#to the end of the copper smelting cycle SO4 and force precipitation...? Which would be interesting. But fundamentally you

[iamthepulta]

Iron ore isn't my specialty, definitely not steelmaking proper, but I do know a little about the differences.

Iron loves oxygen, so unlike a lot of metals we mine bonded with sulfur, iron ore is bonded with oxygen, which takes a lot of energy to break. In order to do that, we basically give it something that oxygen likes more, like carbon. Coal/coke starts the reaction, being a combustible, and lime Ca(OH)2 allows CaCO3/CaSi2O6 to form, along with any other impurities from the ore. The molten liquid that doesn't form a gas is lighter than iron, so it floats to the top and is periodically 'tapped' out. Cast iron (little to no carbon) is produced, and sent to the Basic Oxygen Furnace, which is just a way we can control the amount of carbon that volatilizes. Steel is iron with about .8-2.0% carbon. I assume this is the point where we add other alloys. So you could make a batch of chromium steel, a batch of manganese steel, etc.

To run a blast furnace though, you have to continuously blow hot air through the chamber where the ore, coke, and lime are being fed in order to properly remove the carbon. Iron oxides only melt at very high temperatures, which is why it was a relatively late metal innovation.* These are also continuous processes; there's no stopping a blast furnace unless you use a lot of energy to restart it. Tapping out the iron and the slag is done continuously day/night.

*Footnote: Iron Age really doesn't count, in my opinion. Europe used very basic batch process methods to make iron until essentially late 1700s. Since they're hot enough to melt the ore it means you can cast the product into whatever you want rather than hammering it piecemeal via blacksmithing. China was the only one who invented the blast furnace and that technology was later lost and had to be rediscovered. However, this is a personal opinion. Take with grain of salt, etc.

I'm reading a paper on the production of steel through EAF so I hope this translation actually sounds coherent, lol.

Arc furnaces only take steel because they're batch processes. Coke/graphite is added to stimulate the arc, and then melting occurs gradually. Desirable and undesirable elements, like Chromium, Manganese, Sulfur, and Phosphorus are already included in the steel, or have been added, via gradual oxidation. (Usually not the case for proper iron ore. There's a lot of magnesium, but otherwise mostly iron, silica, aluminum, and oxygen.)

It's at this phase (and/or a BOF), which is basically the same process but only for iron ore, that sulfur and phosphorus are removed. Both will make your steel very brittle. Oxygen is usually added to collect the elements that had been added, or partition the alloy elements you do want into the steel. Then oxygen is removed again by adding silica and aluminum, and the steel is cast.

The idea, I think, is that an EAF is a more controlled environment than the blast furnace and focused on refinement, but still requires coke/coal/carbon/graphite to start and regulate the process. For the BOF, the iron is already molten and fairly pure, so it's refinement, but mostly adding carbon and alloys in.

Fundamentally, iron production is the opposite of stuff like copper's production. Iron is already oxidized, and we need to reduce it to make steel. We want to oxidize copper in order to separate it from other elements. Carbon just happens to be the way we reduce iron. So if we can find another reductant, like sulfur, theoretically we could transition away from coal.

However, this is NOT my specialty so I'm CC'ing @weekendviking in case he has some experience to add, along with thoughts about transitioning away from met coal. (Please correct any inaccuracies I have too. I tried my best but I don't know pyrometallurgy.)

success, everybody, i thought about something other than vampires for like a twenty minute stretch. the something was: electric arc furnaces

about 7% of us coal consumption is metallurgical coal, which is used (after being coked) as fuel for blast furnaces. blast furnaces smelt ore and scrap metal, usually to make steel. most coal in the united states is used for the power grid & must be replaced with renewable sources, but it's a little more straightforward to see how that swap needs to go; we need better batteries & genuine investment, there are questions about where & how those renewable sources should be generated, & i do think that our power consumption needs to fall. it's less obvious how we might replace metallurgical coal, though, because we still need steel. electric arc furnaces are efficient, cheaper, smaller, and more capable of running variable loads than blast furnaces, but almost all of them are for the scrap metal -> steel process, they're not for iron ore -> iron -> steel. but we are getting better at making them! so i read through part of a DoE powerpoint & glowered at links to mckinsey reports about it. i don't know anything really about metals mining, mostly i've just read about coal & all of that from a labor safety perspective, but i'm very curious about the, like. engineering problems (and also still labor safety & environmental problems) presented by trying to genuinely transition away from coal, which we absolutely must do, like guys even UMWA is out here like 'we gotta stop pulling this shit out of the ground' [official position of union president cecil roberts is that coal miners & their communities need a 'just transition' away from coal]