Are the metals in a city dump comparable to that in a mine?

I’m talking parts per million etc.
(Not interested why miner don’t bother, that’s not the question.)
When you read about mining, they always brag about how many tonnes of earth they have to move to get a pound of finished metal.
Are the ratios of metal in a dump comparable to metals in a mine?

Most city dumps/landfills/recycling centers separate out major metals before they go into the waste stream.

They do now.

Not all that long ago, there was no attempt to sort things out before being buried for eternity.

It’s an intersting question, really. Even with recycling efforts, a lot of metals make their way into the landfill. As one example, is anyone recycling used headphones or earbuds? There’s copper wire in those things. Likewise any junked cassette players, CD players or any toys or small appliances with motors - they all have yards and yards and yards of copper wire in their motors.

How about gold? Lots of it, I’m sure. It’s all over things like audio/video connectors, computer hardware and even the heartbreaking things like lost jewelry. (As a side question, how much gold is in the sewage system at any moment from being worn off of dental work, or the flakes in Goldschlager liqueur?)

If you’re not paying attention cleaning up after a fancy dinner, silverware may slip into the trash. Twenty five years later, my mother is still annoyed that her service is missing a fork.

There was a study recently that concluded that for valuable metals like copper, of the total practically retrievable supply, 30% was in the ground (unmined), 30% was in use in houses and infrastructure, and 30% was in landfills. I haven’t heard if the study was confirmed by other scientists.

I believe it was this study, but the summary is pretty sparse: http://www.terradaily.com/reports/Yale_Study_Not_Enough_Metals_In_Earth_To_Meet_Global_Demand.html

Instead of of putting mine rocks into a grinder and then a smelter, maybe the garbage trucks could just dump directly into that grinder. You’d get a lot of heat generating from the combustibles, but you should have a rich pool of metals also. That’s a guess.
But the question is would you find more metal per ton in a dump or a carload of mine diggings?

There are already trash->power plants in operation.

http://www.china.org.cn/english/2003/Feb/56309.htm

There are lots more, I just found this on the first hit.

I am not an expert, but I remember a discussion saying that a big part of mining the dump is the range of materials. While there may be several parts per million of gold (for instance) there is also lead, lithium, iron, Al, copper, zinc, etc etc. Coming up with ways to separate this wide variety of metals is new. Today, a mine extracts copper and zinc, or iron, or manganese, or some subset of metals. That makes the job much easier than having to extract a little bit of everything.

The Mars books by Kim Stanley Robinson are set in a future where earth is overpopulated and facing shortages of all sorts of resources. He describes a machine called a Super Rathje that is designed to dig through landfills to mine anything useful.

The name Super Rathje is an homage to Bill Rathje, an archaeologist who is known for his study of garbage.

Ditto Space Merchants by Frederik Pohl and Cyril M. Kornbluth. The corporation that mined the dumps was called Dump Mines IIRC.

Of course the Moties have so mined-out their system, that they can’t afford to waste any metal. We could learn from them…

There are lots of dealers out there that specialize in replacing missing silverware or dinnerware pieces. (Google ‘missing silverware pattern’.)

Be a good child, look this up online, locate a replacement piece, and buy it for her for Mothers Day!

Yeah, a traditional mine is able to set up an economy of scale that is very hard to beat for a “garbage” mine. Even if there are other metals mixed in with the target ore of a traditional mine, that mix is consistent and the mine can custom tailor its process to maximize efficiency. A garbage mine doesn’t have that benefit. Maybe a technological solution can be found, but that’s still in the future.

It seems like the basic process is simple, but the implementation and business plan are where you’d get burned. Surely some other engineer has already thought of this:

(1) Heat the trash to the melting point of the metal you want to extract
(2) Compress or centrifuge the trash so that any metals with lower melting points all come out at once, and the solid non-metal trash that hasn’t been burned up gets moved along to the junk pile. If there are acids or other chemicals that are typically used to strip out metal from ore, go ahead and try them in this step.
(3) Run the ingots of hodge-podge metals through a series of furnaces kept just below the melting point of the metal you want to extract in that stage (and stage these cooling furnaces in order of descending temperature).
(4) At each cooling furnace, pull out the solid metal that you’re interested in, and move the leftovers to the next stage.

In lieu of step (3) you could also just use a gravity separator so that the most dense metals gathered on the bottom. You use a single drain plug at the bottom, and a series of ohmmeters built into the column tells you when you’re about to switch layers. When it says you’re almost out of (e.g.) gold, you pour one last ingot of mostly-gold and then bring clean molds for the (e.g.) silver.

I’m sure it’s more complicated than that, and providing the heat to keep the metals melted is probably not worth the expense, but if you could perhaps combine it with a hydrocarbon extraction plant, maybe you’d have something…?

In trash, there is also chemicals that need to be seperated out and disposed of safely, too.

Paint, plastics, rubber, biological waste, and so on.

You cn burn those off to seperate them from the metals, but you can’t just release that cloud of nastiness into the atmosphere.

Traditional mines and smelting facilities dont have to deal with that wide array of stuff.

I forgot to mention a big exception to much of the above: aluminum. One of the reasons there is still a big incentive to recycle it is because of the incredible expense of smelting new aluminum versus recycling old stuff. Old aluminum can be relatively easily and cheaply melted down whereas aluminum ore (bauxite) requires massive quantities of electricity to separate the AL from the rest. The cost is so big that it’s actually more economical to ship the unprecessed ore from places like Jamaica to smelters near hydroelectrical generators in the NE United States instead of processing it near the mine.

As a kid one recycling fact that I learned was that the cost of making a soda can from new aluminum was equivalent to 3 hours of TV power.

it is true, mixtures of metals are rarely worth sepeartion. I’ve also heard that scrap aluminum isn’t alwats of the best quality: you might not want to build a boeing 777 from scrap. I’m sure the USA throws away enough metal to equip a small country though- are tin cans worth recycling? Glass is another story-it is probabaly cheaper to make new glass from scratch-rather than melt recycled stuff. anybody know if it makes sense to recycle glass?

You might want to check out landfill mining:

http://en.wikipedia.org/wiki/Landfill_mining