Designing a DIY silver cell

[Mudville9]

Do you have experience on how high palladium content could be in the anodes, and after electrorefining, what proportion will end up in electrolyte and what proportion goes to the slimes and "fine" silver ?

I have one feed material that averages around 1% Pd and I try to gain some insight on how it could be effectively refined to obtain pure silver and palladium "something" in the end

I hated to have much palladium in silver since we used a common electrolyte distribution system for numerous cells. The distribution tank holds up to 10,000 L so any palladium introduced into a single cell would be spread throughout the system. We used a chemical treatment for waste solutions which was fairly good at recovering PGM's, but even 2 ppm residual palladium in treated solution added up to substantial losses, or at least very difficult to recover values. I know large refiners get mostly a bad rap for PGM payouts, but this is just one of many reasons accountabilities are so low for these elements.
Better for us to add high PGM material to a gold chlorination melt where the resulting material can be put through wohlwill cells where PGM recovery is better.

Recent improvements in ion exchange resins that can stand up to nitrate environments also offers an effective alternative. A Russian refinery has switched to resins and reports keeping PGM's to less than 1 ppm throughout their silver electrolyte.

 

[4metals]

When Palladium climbs above 50 ppm it will deposit with the Silver as an impurity. I have had great success running electrolyte through a tank to which Dimethylglyoxime is added, which drops the Palladium to be collected in a spiral wound filter tube.

For smaller refineries without an instrument lab, Dimethylglyoxime is also excellent for quantitative Palladium analysis. When the Palladium content climbs to 30 ppm the electrolyte is treated with Dimethylglyoxime and returned directly to the cells sans Palladium.

 

[orvi]

Challenges in the Electrolytic Refining of Silver—Influencing the Co-deposition Through Parameter Control​

Search for that on google

Thanks

 

[diclame]

Running up to 120 g/L copper still produced 99.9% purity with 500-600 ppm copper. Perfectly acceptable.

Do you know the process to precipitate the copper in this solution. To be able to continue using the electrolyte solution back into the silver cells???

 

[Mudville9]

For the most part, it isn't worth trying to regenerate electrolyte. Better to precipitate the silver and dissolve it for fresh solution. There is one very promising route but it is subject to a pending patent and I can't disclose it yet, sorry.

 

[Shark]

This would also come under titration I think. But with decent calculations it may be possible for the cell volume to handle the copper from a known amount of sterling and only need to worry about the copper build up near the end of the week cycle.

Example:
The cell would need to be X-gallons to hold Z- ounces of copper. A-ounces of sterling = Z-ounces of copper. On shut down for clean out the silver, the electrolyte would be changed based on the sterling consumption.

I am sure there are other ways to figure this out but that would be a basic way for a simple cell design.

 

[4metals]

There is some chatter about a method involving heating the electrolyte and raising the pH. Silver Oxide is added to scavenge the base metals. It supposedly will remove the copper and some but not all of the Silver and the Silver Oxide will scavenge the balance of the base metals. The nitric is then replenished and the solution is re-used in the cell.

In Silver, by Butts & Coxe, they discuss using sodium carbonate to remove copper as a basic salt.

The description I read was vague and had some errors. I have not yet had an opportunity to get back into the lab and try a few options. It sounds promising but I don’t have a working process yet.

 

[Mudville9]

There is some chatter about a method involving heating the electrolyte and raising the pH. Silver Oxide is added to scavenge the base metals. It supposedly will remove the copper and some but not all of the Silver and the Silver Oxide will scavenge the balance of the base metals. The nitric is then replenished and the solution is re-used in the cell.

In Silver, by Butts & Coxe, they discuss using sodium carbonate to remove copper as a basic salt.

The description I read was vague and had some errors. I have not yet had an opportunity to get back into the lab and try a few options. It sounds promising but I don’t have a working process yet.

The silver oxide works, as does sodium hydroxide and sodium carbonate, but I would only use them for the removal of smaller amounts of copper. Small amounts of copper form an easily filtered copper hydroxide floc, but as more and more copper hydroxide forms, the floc becomes very finely divided, slimy and extremely difficult to filter. I never found a suitable flocculating agent that would allow for easier filtration.

 

[4metals]

I’ve used the Silver Oxide to clean up silver nitrate solutions for many years. But, as you say, the levels of impurities were low. It is an effective way of making 4 9’s + Silver by treating the dirty Silver Nitrate solution with Silver oxide, filtering, and dropping the Silver as an oxide with high grade sodium hydroxide. The Silver oxides decompose in the furnace and the resultant Silver is high purity.

I never did push the limits of just how dirty the Silver Nitrate could be and still be effective.

 

[4metals]

I also have converted the copper nitrate (after cementing out all of the Silver), into copper sulfate and distilled off and collected the nitric for reuse. Then the copper was plated out of the solution to generate clean copper metal. This made the waste product easier to handle as most of the hydroxide forming metals were recovered. I did this for a 30 gallon cell which required changing out of the electrolyte every 4-5 weeks. That allowed me to distill off 5 gallons a week of electrolyte with a 20 liter reactor which made it manageable.

NurdRage has an excellent video on this method with simple off the shelf equipment and chemical glassware. Commercially, it's a little more challenging only because of scale.
NurdRage video

Truthfully all members electrolytically refining Silver have to deal with the copper nitrate waste and we should start a thread in the safety section.

 

[Lou]

I always found Thum cells complimentary to Möebius cells. The stub butt ends could be put into Thum cell. I was at lower voltage of 1.7-1.9 V and maybe 70 A/sf for the vertical vs 3.7-3.9 V and 40-60 A/sf for the horizontal. Problem with Thums is the floor space they take up, but you can always build them up instead of out I suppose.

I have also done titanium anode hooks that go in the mold and can be used to hang the anodes. These conduct better than stainless. If I had an autoclave then, I would have taken the leftover stub and just dissolved in nitric acid/oxygen overpressure because it saves 25% of the nitric used in the best case to dissolve silver and is effectively NOx fume free and 1:1 Ag:HNO3 vs 1:4/3 or more. The Ti hook can be rinsed off and tossed in a drying oven, while the nitric gets the gold and junk filtered out (sent for burning with the bag) while the solution gets used for electrolyte.Some TiO2 ends up in the slimes because the silver eats the titanium by alloying a small amount. Heating the hooks red hot seems to prevent the alloying somewhat without producing too much resistance to current flow.

Insofar as electrolyte is concerned, this is perhaps one area where I had an active interest, both in preparing large volumes of electrolyte with oxygen pressure oxidation (as used at RMC and at OPM) and maintaining it. I certainly agree that concentration, conductivity, impurity profile, temperature and pH are all critical parameters that should be kept as close to steady state as possible. There is not terrible ohmic heating in silver cells if current densities are not so high as mudville describes. Without active cooling/heat exchange, you sacrifice production and a modicum of electrolyte volume management for the crystal rinse waters that get returned after countercurrent wash/decantation. I never had to cool my cells but I have been to facilities where they do.

Now, as to impurities management, I should start by saying that my actual scientific training was in polymer science and for a time I used to make a bit of polymers (i.e. suspension polymerization for ion exchange resins etc.) so I have always had an interest in using these technologies in a silver cell. And they can in fact be used!

I can say that it is almost entirely possible to maintain silver concentrations and copper, nickel, cobalt and palladium in the electrolyte through the use of resins. Zn hopefully is already largely removed during furnacing. Residual elements like Sn and Pb and some Ag as Ag2O typically just end up as their oxides in the anode bag and can be largely blown from the silver if a reverb or TBRC is used up front. The resin itself ignores the silver and binds the Cu and Ni(Co). The preference for which is contingent on pH. Both of these can be eluted with ammonia to regenerate the resin and then NaOH added and the solution boiled to return the ammonia for reuse and give the Ni/Co/Cu as a feed to the copper/nickel refiner.


I know about that which mudville speaks on the Russian resin but I think people that know just use any weak base anionite resin. I have my own version that I use and like it very much but not in silver duty (though it can be used in a cell and has a very high capacity of about 6 oz Pd/kg of resin in nitric acid conditions and is fully elutable with ammonia water giving [Pd(NH4)4]+2). My opinion on improvements to the best run silver refinery possible is that the converting furnace is a TBRC with removable flue to reprocess the silver mist/condensate. This produces an anode feed that is 98-99% and provides a feedstock slag that can be sent for copper recovery where trace payable silver gets paid back to the refiner. Much of the Cu, Al, W/Mo, Sn, Pb, Sb, Zn and even some Se/Te can be removed.

These anodes should be cast into tapered molds with a stout titanium hook such that they more or less anodically erode in an even fashion, and the butts can be dissolved for electrolyte makeup, under pressure. I have never liked shot under pressure due but bulk solids behave better. The electrolyte is managed by continuous circulation of electrolyte through resins, the first one to fetch the Pd, the second to fetch Cu. Periodically, the pH is adjusted and Ni/Co can be removed onto the same resin. This resin is still very expensive but price will hopefully go down...

 

[orvi]

I always found Thum cells complimentary to Möebius cells. The stub butt ends could be put into Thum cell. I was at lower voltage of 1.7-1.9 V and maybe 70 A/sf for the vertical vs 3.7-3.9 V and 40-60 A/sf for the horizontal. Problem with Thums is the floor space they take up, but you can always build them up instead of out I suppose.

I have also done titanium anode hooks that go in the mold and can be used to hang the anodes. These conduct better than stainless. If I had an autoclave then, I would have taken the leftover stub and just dissolved in nitric acid/oxygen overpressure because it saves 25% of the nitric used in the best case to dissolve silver and is effectively NOx fume free and 1:1 Ag:HNO3 vs 1:4/3 or more. The Ti hook can be rinsed off and tossed in a drying oven, while the nitric gets the gold and junk filtered out (sent for burning with the bag) while the solution gets used for electrolyte.Some TiO2 ends up in the slimes because the silver eats the titanium by alloying a small amount. Heating the hooks red hot seems to prevent the alloying somewhat without producing too much resistance to current flow.

Insofar as electrolyte is concerned, this is perhaps one area where I had an active interest, both in preparing large volumes of electrolyte with oxygen pressure oxidation (as used at RMC and at OPM) and maintaining it. I certainly agree that concentration, conductivity, impurity profile, temperature and pH are all critical parameters that should be kept as close to steady state as possible. There is not terrible ohmic heating in silver cells if current densities are not so high as mudville describes. Without active cooling/heat exchange, you sacrifice production and a modicum of electrolyte volume management for the crystal rinse waters that get returned after countercurrent wash/decantation. I never had to cool my cells but I have been to facilities where they do.

Now, as to impurities management, I should start by saying that my actual scientific training was in polymer science and for a time I used to make a bit of polymers (i.e. suspension polymerization for ion exchange resins etc.) so I have always had an interest in using these technologies in a silver cell. And they can in fact be used!

I can say that it is almost entirely possible to maintain silver concentrations and copper, nickel, cobalt and palladium in the electrolyte through the use of resins. Zn hopefully is already largely removed during furnacing. Residual elements like Sn and Pb and some Ag as Ag2O typically just end up as their oxides in the anode bag and can be largely blown from the silver if a reverb or TBRC is used up front. The resin itself ignores the silver and binds the Cu and Ni(Co). The preference for which is contingent on pH. Both of these can be eluted with ammonia to regenerate the resin and then NaOH added and the solution boiled to return the ammonia for reuse and give the Ni/Co/Cu as a feed to the copper/nickel refiner.


I know about that which mudville speaks on the Russian resin but I think people that know just use any weak base anionite resin. I have my own version that I use and like it very much but not in silver duty (though it can be used in a cell and has a very high capacity of about 6 oz Pd/kg of resin in nitric acid conditions and is fully elutable with ammonia water giving [Pd(NH4)4]+2). My opinion on improvements to the best run silver refinery possible is that the converting furnace is a TBRC with removable flue to reprocess the silver mist/condensate. This produces an anode feed that is 98-99% and provides a feedstock slag that can be sent for copper recovery where trace payable silver gets paid back to the refiner. Much of the Cu, Al, W/Mo, Sn, Pb, Sb, Zn and even some Se/Te can be removed.

These anodes should be cast into tapered molds with a stout titanium hook such that they more or less anodically erode in an even fashion, and the butts can be dissolved for electrolyte makeup, under pressure. I have never liked shot under pressure due but bulk solids behave better. The electrolyte is managed by continuous circulation of electrolyte through resins, the first one to fetch the Pd, the second to fetch Cu. Periodically, the pH is adjusted and Ni/Co can be removed onto the same resin. This resin is still very expensive but price will hopefully go down...

High-end technology for metals refining is so fascinating... Saying from old burnt bench with old corroded oxy/propane torch and dirty quartz dish

Small version of TBRC furnance would make my life so much easier Now, we need to proceed with our 30kW induction furnance veteran. But small tilting furnance was planned to be built... Thanks for reviving and improving my view about what could be best suited for our use.

As we are now regularly battling quite complex metal mixtures containing PGMs - usually Pb-Sn-Cu-Ag-PGM alloys.

 

[diclame]

the Chinese solved this problem a long time ago and the patent expired so it can be reproduced but I don't know anyone in China who prints the process from the patent office

For the most part, it isn't worth trying to regenerate electrolyte. Better to precipitate the silver and dissolve it for fresh solution. There is one very promising route but it is subject to a pending patent and I can't disclose it yet, sorry.

 

[Palladium]

I always found Thum cells complimentary to Möebius cells. The stub butt ends could be put into Thum cell. I was at lower voltage of 1.7-1.9 V and maybe 70 A/sf for the vertical vs 3.7-3.9 V and 40-60 A/sf for the horizontal. Problem with Thums is the floor space they take up, but you can always build them up instead of out I suppose.

I have also done titanium anode hooks that go in the mold and can be used to hang the anodes. These conduct better than stainless. If I had an autoclave then, I would have taken the leftover stub and just dissolved in nitric acid/oxygen overpressure because it saves 25% of the nitric used in the best case to dissolve silver and is effectively NOx fume free and 1:1 Ag:HNO3 vs 1:4/3 or more. The Ti hook can be rinsed off and tossed in a drying oven, while the nitric gets the gold and junk filtered out (sent for burning with the bag) while the solution gets used for electrolyte.Some TiO2 ends up in the slimes because the silver eats the titanium by alloying a small amount. Heating the hooks red hot seems to prevent the alloying somewhat without producing too much resistance to current flow.

Insofar as electrolyte is concerned, this is perhaps one area where I had an active interest, both in preparing large volumes of electrolyte with oxygen pressure oxidation (as used at RMC and at OPM) and maintaining it. I certainly agree that concentration, conductivity, impurity profile, temperature and pH are all critical parameters that should be kept as close to steady state as possible. There is not terrible ohmic heating in silver cells if current densities are not so high as mudville describes. Without active cooling/heat exchange, you sacrifice production and a modicum of electrolyte volume management for the crystal rinse waters that get returned after countercurrent wash/decantation. I never had to cool my cells but I have been to facilities where they do.

Now, as to impurities management, I should start by saying that my actual scientific training was in polymer science and for a time I used to make a bit of polymers (i.e. suspension polymerization for ion exchange resins etc.) so I have always had an interest in using these technologies in a silver cell. And they can in fact be used!

I can say that it is almost entirely possible to maintain silver concentrations and copper, nickel, cobalt and palladium in the electrolyte through the use of resins. Zn hopefully is already largely removed during furnacing. Residual elements like Sn and Pb and some Ag as Ag2O typically just end up as their oxides in the anode bag and can be largely blown from the silver if a reverb or TBRC is used up front. The resin itself ignores the silver and binds the Cu and Ni(Co). The preference for which is contingent on pH. Both of these can be eluted with ammonia to regenerate the resin and then NaOH added and the solution boiled to return the ammonia for reuse and give the Ni/Co/Cu as a feed to the copper/nickel refiner.


I know about that which mudville speaks on the Russian resin but I think people that know just use any weak base anionite resin. I have my own version that I use and like it very much but not in silver duty (though it can be used in a cell and has a very high capacity of about 6 oz Pd/kg of resin in nitric acid conditions and is fully elutable with ammonia water giving [Pd(NH4)4]+2). My opinion on improvements to the best run silver refinery possible is that the converting furnace is a TBRC with removable flue to reprocess the silver mist/condensate. This produces an anode feed that is 98-99% and provides a feedstock slag that can be sent for copper recovery where trace payable silver gets paid back to the refiner. Much of the Cu, Al, W/Mo, Sn, Pb, Sb, Zn and even some Se/Te can be removed.

These anodes should be cast into tapered molds with a stout titanium hook such that they more or less anodically erode in an even fashion, and the butts can be dissolved for electrolyte makeup, under pressure. I have never liked shot under pressure due but bulk solids behave better. The electrolyte is managed by continuous circulation of electrolyte through resins, the first one to fetch the Pd, the second to fetch Cu. Periodically, the pH is adjusted and Ni/Co can be removed onto the same resin. This resin is still very expensive but price will hopefully go down...

Would Bipolar membranes have a place in any of this Lou?

 

[Lou]

Alas, they do not remove impurities well enough compared to resins.

I've used them before. They're nice for cationic metathesis (i.e. turning NaNO3 to HNO3 and NaOH) but are power hogs, have fragile membranes, and require, at least in some instances, those nasty expensive iridium oxide coated titanium anodes.

 

[Palladium]

I looked at using them before to make a small machine for producing nitric acid for those people who can't buy or find it. I have several 24 x 24 sample pieces manufactures have sent me.

 

[Shark]

Where are we at for a power supply?

 

[4metals]

This thread is going in many directions, all of them good, but difficult to follow. What I wanted to do is open a poll to ask a few questions and decide where to take this thread and if necessary start new threads accordingly. But the polling function on this software has to be activated by the new admin, and when it is, a poll will appear here so we can all participate and move in the proper direction.

 

[4metals]

The poll in the software only supports 1 question so I cobbled this together and I will tally the results. Instructions on how to post answers are at the end.

1. Is the style of the cell, Thum or Moebius, important or is the production capacity the determining factor?
a. I prefer a Moebius Cell
b. I prefer a Thum Cell
c. I only care about production capacity.

2. As far as production capacity of a silver cell what is a preferred weekly production rate?
a. 100 OZT a week
b. 500 OZT a week
c. 1000 OZT a week
d. 3000 OZT a week
e. > 3000 OZT a week

3. Ability to fabricate the cell.
a. I need to have a cell I can fabricate with common tools and few specialized skills.
b. I would be willing to have a specialist come in to help with fabrication.

4. What additional topics do you want to see to cover the refining of silver.
a. Making electrolyte
b. Casting anodes
c. Analysis of a silver cell to keep it running
d. Treating the waste from a silver cell
e. Operating a break down cell to recover silver from lower grades of scrap
f. Processing anode slimes
g. Let’s discuss it all, in separate threads

How to answer this survey
If I am interested in a thum cell for question 1 answer 1,b

If I want to produce 1000 oz a week as asked in question 2 answer 2,c

If I want to build this myself with no specialized skills (like PVC welding) in answer to question 3 answer 3,a

And if I do not know any of the techniques involved the answer to question 4 but want to see my options, my answer would be, 4,g

If I missed any questions please let me know and I can add to the list.

 

[Shark]

1: Personally, I prefer the bigger refiners decide that. The bigger refiner is what I would like to see a glimpse into as they grow. (Although I would like to see how that extruded cathode would work out.)

2:Refer to #1.

3:B
I can weld plastic, but if not an auto body shop should be able to do it. Our local tech school is always looking for projects to work on and it does teach plastic welding.

4:G

We have a means to see some great stuff here, lets see some votes.