Electrolytic silver refinig

[Platdigger]

Still trying to understand this part Harold...

"The contents of my stock pot, which was cleaned out on an irregular basis, were simply incinerated "

Do you mean, just boiled down and incinerated?
Or....... cemented first?
Randy

 

[Oz]

So you understand, you can expect a high percentage of silver particles in your slimes. That's the nature of the beast. Major refiners used to boil the material in cast iron vessels, using concentrated sulfuric, which would remove the silver. I simply did a nitric acid process, then recovered all the values on copper once again. It really concentrated the palladium, but it worked.

Maybe I am missing something here but if you have a nitric solution containing silver and palladium could you not add sodium chloride to drop the silver and leave the palladium in solution? Just a guess on my part based on palladium solutions I have worked with.

 

[Harold_V]

That was the method I pursued towards the end, but the volume of silver chloride makes it almost impossible to separate all of the palladium from the silver. I used all of the procedures, slowly isolating the values. Well rinsed silver chloride was converted to elemental silver, using aluminum, washed well after conversion, then melted and cast as an anode, and parted once again. The resulting solution was evaporated to reduce volume, then the palladium was recovered. The residue, now much smaller in volume, would then be processed again. Eventually all of it is recycled and separated.

I did not use salt, not wanting to add anything that might be troublesome. I used HCl only in the process. Excess salt could have complicated the processing of palladium once the solution was concentrated (growing crystals). I didn't want to risk that problem.

Harold

 

[goldsilverpro]

Harold,

There is no doubt in my mind, copper is not essential to parting. It is used to increase conductivity of electrolyte, and obviously to create softer crystals, but is otherwise not useful. You are correct in your thinking-you will get greater use from your electrolyte without adding any.

When I started running silver cells, I did a lot of research to determine the bath make-up and found that, without exception, all the formulas added copper nitrate to the cell solution. The copper concentrations ranged from 30 gm/l to 80 gm/l. I treated this data with reverence and, like you with Hoke, I followed it to a tee and started my solutions at about 30 gm/l Cu.

Recently, I reread my books to try and find out why they added the copper and didn't have much luck. Only in Rose's, "Metallurgy of Gold", 7th edition, page 481, did I find any comments. To quote:"Mulligan states that an increase in the copper content of the electrolyte from 55 to 75 gm/l resulted in a better production of silver." Don't ask me what that means. It may be because of better conductivity and, therefore, lower voltage. It may mean that the silver was purer or that it rinsed easier.

In the classic book, "Silver" by Butts and Coxe (yes, Folks, that's their real names), the several formulas, used by the big companies, all added copper to the cells.

One of the best discussions on silver cells is in the last article in IPMI's, "Symposium on Recovery, Reclamation, and Refining of Precious Metals." The title is "Silver Refining at The Torreon Smelter." I know that you also have this book. In it, they only say that they don't let the copper exceed 60 gm/l, but they obviously maintain copper in the cell.

Silver cells were originally designed to part silver from gold in dore' bars and, in all these references, that's what they were used for. These dore' bars had very little copper in them. It was in the order of ppms. For example, at the Torreon Smelter, they only had to bail out 1% (1 liter) of the solution each day to maintain the copper at the desired level. The day-to-day anode makeup in all of these smelters was very consistent and it was easy to maintain the solution at the desired copper/silver levels. However, every reference I've found uses copper in the cell. Therefore, I must assume that it is desirable to do so.

We are doing something that the cells weren't designed for, in that our anode compositions vary all over the map. So, each of us are on our own to make it work for our particular application. For example, I ran tons of sterling through the cells. This isn't easy, and you're not supposed to be able to do that, but I made it work.

It is possible to start a cell with only distilled water and a measured amount of nitric acid. The silver crystals produced re-dissolve until the free nitric gets down to about 1% and the silver in the solution is at a desired level. When I did this, I found the crystals were harder to rinse unless I also had a certain amount of copper in the cell. For this reason, I used some sterling as my anodes when I did this.

I am convinced that some copper is good and I will continue to use it. Just how much I should use is still up in the air. I know that some copper gives better conductivity and I have proven, at least to myself, that I could rinse the crystals with fewer rinses, due to the character of the crystals. I always checked my final rinses with ammonia. To me, fewer rinses required meant that there was a smaller chance of retaining copper solution in the crystal.

Most of my silver was used to make stamped 10 oz and 100 oz bars, for sale to the public. I stamped them at 999.5 Fine. I guaranteed this and therefore followed the procedures of the big guys to help assure it.

I think I remember you saying that all of your silver was used exclusively for inquarting gold. I assume that, after inquarting, you cemented out the silver on copper. If so, why bother with the silver cell? Cemented silver is about 99% and about the only impurity is copper. Why couldn't you add this directly to the gold without purifying the silver first? I can't see how a little extra copper would affect the inquartation. There's a lot of copper in the karat gold, anyway.

Your friend,

Chris

 

[Harold_V]

I think I remember you saying that all of your silver was used exclusively for inquarting gold. I assume that, after inquarting, you cemented out the silver on copper. If so, why bother with the silver cell?

You've lost sight of the material I processed. While some lots that were refined were just gold, the majority of my lots contained at least traces of platinum or palladium. I processed a fair amount of dental material, and many of my customers also worked with platinum, although not all of them did. My cemented silver always contained traces of these metals, so to not part them would have been a foolish decision. Remember, by its nature, silver automatically becomes the carrier of the platinum group of metals. I took advantage of that fact to make the recovery. There was method to my madness, and it paid handsome dividends.

I also did not recycle my silver to be used more than once in inquartation. That invited problems in parting in the silver cell due to the increase in platinum group metals. Many of my anodes were less than willing to shed the slimes as it was. To have added to the percentage of contaminants would not have been in my best interest.

I was fortunate to have silver come in at about the same rate as it was consumed, so I rarely lacked silver for inquartation. Considering it's relatively low value, I'd simply weigh it in, then credit the owner with the value, minus my refining fee. I was not concerned if I gave away a few cents in value in the case where items marked sterling might not be. I processed silver only because it was a necessity.

As for copper in the silver cell, I have the Butts & Coxe book, too, and I'm quite sure it is in that book that the key to the use of copper was made clear. It is to provide conductivity, which, in turn, would obviously enhance the rate of transfer. My logic, which did NOT fail me, was to eliminate the copper at the outset, because it accumulated at a rather fast rate. It is absolutely NOT necessary for a cell to operate. I parted silver crystals that had traces of copper within, at times as much as 200 ounces. They parted perfectly well---leaving behind so little copper that the color of my electrolyte would be, at best, a very light pea green. Copper is absolutely NOT an essential in electrolyte, and is, indeed, the sole contributor to limited life of electrolyte.

I had to change electrolyte after running each anode, roughly 200 troy ounces, because of copper co-deposition, which was the source of the problem with the crystals I'd re-run on occasion. I finally learned to stop before it was too late----using the crystal growth as an indicator. The silver would start growing fine threads instead of coarse crystals. That was the point where I cut off the cell and replaced the electrolyte.

Copper is used by the "big boys" because they have hundreds, if not thousands, of ounces of silver in their electrolyte. They can keep the volume to a minimum by the controlled addition of copper. If you are not parting material with high copper content, maybe that makes sense, but parting either sterling, or silver recovered on copper, copper is added to the cell at a high rate, so starting with copper makes no sense.

My method worked, and never yielded a problem that I could identify, the only negative being that electrolyte with no copper alters the deposition, a point I made perfectly clear. The first few hours of operation often yielded a full covering of silver that was tightly bonded to the cell. I used a fiber glass scraper to remove the layer, which I'd leave until the cell started growing crystals. That was when the copper level increased, but when it was well below a critical level.

Anyone that parts silver that has been recovered on copper is wise to start without copper in their electrolyte. They will part far more silver before they must change their electrolyte, otherwise they will produce silver that has copper content.

That copper may be used to create sterling isn't a point to consider unless the silver is used in-house. If an ingot is stamped with a level of purity, it should be no lower in quality than the stamp. That's part of building a reputation for honesty, and helps others in knowing when they can use an ingot for a given purpose. I tried, to the very best of my ability, to be honest in my operation, never stealing from my customers, nor giving them misleading information. Either of those can lead to rapid failure of a refining business.

Harold

 

[goldsilverpro]

Harold,

I really wasn't trying to start an argument. We've been on this subject before. You did it your way, I did it my way, and both ways worked. I understand your reasoning. It looks like I'll be running tons of silver in the near future. I just wanted to kick this around a bit to come up with some answers as to the copper content. I'm more interested in how I WILL do it rather than how I used to do it.

In Butts/Coxe, page 89, they list several variables that are controlled by the silver/copper ratio, only one of which is conductivity:
(a) Efficient anode reaction
(b) Type of deposit required for removal routine.
(c) Consideration of anode impurities.
(d) Maximum conductivity with minimum silver tie-up.

the only negative being that electrolyte with no copper alters the deposition, a point I made perfectly clear. The first few hours of operation often yielded a full covering of silver that was tightly bonded to the cell. I used a fiber glass scraper to remove the layer, which I'd leave until the cell started growing crystals. That was when the copper level increased, but when it was well below a critical level.

I have also had the cathode completely plate and I didn't like the aggravation one bit. I didn't like the ordeal of scraping it and I didn't like dealing with the scrapings mixed with the crystal in the filter. For no other reason than that, I would think that it would be better to start with at least a small amount of copper in the solution, maybe 1/2 to 1 oz/gal. This would not, very much, alter the time that the cell could be run before having to deal with it.

Chris

 

[Harold_V]

Do you mean, just boiled down and incinerated?
Or....... cemented first?

Yes, cemented first. I'd add fluids to my stock pot on a daily basis. After everything (including copper) had cemented, I'd siphon off the solution and allow it to settle well. Any traces of solids would be returned to the stock pot so nothing was discarded with the now barren solution. When there was a fairly large accumulation of cemented material in the bottom, I'd remove all pieces of scrap steel and recover the cemented materials, which is what got incinerated.

Harold

 

[Harold_V]

I really wasn't trying to start an argument.

Nor do I, Chris. I simply think it's important for readers to understand that adding copper to their electrolyte when parting silver that has been recovered with copper will drastically limit their electrolyte lifespan.

The first time you part silver with a single batch of electrolyte, where it isn't constantly replenished, this will probably make a lot more sense.

The features mentioned were all proven by me when I ran my cell. I would also include temperature. It's hard to say whether it is cause for alteration of crystal growth, because by the time my cell achieved ambient temperature, it also had accumulated a noticeable amount of copper, so it could well be that temperature may play no role in the nature of the deposit. I know for certain, copper is one of the controlling factors in how the silver develops----whether it grows crystals that are easy to harvest, or not.

I did not like scraping my cell when it grew a sheet of silver, but I found it would come out fairly easily if I could get under a corner. I generally used the chunks for making electrolyte because they were a general PITA to handle.

You may recall, my customers were pretty good about accepting crystal in settlement, so I didn't melt my silver. Fact is, I still have a great deal of it, stored in a couple 5 gallon buckets. Haven't laid eyes on it in years, so I don't have a clue if it is still bright and shiny, or not.

It looks like I'll be running tons of silver in the near future. I just wanted to kick this around a bit to come up with some answers as to the copper content. I'm more interested in how I WILL do it rather than how I used to do it.

It will be interesting for me to see if you find it to your benefit to avoid adding copper. For me, it was a no-brainer.

If you do intend to add copper, I'd strongly advise a chemical wash of the cement silver, to minimize the amount of copper carried into the process. I used to rinse my cement silver in a buchner, until the rinse water was clear, then I'd melt with a generous flux cover to absorb oxidation. The lot was poured to a cone mold, then well cleaned before the resulting button was re-melted to be cast as an anode. The anode was always bright, but there was enough residual copper to quickly contaminate the electrolyte. I expect you won't have a different result unless you alter the process significantly. In retrospect, I wonder if a wash of the cemented silver in HCl might have been a good idea.

I would think that it would be better to start with at least a small amount of copper in the solution, maybe 1/2 to 1 oz/gal. This would not, very much, alter the time that the cell could be run before having to deal with it.

My opinion? You'll lose more than 50% of the useful life of the electrolyte. It will be interesting to see the results you get.

Don't get me wrong, Chris. I'm not trying to win a contest here----I'm simply relating my experiences. I read the book and made decisions in keeping with my objective of running batch lots instead of constantly trying to balance my electrolyte by partial replacement for continuous operation. That was well beyond my capability, not understanding the testing techniques, but fully understanding the ramifications of allowing the electrolyte to become overly concentrated with copper. The harsh reality is that copper accumulates rapidly----so any you can eliminate is to your benefit, assuming you're willing to tolerate the short interval where the cell grows a solid film. The time taken to remove the film is small compared to the time you spend changing the electrolyte. It also minimizes the amount of silver you must recycle.

Harold

 

[goldsilverpro]

Quote:
It looks like I'll be running tons of silver in the near future. I just wanted to kick this around a bit to come up with some answers as to the copper content. I'm more interested in how I WILL do it rather than how I used to do it.

It will be interesting for me to see if you find it to your benefit to avoid adding copper. For me, it was a no-brainer.

In this case, I will be running dore' type bars, with very little copper. Therefore, I will definitely start the cells with quite a bit of copper. To me, that is a no-brainer.

Quote:
I would think that it would be better to start with at least a small amount of copper in the solution, maybe 1/2 to 1 oz/gal. This would not, very much, alter the time that the cell could be run before having to deal with it.

My opinion? You'll lose more than 50% of the useful life of the electrolyte. It will be interesting to see the results you get.

I always kept track of the silver and copper in the bath by analysis. A long time ago, I experimented to determine how much copper it took to affect the silver purity. I dissolved some crystal and ran it for copper on the AA. I came up with about 12 oz/gal as the critical limit for copper in solution. Even at 10 oz/gal, I would only lose 5% of the life of the bath, if I started with .5 oz/gal copper. I would lose 10% at 1 oz/gal.

BTW, I read in one of the books that you must have 10 times more Au than Pd in the bar, in order to prevent the Pd from dissolving and entering the solution. If the Pd goes into the solution, it will co-deposit with the silver. Other problem metals are Pb, Se, Te, and Bi.

Chris

 

[Oz]

Every time you 2 debate this I pick up a gem or more.

I have wondered about at what concentration Pd would start to precipitate with the silver as I expected most of it to go into solution instead of staying in the anode basket. Do you expect any Pd in solution to precipitate as readily as the Ag? If not at what concentration would you expect it to?

BTW, I read in one of the books that you must have 10 times more Au than Pd in the bar, in order to prevent the Pd from entering the solution. If the Pd goes into the solution, it will co-deposit with the silver. Other problem metals are Pb, Se, Te, and Bi.

I am surprised to hear that gold will limit this as I expected gold to stay elemental in the basket. Do you have any insights as to why gold would affect it?

 

[goldsilverpro]

Every time you 2 debate this I pick up a gem or more.

Me too!

goldsilverpro wrote:

BTW, I read in one of the books that you must have 10 times more Au than Pd in the bar, in order to prevent the Pd from entering the solution. If the Pd goes into the solution, it will co-deposit with the silver. Other problem metals are Pb, Se, Te, and Bi.

Reading further, I find that, in order for this to work, the Au content of the bars has to be less than 4.5%. This is because, as the Au increases, the anode efficiency (rate of dissolving per amp) decreases. As the anode efficiency decreases, the more likely the Pd will dissolve.

I am surprised to hear that gold will limit this as I expected gold to stay elemental in the basket. Do you have any insights as to why gold would affect it?

None whatsoever. Maybe a Au/Pd alloy forms that is insoluble in these conditions.

 

[Oz]

Reading further, I find that, in order for this to work, the Au content of the bars has to be less than 4.5%. This is because, as the Au increases, the anode efficiency (rate of dissolving per amp) decreases. As the anode efficiency decreases, the more likely the Pd will dissolve.

If you need 10 times more Au than Pd and the gold content has to be less than 4.5% then you can’t exceed .45% Pd, that’s not much. As my silver is from inquartation I am sure I would exceed that in Pd even if I added a bit of gold to limit its dissolution. In the material you are getting ready to run I can see it may work out to your advantage depending on your gold percentage.

I still am left with trying to figure out if Pd precipitation will be a constant problem at any concentration or if there is a threshold as in Cu. In the absence of any other information I will find out by testing my crystal silver by re-dissolving some and testing with DMG. If there is a threshold I could make a habit of testing my electrolyte concentration the same way to assure high purity Ag.

I welcome any other input.

 

[Harold_V]

As the anode efficiency decreases, the more likely the Pd will dissolve.

That was my experience. I commented earlier that an abundance of other elements in the anode can be troublesome.

I can recall only one instance where I had palladium show in my electrolyte. The anode had a serious amount of other elements present, requiring the anode to be scraped. Even then the slimes were difficult to remove. It was that experience that depleted my electrolyte.

If palladium is being dissolved in the cell, it won't go unnoticed visually. The color of the electrolyte will shift to dark green.

Take note that I made mention of dissolving silver from the cell to make the next batch of electrolyte. My routine was to dissolve the needed 30 ounces from the most recently harvested batch, which was generally around 200 ounces. If the silver was contaminated with copper or palladium, it would show in the dissolved silver. That was the indicator to me to either accept the balance of the crystals as being pure, or to return them to the silver cell, where they were parted a second time. No melting, just placing them in the basket and covering them with an anode was sufficient.

Testing of electrolyte after parting will indicate the presence of dissolved palladium. I don't recall it being a problem unless too much was present. When an anode was cast that was low in other values, it parted cleanly, leaving slimes free in the filter bag. When the anode was lifted, it would be a dull light tan color-----and the slimes would rinse off easily with a wash bottle. In such cases, I do not recall ever having any problems with palladium going in to solution. My slimes were exceedingly heavy with them, a sure sign that they did not dissolve in the cell. In my opinion, it's a non-issue unless the percentage is too high.

Harold

edit: I should make note-----my silver contained very little gold. Only what little managed to slip past me when siphoning solutions. I recovered very little gold from my silver cell, so gold did not play a significant role in preventing palladium from dissolving.

 

[Oz]

Thanks for that Harold. I had waited to reply in the hope GSP would weigh in on it. What you wrote helps much in what I should expect as to Pd.

 

[Barthel732]

Does a silver cell have to have shot in the filter basket or can it be sterling bars also( homemade minis bars)

 

[FrugalRefiner]

In the past, anode bars were usually used. The idea of using shot is a recent one.

Dave