# Reducing Silver nitrate to metallic silver



## Anonymous

Greetings to All,

This is my first post in this great forum. It is the best educational forum site I found in the net for PM... So much knowledge and experience.

Here is my question: What are the steps required to reduce silver nitrate to silver metallic powder. :?: 
Thanks and regards,
amoodikh


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## aflacglobal

Welcome to the forum amoodikh.


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## lazersteve

Amoodikh,

Check the Silver videos on my website http://www.goldrecvoery.us .

You'll need a solid copper buss bar or copper tubing.

Steve


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## Anonymous

Thanks Steve for your reply and vedio.

How then to reduce copper deluted in the solution? :?:


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## renatomerino

amoodikh said:


> Greetings to All,
> 
> This is my first post in this great forum. It is the best educational forum site I found in the net for PM... So much knowledge and experience.
> 
> Here is my question: What are the steps required to reduce silver nitrate to silver metallic powder. :?:
> Thanks and regards,
> amoodikh


Hello: 
The metallic copper reduces the silver nitrate in solutions. 
Greetings :lol:


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## Lino1406

Dissolve in distilled water;
Add NaOH;
Filter and rinse;
Melt


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## Lou

Yes, but too much base and your Ag2O will become Ag(OH)2- and will be washed away. Use only enough base as is theoretically required. Sounds easy, but it is not because the alkali bases are all hygroscopic and contain varying amounts of water.


I agree though, much purer silver can be had by just melting the silver oxide. That is of course assuming you had pure silver nitrate that was uncontaminated by other metals!


Lou


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## goldsilverpro

I think he wants powder. From silver nitrate, most of the reducing agents I can think of produce a mirror and not a powder. He may have to convert it to something like a chloride first. One of the cleanest powders I've seen was from AgCl, using NaOH plus Formaldehyde, in a blender. Here's 37,000 possibilities.

http://www.google.com/search?q=%22silver+powder%22+production&sourceid=navclient-ff&ie=UTF-8&rlz=1B3GGGL_enUS259US259


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## Juan Manuel Arcos Frank

Well...the bad boys of Shor International have a SPC (silver precipitant crystals) precipitant that added to the silver nitrate makes pure silver..
Does anybody know what is SPC precipitant?


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## Noxx

Copper powder ?
I could search a little. Should not be so hard to find...


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## Juan Manuel Arcos Frank

Noxx:

You are right as always.Copper,Zinc,Alumium or Iron could work,I think,but I never have tried.This week I will test these metal powders and post what happens.Thanks a lot.

Manuel


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## goldsilverpro

SPC could be something like ascorbic acid, certain sugars, hydroquinone, metol (a photo chemical), tartrates, etc.


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## Juan Manuel Arcos Frank

GSP:

Thanks,I do appreciate,I will test these too.

Manuel


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## Noxx

Be careful, hydroquinone is considered a carcinogen in some countries (ex: France)


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## Lou

Hydroquinone is also dirt cheap. I use it quite frequently...as far as I'm concerned, it's no worse than phenol for your health. Don't eat it, don't rub it on your hands, and just be hygienic whilst using it. I've worked with many, many carcinogens and I'm not terribly worried--proper hygiene, apparatus, and overall common sense will protect you.


Typically almost an aldose or an aldohexose (i.e. glucose) will work fine. Ascorbic acid, aka vitamin C also works but it is significantly more expensive than sugars and HQ.

Parting caveat--I'd be more than a little bit hesitant about adding any formaldehyde to ANY solution with free hydrochloric acid--there are some very nasty chloromethyl ethers than can form, and those are volatile and they are very carcinogenic.


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## goldsilverpro

Good to know about the formaldehyde plus HCl, Lou. I only used it on well rinsed AgCl.


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## Lino1406

with nitrate should be avoided
on explosibility grounds


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## Lou

Good point Lino!


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## 4metals

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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## Noxx

Any patents on this technique ? I'd like to read more.


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## 4metals

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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## goldsilverpro

4metals said:


> The silver is processes as described and comes out 9999+ every time.
> 
> the silver I assay with a Volhard titration in house



I have several questions, but this is the one that really caught my eye.

How on earth are you able to get enough accuracy from a Volhard titration to say that the silver comes out to be 9999+ Fine? I ask this with some experience, since I have run many 1000s of Volhard titrations in my life.


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## 4metals

It's in the burette, 0.01 ml subdivisions and a magnifying eyepiece, my eyes aren't what they used to be!


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## Lou

Um, I can buy 99,9% at the top end. Just because you used 20.21 mL of titrant, does not 4 significant figures make!!

It's possible I suppose, but I would not feel comfortable claiming this. This 10X increase in purity also brings in such factors as:


inconsistency of the glass buret's diameter, and therefore volume along a distance

volume and therefore concentration differences based on temperature fluctuations

error on the chemist's part in making the titrant, delivering the titrant, sample preparation, etc.

the lower bound of where the indicating reagent can be seen (I posted on this already).

Can you give me details of your method, I'd like to dissect it.

Thanks!!


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## 4metals

Here's the method and a cut and paste from the spreadsheet I set up to calculate the working factor for the thiocyanate as calibrated with proof silver. I've calculated the titrants strength and the silver proof weights so a class 'A' pipette is used to deliver the first 75ml followed by up to 10 ml from the capacity of the burette. Now I know that there's an inherent error in pipettes and burettes, and variations of standard temperature and pressure cause volume fluctuations, but I've set up a refinery and lab for a guy who isn't about to spring for an ICP or an AA, and considering the spitting and corrections needed when using a classic fire assay on fine silver the titration produces the most consistent result, and it is reproducable. I am however open to all suggestions.

Volumetric Silver Titration
“Volhard’s method”
The analysis of silver bullion by titration is a very accurate for high silver bullion and fine silver. Samples which are soluble in nitric acid are perfect for this method. The converted silver chlorides from the aqua regia refining process also work well as the gold can be calculated gravimetrically after the parting process and the silver can be calculated via titration. This method eliminates cupellation and proofs required to correct for furnace losses. It also is preferred for fine silver assays providing the titrant is calibrated against fine silver when it is made up.
The basis of the reaction is as follows:
AgNO3 + KSCN = AgSCN + KNO3 (1)
3KSCN + Fe(NO3)3 = Fe(SCN)3 + 3KNO3 (2) 
Reaction (2) does not occur until (1) is completed, therefore the addition of a small amount of a soluble ferric salt serves as an indicator by the formation of red ferric thiocyanate in the presence of an excess of the thiocyanate. When the titrant enters the solution it will produce a red streak which will re-dissolve on mixing until all of the silver has been converted and the solution turns red signifying the end point. Chlorides interfere by reaction with silver so all reagents, glassware, and water must be chloride free.
Potassium thiocyanate Prepare and standardize a solution. (M=N) 5 g KCNS Diluted to 1 L. Standardize against 0.5g fine silver. 

Ferric alum indicator Dissolve 100g of crystals in 1 liter of distilled water, Add 2M Nitric Acid to clear the solution. 
----METHOD----

Dry a small tray containing reagent Potassium Thiocyanate in the drying oven overnight. In the morning place in the dessicating chamber to cool.
Prepare a solution for titrating by dissolving 5 grams of dried Potassium Thiocyanate in 1 liter of distilled water.
Prepare a sample of proof silver (99.99 fine) by digesting approx. 0.5 grams via the procedure below and titrate it to standardize your solution. The validity of this method is you are assuming the silver used to standardize the titrant is fine (proof) silver.
Enter the volume of solution titrated into the spreadsheet, it will calculate the strength of the solution. 
Weigh 0.5 gram of unknown sample on the analytical balance and digest in 15 ml Nitric acid. Heat acid to expel the nitric acid. If analysis is for fine silver bullion the 0.5 gram sample should be sufficient.
Dilute the parting acid and rinse waters to 50 to 75 ml and cool the sample in a tray of cold running water in the sink. Warm samples produce errors on the high side.
Add 5 ml of Ferric alum indicator. 
Titrate with Potassium thiocyanate to a red endpoint which doesn’t fade on mixing. The trick to this is the speed of the mixing bar. Too fast and the swirling white Silver Thiocyanate masks the endpoint. Slow the mixer down when the endpoint is close so the Silver Thiocyanate swirls lower in the flask and more of the solution, which is where the endpoint reaction takes place, is visible. 
Enter the volume of thiocyanate titrated in the spreadsheet and it will calculate the silver purity.
As with any assay duplicates of both standardization and unknowns will increase accuracy. 

Standardizing Solution 
proof # 1 <><><><>	<><><><>	proof # 2
0.4243 grams proof Ag 0.4365
76.43 milliliters KSCN actual 78.71
0.005551 grams Ag/ml KSCN 0.005546
0.005549	WORKING FACTOR	

unknown #1	<><><><>	<><><><>	unknown #2
0.4391 g sample digested 0.4265
79.13 ml KSCN titrated 76.86
0.439059096 grams silver in sample 0.426463821
0.999907 assay 0.999915

Average assay 1 & 2 0.999911009	
difference between cups 4.16271E-06


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## goldsilverpro

4metals,

You are obviously a very knowledgeable person and we are lucky to have your participation on this form. I certainly agree that the Volhard method is the best choice for your client but I feel, along with Lou, that the claim of using it to produce silver assays of 4 significant figures is quite extravagant. As with Lou, I would think that 3 significant figures would be considered a worthwhile achievement. Your method is almost identical to the one I used. You have taken almost every precaution I can think of to get the best results.

The number of significant figures in the answer can be no higher than the lowest number of significant figures in any part of your procedure. I learned that in the first week of College Physics. 

(1) From the sample and proof weights you provided, it seems that your analytical balance only reads to +/- .0001 grams = 3 significant figures for the .5 gram weighings. Also, there are 2 weighings involved, the proof and the sample. 

(2) The tolerance of a 100 ml Class A buret is +/- 0.1 ml. A reading of 90.00 ml would actually be somewhere between 89.9 ml and 90.1 ml. Even if you used the entire 100 ml of titrant, you would be stretching it to get 3 significant figures. As I see it, this is the source of the greatest error.

(3) I assume you achieved a single drop endpoint. I don't know how small the drops are, but I doubt that they are smaller than .02 ml = 3 significant figures.

(4) What is the source of the proof silver? If it is silver that you produced, that would cause a problem. It might be best to buy one of those special high dollar 999.99 Fine Maple Leaf coins.

I'm sure there are others that I haven't thought of.

Also, all these errors are cumulative.

You may be actually getting 999.9 silver from your process. However, if you have based that entirely on a Volhard titration, I think you are fooling yourself.

Chris


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## 4metals

When I set up the procedure to refine the silver the first production batch was sent out to Ledoux for an ICP. The actual analysis was for impurities and they were subtracted from the total silver so it was an assay by difference. So the original assay and hence the claim was better than 4 nines. When the boss saw the tab for the analysis he said theres got to be a better way. Volhard was the best for much less expense and an inexpensive check for production lots. We use Heraeus silver 9999+ to standardize and run 2 titrations to standardize and for each sample we also run two titrations. The buret is a microburet with 0.01 ml subdivisions and 0.01 plus or minus tolerance. The weakest link is the 75 ml pipette with a tolerance of 0.08 ml. As with any fine metal assay the higher the purity the more difficult the assay. 
An old timers indication of purity for fine gold is the cleavage in the bar surface as it cools, exposing the crystal structure. Not quantitative but a good indication, do any of you guys know a trick to infer purity on fine silver?


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## Lou

What Chris said ^.


Anyway, 3N is believable from a volumetric titration.

Gravimetric titration is actually far superior and with the right balance and right setup, you can almost take this down to the equilibrium concentration of silver from its thiocyanate salt (which has a low Ksp). You seem smart enough to figure that one out.


Lou


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## goldsilverpro

With the added info you gave, the potential error is less but, you're right, the pipet is the bad actor. Even though your first batch was proven to be 999.9, it doesn't mean the rest are. If you must produce 999.9, I would get another assay method, in order to back it up. IMHO, the Volhard method just doesn't cut it.

Have you looked into the Guy-Lussac method? It's a pain to set up and a pain to use, but it's considered more accurate than the Volhard method. It was the standard method for silver bullion used by the U.S. Mint. Some use a much simpler combo G-L/V method. They start with Guy-Lussac and finish with Volhard.

There's been a lot of discussion about the "pipe" and the crystal on pure gold and silver on this forum. From my experience, the crystal on silver will appear at least at 999.5 and maybe as low as 999.0.

BTW, the formate refining process is very interesting. I've read about it for years but have never used it. I have found the standard silver cell to be simple and, if it's done right, can produce a consistent 4N product.

How are you melting the silver? Induction? Gas? Was the original sample sent to Ledoux taken before or after melting?

Welcome to the forum!


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## 4metals

The silver is melted by induction and poured through an induction heated shot box because the jewelery industry, where we do most of our business, uses silver in shot form. We have been getting requests for 100 ounce bars but considering how pure silver spits on cooling we would have to set up an argon blanket to cover the melt and the mold, now we're looking for equipment to set it up. The silver sent out to assay was melted and shotted. All of the feedstock for the refining process is sterling and we assay it with the Volhard titration as well. I prefer the sodium formate reduction of silver to a silver cell because we inquart karat into the starting alloy and produce a high purity gold residue as a side benefit. The only cost is the nitric to digest the base metal in the karat. I have sent out samples of the silver both when we were processing only sterling and again when we inquarted the karat, both assayed 4 nines. We found a lab to assay by difference using an AA and it was cheaper so the boss dealt with it, providing it doesn't become a habit. I've never personally used the Guy Lussac method, it seems more complicated than I'm willing to introduce into our lab, but I will read more about it.


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## Lou

I'll have to give this formate reduction a crack sometime. Sodium formate is dirt cheap to make from formic acid and sodium hydroxide. Before I switched over to using hydrazine sulfate and now lately hydrogen gas, I used to use sodium or ammonium formate for reducing Pt, Pd, and the like. It worked well and quantitatively, but I was never happy with the size of the precipitate. Always too fine, even after a prolonged boil.

What's the silver precipitate like?

I'm about to buy some hydroquinone from Shor to use on silver, merely because a little goes a long way and I'm curious if their silver precipitant crystals really are hydroquinone.


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## 4metals

The silver precipitate from the formate reduction is like fine sand. The up side is it rinses well and dries nicely in a Buchner funnel.


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## DNIndustry

I just thought I would bring this up.

Hydroquinone is used quite extensivly in anal bleaching.

Lou if you need some and havent purchased yet shoot me a PM ill send ya some.


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## Lou

Hahahaha,

What am I supposed to make of that comment? Guess I had it coming after not calling on those hoods. I've got the message, I'll give you a buzz and we'll work it out.

Anal bleaching hmm? :lol: :lol:


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## Noxx

Lol ! 

But I wouldn't use that, Hydroquinone is a suspected carcinogen.


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## peter i

DNIndustry said:


> I just thought I would bring this up.
> 
> Hydroquinone is used quite extensivly in anal bleaching.
> 
> ...




Well, I certainly learned a new term today :shock: 

I thought it was a typo, but a little google-fu taught me otherwise... (note to self: if it sounds really weird, think before you google and never start with a picture search!!)


Back on track:
Wasn't sodium formate mentioned somewhere as a nice reductant for silver?


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## Helian

Another way you can do it that has the advantage of being simple is dissolve the silver nitrate in distilled water, add just a few drops of nitric acid, and then stir with a sheet of copper. The silver will drop out of solution as you stir. It's a little tedious, but it works.


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## Irons

goldsilverpro said:


> SPC could be something like ascorbic acid, certain sugars, hydroquinone, metol (a photo chemical), tartrates, etc.



Hexamine?

Now he's completely confused.


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## Juan Manuel Arcos Frank

LOL...Irons....Do not annoy GSP...hydroquinone and metol are both photo developers.

Have a nice day.

Manuel


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## Irons

DNIndustry said:


> I just thought I would bring this up.
> 
> Hydroquinone is used quite extensivly in anal bleaching.
> 
> Lou if you need some and havent purchased yet shoot me a PM ill send ya some.



Which end you put the ORP electrode?


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## 4metals

Just an update on the sodium formate method, recently I went back to a refiner who I set up using the formate method. He's been running it for 2 years now and has settled down to refining 500 oz/day of sterling silver. He recently got in some silver odds and ends and processed them the same way as usual. The resultant silver was seriously contaminated with lead. Now I had set them up to test for lead while assaying the bars (qualitatively) but that procedure somehow got swept under the rug. 

We ran a few batches, which I pre screened for lead, and they came out well. To be sure we sent it out to LeDoux for an ICP and it came back .9996, the second days lot came out .9997. Considering silver has to be .999 for sale they're still in good shape. 

The thing I'm most surprised at is the low silver content of the scrap they are getting which is supposedly sterling silver. The best assay is 90%, down to 85 on some bars. Unfortunately that level of copper eliminates a silver cell as an alternative. 

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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## peter i

I'm testing the method as we speak using analysis grade sodium formate and silver nitrate. Seems to give a very pleasant light grey powder.


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## Irons

I love this place. 8)


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## Lou

Funny enough, I still haven't gotten around to the formate reduction.

I really don't like the Karo Syrup/aldose method all that much despite the inherent advantage that it is arguably one of the most selective ways to get pure silver.
Something about dissolving, Cu cementing, and the Thum cell is very attractive... ah yes, no silver chloride!

4metals, ever considered alloying up and putting it through the cell?


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## 4metals

Lou,

Alloying up and running in a cell is only an option if you have a good quantity of almost fine silver to alloy up with. Lately the guys I've worked for are getting in sterling and coin silver. 

I get clients on both ends of the refining spectrum, some have the capital to finance the operation and the support lab properly, lately I've seen the low budget type. If I set up a guy who can put in an AA or an ICP I'd consider a silver cell because the instrumentation makes it easy to monitor the copper levels which climb quickly. It involves quite a bit of electrolyte changing but it is still do-able with less waste acid than the formate method. The low budget guys make management harder. I have yet to find a volumetric analysis for the copper levels in the cell to aid the more frugal refiner. Any suggestions?


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## lazersteve

4Metals,

I'm like Lou in regards to the fact that I've been wanting to try the formate reduction of silver, but I haven't gotten around to it yet. 

The day you posted the reaction I bought a few pounds of sodium formate for the reaction, but I haven't got around to trying it out. I only process silver when I don't have any other PM's to run, and lately I've not had a shortage of gold and platinum to process, so the silver will have to wait.

When I get around to trying the process, i likely film it and post it to my website to go along side my other silver reduction videos.

Thanks for the great tip again!

Steve


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## goldsilverpro

> I have yet to find a volumetric analysis for the copper levels in the cell to aid the more frugal refiner. Any suggestions?


I, also, don't know of any good methods of titrating copper in this matrix. I controlled 12, 30 gallon cells by first analyzing the silver with a Volhard titration and then measuring the specific gravity of the the solution with a hydrometer (of which I had a series of). Before then, I had made up about two dozen different silver/copper solutions, compared the silver concentratration verses the made-up copper concentration verses the S.G., and made up a few graphs. From all this, if I knew the silver concentration, I could determine the approximate copper concentration from a graph. I don't think I explained it very well, but it's pretty simple stuff. About the only things that contribute to the S.G. are silver and copper. This isn't rocket science. All you usually need to control an industrial system are close, quicky, approximations.

This is way off the beaten track. One time, I worked for a huge plating shop that had a job to electroless nickel plate a bunch of stainless screens that were used as the sides in a huge centrifuge to filter out sugar crystals. The screens were made up of very tiny hexagonal holes. The holes were too big. We had to close them up a bit to an exact width with electroless nickel. The quality control problem was to measure the final hole size after we plated them. I discovered that, by placing a screen of known hole size over a plated screen on a light table and then rotating one of the screens, the holes visibly increased in size. This is due to the moire' pattern that was produced. As you turned one of the the screens to a certain angle, the illusion of the average hole size on the light table might increase from, say, 1/64" to 1". That way, you could easily measure with a ruler the ratio of the average hole size to the spacing between the holes and, therefore, estimate the actual hole diameter. This is a very difficult thing to explain, but it was very simple to do.

What I'm saying is that, with ingenuity, difficult quality control problems can be made very simple. Comparing the silver analysis with the S.G. to get the copper analysis is one of those things.


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## 4metals

GSP,

Sounds like an interesting procedure, the silver analysis is simple and accurate. How close to actual levels will a baume reading get you, within 1 oz/gallon? Sounds like you put a lot of effort into making standards and graphs.

I now use the silver content of the anodes going in and the gold content if any, the rest I assume is copper. Using a spreadsheet I can track theoretical levels of copper, or at least what it will be when all of the anodes are dissolved. Analysis is much better!!!!!


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## goldsilverpro

> Sounds like an interesting procedure, the silver analysis is simple and accurate. How close to actual levels will a baume reading get you, within 1 oz/gallon? Sounds like you put a lot of effort into making standards and graphs.


I would say that the copper estimate was accurate within 0.1 - 0.2 oz/gal. It didn't take long to make the standards and graphs, maybe 3 or 4 hours. I just started on the low end and then made additions - with mathematical adjustments, of course. Temperature, of course, had to be considered. I surely used S.G. hydrometers, since baume' is a pain. I think each chart had a single silver content - 1 oz/gal, 2 oz/gal, etc. The intermediates could be estimated (can't think of the mathematical word I really want to use here - interpolated?).

Probably, when all was said and done, my true calling was that of a Q.C. guy - or a math teacher. I never did either.


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## dick b

extrapolate


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## goldsilverpro

extrapolate

Right. It's amazing how 4 scotches will taint one's memory.


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## dick b

Who cares. TGIF!


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## Oz

Although it is less than scientific I watch the color of my electrolyte and do my best to monitor my feedstock to keep track of copper concentrations. Maybe I reverse engineer it a bit but I take some of the produced silver crystal near the end of the electrolytes life and after washing dissolve a small sample in nitric. It takes very little copper contamination to change the color of the solution. My greater concern in the cell is palladium contamination.


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## Palladium

goldsilverpro said:


> Probably, when all was said and done, my true calling was that of a Q.C. guy - or a math teacher. I never did either.



I would say your both. And dam good at it to. 8)


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## Harold_V

Oz said:


> Although it is less than scientific I watch the color of my electrolyte and do my best to monitor my feedstock to keep track of copper concentrations. Maybe I reverse engineer it a bit but I take some of the produced silver crystal near the end of the electrolytes life and after washing dissolve a small sample in nitric. It takes very little copper contamination to change the color of the solution. My greater concern in the cell is palladium contamination.


It was my routine to make the new batch of electrolyte from crystals that were removed from the cell at the time of operation, and always that which represented the tail end of the session. I ran my cell as a batch cell, it was not continuous. I could almost always part a 200 ounce anode and get pure silver. 

As Oz stated, it took almost nothing in the way of contamination to create an indication of purity of the silver. In preparing my electrolyte, the solution was boiled, with a small amount less of nitric than would be expected to dissolve the allotted amount of silver (30 ounces). I'd balance pH by adding a few drops of nitric to the operational cell. By boiling, all traces of the big red cloud were removed from the solution, yielding a clear color. A tint of any description was an indicator of contamination. Running an anode that was too heavily concentrated in platinum group metals was occasionally a problem, causing a trace of palladium to co-deposit, as Oz suggested. 

The best indicator I had was the nature of the crystals that were developed. I always started my cell sans copper. It accumulated fast enough that I didn't wish to lose any production. Initially, the deposit of silver was strongly attached to the cell, and often was a solid sheet. It would strip, but required a little effort. I used to use a fiber glass scarper (shop built, with a stainless handle) to remove the deposit. As the copper level climbed, the deposit turned more towards crystals, and were attached much looser. 

When the copper level approached being too high, the nature of the deposit changed drastically. Instead of growing crystals, my particular setup would start growing thin strands of silver, much like strands of steel wool. That was a sure sign it was time to change electrolyte, and usually came at the end of the anode's life. 

To insure that the production was pure, I always dissolved the fine strands, along with crystal. The strands, being the last to be grown, were an excellent measure of the over-all quality, usually yielding a clear solution. Any crystal harvested from a batch that made an off color electrolyte was placed back in the basket, with an anode placed on top. The crystal was parted a second time to insure purity. There was no need to melt. 

I believe I have discussed this previously, but old age is taking a toll on my memory. 

Harold

P.S. 
Four scotches?

Damn, that sounds good!


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## Oz

Harold_V said:


> By boiling, all traces of the big red cloud were removed from the solution, yielding a clear color


This is important in that the color of the solution while driving out the gases and hot will resemble that of a slight palladium contamination. Until cool it can also have a slight bluish green hue that looks like a slight copper contamination.



Harold_V said:


> Running an anode that was too heavily concentrated in platinum group metals was occasionally a problem, causing a trace of palladium to co-deposit


I have not found to date any PGM other than palladium in my electrolyte. When one is concerned about palladium due to feedstock, DMG will tell the tale. Nickel can be a problem as well but is seldom seen unless running material from white gold inquartations in my experience.

I owe a huge thank you to Harold, GSP, and 4metals for most of what I know on this topic.

Thank you


----------



## goldsilverpro

Harold,

What you say is great with one small cell. However, I was controlling 12 cells, each of which started with 200 oz of silver. I preferred a more quantitative approach rather than flying by the seat of my pants. I could analyze the 12 cells in less than an hour. Through experience and a little experimentation, the analysis results were easily related to the silver quality.


----------



## golddie

There seems to be lots of coin silver being refined
What would be the best and most econmical method for refining coins
Would it be to use half half nitric and water
then drop the silver with suger then drop the copper
or this method is not that great of an idea


----------



## Oz

Much depends on the purity of the coins.

I would keep sugar away from nitric as it could have unintended entertainment value.


----------



## Lou

4metals,

One could easily analyze for copper concentration using simple colorometric titration with a cheapo Spec 20 spectrophotometer. Ammonia would be the titrant. Of course, a standard curve would need to be constructed.

Chris's idea of using specific gravity might be better. Back in the day it was baume that used to be on the sulfuric acid bottles, indicating their strength. I think the number may of been 67. Way back in the day.


Scotch sounds good. I just got a bottle as a present the other day: The Distiller's Edition Isle of Skye Talisker. It's a double matured single malt, distilled 1990.


----------



## PreciousMexpert

> 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)


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


----------



## cmethowusa

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?


----------



## butcher

tin and HCL = stannous chloride 
tin nitric =jell
nitric + HCl = aqua regia
I dont think it will work worth a hoot.


----------



## Oz

I agree


----------



## Harold_V

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


----------



## SilverNitrate

Here is my famous 'Candy Lava' video. Mixed with sugar you can convert Silver oxide or nitrate straight into metallic silver.
http://www.youtube.com/watch?v=s5Yg0gCOlXA


----------



## Refiner232121

SilverNitrate
How much suger did you use


----------



## SilverNitrate

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.


----------



## peter i

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.



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.


----------



## jsargent

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.


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

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.


----------



## jsargent

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.


Excellent! I'm looking forward to trying your method. Thanks!


----------



## HAuCl4

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.



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:


----------



## 4metals

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.


----------



## Barren Realms 007

> 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!.



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


----------



## HAuCl4

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)


----------



## HAuCl4

4metals said:


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



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.


----------



## Lou

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


----------



## HAuCl4

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.


----------



## HAuCl4

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.



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+.


----------



## Lobby

4metals said:


> ...
> 
> Volumetric Silver Titration
> “Volhard’s method”
> The analysis of silver bullion by titration is a very accurate for high silver bullion and fine silver. Samples which are soluble in nitric acid are perfect for this method. The converted silver chlorides from the aqua regia refining process also work well as the gold can be calculated gravimetrically after the parting process and the silver can be calculated via titration. This method eliminates cupellation and proofs required to correct for furnace losses. It also is preferred for fine silver assays providing the titrant is calibrated against fine silver when it is made up.
> The basis of the reaction is as follows:
> AgNO3 + KSCN = AgSCN + KNO3 (1)
> 3KSCN + *Fe(NO3)3* = Fe(SCN)3 + 3KNO3 (2)
> Reaction (2) does not occur until (1) is completed, therefore the addition of a small amount of a soluble ferric salt serves as an indicator by the formation of red ferric thiocyanate in the presence of an excess of the thiocyanate. When the titrant enters the solution it will produce a red streak which will re-dissolve on mixing until all of the silver has been converted and the solution turns red signifying the end point. Chlorides interfere by reaction with silver so all reagents, glassware, and water must be chloride free.
> Potassium thiocyanate Prepare and standardize a solution. (M=N) 5 g KCNS Diluted to 1 L. Standardize against 0.5g fine silver.
> 
> *Ferric alum indicator* Dissolve 100g of crystals in 1 liter of distilled water, Add 2M Nitric Acid to clear the solution.
> ...




I'm in the process of setting up to do some Volhard titrations and have a question. 

Rxn 2 shows the use of Ferric nitrate as the source of the iron indicator, but later in the procedure you mention ferric alum indicator: iron (III) ammonium sulfate.

I suppose all that's needed is a source of Fe, so it shouldn't matter what iron chemical is used. But before I purchased anything, I thought I'd ask.

Thanks, folks!


----------



## IgorGreece

Lou said:


> 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



Looks like PGMs drop @ pH 4.3-4.5 and T 70-100C
US Patent 6290749


----------



## Palladium

Just looking through the old stuff. Does anyone know what the ratio of sodium formate is for each gram of silver dropped from the nitrate solution? I'm not good when it comes to those type calculations.


----------



## butcher

silver nitrate
AgNO3 = 169.8g/mol
Ag = 107g/mol
(About 63% silver)

Sodium formate
HCOONa = 68g/mol

Formula:
Reduction of silver metal from a solution of silver nitrate using sodium formate as the reducing agent.
2AgNO3 (aq) + HCOONa (aq) --> 2Ag (s)+ CO2 (g)+ NaNO3 (aq)+ HNO3 (aq)

2AgNO3 = 2 x 169.8g/mol = 339.6g for (2mol AgNO3)
(OR 2(Ag) X 107g silver = 214 grams of silver in solution)

We want about 10% excess sodium formate
68g X 1.10 = 74.8 grams

So it looks like for 2 moles of silver nitrate (or 214grams of silver) we need about 75grams of sodium formate.
If my math is right.

I notice in the reaction above we are left with the byproduct of HNO3 and NaNO3 left in solution, this would be useful, (some base metal may be involved). you could add some sulfuric and distill off some useful nitric acid from this stuff.


----------



## butcher

I haven't gone back and re-read this topic (I will), this may have already been discussed.

Kodak patent for making high purity of silver nitrate.
Interesting using pH to separate base metals and most of the valuable metals from the silver nitrate salts before re-crystallizing fairly pure silver nitrate salts.

http://www.google.co.in/patents/US5000928
http://www.freepatentsonline.com/6290749.html
http://www.google.com.tr/patents/WO1987005591A1?cl=en


----------



## Palladium

Thanks butcher. I'm wanting to try 4 metals method on large volumes of silver nitrate. sure would be the cats meow for side stepping the cell when using it with sterling. Anyone have first hand do's and don't's or pointers from what metals posted? I'm on my phone today so please excuse my typing.


----------



## Lou

I think the formate method is really only useful if your waste disposal costs are very cheap; otherwise you have quite a bit of residual formate that needs to be electrochemically oxidized to CO2 before it can be disposed of cost-efficiently.

PPOP is higher with formate than the cell; actually, pretty much anything is higher on a price-per-ounce-processed than electrochemical refining. Gold/silver both are cheapest to refine if one can afford to do the cell maintenance and inventory significant units in the electrolyte. 

Of course you only want to use 99% Au for Wohlwill and 85%+ Ag for the Thum/Mobeius.


----------



## lazersteve

I'm getting 99.99+% fine silver (on table top XRF) from silver chloride using the sugar and lye method. 

With careful filtration and hot water rinsing prior to precipitation of the chloride using muriatic acid I can even get away with leaving a little copper nitrate in the silver chloride slurry prior to conversion. My muriatic, sugar, and lye costs on 50#'s of final pure silver is less than $20 for the batch and can be achieved in less than 1 week (preparing the silver chloride takes longer). The actual conversion step is nearly instantaneous and takes very little precision to achieve consistent results. 

I've got a silver cell and formic acid, but I see no reason for me to go through all of the headaches, tie up silver, and create the wastes when I can get equal purity silver with the AgCl method of lye and sugar. The only exception may be if you are doing huge quantities of silver that has known trace gold or PGMs. My silver is treated to remove these impurities prior to conversion to the chloride.

Here's an example of my silver using this method:







The bar is not very pretty, but it is very pure. A pin sample shot 100% on table top XRF. The bar was melted using an induction furnace and cast into graphite. The source silver was sterling silver and was converted to Ag from AgCl via table sugar and lye.

Steve


----------



## butcher

That bar of silver makes that dollar bill look almost worthless. :lol:


----------



## Palladium

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.



Is that ph adjustment in the hydroxide step really 1.5 ? Not questing you, but all the patents i've read calls for a higher ph value most seem to say about the 4-5 range. Seems with a lower ph you would still have a lot of contaminates to carry over in the next step. I'm fixing to do the 2nd half of my video and i don't want to screw it up because i missed that one point. Can anybody clarify that before i embark on this escapade? The rest i understand.


----------



## g_axelsson

Palladium said:


> 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)
> ...
> 
> 
> 
> 
> Is that ph adjustment in the hydroxide step really 1.5 ? Not questing you, but all the patents i've read calls for a higher ph value most seem to say about the 4-5 range. Seems with a lower ph you would still have a lot of contaminates to carry over in the next step. I'm fixing to do the 2nd half of my video and i don't want to screw it up because i missed that one point. Can anybody clarify that before i embark on this escapade? The rest i understand.
Click to expand...

As I see it (from a purely theoretical standpoint as I have never tried this myself) you filter off any solids first, then adjust pH and precipitate the silver. If the pH is adjusted too far some dissolved metals could precipitate and contaminate the silver in the next step. Obviously the pH adjustment isn't for precipitating contaminations as it is after the filtering step.

... theoretically speaking. 8) 

Göran


----------



## Palladium

Hummmm.... No answer on the ph? Are those crickets i hear? :| 

Moving right along then. That's what learning is about.

Part 2 is in post production now. 8)


----------



## Tub Buster

goldsilverpro said:


> I have yet to find a volumetric analysis for the copper levels in the cell to aid the more frugal refiner. Any suggestions?
> 
> 
> 
> I, also, don't know of any good methods of titrating copper in this matrix.
Click to expand...

That quote was from January, 2010. I'm reactivating this thread because I may have a workable method to titrate the copper. It is an iodometric assay, based on these reactions:

(1) 2 Cu(+2) + 4I(-1) => Cu2I2 + I2

(2) 2 Na2S2O3 + I2 => Na2S4O6 + 2NaI

Ionic copper plus ionic iodide combine, forming elemental iodine (I2), and then the I2 is titrated with sodium thiosulfate. When the free iodine is used up, a soluble starch indicator loses color and the assayer knows the endpoint has been reached.

The original method is for ore and mill product, so it contains procedures for eliminating other elements. However when testing a silver cell most of these interfering elements will not be a problem, so the method can be simplified.

The attached file is a scan and OCR from an out-of-print book. It contains notes on working with iodine that may be useful for anyone doing iodine leaching.

I hope this is of some value.


----------



## Lou

This is the copper assay after silver has been removed, no?


As for Ralph's question--formate works nicely on silver if there is no PGM present, in which case it contaminates the silver. A lower pH helps in preventing some of that, but Pd will still greatly contaminate silver produced in that process.


Lou


----------



## nh6886

Tub buster,

Thanks for sharing that. I am not doing this presently but I'm adding this to my collection of information for later.

Lou,

In your earlier comments on the formate method you mentioned waste disposal cost being high unless you electro chemically oxidize the formate waste, would you be willing to expand on that or point me in the right direction to find this information. 

All the Best,
John


----------



## Tub Buster

Lou said:


> This is the copper assay after silver has been removed, no?


The author writes,


> "Lead, bismuth and silver react with potassium iodide to form insoluble iodides, but moderate amounts of these elements do not interfere. Interference from large amounts can be minimized by
> adding a large excess of potassium iodide (6)."


Bromine could be used to remove silver, but it interferes with the assay,
and would have to be removed somehow. I'm attaching a spreadsheet of solubilities and K_sp's.

I don't understand solubility products. Someone educate me...

PS. Haloacetic acids (HAAs) are said to be carcinogenic. Just a caution--copper acetate is used in this assay.


----------



## Research135

Lou said:


> This is the copper assay after silver has been removed, no?
> 
> 
> As for Ralph's question--formate works nicely on silver if there is no PGM present, in which case it contaminates the silver. A lower pH helps in preventing some of that, but Pd will still greatly contaminate silver produced in that process.
> 
> 
> Lou


Tried this and it worked:
1-Removed Pd quantitatively from nitrate solution using DMG.
2-Adjusted Ph to 1.5 in the nitrate solution, and 3.5 in the sodium formate solution added. Temperature at 40 degC. It took a while but all silver dropped. It is at least 9995.
3-Dropped the Pt using same formate solution with pH at 6.0 and temperature at near 100 degC.
4-All Pt and Pd losses less 1/10000. Silver losses less than 1/1000.


Thanks to 4metals and everyone else for posting these procedures. Fast, clean, precise.


----------



## Mudville9

I had some free time and played a bit with the sodium formate reduction method. Each lab run was slightly different from 4metals method as I wanted to determine the effect of the various parameters. Starting with a fairly strong, but dirty solution (Ag = 250 g/L, Cu 40 g/L, many minor elements), the resulting silver powder ranged from a low of 99.959% to a high of 99.993%.

Contaminants were measured by ICP-OES and silver by difference.
Lead did not present a problem. Starting solutions contained 3500 ppm and the powders contained 0-36 ppm, depending on the procedure used. Palladium can precipitate, but platinum stays in solution to a much greater degree. The majority of the copper in the powder is likely the result of my washing procedures. Tellurium, iron, selenium, bismuth, zinc and arsenic were the only other contaminants in the silver powder that were ever higher than 4 ppm, and these can be reduced to near zero through process modifications, if required.

I’m afraid I can’t discuss the actual procedures I used, but can confirm the validity of 4metals process, as written.


----------



## FrugalRefiner

Thanks for sharing what you can. 8) 

Dave


----------



## Lou

Best to conduct two precipitations. First for Pd. Second for silver.


----------



## Owltech

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.



Very sleek! Can't thank you enough for sharing this method! One thing I've noticed is that if I boil the solution for about half an hour the silver clumps together, making it very easy to wash (just like the gold sponge from precipitation with oxalic acid)


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## cuchugold

When I open my next bottle of Talisker, hopefully soon, my first toast will be to Lou and 4metals!. Then I'll drink the rest of the bottle!. :G


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## Palladium

Here's a video i shot of the process 4-5 years ago! I love it and still use it from time to time.

[youtube]http://www.youtube.com/watch?v=qSzjH9cSDpw[/youtube]


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## Owltech

Palladium said:


> Here's a video i shot of the process 4-5 years ago! I love it and still use it from time to time.
> 
> [youtube]http://www.youtube.com/watch?v=qSzjH9cSDpw[/youtube]



 I used the series as reference(as well as most of the videos you've made)! One of the first channels I subscribed to! Just didn't know it was you  

Thank you!


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## Palladium

Thank you sir!


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