It takes me 7 to 8 lignite coal to smelt Hematite. I’ve used 26 lignite coal with 10 iron dust and it refused to smelt. The recipe doesn’t show anything else required to smelt iron dust.

1 hematite by mass is smaller than 1 iron dust, as such you’re probably going to need quite a bit of fuel to smelt 10 of them together to 1811~k, have you built a thermometer yet? it’s pretty crucial for any real use of the crucible. It also depends what burning box you are using somewhat.