 mm in size (Donald & Scholey, 2005). Grinding the matte to a mean particle size of 70 mm liberates the minerals.
21.2.2. Isolation of the Liberated Grains The ground matte is separated into three concentrates. Two major methods are used for this purpose: (a) magnetic separation of the precious metals-rich alloy particles into a magnetic alloy concentrate; and, (b) flotation separation of the remaining sulphides particles into copper-rich and nickel-rich sulphide concentrates (this separation is not always done; Jacobs, 2006).
Chapter | 21 Slow Cooling and Solidification of Converter Matte
265
FIGURE 21.4 Casting of low-iron, sulfur-deficient matte into floor-level molds in preparation for slow cooling. Slow cooling causes the matte to separate into ~100 mm Cu2S, Ni3S2 and alloy grains, which are separated by comminution then magnetic separation and froth flotation. The alloy grains contain most of the silver, gold and platinum-group elements in the matte. The newlyfilled molds will be covered with the lid (left). Photograph courtesy of Anglo American Platinum.
21.3. CONCENTRATE DESTINATIONS Matte concentrate destinations vary from smelter to smelter. The most straightforward arrangement is that at the Waterval, South Africa, smelter (Anglo American Platinum). A magnetic concentrate that is rich in platinum-group elements and a non-magnetic concentrate are made. The magnetic fraction is upgraded by leaching and then sent to a precious metals refinery. The non-magnetic fraction is sent to a nickel–copper refinery (Jacobs, 2006). This arrangement maximizes the recovery of the metals and minimizes the in-plant residence time.
266
PART | I Extractive Metallurgy of Nickel and Cobalt
The Sudbury, Canada, smelter (Vale) makes three major concentrates: (a) a magnetic alloy concentrate, which is sent directly to its nickel refinery; (b) a copper-rich sulphide flotation concentrate, which is smelted in a copper smelter; and, (c) an nickel-rich sulphide concentrate, which is oxidation roasted to nickel oxide. Residues from the nickel refinery are treated for copper, cobalt and precious metals extraction. The nickel oxide from the oxidation roasting is either sold or it is refined to high-purity nickel in the company’s carbonyl refineries in Sudbury, Canada, and Clydach, Wales. Carbonyl refining is described in Chapter 22.
21.4. SUMMARY The converter matte contains nickel, iron and sulfur. It may also contain copper, cobalt, silver, gold and platinum-group elements to a greater or lesser extent. These elements are ultimately separated and made into metal either hydrometallurgically or vapometallurgically. Often, however, the elements are given a preliminary separation by (i) slow cooling and solidification of the molten matte; (ii) ingot breaking, crushing and grinding; (iii) magnetic separation; and, (iv) froth flotation. This treatment results in the following concentrates: (a) an alloy concentrate that is rich in precious metals; (b) a copper sulphide concentrate; and, (c) a nickel sulphide concentrate. These concentrates are then transferred to specialist metal refineries for the recovery of metal.
REFERENCES Boldt, J. R., & Queneau, P. (1967). The winning of nickel. (pp. 280–283). Longmans. Donald, J. R., & Scholey, K. (2005). An overview of Copper Cliff’s operations. In J. Donald & R. Schonewille (Eds.), Nickel and cobalt 2005, challenges in extraction and production (pp. 457–477). CIM. Dorigo, U. A., Yalcin, T., Duncan, D., & Montgomery, J. (2009). Front line planning and scheduling at Vale Inco’s Ni-Cu matte processing plant. In J. Liu, J. Peacey & M. Barati, et al. (Eds.), Pyrometallurgy of nickel and cobalt 2009, proceedings of the international symposium (pp. 391–399). CIM. Jacobs, M. (2006). Process description and abbreviated history of Anglo Platinum’s Waterval smelter. In R. Jones (Ed.), Southern African pyrometallurgy 2006 (pp. 17–28). SAIMM. 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.
Chapter | 21 Slow Cooling and Solidification of Converter Matte
267
SUGGESTED READING Donald, J. R., & Scholey, K. (2005). An overview of Copper Cliff’s operations. In J. Donald & R. Schonewille (Eds.), Nickel and cobalt 2005, challenges in extraction and production (pp. 457–477). CIM. Marcuson, S. W., & Diaz, C. M. (2005). The changing Canadian nickel smelting landscape – late 19th Century to early 21st Century. In J. Donald & R. Schonewille (Eds.), Nickel and cobalt 2005, challenges in extraction and production (pp. 179–207). CIM.
Slow Cooling and Solidification of Converter Matte The molten converter matte, discussed in Chapter 19, contains nickel, sulfur and a small amount of iron. It also contains copper, cobalt, silver, gold and platinum-group elements to a greater or lesser extent. These elements cannot be separated while the matte is molten. They are separated by solidifying the matte and treating it by two different techniques as follows: (a) vapometallurgical refining (Chapter 22); and, (b) hydrometallurgical refining (Chapters 23 through 27). However, about half of the global production of converter matte from sulfide smelting undergoes a preliminary treatment before these processes (Warner et al., 2007). The following steps are used: (a) between 12 and 25 tonnes of molten matte are poured into large molds; (b) this matte is slowly solidified and cooled in covered molds, which results in the formation of large individual grains of heazlewoodite (Ni3S2), chalcocite (Cu2S) and metallic alloy (see Figures 21.1 and 21.2); (c) the solid matte is crushed and ground, which liberates the grains of the different minerals from each other; and, (d) the ground ore is separated into alloy, copper–sulphide and nickel–sulphide concentrates by magnetic separation and froth flotation. A schematic diagram of the process is shown in Figure 21.3. Operating details are given in Tables 21.1 and 21.2. The advantages of this preliminary separation are that it simplifies the subsequent metal extraction and minimizes the in-plant residence times.
21.1. SOLIDIFICATION AND SLOW COOLING PROCESS The equilibrium phase diagram for the Ni–Cu–S system is shown in Figure 21.2. This phase diagram indicates that the products of solidifying the molten matte, then cooling it to ambient temperature, are nearly pure Ni3S2 and Cu2S. Extractive Metallurgy of Nickel, Cobalt and Platinum-Group Metals. DOI: 10.1016/B978-0-08-096809-4.10021-8 Copyright Ó 2011 Elsevier Ltd. All rights reserved.
259
260
PART | I Extractive Metallurgy of Nickel and Cobalt
(a)
(b)
FIGURE 21.1 Photomicrograph (100) of (a) quenched and (b) slowly cooled nickel-copper converter matte, showing that the quenched matte is much more finely grained than the slowcooled matte. The grain size of the quenched matte is about 10 mm while that of the slow-cooled matte is about 100 mm. The dark grey grains are Cu2S; the light grey grains are Ni-Cu alloy. The matrix is Ni3S2. Grinding the solidified matte to a mean particle size of 70 mm liberates the three phases so that they can be separated from one another by magnetic and froth flotation processing. Source: Boldt and Queneau, 1967, courtesy of Vale.
The equilibrium conditions are closely approximated industrially by solidification and slow cooling of the converter matte. Slow cooling encourages the precipitated grains of Ni3S2 and Cu2S to grow to a size of approximately 100 mm in size, as shown in Figure 21.1. 1100 Liquid
Temperature, °C
1000
L+α
900 800
α
L+β 720°C
700
535°C 500 Cu2S
β
β+α
600
β + β’
β’ + α 20
40 60 Percent Ni3S2
β’ 80
Ni3S2
FIGURE 21.2 Equilibrium Cu2S–Ni3S2 phase diagram. The complete miscibility of Cu2S and Ni3S2 above the Cu2S melting point (~1130 C) and the almost complete immiscibility of Cu2S and Ni3S2 below 450 C are notable. The latter causes molten matte to separate into two individual phases during slow cooling.
magnetic separator
broken/crushed slowly frozen/cooled converter matte, 35% Ni, 41% Cu
ball mill
magnetic
Cu, Ni, Au, Ag, Pt group alloy
fraction
65% Ni, 17% Cu
to carbonyl nickel refinery
non-magnetic fraction: Cu2S and Ni3S2
pH = 12 –70 m diameter
Cu2S concentrate
to company's Cu smelter
4% Ni, 74% Cu
diphenyl guanidine collector-frother
froth
Cu2S flotation
underflow
Ni3S2 concentrate 71% Cu, 0.9% Cu
to roasting then to market or refining
261
FIGURE 21.3 Simplified flowsheet for separating slowly solidified and cooled converter matte into (i) magnetic alloy concentrate; (ii) copper-rich sulphide concentrate; and, (iii) nickel-rich sulphide concentrate (Tables 21.1 and 21.2). Concentrate cleaning circuits are not shown. Donald and Scholey (2005) and Dorigo, Yalcin, Duncan, & Montgomery, (2009) give more details. Wet magnetic separation is done with a magnetic drum, which rotates and lifts magnetic particles up and out of a slurry bath. The magnetic particles overflow, and the non-magnetic particles underflow.
Chapter | 21 Slow Cooling and Solidification of Converter Matte
water + CaO
262
PART | I Extractive Metallurgy of Nickel and Cobalt
TABLE 21.1 Details of the Sudbury Matte Separation Plant (Vale) for Making Magnetic Alloy, Copper Sulphide and Nickel Sulphide Concentrates from Solidified Low Sulfur (21% S) Converter Matte Location
Sudbury, Canada
Startup date
1948
Nickel production all products
~140 000 tonnes per year
Casting and slow solidification/cooling Source of matte
Peirce-Smith converters
Matte casting temperature
980 C
Molds Number
220
Material
Castable fire clay, coated with lime wash (imbedded in floor)
Size
4 2.4 0.6 m deep with 45 walls
Matte mass per mold
23 tonnes
Cover
Refractory-lined steel
Casting method
Molten matte poured from ladle via overhead crane
Cooling duration
Three days with cover on to ~480 C followed by 1 day with cover off to 200 C
Breaking, crushing and grinding Ingot transport
Via overhead crane using ‘scissor’ tongs.
Ingot breaking
With overhead chisel-tipped hammers (pile drivers)
Crushing
Jaw crusher (to ~1 m) then two open-circuit gyratory crushers in series to ~0.01 m
Grinding
Rod mill (open circuit) then ball mills (closed circuit)
Size control
Cyclone classifiers
Final matte Particle size
99% < 70 mm diameter
Destination
Magnetic and froth flotation separation of alloy, Cu sulphide, and Ni sulphide concentrates (Table 21.2)
This table gives matte casting, slow cooling, crushing and grinding details (Donald & Scholey, 2005). Similar procedures are followed at the Waterval Smelter, South Africa (Anglo American Platinum) but with round molds (Jacobs, 2006).
Chapter | 21 Slow Cooling and Solidification of Converter Matte
TABLE 21.2 Details of Magnetic and Flotation Separations at Vale’s Sudbury Matte Separation Plant* Location
Sudbury, Canada
Startup date
1948
Nickel production all products
~140 000 tonnes per year
Particle separations Isolation of magnetic metallic concentrate
Magnetic separation, consisting of the following steps: (a) magnetic separation of magnetic metal particles from non-magnetic sulphide particles; (b) ball mill regrind; and, (c) second magnetic separation (cleaning)
Product
Alloy concentrate: 65% Ni: 17% Cu with high concentrations of Ag, Au and Pt-group elements
Destination
To top blown rotary converting (Appendix G) and carbonyl refining (Chapter 22)
Isolation of Ni3S2 concentrate, low in Cu2S
Cu2S is floated from non-magnetic matte fraction by froth flotation using CaO for pH control (pH > 12) and diphenyl guanidine collector/frother Underflow Ni3S2 slurry is reground and has (i) Cu2S removed in a column flotation cell; and, (ii) alloy removed in a drum magnetic separator
Product
Ni3S2 concentrate: 71% Ni and 0.9% Cu
Destination
To NiO production by oxidation roasting. The NiO is sold or sent to Clydach, Wales for reduction, sulfur activation and ambient pressure carbonyl nickel refining (Chapter 22)
Isolation of Cu2S concentrate Product
Cu2S concentrate: 4% Ni and 74% Cu
Destination
Company’s copper smelter
Middlings concentrate
Underflow from grinding and cleaning Cu2S concentrate
Product
Ni3S2 middlings concentrate: 66% Ni and 6.6% Cu (not shown in Figure. 21.3)
Destination
Roasted then sent to Sudbury nickel refinery for high-pressure carbonyl nickel refining
The Anglo American Platinum (South Africa) Magnetic Concentrator Plant uses only magnetic separation (that is, no flotation) to produce a magnetic concentrate rich in platinum-group elements (~30% platinum-group metals) and a non-magnetic bulk sulphide concentrate (Jacobs, 2006). *Donald & Scholey, 2005
263
264
PART | I Extractive Metallurgy of Nickel and Cobalt
The driving force for the grain growth is the minimization of the interfacial energy. The nickel converter matte purposely contains slightly less sulfur than is required to form stoichiometric Ni3S2 and Cu2S (Donald & Scholey, 2005). The low sulfur content is achieved by converting at a high temperature. This deficiency of sulfur causes a third phase to form during solidification and slow cooling. This third phase is a magnetic alloy that contains nickel, copper and most of the silver, gold and platinum-group elements in the feed matte.
21.2. INDUSTRIAL MATTE CASTING, SOLIDIFICATION AND SLOW COOLING Between 12 and 25 tonnes of molten converter matte, at about 1000 C, are cast into large refractory-lined steel depressions, or molds, at floor level. This is shown in Figure 21.4. A steel loop is placed into the solidifying matte, and the mold is covered with a steel lid. The matte is allowed to cool for 3 days. After 3 days, the lid is removed, and the matte is cooled for another day. The solid casting is lifted out of the mold using the steel loop and then sent to breaking, crushing, grinding and mineral separation.
21.2.1. Matte Structure The solidified matte contains grains of three major components: (i) a magnetic nickel–copper alloy (containing most of the silver, gold and platinum-group elements); (ii) chalcocite (Cu2S); and, (iii) heazlewoodite (Ni3S2). A small amount of other minerals, for example, bornite (Cu5FeS4) may also be present. As mentioned earlier, the grains are quite large, approximately 100 mm in size (Donald & Scholey, 2005). Grinding the matte to a mean particle size of 70 mm liberates the minerals.
21.2.2. Isolation of the Liberated Grains The ground matte is separated into three concentrates. Two major methods are used for this purpose: (a) magnetic separation of the precious metals-rich alloy particles into a magnetic alloy concentrate; and, (b) flotation separation of the remaining sulphides particles into copper-rich and nickel-rich sulphide concentrates (this separation is not always done; Jacobs, 2006).
Chapter | 21 Slow Cooling and Solidification of Converter Matte
265
FIGURE 21.4 Casting of low-iron, sulfur-deficient matte into floor-level molds in preparation for slow cooling. Slow cooling causes the matte to separate into ~100 mm Cu2S, Ni3S2 and alloy grains, which are separated by comminution then magnetic separation and froth flotation. The alloy grains contain most of the silver, gold and platinum-group elements in the matte. The newlyfilled molds will be covered with the lid (left). Photograph courtesy of Anglo American Platinum.
21.3. CONCENTRATE DESTINATIONS Matte concentrate destinations vary from smelter to smelter. The most straightforward arrangement is that at the Waterval, South Africa, smelter (Anglo American Platinum). A magnetic concentrate that is rich in platinum-group elements and a non-magnetic concentrate are made. The magnetic fraction is upgraded by leaching and then sent to a precious metals refinery. The non-magnetic fraction is sent to a nickel–copper refinery (Jacobs, 2006). This arrangement maximizes the recovery of the metals and minimizes the in-plant residence time.
266
PART | I Extractive Metallurgy of Nickel and Cobalt
The Sudbury, Canada, smelter (Vale) makes three major concentrates: (a) a magnetic alloy concentrate, which is sent directly to its nickel refinery; (b) a copper-rich sulphide flotation concentrate, which is smelted in a copper smelter; and, (c) an nickel-rich sulphide concentrate, which is oxidation roasted to nickel oxide. Residues from the nickel refinery are treated for copper, cobalt and precious metals extraction. The nickel oxide from the oxidation roasting is either sold or it is refined to high-purity nickel in the company’s carbonyl refineries in Sudbury, Canada, and Clydach, Wales. Carbonyl refining is described in Chapter 22.
21.4. SUMMARY The converter matte contains nickel, iron and sulfur. It may also contain copper, cobalt, silver, gold and platinum-group elements to a greater or lesser extent. These elements are ultimately separated and made into metal either hydrometallurgically or vapometallurgically. Often, however, the elements are given a preliminary separation by (i) slow cooling and solidification of the molten matte; (ii) ingot breaking, crushing and grinding; (iii) magnetic separation; and, (iv) froth flotation. This treatment results in the following concentrates: (a) an alloy concentrate that is rich in precious metals; (b) a copper sulphide concentrate; and, (c) a nickel sulphide concentrate. These concentrates are then transferred to specialist metal refineries for the recovery of metal.
REFERENCES Boldt, J. R., & Queneau, P. (1967). The winning of nickel. (pp. 280–283). Longmans. Donald, J. R., & Scholey, K. (2005). An overview of Copper Cliff’s operations. In J. Donald & R. Schonewille (Eds.), Nickel and cobalt 2005, challenges in extraction and production (pp. 457–477). CIM. Dorigo, U. A., Yalcin, T., Duncan, D., & Montgomery, J. (2009). Front line planning and scheduling at Vale Inco’s Ni-Cu matte processing plant. In J. Liu, J. Peacey & M. Barati, et al. (Eds.), Pyrometallurgy of nickel and cobalt 2009, proceedings of the international symposium (pp. 391–399). CIM. Jacobs, M. (2006). Process description and abbreviated history of Anglo Platinum’s Waterval smelter. In R. Jones (Ed.), Southern African pyrometallurgy 2006 (pp. 17–28). SAIMM. 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.
Chapter | 21 Slow Cooling and Solidification of Converter Matte
267
SUGGESTED READING Donald, J. R., & Scholey, K. (2005). An overview of Copper Cliff’s operations. In J. Donald & R. Schonewille (Eds.), Nickel and cobalt 2005, challenges in extraction and production (pp. 457–477). CIM. Marcuson, S. W., & Diaz, C. M. (2005). The changing Canadian nickel smelting landscape – late 19th Century to early 21st Century. In J. Donald & R. Schonewille (Eds.), Nickel and cobalt 2005, challenges in extraction and production (pp. 179–207). CIM.