Reducing Silver nitrate to metallic silver

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1 Filter solution to remove all ppt's
2 Raise pH to 1.5 using liquid caustic
raise the temp to 130 degrees F
3 Reduce the silver by adding a solution made of saturated sodium
formate which has been reduced to a pH of 4 using formic acid (filter
any precipitate)
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You have silver nitrate and from what I know it is silver dissolved in nitric acid.
You filter this solution to remove foreign metals
Now you have the silver nitrate powder.
Do you evaporate this solution to reduce the liquid to silver nitrate powder.

How do you add Sodium hydroxide to raise pH to 1.5
Also how much

Thanks
 
I got a response from Shor Int. concerning SPC. They said it was stannous chloride crystals and they do not sell it. If I recall, stannous chloride crystals can be formed with tin and muriatic acid? Is this a good precipitant, and better than copper? What's the hazards using stannous chloride in a silver nitrate solution?
 
Aside from testing with stannous chloride, avoid tin like the plague. It is likely the one single most troublesome element you must deal with when refining precious metals.

Harold
 
I don't know the exact ratio, but a 1 to 5 sugar to silver seems to go quite complete. I like to do the oxide for the fact that it will decompose to metallic silver around 400F. When converting from a nitrate I use flour or starch as the reaction is less intense.
 
SilverNitrate said:
I don't know the exact ratio, but a 1 to 5 sugar to silver seems to go quite complete. I like to do the oxide for the fact that it will decompose to metallic silver around 400F. When converting from a nitrate I use flour or starch as the reaction is less intense.
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It looks fun, but you get the same result from heating the silver oxide directly in a crucible......... apart from the fun, I see no advantage.
 
4metals said:
An easy method of producing 4 nines silver even if base metals are in solution is to reduce the solution with sodium formate as follows
1 Filter solution to remove all ppt's
2 Raise pH to 1.5 using liquid caustic
raise the temp to 130 degrees F
3 Reduce the silver by adding a solution made of saturated sodium
formate which has been reduced to a pH of 4 using formic acid (filter
any precipitate)
4 The solution will turn brown from the reduction of the silver and will
turn a bright blue (if the silver nitrate was from sterling) when the
reaction is completed.
5 Test for completeness of the reaction by sampling the solution on a
glass rod and dripping a drop into chlorinated tap water. White ppt
means more silver is present. Add more formate solution until test
yields clear drops into chlorinated tap water.

Needless to say no chlorides in the make up chemistry water
Works extremely well on sterling silver scrap digested in 50% Nitric/Distilled water. The starting pH is critical as is the pH of the formate reducing solution.
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4Metals I am going to try your formate reduction method for dropping silver but I have a question... The silver I am working with is from an inquart digest of impure gold that has some amount of platinum in it. Some of the platinum is taken up in the silver nitrate solution as one would expect. So what happens to the platinum when performing this method? Does it remain in solution with the base metals or does it drop out with the silver?
 
4metals said:
I have recovered both Pt and Pd from the waste stream after dropping the silver with this method. It has never come down to contaminate the silver precipitate.
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Excellent! I'm looking forward to trying your method. Thanks!
 
4metals said:
I got the method 2 years ago from a sterling refiner processing 30,000 ounce batches, we scaled down to 1000 ounces a day because we melt 350 ounces of karat gold scrap in with the 1000 ounces of silver (essentially inquarting) and digest the alloy in 50% nitric. The gold doesn't react and is filtered out and cleaned up in another nitric dissolve and melted with a borax, soda ash, manganese dioxide flux which scavenges any remaining silver and produces a 999.5 fine bar consistantly. The silver is processes as described and comes out 9999+ every time. The gold assay comes from a JM assay and the silver I assay with a Volhard titration in house because we sell the silver ourselves. We take care not to include any bars of gold with PGM's in the process because it will effect the gold purity, as it too will not dissolve completely. There is some on line literature about the method but it is sketchy and I go by the procedure I've outlined above. As with any process, familiarity will allow you to know when the drop is done just like you can look at a gold precip and know by looking that you've gassed enough. (of course I always have the guys check with stannous just in case) Recovery from the acid is complete and accountability is excellent. Just watch the pH, if the solution is stable at 1.5 when you start adding the reducing solution, and the reducing solution has been reduced to 4, you're OK. We make 55 gallon batches of reducing agent so it's on tap when we need it, it has never gone bad. One more thing, the digestion gets hot, which I'm sure you know, so heavy walled 316 stainless tanks hold up the best. Polypro is fine for the mixing and storing the sodium formate solution. Once you see the sponge this drops, you'll be hooked.
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Questions from a deranged theoretical alchemist:

1-Why is the pH so critical here?
2-What if, after dropping the silver and filtering the solution, one increases pH closer to 7 or above 7 (ammonia or NaOH ? )?.
3-Will any Pt in solution and/or Pd drop cleanly, and at what pH?.
4-At what pH will copper drop?.
5-What is a reliable, yet affordable digital pH meter and/or ORP meter that a dedicated amateur can purchase for these very precise experiments?.8)

Of course you are already guessing where I'm going with this?. :shock:
 
HAuCl4,

I have been contributing to this board for a bit over a year and a half and many of my posts have detailed techniques which I felt could benefit our members, both those refining on a small scale and those operating commercially, although the commercial refiners rarely reveal their identity. Your posts of late have made me question my rationale for posting.
Recently on a post you wrote;

These guys are processing scrap silver from all sources, and they want a filter and a filter they'll get...after they pay my fee and I move on!.

If they want something else, they can pay more fees. I got to eat too.

Now you’re dissecting an old posting about silver refining and again I’ll quote you;

Questions from a deranged theoretical alchemist:

1-Why is the pH so critical here?
2-What if, after dropping the silver and filtering the solution, one increases pH closer to 7 or above 7 (ammonia or NaOH ? )?.
3-Will any Pt in solution and/or Pd drop cleanly, and at what pH?.
4-At what pH will copper drop?.
5-What is a reliable, yet affordable digital pH meter and/or ORP meter that a dedicated amateur can purchase for these very precise experiments?.

Of course you are already guessing where I'm going with this?.

Well it’s my guess you are going back to the silver refiner to sell him some more services.

It is my feeling that a client pays a consultant for his knowledge and his experience, not for something picked up on the internet.

I feel it is time to tell you that if you really deserve to be paid for this knowledge you should be able to answer your own questions.

This situation really rubs me the wrong way; I truly feel that we should be helping each other to solve our refining issues. But I don’t feel that reading about a procedure on the internet is a license to go out and sell it under the guise of experience.

I have worked for many years to gain my experience and I have no qualms sharing what I know. I guess I’ll have to temper that by questioning the motives of the person doing the asking.
 
HAuCl4
These guys are processing scrap silver from all sources, and they want a filter and a filter they'll get...after they pay my fee and I move on!.
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How would you feel if you were treated like that?

It has been my experience that I would rather have 1000 customers that call on me on a regular basis rather than one that I try to make all my profit on in a short period.

4mteals please don't stop posting.

Thanks
 
Sorry if I rubbed you guys the wrong way. I apologize. I'll stop asking questions.

The fact of the matter is that what little commercial refining experience I had on my own was many years ago, and everything I knew I posted and shared it here for free in the 99.5% thread. Everything precious metals related I have done since then, has been on the hobbyist scale, except for a few consulting clients, like these recent ones. I take no shame in that, and the Buchner you suggested is probably a good idea on a part of their process, but I can buy it or make one locally for a fraction of the cost.

I have had clients on smelting, concentrating, etc. much before I came to this forum, and my strengths are on engineering solutions mainly, because I'm a Mechanical Engineer, not Electronic, nor Chemical, but I have pursued these areas for my own personal satisfaction.

The other filter will be a coarse filter which I already knew about, and a plug filter that I learned the technique right here.

I have not had any consulting clients done since I came to this forum on gold refining or platinum refining (on which I do not feel qualified, except to give very general recommendations), and all my questions have been bona-fide searches for knowledge for my own private satisfaction and/or occassional experiments on the hobbyist scale and without commercial profit.

I am most distressed by having upset 4metals, from whose generous knowledge I have learned A LOT, and I'm sorry if I upset others too, but since I have not resold any of his expertise, I do not feel bad about that.

If I look too eager to learn and ask too many questions, is because I'm fascinated by so much knowledge available here, and this area has fascinated me since I was in high school.

I'll try to temper my behaviour from now on, and will likely not post unless asked directly about something. It'd be a shame to pollute this magnificent forum with petty fights, and I'll do my part right now by standing down.

Cheers!. 8)
 
4metals said:
Well it’s my guess you are going back to the silver refiner to sell him some more services.
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I feel I owe you a direct answer on this issue:

I'm not going back to them to sell services, because they are not interested in changing anything they already do, except purchasing a filter from me.

Where "I was going with this" was back to the process of melting Pt scrap with 90% silver and digesting the lot in nitric.

After formate reduction of silver (your process that you learned along your career), then I was wondering if changing the pH and/or introducing ammonium formate at a higher pH would reduce cleanly the Pt, and therefore I asked those questions candidly.

You always have the right to refuse to answer. I don't know the answers either, but I will eventually researching on my own.

I do not have anybody to sell this process or knowledge to, nor I'm seeking someone to. Especially since Pt is so rare, and clients dealing with it, rarer.

Once again I apologize for upsetting you, since I've learned much from your posts. And believe that the fees I collect for my services are very meager and rare, and very little of them come from the PM industry.
 
Sodium, potassium, and ammonium formate will all reduce platinum and palladium, with no discrimination. The fact that this does not reduce the metal down is because a.) pH is too low, b.) temperature is too low. I would be certain to keep the temperature down when doing this reaction and maintain careful pH control. Most of my reductions with formate for PGM group metals are done at about 80*C at pH >6.

and HAuCl4, what we offer here, we offer. I for one am grateful to 4metals for the formate reduction. Beats hydroquinone, and it's cheaper.
Lou
 
Thanks for the answers Lou. I'm grateful to 4metals for his posts too. I hope he will eventually perceive my questions as coming from a fellow alchemist seeking higher knowledge, as they are.

His process, followed by my questions and now your answers have revealed a path for the expedite processing of Pt and Pd and Ag, simultaneously that must be apparent to all, and that was previously unknown to me

Cheers. 8)

edit: My intuition also tells me also that, at some intermediate pH, only one of the metals Pt, Pd, will remain in solution, the other having dropped cleanly, but this remains to be proven, and I don't know how practicallly it can be achieved. Just a hunch for now.
 
4metals said:
We cleaned up the lead contaminated silver by digesting it, dropping it as a chloride, hot water leached the lead, and reduced the chloride with sugar. The bar now had no traces of lead and it was processed by the formate method for sale.
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I'm sure you are aware of this, but how about just adding a little % of sulfuric and filtering out whatever lead sulphate is producing the contamination in every bar, before doing the formate reduction. That way, screening or not, the lead will be out. If one adds very little sulfuric, very little silver nitrate converts to sulphate, and the silver drop is rather clean. Or that's my recent experience in small batches of 10 oz or less. I haven't tried the formate reduction yet, but dropping the AgCl and treating with NaOH and H2O2 produced 999 silver. 8)

edit: If the silver drop is further contaminated with copper (from poorly washing the AgCl), then a 1 hour leach of the silver metal in ferric chloride (clean and filtered), with stirring, has always been enough to bring it back to 999+.
 

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