Copper dissolves while cementing.

[zumka]

Hello, everyone.

I searched a lot but couldn't find a similar problem and i hope i didn't open an unnecessary thread.

I have a stockpot with AR waste in mostly. And a few failed attemps which i directly put it in without causing more acid waste. (Total around 5 litres of water, hcl, nitric, a few ml sulphuric, sulfamic, urea and smb)

I tried to cement out but the copper plate and copper wires i add in dissolved after a few hours. And no solid at the bottom. Waited anyway till morning with air-bubble in, tried two different times but same problem. (Expecting minimum 4-5 grams gold alone just from failed attemps i added in)

So, what am i missing? What should i do?

Thank you in advance.

Zuma.

 

[Yggdrasil]

Hello, everyone.

I searched a lot but couldn't find a similar problem and i hope i didn't open an unnecessary thread.

I have a stockpot with AR waste in mostly. And a few failed attemps which i directly put it in without causing more acid waste. (Total around 5 litres of water, hcl, nitric, a few ml sulphuric, sulfamic, urea and smb)

I tried to cement out but the copper plate and copper wires i add in dissolved after a few hours. And no solid at the bottom. Waited anyway till morning with air-bubble in, tried two different times but same problem. (Expecting minimum 4-5 grams gold alone just from failed attemps i added in)

So, what am i missing? What should i do?

Thank you in advance.

Zuma.

Most likely way too much Nitric and Sulfuric.

 

[Lino1406]

Maybe air (oxygen) bubbling has negative effect for reduction

 

[Martijn]

Don't put AR in your stockpot! Refine gold with it.
When the oxidizer (HNO3) has depleted, return the used HCL with left over traces of pm's salts to your stockpot.
Martijn.

 

[nickvc]

My advice follows on from yggdrasil reply consume any free nitric with additions of sulphamic and try again.

 

[zumka]

Thank you all for the replies.

Yeah, one of the reason of a falied attempts was the free nitric. I added sulfamic to the stockpot. I think i even overdosed. (Around 10 tablespoons). About sulphuric, i'm sure it's not more than 5 ml. But as i'm not an expert, if you say that still can be a reason, i would love a way to get rid of it.

I will be more careful next time about AR as Martijn said.

And about air bubble makes negative effect, i would try again without air bubbling if it makes sence.

Thanks

Zuma

 

[FrugalRefiner]

An air bubbler is a double-edged sword with pros and cons.

Any cementation reaction, like your stock pot, benefits from circulation. The solution bearing your values has to come in contact with the metal being used to cement the values out. An air bubbler is a simple, low cost way of circulating the solution.

But, an air bubbler also helps oxygen to dissolve into the solution. The AP process (copper chloride leach) relies on oxygen to convert CuCl to CuCl₂ which then dissolves more copper. So cementation needs to be monitored to determine when the process is complete.

The AP process is slow. It takes a long time to digest copper plate or even heavy wire. Since your copper dissolved in a few hours, I would expect the excess nitric was the culprit.

Dave

 

[zumka]

Thank you, Dave.

So, as sulfamic didn't work on nitric, what would you suggest to neutralize the nitric? Or there is no recover? (Stannous test positive)

 

[FrugalRefiner]

Can you post a picture of your stannous test please?

If it is a true positive test, and the purple / black color remains, it would indicate that there is no longer any excess oxidizer (nitric in this case).

If that's true, I would add more copper and watch what happens. You can test by dipping a clean piece of copper wire into the solution for 30 seconds, then pulling it out. Is it still clean copper colored, or is it coated with a gray or black color?

Dave

 

[zumka]

Can you post a picture of your stannous test please?

If it is a true positive test, and the purple / black color remains, it would indicate that there is no longer any excess oxidizer (nitric in this case).

If that's true, I would add more copper and watch what happens. You can test by dipping a clean piece of copper wire into the solution for 30 seconds, then pulling it out. Is it still clean copper colored, or is it coated with a gray or black color?

Dave

Sure. I will post a picture as soon as i'm in my workshop.

I already tested with a clean copper wire. It turns into a whitish gray colour in a few minutes.

 

[Geo]

You can dilute the solution to effectively raise the PH. Diluted solution tend to work better than concentrated solutions when cementing.

 

[orvi]

Thank you, Dave.

So, as sulfamic didn't work on nitric, what would you suggest to neutralize the nitric? Or there is no recover? (Stannous test positive)

sulfamic acid should work, but it perform better at higher temperatures.
afterall, the classical options how to get rid of nitrates are: evaporating down with HCl, sulfamic acid, adding metal to deplete it completely.
I am sure evaporating the stockpot is way too impractical. Sulfamic acid did not work for you... So... maybe the easiest (but not best) option is to add more copper to deplete nitrates. Or adding iron to the pot could cement some copper back as precipitate, which in turn redissolves back with help of that nitric overall consuming iron = cheaper. But this will also cement out your gold.

 

[nickvc]

You could also add some zinc if you have any , this will consume the acid but may allow other metals to cement out but this is only a problem if you want to recover the values now, if not adding more solutions to your stockpot later will dissolve any base metals and also cement out values.

 

[Geo]

I have a seemingly endless supply of rusty nails. When I collect a few gallons of solution in a five gallon bucket, I add a small hand full of nails. I expect some copper to come down. For me, it's not a problem. If it is time sensitive, I will use steel wool from the hardware store. I buy a variety pack that weighs a couple of pounds for around $9 USD. When I have a solution that is being very stubborn and I need to "get on with it", I use steel wool and a couple hours later I am re-dissolving and trying not to make the same mistake that caused it the first time.

 

[zumka]

Well, while i was still confused about what to do, now i have this.

I layed a copper wire without air-bubble as suggested. And next morning, i see that thick layer as you see in the picture, attacked to the wire. What that should be?

 

[zumka]

I dipped the second wire 2 hours ago and it's like this. (So whatever the metal is this, still cementing)

 

[upcyclist]

How much copper are you adding? Using some very fuzzy math, it'll take about 250g of copper to consume 1 L of nitric. So, that's about a half pound of copper for every liter of 70% nitric you have in there. For perspective (and more math), that works out to about 25 or 26 feet of 12g AWG copper wire.

Hopefully I didn't flub the math

 

[Lino1406]

Well, while i was still confused about what to do, now i have this.

I layed a copper wire without air-bubble as suggested. And next morning, i see that thick layer as you see in the picture, attacked to the wire. What that should be?

When copper cements metal, it should be nobler then copper, e.g. silver, mercury, palladium, gold...

 

[speed]

Just make sure there is copper in there for a few weeks and it will sort itself out. You can then collect what has cemented out and try again.

 

[zumka]

Thank you, all. I will update with the news.