AP process and color changes

[KreAture]

I was wondering as I keep reading conflicting information.
Most here seem to describe equations that are really base formulas without the ion aspect.

My understanding is that for the AP process (which I agree with some here should be called the Copper Chloride process) the CuCl2 is doing the work and being very soluble in water. In water however it becomes Cu+2 and 2 Cl- ions. Being highly soluble (757g/l @25c) and the [stt]Cl- ions are what does the work attacking the metallic copper. (CuCl also does some work but due to it's low solubility it cannot be as important in the process directly.)[/stt] Edit: Wrong. The correct reaction is the Cu+2 is what is attacking the solid state copper. It creates two Cu+ ions or Cu(s) + CuCl2 makes 2CuCl.

This attack causes it to become CuCl (not directly CuCl2 which is very important!) which is not broken easily up into ions by water and just sits on the surface of the metallic copper. HCl helps here as it can dissolve it and addition of oxygen can convert CuCl into CuCl2 through the equation CuCl + O2 + HCl => CuCl2 + H2O consuming HCl in the process.
CuCl2 is Cu+2 and 2 Cl- ions and the cycle continues.

But there appears to be some fun stuff.
The colors! CuCl2 when dissolved in water changes color based on the amount of Cl- ions!
Greenish-yellow: high concentration of Cl- which also means high potential for reducing more copper.
Just greenish: middle levels of Cl-.
Blue: Very low in Cl-.

This brings me to the reason I started this topic. All my digging into this lead me to a fun tidbit about complexes. CuCl when dissolved with HCl can form complexes with CO (carbon monoxide) to [CuCl(CO)]2 and that is colorless! This may have been seen by members of the forum when they claim their solutions became colorless, not just pale blue.

Any thoughts on this? Any errors?

 

[butcher]

I do not see any errors.
I am not what you mean by you keep seeing conflicting information...

 

[KreAture]

Well, not necessarily conflicting, but incomplete or tangential.
Statements like "the HCl does not dissolve the copper" is correct, but in order to keep the process going it does not work well to have only CuCl2 in water. It does not move the created CuCl and so it just grinds to a halt.

Also, I felt it was nice to put the colorless complex into perspective. It can apparently even crystallize out.

Edit:
I have also found one needs to read through a thread fully to make sure no corrections are posted later in the thread. Like Göran has done multiple times (like here: https://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=27177#p288235 ) for small discrepancy that made a huge impact on my understanding. I thank him for that.

 

[g_axelsson]

I have also found one needs to read through a thread fully to make sure no corrections are posted later in the thread. Like Göran has done multiple times (like here: viewtopic.php?f=37&t=27177#p288235 ) for small discrepancy that made a huge impact on my understanding. I thank him for that.

You're welcome. Glad to help.

I also points out errors or inconsistency in people's posts.

I believe that you are correct in that CO may form a colorless complex with copper chloride but I think you are overthinking the problem. If carbon monoxide was absorbed into solution to that grade then I think everyone in the vicinity have already suffocated by the carbon monoxide in the air. In that case you have a more serious problem than your copper chloride turned colorless.

A more probably reason is that other base metals in the scrap cemented out all the copper, killing the reaction. For example tin, zinc, lead or aluminium can have that effect and is much more probable than carbon monoxide.

CuCl is a white precipitate when the concentration gets too large or when the Cl^- concentration goes below a certain level. It is actually possible to dissolve CuCl with NaCl instead of HCl, but it's a lot more tricky to get a working leach.
Sometimes when adding water to a copper chloride leach you can get a white precipitate since the Cl^- concentration drops too low.


Last time I used hydrogen peroxide with HCl to etch copper was over ten years ago. It was when Lasersteve first suggested that process... and I did dissolve gold in that process. Since then I've always started it with a bit of old saved copper chloride and some hydrochloric acid. I've also started a couple batches from scratch with pure HCl, mostly from forgetting about a batch where I dissolved tin with HCL and left it in too long.
I've never used a bubbler either, never taken the time to bother with that. A beaker with acid (no heat) and only oxygen absorption through the surface. It takes a couple of weeks or even longer, but I've never been in a hurry. Adding new fingers and picking up any that lost the gold now and then. It creates a nice layer at the bottom with gold foils.

But not warming the beaker can sometimes make it take a long time...


... this is also the reason I do very little refining during the winter...

Göran

 

[butcher]

I have also found one needs to read through a thread fully to make sure no corrections are posted later in the thread. Like Göran has done multiple times (like here: viewtopic.php?f=37&t=27177#p288235 ) for small discrepancy that made a huge impact on my understanding. I thank him for that.

I made a correction to that post today, where I mistakenly said and typed the word lead when I was thinking of white powder of silver...
https://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=27177#p288235

 

[AuPure]

Love the pics Goran!

Right now I'm processing some fingers in jars just like that. Except mine aren't in snow. lol. But the solution does have the gold foils all mixed in with the white copper powder just like your top pic. I too do not get in a hurry. I find that even when the solution is that saturated it still removes the copper and releases the foils. It just happens slower and the copper just converts to that powder at the bottom that is easily dissolved later in fresh HCL. I find that being patient, and not adding oxidizing agents really helps with reducing my waste generated.

 

[KreAture]

My little test-cell seems to work great now though.
I wanted to make sure I am not adding anything I did not want this time as I plan on running the Cl gas method on this and finally test out some "pear-shaped" glassware for the gold drop. The glassware will force the settled gold into the center as it has a conical bottom like a V.
This type of glassware should also be great for the Cl gas bubbling.

Here's my little reaction vessel with scrubber before I added anything active to the vessel:
[youtube]https://www.youtube.com/watch?v=EfzumktdRbY[/youtube]

In vid it is just started with some ram fingers and later a tiny squirt of H2O2. The next day I tested it and now it only took a night to completely remove all base metal from two slot cpu's and a PCI fingerset I used for testing. The picture shows the color it had at this point but again the camera does not do it justice. It was green not blue. The ammount of available free HCl is important for the speed of the process along with the concentration of CuCl2 though and I added a splash more HCl and it turned much greener.

I am so glad I have a buddy that could help me understand this stuff as I really dislike not fully understanding the reactions. He came over today to enjoy the pretty CuCl2 colors :lol:
I think the gold is prettier though.

 

[g_axelsson]

That's a nice setup. I like it!

Göran

 

[g_axelsson]

That's a nice setup. I like it!

I hope you have a proper place to run the system, the first container will have a positive pressure so any leak in it will push HCl vapors out. The scrubber will probably not scrub all the vapors from the air.
Also keep the pump above the top of the liquid level. In case of a power outage or if the hose comes loose the pressure might push enough liquid back into the hose and pump to create a siphon that will drain the acid out of the beaker.

Göran

 

[KreAture]

All valid points Göran!
The pump level has been considered and it also has a backflow valve.
The positive pressure is more or less unavoidable so running in fumehood or similar is still wise.
As for the scrubber... That will mostly depend on bubble size and liquid depth. I have some better tubing coming for that. I plan on using that in the reaction tank as well.

Regardless, I much prefer this to the open setup.
It seems very effichient as well.

 

[KreAture]

Got my new glassware
Pear shaped to focus any precipitate. Idea being to pull out the precipitate while leaving the rest in flask to "stew" in case there is more settling later.

I tested it on some CuCl2 and added iron to create some precipitate and indeed it settled into a nice pile in middle indentation. What a joy!
This is my new favourite flask :wink: