I know a lot of water treatment plants remove the gold from their water. I have seen rods from one here in Michigan, the guy told me they removed them about every six months. I was cool but didn't look like much of a money maker. He told me Gold was considered a heavy metal and it was required that they remove it like all other heavy metals. I suppose in a big enough city the Gold produced might be profitable.
Sounds alot like removing gold from pyrite ash, at least this is old school and not something being done by only a few rare locations.
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