My New Silver Refinery - Thum Cell

[rybak97]

Here’s my new Thum Cell….. Basically it’s a 1.5 Gallon Rubbermaid container from Wal-Mart ($5.00), and smaller Rubbermaid container from my cabinet (Anode basket, free) and one of my dog’s old water bowls (Cathode, cut and smashed to fit the container, free).

I’m using pure cemented silver shot for the anode. I've got a small ingot with a SS screw melted into it for the electrical connection (well out of the electrolyte so no SS is involved with the reaction) and a power supply from EBay (recommended on another thread).

My solution is 6 Toz of Ag and 36 grams of Cu in 1 Gal of distilled water. The container on the left is just to use up some volume so I didn’t have to make an entire 1.5 Gal’s of electrolyte.

There is so much surface area in the anode because of the shot I’m getting great amperage through the cell and am currently running at 3.8V which results in current flow of 3.1 amps. The cell has been running for an hour and I've all ready got some good silver depositing on the Cathode, aka dog bowl!!

Please take a look and give me all the constructive criticism you can. My father always told me you don’t even know how to eat until someone tells you how to so take all the advice you can get!!

 

[rybak97]

Bumped it up to 4.0V after an hour and are now running 4.3 amps. Photo of crystals after two hours attached...

 

[FrugalRefiner]

Brian,

Based on the pictures, I believe you've created more of a Moebius cell than a Thum cell. The Thum cell is characterized by a horizontal cathode at the bottom of the cell. A Moebius cell has a vertical cathode, usually with vertical anodes. They both have their advantages and disadvantages, but they both produce silver crystals. It's more just a technical/semantic difference. Yours is sort of a combination.

In your second post you mention raising the voltage to 4.0V. You would be better served keeping it closer to 3 volts. As you increase the voltage, you're more at risk of co-depositing other metals along with the silver you're trying to purify.

Dave

 

[rybak97]

Brian,

Based on the pictures, I believe you've created more of a Moebius cell than a Thum cell. The Thum cell is characterized by a horizontal cathode at the bottom of the cell. A Moebius cell has a vertical cathode, usually with vertical anodes. They both have their advantages and disadvantages, but they both produce silver crystals. It's more just a technical/semantic difference. Yours is sort of a combination.

In your second post you mention raising the voltage to 4.0V. You would be better served keeping it closer to 3 volts. As you increase the voltage, you're more at risk of co-depositing other metals along with the silver you're trying to purify.

Dave

Hi Dave,

Thanks for the input.

The cathode is L shaped but the solution was cloudy so you really couldn’t see the bottom. I’ve attached a picture of the cathode out of solution so you can see it. I wrapped the upper part of the cathode with electrical tape per another member’s recommendation as he said I’d get better purity with crystals forming only on the bottom due to a higher Cu concentration towards the top of the electrolyte. Have you heard of this??

I dropped the voltage to 3V's and am now running at 3.3 amps. I did some more reading and read about depositing other metals at higher voltage like you said and we certainly don’t want that!! Plus, when I pulled out the cathode to take a picture there was a 3in tall silver crystal forming directly below the basket!! From what I read a lower voltage will result in smaller, denser and less "leggy" crystals. That will let me run for longer before I need to clean out. The basket is only 3.5in away from the SS cathode on the bottom.

Thanks again, keep it coming.

 

[mikeinkaty]

Mine is like a Moebius cell. I now have a 500 sq cm SS cathode that is 6" x 13" that makes a semi-circle inside of the glass container. When I hang 2 anodes (5 ozt each) in the cell I get 3 amps at 1.0 volt. At 2.5 volts it runs close to 10 amps. But, I generally set it at 1.5 volts producing 4 to 5 amps. At the higher amperages (> 6 amps) I get the feather crystals on the edges of the SS which is not good. That is one advantage of using a SS bowl - you get no edge effects as there are no edges! My cell generally takes about 14 hours to digest 10 ozt of anodes when running at 5 amps. Also, with the increase in cathode area I get no buildup under the anodes. Letting it run 20 ozt before cleanout produces bigger crystals. The idea of running shot in a Thum cell is a very good idea as it increases the anode area, and likewise, the amperage. My anode to cathode distance is about 3".

Bryan - keep up the good work! The experimentation is half the fun! Mike

 

[rybak97]

Bryan - keep up the good work! The experimentation is half the fun! Mike

Thanks Mike. I should be getting more amps out of this cell I think. I think the problem is the sive of my cathode. That shot in my anode has such a huge amount of surface area I think there might be more anode surface area than cathode surface area. The cathode Im using is probably only 16in^2. Theres no way for me to calulate the surface area of all the shot, but id bet money its more than 16in^2. Not sure how to fix that problem without increasing the volume of the cell??

 

[FrugalRefiner]

Brian,

You're right, I couldn't see that your cathode continued down to the bottom of your cell.

I haven't read anything about higher copper concentrations towards the top of the electrolyte, so I can't answer that question.

But you did bring up an interesting point. Why is your electrolyte so cloudy? If all you dissolved was silver and copper in HNO₃, it should be a clear blue, not cloudy. Take a look at some of the other cells on the forum. Whatever is causing the cloudiness could become trapped in your crystals as a contaminant.

Watch out for those long crystals. If your power supply isn't sufficiently protected, the crystal could grow to contact the anode, shorting the circuit and possibly damaging your power supply. With clear electrolyte, you can see when this is happening and knock them down before they can do any harm.

Dave

 

[goldsilverpro]

There are better masking materials to use with chemicals than electrical tape.

http://www.3m.com/product/information/Electroplating-Tape.html
http://www.amazon.com/s?ie=UTF8&field-keywords=electroplating%20tape&index=blended&link_code=qs&sourceid=Mozilla-search&tag=mozilla-20

http://www.darentwax.com/products/engineering/stopping-off-wax

http://www.tolber.com/products.htm

http://www.amazon.com/b?ie=UTF8&node=700782011

 

[rybak97]

At the higher amperages (> 6 amps) I get the feather crystals on the edges of the SS which is not good. That is one advantage of using a SS bowl - you get no edge effects as there are no edges!

Mike, Im getting some of these "feathers" at the edges of my cathode just like you mentioned above. Why is this a bad thing???

 

[rybak97]

http://www.3m.com/product/information/Electroplating-Tape.html
http://www.amazon.com/s?ie=UTF8&field-keywords=electroplating%20tape&index=blended&link_code=qs&sourceid=Mozilla-search&tag=mozilla-20

Awesome, never even would have known it existed if it weren't for this forum!! The electrical tape Im using is vinyl as well, but Im sure this tape has something that makes it less reactive, stronger, longer lasting, or something......

 

[rybak97]

But you did bring up an interesting point. Why is your electrolyte so cloudy? If all you dissolved was silver and copper in HNO₃, it should be a clear blue, not cloudy. Take a look at some of the other cells on the forum. Whatever is causing the cloudiness could become trapped in your crystals as a contaminant.

I didn’t even realize that it was so important to use pure "ingredients" for the electrolyte. For it I used some of the silver shot I made from the cementation, but I also tossed in some of the fine powder I found at the bottom of the cementation vessel that I couldn’t filter. Perhaps it wasn’t silver? What do you think?

 

[lazersteve]

I have a case of the acid proof circuit board etching mask tape. Each roll is 3/4" wide. I use it to mask off my stainless cathode contact leads. It's really great stuff.

Steve

 

[mikeinkaty]

At the higher amperages (> 6 amps) I get the feather crystals on the edges of the SS which is not good. That is one advantage of using a SS bowl - you get no edge effects as there are no edges!

Mike, Im getting some of these "feathers" at the edges of my cathode just like you mentioned above. Why is this a bad thing???

They make like (what I call) silver wool. Hard to work with. The big nodules are much better. Easier to scoop, easier to wash, etc. If they start growing they will spread across the floor and start piling up under the anode. (in my case the floor is glass) I covered the edges of my cathode with plastic report binders. They cover the edge about 1/4". I thought about black tape but didn't know if the glue might contaminate the solution. From what I read here I gather not. I may try that as I'm out of sterling and my cell is shut down. ps - I liked the beauty of the wild growing feathery crystals at first as did my granddaughters. The would stare at them a long time trying to see them grow. By the way, one publication I read said that 30 ma per square cm for a SS cathode is about the most current recommended. They also said that most Moebius cells were run at 1.5V-2.5V. Then as much current as possible without exceeding the 30ma/sqcc rule. I think they said Thum cells are generally run with 3.5-5.5V. The objective here is speed and likeable crystals. Mike

http://books.google.com/books?id=E_...AEwAA#v=onepage&q=moebius silver cell&f=false See around page 240.

 

[FrugalRefiner]

Brian,

It's impossible to know what your fine powder might have been. The most common metal alloyed with silver is copper, but there is no guarantee that some other metal(s) may not be in the mix.

As with most things in life, the acronym GIGO (Garbage In, Garbage Out) applies in refining. Consider that most of us are striving for the purest metals we can get. I know that's not true in every case, as there are many for whom recovery provides them a satisfactory result. But if you're running cemented silver through an electrolytic cell, you're likely shooting for at least 999 fine silver. That only allows you a 1 part out of 1,000 tolerance. So if your final silver crystals contain more than 1 milligram (.001 gram) of contaminant per gram of crystal it's not 999. If the particles are big enough to make your electrolyte cloudy, it's likely some of them are going to settle out onto your crystals, and as the crystals grow around them they will become trapped in the crystal structure. Mother Nature does it all the time!

The cell is capable of producing 999.9 silver if you're careful. When you make your electrolyte, if it's cloudy you should filter it till it's perfectly clear before using it.

Dave

 

[mikeinkaty]

But you did bring up an interesting point. Why is your electrolyte so cloudy? If all you dissolved was silver and copper in HNO₃, it should be a clear blue, not cloudy. Take a look at some of the other cells on the forum. Whatever is causing the cloudiness could become trapped in your crystals as a contaminant.

I didn’t even realize that it was so important to use pure "ingredients" for the electrolyte. For it I used some of the silver shot I made from the cementation, but I also tossed in some of the fine powder I found at the bottom of the cementation vessel that I couldn’t filter. Perhaps it wasn’t silver? What do you think?

I always filter my AgNo3 solutions whether being used for electrolyte or going into a dropping tank. I clean off the tarnish too on the sterling before dissolving using Bonami and hot water. ps - I'm on my 3rd cell design now. Will probably have more! Mike

 

[rybak97]

Brian,

It's impossible to know what your fine powder might have been. The most common metal alloyed with silver is copper, but there is no guarantee that some other metal(s) may not be in the mix.

As with most things in life, the acronym GIGO (Garbage In, Garbage Out) applies in refining. Consider that most of us are striving for the purest metals we can get. I know that's not true in every case, as there are many for whom recovery provides them a satisfactory result. But if you're running cemented silver through an electrolytic cell, you're likely shooting for at least 999 fine silver. That only allows you a 1 part out of 1,000 tolerance. So if your final silver crystals contain more than 1 milligram (.001 gram) of contaminant per gram of crystal it's not 999. If the particles are big enough to make your electrolyte cloudy, it's likely some of them are going to settle out onto your crystals, and as the crystals grow around them they will become trapped in the crystal structure. Mother Nature does it all the time!

The cell is capable of producing 999.9 silver if you're careful. When you make your electrolyte, if it's cloudy you should filter it till it's perfectly clear before using it.

Dave

That does not sound good!!

I filtered the electrolyte through two layers of muslin, but not enough to remove the cloudiness. I tried to filter through a coffee filter but it got clogged almost immediately. The cell is clearing up now so I have to assume you’re exactly right; the sediment is settling to the bottom and becoming trapped in the crystalline structure. D*&M!

Well, I’m going to keep it running to completion and make my final ingots as planned. I have a local assayer that is going to check them for me on Monday so I should know if I hit .999 pretty soon. If not, I’m going make some new electrolyte with just pure silver and copper and try again. Can’t sell it unless it’s .999!!

Thanks for the input everyone.

 

[FrugalRefiner]

Let us know how it turns out. We can all learn through your experience.

Keep studying. There is so much to learn.

Dave

 

[Palladium]

Did you use tap water to make the solution? If you did then the cloudiness could be silver chloride.

 

[rybak97]

Did you use tap water to make the solution? If you did then the cloudiness could be silver chloride.

No, I used distilled water for everything.

 

[rybak97]

OK. I did an early "clean out" of the cell and sure enough there was a VERY fine grey powder that had settled out of the solution and was at the bottom of the cell. The good news is that once I removed all the silver and placed it on Muslin all of the grey powder washed right off (at least what wasn’t trapped by the crystals). This left me with my first container of beautiful silver crystals (see photo).

I removed the electrolyte and filtered it once through 4 coffee filters, then through 5 and finally through 6 coffee filters and the solution came out much clearer than it was originally. I let that sit for 30 mins and nothing settled to the bottom of the beaker so I’m pretty sure it won’t in the cell either.

Just got her fired back up and she’s running like a champ.

I’ll keep the updates coming and post the assay results on Monday. Thanks for all the help everyone.