Copper Nitrate / Aluminium Reaction?

Hi, I’m hoping someone can help me identify what I’ve produced.

I was trying to produce a fine copper powder by reacting Aluminium with Copper Nitrate. I started with some copper wire and some 30% nitric acid. I kept adding pieces of wire to the acid until they stopped dissolving any more. The solution was still mildly acidic at this point, but I guess the Cu Nitrate concentration had reached saturation and thats why the acid wouldn’t dissolve any more metal?

In any case I then added some Al foil as well as the pull tab of a soft-drink can that I had scratched up to get through the oxide layer on the surface. The foil floated, the tab sank but apart from that Nothing Happened. I did a little more research and found out that Cu Nitrate and Cu Sulphate find it difficult to react with Al metal because of the oxide layer, and the addition of Cl- to the mixture will help the solution penetrate through to the Al metal itself.

I grabbed my table salt and sprinkled liberally. Two changes were immediatley obvious. the first was that the areas of around the NaCl became distinctly green in colour and the second was that both pieces of Al began fizzing. Cu metal began forming and all was well.
After a while the Al was consumed and I added more. Again, nothing happened until I sprinkled some more NaCl on the floating ball of Al foil. The salt began to eat through the foil as if it were some powerful acid. Then something rather peculiar began happening…. I could see the Cu metal forming on the Al and then flaking away, and then the Cu was immediatley dissolving again and a decent quantitiy of NO2 was being evolved. I guess there was a bit of an equlibrium developed because of the excess HNO3 that was causing copper to be created and then immediatley dissolved again.

Anyway, I continued to add Al metal until all reaction ceased. By this stage the solution was a dark green-black colour. And there was a ppt of both (I assume) Copper Metal and another solid which is a greyish white colour.

I decanted off the dark solution and rinsed the ppt a few times. The grey-white material does not seem to be soluble in water, and there is at least an even quantity of when compared to the Cu metal…maybe even more of it.

My questions are
1) Any clues to what this white ppt is? Perhaps an Aluminium Oxide?
2) Given the point is to try and obtain fine copper powder, any suggestions for how I could separate the copper from the white ppt?
3) Any clues to the indentity of the dark green-black solution?. I thought maybe Copper Chloride, but in the presence of excess Al should it not have reacted to form Cu metal and Al Chloride?
3) Any suggestions for a better way to (Chemically) produce a Cu powder from Cu metal?


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