pin foils with vinegar, peroxide, and salt

[meatheadmerlin]

I came into some unused pins that came on a strip for a pin crimping machine.
They appear to be a brass base metal, with a nickel strike, and golden tips.
I suspected that they were plated very thinly with gold.

I mixed a solution that is roughly:
1 part table salt (iodized)
3 parts hydrogen peroxide (3% USP)
9 parts distilled white vinegar (5% acidity)

I checked it after sitting for 5 days.
The solution is light blue-green.
There appears to be a precipitate I would assume is copper (II) chloride, (CuCl2).
And the pins are starting to flake very thin foils.

I still have a long wait for completion of foil removal,
but I was wondering where to take it from here.
I am thinking that filtering or decanting is in order,
and rinses with vinegar should redissolve the copper chloride.

I plan to save the solution to try cementing copper with steel/iron.
I had heard in another post of a "type of battery" for this.
It uses a sheet of steel connected to a copper plate with a wire,
where the copper should deposit on the copper plate instead of the steel.

I am a little concerned about the formation of nickel compounds,
I have seen a few places where blue-green can indicate copper or nickel,
and have heard how dangerous nickel compounds can be.

Any advice is more than welcome.

 

[chlaurite]

The precipitate most likely consists of - Salt. You shouldn't have copper (in any form) precipitating out anywhere near so soon. Add a few ounces more vinegar, and I'll bet it goes back into solution.

As an aside, with vinegar, you don't really need the peroxide. First, I find that it naturally forms CuCl2 a lot quicker than HCl does; and it takes so long to run anyway (plan on six+ months) that the extra few days you'll gain by kick-starting it with H2O2 doesn't make much difference.

As for toxicity, don't drink it. Neither copper nor nickel in solution pose much of a threat to you - Just dispose of it properly (several threads on this forum explain how to plate down to iron, then convert to oxides and neutralize).

 

[meatheadmerlin]

Thanks for the reply.
I suspect I may need to add more salt over that 6 months to provide more chloride ions for precipitation.
I am so tempted to add more peroxide, but your advice makes me want to wait to see what happens.

 

[meatheadmerlin]

I will admit that my chemistry needs quite a bit of polishing, but
I would presume that my precipitant is in fact copper chloride,
since, upon agitation my solution turn a deeper blue-green.

 

[Lou]

Precipitate is likely CuCl produced by excess metal in the solution.

Remember, the solution only works when an oxygen or a source of oxygenating power (i.e. peroxide, air bubbler, etc) is present. Take that away and you'll see the copper metal reduce the CuCl2 to CuCl.

It would be neat to have a continous ORP/pH monitor in the solution and have it connected to a dosing pump. I bet that six months would turn into a few weeks, or much less!

 

[meatheadmerlin]

I have been agitating the solution to try and
introduce more oxygen, and the reaction appears
to have been happening faster.

I have successfully produced foils, and a precipitate.
There were some small pieces of pins still undissolved,
I removed them to try with new solution later.

I decanted the excess liquid and tried rinsing with vinegar.
Most of the blue-green precipitate dissolved,
but then I was left with a white precipitate.
It seems that the blue-green was Copper(II)Chloride,
and the white is Copper(I)Chloride.

A quick read on wikipedia says the easy answer is to rince with HCl,
but I am trying to avoid using that just yet.
It also suggested that excess chlorine ions
or an ammonia water rinse (NH4OH) might be effective.

I hesitate to add chlorine ions with bleach (hypochlorite),
for fear of dissolving the gold (Acid-Clorox).
And, I don't want to complicate my waste solutions yet
with the addition of ammonia water.
So I tried a rinse in vinegar and salt.
I should have more patience and maybe try adding some heat,
but I decided to also add more peroxide instead.
It seems to be turning the precipitate blue-green.
Time will tell.
This method definitely requires a lot more time
than the regular AP route, but does appear effective.

I will need to run more trials under stricter conditions,
but it seems that ensuring enough free chloride ions
and adding oxygen are very important to the process.

If time isn't a factor, this may prove more economical
in cost of reagents and perhaps waste disposal.
Again, any comments or advice on this process or waste treatment are welcome.

 

[jabukanac]

I wonder if stannous chloride can be effective to test for any presence of gold in the solution i do remember 20 years ago i have placed gold plated watch band in vinegar and salt just for cleaning ,after 3 weeks gold plated band was only stainless still and nice silvery color

I do remember using white vinegar and cooking salt (probably sea salt)

i would like to know how can you test as i believe that vinegar will neutralize solution not chemist by any means would like to hear from someone with more knowledge :?:

 

[chlaurite]

This method definitely requires a lot more time than the regular AP route, but does appear effective.

Wait, what? Lou's suggestion that you already had CuCl kinda made me go "Hmm..." - 5% salt and vinegar (SSV? 8)), saturating with copper after less than a week? Oh...kay, but I deferred to him as having a lot more experience with this than do I.

But then what you just wrote... A lot more time??? You've already dissolved pins and removed foils from them, with vinegar, in under two weeks? Unless I missed the chapter in Hoke where she mentions that the CH3COO anion aggressively attacks copper, I don't know what to make of this.

I've run the same experiement and it took over a week just for the solution to start turning blue/green, with well over two months for even the smallest of pins (those almost microscopic Omega-shaped hair-like ones in mylar ribbon cable connectors) to start shedding foils. Heavier ones (like pin headers / Berg strips) still haven't thoroughly shed their foils almost five months later.

 

[Lou]

If it's a grey powder, it might be copper (I) acetate or its chloride. If it has a verdigris color, then it is likely that acetate.

I've noticed a lot of people getting Cu(I) salts from not maintaining an oxidizing environment (i.e. when no more peroxide or air or whatever is in solution, the copper acts as its own reducing agent and you get this salt deposition). Not that it's a big deal. CuCl is freely soluble to a pretty dark green solution in HCl.

 

[meatheadmerlin]

But then what you just wrote... A lot more time??? You've already dissolved pins and removed foils from them, with vinegar, in under two weeks?

There was also H2O2 in the vinegar and salt.
My solution started turning blue-green the first day.
And, I had produced some foils, but the pins weren't fully dissolved.
The parts of the pins with more base metal exposed readily dissolved,
but the fully plated parts are going to need to sit in a new solution
for a quite a while longer to get up under the plating.

 

[bmgold2]

In case anyone here hasn't seen these videos, here's a couple YouTube videos on copper etchants that might work to remove the gold foils.

[youtube]http://www.youtube.com/watch?v=Q4tWEse2rDI[/youtube]

and one on making ferric chloride

[youtube]http://www.youtube.com/watch?v=43Xsh9J7S-g[/youtube]

bmgold2

 

[meatheadmerlin]

After using the vinegar, peroxide, and salt method;
and seeing how important periodically adding
additional salt to provide sufficient chloride ions is
(often resulting in an immediate visible reaction);
I am wondering about the tradition HCl/H2O2 AP route.

From what I understand:
once CuCl2 is formed it does the work of etching the copper;
aeration will regenerate the solution instead of using more peroxide;
and, typically more HCl is added to increase the available chloride ions.

My thought is, wouldn't adding salt to traditional AP
be sufficient to provide the needed chloride ions,
saving the expense of using more acid?

 

[meatheadmerlin]

I think it is important to note that my pins are not from computers.
They are for use in other electronics, and unused waste from a pin crimping machine.
Another point of interest is that some of the pins seem to be dip plated
while others appear to be fabricated from an already-plated sheet of brass.

The difference is quite noticeable in that the dip plated pins take
a significantly longer time to produce foils, while the others produce foils rapidly.
It may behoove me to cut the dip plated pins to pieces
to provide more exposed base metal for faster reaction.

 

[meatheadmerlin]

It would seem that a second processing is in order.
While Vinegar, Salt, and Peroxide are effective
at producing gold foils by removing brass, copper, or other base metals,
further refining is still necessary.
I should also note that the solution seems to have some difficulty with nickel,
in that it takes longer to dissolve but does in fact dissolve it.
So, in the event that HCl is prohibitively expensive
and time is not a major factor,
pre-processing materials for base metal removal
with this solution could be economical,
yet further processing seems best done with Hydrochloric Acid.
And, I also cannot comment yet on waste disposal procedures.

The main reason for stating this at this point is
that CuCl2 is soluble in vinegar but CuCl is not,
where both are soluble in HCl.
As I understand the chemistry, but have not tried myself,
this could be side stepped if ammonia water were used as a rinse.

But further refining using some method of dissolving
and depositing the gold, be it acid-clorox or aqua regia,
would still be in order, regardless.
Not to mention the additional rinses indicated in Harold's washes
(which seem a bit tricky to track down on the forum).

 

[FrugalRefiner]

Not to mention the additional rinses indicated in Harold's washes
(which seem a bit tricky to track down on the forum).

Getting pure gold(shining) in the Help section.

Dave

 

[meatheadmerlin]

Thanks for the pointer, that's a lot to absorb.
I hope to move into stronger acids and such soon.

 

[meatheadmerlin]

The presence of free H+ ions seems vitally important to the process.
The additional addition of hydrogen peroxide and salt, at some point, prove ineffective.
It seems that the hydrogen ion concentration is also an important factor.

Whatever factors be most important, the peroxide and salt and vinegar solution
definitely has its limits, but still may be a viable option if the reagents are cheap
and further processing for the refining of the gold are planned for.
But, this solution is definitely effective at removing base metals.

If one where to produce their own vinegar from waste sugars,
this could be a cheap alternative to expensive acids for pre-processing.

 

[dwt9999]

This thread has been most helpful, I look forward to trying this method!

 

[meatheadmerlin]

After working with this method for some time,
I ran into a batch that was particularly stubborn.
I suspect there were other base metals present
than I had dealt with in other batches,
perhaps higher nickel levels under the plating too.

I added a small amount (perhaps 2 tablespoons to a pint of solution)
of muriatic acid (approx 30% HCl)
and noticed a definite improvement.

Previously, when my Vinegar Salt Peroxide solution
was reaching saturation it would approach a deep blue color,
and return to a sea-foam green color with the addition of more salt.

After I added the HCl:
it remained a nice green for a lot longer,
turned a lighter blue-green when saturated,
produced more light-green precipitate I could filter out,
made easy work of what was previously so stubborn,
and is working for a lot longer than the original solution.

 

[Topher_osAUrus]

Why not just use regular old HCl and peroxide then if you have it?