Process energy, metal production

The most efficient processes in Table I are for steel and alumintim, mainly because these metals are produced in large amounts, and much technological development has been lavished on them. Magnesium and titanium require chloride intermediates, decreasing their efficiencies of production lead, copper, and nickel require extra processing to remove unwanted impurities. Sulfide ores produce sulfur dioxide (SO2), a pollutant, which must be removed from smokestack gases. For example, in copper production the removal of SO, and its conversion to sulfuric acid adds up to 8(10) JA g of additional process energy consumption. In aluminum production disposal of waste ciyolite must be controlled because of possible fiuoride contamination. 

The scale of production also influences efficiency. Small-scale batch processing for metals such as titanium, tungsten, and zirconium leads to higher energy use and costs. 

The process needs input of lime and water next to the PVC waste. No energy input is needed since the organic condensate provides for the energy needed in the process. Energy needed for pretreatment can be up to 25-35 kWh/tonne. Downstream separation of the coke products needs another 30-40 kWh/toime. The process does not emit dioxins, metals or plasticisers. Due to internal recycling there are no aqueous waste streams. The reaction of lime with HCl forms some CO2. The coke product provides a calorific value. 

Table 7.3 Process energy for metal production from concentrates.

Secondary metal production is advantageous not only with respect to energy consumption but also to environmental impact as compared to primary metal production. The important environmental problems pertain to the formation of dioxins during thermal processing and the generation of dusts of the oxides of zinc, lead, and other metals in secondary steel, copper, and zinc production. 

Metals, which are also nonrenewable and use energy-intensive production processes, are best reserved for special applications for example, around balconies and roof gardens where their strength and lightness is essential. Decorative ironwork may also be required to preserve the architectural style of a building it can often be found in salvage yards. 

Actinide metals with lower vapor pressures (Th, Pa, and U) cannot be obtained by this method since no reductant metal exists which has a sufficiently low vapor pressure and a sufficiently negative free energy of formation of its oxide. For the large-scale production of U, Np, and Pu metals, the calciothermic reduction of the actinide oxide (Section II,A) followed by electrorefining of the metal product is preferred (24). In this process the oxide powder and solid calcium metal are vigorously stirred in a CaCl2 flux which dissolves the by-product CaO. Stirring is necessary to keep the reactants in intimate contact. 

Ch.H. Grant, USP 3307986(1967) CA 66, 117567u (1967) [High-energy water-resistant AN-alkali metal nitrate expls contg A1 of particular size distribution and processes for their production were described. A 1000-lb batch of expl was prepd as follows ... 

Fig. 2. Continuous rolling plant (Hot Spring, Arkansas) has cast nearly two bilticn pounds (0.9 billion kg) of aluminum foil feedstock since it began operations in 1979. That quantity of foil would wrap die earth almost 1600 times at the equator. The plant produces coils of feedstock for aluminum foil and flexible packaging products at a 40% energy saving compared to conventional rolling processes. (Reynolds Metals Company.)...

Affinity of a reaction, A — The decrease in - Gibbs Alcoa process/Alcoa electrolyzer — This is a process energy on going from the reactants to the products of to manufacture metallic aluminum by electrolysis of... 

Such a process is called an Sn2 (substitution, nucleophilic, bimolecular) process. The term bimolecular indicates that two species are required to form the transition state. Because the transition state is formed by the association of the two reactant species, this type of reaction mechanism is also known as an associative pathway. In an SN2 process, the metal has a higher coordination number in the transition state than it does in either the initial complex or product. The energy profile for this type of process is shown in Figure 20.2. 

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