Step by step instructions for AP processing circuit boards

[haveagojoe]

In the video section there are two video's by Sreetips one using nitric and one using AP. HERE & HERE The nitric is much quicker and the dilute AP is much slower, actually much much slower. It would be interesting to see on a time line where the 2 parts Hydrochloric Acid 1 part peroxide falls.

I would not think it's as fast as nitric, I guess it depends on the concentration of nitric and the temperature. The main advantage of course would be that the fumes are less noxious. In my experience even small amounts of peroxide will definitely dissolve some gold along with base metals. It's not a huge problem as the gold eventually cements out again as black powder because of the copper when the oxygen level falls. Peroxide does make the leeching process much quicker but then the filtering becomes much slower and the black powder is so fine it gets stuck in the filter. It can be a useful approach on larger plated items such as SMA connectors which I think are brass- at room temperature it can release the gold in 24 hours in large flakes, before the underlying base metal has much of a chance to be attacked, whereas copper chloride alone is very slow and only partially releases the gold plating before attacking the base metals and forming brown-green ferric chloride, at which point it slows almost to a halt.

I think generally the usual copper chloride approach is best for fingers and pins but extra peroxide does have its place with larger items, I would not attempt to use it to digest all the base metals as with nitric and I would never go as high as a 2:1 ratio, but for certain types of scrap a generous glug of peroxide can really help things along, I just have to just expect to deal with black powder in the filter, and the larger size of the foils also makes filtering slower.

An approach I haven't tried yet is to avoid filtering the foils altogether, simply removing the stripped base metal carcasses by decanting or sieving before adding more peroxide to dissolve the foils completely and then cementing everything out as black powder using a piece of copper. I think that could work quite well for these plated connectors but it would be a rather dirty precipitate containing copper and zinc etc.

One thing which is not clear with the proposed 2:1 ratio is the concentration of HCl and of Peroxide used. Perhaps if it were meant for >30% HCl and 3% Peroxide it would make sense but still I'm sure gold would be dissolved.

 

[Yggdrasil]

I would not think it's as fast as nitric, I guess it depends on the concentration of nitric and the temperature. The main advantage of course would be that the fumes are less noxious. In my experience even small amounts of peroxide will definitely dissolve some gold along with base metals. It's not a huge problem as the gold eventually cements out again as black powder because of the copper when the oxygen level falls. Peroxide does make the leeching process much quicker but then the filtering becomes much slower and the black powder is so fine it gets stuck in the filter. It can be a useful approach on larger plated items such as SMA connectors which I think are brass- at room temperature it can release the gold in 24 hours in large flakes, before the underlying base metal has much of a chance to be attacked, whereas copper chloride alone is very slow and only partially releases the gold plating before attacking the base metals and forming brown-green ferric chloride, at which point it slows almost to a halt.

I think generally the usual copper chloride approach is best for fingers and pins but extra peroxide does have its place with larger items, I would not attempt to use it to digest all the base metals as with nitric and I would never go as high as a 2:1 ratio, but for certain types of scrap a generous glug of peroxide can really help things along, I just have to just expect to deal with black powder in the filter, and the larger size of the foils also makes filtering slower.

An approach I haven't tried yet is to avoid filtering the foils altogether, simply removing the stripped base metal carcasses by decanting or sieving before adding more peroxide to dissolve the foils completely and then cementing everything out as black powder using a piece of copper. I think that could work quite well for these plated connectors but it would be a rather dirty precipitate containing copper and zinc etc.

One thing which is not clear with the proposed 2:1 ratio is the concentration of HCl and of Peroxide used. Perhaps if it were meant for >30% HCl and 3% Peroxide it would make sense but still I'm sure gold would be dissolved.

In the beginning that ratio was used and no air bubbling.
One simply added more Peroxide to keep up the Oxygen level.
Later it was discovered that one really do not need the Peroxide at all.

 

[Shark]

Using nitric on fingers I have had them stripped, washed and dissolved in AR, and dropped in one day. Would have had the wash cycles done but the wife ask to go out and eat. She won with no argument from me.

 

[haveagojoe]

Miniature experiment today on removing contaminant metals from saturated AP solution with electrolysis- it went well, I only ran it for a few hours and the solution was noticably cleaner after depositing 0.5g of metal from 150ml. I ran it at 2.5V and it drew only around 100mA. I started with pencil lead electrodes, then switched the cathode for a copper one; both seemed to work equally well but I'll wait for some proper graphite electrodes to run a bigger experiment. It's possible to use stainless steel for the anode but it can introduce cadmium chromium into the solution so best avoided.

Chlorine gas production was not insignificant even at that tiny scale, it will need to be properly managed in a larger setup.

Definitely an idea worth pursuing though in my view.

 

[Yggdrasil]

Miniature experiment today on removing contaminant metals from saturated AP solution with electrolysis- it went well, I only ran it for a few hours and the solution was noticably cleaner after depositing 0.5g of metal from 150ml. I ran it at 2.5V and it drew only around 100mA. I started with pencil lead electrodes, then switched the cathode for a copper one; both seemed to work equally well but I'll wait for some proper graphite electrodes to run a bigger experiment. It's possible to use stainless steel for the anode but it can introduce cadmium into the solution so best avoided.

Chlorine gas production was not insignificant even at that tiny scale, it will need to be properly managed in a larger setup.

Definitely an idea worth pursuing though in my view.

There should not be Cd in Stainless steel.
Unless you have some kind of odd alloy.

 

[haveagojoe]

There should not be Cd in Stainless steel.
Unless you have some kind of odd alloy.

oops sorry I meant chromium. Editted to correct.

 

[4metals]

Definitely an idea worth pursuing though in my view.

Worthy of a separate thread perhaps as you are dealing with the waste not the foil releasing process. But an interesting concept to follow for sure.

 

[haveagojoe]

Worthy of a separate thread perhaps as you are dealing with the waste not the foil releasing process. But an interesting concept to follow for sure.

Yes I intend to make a full post once I've got something to show. I've found a graphite rod I can use for an anode so I'll make a start tomorrow.

 

[4metals]

Yes I intend to make a full post once I've got something to show. I've found a graphite rod I can use for an anode so I'll make a start tomorrow.

Great, but not here, start a new thread and name it appropriately so the title reflects the topic so future members can find it in a search. At risk of sounding like a pain in the arse, it is getting harder and harder to keep the forum organized and searchable that is why I stress this point.