[liviug]

I am processing some waste material back into copper sulfate. I had some elemental copper pouder and some copper carbonate mixed with sodium bicarbonate (resulted from washing of copper sulfate ustensils with sodium bicarbonate).

I started by filtering the copper carbonate and washing it 2 times with distilled water. Then I dissolved the teal pouder with some sulfuric acid resulting in the expected copper sulfate solution.

Expecting the solution to contain an excess of sulfuric acid I looked into some ways of converting that and the elemental copper pouder I had from attempting to reduce some Copper citrate with iron.

I added the copper pouder to the solution, poured some H₂O₂ and some H₂SO₄. It worked, the elemental copper, with help from the peroxide dissolved into the sulfuric acid and I was left with a blue Copper sulfate solution. However when heating it in order to concentrate it, I noticed a black pouder forming on the bottom which  exhibits magnetic properties. It is likely iron oxide impurities. My question is how did I get the pouder? what iron compound may have been in the solution that decomposes below 100˙c? It surely can't have been Iron sulfate, since that decomposes at waaay higher temperatures?

How can I remove as much Iron as possible? I can obviously filter it, but there's likely more iron compounds in the solution and it doesn't help I don't know the compounds or quantities exactly.

Thank you.