Problem when processing with Nitric

[gold4mike]

I recently decided to begin the next phase of my refining education by dissolving some higher grade material (pins) in 35% nitric. I used 30% H2O2 and a touch of Ethylene Glycol with the Nitric and everything seemed to work fine, up to a point. The reaction slowed to a crawl, I placed the beaker in a crock pot and warmed it. The reaction picked up for a while then slowed significantly again. I added more 35% nitric and the blue solution went cloudy.

The undissolved metals continued to go into solution until I had gold foils floating in the cloudy blue suspension. The solution cleared after allowing it to settle overnight and I now have a white/grey mud on the bottom of the beaker, mixed with the gold foils.

I tried more nitric (not a lot) to see if I could get the mud to go back into solution. There was no reaction and, after settling, the nitric remained a clear liquid on top of the mud.

Before I muck this up, please correct me if my following assumptions are wrong:

I believe I now have nitrates of nickle and copper as salts on the bottom of my beaker. I think I should heat to dry the salts & gold foils, incinerate to dull red heat, then dissolve it in HCl to liberate my foils from the mud.

Am I correct or do I have a lot more to learn?

Thanks in advance for your help!

 

[Anonymous]

I,and several people I know,do not use the ethylene glycol method,and that "mud" is one of several reasons why.The mud that we experienced was not silver,and was a bear to seperate from the rest of the solution.
I have been processing the same way for a long time.I am open to try new things,but mostly just to experiment with the new methods.Very rarely does any idea come along that makes it worth my while to change my methods.And this method is definitely one that I won't be utilizing.I use dilute nitric,decant,AR,filter,precipitate,wash.I use that method for most of my processes and it has never let me down.Hopefully you can figure out what went wrong.

 

[qst42know]

gold4mike

Did you use tap water to dilute your nitric to 35%?

Was there any solder on your pins?

Was the source of ethylene glycol automotive antifreeze?

 

[Harold_V]

I believe I now have nitrates of nickle and copper as salts on the bottom of my beaker. I think I should heat to dry the salts & gold foils, incinerate to dull red heat, then dissolve it in HCl to liberate my foils from the mud.

That may not liberate the foils from the mud, and probably won't, but what it will do is yield material that lends itself to filtration when you dissolve the values, which you don't have right now. Do exactly as you suggested, then rinse well before you dissolve the values.

I have no idea why one would use ethylene glycol in this process, bit I highly recommend you stick to known processes, particularly when dissolving precious metals. Some of them are easily converted to explosives that are very unstable.

Harold

 

[goldenchild]

I have no idea why one would use ethylene glycol in this process, bit I highly recommend you stick to known processes, particularly when dissolving precious metals.

I have an idea of why he tried this but I want to verify before I correct him.

 

[gold4mike]

qst42know - I did use tap water, there was no solder on the pins, the source of the Ethylene Glycol was antifreeze - I checked the label to make sure it did contain ethylene glycol. I used very small additions and only when the reaction tried to foam out of the beaker. The volume of mud that was deposited is about half the volume of pins I started with, which makes me think that the copper/nickle dropped back out.

Harold - The ethylene glycol is part of a formula posted by Noxx which was to include H2O2. The intent is to strengthen the nitric and prevent NOxx red fumes.

Once I get this batch sorted out I'll probably try 35% Nitric alone on my next batch for simplicity and learn these techniques one at a time.

I need to understand why something that initially dissolved has dropped and now won't go back into a fresh solution of the same chemicals that originally dissolved it. Not being a chemist makes it hard for me to wrap my brain around it!

 

[goldenchild]

qst42know - I did use tap water, there was no solder on the pins, the source of the Ethylene Glycol was antifreeze - I checked the label to make sure it did contain ethylene glycol. I used very small additions and only when the reaction tried to foam out of the beaker. The volume of mud that was deposited is about half the volume of pins I started with, which makes me think that the copper/nickle dropped back out.

Harold - The ethylene glycol is part of a formula posted by Noxx which was to include H2O2. The intent is to strengthen the nitric and prevent NOxx red fumes.

Once I get this batch sorted out I'll probably try 35% Nitric alone on my next batch for simplicity and learn these techniques one at a time.

I need to understand why something that initially dissolved has dropped and now won't go back into a fresh solution of the same chemicals that originally dissolved it. Not being a chemist makes it hard for me to wrap my brain around it!

This is what I thought to be the case. I actually made a video about this http://www.youtube.com/watch?v=8PhE7GIUrxA As you stated Noxx put up a patent for this technique. Its main purpose is to suppress the NOx fumes derived from dissolving metals in nitric. This in turn makes the solution "stronger" because of the nitric being recycled.

So my question to you is this. Why were you using the ethylene glycol to keep foam overs from occuring? Adding ethylene glycol to a foam over does absolutely nothing water couldnt do. You make no mention of H202 either. This formula and technique calls for a very specific ratio of ethylene glycol, H202 and nitric. Just adding arbitrary amounts of chemicals to solutions without knowing its purpose or behavior is dangerous and just plain foolish!

Sorry to be hard on you but safety clearly needs to be addressed here. I suggest you do as you said and learn these processes and behaviors one at a time before you just start throwing chemicals together. Study each individual chemical and their MSDS' and do more research. You will be better for it.

 

[gold4mike]

goldenchild - You are correct, I did not use the three components in the exact ratios originally suggested by Noxx. I had, however, watched your Youtube video and noticed that you added a small amount of H2O2 as the red fumes began to appear. I assumed from this that the ratio did not have to be exact.

I will, for the time being, either use straight 35% Nitric for my pins or go back to the reverse plating cell. I was trying to broaden my horizons with this effort.

To that end, I think it will be a good lesson for me and my fellow noobs if I can get this mess to let go of my gold flakes.

Since no other ideas have been suggested, and Harold seems to think I'll make some progress using my own suggestion, I'll proceed that direction and post the results here.

 

[qst42know]

Antifreeze can contain a variety of additives that may not make the label. I seem to recall silicates as a corrosion inhibitor for one.

Chloride contamination from tap water or any other source is a big pain in the back side. Switch to distilled for use with nitric acid.

 

[Harold_V]

Chloride contamination from tap water or any other source is a big pain in the back side. Switch to distilled for use with nitric acid.

I'm not sure I'd agree with that in that I used tap water routinely as long as I refined. The only exception was when working with the silver cell, or making test solutions and/or standard solutions. I even used tap water when washing my re-refined gold. Purity flirted with 4n's regularly, although I make no claims to having produced 4 n's gold.

Harold - The ethylene glycol is part of a formula posted by Noxx which was to include H2O2. The intent is to strengthen the nitric and prevent NOxx red fumes.

Thanks for the explanation. I recall seeing the post in question, but I obviously do not recall the contents.

My real concern for anyone that works with dissolved precious metals is the risk of creating explosive compounds. Not being a chemist, I don't understand the reactions, so I'm not able to foresee trouble when combining substances. As a result, I didn't do much experimenting, preferring to spend my time pursuing that which was known to work.

Harold

 

[goldsilverpro]

The additions of H2O2 and ethylene glycol to nitric systems were covered in a patent(s) that I posted a long time ago. I think Noxx has some experience with this.

 

[goldenchild]

My real concern for anyone that works with dissolved precious metals is the risk of creating explosive compounds. Not being a chemist, I don't understand the reactions, so I'm not able to foresee trouble when combining substances. As a result, I didn't do much experimenting, preferring to spend my time pursuing that which was known to work.

Harold

Yes. After experimenting with this a few times I have come to the conclusion that its just too unstable to deal with. Each time, no matter how controlled the experiment, there was either a much too rapid depletion of the H202 or a boil over. I even tried leaving the H202 out of the primary solution and adding H202 in small increments with no luck. Seems that there needs to be some type of special set up to accomodate for these factors. Worse still, the antifreeze goes into the atmosphere and leaves a sticky residue on whatever it touches.

 

[qst42know]

I suppose you could test your tap water for chlorides. Are you on a well or municipal supply? City water chlorine levels will change some with the seasons.

Dilute your nitric as before and dissolve a small amount of known purity silver. Any cloudiness or residue would indicate chlorides correct?

 

[Oz]

It is better to make up some silver nitrate with distilled water, nitric, and pure silver. Then get a clear sample of your water and add a bit of your silver nitrate. If your water sample remains clear it is chloride free since all it will do is dilute your silver nitrate. It is a very sensitive test.

 

[gold4mike]

I'll have to post a picture of my mud and of the pins I'm trying to process. I doubt there is any silver in them and, if there is, I can't imagine it would be as much as it appears I now have in the beaker.

The source pins are mostly from server backplane boards, the game port on old sound cards, and the vga port from some ATI cards. These pins all have a similar buttery yellow appearance which led me to believe that they are more heavily coated with gold than the average flash plated silvery pins. I went on the assumption that they would be copper with a layer of nickle under the gold.