For years I collected the sludge from the bottoms of my flow-through wet
tumbler system, thinking that there must be some precious metal in it, but
always wondering if there would be enough to make it profitable to send
off to refining.
I would ask the reps from the refining companies what they thought and
they didn't get too excited about it. They would ask for samples, say,
"send it in and we will see", not especially encouraging. Turns out it was
16 years of accumulated sludge, dried out, weighed 171.5 lbs.
The yield was 1.26 ozt gold, 138.27 ozt silver
Total was 139.53 ozt precious metal or 9.57 lbs. So my waste stream was
5.6% precious metals.