Magnets=the big junk yard type magnets.
Per stories like these metal scrap is so valuable right now many junk blighted areas are getting cleaned up via scrap collectors. Is there enough metal scrap in landfills to justify using a giant magnet to pull the iron and steel out of the mix, or is most metal sorted out before being dumped?
I have no clue what happens to my trash bags once they get picked up and head to the landfill.
Wikipedia has a small article on it. Interesting subject; I’m sure more and more municipalities are exploring the option.
It’s relatively easy to strip ferrous metals out of the waste stream with magnets, so most waste processing facilities already do this, and have for years.
Also, landfills are not as easily mined as you might think. Landfills are not the old “dumps” of years past. Modern landfills have elaborate, expensive baseliners and caps encapsulating the waste, as well as leachate collection systems, gas vents, and monitoring wells. Any mining effort for a closed landfill would have to take into account the expense of removing and replacing the liner and/or cap, and any disturbed appurtenances.
Any landfills currently in operation are almost certainly already separating out the metals, as well as any other recyclable material.
Also, keep in mind that not all steel alloys are magnetic; some, known as austenitic steels, are generally non-magnetic. Given that these alloys are generally more expensive (since they contain less iron and more of other metals), a method that leaves them behind might not be all that cost-effective.
Many solid waste authorities which incinerate waste have in-line metals recovery - typicaly post-incineration, and that does employ magnets. Most of the recovered material is the remains of tin cans.
General use landfils afaik are not mined like you describe - it would damage the creful structure (drainage, cover, etc). Usually the associated municipalities have recycling programs, and given that tin cans make up the large majority of metal post-consumer waste, this captures a lot of it - the tin can recycling rate is estimated at 60-67%
Some specific-use landfills are mined - there are some lanfills that were used to only dispose the waste from automobile shredders, and they are being mined by the scrap companies that filled them in the first place - but most all of the reclaimed metal is non-ferrous, so magnets are not used there.
Many old steel mill sites, who dumped a staggering amount of slag on their propery, are being mined to free the metallic content of the slag. (Employs crushing and magnets)
Your area doesn’t have scrap metal recycling?
Last I knew (four years ago), most trash-to-energy incinerators just burned everything (except propane tanks or whatever other dangerous stuff they noticed). Some do sort out metals (by magnets and by weight), but that kind of plant was out of style, as the costs of separating the metal wasn’t worth it. I don’t know if current scrap metal prices have changed the calculations.
Maybe Una is more current?
Coincidentally, I had a meeting with a municipal client yesterday and the subject of recycling was raised. Not surprisingly, perhaps, given that it is very much on the minds of cities and towns these days. I don’t have a background in waste management, but people in my company do; my response is based on my conversations with them, and projects where we worked together rather than definitive knowledge.
If the OP referred to recently constructed landfills, then there is probably not a lot of point in opening them up again. As stated above, once recycling became commonplace, a lot of material never made it into the waste stream. Incidentally, if you are interested in waste recycling, a current trend is toward “single stream” recycling. People don’t need to sort their recyclables; that takes place at the plant. It’s dumped on a conveyor belt and optically scanned, then directed to the proper location. Kinda cool, actually.
However, a lot of landfills date back to before recycling and there are two reasons I know of to open them up.
The first is due to space constraints. I’ll give two examples with which I am familiar: Nantucket and Martha’s Vineyard. These are two islands with limited space and high real estate costs. As the landfills started to fill up, the islands were faced with either buying more real estate at premium rates, or being more efficient with their waste management. Their approach was to open the landfills and remove the recyclables to maximize capacity. They also removed wood products for composting.
The second reason is to remove combustible materials. This is a direct result of the recycling movement on the waste-to-energy providers (incinerators). As more and more plastics are removed from the waste stream, incinerator operators are finding their waste is much more difficult to incinerate. In one case I know of, one of these operators is mining a landfill for anything combustible (wood, paper, plastic) in order to keep the incinerator going.
If the word “paper” in the above sentence surprised you, I have an interesting anecdote. Years ago I read an interview with an “urban archaeologist”. His team would open old landfills to see how people lived by what they threw in the trash. They could always get a very clear idea of the date of their discovery by the piles of newspapers, magazines or letters dating back 100 years or more. Eventually one of them thought to ask “Isn’t this stuff supposed to be biodegradable?” Our landfills generate methane which stops decay and preserves these materials for posterity. So, when they ask “Paper or plastic?”, you’re really not being any more virtuous by asking for paper unless you recycle it.