I'd like to suggest that Alloy Smelting Lvl 4 include a recipe for the Blast Furnace of "Burn Tailings". The recipe should produce nothing but CO2 and destroy 1 tailing.
Right now, the ways to deal with Tailings make it feel very much that there is a right way to play. Players should minimize tailings and get the Blast Furnaces as efficiently as possible. By providing on alternate way to deal with Tailings, it would feel like players could approach the problem different ways.