Waste

[Inziladun]

Originally Posted by alatar

I'll even grant that the elves and dwarves used some type of process that produced no waste, or that the waste products were carried away and dropped into volcanoes by friendly winged balrogs. But men?

If we allow that the Elves used an unknown, ultra-efficient process for their ironworking, I wonder if we could not grant the same licence to the Dúnedain. After all, it seems likely they would have learned metal-work from the Eldar.
If one goes that far, then it should be noted that the other major, warrior-people of Third age Middle-earth were the Rohirrim, who apparently got their weapons and armour from the Dúnedain.

The Rohirrim had the advantage in being supplied by the metal-workers of Gondor.

UT The Battles of the Fords of Isen (footnote 11)

What other settlements of Men were there in that time? The Men of Bree apparently had no great store of metal weapons and armour, as Butturbur had only a club with which to fight the Ruffians. What metal crafts they did require probably came from the Dwarves.
Same goes for the Men of Dale, who had the Lonely Mountain for a neighbour.

As for Hobbits, they were said to have forges (by Gandalf). Maybe, along the lines of what Rumil said, they had some out of the way place where the waste was stored, or maybe they buried it.
Also, if they in turn learned their smith-craft from the Dúnedain, maybe they used the same environmentally friendly process.