muriatic acid is cheap. If you have the time, fill a large rubbermaid with fresh water, add half a bottle of acid, add rock. It should fizz on the surface. LEt it soak for 10 minutes or so, then remove to a new tub of RO water, and let it soak overnight. Test the RO tub for Cu the next day. You'll need to add a big box of baking soda to the acid tub to neutralize it before dumping. Wear old clothes and long rubber gloves. Do this outside and don't drip the acid on your sidewalk.
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Brad
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