How to extract the iron out of blood to make a sword from one's foes?

[Strigon]

You would basically have to remove them the same way that impurities are removed from most metal samples. The sample is heated to a liquid state, and everything that boils or has a smoke point below that temperature vaporizes off. That handles most impurities. Silicates and similar, which are unlikely to be found in blood-iron, are removed via the addition of lime to the metal, which forms the slag on the surface of the metal. Other metals might float to the surface or sink to the bottom, or just find themselves alloyed into the iron. I would imagine that, especially in cities that use a Roman plumbing system, the lead content of blood-iron would be notably higher than that of regular iron.

I can't say much more than that. Any metallurgists happen to be on this forum?

Perhaps I'm missing something obvious. Wouldn't that get rid of all impurities below a certain boiling point? We were discussing identifying, and selectively retaining, beneficial impurities. How would you, for example, get rid of a harmful impurity that boils at 200 degrees without getting rid of a beneficial one that boils at 175?
This feels like one of those mathematical/logic puzzles that goes about on the internet, and I'm sure somebody's going to point out the glaringly obvious thing I'm missing.

I believe the point is less to get an entirely practical way of "mining" iron, and more "I FORGED THIS SWORD FROM THE BLOOD OF MY ENEMIES" symbolism for a tyrannical ruler.

Exactly. I mean, if you're willing to extract it from the food they ate, why not just go one step further and extract it from where the food gets it? That is, mine it the normal way.

''I FORGED THIS SWORD FROM THE BLOOD OF MY ENEMIES! ... Okay, well technically not, but it would have been in their blood, eventually. Probably. Some of it, at least. AND IN FORGING IT I HAVE DEPRIVED THEM OF VITAL NUTRIENTS; ITS MERE EXISTENCE WEAKENS MY FOES!''