Alcoa Tennessee lead-contaminated aluminum beverage can recycling failure

Early 1990s. Alcoa Tennessee can-stock production fouled by lead from Mexican aluminum scrap. Initially suspected slugging (lead weights for price-by-weight fraud). Root cause: leaded-gasoline exhaust deposited on roadside cans collected by informal Mexican scavengers; lead concentration dropped sharply within 200 feet of highway edge. Alcoa stopped buying Mexican aluminum scrap.

Give you an example. In making aluminum, lead is just as bad as bismuth is to steel. It doesn't alloy with the aluminum, it goes to the grain boundaries. You try to roll the aluminum and it'll just crumble to pieces when you try to hot-roll it, because the lead's at the grain boundaries, it melts, and the aluminum just falls apart into pieces. A number of years ago, Alcoa Tennessee, which makes a lot of can stock, was having all kinds of problems with Mexican aluminum scrap. They traced it down — they had too much lead in the Mexican scrap, and they thought the Mexicans were slugging, because they buy scrap by weight. They thought they were throwing in lead weights, because lead is cheaper than aluminum, just to get the price up. And they couldn't find it.

~30 years prior (~mid-1980s). Alcoa Tennessee finding lead-contaminated Mexican aluminum can scrap. Initial hypothesis (slugging with lead) ruled out by x-ray. Actual cause: leaded gasoline exhaust deposition on highway-discarded cans, no Mexican deposit law. Alcoa's solution: stop buying Mexican scrap.

The other story comes from aluminum. Lead itself is very harmful to aluminum. About seven parts per million lead in aluminum makes the aluminum brittle. They don't mix — the lead goes to the grain boundaries and makes the aluminum brittle. So Alcoa Tennessee was having a problem thirty years ago. They were getting aluminum cans back that had lead impurities. They'd melt everything, do the analysis, find too much lead, scrap it. They had to send it back to the refinery — they couldn't just remelt and recycle. They thought, maybe people are slugging this with lead, since they buy the scrap by the ton — lead has eight times the density of aluminum. It's easy to check — x-ray the bundle and you'll see if there's a slug of lead in there. Aluminum isn't very x-ray dense, and lead is. They did it. They couldn't find people slugging it with lead — that was the first hypothesis.