processes for producing materials
processes for producing materials
Introduction All of our steel, copper, aluminum and silicon(including semiconductor grade silicon) is made by processes that at some point use high temperatures In producing ceramic parts, high temperature"?"is common. This part of the course is therefore devoted to some of those high temperature operations. By high temperatures" is meant temperatures between about 400 and 1500 C. Earlier we learned that many oxides can be reduced to metals by the inexpensive reducing agents carbon and hydrogen at high temperatures. However, as shown on the next slide. many ores exist as sulfides
Introduction. All of our steel, copper, aluminum and silicon (including semiconductor grade silicon) is made by processes that at some point use high temperatures. In producing ceramic parts, high temperature “sintering” is common. This part of the course is therefore devoted to some of those high temperature operations. [By “high temperatures” is meant temperatures between about 400 and 15000C.] Earlier we learned that many oxides can be reduced to metals by the inexpensive reducing agents carbon and hydrogen at high temperatures. However, as shown on the next slide, many ores exist as sulfides
Oxide and sulfide ores Aluminum occurs in the lithosphere as an oxide e Iron as oxides(mostly) Copper as both sulfides and oxides Nickel(ditto) Zinc as sulfides Silicon as oxides Lead as sulfides Gold and silver as metals Magnesium as chloride (in the hydrosphere)
Oxide and sulfide ores. Aluminum occurs in the lithosphere as an oxide. Iron as oxides (mostly). Copper as both sulfides and oxides. Nickel (ditto). Zinc as sulfides. Silicon as oxides. Lead as sulfides. Gold and silver as metals. Magnesium as chloride (in the hydrosphere)
The problem with sulfides slide)which should be contrasted with the Ellingham A is illustrated in the ellingham diagram for sulfides (ne diagram for oxides In contrast to the oxide diagram the lines for the inexpensive reducing agents carbon and hydrogen(going to their sulfides) lie high in the diagram Consequently the sulfides of most metals cannot simply be reacted with carbon or hydrogen to produce the metal Expressed another way neither carbon nor hydrogen have sufficient affinity for sulfur to be used to remove sulfur from most metal compounds
The problem with sulfides... …is illustrated in the Ellingham diagram for sulfides (next slide) which should be contrasted with the Ellingham diagram for oxides. In contrast to the oxide diagram, the lines for the inexpensive reducing agents carbon and hydrogen (going to their sulfides) lie high in the diagram. Consequently the sulfides of most metals cannot simply be reacted with carbon or hydrogen to produce the metal. Expressed another way, neither carbon nor hydrogen have sufficient affinity for sulfur to be used to remove sulfur from most metal compounds
Alternative processes for sulfides are illustrated on the next slide. One possibility is to oxidize the sulfide to an oxide and then carbon or hydrogen can be used to reduce the oxide. This works fine for metals that have a high affinity for oxygen(i.e metals about half-way down the ellingham diagram for oxides, or lower, zinc is a good example) and is carried out in an operation known as" roasting,. An alternative route can be used for metals with a lower affinity for oxygen(e.g copper); this alternative relies on oxidizing the sulfide to metal(rather than oxide)and is known as smelting
Alternative processes for sulfides.... …are illustrated on the next slide. One possibility is to oxidize the sulfide to an oxide and then carbon or hydrogen can be used to reduce the oxide. This works fine for metals that have a high affinity for oxygen (i.e metals about half-way down the Ellingham diagram for oxides, or lower, zinc is a good example) and is carried out in an operation known as “roasting”. An alternative route can be used for metals with a lower affinity for oxygen (e.g copper); this alternative relies on oxidizing the sulfide to metal (rather than oxide) and is known as “smelting
Alternative processes for sulfides(cont) Sulfide concentrate of metas with f metals with igh affinity tor o (e. g. copper Oxide concentrate Roast in air to Smelting to produce form oxide metal and So2 Reduction with carbon drogen or other Impure metal reducing agent Impure metal Meta Metal of Metal of requrred purity
Alternative processes for sulfides (cont)
Alternative processes for sulfides(cont) The predominance diagram for the Cu-S-o system appears in the next slide and should be contrasted with that for ni shown earlier in the course. For Ni, which has a fairly high affinity for oxygen, the area of the predominance diagram where the metal exists is small. For copper it is quite large and it is possible to engineer the oxidation of copper sulfide to operate in the metal predominant region. We will return to copper smelting later. But first let's look at roasting
Alternative processes for sulfides (cont). The predominance diagram for the Cu-S-O system appears in the next slide and should be contrasted with that for Ni shown earlier in the course. For Ni, which has a fairly high affinity for oxygen, the area of the predominance diagram where the metal exists is small. For copper it is quite large and it is possible to engineer the oxidation of copper sulfide to operate in the metal predominant region. We will return to copper smelting later. But first let’s look at roasting
Roasting The objective is usually to remove(or diminish) the sulfur content of a concentrate by oxidation. E g for a lead concentrate 2PbS+ 302=2PbO2+ sO2 Such reactions are typically exothermic and the heat produced is usually sufficient to bring the reactants up to reaction temperature. The equipment is illustrated in the next four slides(see reader for details)
Roasting. The objective is usually to remove (or diminish) the sulfur content of a concentrate by oxidation. E.g for a lead concentrate: 2PbS + 3O2 = 2PbO2 + SO2 Such reactions are typically exothermic and the heat produced is usually sufficient to bring the reactants up to reaction temperature. The equipment is illustrated in the next four slides (see reader for details)
Roasting(cont) Although the objective of roasting is to produce oxide from sulfide, there exists the possibility of producing sulfates, as illustrated for the pb-0-s system in the next slide. good control of temperature and gas composition are required to avoid sulfate formation Which of the four reactors illustrated might be most suitable for this
Roasting (cont). Although the objective of roasting is to produce oxide from sulfide, there exists the possibility of producing sulfates, as illustrated for the Pb-O-S system in the next slide. Good control of temperature and gas composition are required to avoid sulfate formation. Which of the four reactors illustrated might be most suitable for this?
Predominance diagram, Pb-S-O 6 100oK s PbsO4 PbSo4.2Pbo PbS PbSO4→PbO PbSO4.4Pbo Pb Pbo 12 20-18-16-14-12-108_6 Log io(oxygen partial pressure, atmosheres)
Predominance diagram, Pb-S-O
