crust is bauxite, followed by corundum and cryolite. Common copper ores include copper pyrite, copper glance (chalcocite), and malachite. Tin ores frequently encountered include tin pyrite and cassiterite, but these represent a relatively rare ore in the Earth's crust. Indonesia and China are two of the more common sources of mined tin ore.
Figure 2.2 shows commodities and the raw materials, core ingredients, and fabrication aids used in their manufacture. Iron and steel melt at approximately 1540 °C, for example, and are converted from iron ores though smelting to crude high‐carbon cast iron and then through various subprocesses to remove high concentrations of carbon to wrought iron and mild steel. Stainless steel involves mixing mild steel with traces of chromium (see Section 3.3). The basic ingredients for cast iron (pig iron) ingot production are coke (coal), lime, and iron ore; production is usually undertaken in a blast furnace or metallurgical furnace [7] at around 2000–2300 °C. Blast furnaces are also used for metals such as lead or copper. Iron from a blast furnace is typically converted to steel in a process developed by Henry Bessemer in 1855, which involves blasting air via tuyère pipes through molten pig iron or using a more expensive electric arc furnace (EAF) process developed in full working form by James Readman in 1888. Melting is accomplished by supplying energy to the furnace interior. This energy can be electrical or chemical. Electrical energy is supplied via the graphite electrodes and is usually the largest contributor to overall powering cost in melting operations. Initially, an intermediate voltage tap is selected until the electrodes bore into the scrap. As the furnace atmosphere heats up the arc stabilises and, once the molten pool of steel is formed, the arc becomes quite stable and the average power input increases.
Figure 2.2 Commodities and principal types of raw materials used for packaging. *Polyolefins, cellulosics, and rubber.
The iron ore blast furnace as the basis for all iron‐ and steel‐making via the production of pig iron is used in a form that is little altered from the original 1855 Bessemer configuration or the simpler format that Abraham Darby used in 1709. At the base of the furnace is a hearth (at 1300 °C); above this portion of the furnace is a zone called the bosh (at 1700 °C), which is the hottest part; at the bosh, molten iron exits the furnace and liquid or gaseous fuel and air are injected via tuyère pipes. The bosh lies below the barrel (at 1500 °C), which ascends up the furnace to the upper portion and to the stack, the throat (at 1000 °C), and finally the flue (at 500 °C). The lining of the blast furnace is constructed from refractory fire bricks that insulate the material and retain a suitable melt temperature in the core of the furnace. Chemical energy is also supplied to the liquid pool of metal via oxygen fuel burners and oxygen lances. Oxygen fuel burners use natural gas mixed with oxygen or a blend of oxygen and air. Heat is transferred to the metal by flame radiation and convection by the hot products of combustion, and heat is transferred within the molten metal by simple conduction. Modern cylindrical blast furnaces can be 20–40 m tall with a maximal width at the base hearth of 5–15 m. Output varies but modern production can make between 1000 and 10 000 tonnes of pig iron per daily campaign. The modern blast furnace process starts with a means of placing the iron ore as a starting point in the furnace with a top‐loading filling device, which charges the furnace with coke, iron ore, recycled iron, and limestone. At the base of the furnace is a sage hole to remove waste and a tap hole to extract the liquid pig iron. Waste gases such as carbon dioxide, carbon monoxide, and various sulfurous gases leave via the stack and through the flue gas [7].
There are, in principle, six main types of materials used for packaging materials (Figure 2.2). The main categories are aluminium, steel‐iron, glass, paper, plastics (of which there are many types), and wood. Of course, as shown in the figure, the individual types and sourcing for all materials have a large influence on the manufactured end product. Taking wood as an example, there are softwood and hardwood varieties with different grain structures that can be used to produce different types of transport crates, palettes, or shipping boxes as well as different grades of paperboard and paper. With metals, plastics, and glass the background concentration of impurities might be expected to influence the physical and mechanical properties of the material. Copper, for example, incorporated as an impurity in aluminium at 4–6% w/w makes the aluminium stronger; below this, mechanical performance is unaltered from pure aluminium. As basic forms of commodity other than naturally occurring ores and recycled materials the remaining commodities used for packaging include silicate sand as the basis for glasses, crude oil, crude oil‐cracking products, natural biopolymers and natural gas for plastics, and wood or straw for paper.
2.3 Industrial Processes, Wood‐Pulping, Processing, and Smelting
2.3.1 Refining Ores
Metals are manufactured from mineral ores. When these are crushed into fine particles and combined with various smelting agents (e.g. limestone flux) at appropriate temperatures, this allows the release of liquid metal (Figure 2.3). The melting point (Tm) of the iron in iron ores (haematite, magnetite) is in the region of 1540–1560 °C [7]. Limestone (CaCO3) is converted to lime (CaO), which reacts with silicate in the ore to create iron‐contaminated calcium silicate waste (slag or clinker). The ore undergoes three reduction reactions in the furnace and the iron material reacts with carbon monoxide (CO):
Top of the furnace at lower temperature (<1000 °C), Fe(III) to Fe(III/II):
(2.1)
Higher temperature, Fe(III/II) to Fe(II):
(2.2)
Hottest zone, Fe(II) to Fe(0):
(2.3)
It is noteworthy that, at each step of the process to form pure metal, carbon dioxide, a so‐called ‘greenhouse gas’ and one of several causative agents of the ‘global warming’ phenomenon, is generated, as indicated by the ‘given off’ arrow (↑) in the illustrated chemical process. In the above chemical equations brackets show the oxidation state, which for iron means Fe(II) is changed to Fe(III) by the liberation of a negatively charged electron (e), thus Fe2+ → Fe3+ + e. An oxidation state of zero for a metallic element, Fe(0), indicates a pure elemental substance (pure iron in this case).
Iron ore is first heated in a blast furnace at 2300 °C along with limestone varieties such as dolomite (CaCO3) and coke (a source of carbon monoxide) and fuel to produce crude, high‐carbon, liquid iron that is cast into the ‘pig iron’ ingots (25 kg). Ingots can then be rolled into sheets or rods and moulded according to requirements in a hot‐press process. Further refinement of iron ingots takes place in a Bessemer (converter) furnace to produce mild steel or Linz–Donawitz‐steel‐making (basic oxygen furnace) at about 1700 °C or with a graphite electrode (EAF) at 1800 °C. The advantage of the EAF is that scrap steel can be used in the process. Aluminium ores are converted via the Bayer process from bauxite (30–60% alumina) with iron, silica, and contaminated sodium hydroxides of aluminium (Na[Al(OH)4]) to aluminium oxide or alumina (Al2O3) at 180 °C under pressure. The alumina alone has a Tm of greater than 2072 °C, but
