Is it possible to smelt blood into usable iron?
How many gallons of blood would it take to make a broadsword?
A lot.
There’s around 3.3g of iron in 6 liters of blood.
A broadsword might be, what, 15 lbs?
So, that’s around 6,800 grams which means it would take 12,300 liters of blood.
Beter start slaughtering…
Definitely, a broadsword made of the blood of your enemy would be bad-ass but you might have to settle for one made from the blood of your enemy’s army.
Not too hard to separate the hemoglobin while wet in a centrifuge. After you separate and dry the stuff I assume you have a lot less volume to reduce to iron, but sounds like you’ll need a swimming pool full of blood to start.
At 5 liters per adult human that’s about 2500 people per sword. A not impossibly large number for an evil overlord!
Can you just pour the buckets of blood straight into a blast furnace and let it work its magic? Or is there some aspect of using blood as a starting point that will require additional steps?
Not sure about the rest of your math but a single handed sword would be more like 2.5-3.5lbs and a two-handed sword would be more like 4.5-5lbs.
Sorry, I was never a member of the SCA…
You could just give your enemies Deferoxamine, than collect their urine, boil it down and separate the iron. That way you don’t have to kill anybody, and separating the iron from the urine will be much easier than starting with blood.
However. “This sword was forged from the piss of my enemies”. Doesn’t have the same ring to it.
Oh, that’s even better! So I only need to slaughter 500 people to make my 3 lb. blood-iron long sword.
Still looking for an answer to this though: Can I just pour buckets of blood straight into my smelting furnace like I was working with normal iron ore?
This is how the inhabitants of The Blue World (in Jack Vance’s novel of the same name, based on his shorter The Kragen) made iron. They were the descendants of people from a colony ship (actually, as careful reading shows, it was clearly a Botany Bay-like ship carrying prisoners as probably unwilling colonists) that had landed on an ocean world with no exposed land. The colonists had to make a civilization without access to land or minerals, having to cope with the semi-intelligent megafauna. When they needed iron weapons, this was their recourse.
You’ll be left with a lot more carbon than iron. I do not know if it would all boil off but there would probably be enough left to alter the properties of your iron ore, not to mention the other trace elements found in human blood such as cobalt, selenium, and zinc. I’m not sure how they’d affect the iron ore however.
Sort of a Catch-22 if you need the sword to do the slaughtering. Almost ironic.
No.
About half the iron in a body will be stored in the liver in the form of ferritin. Most of the rest will be in the form of hemoglobin. You are going to need a chemistry lab to separate those out. Burning them will just give you a bunch of ash, and you will lose a lot of your iron atmospherically.
Cheating it out with the Deferoxamine into the urine is giving to leave you with iron sulfur clusters, and some kind of iron phosphorus hydride. I would need to figure out which ones. They would be a lot simpler than dealing with the thicker more complex soup that is blood. You’ll still need a chemistry lab, though.
There will be some free iron in aqueous form in the cytoplasm inside cells in what is known as the labile iron pool. The easiest way to get that will be to grind up the whole bodies of your enemies to such a degree that you destroy the cell walls. Pour the resulting human soup into a large container. The clear fluid that rises to the top will be the stuff that contains your iron. Just be careful not to heat the soup, or you will render the fat.
You do know that you could just heat your sword up, than submerge it in a bucket of blood, don’t you? That way you could say your sword was tempered with the blood of your enemies, and doubtless some of the iron from the blood would get incorporated into the sword.
Do you really want to go the whole chemistry route with this?
While I am a member of the SCA I was using real world numbers. Just to make sure I wasn’t nuts I have a fairly good replica single handed sword that I put on the kitchen scale before I posted. It came in at 3lbs 3/4oz.
Thanks for thinking of it though. 
p.s. I don’t belong to ARMA, it was just the first site that came up in the Google search.
Not unless you want a steam explosion and super-hot stuff splattering everywhere.
Water (which is what blood mostly is) and blast furnace temperatures don’t play nicely together. You’ll want to remove as much moisture as possible, so you’ll want to dry the blood out first.
If the object is to temper the sword, I think the usual process is to forge the sword then submerge it at plain old out-of-the-forge red hot temperature into water (or blood of your enemies where available and not prohibited by law). That’s safe as houses.
How bad is/are traces of iron phosphorous hydride for the metallurgy? (I hear hydride. That can’t be good. And don’t get me started on phosphorous swords.)
Hemoglobin can be separated out with a simple centrifuge. They do it to my blood regularly. Ferritin may be a little more complex but ferritin is a protein mainly encapsulated an iron compound and it shouldn’t be that hard to break down the protein and release the iron for centrifugal separation as well.
How (and why) is the hemoglobin separated from your red cells in a centrifuge?
Previous thread on this topic: Making a wedding ring out of blood.