# Stockpot copper problem



## Bluebloomer (Aug 24, 2017)

Hi all,

Due to a lot of health issues (inguinal hernia, with damaged nerves, broken foot in 9 places, etc) I am way way behind all my information, and projects with my gold recovery.

Last couple of days I'm trying to clean and sort all the mess out, because I have way too much buckets, and jars filled without knowing what it is.

I was checking out my stockpot, and noticed all the copper had a solid white plating / cement on it. Put a piece in fresh HCL and it cleaned right up. But there is a bunch of copper in about 20 L of stockpot residue, and it is all white / grey.. 

Can you guys explain what is is, and how to fix it, besided cleaning the copper in fresh HCL?

I suspect it is either tin metal, of perhaps even silver because I have added AR that failed to drop the gold, so there are different metals in the stockpot, perhaps even Pd. 

I'm afraid that if I clean all the copper with HCL and put it back in the stockpot, the reaction repeates it self, and the copper turns white / grey again. Any suggestions any one ?

Thanks, Gilbert


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## butcher (Aug 24, 2017)

Many metals make white salts, besides the metals we are normally concerned with like lead, copper, silver.

You said that fresh HCl "cleaned up" your white powder (what ever that means), CuCl (one of the many white salts) is soluble in copper and will form a green (or brown depending on concentration and oxygen levels...) solution.
Silver chloride AgCl (another white salt), is basically insoluble in HCl (only tiny amounts can form soluble AgCl2).
Lead salt also are fairly insoluble in very dilute HCl acid solutions, much less soluble cold than hot. (a few drops of H2SO4) will convert and soluble lead chloride salts to insoluble lead sulfate...

There can be several ways to go about this (trying to figure out what the white salts are), I will just discuss on way I may go about it.

Lets say I am only concerned a few of the metals that form white salts.

In the stock pot, I used copper to cement or replace metals that were in solution below copper in the reactivity series.
https://en.wikipedia.org/wiki/Reactivity_series

Note: if iron was used(to cement metals), I could end up with many more metals to deal with which would have cemented out, and I would have besides iron compounds or salts other elemental metals,basically I would have many more metals to deal with... We will discuss it a little bit more later on.

Cementing on copper, the metals below copper have converted to metal metal powders (my precious values), and possibly silver chlorides, lead chlorides, maybe (some copper I chloride, depending on free HCl in solution), tin chlorides are fairly soluble(not metastannic acid) so basically tin would not be much of concern as being the white salt. (mercury, and tungsten salts are normally not of concern in most of our stock pots).

So I can take the white salts and add fresh HCl (No oxidizers at this point), I can end up with a green or brown solution, if green CuCl2 is formed (from the white insoluble CuCl salts), or it could go brown (CuCl and CuCl2 in solution), adding a little more dilute HCl and a mild 3% H2O2 oxidizer will form the green CuCl2 solution. leaving me with white powders which did not dissolve, I can let these settle and decant the copper solution from them. This solution can be saved for use as a leaching solution...

Lead chloride is Fairly soluble in almost boiling hot water, silver chloride is still insoluble (trick is to keep solution hot and still let the fluffy white AgCl salts settle to separate them) decanting the soluble lead salts (clear solution) while still hot, removing the solution to a cooling vessel for the lead salts to re-precipitate as long crystals (when undisturbed) this same cooled water can be returned and reused to gather more lead salts from the original batch, usually I use two batches of water and reuse the same water to keep toxic waste to a minimum, using one hot while the other is cooling....

Now your pretty much left with silver salts, once washed well these will darken in sunlight, converting a portion of these to silver metal mixed in AgCl, a little HCl in the water above them will keep the batch white (AgCl) which can be saved with a little water cover in your silver chloride jar...

All right lets get back to what if you cemented with iron in your stock pot. (not normally always the best choice, but sometimes needed).
The iron will replace many more metals from solution, cadmium, cobalt, nickle, tin, lead, antimony, bismuth, copper, tungsten, silver, gold, and the platinum group, besides the iron hydroxides or compounds, most of these would form elemental metals and salts depending on acidity, and oxidizer agents left in solution of the stock pot. so basically we would have to redissolve these back into solution with (say) HCl and an oxidizer, I would start with one that would not dissolve much or any of my more noble metals, using say HCl and 3% H2O2, at first to put many of the more reactive metals in solution before going after those which need a higher oxidizer to oxidize them into solution... Leaving with less to deal with (note some of the iron salts are not easily soluble like the hydroxides or the rouge red (rust) iron compounds...
I think you can figure it out from here.


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## Bluebloomer (Aug 25, 2017)

Butcher, thank you for the elaborate explanation ! It helps a lot..!

What I meant earlier, is that all the copper in the stockpot has a solid white/grey layer on it, and it can not be washed off with water. It is cemented on the copper like a plating. Hot water, or spraying with water does not remove the coating on the copper. Putting some pieces in fresh 30% hcl and the layer on the copper goes away.

I should of conducted a test to put more copper with the white layer in fresh hcl, and see what the precipitate does if the hcl is left standing so it can settle after removing the copper. Cannot make a picture at this time as I am not home for a couple of days, but I get the idea that the stockpot does not do anything at this time as the copper is covered in that white grey/layer and even scratching the copper barely removes it. It's like the copper is completely pacified. What ever it is, it attached to the copper.
I added 250ml of fresh AP with 250 ml of fresh HCL 30%, and I'll leave the stockpot bubbling until sunday, to check it out.

I only use iron for the waste treatment, or totaly botched jobs. Then I put the acid in a bucket with iron to collect the precipitate, incinerate and start over, by leeching in HCL.
As for the lead, cool trick and I will use it in future jobs. H2SO4 is always used in AR to precipitate the Pb.

Over time I have taken many notes from members like you, the tips and advice are priceless and so again thank you for that, you always seem to take the time to reply in a very helpfull way.

With all the information given by you, I still have the question what metal could pacify the copper in such a way it cannot be sprayed off with water, cold or boiling. It cannot be Sn, or Pb as these salts should wash off easily, AgCl should settle on the bottom and not on the copper. 

I should add that I never tried to test my solutions with stannous chloride, I assumed the gold I was after precipitated, then I just added the remaining acid to my stockpot and let it bubble away. The source of gold I was after was, a batch of about 200 AMD/Intel cpu's, 2 pounds of ceramic cpu's , and a bit of ENIG plating from older PCB's. Could it be a noble metal salt like Pd or Pt plating on the copper ?

When I get home, I will siphon the stockpot, collect the precipitate, and make a picture of the color of the liquid, and a picture of the copper. Then I will wash the copper with the solid white layer in dilluted HCL, collect the precipiate again, and see what it does with hot water.

And yes, from now on I will test any solution with stannous, once the new lab grade SnCl2 is in..


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## g_axelsson (Aug 25, 2017)

CuCl. 

For more details, see Butchers post above.

Göran


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## butcher (Aug 25, 2017)

Testing and observe what you see in those tests, the answers are there you just have to see them.


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## Bluebloomer (Aug 26, 2017)

The language barrier makes it sometimes a bit difficult to fully understand what you guys are really saying but I know what to do now. I will try to update this post as soon as I'm back home.

Is it oke to assume that if I remove all the copper from the stockpot, then clean all the copper with fresh and dillute HCL, then add it back to the stock with a bit more free HCL, the problem could be solved ?
The CuCl will convert to CuCl2 with HCL, and this can be used for AP, and then add some more free HCL to the stocpot to prevent the problem in the future. Correct ?

Only thing I still wonder is, why this white metal salt is so firmly attachted to the copper, is it because copper metal and copper salt like to bond, because there are both copper ?


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## butcher (Aug 26, 2017)

I cannot explain why, but if we hang a string in a jar full of saturated salt NaCl, or sugar, the crystals like to grow on the string and cling to it, something to do with the crystal seed and liking to bond to other salts as the crystals grow....

HCl will dissolve all salts soluble in it back into solution as ions, CuCl to CuCl2 for example.
silver chloride (reduced silver powder black or violet) or lead chloride... will still be insoluble in HCl.

CUCl2 in solution is green (excess HCl, water and a little oxidizer oxygen), saturated or low in acid or oxidizer some of the green CuCl2 converts to CuCl in solution making the solution brown, (which can be converted back with addition of HCl and oxygen), when heavily saturated the brown solution of CuCl2/CuCl will begin to precipitate a white powder of CuCl salts...

Everyone should do a thorough study of the copper II chloride leach to gain a good understanding how it works and why it works, and also understand how oxidizer too much or too litle affect its operation on metals like thin gold, keeping the solution active to dissolve more copper, and not attack gold, how to regenerate the solution... Laser Steve had a very good document on his web site, which was a good place to begin that study....

silver chloride darkens in the sunlight, and in water where the fresh HCl has been rinsed out, only the thin surface of the AgCl cluster is converted to silver metal, fresh HCl will normally make it white again as the silver coating is converted back to AgCl, silver chloride is insoluble in HCl, or hot or cold water.

Lead chloride is fairly insoluble in HCl, almost totally insoluble in cold water, (not completely so remember it can still be in the water as a toxic substance), and becomes much more soluble in hot water.

Black powder (besides silver chloride discussed above can be a dirty (copper/gold) gold powder, which is not soluble in HCl, or hot or cold water, it can be washed (Harold's gold wash, and refinined)

silver chloride is soluble in ammonia (CAUTION HERE the compound can be extremely explosive if dried, touched with a feather or the temperature slightly changed).
If dissolving AgCl in ammonia, do not store it, but as soon as possible add acid HCl (or HNO3) acidification of the solution, will again re-precipitate the AgCl making it safe again.
(Silver is not effected (or the dark coating) of silver converted in sunlight).
This being dangerous is not normally needed!!!

This gives you a way to test, and separate, or even refine these salts.

Gather the white powders and do some experimenting with them, once you do you will understand much better.


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## Bluebloomer (Sep 4, 2017)

Butcher, thank you for the additional information. Very helpful indeed !

I have read that tin II chloride will reduce copper II chloride to copper I, is this true and how does this affect the AP / Stockpot copper issue ? Too much tin in solution might contribute to the rapid reduction of Copper II to copper I ?


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## butcher (Sep 5, 2017)

Reduction of the CuCl2 to CuCl is not much of a problem to deal with.

Making colloidal gold is the big problem, the colloidal gold will stay a colloid in solution, you cannot cement it out (as it already has a full shell of electrons) and cannot be reduced by copper or another base metal, and cannot be reduced with a chemical reducing agent.

Tin or its salts are a big problem with recovery or refining, even in your stock pot...


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