Foils wont get clean completly

[Marcel]

Well this sounds trivial maybe, but has been a problem for me for months.
1. I bought 500 bare PCB PCI cards - so they are all the same.
2. Cut off the fingers and one gold plated area on the PCB.
3. Used AP to harvest the foils.
4. Washed the foils over and over in HCl. Let it soak in HCl overnight. Solution gets green, but the foils remain "dirty"

But now these foils have a red/brown layer on one side. I assumed it was copper, but it is very hard to get rid of that. I doesn´t seem to dissolve in HCl.
Anyone made a similiar experience ? Can it be some other metal that is involved here?

Last time I made the mistake and started the HCl/Cl leach after washing it several times , I never recovered the gold that was in the batch. So it cruicial to have the foils cleaned befor next step. But how?

EDIT: After checking some cuts that were not completly processed I found the redish/brown stuff to be some cement, maybe copper. I never had that, it can me wiped off from the card edges, but of course not from the foils. When applying HCl/Cl it will remain undissolved in the vessel.

 

[tek4g63]

I'm still pretty new at this but I do ase the AP process for recovery and have tried the HCL/CL on a tiny scale to get use to it.

I believe that even if the foils are a little dirty with copper you can still do the HCL/CL refine and get your gold. You may just hav to do the refine process a second time to clean the powder throughly. But I would check out the "Data" thread and do the math to be sure and only use the exact ammount of HCL/CL to refine your foils. Because you are supposed to delute the solution with water before you drop your gold, and if the solution is too delute to begin with it may be difficult to get your gold out.

But again I'm very new at this so I hope a more experienced member will correct me if I'm wrong.

Also I noticed you said that you change out the HCL when it gets green. I wouldn't do that, because the greener it gets the better it removes copper. The HCL is not doing a good job removing the copper untill culpric chloride is formed. (I probably spelled that wrong, I've been awake for over 30hrs straight now, please forgive me).

Good luck and thake care!

 

[goldenchild]

Honestly... you dont have to "wash" your foils. You dont even have to totally rinse the foils clean of the ap. You could simply decant the ap as best you can put the foils in a beaker and use HCL-CL or AR. After digestion a really good filtration is what you should focus on. This will get any organic material out of solution. So my point is, dont get too anal about washing your foils.

 

[philddreamer]

I agree with you Mario!

Phil

 

[maynman1751]

4. Washed the foils over and over in HCl. Let it soak in HCl overnight. Solution gets green, but the foils remain "dirty"

If you are going to do this, adding some heat really helps. Heat to below boiling but don't let it cook dry!

 

[Geo]

why would you not reclaim the gold from hcl/Cl? if all else fails, you can cement the gold out with copper. when i first started these processes, i was very wary of taking gold i could see and turning it into a liquid. take a known weight of foils (lets say three or four grams) out of what you have now and dissolve it in hcl/Cl.filter into a clean vessel. any non-metal will stay in the filter. let the solution set out for 24 hours uncovered. dilute with equal volume of water. add the equal weight of SMB in solution of water to the solution and stir. you should see an immediate shift in color from some form of yellow, yellow-green to clear and then a murky brown.let everything settle till the liquid is clear. if the solution was green, you may need to reprocess to remove any impurities.

 

[Marcel]

I assume, that I didnt us enough water/HCl and the copper cemented right back, because the solution was too saturated. Seems to be a much thicker copper layer on the boards as usual..

 

[Geo]

ahh, i see what you are talking about. i looked at the picture closely.i dont think it is a contamination you see, the gold on one side is shiny and the other side is dull and looks brown.i think this is just a diffusion of the light because they look very clean to me. my foils always have a shiny side and a dull side.

any one else?

 

[maynman1751]

ahh, i see what you are talking about. i looked at the picture closely.i dont think it is a contamination you see, the gold on one side is shiny and the other side is dull and looks brown.i think this is just a diffusion of the light because they look very clean to me. my foils always have a shiny side and a dull side.

any one else?

I think you're on it Geo! :mrgreen:

 

[goldenchild]

I agree with you Mario!

Phil

 

[Marcel]

Now next updates:

- tried to process the remaining cuts with some remaining fingers.
- Instead of further trying AP, I prepared HCl+Cl and put the unfinished cuts into it.
- Warmed the solution
- after some time it turned black, (chlor evaporated)
- tested with stannous chloride = negativ
- Most of the gold was gone now, only some copper on cuts were left.
- Dropped in a piece of leaf gold, wasn´t affected or dissolved.
- Took the solution and filtered it, some goldflakes + Cu(II)chlorid powder
- dropped in some aluminium chunks, a hefty exothermal reaction started and lasted for about 30 mins, always adding little alu chunks.
- When it ended filtered the dark purple solution angain and received some purple powder in the filter.

- This should be the unknown metal involved with my AP problems.
- What is this that I dropped? What should I do with it next?

Marcel

 

[qst42know]

Aluminum would cement near any metal in solution, so that does not narrow it down at all.

What is in your filter looks to be mostly cemented copper, and would include what didn't dissolve in HCL/Cl.

The dark on the backs of your foils I suspect is only copper protected by some poly bonding agent that sticks the copper to the board. If you want it all to digest try incinerating the foils after recovering them from the AP.

 

[Harold_V]

If you want it all to digest try incinerating the foils after recovering them from the AP.

I have recommended that as long as I've been on this forum. It has been, for all practical purposes, ignored.
I can't stress enough, the value of incineration.

Harold

 

[kurt]

I would suspect nickel – they use (or so I have heard) a thin plate of nickel between the copper & gold to keep the gold from migrating into the copper over time.

Kurt

 

[Harold_V]

I would suspect nickel – they use (or so I have heard) a thin plate of nickel between the copper & gold to keep the gold from migrating into the copper over time.

Kurt

I am not familiar with nickel responding in that fashion. What I expect is that the purple color is colloidal gold, and I somewhat suspect there's traces of tin involved.

If I was to make a recommendation, it's pretty simple. I'd incinerate, screen, wash in hot HCl, followed by a good rinse, then dissolve with AR. The incineration process is critical to success, as is the HCl wash afterwards. I'm not the least bit concerned that it may have already been subjected to HCl----for it was not incinerated previously. That changes things considerably.

Incineration---the magic bullet of refining.

Harold

 

[kurt]

Opps – my bad – I should have stated that my reference to nickel was to his original post asking why his foils have a dull tint on one side & not the clean gold look of the other side.

Thanks for catching that Harold – concerning the purple in the filter I agree with you Harold so no need for me to comment further on that.

I think the reason so many do not listen to your advice about incinerating when it comes to foils is because the word incinerate suggests the use of a direct flame which in turn suggests the use of a torch which of course is going to blow all the foils away so they skip this “important” step out of fear of blowing away all their foils – even though Hokes – your self - & others have talked about incinerating – in a pan – to red hot – on a propane burner (I use a single burner propane camp stove) something gets lost in translation when the importance of incineration is suggested with foils

In my Fire Assay Home Study Course book (from Action Mining) it talks about the need of doing an oxidation roast.

Maybe what we need to do here is use the word incinerate when referring to the use of a direct flame (such as incinerating contact point to rid them of oil & grease) & then use the word roast when using indirect heat – such as foils in a pan on a burner &/or in a crucible in a furnace.

Kind of like the difference between boiling a solution & evaporating a solution.

This of course is just a suggestion to help with the understanding of the importance of this step & not skipping it out of fear of blowing everything away because incinerate implies direct flame which in turn implies torch – so the step is skipped out of fear of blowing away foils – when really what needs to be done is to roast them.

Kurt

 

[Harold_V]

That's certainly a consideration. However, in roasting, you may or may not achieve the desired objective, which is to remove carbonaceous materials. It's all temperature related, and is achieved by heating to the point where carbon combusts. That requires a red heat (1,100°F+), and free oxygen (often supplied by a torch without using any fuel) to ensure it is all consumed.

You can play a torch on foils, too, but you have to use considerable wisdom. Low pressure and a lazy flame. They are not only easy to blow about, but easy to melt, too, although, in truth, melting them isn't a problem, assuming your objective is to dissolve them anyway. They're still so small that they will readily dissolve.

Bottom line---what ever one may decide to call the operation, heating to eliminate unwanted materials, and to oxidize undesired base metals is always a good idea. The purple material shown could prove to be very difficult to filter once values were dissolved without that very important step. That's a lesson I learned long ago, when it took me the better part of two days to filter a liter of solution.

Harold

 

[butcher]

Tin can rob you of value, and gives you many troubles; incineration is key to keep this from happening.

I have learned how valuable Harold’s advice is on incineration; especially when dealing with electronic scrap.

Tin is also found in many other forms of scrap.

Tin not only gives trouble filtering, but will reduce gold in solution, this gold will not precipitate, you can miss it in testing solutions (the gold is already reduced to colloid’s) so it will not show up in stannous chloride tests for gold in solution.

Incineration how can anyone recover or refine values without it? If they do not use the process I would like to buy their waste, it would be loaded with valuable metals (most likely richer than many ores mined).

 

[kurt]

Yes – I agree – incineration (or an oxidation roast) & then treatment with HCL is vital to true success. Hokes talks about its importance in her book. Harold as well as others have stressed the importance of it here on the form repeatedly - & yet the vital importance of it some how gets lost in translation.

I could be wrong but I can’t help but believe its because the word incinerate invokes the idea of the use of a direct flame which in turn invokes the idea of the use of a torch & so the step gets skipped out of fear of blowing their foils away.

The Action Mining Fire Assay Home Study Course book & their reference to doing an oxidation roast (as well as doing a reduction roast) was a big help in helping me to understand this.

I highly recommend the book for anyone doing refining – even if you have no plans of actually doing fire assay. Their reference to reduction roasting (750 F) & oxidation roasting (1350 F) as well as their detailed explanation of different fluxes has been a huge help in the success of my refining.

Kurt