Waste solutions

[FrugalRefiner]

Also. How do chloride solutions get dissolved silver if they don't dissolve silver? People extracting gold only use ap (a chloride solution), so how does the silver get in there before using ar to later refine I wonder?
There should be no silver chloride around by the time one uses ar, yet I often hear of problems with it at that point.

A tiny amount of silver can be dissolved in a strong chloride solution. It's why we dilute AR and filter it before dropping gold.

Silver usually gets into AR because a small amount has remained allowed with the gold. When the gold is dissolved, the silver can dissolve as well.

Dave

 

[MvK]

If the solution is saturated with copper, would that prevent any PGM going back in solution?

 

[Yggdrasil]

If the solution is saturated with copper, would that prevent any PGM going back in solution?

Why should you have a saturated Copper solution when there are PGMs in it?
Is it AR or something else?

 

[MvK]

Why should you have a saturated Copper solution when there are PGMs in it?
Is it AR or something else?

Sorry,

If copper would would cement out all PM from (dirty) waste solution, and Pd would want to go back into solution like stated above.
Would a saturated copper solution prevent Pd going back insolution?

So does the copper metal need to be fully consumed in the stock pot in order to keep the Pd from going back in solution?

Or am i overthinking this..

 

[Yggdrasil]

Sorry,

If copper would would cement out all PM from (dirty) waste solution, and Pd would want to go back into solution like stated above.
Would a saturated copper solution prevent Pd going back insolution?

So does the copper metal need to be fully consumed in the stock pot in order to keep the Pd from going back in solution?

Or am i overthinking this..

Yes, you are overthinking it
As long as there are metals with higher reactivity than PMs available, the PMs will cement out.
The issue with PGMs is that they cover the surface fast and pacifies it.
So you need vigorous stirring.
And then brushing it iff the copper after.

 

[Martijn]

One of our members leaches whole boards and more in AP and gets Pd out in a certain way by cementing on copper. I think the main goal here is to get the AP in a lesser active state, not so much free acid left. And not much cupric chloride, but more cuprous chloride. It's a fine balance as Orvi stated. I can't remember who wrote that though.

And one more thing:

Cementing on copper can be peculiar in some ways, as cupric chloride is quite strong oxidizer, and you have always oxygen present. PGMs are very easily re-dissolved after cementation, and whole copper cementing is finely balanced process.

Nobody mentioned it here, but black deposit growing on the copper, and eventually completely disintegrating it is mix of various copper oxides and oxohydroxides. This is completely normal, and it will happen as acid is mostly used up, so oxygen dissolved in the juice oxidize the copper... But it has no free acid to bond with, so it forms some sort of "chloride deprived" deposit - which is obviously insoluble.

That does not say you do not have any values in it. There could be PMs, but usually the cementation is relatively quick process, compared to growth of these black copper "oxide" deposits.

I really appreciate your knowledge and clear explanations. Good you're with us Orvi! Those little info gems are adding up. Simple things we can see happen, never bothered asking why, until you come along and explain it and it makes sense.

 

[MvK]

Yes, you are overthinking it
As long as there are metals with higher reactivity than PMs available, the PMs will cement out.
The issue with PGMs is that they cover the surface fast and pacifies it.
So you need vigorous stirring.
And then brushing it iff the copper after.

This evening im siphoning off the liquid, lets see if round 2 of bubbling payed off.

Thanks again for the help!

 

[MvK]

One of our members leaches whole boards and more in AP and gets Pd out in a certain way by cementing on copper. I think the main goal here is to get the AP in a lesser active state, not so much free acid left. And not much cupric chloride, but more cuprous chloride. It's a fine balance as Orvi stated. I can't remember who wrote that though.

And one more thing:

I really appreciate your knowledge and clear explanations. Good you're with us Orvi! Those little info gems are adding up. Simple things we can see happen, never bothered asking why, until you come along and explain it and it makes sense.

Maybe im asking stupid questions, but im learning from every answer. Thanks guys!

 

[orvi]

One of our members leaches whole boards and more in AP and gets Pd out in a certain way by cementing on copper. I think the main goal here is to get the AP in a lesser active state, not so much free acid left. And not much cupric chloride, but more cuprous chloride. It's a fine balance as Orvi stated. I can't remember who wrote that though.

And one more thing:

I really appreciate your knowledge and clear explanations. Good you're with us Orvi! Those little info gems are adding up. Simple things we can see happen, never bothered asking why, until you come along and explain it and it makes sense.

I was curious about this some time ago. I was doing small ceramic SMD chips (USSR made), and I left the juice after gold drop over the copper (I have some doubts about completness of gold drop). One spiral of very thick copper wire. This was hanging in over weekend, and when I came back, quite a bit of black powdery "crust" grown on the copper. I was very shocked, since there should be no reason for PGM presence in this material. But you know, Soviet stuff, you never know... I harvested the black ppt and shot it with XRF. To my surprise, practically plain copper reading, some low decimals Au (expected, as microfine particles of gold can pass the filters etc) but nothing else...

This is how I came across this realisation. Next time I left solid copper bar in the canister of some spent liquid with minor PGMs still in there. Of course, I got the PGMs out, but what shocked me was the vast ammount of black powder left, and ammount of copper eaten (around 5 days in, covered cut canister, but not air-tight). So again, I shot with XRF and this time of course, PGMs were there, but like few %. Rest was reading copper. And this came to be true during the processing of this black residue. Very much negligible PGMs came out, and vast ammount of copper was the "black" thing left

 

[kurtak]

Edit: Cementing Precious Metals will follow the order of the Redox Series of Metals. So expect the highest metals in that series to come down first. If your drum contains a "wild" mix of PMs, change those copper elements once they have harvested one type of metal.

Per the bold print - I am sorry but that just flat out is NOT true !!!

If you have mixed PMs (gold & PGMs) in a solution & you put a piece of copper in that solution the copper will NEVER selectively cement out one metal over that of another metal

In other words - it is NOT going to cement out the dissolved gold FIRST - then the dissolved palladium SECOND - then the dissolved platinum THIRD

It just doesn't work like that !!!!

I see you are using the electromotive series rather then the reactive series which flips the series of the metals (which metals are at the top & which ones are at the bottom - basically - though there is some variance)

https://en.wikipedia.org/wiki/Reactivity_series
When we talk about cementing metals (here on the forum) we use the reactive series & that is because the cementing process has little to do with the electro potentials of metal - but rather whether the metals are (simply) more reactive - or less reactive - when dissolved (as ions) in a solution

So - if you put a more reactive (actual) metal (copper) in a solution that has less reactive metals (Au, Pd, Pt etc.) dissolved in it --- when those less reactive (dissolved) metal ions make contact with the (actual) more reactive metal - an ion exchange takes place wherein the more reactive metal (copper) dissolves (putting copper ions into solution) thereby reducing the less reactive metals as the less reactive metal ions (in the solution) are exchanged by the more reactive ions go into solution

Therefore - it does not matter to the copper which dissolved less reactive ion (PMs) make contact with copper - the ion exchange between the copper & the dissolved PMs is going take place - at the point AND time of contact

In other words - if you have Au, Pd, & Pt all dissolve in a solution & you put a piece of copper in the solution - as soon as Au, Pd, Pt ions make contact with the copper ALL of those (PM) ions are going to make the exchange with the copper - AND they are ALL going to cement out at the point/time of contact --- in other words cement out at the same time

That is why cementing is a recovery process & not a refining process - & that is because the copper does not care what less reactive (dissolved) ions are making contact with it --- it simply makes the ion exchange (reduction) upon contact

You can NOT selectively cement mixed PMs from a solution !!!

Kurt

 

[orvi]

In order to cement any precious metals (PMs) out of your solution, the ions of those PMs need to come into contact with the copper you placed inside. No contact means no cementing.

Now, to improve the process, consider enlarging the surface area that you offer to those few scattered atoms floating around in your drum. Give them something to hit. A one square meter copper sheet is far more effective than a simple piece of copper from a pipe.

A copper mesh may be even more effective, and so on. You could also try pumping your solution through copper pipes, maybe adding a copper mesh inside.

But do not forget one thing: once one atom of the PMs has cemented out on the copper, the attraction of the Copper (at this very spot) will decrease exponentially. New layers will only stack up very unwillingly. Bare polished Copper is your friend here! Keep it free from grease, paint, oil, and other barriers that will hinder the cementation. Once they have a black layer on them, remove and replace the Copper to harvest other free PM atoms/ions.

Edit: Cementing Precious Metals will follow the order of the Redox Series of Metals. So expect the highest metals in that series to come down first. If your drum contains a "wild" mix of PMs, change those copper elements once they have harvested one type of metal.

Gold will form a deep black layer.
Palladium will form a light gray layer

Sometimes Gold cements onto the copper and Palladium on top.

Silver will not cement out, even if present, due to the high content of chlorides. Silver will drop as Silver chloride but never (1) cement out on copper.

To understand what is going on in your drum, verify the voltages in the right column of the table below. The higher the difference between Copper (or any other metal that you use for cementation), the higher the attraction of those two elements to each other. Since your Copper (0.5V) pipe will not move from its place, the Gold atoms (1.7V) will connect to it like magnets do, since the difference in their potential is around 1.2V, which is a lot, similar to the voltage of an AAA battery.

Once all the gold atoms have found their place on the Copper and the Copper still has free spots, the next metal with the highest difference in voltages will be attracted by the Copper. Some metals will plate out on top of others that have been cemented, but some metals not, depending on the voltage difference they have.
Platinum and Iridium are quite rare in our typical use-case, so the next one will be Palladium with a voltage difference of around 0.4V. This is one-third of the voltage difference between Gold and Copper, so the process will be slower and take longer to cement all the Palladium onto your Copper piece.
The cementing process will stop once there are only free Copper ions and all those base metal ions below it, left.

So, if you use a metal like Iron to cement your metals, all metals above Iron will come down, such as Copper Nickel, Tin etc. togehter with the PMs.

If you make clever use of the Redox Series, you can cement out valuable base metals quite precisely for resale as well. It can also make your waste less toxic.

Here is a simplified Redox Series of Metals to get a better picture. Maybe if that table is need more often the admins could pin it somewhere so only a link will be required. Free of use ;-)

(1) Silver nitrate will cement on Copper, but if any free chloride is present, like in Aqua Regia, Silver nitrate will replace the nitrate ions against the chloride ions which forms Silver chloride and therefore will not cement on Copper

View attachment 56817

I do not say you are wrong, but there are many things which I feel I need to correct slightly.

Silver will cement on copper, even from chloride solutions. You can drop it as silver chloride, but we are dealing with fairly concentrated chloride solutions, where silver is appreciably soluble as AgCl and even AgCl2-. That is why you cannot get 999 gold by cementation on copper - because all of the silver will follow the gold.

Gold can be cemented fairly quickly on copper, heating the solution help a lot. Unlike PGMs, gold flake/dust off nicely from copper and does not adhere that badly to the surface.

Colour of the deposit is GREATLY dependent on particle size formed. One of the greatest factors here is concentration of the precious metal in solution. If PM is very low, particle size is usually smaller and precipitates tend to be black. But I regularly cement gold from pregnant AR solutions on copper, and deposit is nowhere to black. To be honest, I produced blackish gold cement only like twice in my refining career. Most of the times, it came down brown coloured.

If you are getting black coloured precipitates, it can be that they are contamined with other things like copper oxides or PGMs.

 

[orvi]

Per the bold print - I am sorry but that just flat out is NOT true !!!

If you have mixed PMs (gold & PGMs) in a solution & you put a piece of copper in that solution the copper will NEVER selectively cement out one metal over that of another metal

In other words - it is NOT going to cement out the dissolved gold FIRST - then the dissolved palladium SECOND - then the dissolved platinum THIRD

It just doesn't work like that !!!!

I see you are using the electromotive series rather then the reactive series which flips the series of the metals (which metals are at the top & which ones are at the bottom - basically - though there is some variance)

https://en.wikipedia.org/wiki/Reactivity_series
When we talk about cementing metals (here on the forum) we use the reactive series & that is because the cementing process has little to do with the electro potentials of metal - but rather whether the metals are (simply) more reactive - or less reactive - when dissolved (as ions) in a solution

So - if you put a more reactive (actual) metal (copper) in a solution that has less reactive metals (Au, Pd, Pt etc.) dissolved in it --- when those less reactive (dissolved) metal ions make contact with the (actual) more reactive metal - an ion exchange takes place wherein the more reactive metal (copper) dissolves (putting copper ions into solution) thereby reducing the less reactive metals as the less reactive metal ions (in the solution) are exchanged by the more reactive ions go into solution

Therefore - it does not matter to the copper which dissolved less reactive ion (PMs) make contact with copper - the ion exchange between the copper & the dissolved PMs is going take place - at the point AND time of contact

In other words - if you have Au, Pd, & Pt all dissolve in a solution & you put a piece of copper in the solution - as soon as Au, Pd, Pt ions make contact with the copper ALL of those (PM) ions are going to make the exchange with the copper - AND they are ALL going to cement out at the point/time of contact --- in other words cement out at the same time

That is why cementing is a recovery process & not a refining process - & that is because the copper does not care what less reactive (dissolved) ions are making contact with it --- it simply makes the ion exchange (reduction) upon contact

You can NOT selectively cement mixed PMs from a solution !!!

Kurt

I know what you describe, and you are correct. But...

Cementation is very easy to perform, but what actually happens on the phase boundary and all electron transfer things and kinetics can be hard to understand.
Just stating that cementation on copper from mixed PM solutions isn´t a selective operation - YES, that is correct, but only in absolute terms.

In fact, even cementation on iron can favour some PMs over the others. This has very much to do with coordination sphere, ligands, oxidation state of the PM atom, temperature, free acid concentration, relative PM concentration and so on and so on...
Of course, this is not absolute, all metals will come at the same time, but some much quicker than the others. And if you can regulate this process and stop it in the correct point, you can make it into real application.

On copper, cementation is different than on more reactive metals like iron, aluminium or zinc as the layer of PM created on surface cannot be undermined by fresh acid so easily - for PMs to easily flake off. This is in fact the reason why cementation on copper is slower as for example in case of PGMs. Bubbler is in fact more important for oxygenating the solution = thus dissolving the copper from underneath the deposit of PMs, than for agitation (also very important).

And these slight tweaks and differences can make this even usable on process scale as pre-treatment step. Precisely for the ease of the whole process. And metallic precipitate - oposite to metal salts, which are much harder to deal with, espetially speaking of PGMs.

 

[MvK]

So, i siphoned most of the liquid off and transfered it to a 2l beaker to let it settle again. I forgot to take out one small piece of copper, this has some grey ish and black deposits on it.

The copper is back in the container for the next round, tomorrow we will find out if the sediment contained PM.

In the mean time i still run a smaller stockpot, i transferred the liquids to the big one and the small one contained alot more sediment then the second round in the big one.

This confirms what you guys are saying that the initial cementation is fast, but im still looking forward to find out what i missed during the first cementation.

 

[MvK]

So i like to do this experiment to see what was left in solution. After that im going to process the bigger amount of sediment that i have aquired from my wastes.

My plan to process the sediment is:

-Siphon off the excess liquid
-Dry it in the beaker
-(incinerate if enough material)
-Dillute nitric to take possible Ag and Pd
-Drop Ag with HCl from nitric solution, test for Pd with DMG. If Pd is present cement it out with copper for storage. I dont have enough PGM or experience to risk fooling around with salts and i dont like Platinosis.

-Remaining sediment in AR, drop possible gold with SMB and cement out possible Pt with copper for storage/stockpiling.

-Add remaining liquid to the stock pot.

Do i get this right?

 

[Proffshuggarn]

Mia070
Have you found out what that “orange-juice” fine powder is?

I have the same situation as you, but on my copper metal in the tub of bubblers, there was lots of this yellow/orange powder stuck firmly to the copper. I have described everything in another thread “I cemented out on copper” and will today follow the advice I received from the members here. That powder settled almost immediately on the clean copper in about 25 liters of old acid mixture that I had failed to drop from before I found this forum
/Dennis

 

[MvK]

Mia070
Have you found out what that “orange-juice” fine powder is?
View attachment 56924
I have the same situation as you, but on my copper metal in the tub of bubblers, there was lots of this yellow/orange powder stuck firmly to the copper. I have described everything in another thread “I cemented out on copper” and will today follow the advice I received from the members here. That powder settled almost immediately on the clean copper in about 25 liters of old acid mixture that I had failed to drop from before I found this forum
/Dennis

I am not sure yet, i think those are ferric compounds because this was a by-product from cpu lids in nitric. This beaker is on hold for now, i dont want to throw it in the new stock pot before it contaminates everything.

 

[MvK]

Mia070
Have you found out what that “orange-juice” fine powder is?
View attachment 56924
I have the same situation as you, but on my copper metal in the tub of bubblers, there was lots of this yellow/orange powder stuck firmly to the copper. I have described everything in another thread “I cemented out on copper” and will today follow the advice I received from the members here. That powder settled almost immediately on the clean copper in about 25 liters of old acid mixture that I had failed to drop from before I found this forum
/Dennis

I had some extra time, dried the 'orange juice' and appied HCl.

The sediment dissolved fast in HCl, stannous showed nothing so in my opinion this stuff is probably iron.

 

[MvK]

The 2l beaker containing the sediment that i poured off from the stock pot did not settle yet. About 18 hours in and only about 15mm of the top of the liquid was clear.

I transfered the liquid to another vessel to give it some more time, this would be a nice test to see how fast the fine particles take to settle. I continued to work on the stuff that already had settled down.

I applied dillute nitric to the sediment, liquid started to turn green. Tested for Ag, no results. I did get a yellowish orange stannous test, but DMG showed some Pd.

Remaining material took a bath in AR, stannous showed little gold and a nice orange filter paper test strip. Dropped gold with SMB, these were minor traces just visible in the cracks of the glass. Next stannous looked like Pt to me.

Conclusion:

The sign of practicly no gold shows that @orvi was right. I took all of the gold in the previous run of the stock pot.

The presence of PGM can mean 2 things.
-Either i accidentily threw the waste from the last stock pot refining back in this batch..
-Or the fine particles of the PMG are taking longer to settle down and i just missed those, because i siphoned off too quick.

This was fun, thanks for the input everybody.

Edit: changed PMG to PGM

 

[Proffshuggarn]

I had some extra time, dried the 'orange juice' and appied HCl.

The sediment dissolved fast in HCl, stannous showed nothing so in my opinion this stuff is probably iron.

I did the exact same thing tonight. Added Hcl to a small amount of dried juice powder, all dissolved except for a few minimal "dots", continued with a little nitric acid until the "dots" dissolved. But Stannous's test was completely blank. Yep, Orvi and c/o had 100% in their theories. Tomorrow it will be exciting to process the black powder from the bottom of the tub
/Dennis

 

[Martijn]

The 2l beaker containing the sediment that i poured off from the stock pot did not settle yet. About 18 hours in and only about 15mm of the top of the liquid was clear.

I transfered the liquid to another vessel to give it some more time, this would be a nice test to see how fast the fine particles take to settle. I continued to work on the stuff that already had settled down.

I applied dillute nitric to the sediment, liquid started to turn green. Tested for Ag, no results. I did get a yellowish orange stannous test, but DMG showed some Pd.

Remaining material took a bath in AR, stannous showed little gold and a nice orange filter paper test strip. Dropped gold with SMB, these were minor traces just visible in the cracks of the glass. Next stannous looked like Pt to me.

Conclusion:

The sign of practicly no gold shows that @orvi was right. I took all of the gold in the previous run of the stock pot.

The presence of PMG can mean 2 things.
-Either i accidentily threw the waste from the last stock pot refining back in this batch..
-Or the fine particles of the PMG are taking longer to settle down and i just missed those, because i siphoned off too quick.

This was fun, thanks for the input everybody.

For the record, it's PlatinumGroupMetals aka PGM's.
Your stannous test looks more brown to me, which indicates copper.