 |
Bauxite
What is bauxite?
Bauxite is ore from which aluminium can be extracted.
Most bauxite, including Australian bauxites are lateritic, formed by intense weathering of various rock formations. The alumina in lateritic bauxite is mainly in the form of gibbsite, an aluminum oxide trihydrate. Other bauxites contain boehmite and diaspore which are monohydrates.
Bauxite production
World output of bauxite in 2007 was 207Mt, a rise of 10.5% on the previous year, due principally to increased output in India, Indonesia and China. Bauxite production has increased annually since 1998 at an average rate of almost 6%pa. With the exception of a 1.7% decline in 2004, world alumina production has increased annually since 1994, and was about 77Mt in 2007. The average year-on-year increase in output between 1994 and 2007 was 5.2%, and since 2004 has increased at about 10%pa, largely due to rising Chinese production. (Roskill Report 2007).
In 2007, Australia was the top producer of bauxite with almost one-third of world share, followed by China, Brazil, Guinea and India.
| (x1000 tonne, Numbers for 2008 estimated) |
| Country |
Mine production |
Reserves |
Reserve base |
| 2007 |
2008 |
| Guinea |
18,000 |
18,000 |
7,400,000 |
8,600,000 |
| Australia |
62,400 |
63,000 |
5,800,000 |
7,900,000 |
| Vietnam |
30 |
30 |
2,100,000 |
5,400,000 |
| Jamaica |
14,600 |
15,000 |
2,000,000 |
2,500,000 |
| Brazil |
24,800 |
25,000 |
1,900,000 |
2,500,000 |
| Guyana |
1,600 |
1,600 |
700,000 |
900,000 |
| India |
19,200 |
20,000 |
770,000 |
1,400,000 |
| China |
30,000 |
32,000 |
700,000 |
2,300,000 |
| Greece |
2,220 |
2,200 |
600,000 |
650,000 |
| Iran |
- |
500 |
- |
- |
| Suriname |
4,900 |
4,500 |
580,000 |
600,000 |
| Kazakhstan |
4,800 |
4,800 |
360,000 |
450,000 |
| Venezuela |
5,900 |
5,900 |
320,000 |
350,000 |
| Russia |
6,400 |
6,400 |
200,000 |
250,000 |
| United States |
NA |
NA |
20,000 |
40,000 |
| Other countries |
7,150 |
6,800 |
3,200,000 |
3,800,000 |
| Total world (rounded) |
202,000 |
205,000 |
27,000,000 |
38,000,000 |
| |
|
|
|
|
Source: U.S. Geological Survey, Mineral Commodity Summaries, January 2009
Characteristics Of Darling Range Bauxite
The three structural forms of bauxite are gibbsite, boehmite and diaspore. Gibbsite is a true aluminium hydroxide and boehmite and diaspore are both aluminium-oxide-hydroxides.
Extreme lateritic weathering in the Darling Range has resulted in the formation of the trihydrate bauxite Al(OH)3, gibbsite (Refer Figure 1: Typical Darling Range Cross Section)
Figure 1: Typical Darling Range bauxite profile
Benefits of Darling Range Bauxite
In an alumina refinery, bauxite is digested using the Bayer Process and involves washing the ore with a pressurised hot solution of sodium hydroxide (caustic soda). Two reasons why refineries that use Darling Range Bauxite operate with lower production costs is:
1. Cheaper capital costs and less energy consumption – the gibbsite nature of the Darling Range Bauxite means that alumina may be extracted for less capital cost and less energy consumption (Refer Figure 2: Process Requirements).
2. Less Caustic Soda Wastage – The low level of reactive silica minimises the caustic soda that can be consumed by reactions with silica. In addition, the loss of alumina is reduced.
Requirements for the extraction of alumina
| Bauxite from Darling Range |
Gibbsite |
Boehmite |
Diaspore |
Temperature
Degrees Celsius |
145°C |
250°C |
Higher |
| Pressure psi |
75psi |
550 psi |
Higher |
Figure 2: Processing Requirements
(Note 1: Diaspore Bauxite is extracted using the Bayer Sinter process and the temperature and pressure requirements are materially higher than Gibbsite and Boehmite digestion requirements.)
Figure 3: Typical Darling Range Bauxite Ore Structure
|
|
 |
|