Aluminum production by electrolysis

Q <33 Research the extraction of aluminum by the electrolysis of bauxite. Write a report on your findings. Include a description of the electrolytic cell and how it operates. Indicate where aluminum is produced in Canada. Also include any environmental concerns associated with aluminum production by electrolysis. 

The study of molten haloaluminates was initiated because these melts are interesting from a scientific point of view. Practically, these melts are used for aluminum electroplating, as electrolytes in low temperatures batteries (see below) and, likewise, aluminum production by electrolysis of these melts has been tried (see Section II.A.7 Aluminum Chloride Electrolysis ). 

Fluorine Hydrofluoric acid (HF) is a by-product of aluminum production by electrolysis cind the synthesis of chlorofluorocarbons (CFCs). Although in water HF is a weak acid, it s extremely toxic. HF poisoning causes deep ulceration or scarring of body tissue with a delayed effect, slowly replacing calcium in bodily tissue (flesh and bones). There s no pain at first because it s a weak acid, but when the calcium in the bones starts to be replaced by the more electronegative fluorine it feels similar to growing pains, and may be too late. Merely five-minute iexposure to 10,000 ppm concentration in the air is fatal to humans. 

FIGURE 10.8 Aluminum production by electrolysis. At the cathode, aluminum ions are reduced to aluminum metal. The anode reaction is production of oxygen gas, which reacts with the carbon anodes. (The cell reaction is 2 AI Oj + 3 C... 

Insufficient pre-orientation in the mesophase stage, as a result of low aromaticity of the respective residue, or through too rapid a heating to temperatures in excess of 500 °C, leads to isotropic cokes, which are principally used for the manufacture of anodes for aluminum production by electrolysis. 

Aluminum oxide 2A1 + 30 —> Al O is known as the mineral bauxite. Its main use is for the production of aluminum metal by electrolysis. It is also used in many other chemical reactions. 

The method of obtaining aluminum metal by the electrolysis of alumina dissolved in cryolite was discovered in 1886 by Hall in the U.S. and at about the same time by Heroult in France. Cryolite, a natural ore found in Greenland, is no longer widely used in commercial production, but has been replaced by an artificial mixture of sodium, aluminum, and calcium fluorides. 

The first production of aluminum was by the chemical reduction of aluminum chloride with sodium. The electrolytic process, based on the fused salt electrolysis of alumina dissolved in cryolite, was independently developed in 1886 by C. M. Hall in America and P. L. Heroult in France. Soon afterwards a chemical process for producing pure alumina from bauxite, the commercial source of aluminum, was developed by Bayer and this led to the commercial production of aluminum by a combination of the Bayer and the Hall-Heroult processes. At present this is the main method which supplies all the world s needs in primary aluminum. However, a few other processes also have been developed for the production of the metal. On account of problems still waiting to be solved none of these alternative methods has seen commercial exploitation. 

One of the most important electrolytic processes is the extraction of aluminum from an ore called bauxite. This ore is mainly composed of hydrated aluminum oxide, AI2O3 XH2O. (The x in the formula indicates that the number of water molecules per formula unit is variable.) In industry, the scale of production of metals is huge. The electrolytic production of aluminum is over two million tonnes per year in Canada alone. As you know from Faraday s law, the amount of a metal produced by electrolysis is directly proportional to the quantity of electricity used. Therefore, the industrial extraction of aluminum and other metals by electrolysis requires vast quantities of electricity. The availability and cost of electricity greatly influence the location of industrial plants. 

Using the Hall process exclusively, the aluminum industry in the United States alone produces more than 150,000 tons of aluminum each year, and it is impossible to estimate the magnitude of probable future production. The commercial product obtained directly by electrolysis has a purity greater than 99%. It is of interest to note that a few months following the discovery of the Hall process an identical method was discovered independently by the French chemist Paul-Louis-Toussaint Heroult. 

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... 

Hall - he elaborated the effective technology of production of aluminum by electrolysis (see - aluminum production, - Hall-Heroult process). 

Electrolysis is often used to reduce the most active metals. In Chapter 11 we considered the electrolytic production of aluminum metal. The alkali metals are also produced by electrolysis, usually of their molten halide salts. 

The zinc oxide can also be reduced by electrolysis. It is dissolved in sulfuric acid, and electrolyzed with aluminum sheets as cathodes. The deposited zinc, which is about 99.95% pure, is stripped off the cathodes, melted, and cast into ingots, for use where pure zinc is needed, as in the production of brass. The sulfuric acid is regenerated in the process, as is seen from the reactions ... 

The recovery of aluminum metal is divided into two steps, i. e., the production of pure alumina (Bayer Process) and its molten salt electrolysis. Raw aluminum obtained by reduction electrolysis already has a high purity (99.5-99.7%). Refining methods for raw aluminum to obtain higher purities include the segregation process (99.94-99.99% Al) and three-layer electrolysis (99.99-99.998% Al) [142, 236]. Besides these, processes are available whereby the aluminum is anodically dissolved in an organic electrolyte and then cathodically deposited [37, 118, 217, 221]. The dissolution as well as the deposition process contribute to the electrolytic refining of aluminum. 

There have been sporadic attempts to produce aluminum by carbothermic reduction [3, 4]. In this approach, akin to the way iron oxides are reduced to iron in the iron blast furnace, the consumption of electrical energy is avoided or at least reduced. There have also been investigations of the production of aluminum by electrolysis of aluminum compounds other than the oxide (e.g. [5]). Some of these alternative electrolytic technologies have even reached a commercial scale [6] but the only method for aluminum production in industrial use today appears to be electrolysis in Hall-Heroult cells. Consequently, the present paper is confined to these cells. The literature on these cells is large. A recent search of the web of science with the subject Hall cell and similar subjects revealed 79 titles aluminum electrolysis yielded 109 publications. This number excludes papers published in the annual Light Metals volume of the Minerals Metals and Materials Society (TMS). Light Metals contains approximately forty papers each year on Hall cells. Consequently, the authors have made no attempt at a comprehensive examination of the literature on these topics. Rather we have included... 

Aluminum is an indispensable metal to modem mannfacturing. Its low density and corrosion resistance make it the preferred metal for many manufactured products, from spacecraft components to beverage cans. As is known, the main commercial production of aluminum is carried out by electrolysis of molten cryolite (NajAlF ) in which aluminum oxide is dissolved at an elevated temperature of about 1,200 K. 

Alumimun is the metal of choice for soft-drink cans, as shown in Figure 20.11. It is lightweight, has a low specific heat (0.902 J/g°C), and conducts heat rapidly. As a result of its low specific heat, the aluminum itself absorbs litde heat, so the beverage inside the container can be cooled quickly. In Chapter 17, you learned that aluminum is produced by electrolysis of its principal ore, bauxite. The production of aluminum requires large amounts of energy, particularly electrical energy. Therefore, one... 

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