New Guy Figuring This All Out

[Crank]

Hey all -
I've already spent a couple days reading through a number of threads here, and obviously this is quite overwhelming. Without a doubt, there is a lot of really great info to digest.
My situation is this - I've come into owning a fair amount of scrap gold plated parts. I also have some scrapped PCBs that I will process, I've not yet done anything with these yet. I wanted to try the gold plated parts first as it accounts for nearly all of the scrap that I have.
I figured the best place to start was using the AP method as the materials used are easy to acquire. I've done some small batch testing and the results seem good, but not great. What I am finding is the plated gold is flaking away from the base metal but the release isn't complete (95% of the plating is releasing). Ive found the composition of the on the underlying material as being a metal foil which contains-
Nickel (Ni) 80-81%
Molybdenum (Mo) 4.5-6%
Silicon (Si) 0.05-0.4%
Manganese (Mn) 0-0.5%
Carbon (C) 0.01%
Iron (Fe) Balance

Based on what I've read, I believe that the AP method may not be the ideal way to go for the plated parts as I suspect there is only gold and not really anything for the AP to react with (which seems somewhat odd as there definitely is a reaction). I am thinking I may be best with the AC method which I am now in the process of trying to figure out. I may do some additional testing this evening and compare the yield.

I dont want to go the Aqua regia direction as it seems to have a higher initial investment that will have no ROI as I don't intend on doing this project more than once or twice.

 

[FrugalRefiner]

Tell us what kind of plated parts you're dealing with. If it's escrap, like the "fingers" on RAM and add-on cards, then the CuCl₂ (aka AP) process is probably your best option. If it's plated material like gold plated jewelry or other similar material, a sulfuric acid "stripping" cell is probably better.

CuCl₂ is best when the base metals like the copper traces and nickel plating beneath the top layer of gold plating are minimal compared to the gold. The CuCl₂ can dissolve the small amount of base metals efficiently and economically. But on items like jewelry, the base metals represent a huge percentage compared to the gold plating, so you'll use a lot of acid to dissolve all the base metals. Here, a stripping cell will dissolve the gold without having to dissolve all the base metals.

Dave

 

[Crank]

Dave,
Thank you for the quick response. I think I may have just found my answer. I realized these parts are coated per ASTM B488 to a thickness that would use nickel as an underplate substrate. Knowing this, it seems that the CuCl2 would be preferred.
I have a few pieces in an AP solution right now that have been processing for about 18 hours. I will check them again this evening to see if there is a complete strip. Its possible I may not have waited long enough for the reaction to take place.
I am using muriatic acid with 31.45% HC and 3% hydrogen peroxide.

 

[Palladium]

18 hrs the ap hasn't even started to work yet. You need to leave it about a week to 10 days and about every 2 days you need to stir the materials around to help the gold flake off. You didn't mention it, but you need an air bubblier also.

 

[Jimbriese]

Also if the solution is green from copper do not add more h2o2 or it with dissolve the gold and in my case precipitated a collide of gold that would not settle. Just use the aquarium pump.

 

[Crank]

I see 3:1 pretty frequently referenced. Does this still hold true?

 

[Shark]

I see 3:1 pretty frequently referenced. Does this still hold true?

No.

If you make up 1 gallon or less a single cap full of peroxide with get it started.
Use an air pump from a fish aquarium as this is a huge boost, it is the oxygen that keeps it working over time.

 

[Palladium]

Save some of the used ap. On the next batch you add the used ap and some hcl, no peroxide needed. The used ap will kick it off 10 times faster than the hcl peroxide alone. Saves a lot of time.

 

[Crank]

Thank you for that suggestion. I suspect I will have to keep all the AP I currently have for my test runs. I did a 3:1 and suspect I may have a small amount of dissolved gold in solution. It may be a good way to figure out the stannous chloride test that comes later in the process.

 

[Martijn]

If there is still solid copper in the solution after a couple of days, most of the dissolved gold will have cemented back out and the H2O2 will be depleted.
If you have doubts, just replace the old with new material to dissolve in the same AP or add a clean piece of copper.
In AP, the gold is actually not stripped, the copper and basemetals are dissolved from underneath.
Leaving gold behind.
Thats why solid plated pieces are not for AP.