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Old 20th December 2017, 10:10 PM   #33
Timo Nieminen
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Quote:
Originally Posted by A. G. Maisey
Terrestrial iron ores need to be reduced to turn them into usable material. Iron rusts, which means it combines with moisture, so before terrestrial iron ores can be worked they need to have the moisture removed from the ore, this is what the smelting process does, it removes moisture and produces a solid lump of material called a bloom. This bloom can then be worked in a forge.
Smelting can be used with any ferric raw material, including meteoritic material.
However, in the case of meteoritic material, and also limonite, forge processing is also possible, which is not the case with haematite. Haematite is probably the most prolific source of iron. I doubt that haematite is found in combination with nickel, but limonite is found in combination with nickel, and also with cobalt, however the nickel percentage in limonite is far less than is usual in an iron-nickel meteorite.

This brings us back to the KT dagger:- if the nickel in that blade is 10% it is almost certainly meteoritic.


Jambon doesn't analyse the dagger; he uses the measurements by Comelli et al. 2016, (10.8% Ni, 0.58% Co, and also quotes the measurement given by Ströbele et al. 2016 (ref at end), 12.9% Ni.

A few comments on smelting etc.:

"Smelting" is the conversion of ore to metal. For iron, this is typically done by using carbon to bond to the oxygen in an iron oxide, giving CO or CO2 and metallic iron. For a metallic meteoric, there is no need for smelting, because it's already metallic. For any ore, you smelt, by definition, to obtain metal. For iron, the temperature required is well below the melting point of iron, and the chemistry can be made to happen in the solid state, giving a bloom. The is some conflation of "smelting" and "melting" in non-technical usage. You can melt with smelting (just start with metal instead of ore) and smelt without melting (as possible with iron).

When an ore is heated to remove moisture, the process is "roasting", not smelting. Some ores (like limonite) are hydrated, and some are not. Roasting can also be used to make other changes in the ore, such as converting sulphides to oxides. The difference between smelting and roasting is that smelting produces metal and roasting produces a different type of ore. When limonite is roasted, it's converted to haematite, which is then smelting as usual.

The usual early traditional method to smelt limonite (e.g., bog iron) was to roast and then smelt in a bloomery furnace.

For details of the chemistry of smelting and roasting:
https://www.tf.uni-kiel.de/matwis/a...one/ra_2_2.html
or the version with frames if you want to navigate to elsewhere in the document:
https://www.tf.uni-kiel.de/matwis/amat/iss/index.html

I haven't heard of limonite with significant amounts of nickel. The common high-nickel iron ore is laterite. Jambon gives some data for nickel and cobalt content of various laterites.

Other refs:

Comelli et al. 2016: https://doi.org/10.1111/maps.12664

Jambon: https://doi.org/10.1016/j.jas.2017.09.008

Ströbele et al., 2016:
F. Ströbele, K. Broschat, C. Koeberl, J. Zipfel, H. Hassan, Ch Eckmann
The iron objects of tutanchamun. Metalla
Archäometrie und Denkmalpflege 2016, Göttingen
Sonderheft, 8 (2016), pp. 186-189
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