Revision as of 21:07, 12 June 2012

Aluminum making

Aluminum making needs huge amount electricity (15kwh/kg), some carbon source to smelter electrodes, little fluoride to lower melting point and lot of pure alumina (Al2O3). It is known Hall process http://en.wikipedia.org/wiki/Hall_process. There are no other more economical process.

Key material to aluminum is ultra pure alumina and cheap energy. There are many process to make pure alumina, we should select some best fit to small scale production. Clays are posible start material or feldspar mineral (weather to clay). Bauxite are rare.

Diffrent Alumina extraction processes

Acid process from clay

Alumina (alumium ore) extraction from clay. Bauxite are rare minera, clay are common so chemical process based on clay- not bauxite. Alumina are leached out with hydrochloric acid: http://www.freepatentsonline.com/4388280.html.

- sulphurous acid process
- nitric acid process

Alkali process from clay

- bayer process (very limited, high viscosity if SiO2 present)
- Soda sintering process
- Lime sintering process

Carbon dioxide process from feldspar

- Feldspar mineral (sand) and high pressure carbon dioxide can be used to produce alumina. CaAl_2Si_2O_8 + 2CO_2 +4H_2O -> CaCO_3 + 2SiO_2 + 2Al(OH)_3

High temperature proceses

Kaolin clay is composed of aluminum and silicon (Si2Al2O5(OH)4). Reduction of Kaolin would then result in an aluminum/silicon alloy. In practice, carbides (usually SiC) resist further reduction except at very high temperatures (2050°C). Thus, the smelted product is likely some aluminum-rich alloy with various highly refractory simple and complex carbides.

Parent material is reduced carbothermically, that is, it is reduced in the presence of carbon and the absence of oxygen at high temperatures. The carbon is oxidized to produce carbon mon- and di-oxide and the metal oxides are reduced.

The paper carbothermal reduction of alumina by m.halmann (at) weizmann.ac.il describes the carbothermic reduction of alumina rich material in an atmosphere of methane gas at high temperatures. Internal copy of this paper: File:Halman.pdf

Such temperatures could be produced with a point focusing solar collector (see Metal Refining for more)

Page 66 in this online book talks about a plant in the Ukraine that smelts kaolin into an aluminum/silicon alloy: The Handbook of Aluminum by George E Totten, D Scott MacKenzie

At temperatures below 2000°C, I assume aluminum metal may be separated from silicon carbide (SiC).