Typical rules about recycling trash are that certain types of things go in the (common) recycling bin. But it’s several different types of things. Where I live, it’s plastic bottles, narrow-necked glass bottles, and corrugated cardboard, for example. So the first thought is how you sort these from each other. But that’s relatively simple compared to the real question, which is about all the other stuff stuck on. E.g. paper labels attached to the bottles (not to mention residue of whatever came in them) and plastic bags etc.
I imagine the stuff is not much use unless you can get it into some sort of pure form, but it seems like a lot of work just to separate all the stuff and it’s not like it sells for all that much once you do it.
Exactly how your recyclables are processed varies from place to place, but in general, machines do the bulk of the sorting.
For example, you can use magnets to remove metal. Screens can separate things by size. Some machines even do things like shine infra-red lasers onto various materials, looking for the specific reflections from different types of plastic. Compressed air is then used to blow that particular plastic piece into a particular bin or chute.
Human labor does the stuff that the machines can’t do. Generally, the stuff is moving by on a conveyor belt, so the humans at each station have to react fairly quickly. It’s not a job that I would particularly care for, but some folks do it well.
Even with all of that sorting, some things are still not very pure, as you note. Metals are melted down, and impure materials either float or sink and are skimmed off one way or the other. I don’t know how they purify glass, but I suppose one way to do it would be to crush the glass and then use something like compressed air or a comb filter to separate out the labels and such.
Even non-ferrous metal, incidentally. If you rapidly change a magnetic field, you can induce eddy currents in any sort of metal at all, which then allows you to attract or repel them with a magnet.
I’ve seen videos of the process, and as mentioned above, it’s a logical pathway that sorts different commodities out with different technologies or simple physics.
I’m pretty sure when they melt metals or glass, the paper labels and glue are burned off at some point. Not sure how plastics work.
I was once involved in designing a children’s museum exhibit about waste management, including recycling. One of the boffins we met with told us that separation was very efficient nowadays, known as “single-stream” - just have one bin/can per household, and everything gets sorted offsite. The biggest problem with single stream? Buy-in from householders. They’ve been trained to separate recycling. People feel good about it. They’re contributing! Never mind that now the city has to pay for another truck to do another circuit, staffed by another team of personnel. This expert said that there was no way any of our local municipalities would move to single-stream, as they’d face too much public backlash.
It was not until single stream recycling that it was worth my effort to do it at all. Which leads to the story about it. Talking to a fellow firefighter who is very environmentally conscious, he was surprised that I didn’t recycle. I told him it is ridiculous to have all those pails and they should have one if they expect people to do it. I said the current system is diminishing the quality of what goes to the landfill, which means it would never get mined which means more material gets buried forever. Better to just throw everything out and that would increase the value of that waste for landfill mining till we can figure out this single stream system (which I still think is flawed, we should be able to throw away everything in one, but it’s close enough and gets me another garbage pail). Well right after that conversation, about me not recycling till single stream and I get home and they dropped off my new single stream pail. So now I recycle.
How can I not know this already? I assume this is how metal detectors work. Do you need different frequencies of field change to attract/repel different metals?
It may not be separated enough for anybody but China. In Québec, for several years, many recycling centers have been grossly separating paper from the rest, then sending it in bulk to China. Now that that market is closing up, the local paper mills say they’d be interested… if the paper were sorted by grade and free of contaminants such as plastics or glass.
Yes, metal detectors use the same basic physics. For sorting, there’s no frequency involved: Usually, it’s just turning on a strong field very quickly. For detecting, I’m not certain. The difference between metals is from different conductivity, and conveniently, the metals with the best conductivity tend to be valuable and to have coins made out of them. Since most metal waste is either iron or aluminum, I expect that the recycling places probably don’t bother in any more detail than iron - noniron metal - nonmetal.
You can see the same effect on a less dramatic scale by sliding coins down a magnet with a large, tilted surface. A zinc coin will slide fairly quickly, because zinc isn’t all that great a conductor, but a silver coin will be much slower.
My area doesn’t have municipal trash collection, much less recycling. Where I live, you have to go out yourself and contract with a company to pick up your trash.
So we recycle by taking such items to a local recycler (another private company) which pays you by the pound for various items. So YOU are sorting them out because you put all your scrap steel on the scale, then all your aluminum cans, then your paper… and they issue you a ticket listing items and weight and you go to the cashier to collect.
So you’re doing the labor. On the other hand, you are getting paid. It’s not a huge amount, but for a couple years it paid for about half the gas I put in my pick up which, given my finances at the time, was very helpful.
And you don’t have to have your household garbage picked up as often, because you aren’t filling the dumpster as fast, so that saves you money on that end.
Here in Minneapolis, they switched from separated recycling to single-stream a few years ago. The number of households doing recycling increased dramatically – more than doubled. And the volume has increased so much that there are now calls for the city to increase collection of recycling to once every week, and reduce garbage collection to only once per 2 weeks.
There were some complaints about single-stream at first, but those doing recycling at that time were mostly hard-core environmentalists – they generally understood that the volume increase in recycling made it worthwhile. (There were also complaints from scrap-metal thieves, who could no longer go down the alleys the night before collection and steal aluminum cans; but the city ignored them.)
The big problem now is that people put non-recyclable things into the recycling bins. Sometimes just laziness; sometimes ‘wishful’ recycling – people wish this was recycled, so they include it.
I dunno, pissing off an army of little old asian women like that. At least that’s who owned the area when I lived in North Minneapolis 15 years ago. Tiny little women carrying bags of cans on their backs that were larger than they were.
There’s a “Dirty Jobs” episode where Mike Rowe goes to a recycler, and they would use a laser on large pieces of metal; IIRC, it bored a microscopic hole in the metal and analyzed its content. They would then sort it by percentage of this or that.
Around here, people do the initial sorting. The private company we use is a jobs program for people with disabilities, but there’s others for social upliftment programs etc.