Silver Digestion in Dilute Nitric Question

[DaleCarr103]

Hi Guys,

I have a couple of questions concerning the Silver digestion. Not sure if I'm just expecting something different or if I may be doing something wrong.

I mostly digest .925 Silver to run in a Silver Cell. I use the Cold Nitric Recipe and have had no trouble making over 10 batches and experimenting with it. I studied the forum yesterday again and read that some of the members were evaporating the Cold recipe to achieve a little higher percentage of Nitric. I tried this today and it seemed to produce stronger results.

If I am deluting this recipe 50/50 and it is only 35% to start with is it even strong enough to do the job?
I figure my needs based on the 1 ml per Silver gram and 3.5ml per copper. I have yet to get close to digesting the amount of .925 that I wanted to. ( I may be expecting it to work faster than it does).
How long should it take 1ml of solution to digest 1ml of Silver?
I've tried it at many different temperatures but have tried to stay away from the boiling point. Although it does boil sooner with the watch glass on. (Stops Boiling when I take it off). I do get the Brown nasty fumes and the reaction "Looks" good just seems to be alot slower process than I expect. I searched Hokes Book forever and read till my eyes hurt trying to find some answers so if you could shed some light on this I'd really appreciate it.

Thanks
Dale

 

[METLMASHER]

If you don't know the standard strength of nitric, you need more knowledge, before further use. Read a lot. My first months here were as much a college course, as anything I ever studied, before, or since.

Know exactly what you use, exact recipes, measurements, and processes which work. I'd say read Hoke, but you couldn't possibly be here, and have missed this advice. I will say; read the safety thread, here. http://goldrefiningforum.com/phpBB3/viewforum.php?f=47

Might save your life.

Might save your children, or spouse, or pets, or all.

 

[butcher]

35 to about 45% nitric acid (or even more dilute with heat) is about the best concentration needed, if more dilute you will loose less nitric to the fuming of NOx gases, as the water can hold these gases as you heat the solution and dissolve more metals.
Dale,
If the nitric is too strong the reaction will be slower, until the nitric breaks down.
Very dilute nitric can be heated with the metal, heating will drive off water and concentrate the acid, the hotter acid will assist in attacking the metal.

Some metals dissolve in dilute acids better than they will in concentrated acids, there are times where a metal will passivated in a strong acid and will not dissolve, but can be easily attacked by the same acid if it is very dilute.

Poor mans nitric acid will contain sulfates, (unless the nitric was distilled leaving the sulfate salts in the reaction vessel), these sulfate salts will give you trouble with silver, silver sulfate has a low solubility, this and the fact that converting silver sulfate to silver becomes a more complicated process, it is not recommended to use poormans nitric with silver.

You can distill the poormans and get a nitric acid free of sulfates.

 

[Palladium]

Are you using this type of nitric for you silver cell solution also?

 

[DaleCarr103]

Are you using this type of nitric for you silver cell solution also?

Yes I use the same for my Silver cell. AlthoughI am on my first run with my cell and haven't encountered any problems as of yet.

You can distill the poormans and get a nitric acid free of sulfates.

I am looking to get a distilling set up to rid myself of this problem as I have encountered it before.

Some metals dissolve in dilute acids better than they will in concentrated acids, there are times where a metal will passivated in a strong acid and will not dissolve, but can be easily attacked by the same acid if it is very dilute.

Makes sence. Same principle as the gold stripping cell not attacking the Copper due to its Concentrate. I should have figured that out on my own. Duh.

Thanks for the advice and i will work on being able to distill my Nitric.

thanks for the input Palladium although I have already read Hokes book 3 times and am really still in the experimental stage of the processes. Hokes book is an abundant book of knowledge but it can't answer every bump in the road during the actual process sometimes.

Butcher,

Is there any other way to distill it other than an actual lab distilling setup?

Thanks again for the input Gentelman
Dale

 

[g_axelsson]

Thinking of it, just as we can remove lead from our chloride solutions by adding sulfuric acid, we should be able to remove sulfate from home made nitric by adding lead nitrate (or barium nitrate).
Lead nitrate could be produced by dissolving lead in nitric acid, but if it is contaminated with sulfates it could passivate the lead and stop the dissolving. If you have managed to produce lead nitrate once it should be possible to clean up the home made nitric by adding a solution of lead nitrate in water until there is no more precipitation. That sulfate free nitrate could easily be used for producing more lead nitrate.
The nitric acid would be contaminated with lead nitrate afterwards but for silver work that would not be an issue.
As noted above, barium nitrate could also be used but it is also toxic and a lot harder to make yourself. It probably needs to be bought.

Just a warning at the end, lead nitrate seems to be a carcinogenic substance and is highly toxic as it is a water soluble lead compound so it should be handled with care.

Göran

 

[DaleCarr103]

Thinking of it, just as we can remove lead from our chloride solutions by adding sulfuric acid, we should be able to remove sulfate from home made nitric by adding lead nitrate (or barium nitrate).
Lead nitrate could be produced by dissolving lead in nitric acid, but if it is contaminated with sulfates it could passivate the lead and stop the dissolving. If you have managed to produce lead nitrate once it should be possible to clean up the home made nitric by adding a solution of lead nitrate in water until there is no more precipitation. That sulfate free nitrate could easily be used for producing more lead nitrate.

Thanks Goran

I'll jot that one down for maybe future use. I might test tube that as an experiment before I get to carried away with something as dangerous as Lead in Solution.

Dale

 

[DaleCarr103]

Well the salts seemed to be the problem. I went back to a less effect method of Bubbling the gas through water. Produces a weak acid but is free of salts and works. I still have one issue with the Silver Oxidizing and turning Black though. My reaction is good even without putting a lot of heat to it but then it turns black and everything stops. Any ideas on what I'm doing to make this happen? So far I haven't seen anything come up on searches about something like that.

Thanks again for all your inputs.

Dale

 

[g_axelsson]

Black on silver sounds like silver sulfide. According to wikipedia silver sulfate is a white solid. Maybe the silver sulfate is reacting with the silver and creates silver sulfide.
At least it shouldn't be silver oxide because that is soluble in nitric acid.

I haven't had this problem myself so this post is purely theoretical.

You can test to see if you got any silver in solution by taking a few drops of the solution and adding salt water to it. If there is some silver in solution you will get a white precipitation.

Göran

Edit : Wrote sulfide above but it should of course be sulfate. Edit marked in dark red

 

[Geo]

Sounds like it could be passivization of some kind. The black sounds like silver sulfide (tarnish) which is an indication of hydrogen sulfide gas is present.

 

[Palladium]

Hi Guys,

I use the Cold Nitric Recipe and have had no trouble making over 10 batches and experimenting with it.


Thanks
Dale

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=315&p=2572#p2572

 

[DaleCarr103]

Black on silver sounds like silver sulfide. According to wikipedia silver sulfate is a white solid. Maybe the silver sulfide is reacting with the silver and creates silver sulfide.

Sounds like it could be passivization of some kind. The black sounds like silver sulfide (tarnish) which is an indication of hydrogen sulfide gas is present.

Thats what it is I do believe and have no idea how I got it in there. I went back and started a fresh batch with Silver that I knew was clean and with Nitric Acid that was clean of Salts. No Black as of yet and I am stepping my Nitric additions very carefully. I think my problem before was not thinnking I was getting enough reaction and I answered with adding more Nitric which just compounded the problem by not letting it get weak enough to really do the job. I've noticed that the best indicator of nitric being used up is since I don't touch the temperature during this when I see the reaction go from digestion to boiling which means the boiling temperature is lowering due to mostly H2O then I add just 5mls of Nitric and the reaction starts again and the Boiling stops.

If any of this sounds wrong please let me know.

Thanks
Dale

 

[Palladium]

Cold nitric is made with H2So4!

 

[DaleCarr103]

Palladium,

Cold nitric is made with H2So4!

The link you provided is the one I use. Although I have twicked the Filtering a bit to rid most of the Salt.

I'm not a chemist H2So4 I believe (without looking at a cheat sheet is Sulphuric Acid. I am now using Rotoo as it seems to work the best. I've tried a few so far.

I do believe I have found the solution to the Hydrogen Sulfate problem. Apparently the last few batches that I made I was grabbing the wrong water Jug. I was using tap water instead of my Distilled. I figured this out by starting a batch to digest and with just the watter heated up to temperature with no change I put 10g of clean shiney Silver in. Waited 10 min with no cloudiness. Put 5ml of Nitric...another 10 min and still clear with no reaction. As soon as I put the next 5ml of Nitric in the white precipitant ccloud went from silver piecs to Silver piece untill the entire liquid was cloudy. I took it off the heat, Let it cool and the Silver was black as coal. Thats when I checked my water and found out I'd been using Tap Water. (Which where I live is so bad we won't even drink it. We buy our water in 5 Gallon jugs for the House)

Dale

 

[METLMASHER]

If I am deluting this recipe 50/50 and it is only 35% to start with is it even strong enough to do the job? Thanks
Dale

Dale, my answer was in error, and I apologize. I had missed that you were making your nitric, not using standard 68%.