It's pretty strange that it got included in that category and it doesn't show up in any of the subcategories either. I checked and neither of it's products are used in smelting directly. Closest would maybe be hydrogen in the silicon reactor, or maybe the fuel gas in the gas rotary kiln (which isn't in that category).
Ok, I apparently totally missed the other recipe in the recipie list, but anyways, it showing up in there before you actually unlock the tech is pretty confusing.
