How do you get alkali metals?
Electrolysis of molten salts, typically with a halogen. Upon electrolysis the halogen is released at one electrode (usually chlorine, in which case it just dissipates) and the alkali builds up at the other. Sodium and potassium were also used to purify aluminium from aluminium oxide, but this method was very costly so aluminium's value wouldn't have to be changed from what it is now.
Interesting.
Were these methods available by 1400?
Electrochemistry was developed in the 1700s as far as I remember, but the technology of making working cells was definitely available since the Middle Ages - a lead-acid battery uses lead electrodes in sulphuric acid. Lead was obviously being produced since the Roman era, and sulphuric acid was easily produced by burning brimstone (sulphur) and collecting the runoff, which was developed during the early days of alchemy. The only novel part was combining the two and hooking up wires to the electrodes to see what happened. When this method of making batteries was discovered, scientists soon discovered that water decomposed into hydrogen and oxygen (or inflammable air and vital air, I think?) and trying this method with other liquids (like... molten table salt, see above) yielded much different results (a flammable metal and a toxic gas!).
The problem with aluminium is that bauxite, its oxide, could not be melted by conventional means, so electrolyzing it was impossible. Instead, potassium was used to reduce bauxite (or another aluminium mineral, I don't remember), leading to impure samples of the metal. Once someone else had the idea to use sodium instead of potassium, they created the first appreciable pure samples of aluminium (if you discount a few mysterious aluminium artifacts found in millenia-old Chinese tombs). Unfortunately, since sodium was very expensive, aluminium's value remained very high until the Hall-Heroult process was devised (which may be beyond our dwarves' tech level, but the individual materials of the process are not so hard to produce).
This process is more complex than simple electrolysis of a molten compound, because bauxite (Al
2O
3) could not be melted. So, research ensued, and it was found that another aluminium mineral, cryolite (which couldn't be smelted either), could be melted at achievable temperatures, and that bauxite was very soluble in molten cryolite. Finally, a workable aluminium-bearing liquid was produced, but the oxygen created by the decomposition of the bauxite reacted with the aluminium too much and the method still didn't work. Luckily, using carbon electrodes (or graphite - not a difficult thing to find) solved the problem, as the free oxygen reacted with the more attractive carbon to produce carbon dioxide, which does not react with aluminium and has the bonus side-effect of creating heat to help keep the cryolite molten. After all this, a process to cheaply produce aluminium was developed and it is now the second most-used metal in the world.
So, here's what you'll need to produce aluminium in both ways:
1. Alkali Method
- Bauxite
- Sodium
- Fuel
- Smelter
This would go like a standard smelting reaction, probably.
2. Hall Method
> A Hall apparatus workshop, constructed with
- Graphite (electrodes)
- Copper (wiring)
- Cryolite (I don't think it's consumed by the process)
- A magma-safe material to make the tank out of
- Bauxite
- Fuel to melt the cryolite
- A battery cell
- Lead
- Sulphuric acid
The above isn't really affordable but it would probably lower the value of aluminium a bit.
If someone ninjaed me on this I'm going to be BLANGRY