Do different metals dissolve simultaneously, or consecutively in 30% concentrated nitric acid?

[Jakes.vdv]

Hello Everyone.

I have a question.
I’ve been studying how to recover Silver from electroplated plated items and also from electrical contacts. My success has been inconsistent thus far.

Recently, as an experiment I added a small silver electroplated plated cup and a very small sterling silver item to 30% concentrated nitric acid (it’s all I can get in my area), which I then placed in a fume hood on a hotplate which heats the solution to about 100 degrees Celsius. I left it on for the whole day (the hot plate runs off solar power), and I then let the solution settle over night.

In the morning I filtered the clear liquid into a beaker and added a sodium chloride solution. I got a fairly nice precipitation of silver chloride considering the quantity of the material.

I noticed that the sterling silver item hadn’t dissolved much, and the silver plated cup had a film coming loose on it, which most likely is the coating of silver.
But now the nickel silver underneath that film was exposed.

So, I then added fresh dilute nitric acid (the same 30% concentrate), and repeated the process.

This time, upon adding the sodium chloride solution there was no precipitation.
I noticed that the film on the cup was largely untouched, the nickel silver base metal wasted away some more, and the sterling silver item seemed as it were before.

I repeated the process with for a third time with fresh diluted nitric acid, and got roughly the same effect, with no precipitation.

Now am I correct in saying that the dilute nitric acid first dissolves the more reactive nickel silver (composed of zinc, copper, nickel as I understand it), and only then will it dissolve the less reactive Silver?
And the reason that I got successful precipitation on the first round was because of the outer layer of silver on the electroplated item, and obviously the small sterling silver item in the solution?
And the reason I didn’t get a successful precipitation on the other rounds is because the nitric was too busy with the base metal to do much to the silver?
And that once the base metal has been dissolved fully, I can expect Silver to dissolve, and precipitation of silver chloride to be successful?

Thanks everyone. I appreciate your response.

Kind regards.
Jacques.

 

[Christian333]

Hello Everyone.

I have a question.
I’ve been studying how to recover Silver from electroplated plated items and also from electrical contacts. My success has been inconsistent thus far.

Recently, as an experiment I added a small silver electroplated plated cup and a very small sterling silver item to 30% concentrated nitric acid (it’s all I can get in my area), which I then placed in a fume hood on a hotplate which heats the solution to about 100 degrees Celsius. I left it on for the whole day (the hot plate runs off solar power), and I then let the solution settle over night.

In the morning I filtered the clear liquid into a beaker and added a sodium chloride solution. I got a fairly nice precipitation of silver chloride considering the quantity of the material.

I noticed that the sterling silver item hadn’t dissolved much, and the silver plated cup had a film coming loose on it, which most likely is the coating of silver.
But now the nickel silver underneath that film was exposed.

So, I then added fresh dilute nitric acid (the same 30% concentrate), and repeated the process.

This time, upon adding the sodium chloride solution there was no precipitation.
I noticed that the film on the cup was largely untouched, the nickel silver base metal wasted away some more, and the sterling silver item seemed as it were before.

I repeated the process with for a third time with fresh diluted nitric acid, and got roughly the same effect, with no precipitation.

Now am I correct in saying that the dilute nitric acid first dissolves the more reactive nickel silver (composed of zinc, copper, nickel as I understand it), and only then will it dissolve the less reactive Silver?
And the reason that I got successful precipitation on the first round was because of the outer layer of silver on the electroplated item, and obviously the small sterling silver item in the solution?
And the reason I didn’t get a successful precipitation on the other rounds is because the nitric was too busy with the base metal to do much to the silver?
And that once the base metal has been dissolved fully, I can expect Silver to dissolve, and precipitation of silver chloride to be successful?

Thanks everyone. I appreciate your response.

Kind regards.
Jacques.

I believe your assessment is correct.

Janie

 

[orvi]

Hello Everyone.

I have a question.
I’ve been studying how to recover Silver from electroplated plated items and also from electrical contacts. My success has been inconsistent thus far.

Recently, as an experiment I added a small silver electroplated plated cup and a very small sterling silver item to 30% concentrated nitric acid (it’s all I can get in my area), which I then placed in a fume hood on a hotplate which heats the solution to about 100 degrees Celsius. I left it on for the whole day (the hot plate runs off solar power), and I then let the solution settle over night.

In the morning I filtered the clear liquid into a beaker and added a sodium chloride solution. I got a fairly nice precipitation of silver chloride considering the quantity of the material.

I noticed that the sterling silver item hadn’t dissolved much, and the silver plated cup had a film coming loose on it, which most likely is the coating of silver.
But now the nickel silver underneath that film was exposed.

So, I then added fresh dilute nitric acid (the same 30% concentrate), and repeated the process.

This time, upon adding the sodium chloride solution there was no precipitation.
I noticed that the film on the cup was largely untouched, the nickel silver base metal wasted away some more, and the sterling silver item seemed as it were before.

I repeated the process with for a third time with fresh diluted nitric acid, and got roughly the same effect, with no precipitation.

Now am I correct in saying that the dilute nitric acid first dissolves the more reactive nickel silver (composed of zinc, copper, nickel as I understand it), and only then will it dissolve the less reactive Silver?
And the reason that I got successful precipitation on the first round was because of the outer layer of silver on the electroplated item, and obviously the small sterling silver item in the solution?
And the reason I didn’t get a successful precipitation on the other rounds is because the nitric was too busy with the base metal to do much to the silver?
And that once the base metal has been dissolved fully, I can expect Silver to dissolve, and precipitation of silver chloride to be successful?

Thanks everyone. I appreciate your response.

Kind regards.
Jacques.

You are right, reactivity of metals in nitric acid varies. But it is not that sharp and straightforward in most of the cases.

Generally, more reactive metals react faster. From my observations alloys like bronze or brass, or CuNiZn spring alloys dissolve faster than plain copper. Then, silver alloys like typical "hard silver" contact points (AgCu) or AgCd10-20 contact alloy are more reactive than pure silver. And finally, silver is much more reactive than AgPd30 alloy, and pure palladium can dissolve very slowly and generally need higher nitric concentration to proceed at significant rate.

Truth is, you will never get clean sharp separation doing this, as all of the metals do react simultaneously, just the more precious metals tend to react much slower.
Another story is when you have contact point (like AgPd30 alloy point) pressed into base metal carrier like said CuNiZn alloy or bronze spring. This time, there is conductive contact between these two, and the whole reacts as electrochemical cell (simplified, I do not want to dive into too much theory). Contact of the two different metals with relatively big difference in redox potentials result in preferential consumption of the less noble metal. But as soon as it is disconnected from the noble contact point, it lose the effective electrical contact and behave as it should = start to dissolve.
I have used this technique only two times for separation of contact points from their carriers - once, I had ferrous alloy with AgPd30 points pressed in. And second time, I had AgPd30 contact points, which were gold plated, pressed into CuNiZn alloy carriers.

With case of ferrous bases, dilute nitric acid reacted vigorously with these, and with slow addition and proper dosing of nitric and sulfuric acids (not to add too much), I was able to dissolve these carriers without measurably dissolving AgPd30 points. I posted this summarized refining lot here, continuing with rough separation of Ag and Pd (gallery section).

With CuNiZn bases, reactivity gap between points and carriers was much smaller. And only gold plating of the actual contact points was preventing the unwanted dissolution, and allowed the separation of the two without losing the AgPd into the solution. Actually, many points were seemingly performing under quite some load, as places where contacts touched were burnt through the gold layer and AgPd was exposed here. Due to this, some Pd was actually leached out, but overall it was less than 1% from overall lot (easily scavenged with DMG afterwards).

Bare silver points in copper-based carriers cannot be separated in nitric acid effectively, as silver will also dissolve. Even AgPd30 won´t separate cleanly from brass or bronze carriers - in these cases, you will need to dissolve the bulk and then refine.

 

[Jakes.vdv]

You are right, reactivity of metals in nitric acid varies. But it is not that sharp and straightforward in most of the cases.

Generally, more reactive metals react faster. From my observations alloys like bronze or brass, or CuNiZn spring alloys dissolve faster than plain copper. Then, silver alloys like typical "hard silver" contact points (AgCu) or AgCd10-20 contact alloy are more reactive than pure silver. And finally, silver is much more reactive than AgPd30 alloy, and pure palladium can dissolve very slowly and generally need higher nitric concentration to proceed at significant rate.

Truth is, you will never get clean sharp separation doing this, as all of the metals do react simultaneously, just the more precious metals tend to react much slower.
Another story is when you have contact point (like AgPd30 alloy point) pressed into base metal carrier like said CuNiZn alloy or bronze spring. This time, there is conductive contact between these two, and the whole reacts as electrochemical cell (simplified, I do not want to dive into too much theory). Contact of the two different metals with relatively big difference in redox potentials result in preferential consumption of the less noble metal. But as soon as it is disconnected from the noble contact point, it lose the effective electrical contact and behave as it should = start to dissolve.
I have used this technique only two times for separation of contact points from their carriers - once, I had ferrous alloy with AgPd30 points pressed in. And second time, I had AgPd30 contact points, which were gold plated, pressed into CuNiZn alloy carriers.

With case of ferrous bases, dilute nitric acid reacted vigorously with these, and with slow addition and proper dosing of nitric and sulfuric acids (not to add too much), I was able to dissolve these carriers without measurably dissolving AgPd30 points. I posted this summarized refining lot here, continuing with rough separation of Ag and Pd (gallery section).

With CuNiZn bases, reactivity gap between points and carriers was much smaller. And only gold plating of the actual contact points was preventing the unwanted dissolution, and allowed the separation of the two without losing the AgPd into the solution. Actually, many points were seemingly performing under quite some load, as places where contacts touched were burnt through the gold layer and AgPd was exposed here. Due to this, some Pd was actually leached out, but overall it was less than 1% from overall lot (easily scavenged with DMG afterwards).

Bare silver points in copper-based carriers cannot be separated in nitric acid effectively, as silver will also dissolve. Even AgPd30 won´t separate cleanly from brass or bronze carriers - in these cases, you will need to dissolve the bulk and then refine.

Hi Orvi. Thank you for taking the time to share your knowledge and experience. I appreciate it.

 

[anarxi]

Bare silver points in copper-based carriers cannot be separated in nitric acid effectively, as silver will also dissolve. Even AgPd30 won´t separate cleanly from brass or bronze carriers - in these cases, you will need to dissolve the bulk and then refine.

simple solution 5 grams of table salt
30 grams of citric acid
100 ml hydrogen peroxide 3%.
dissolves up to 3 grams of copper.
if you heat it up to 60 degrees Celsius the reaction goes quickly...

 

[Martijn]

simple solution 5 grams of table salt
30 grams of citric acid
100 ml hydrogen peroxide 3%.
dissolves up to 3 grams of copper.
if you heat it up to 60 degrees Celsius the reaction goes quickly...

Welcome to the forum.
Can you explain the chemistry behind it, what the different ingredients do, and how to deal with the chemical waste it creates?
Is it the same as dealing with waste from the usual chemicals?
Is the precipitation, etc. comparable to AR?
Martijn.

 

[orvi]

simple solution 5 grams of table salt
30 grams of citric acid
100 ml hydrogen peroxide 3%.
dissolves up to 3 grams of copper.
if you heat it up to 60 degrees Celsius the reaction goes quickly...

Welcome to the forum.
Can you explain the chemistry behind it, what the different ingredients do, and how to deal with the chemical waste it creates?
Is it the same as dealing with waste from the usual chemicals?
Is the precipitation, etc. comparable to AR?
Martijn.

This technique can be used in many cases, but there are some considerations to be made.

I never used method you describe, but generally, chloride based media is good etchant for copper and copper alloys, as silver will coat itself in AgCl layer and won´t dissolve much afterwards.

But purity of the silver point must be high. Anything below 90% and AgCl layer start to disintegrate and crumble. You can in fact use regular AR, but add nitric acid slowly. Reaction is usually vivid and quick, and good majority of silver is virtually untouched by the acid. Silver chloride will eventually form and some will crumble to the solution. If you do not mind some losses due to dissolution of AgCl into saturated chloride solution, you can treat it as waste after operation. If you are diligent, you can cement the silver out on copper, as we do from nitrate solutions. Just be prepared that the Ag powder is very fine.

Benefit of using this method is that it save significant ammount of nitric and any solder (SnPb) is dissolved with copper based carriers. Ferrous carriers are also dissolved, opposed to nitric treatment.

Product of this "stripping" is AgCl precipitate and AgCl coated silver contacts. You can strain the contacts using ordinary strainer and by shaking, liberate majority of AgCl from them. As they are still coated with AgCl, they will not dissolve in nitric very well. They will need some washing with ammonia to remove silver chloride passive layer - then they react as they should.

PS: process or discard ammonia AgCl solution immediately afterwards to prevent any dangerous silver nitrogen species formation

 

[anarxi]

They will need some washing with ammonia to remove silver chloride passive layer - then they react as they should.

PS: process or discard ammonia AgCl solution immediately afterwards to prevent any dangerous silver nitrogen species formation

Thanks for the clarification of chemical processes.
I use this method to obtain contacts for their subsequent sale.
in my country, and I am in Ukraine, you can simply sell cleaned contacts.
I usually buy different relays at the flea market and cut them up. You can still buy good things for little money.

ammonia also shows well where the silver buttons are and where the silver-palladium alloy is located.
20% USSR or 30% alloy from the German Democratic Republic.
silver - milky
palladium - gray after treatment with ammonia.

 

[eaglekeeper]

simple solution 5 grams of table salt
30 grams of citric acid
100 ml hydrogen peroxide 3%.
dissolves up to 3 grams of copper.
if you heat it up to 60 degrees Celsius the reaction goes quickly...

Would this method be good for removing base metal contamination (mainly Cu) from PGM blacks. I have a couple of dram bottles with PGM blacks (slightly contaminated with Cu) that was recovered from e-waste. I really don't think refining it further would be cost effective. So, I've been looking for a cost effective way to clean up the blacks with out re-dissolving it again.