Hacker News Reader

Comment by blacksmith_tb | Hacker News Reader

Trash is full of valuable materials! Right now it may not be economical to recover those, but I would be surprised if we aren't mining our landfills in the next 100 years. That said, the CO2 emissions from launching anything non-essential into orbit are huge, I'd wait until we have a space elevator to (intentionally) throw trash into space.

View on HN

I was just watching a video where they made the claim that the slag from steel production 100 years ago has more metal than some ores, so it's becoming worthwhile to re-mill slag.

Video games have largely misled us here. Iron ore is incredibly common, it’s not a rare resource at all. The limiting factor for steel production has historically been energy, not ore, and in the modern context the ability to produce pure oxygen for carbon reduction. Historically iron mines were put near forests for fuel, not wherever the richest ore was.

The advantage of re-using slag isn’t that it’s richer in metal, iron oxides being pretty easy to get, it’s that it would take less energy or Oxygen to finish refining.

Recommended reading: Bret Devereaux’s blog series about iron & steel production. https://acoup.blog/2020/09/18/collections-iron-how-did-they-...

It might also be that slag might be closer to smelters than ore, reducing transport costs.

That also seems quite likely.

That or slag is much lighter per lb of refined product, reducing the transit cost. Iron ores are incredibly common, but they’re also very heavy, what with them being literally rocks.

of course I can't find the original video I was watching, but since the slag is directly outside the steel mill, transit is about as low as it could get.

If you search on YouTube for "deskulling slag pot", you'll find a bunch of videos showing slag trains going maybe a couple miles from the mill to a pit to deskull?

I wonder how much silver comes from recycling old copper, lead and zinc.

Only about a quarter of « new » silver comes from silver mines. The rest as a byproduct of other mineral mining where they separate out the silver.

https://www.globalxetfs.com/silver-explained/

Or a rail gun.

My understanding for why we don't use those for spacecraft is because people and fine machinery can't take the Gs.

Trash could.

The main issue with concepts like rail guns and what-not for orbital launches is atmosphere. Your atmospheric drag is a function of velocity squared times the density of the atmosphere- a very non-linear function of how close to the ground you are.

Rockets have a huge advantage in that they go slow near the ground, where the atmosphere is thick. They're not dealing with as much air resistance. As they reach altitudes with less atmosphere, they can throttle up. This saves a lot of fuel, mass, energy.

A rail gun, however, can only add velocity, energy, at the beginning, and will slow down every moment for the rest of the launch. This is the worst possible condition. You're at your highest velocity while you're in the thickest part of the atmosphere. You'd need to put an incredible amount of extra energy into the system because of that.

So maybe you put the end of your rail gun on the top of a very high mountain. But the construction costs, the transportation costs, all of this, probably makes it simpler to just use rockets instead.