Aluminium

Mining

Today (2016) Aluminium is still only economically extractable from minerals that do not contain silicon. Silicon is the second most common element in earth's crust just after oxygen.

As waste copious amounts or red mud [1] are produced. Red mud is mostly composed out of iron oxides, titanium oxides and alkaline silicic acid compounds. The problematic part is that red mud also contains ~1% soluble heavy metal salts (V Cr As) which makes it rather toxic. Advanced atomically precise technology should make it possible to fully extract those (potentially valuable) heavy metals directly by efficient chemomechanic processing and indirectly by the availability of very cheap energy. This is a form of atomically precise disassembly which is harder than mechanosynthesis and thus not to expect early on.

== Limitedness of stable binary compounds ==

The most obvvious form to use aluminium in advanced atomically precise technology is in the form of the gemstone leukosapphire Al₂O₃
Most other nonmetal compounds of aluminium strongly react with water and thus do not form useful structural building materials.

• aluminium nitride AlN (surface hydrolysis creates passivation layer) this may still be useful
• aluminium carbide Al₄C₃ (reacts with water to aluminium hydroxide and methane - irritant)
• aluminium fluoride AlF₃ (water soluble; interestingly low toxicity)
• aluminium sulfide Al₂S₃ (toxic due to hydrogen sulfide H₂S generation when contacting water)
• aluminium phosphide AlP (highly toxic due to generation of phosphine PH₃ when contacting water)
• aluminium chloride AlCl₃ (water soluble; toxic neurotoxine)

Mechanosynthetisized nonthermodynamic checkerboard pattern compounds like the following may be stable:

• aluminium sulfoxide Al₄O₃</sub>S₃
• aluminium phosphonitride Al₂NP

More aluminium based gemstone materials

A good point to start are always the natural aluminium minerals [2]. Since they need to be insoluble to persist on the surface (except in very dry environments).

There are many aluminium silicate minerals [3] like:

• Al₂SiO₅ Andalusite [4] & Sillimanite [5] (Mohs 6.5-7)
• Al₆Si₂O₁₃ Mullite [6] (Mohs 6-7)
• Al₂SiO₅ Kyanite [7] (Mohs 4.5-7 anisotropic)

Interesting facts

Salts of aluminium usually have low solubility in water. Albeit aluminiums extreme abundance in our environment (most abundant metal in earth's crust) it does not play a known role in human biology. Elevated intake of aluminium salts (rare in nature) is suspected of having detrimental effects on health.