Advanced questions re Silver Refining - Please Help

[buckrogers1]

i have been processing batches of sterling silver ware with nitric acid, cementing with copper, melting into shot, then through a silver cell obtaining beautiful shiny pure crystals.
After a lot trial and error , and following all youtube videos i could find, i'm very satisfied with the results. But i have a few questions.

a) last batch of AGNO3 electrolyte i created by dissolving pure silver rounds came out a bit yellowish , is it because i used 68% Lab grade Nitric? Organic Contaminants? will that affect the Crystals purity in the cell?

b) i'm left with gallons of spent Copper Nitrate after cementing, i read that by adding Sulfuric Acid and distilling the liquid i can obtain Nitric Acid back. Anyone doing this? Is it worth it? Dangerous as Nitric is. And Sulfuric is no joke either. Working with NOx fumes isn't for the faint hearted. If someone has a SAFE system please share.

c) What is the Yield you achieve on average starting with sterling silver? I noticed i must not be very efficient yet, as 1Kg of Sterling Silverware, yields me in the end probably around 500g of pure silver.

d) I have batches of mixed powder silver/copper and probably other trace metals. If i add these to pure AGNO3 solution, shouldn't the copper dissolve into the solution (become Copper Nitrate) and leave me only with silver (and other impurities probably) but at least i can remove the copper and process the silver in a silver cell.

e) Very Important Question (as it would save me a lot of time and effort) Can i instead of melting into shot, just use the cemented silver powder in the filter bag to run my Silver Cell ? Isn't it easier for the electrolytic process dealing with smaller particles like powder instead of shot? That i did not understand.

I'd be deeply grateful for the answers , thanks !

 

[Yggdrasil]

i have been processing batches of sterling silver ware with nitric acid, cementing with copper, melting into shot, then through a silver cell obtaining beautiful shiny pure crystals.
After a lot trial and error , and following all youtube videos i could find, i'm very satisfied with the results. But i have a few questions.

a) last batch of AGNO3 electrolyte i created by dissolving pure silver rounds came out a bit yellowish , is it because i used 68% Lab grade Nitric? Organic Contaminants? will that affect the Crystals purity in the cell?

Yes ,No and maybe. Since you have said nothing about the previous its hard to say. Additives in the Nitric, unlikely but can you specify whoat you used this time and earlier.
Elements from the dissolved batch may have followed the cemented Silver.

b) i'm left with gallons of spent Copper Nitrate after cementing, i read that by adding Sulfuric Acid and distilling the liquid i can obtain Nitric Acid back. Anyone doing this? Is it worth it? Dangerous as Nitric is. And Sulfuric is no joke either. Working with NOx fumes isn't for the faint hearted. If someone has a SAFE system please share.

Well I think they uses solid Copper Nitrate not a dissolved nitrate.
I think the forum have many posts dealing with the specifics of dealing with Copper Nitrate.

c) What is the Yield you achieve on average starting with sterling silver? I noticed i must not be very efficient yet, as 1Kg of Sterling Silverware, yields me in the end probably around 500g of pure silver.

Then something is off, one Kg of Sterling should yield 925 g of fine Silver more or less. Is it table ware and not plated?

d) I have batches of mixed powder silver/copper and probably other trace metals. If i add these to pure AGNO3 solution, shouldn't the copper dissolve into the solution (become Copper Nitrate) and leave me only with silver (and other impurities probably) but at least i can remove the copper and process the silver in a silver cell.

No, the Copper will cement out your Silver and destroy your electrolyte.
Dissolve in Nitric and cement out again, it will remove the copper and other more reactive metals.
Then you can melt and make bars again.

e) Very Important Question (as it would save me a lot of time and effort) Can i instead of melting into shot, just use the cemented silver powder in the filter bag to run my Silver Cell ? Isn't it easier for the electrolytic process dealing with smaller particles like powder instead of shot? That i did not understand.

Theoretically speaking yes, in practical terms no. You have no control on the internal contact/resistance between the grains in the cement.
Ideally speaking shot is not recommended either.
Best is solid bar/electrode as the anode.

I'd be deeply grateful for the answers , thanks !

There is a lot here so I have answered in the quote.

One question at the end, what design have you used?

 

[buckrogers1]

Yes ,No and maybe. Since you have said nothing about the previous its hard to say. Additives in the Nitric, unlikely but can you specify whoat you used this time and earlier.
Elements from the dissolved batch may have followed the cemented Silver.

Well I think they uses solid Copper Nitrate not a dissolved nitrate.
I think the forum have many posts dealing with the specifics of dealing with Copper Nitrate.

Then something is off, one Kg of Sterling should yield 925 g of fine Silver more or less. Is it table ware and not plated?

No, the Copper will cement out your Silver and destroy your electrolyte.
Dissolve in Nitric and cement out again, it will remove the copper and other more reactive metals.
Then you can melt and make bars again.

Theoretically speaking yes, in practical terms no. You have no control on the internal contact/resistance between the grains in the cement.
Ideally speaking shot is not recommended either.
Best is solid bar/electrode as the anode.

There is a lot here so I have answered in the quote.

One question at the end, what design have you used?

Thanks fpr the prompt reply.
As for the electrolyte i used 70% acs before.
I guess there is a small difference in purity.
Let's see if it will affect my crystals.

As for yield possibly at the beginning i wasn't cementing all the silver out of the dissolved solution and possibly there was some silverplated stuff in the mix. I'm still not done dissolving everything. Its all in a big stainless steel pot waiting for more nitric.

As for the cell i used the same setup that streetips has in his videos with a stainless steel bowl .

Interesting you mention the anode should be a bar rather than shot.

How big a bar? 10 oz tops?

I still have the issue of recovering nitric from copper nitrate open, i didnt find much info. If anyone went through the process please share.

Thanks again

 

[Yggdrasil]

Thanks fpr the prompt reply.
As for the electrolyte i used 70% acs before.
I guess there is a small difference in purity.
Let's see if it will affect my crystals.

As for yield possibly at the beginning i wasn't cementing all the silver out of the dissolved solution and possibly there was some silverplated stuff in the mix. I'm still not done dissolving everything. Its all in a big stainless steel pot waiting for more nitric.

As for the cell i used the same setup that streetips has in his videos with a stainless steel bowl .

Interesting you mention the anode should be a bar rather than shot.

How big a bar? 10 oz tops?

I still have the issue of recovering nitric from copper nitrate open, i didnt find much info. If anyone went through the process please share.

Thanks again

Search the forum, that’s are several threads regarding this.
As to the bars, if you have a setup like Sreetips, cast the bars so they fit in the box for the Anode. Some have shots under and bar on top, others stack bars on top if each other.
Many ways to do it. Good contact is what counts.

 

[nickvc]

I do not know if you simply omitted that you were adding distilled water to your nitric solution or that you simply didn’t use it at all, but if you are not adding water you will use more nitric as there is nowhere for the material to dissolve into, again you make no mention of heating your solution and that will also increase your acid use.

 

[eaglekeeper]

b) i'm left with gallons of spent Copper Nitrate after cementing, i read that by adding Sulfuric Acid and distilling the liquid i can obtain Nitric Acid back. Anyone doing this? Is it worth it? Dangerous as Nitric is. And Sulfuric is no joke either. Working with NOx fumes isn't for the faint hearted. If someone has a SAFE system please share.

I have never tried the process in the video..... This seems rough on some of the lab ware. I don't know if it's worth the effort. I can make home made nitric cheap, then distill it if needed and at a far lower temperature.

If you plan on doing a lot a silver, then it's probably best to buy the good stuff.

This is a 4 part video.... This is part 1.

 

[orvi]

There are several possibilities - yellow colour can also result from dissolved nitrogen oxides in the liquid - and this is fairly common after end of the dissolution. Quick boil will remove them and solution will stay clear and colourless - IF the silver used was pure. Yellow colouration can be atributed also to trace Pd contamination - and despite claiming 99,9%+ purity, even that 0,1% consisting of Pd can colour the solution in a way you can see it Just hypothetical scenario - but Pd is relatively hard to remove from the silver via classical refining routes and even electrorefining cannot remove it all in one go.

Recycling of nitric from nitrate - not very pleasant technique. Hydrometallurgy is often awful technique of recovery when scaled up. That said, dissolution of silver takes up significant nitric acid - that solely is quite a cost. But then, people massacre that profit margin by cementation on copper - simultaneously using relatively expensive base metal to extract silver of non-sellable quality, creating heavy metal waste solutions (from which extraction of valuable nitric acid, and valuable copper is labor and resource intensive) and only then paving the path towards ultimate cleaning operation - electrolysis. That is why cementation on copper is rarely, if ever, seen on industrial scale refining of silver.

That being said, if one steps up from the hobby refining to semi-mid-scaled process with multiple kilos batches of sterling feed - copper cementation is nowhere nice in the terms of user friendliness and "clean" operation. Most of the semi-mid-scaled refiner use two-cell approach, pyrometallurgical oxidative cleaning of sterling or abandon copper cementation step in the hydro process - replacing it with silver chloride/sulfate production and treatment of silver chloride either by pyro route or wet route.

If you still need to proceed with hydrometallurgical treatment, logical way of making the process more efficient is to abandon the copper cementation step. Dropping silver sulfate instead of silver chloride can be done with concentrated sulfuric acid - thus re-viving the nitric acid of high concentration -> which could be used in dissolution of more silver feed in the future, making several cycles until the liquid is too heavily contamined with copper and need the final treatment and disposal. Silver sulfate is also convertible to silver by caustic route, altough bit more difficult for the first time.

This way, only waste feed which need hard treatment is the copper from actual sterling. Paired with use of oxygen to re-oxidize the NOx gasses from dissolution of sterling in nitric, you drastically cut down fresh nitric acid use. One oxygen concentrator paired with controlled dissolution of sterling in nitric produce practically no NOx exhaust. You can achieve close to 1:1 ratio of nitric spent to silver (stoichiometrically).

Finally - only 500g out of theoretical 900+grams of silver from kilo of sterling does not make a good business plan Nice thing about silver is = no matter how badly you screw up the batches, recovery or anything - you can always pour brine into the liquid and easily reclaim practically all of the silver. So losses by simply not precipitating all Ag are theoretically non-existent. Second most reasonable explanation is - the silver was never actually in your batch in claimed quantity Fake sterling is everywhere - many metals can make alloys that looks like silver, but they never were genuine 925. I never buy silver without XRF analyzing the melt.

 

[orvi]

e) Very Important Question (as it would save me a lot of time and effort) Can i instead of melting into shot, just use the cemented silver powder in the filter bag to run my Silver Cell ? Isn't it easier for the electrolytic process dealing with smaller particles like powder instead of shot? That i did not understand.

I'd be deeply grateful for the answers , thanks !

In order to attain good efficiency, you need to assure good electrical contact between pieces of silver. With that said, you can already see where the problem is. Particles of cement silver will make poor electrical connecton between themselves, leaving awful lot of silver-full anode slime, which would be nightmare to process.
If you proceed with shortcut on the one end, more problems will usually arise from that shortcut on the other end of the refining stream that is how it usually works (not saying there are no exceptions).

Easiest way is to cast anodes. Follow what big guys are doing - it is probably the most effective way invented to the date

 

[buckrogers1]

I do not know if you simply omitted that you were adding distilled water to your nitric solution or that you simply didn’t use it at all, but if you are not adding water you will use more nitric as there is nowhere for the material to dissolve into, again you make no mention of heating your solution and that will also increase your acid use.

Sorry , yes i diluted w distilled water. the most plausible explanation is trapped NO in the solution

 

[buckrogers1]

In order to attain good efficiency, you need to assure good electrical contact between pieces of silver. With that said, you can already see where the problem is. Particles of cement silver will make poor electrical connecton between themselves, leaving awful lot of silver-full anode slime, which would be nightmare to process.
If you proceed with shortcut on the one end, more problems will usually arise from that shortcut on the other end of the refining stream that is how it usually works (not saying there are no exceptions).

Easiest way is to cast anodes. Follow what big guys are doing - it is probably the most effective way invented to the date

will do that, thanks

 

[buckrogers1]

There are several possibilities - yellow colour can also result from dissolved nitrogen oxides in the liquid - and this is fairly common after end of the dissolution. Quick boil will remove them and solution will stay clear and colourless - IF the silver used was pure. Yellow colouration can be atributed also to trace Pd contamination - and despite claiming 99,9%+ purity, even that 0,1% consisting of Pd can colour the solution in a way you can see it Just hypothetical scenario - but Pd is relatively hard to remove from the silver via classical refining routes and even electrorefining cannot remove it all in one go.

Recycling of nitric from nitrate - not very pleasant technique. Hydrometallurgy is often awful technique of recovery when scaled up. That said, dissolution of silver takes up significant nitric acid - that solely is quite a cost. But then, people massacre that profit margin by cementation on copper - simultaneously using relatively expensive base metal to extract silver of non-sellable quality, creating heavy metal waste solutions (from which extraction of valuable nitric acid, and valuable copper is labor and resource intensive) and only then paving the path towards ultimate cleaning operation - electrolysis. That is why cementation on copper is rarely, if ever, seen on industrial scale refining of silver.

That being said, if one steps up from the hobby refining to semi-mid-scaled process with multiple kilos batches of sterling feed - copper cementation is nowhere nice in the terms of user friendliness and "clean" operation. Most of the semi-mid-scaled refiner use two-cell approach, pyrometallurgical oxidative cleaning of sterling or abandon copper cementation step in the hydro process - replacing it with silver chloride/sulfate production and treatment of silver chloride either by pyro route or wet route.

If you still need to proceed with hydrometallurgical treatment, logical way of making the process more efficient is to abandon the copper cementation step. Dropping silver sulfate instead of silver chloride can be done with concentrated sulfuric acid - thus re-viving the nitric acid of high concentration -> which could be used in dissolution of more silver feed in the future, making several cycles until the liquid is too heavily contamined with copper and need the final treatment and disposal. Silver sulfate is also convertible to silver by caustic route, altough bit more difficult for the first time.

This way, only waste feed which need hard treatment is the copper from actual sterling. Paired with use of oxygen to re-oxidize the NOx gasses from dissolution of sterling in nitric, you drastically cut down fresh nitric acid use. One oxygen concentrator paired with controlled dissolution of sterling in nitric produce practically no NOx exhaust. You can achieve close to 1:1 ratio of nitric spent to silver (stoichiometrically).

Finally - only 500g out of theoretical 900+grams of silver from kilo of sterling does not make a good business plan Nice thing about silver is = no matter how badly you screw up the batches, recovery or anything - you can always pour brine into the liquid and easily reclaim practically all of the silver. So losses by simply not precipitating all Ag are theoretically non-existent. Second most reasonable explanation is - the silver was never actually in your batch in claimed quantity Fake sterling is everywhere - many metals can make alloys that looks like silver, but they never were genuine 925. I never buy silver without XRF analyzing the melt.

Wow thanks, lots of great info to follow up on.

 

[cejohnsonsr1]

I wouldn’t be using silver rounds to make electrolyte. Too expensive and despite what the producers claim, purity is often questionable. After your initial run you should have plenty of pure silver to make your electrolyte with.

Your yield should be somewhere in the neighborhood of 900 g per kilo of Sterling, with the rest in your slimes and stockpot. 500 g is so far off that you should probably stop and figure out why.

If you think you’re having difficulty refining silver, you probably shouldn’t even consider trying to make nitric. No offense intended.

The powder will seep through your filter bag and contaminate everything in the cell. The shot method you see Sreetips use works great because the copper contamination of the powder used to make the shot is very low. Probably way less than 005. That’s because he spends a lot of time rinsing the copper nitrate out of the powder.

 

[orvi]

I wouldn’t be using silver rounds to make electrolyte. Too expensive and despite what the producers claim, purity is often questionable. After your initial run you should have plenty of pure silver to make your electrolyte with.

Your yield should be somewhere in the neighborhood of 900 g per kilo of Sterling, with the rest in your slimes and stockpot. 500 g is so far off that you should probably stop and figure out why.

If you think you’re having difficulty refining silver, you probably shouldn’t even consider trying to make nitric. No offense intended.

The powder will seep through your filter bag and contaminate everything in the cell. The shot method you see Sreetips use works great because the copper contamination of the powder used to make the shot is very low. Probably way less than 005. That’s because he spends a lot of time rinsing the copper nitrate out of the powder.

Most of the copper contamination in cement silver comes from flaking the copper together with silver during cementation. Washing is very important, of course, but generally you are left with 98-99% silver after this operation (when done diligently from diluted solution of AgNO3 - not concentrated). With copper in the cement arising from flaking, not the actual dissolved copper from the solution. Add non-diluted strong AgNO3 liquor to this, and then you can also precipitate copper oxy-nitrates and other strange stuff (recognizable blackish sludge on the surface of copper), which will decompose to copper oxide upon heating, liberating NO2 gas. This can go even lower than 92% Ag in the cement actually.

 

[buckrogers1]

I wouldn’t be using silver rounds to make electrolyte. Too expensive and despite what the producers claim, purity is often questionable. After your initial run you should have plenty of pure silver to make your electrolyte with.

Your yield should be somewhere in the neighborhood of 900 g per kilo of Sterling, with the rest in your slimes and stockpot. 500 g is so far off that you should probably stop and figure out why.

If you think you’re having difficulty refining silver, you probably shouldn’t even consider trying to make nitric. No offense intended.

The powder will seep through your filter bag and contaminate everything in the cell. The shot method you see Sreetips use works great because the copper contamination of the powder used to make the shot is very low. Probably way less than 005. That’s because he spends a lot of time rinsing the copper nitrate out of the powder.

i'm definitely using my cells silver batches for the next electrolyte, also i can rectify the yield numbers now, the last batch is closer to 90% weight. But i realized my biggest issue remains copper contamination when cementing. I will stop using this method and instead go the NACL >lye >Sugar route for the next ones, might be a bit messier , but seems the silver product to work with is way higher in purity than dealing with cemented silver from copper. Not to mention the quantity of copper i'm going through as these bars get eaten up. Is that excess nitric in the solution or as @cejohnsonsr1 pointed out a too high concentration of AgNo3. It's definitely a lot of trial and error with the quantities / solution strengths etc. In fact the last batch of electrolyte isn't producing as beautiful and big crystals as my previous batch, i suppose a) the dilution of this AgNo3 isn't ideal, b) the Silver Shot i'm using now doesn't make for good and even current passthrough (i'm using on average 3V, 3A, between 8 to 11 w absorption on my power source) , But as @orvi correctly pointed out, with silver i can simply start again and recover. My mistake at the beginning that probably affected my yield was that i didn't recover all silver out of the AgNo3 solution after dissolving my metals in nitric.
As i said, i'm tired of cementing and all the painstakingly cleaning rinsing filtering of cement to still have copper issues, so i will go for AgCL precipitate instead.

btw. additional question . What do you guys do with the sludge in the anode bag? Shall i just throw it back into the Nitric in the next dissolve batch?

Thanks BTW for all the feedback, great replies !

 

[FrugalRefiner]

i'm definitely using my cells silver batches for the next electrolyte,

I use sterling silver to make my electrolyte. Why? First, I need to refine it anyway, so dissolving it one time to make electrolyte kills two birds with one stone. Second, electrolyte should have some copper in it. It helps form the type of crystals we want. Without it, crystals at the start of a run tend to be long and thready, requiring frequent knock down to keep them from shorting out on the anode. Third, copper in the electrolyte helps to keep any lead in the anode slimes instead of dissolving into the electrolyte.

NACL, AgNo3. AgCL

Please be careful when using chemical formulas.
NaCl, not NACL
AgNO₃, not AgNo3
AgCl, not AgCL
See Chemical Formulas

Dave

 

[cejohnsonsr1]

Most of the copper contamination in cement silver comes from flaking the copper together with silver during cementation. Washing is very important, of course, but generally you are left with 98-99% silver after this operation (when done diligently from diluted solution of AgNO3 - not concentrated). With copper in the cement arising from flaking, not the actual dissolved copper from the solution. Add non-diluted strong AgNO3 liquor to this, and then you can also precipitate copper oxy-nitrates and other strange stuff (recognizable blackish sludge on the surface of copper), which will decompose to copper oxide upon heating, liberating NO2 gas. This can go even lower than 92% Ag in the cement actually.

The contamination i was referring to is due to there being 2 metals in solution at the same time. Cementation removes the silver from the solution, but in a muddy form where all the moisture in the mud is copper nitrate. You have to be very thorough in rinsing, but you’ll never get it all out. Same with silver chloride. So the difference between the 2 processes is 2 extra steps for little to no difference results. And it should be noted that cementation isn’t fire and forget. The condition of the copper has to be monitored. When the copper begins to get thin it has to be be replaced. There shouldn’t be any flaking.

 

[cejohnsonsr1]

i'm definitely using my cells silver batches for the next electrolyte, also i can rectify the yield numbers now, the last batch is closer to 90% weight. But i realized my biggest issue remains copper contamination when cementing. I will stop using this method and instead go the NACL >lye >Sugar route for the next ones, might be a bit messier , but seems the silver product to work with is way higher in purity than dealing with cemented silver from copper. Not to mention the quantity of copper i'm going through as these bars get eaten up. Is that excess nitric in the solution or as @cejohnsonsr1 pointed out a too high concentration of AgNo3. It's definitely a lot of trial and error with the quantities / solution strengths etc. In fact the last batch of electrolyte isn't producing as beautiful and big crystals as my previous batch, i suppose a) the dilution of this AgNo3 isn't ideal, b) the Silver Shot i'm using now doesn't make for good and even current passthrough (i'm using on average 3V, 3A, between 8 to 11 w absorption on my power source) , But as @orvi correctly pointed out, with silver i can simply start again and recover. My mistake at the beginning that probably affected my yield was that i didn't recover all silver out of the AgNo3 solution after dissolving my metals in nitric.
As i said, i'm tired of cementing and all the painstakingly cleaning rinsing filtering of cement to still have copper issues, so i will go for AgCL precipitate instead.

btw. additional question . What do you guys do with the sludge in the anode bag? Shall i just throw it back into the Nitric in the next dissolve batch?

Thanks BTW for all the feedback, great replies !

Your voltage should be 3.5. Amps will be whatever your circuit is capable of passing. The concentration of silver in the electrolyte needs to be about 500 g/liter minimum. The point I was making previously was that you won’t avoid the rinsing by doing the sugar and lye method. You’ll just be rinsing chloride instead of nitrate and adding 2 steps to the process only to wind up with the same mud with the same amount of contamination. Really 3 extra steps since you’ll have to convert the nitrate to chloride before you can convert it back into mud. You save the anode filters because the slimes contain precious metals that you can recover when you have enough to be worth the time and effort to process. Same principle as a stockpot. Sreetips has a very recent video on making electrolyte and his silver cell setup and operation. It was posted 2 or 3 weeks ago. It would be well worth your time to watch it.

 

[orvi]

The contamination i was referring to is due to there being 2 metals in solution at the same time. Cementation removes the silver from the solution, but in a muddy form where all the moisture in the mud is copper nitrate. You have to be very thorough in rinsing, but you’ll never get it all out. Same with silver chloride. So the difference between the 2 processes is 2 extra steps for little to no difference results. And it should be noted that cementation isn’t fire and forget. The condition of the copper has to be monitored. When the copper begins to get thin it has to be be replaced. There shouldn’t be any flaking.

My experience is that silver chloride and also cement silver are washed nicely from copper residues. Nothing that stubborn as Pd contamination in AgCl. Achieving 999 Ag from chloride is relatively consistent for me, even if the feed contain more than 10+% Cu.

About co-flaking of Cu I learned when washing cement silver. It could be seen that even if the wash-waters test negative for Cu, you will obtain copper in final silver product. Silver chloride, you can wash thoroughly to negative Cu test and Cu will be present at the end at less than 0,05%. Since I do not use this method very often and practically never on large scale, I did not tested it further to see which conditions help to form more consistent and pure cement precipitate. Sometimes, it is just logical to use this precipitation instead of AgCl (like heavy Pb/Bi solutios).

From process point of view, I am doing batches through AgCl process, with elaboration on possible Ag2SO4 process. Overall, processing BM waste is much more tedious for me, than rinsing several times with water. And as I am more filtering the precipitates than wash-decanting them, 3 filtrations are enough to produce 999 silver pretty consistently. I do not have interest to refine it to higher purities = no economical point for me right now.

 

[buckrogers1]

Dear all,
i've tweaked and tuned my process to my satisfaction. Initial loss % were skewed because of material that was not sterling, but likely plated brass, i tried the sugar and lye method, but it becomes literally sticky (pun intended, lots of sugar residue to wash away) , cementing on copper works best i realized when the concentration of the dissolved metals in solution is high, and when a little nitric is still present in the solution. Silver gets knocked off in copious amounts, until the dark green solution has turned light blue. Testing with drops of HCl if any silver remained in the solution > no AgCl dropping (no white streaks or clumps forming) . I noticed that the best way to get rid of copper that might have flaked by cementing, is after draining the remaining Copper Nitrate solution ( i don't process this , too cumbersome to recover nitric acid from it, and Cupric Nitrate crystals are not worth the effort i think ) , anyway by adding a little bit of my Silver Cell spent electrolyte (which still has Silver Nitrate in it) and vigorously mixing the cement, the remaining copper goes into the solution and the remaining silver of the electrolyte cements out as well. Leaving me with after rinsing and washing a very nice , shiny, almost white Silver powder. Then i melt the powder into bars for the silver cell. These bars are already 99% pure. ( tested with the Sigma precious metal verifier, on 99.9% setting the indicator almost falls into the brackets , which indicates were close to 99.9% )
Then i run the bars as anodes in a stainless steel bowl.

here comes my question, i do not care about size or beauty of crystal growth as i want to pour the final product into bars again.
I've been testing various batches varying, a) concentration of electrolyte b) purity of electrolyte (+/- copper contamination) c) varying voltage/amperage
As you can see from the pictures, i get results ranging from foil like flakes, to wool like clumps, to nice tree crystals , to small hard crystals.
To be honest i have not still figured out what influences what , regarding crystal growth, I have looked up the forum and youtube on this but it's not conclusive and clear.

So , my question is. What is best to obtain the purest (not nicest) form of crystals to melt into bars?
Correct me if i'm wrong:
a) low voltage and low current
b) high concentration of electrolyte
c) low contamination by copper

So far i'm working with a 6 inch diameter stainless steel bowl , the anode is placed in the middle, held up with a plastic coffe filter ( with 3 layers of coffe filter paper that i change and discard every 8h with the black slimes that accumulate ) using only poured bars (no shot ) as anodes.
Current is around 2A to 3A , Voltage from 1.1V to 3V ( depends on Electrolyte concentration and size of anode bars )

Clarification on parameters to use and how they influence crystal growth would be greatly appreciated, and i believe many in this forum are seeking similar answers.

( p.s. also is it possible to run 2 cells in series or parallel with one power supply? )

And also another question, any tips on how to prevent ( when pouring the silver into graphite molds ) the layering gaps of the silver bar?
I am blasting the graphite mold with a propane torch while pouring to eliminate the oxygen , but still i do get either little bubble holes or layer line on the bar side . (i'd like to pour an almost perfect bar) Any tops on that? See last pic for how the bars look like now (granted i poured them quick and dirty as i use them as anodes first , not for beauty. But still, knowing how to pour them as perfect as possible , TIPS appreciated )


Thank You in advance.

 

[buckrogers1]

Update. I decided to put a heating fan next to the Stainless Steel bowl. That allowed me to reduce Voltage to 1V and increase Amperage at 3 A.
Now i'm able to literally peel the layer of silver off the stainless steel bowl , like aluminum foil, also crystal growth is much faster.
Any comments? Explanations? i'm testing in the blind, i greatly would appreciate input on which variables affect crystal growth and how.
Thank You.