# Why is my silver nitrate coffee brown!?



## renkenbw (Jun 11, 2019)

I was precipitating silver from nitric acid solution (used in gold refining) and did NOT know that the copper I got from Lowes was only "copper plated steel". It was NOT labeled as such at the store. All was well at first, but then it turned an ugly, cloudy green and my beautiful silver fluff settled to the bottom as heavy sediment and not so silvery. I pulled out he all of the "copper" and let it settle. I then decided to add a little Nitric Acid and put it back on the heat. Now it is dissolving the sediment, but it looks like coffee with cream in it! I don't know what it is or why, and I am wondering if I will still be able to recover my silver from it. This is half of my batch, and I was planning on about 4 oz of silver. Here is a picture of my other half, which is still a beautiful blue and ready to have copper added. The good bottle is pictured next to the screwed up batch that is brown and opaque. Please help!


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## butcher (Jun 11, 2019)

Iron can passivate with nitric acid, the NOx fumes indicate free nitric in solution, the more concentrated the nitric the more problems with passivation.

luckily silver will not alloy with iron, but then the copper will, and the iron can push the copper out of solution with your silver...


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## renkenbw (Jun 11, 2019)

Right. The fumes are because I added more Nitric Acid to re-digest the silver. I have let that run it's course. It turns out that, if i let it sit long enough now, the rust colored silt that remains (which is why it looks like coffee) settles to the bottom, and my solution is a more familiar blue-green. However, I have found that it stirs up at the slightest motion, and much of it passes through my filter. So, I will try to syphon as much solution as I can and use double filters for the remainder.
My question now is, what kind of rust colored sediment is it that won't dissolve in Nitric Acid solution!? If it is iron or copper, wouldn't it go into solution and the silver cement out? I put in a little nitric acid, and heated it until all my silver colored sediment was gone, and until the fumes stopped. However, there is still MUCH of the rusty sediment. Do I need more nitric acid? Again, back to the question of wouldn't any base metals have dissolved BEFORE the silver did, or be replaced by silver?


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## FrugalRefiner (Jun 11, 2019)

When a metal precipitates as a salt, you can't just assume that adding more acid will "redissolve" the "metal", because it's not a metal anymore. I'll use a simple example.

We know that silver dissolves in nitric acid. But if it is in solution and we add some salt or HCl to the solution, the silver will precipitate as silver chloride (AgCl). No amount of nitric acid will "redissolve" the silver because it's no longer in a metallic form.

If you feel your silver is in the solution, decant/syphon it off and cement it out. If you get about what you're expecting, treat the sediment as waste and dispose of it properly.

Dave


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## Lino1406 (Jun 11, 2019)

Take a sample from the sediment, add caustic soda, if it turns black (Ag2O) then it's silver chloride and can be washed and Ag2O directly melted


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## renkenbw (Jun 11, 2019)

Lino1406 said:


> Take a sample from the sediment, add caustic soda, if it turns black (Ag2O) then it's silver chloride and can be washed and Ag2O directly melted


 Thanks. Here are my final images with my solution poured off and in a bottle, and the last of the sediment being filtered. There is quite a bit of sludge. I may dry it and melt it, just to see what I get. I don’t have any caustic soda (sodium hydroxide/lye). If I were to buy some, what’s strength? Should I get powder and dissolve it, or get liquid? The sediment seems like it could be copper, but I would’ve thought that any copper would digest before the silver, and I know there is silver in ther.


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## Shark (Jun 11, 2019)

Caustic Soda = Sodium hydroxide sometimes referred to as Lye.

It is nice to see someone refer to looking it up for themselves, it shows your willing to work for it.


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## renkenbw (Jun 11, 2019)

Shark said:


> Caustic Soda = Sodium hydroxide sometimes referred to as Lye.
> 
> It is nice to see someone refer to looking it up for themselves, it shows your willing to work for it.


Yah, I actually looked it up and then modified my post. So, my question about “what is it” isn’t in there anymore. 
Keep in mind, this all started with a wonderfully clear blue solution, like the bottle in the top picture. It was those damn copper plated steel wires that screwed everything up. It was working perfectly, and I came out to look at it about an hour later and it was a mess.


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## renkenbw (Jun 12, 2019)

OK, after a little more researching, I think I’m figuring this out.
When trying to cement out the silver, the copper plating on those damn wires was digested, exposing the steel underneath. Then the steel started digesting and pulling copper out of solution. I also had solid copper pipes in there. All the copper was trying to pull silver out of solution, but the steel was also pulling copper out of solution . What I ended up with was a mix of copper and silver sediments. How it decides what goes into solution and what comes out, at what rates, it’s hard to say. 
When I removed the copper (and steel), and added a little more nitric acid and applied heat, it appears that it digested more silver back into solution than it did copper. So, the predominant color of the remaining sediment was from the copper. 
Bottom line - the coffee color was due to the copper colored sediment mixed with the green colored solution. The reason the solution color was now green was due to the iron content (from the friggin steel) in the nitric solution.
With the remaining sediment (mostly copper with some silver) I plan to melt it down after rinsing it, and turn it into shot for future inquartation. I will still use new copper to cement out my silver from my greenish solution. I think that will work.
Of course, I may be wrong about all of this, and i guess I’ll find out! If anyone has any insight or advice to prevent me from doing anything awful, feel free to let me know!


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## g_axelsson (Jun 12, 2019)

Sorry, but I think you are wrong. The brown sediment can't be copper, it would cement back the silver instantly.

To me it looks like rust. Nitric acid is an oxidizing acid and what you are looking at is iron oxides and hydroxides from the iron below the silver.

I can think of two ways I would test if I was in your situation. Sometimes liquids aren't behaving as we expect, so you might do small scale tests to see what works best for you.

1. Boiling the solution to see if it will make it easier to filter... and maybe get a finer filter. Especially if you are using a coffee filter, they are quite coarse and will let large particles through.

2. Cement the silver with copper, the silver will be a lot denser than the brown precipitate. You could probably wash away most of the brown silt with minimal losses of silver by just doing a couple of aggressive washes.

Göran


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## renkenbw (Jun 12, 2019)

I think you are correct. I was thinking that same thing last night as I tried to go to sleep. Any copper should have (would have) gone to solution. If any metals dropped out, it would be silver.
Below is the last (doubled) filter I used when I poured the last from the bottom of the beaker - a #90 made for the vacuum flask. When I drained the last of my beaker, I also noticed what settled to the bottom, below the "rust" (as you said). Not sure if it is silver chloride, or pure silver. Do you think it can be rinsed and melted directly?


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## Shark (Jun 12, 2019)

Was your silver source from jewelry? I have seen that same brown goop when doing gold filled in nitric, usually when I am in a hurry and don't prep it very well. It has always been iron in my case. Those annoying clasp and rings that attach the jewelry can often be the source.

Just caught that you found the source to be your wire for cementing. I lean toward using copper water pipe, split open as it has to meet strict requirements concerning purity.


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## renkenbw (Jun 12, 2019)

Shark said:


> ...I lean toward using copper water pipe, split open as it has to meet strict requirements concerning purity.


That's my plan now. Copper pipe worked perfectly for me before, so I plan to stick with that from now on. Didn't think about the fact that it is more regulated also. Thanks!


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## renkenbw (Jun 12, 2019)

It works so much better with real copper!


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## rickzeien (Jun 12, 2019)

Beautiful!

Sent from my SM-G950U using Tapatalk


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## Shark (Jun 12, 2019)

That is A-Team silver.....Love it when a plan comes together.. :lol:


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## FrugalRefiner (Jun 13, 2019)

You should cut the copper pieces so they are completely submerged in the solution. When they extend above it, they tend to oxidize and shed bits that contaminate the silver.

Dave


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## Shark (Jun 13, 2019)

Nice catch by Dave there. While your at it, split it open so your working with two somewhat flat sides, it saves a bit of silver that could be trapped inside your tubing. In a pinch teflon tape makes a good string to suspend your copper from in smaller jobs.


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## renkenbw (Jun 13, 2019)

Thanks for the suggestion guys. I weighed the effort vs results and settled on pipe. Small loss at the water line, and, when I shake, I squirt distilled water through the pipes during a quick remove and replace, which flushed them out. Much easier (for me) to work with regular pipe. I do sand and brush them before and after use.
Again... thanks for the input! This board has been very helpful, and I hope my posts contribute to others in some way.


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