I think a better example might be cement production. For a blast furnace you don't just need heat, you need to chemically react some reducing agent with the iro

I think a better example might be cement production. For a blast furnace you don't just need heat, you need to chemically react some reducing agent with the iron ore. Generally that's either coal coke or methane reacting with the iron oxide to produce iron and carbon dioxide. There's technologies on the horizon that could enable electrolytic refining of iron much like how aluminum is refined. With cement production there's no potential method to eliminate the carbon dioxide. You still have the extreme heat of the process so natural gas and coal are a pretty good fit but even if you sidestepped that and heated it through other means, you're ultimately taking calcium carbonate and calcining it to calcium oxide. Even if you eliminated all coal usage you'd at best cut the amount of CO2 released by half. With a good carbon capture system connected to cement kilns you could actually use concrete to capture CO2 from the air. Concrete naturally forms calcium carbonate over time as it ages so you could use it to have concrete production effectively be a net negative for atmospheric CO2. Concrete production currently accounts for 8% of CO2 emissions globally and direct atmospheric capture has been something that's historically difficult due to the low concentration of CO2 in the atmosphere so you could kill two birds with one stone.