[Morte42]

Generally speaking anything that cant be extracted profitably will be left behind, depending on the circumstances metals like iron and copper will even end up being discarded in some places. What ends up in a mines slurry might vary batch by batch. Then theres the fact that some things are only dangerous when in gas or dust form or are benign unless in very high concentrations. Sometimes there's a reaction between multiple things in the slurry that leads to the danger. Other times the slurry might be benign until it reacts with something where it is dumped. Acidity and deoxygenation can cause bigger problems than even very toxic mining waste in some circumstances.

Consider that for every kilogram of usable Lithium we extract we need 170KG of raw ore which requires us to remove 1600KG of material. With Platinum we are moving 670,000KG to get a kilo of the metal. The waste vastly outweighs the end product but the end product is where the money is so we know little about the waste aside from that it needs to be disposed of.