It works completely differently here. The yard I sell my scrap to is family owned, I have known the family since 95. They also, on the same 10 acres or so, own a new steel distributor, which, I think, makes them more money.
They have no "quotas". They are savvy businessmen, now in 3rd generation ownership, so the may, for example, stockpile an acre of aluminum if they think aluminum prices will go up soon, but largely, they sell through as quickly as possible. Taxes, labor, and the cost of land here are all high, and sitting on a lot of material is a money loser.
they only sell steel and iron to one mill- its pretty much the only buyer within a reasonable distance- the Nucor mill in Seattle. Every week, they send several truckloads to that mill, which buys most of the steel scrap for Washington and Northern Idaho. The next nearest mills are about 6 hours farther, in Northern Oregon. The Nucor mill usually stockpiles several hundred thousand tons of scrap in its yards, as most Nucor mills do.
We (the USA) have not exported significant amounts of steel scrap to China or Japan or Korea in 40 years or more- the vast majority of US scrap steel is made into new US steel.
Non-ferrous, and SS, however, are, indeed, exported. There are a number of buyers, who generally represent middleman processing companies, who travel the USA. It was almost all chinese, for 20 or more years, but the Chinese government has been cracking down on that, and my guess is some of it is going now to Taiwan, Indonesia, and India.
And those guys do, indeed, make regular visits to most US scrapyards, and buy in 40,000lb increments.
There is a great first hand description of how all this works in the book Junkyard Planet, by 3rd generation Minneapolis scrap yard kid Adam Minter, who is now a leading journalist globally on recycling.
He travels with some of the Chinese buyers, and writes about how the whole thing works, from your neighborhood scrapyard, to the smelters in China that are remelting ingots of aluminum and copper.
Great book, and it clears up a lot of myths about how the scrap business works.
Here is a link to him giving a one hour synopsis, with photos, of his book. He doesnt come on until about 5 minutes in.
https://youtu.be/0RZZL4PQdbo
Most scrapyards in the USA operate on very thin margins, and only make money if they can buy cheap, and sell fast. The longer stuff sits in the yard, the less they make.