Copper Nitrate Distillation

jakospence

New member
Joined
Jun 2, 2019
Messages
4
So I am moving from my house and wanted to reduce the number of jugs of copper nitrate waste that I’ve been collecting from silver refining so I have been using the method that I’ve seen on this board and also in NurdRage’s video where you convert the copper nitrate to copper sulfate and distill off the dilute nitric.

It’s been going well, as I have recovered a ton of distillate, but I decided to try to cycle some of the aqueous layer that’s on top of my copper sulfate beaker because I noticed that it had a decent amount of NOx collecting at the surface.

After THREE hours I stopped it because the volume of the boiling flask had only reduced by about 50% and I had no precipitation of copper sulfate that I usually get which causes me to stop early due to bumping despite having boiling chips in the flask.

What doesn’t make sense to me is that the solution in the boiling flask is a deep emerald green, and not the rich blue color that is easily recognizable as copper sulfate.

Another strange observation that I had is that after about 10 minutes of boiling, the vapor temp was at 119°c which made me think that I was distilling off azeotropoic nitric acid from the very beginning. However, about 90 mins later, I was only at about 108°c and when I turned off the heating mantle, it was about 103°c.

Once the column had cooled off enough (but still too hot to remove) I dropped a thermocouple down to the solution in the flask and it was still about 255°c making me think that I had a ton of excess sulfuric acid in there, which would make sense as most of the copper had been converted to copper sulfate prior to the previous distillation.

The question I have is, what could this green solution be? My nitric has only been used to refine sterling silver and after cementing out the silver, I would always leave it in the stockpot with excess copper for weeks to ensure all less reactive metals dropped out of solution.

The only green sulfates that I know of are nickel, iron and chromium, which all could be present in Raw silver, just not as common in sterling. As far as nitrates are concerned, I am only used to seeing my silver nitrate looking this deep emerald color when there is some palladium present, which it shouldn’t be because it’s been in the stockpot with copper for so long.

Any ideas?
 

butcher

Moderator
Staff member
Moderator
Joined
Jan 6, 2008
Messages
9,905
Location
Pacific NW
Most likely the green is from nitric remaining in solution, the blue copper salts and the red gases of NOx can make the solution look green, it sounds like you just need to proceed to complete the distillation process. I would not be too concerned of temperatures at this point, your not going to distill off the sulfuric or sulfates.
 

jakospence

New member
Joined
Jun 2, 2019
Messages
4
Thank you for the suggestion! I just kept going and you were right, everything eventually stopped boiling, I poured off the distillate, and whatever was left in the boiling flask I labels as dirty h2so4, and that's good enough for the work that I'm doing!
 

g_axelsson

Administrator
Staff member
Administrator
Moderator
Joined
Nov 17, 2007
Messages
5,499
Location
Sweden
I think Lino might be a better man than me to answer this but here I go...

Copper sulfate gets it's blue color from complexing with five water molecules. Strong sulfuric acid has the ability to rip off loosely attached water molecules so the copper sulfate solution changes color. Anhydrous copper sulfate is white.

When you heated your solution you drove off water until the liquid left was strong sulfuric acid and the color of the dissolved copper sulfate turned green.

I have vague memories of a chemistry lesson 35 years ago where we heated copper sulfate in several steps until it turned into copper oxide, at the first step it turned green when water boiled off.

But that's just my theory.

Göran
 

Latest posts

Top