Aluminum extraction

Even today, almost all aluminum is manufactured by the Hall—Heroult process [4, 12-16]. Unlike the chlor-alkah industry, the anode technology remains based on carbon, and the stoichiometric consumption ofthe carbon anode is an essential part ofthe anode chemistry. 

In the Hall-Heroult process, the overall chemical change 

C02)- The prebaked anodes are produced in more controlled conditions leading to better-defined structures. These lead to lower cell voltages and higher current efficiencies. In addition, external thermal treatment allows much superior control of emissions to the environment. 

Because of the highly aggressive conditions in the high-temperature, molten salt media, attempts to find alternative anode materials or cell chemistries have been unsuccessful and developments in anode technology have been limited to minimizing the carbon consumption toward the stoichiometric requirement. Indeed, carbons are one of the few materials to be stable to cryolite at the operating temperature and hence, for example, it is also employed as an internal lining to the steel cell bodies. 

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The Alcoa (Aluminum Company of America) process involves the electrolysis of aluminum chloride which is carried out in a molten bath of the composition 50% sodium chloride, 45% lithium chloride and 5% aluminum chloride, maintained at 700 °C. The Bayer process, which involves the production of pure alumina by the dissolution of bauxite with caustic soda and which has been described in the chapter on hydrometallurgy, must be taken into account while presenting a complete picture of the aluminum extraction flowsheet. It... 

The steam treatment does however affect the Al-surroundings in the zeolite crystal. As seen in Fig. 2b, the intensity of both the tetragonally (at 0 ppm) and octahedrally (at 55 ppm) coordinated aluminum species decreases considerably after steam treatments for more than 4 h. Steam treatment for more than 8 h did not lead to a further decrease in the signal intensities. The decreases confirm that aluminum is extracted from the framework during the steaming process, as was also concluded from the 29Si MAS-NMR spectra (Fig. 1 b). This may lead to the formation of additional (micro) porosity, but the aluminum extraction could negatively affect the catalytic activity. 

Wolstenholme, G. A., Aluminum Extraction, in Molten Salt Technology, D. G. Lovering, Editor. 1982, Plenum Press New York. p. 13. 

X-ray studies carried out by Gallezot et al. (46) on a 53 percent EDTA-dealuminated Y zeolite, have shown that the aluminum extraction does not leave any vacancies in the framework after calcination at 400°C in flowing, dry oxygen and nitrogen (46). It was suggested that a local re-crystall-ization of the framework occurs even in the absence of steam. The silica necessary for the process presumably originates in the destroyed surface layers of the crystallite and diffuses into its interior. 

FIGURE 8 Aluminum extracted from type II glass containers and from polyethylene containers by action of NaCl, KC1, albumin, glucose, heparin, HC1, and NaOH solutions after 30 and 60 days storage at room temperature. The three different albumins are A, bovine (Merck) B, bovine (Reagen), and C, egg (Sigma) [50]. 

FIGURE 9 Aluminum extracted from glass particles (18 mesh) and Al-form exchanger (18 mesh) as function of time by action of some amino acids and complexing agents. Concentration of ligands 0.05mol/L [51]. 

Since heating conditions (32) and aluminum extraction leading to a high stability have been avoided, the increased stability of the catalysts seems related to the presence of exchanged lanthanum. A zeolite with high thermostability can be obtained by introducing only 3.7 La3+ ions/unit cell into a decationated zeolite. A higher content of lanthanum does not... 

The Al3+ in alkaline solution then forms a white fluffy-looking precipitate of Al(OH)3, which can be arranged to descend into a suitable space below the electrodes, the material being recycled in an aluminum extraction plant. Aluminum batteries had not yet been commercialized by 1998, but they stimulate interest in two directions. 

The most used liquid metal pool electrode is the aluminum cathode (m.p. 660°C) in the Hall-Heroult aluminum extraction cell. Alkali metals and alkaline-earth metals are also used as liquid cathodes in their molten salt extraction processes. 

As a general rule, samples should be collected in decontaminated flasks and even those considered metal-free should be pre-washed. Glass recipients should be avoided. A good procedure for cleaning plastic containers is keeping them at least 24 h in a 10% (v/v) ethanolic nitric acid solution. Aqueous solutions do not leach out the aluminum well, because water does not wet plastic surfaces better contact occurs when an alcoholic solution is used. It can be seen that all alcoholic solutions were more efficient than the aqueous solutions. Table 10 shows the aluminum extracted from polyethylene by the action of some washing solutions. Just before use, the containers should be abundantly washed with ultrapure water. The best option is to use the flasks just after rinsing them, however if they must be dried, they should not be placed in an oven, even with the open side on tissue paper (paper contains aluminum). The best way is let them dry under a laminar flow. The proper heat and air movement inside the hood will help to rapidly dry the flasks. 

Fig. 15 shows the aluminum extracted from PE powder and glass powder by action of aqueous and ethanolic HN03 solutions during 7 days of contact. It can be seen that 24 h is enough to withdraw the aluminum from the PE surface when a ethanolic solution of HN03 is used. The aqueous solution acts slower because PE and the solution do not have good contact. With glass, the contact is effective but the extraction process did not end even after 7 days. 

Table 10. Aluminum extracted from polyethylene powder by action of different washing solutions by shaking 0.1 g PE in 10 mL solution for 24 h (blank discounted)...

Bouchard NC, Malostovker I, Harbord N, et al. Acute aluminum encephalopathy aluminum extraction with high flux hemodialysis is superior to charcoal hemoperfusion (abstract). Clin Toxicol. 2005 43 677-678... 

H-mordenites with various Si/Al ratios (5.9 - 16.9) have proved to be active for the SCR of NO with CH4 in the 400-600 C temperature range. However, they suffered an irreversible deactivation after an incursion at 650°C for 1 h under reaction stream, due to a dealumination process. While acid dealumination only affects the free exchange of gaseous molecules between the main channels and the side-pockets (as seen by t29Xe NMR), the aluminum extracted from the lattice of the mordenite during the SCR of NOx at 650°C (without water vapor in the feed) also hinders the diffusive transport along the main channels. 

Since in previous studies (3,4) we found that the NO conversion is related to the presence of Aliv sites of the zeolitic structure, it is possible to assume that the origin of the deactivation observed is, in part, due to the loss of these sites by dealumination. Together with the loss of active sites, the aluminum extracted from the network could block the channels of the mordenite, thus affecting the adsorption and diffusion properties. 

Table 2 shows the results of ethylene diffusivity values together with NOx conversion for the different H-mordenites studied in this work. Note that while D/R2 decreases an order of magnitude in the deactivated sample (if compared with the fresh one), it remains approximately constant for the samples subjected to acidic dealumination. This result suggests that the aluminum extracted from the lattice of the mordenite during of the mordenitic structure along the for the deactivation observed in the... 

The framework-aluminum extracted during acid leaching is not fully washed under the conditions used in this work. Part of it remains inside the mordenitic side-pockets, partially obstructing the free exchange of gaseous molecules between the former and the main channels. 

An explanation might be found if monomer chemisorption takes place instead. Indeed boehmite dissolution occurs by means of its lateral surfaces [19] monomer chemisorption on lateral boehmite surface would block surface functional sites and thus inhibit at least partially boehmite dissolution. Therefore, at intermediate molybdenum loading, as monomer concentration in solution is not negligible compared to AHM concentration, monomer adsorption on boehmite lateral surfaces should compete with aluminum extraction. Fig. 8 reports boehmite dissolution kinetics carried out at pH=4.8, for two [AHM] concentrations (intermediate and high molybdate loading). This result could support the fact that aluminum dissolution is slowed down at intermediate molybdenum loading and that no substantial moly-bdate adsorption could take place a plateau is reached in the adsorption isotherm (Fig. 1). 

FIGURE 26.15 Hall-Heroult cell for aluminum extraction process [30] (with kind permission from Springer Science and Business Media). 

Anhydrous aluminum nitrate [13473-90-0] is covalent in character, easily volatilized, and decomposes on heating (22). Hydrated aluminum nitrate is used in the preparation of insulating papers, on transformer cote laminates, and in cathode-ray tube heating elements. Solution of aluminum hydroxide through digestion of cote materials in nitric acid has been proposed in aluminum extractive metaUuigy. The resulting solution of aluminum nitrate is separated from other metal ions, and the aluminum oxide is recovered by thermal decomposition of the aluminum nitrate solution (23,24). 

The available data concerning the adsorption of different bases indicate that adsorbed bases interact with zeolites more strongly than hydrocarbons of similar structure and molecular weight [21], A comparison of the heats of adsorption of various bases, such as ammonia, pyridine and -butylamine, with those of benzene on A, X, Y and mordenite zeolites, modified by ion exchange and aluminum extraction, has been carried out by Klyachko et al. [21]. Surprisingly, the heats of pyridine adsorption were found to be virtually the same on sodium and on hydrogen zeolites. Furthermore, the sorbed amounts of large molecules such as pyrichne and w-butylamine were veiy limited, due to the finite void... 

Electrochemical technology has a history dating back deep into the nineteenth century and carbon electrodes have been major players in this success [1-4]. In the early cells for both the two largest electrolytic industries, chlor-alkali and aluminum extraction, the electrodes were blocks of carbon or graphite. The past 50 years, however, has seen the development of carbons with different structures and often their availability in a range of forms. Thus, it is possible to purchase electrodes based on graphites, carbons, thermally treated carbons (e.g., vitreous or glassy carbon), expanded carbons, carbon/polymer composites, and doped diamond materials. Moreover, some of these materials are available in many forms as follows ... 

In addition to the two largest electrolytic industries, chlor-alkah and aluminum extraction, carbon anodes have been used for the manufacture of other inorganic products. These include fluorine and ozone manufacture, two chemistries requiring the anode to operate at extreme positive potentials. In organic electrosynthesis, carbons have been used as both anodes and cathodes. 

Pressure Acid Leaching. As discussed above, net aluminum extraction is around 1% when pressure acid leaching is carried out in saline waters. Thus aluminum removal in the PAL process step has the potential to be an out for aluminum, even if downstream removal steps prove to be ineffective. 

Petroleum coke (also known as pet coke) is a carbonaceous solid derived from the cracking processes of oil refineries and has been a source of relatively cheap pulverized fuel for the kiln industry. It is called green coke until it is thermally treated into crystalline or calcined pet coke used in the manufacture of electrodes for steel and aluminum extraction. Green coke comes from several sources, all from the petroleum refinery industry. Table 6.2 gives some green coke analyzed by Polak (1971) showing their sources and their elemental analyses. 

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