That's contact water, dude. It's not supposed to be clean. they have those ponds to manage their water so it doesn't get released to the environment. They then take the water from the ponds (and TSFs) and run it through the treatment plant or some other form of treatment and then discharge it once it meets water quality guidelines.

tailings storage facilities (TSFs) are what you're thinking of. Settling ponds are those that are specifically designed to settle out suspended solids. TSFs will often contain a pond on them, but much of the impoundment area is beach (with varying degrees of water content). what I'm getting at, is that TSFs are more solid than water, while settling ponds are more water than solid (AFAIK). Mining terminology is weird.

And yes, in some cases tailings are reprocessed when technology catches up. It's kind of hard to do though.

Oppon smiles on you

True, but mine water quality is a huge barrier to successful mine closure.

This has the potential to allow for way less chemical treatment, and therefore lower costs of closure and less likelihood of abandoning mines.... Provided it can also address other metals too.