# precipitating with copper



## solarsmith (Jul 26, 2017)

just tossing out a question on copper plate precipitation from well de noxxed aqua regia. 

I want to know what would effect it? ph? temp? having an air sparger? stiring? adding hydrogen peroxide? should the aqua regia be concentrated? or diluted? Would having lots of plates speed it up enough to be worth the trouble? thanks In advance Bryan In Denver Colorado


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## kernels (Jul 26, 2017)

Hi Bryan, what is the reason that you are considering precipitation with copper plates ? Knowing your motivation might allow us to give you better answers.

I believe to have the single displacement reaction work, the solution must be acidic. In my case copper is usually for when I've done something wrong and am hitting the 'reset' switch. I believe similar to waste treatment, it would help quite a lot moving the solution around, either by stirring or air bubbling.


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## nickvc (Jul 26, 2017)

To add to kernels post it also depends on what you want to cement, I assume you have already precipitated any gold so you are either after the last traces of that or are trying to recover PGMs. 
With any reaction heat and agitation will speed the process but especially with PGMs, they can take some time to cement out so patience is also your friend along with good testing.
I tended to add a small piece of steel at the end which will cement some copper which was then used in the next batch for cementation working on the principle that if copper was cementing any values should be out.


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## Geo (Jul 26, 2017)

I have found that cementing out of a concentrated solution causes some problems with contamination. It seems that cementing from a more diluted solution gives a better final product. The solution needs to be acidic but not so much that it attacks the copper directly. The metal salt is already acidic by nature. Since it is an AR solution, the salt will be chlorides. All chloride salts are acidic so ionic exchange should not require extra acid. A small amount of added HCl will speed the process slightly and stop oxides from forming. Heat will also speed the process but leads to more contamination because the solution becomes more reactive and attacks the copper metal directly. 

The same applies to bubbling air through the solution causing the solution to oxidize the copper metal directly. Agitation helps by dislodging the cemented metal and exposing fresh copper metal and although bubbling air through the solution causes agitation, it also oxygenates the solution making it more reactive which causes more contamination.

In my opinion, it is best to cement from a clear (not cloudy) solution that has been diluted, with a small amount of added HCl to keep the PH low enough to keep oxides from forming.


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## anachronism (Jul 26, 2017)

Kernels raised a very good point. Given the whole host of other ways to precipitate your gold available to us now, why would you go down the route of using copper? Is there a particular reason perhaps?


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## g_axelsson (Jul 26, 2017)

Geo said:


> The metal salt is already acidic by nature. Since it is an AR solution, the salt will be chlorides. All chloride salts are acidic so ionic exchange should not require extra acid.


Chloride salts are not acidic by nature, it depends on what the cation is. For example NaCl is a neutral salt.
http://www.ausetute.com.au/phsalts.html

Göran


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## Geo (Jul 26, 2017)

Thank you Göran. Yes, NaCl is the exception because it has equal amounts of strong acid and strong base. I guess I should have said any chloride with a +2 charge.


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## Geo (Jul 26, 2017)

anachronism said:


> Kernels raised a very good point. Given the whole host of other ways to precipitate your gold available to us now, why would you go down the route of using copper? Is there a particular reason perhaps?



When purity is not required, as in the refinery pays based on assay and not purity, the cheapest and most readily available precipitant may be scrap copper metal. Considering how much gold can be cemented out of solution using a pound of copper, it is much cheaper than almost any other precipitant that I can think of. If it's done correctly, you can easily get gold at 95% purity or better cementing on copper.


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## solarsmith (Jul 26, 2017)

Im experiamenting with several ways to precipitate gold and pgms from aqua regia. my goal is to come up with a process for acid leaching for gold and pgms .
I have a flat copper pipe doing a clean up precipitation after the other test. Ph is about 3.5
it is slow but I have not applied any of the tips that are listed above. I am working with very high grade ore that is high in gold and platinum. I am considering doing a copper precipitation as a second step after doing an ice silver precpitation. the soloution now after a very slow fine vac filter is a deep purpple. It started as clear. On the filter is brown pricipitant. I will add a picture tonight. Bryan In Denver Colorado



small surprise . after it dried it now has a green haze (crust) on top of the brown (now tan) precipitant.


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## Geo (Jul 26, 2017)

Have you had the ore assayed? Or, have you recovered any value from the material yet? I have seen many people swear there is values in an ore sample and stake money and reputation on it, but no one can recover it.


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