AgCl vs PbCl

[Jakes.vdv]

Dear Everyone.

My name is Jacques. I’m a beginner in recovering precious metals and refining them.

I’m currently only focusing on obtaining pure silver.

I’d like to ask you a question about lead chloride in silver chloride.

I’ve been recovering Silver from plated silver cups and trophies, by giving them a bath in 96% Sulphuric acid in which I’ve added about 5% 55% conc. nitric acid. The total solution is 5 litres.

I bathed each item individually in order to observe how different items responded. The result was quite mixed, with items having brass as base metal stripping beautifully, epns items were also fairly okay, and silver on copper items often plated copper over the silver plating, inhibiting the stripping of silver.

None the less, after processing about 30 cups/ small trophies, I was certain to have a fair amount of silver in the solution.

I let the solution sit for a few days, then I siphoned off the top to separate the sludge for further processing, and kept the rest for future batches.

I processed the sludge by diluting the solution, adding a bit more nitric, and letting it sit on a 90 degree Celsius hot plate under a fume hood for a day.

I decided to let the solution settle, to siphon off the clear liquid to precipitate with chloride.
However I was bit impatient and didn’t wait till everything had completely settled…I waited about 12 hrs then filtered the liquid through two coffee filters.

I got a decent precipitation using sodium chloride.
However, when I did the first hot wash, the precipitate took a very long time to settle…where I normally experience it to happen quite quickly…I also added a little nitric to acidify the water to promote faster settling, but that didn’t even help.

Anyhow, I did a few more washes, noticing that the precipitate kept getting finer…Not like the “cottage cheese” that I’m used to. I suspected that there was lead chloride mixed with the silver chloride, which would be probable because some of the Cup handles contained lead.

However, upon each hot wash, it didn’t dissolve…. So I was a bit confused, because my understanding is that PbCl will dissolve in hot water, making it easy to separate from AgCl.

I placed the precipitate in the sun, and it turned gray for sure, but it still takes very long to settle, even with a hot acidic wash.

So I don’t know if I have silver or lead and silver mixed?

Will lead chloride turn gray in sunlight with Silver chloride?

Please can you guys look at the picture I’ve attached, it’s a sample off the precipitate that was exposed to sunlight. .

Do you think it’s just silver or silver with lead?

I really appreciate any responses.

 

[Martijn]

If there is PbCl in it, the hot wash water should have a precipitate when cooled down. Does it?

 

[Jakes.vdv]

If there is PbCl in it, the hot wash water should have a precipitate when cooled down. Does it?

Hi Martjin. Thanks for the reply. Whether hot or cold, the wash looks pretty much the same.

I do notice a curdle like chloride precipitate, settling at the bottom, but it is accompanied by a much finer chloride precipitate. Neither of these dissolve in hot wash. And neither seems to get more or less once it’s cooled down.

Could I perhaps be dealing with Mercury chloride (Hg2Cl2)?
I know that Mercury was sometimes used in a silvering technique called “fire gliding” to apply a thin layer of silver or gold to a base metal…which could be the case in some of the items I’ve stripped silver from?

It definitely seems like there is two precipitate that formed…one that’s more curdled (characteristic of AgCl), and the other much more fine and powdery.

 

[Martijn]

That is not what i mean, when washing lead chloride with water, it should dissolve and can be decanted or filtered from the solids.
You're then left with the precipitate in one bottle and the clean wash water in the other bottle.
Let that clear water cool off and look for lead chloride. If there is none and the water stays clear, there is no lead chloride in the precipitate.

I don't expect to find mercury in plated silver.

I have had silver chloride settling in curds and fines before. A second wash always makes it clump better, and the third even more so, is that not happening with your precipitate?

I would let the curd settle, decant the fine floaters and filter it. See if HCl dissolves some of it.
It could be CuCl1.
I don't think metastannic acid will be in it. It would have formed in the nitric digestion.
AgCl will not dissolve much in HCl, a little AgCl will though and it will turn yellow. Easy to spot. Adding water will reprecipitate it back out.
If the HCl turns it green, it is probably copper chloride.

 

[Jakes.vdv]

Ok great, yes that makes sense.

There is no chloride in the wash waste. I’ve checked it now again, and nothing has formed…It’s just clear with a tinge of blue green.

The curd formed nicely on initial precipitation, and then got finer after the first hot wash, with some distinctly curd and distinctly fine precipitate chloride.

I’ll definitely do the HCl test and let you know.

Thanks very much for your advice, I appreciate it.

 

[Lou]

The finer after the wash is due to peptization. Silver chloride does this. Washing it with a dilute acid solution helps keep it filtering nicely.

 

[Jakes.vdv]

The finer after the wash is due to peptization. Silver chloride does this. Washing it with a dilute acid solution helps keep it filtering nicely.

Thanks Lou. I added a small amount of acid to the wash solution, but I will try a bit more and see if the result is different.

 

[Lou]

Usually the more diluted it gets, the worse it filters.

 

[Jakes.vdv]

That makes so much sense, and I think it’s been my experience. I’ve washed it in too much water.

So I’ve taken some of the solution which that I had left after stripping the silver - filtered - and added sodium chloride. It looks good so far.

I’m going to let it settle overnight and start the wash cycles. This time diluting it less and acidifying the wash water.

I’ll keep you guys posted. Thanks again for all the input so far, I really appreciate the help.

 

[Golddigger76]

With silver I always use a little hydrochloric acid to help it settle, sometimes a little heat helps as well.

 

[Martijn]

That makes so much sense, and I think it’s been my experience. I’ve washed it in too much water.

So I’ve taken some of the solution which that I had left after stripping the silver - filtered - and added sodium chloride. It looks good so far.

I’m going to let it settle overnight and start the wash cycles. This time diluting it less and acidifying the wash water.

I’ll keep you guys posted. Thanks again for all the input so far, I really appreciate the help.

You can be pretty sure that's silver chloride.
Rinse and decant well until a drop of wash water in pH+ (lye or soda) water stays clear.

 

[Jakes.vdv]

Hey guys I’m back, been busy with work the past few days.

So I have a few developments that I can update you with.

And thank you so much for all the input…I’m really learning so much!

So as for the initial chloride precipitate that I showed pictures of in this thread (the gray which has exposure to sunlight), I poured off most of the clear water and added dilute HCl to see any of the chloride will dissolve, but it doesn’t seem like it. (See first two attached Pics)

As for the new batch of chloride precipitate which was precipitated from the left over solution that I showed you in the previous pics (the green solution), that took very long to settle.
So I added more distilled water to reduce the viscosity, because I figured that the sulfuric acid was probably still on the thick side and needed more dilution. However it still took very long to settle. It’s been more than two days now, and it still hasn’t settled properly. (See third and fourth attached pics).

There is definitely some precipitate that curdled and others that is more on the fine side. (See fifth pic)

Anyway, I then also took a batch of chloride precipitate from the exact same solution, and then washed it a bit and added sodium hydroxide, like Martjn suggested.
I got the usual browny black oxide reduction, and again some settled more coarse, while others settled more grainy. The finer grainy stuff took a while to settle, even with hot acidic water. (See sixth pic)

I then took the oxide in solution and used dextrose to convert it to what I was hoping would elemental Ag.
It turned the usual gray colour as you would expect with silver, and it settled fairly quickly even after a few hot washes, but there was still some settling distinctively course, and others distinctively fine. (See seventh pic)

So, to test if the finer settlement was Silver, I added HCl to the solution, which seemed to change the colour of the settlement slightly and certainly made it into a finer texture. Yet some remains more coarse. (See last 5 pics)

So there you have it. I’m fairly certain that there is silver in there, however I’m not convinced that it is very pure.

 

[Jakes.vdv]

…Oh, and I took a pic of the wash water waste in which a bit of the precipitate did end up in.

It’s got a slight reddish gray tinge. So maybe it could be CuCl in the mix as Martjin suggested.

But I’m still confused why it didn’t dissolve much in HCl.

Perhaps I need to use stronger concentration?

I’m also thinking to process everything with sodium hydroxide and dextrose, and then reprocessing everything to see what happens.

Anyway. Thanks everyone.

 

[Martijn]

…Oh, and I took a pic of the wash water waste in which a bit of the precipitate did end up in.

It’s got a slight reddish gray tinge. So maybe it could be CuCl in the mix as Martjin suggested.

But I’m still confused why it didn’t dissolve much in HCl.

Perhaps I need to use stronger concentration?

I’m also thinking to process everything with sodium hydroxide and dextrose, and then reprocessing everything to see what happens.

Anyway. Thanks everyone.

CuCl takes some time to dissolve when HCl is added.
To get 99.99 silver from silver chloride: create silver chloride from a clear filtered solution, wash the AgCl several times with boiling water and decant after setlling. Then measure your wash water for copper and other basemetals.
Take a bt of the wash water in a small beaker and add a couple of drops of dissolved lye.
If any salts are still present, you will see a color. That will often be blue.
If no color comes from the test, wash it once more. And then convert it
Hot boiling water washes is key.

The reddish makes me think iron oxide.
Copper chloride is white.
Edited for spelling.

 

[Martijn]

Looking at those last pictures, I think the conversion to silver with lye and dextrose was incomplete.
Treat it as silver chloride, wash it clean and convert it again.

 

[Jakes.vdv]

Thank you Martjin. You’re right about the iron oxide. The waste bucket had slight residue of iron oxide on it from a batch of electrical contacts that I did previously.

I think I’ve been over analysing things. I’m going to slow it down a bit, and try and do the steps more thoroughly.

In my initial attempt, the chloride was created from a cloudy solution, which is probably half my problem.

Thanks for the advice on how to test the waste water.

I’ll post a pic of the silver powder once I’m done with it.