Electrolytic copper refining cell

[Shark]

I pulled the cathode today and started a fresh one twice the size of the old one. The power supply is at it's limit in the current configuration so I will need to make more changes there before anything larger can be used. The cathode is solid, very solid. I think it will do to be reused as a collector metal once again like it is. It took 72 hours to get this build up which is about 2 1/2 ounces of material removed from the anode. The slime's are adding up fairly well, but I am reusing the filter bag as is until the build up poses problems. Any how here is the cathode as it came from the cell.

[youtube]http://www.youtube.com/watch?v=OXsDG3Tkt18[/youtube]

 

[Shark]

Operating temperature, 60 C (140 F)

Is this the temperature that should be maintained in the cell, or is this the maximum? I am starting to think about a larger cell, and have ideas on circulating the solution and filtering it as it circulates. If heated I will need to be very sure the filter will withstand the solution. All of this is just random thoughts right now, but it is stuck in my head to build a bigger cell, while keeping it on a workable home scale.

 

[FrugalRefiner]

Shark, I've been busy and haven't commented, but I love seeing what you're doing!

Dave

 

[Shark]

Operating temperature, 60 C (140 F)

Is this the temperature that should be maintained in the cell, or is this the maximum? I am starting to think about a larger cell, and have ideas on circulating the solution and filtering it as it circulates. If heated I will need to be very sure the filter will withstand the solution. All of this is just random thoughts right now, but it is stuck in my head to build a bigger cell, while keeping it on a workable home scale.

For some reason this kept eluding me, but I finally found it,

I notice the specifications that Chris posted referenced baths operating at lower temperatures than the 160 F that I mentioned. I always prefer warmer for the simple reason that I like to see a good quantity of evaporation so replenishment can be made with settled rinse waters from rinsing clean electrodeposited copper free of electrolyte and form rinsing slimes off of anode bars when they are removed for re-casting. This means your rinse water is no longer a waste stream. To a small refiner this can be a big deal. Electricity is cheaper than hauling waste. If you are a big operation with waste effluent treatment in place, cooler may be your choice. I have no experience running these baths at the lower temperature.

Shark, I've been busy and haven't commented, but I love seeing what you're doing!

Dave

Thanks Dave, I find this very interesting and enjoy it. I am working toward a cell roughly 3 times the size of the one I have been playing with. Until I can get my hands on a true rectifier it will be a slow go yet.

 

[Shark]

I attempted to pour an anode for the new cell today and failed. I just didn't get enough heat in the metal to make a clean pour. My crucible is over it's limit as well. I may need a new furnace so I can go to a larger crucible. Here is the failed anode anyway.

 

[Shark]

Forgot to add the current cell. I just put this one together right quick using things I had on hand. The power supply is one I borrowed from modtheworld, and just now getting around to using it. While it isn't adjustable it is doing a fair job. There is 2 volts at 1.9 amps going into the cell when starting up but quickly drops back to .8 to .9 volts at 1.9 amps. Still a bit strong but will have to do until later this week.

 

[Shark]

I have been thinking about the nodular growth on my cathode and started looking for some answers. I found this in the PDF posted here by GSP;

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=86&t=24397#p258175

To quote it,

Excess sulfuric acid drastically
increases the cathodic overpotential and introduces a smaller
ratio of level plane of electrodeposits resulting in nodular
precipitates. It also drastically changes the X-ray
diffraction pattern by increasing the surface overpotential
and inducing three-dimensional nucleation at the higher
overpotential. Specific conductivity is nearly doubled
when the concentration of sulfuric acid is raised from 50
to 100 g L. An additional increase in free-acid concentration
to 200 g L, which is the level widely used in
electrorefining, reduces the resistivity from 4.2–4.3 to
1.6–1.9mV-cm

I think that explains the nodes extending from my anode. If I am understanding this right, it also means that major changes in the amount of acid can play a critical role in how the cathode turns out. I will need to re read this some more to get a better grasp of the overall of the article. These nodes could pose a potential problem when running larger numbers of anodes and cathodes that sit fairly close together.

edited to correct anode to cathode

 

[Shark]

From the latest configuration. This is the cell I have been tinkering with the past week or so.



A few notes from this cell.
When hanging the electrodes the heavier ones maintain better electrical contact. This aids in a more uniform cathode growth. Good, sound contact is important, it also aids in the uniform reduction of the anode over time. Also aids in better, more even cathode growth.

When hanging small anodes (cathodes as well) use a larger size wire. The larger wire provides a larger contact area as well as useful weight. The larger wire also makes it easier to keep contact between the wire and anode by allowing for a tighter twist where they make contact. The small wires were also a pain to keep formed properly, the slightest movement seemed to cause problems with electrical contact that wasn't as noticeable on the larger wires.

Distance between cathode and anode can cause major changes in electrical properties with in the cell. When running multiple anodes and cathodes, keep the distance equal. It was very hard to do in a cell setup such as this one, while maintaining good electrical contact.

Here are the anodes after eight days of 2 volts at an average of 1.8 amps across two cathodes that were 5 square inchs X 4 sides.



I cleaned the anodes but some maintained a darker finish than others. I still haven't figured that out unless it is due to the anodes being from different pours. The crystalline structure in the anodes are impressive. It didn't show up until being ran in the cell for a day or so.

Edit for correct naming

 

[Topher_osAUrus]

I have been thinking about the nodular growth on my anode and started looking for some answers. I found this in the PDF posted here by GSP;

To quote it,

Excess sulfuric acid drastically
increases the cathodic overpotential and introduces a smaller
ratio of level plane of electrodeposits resulting in nodular
precipitates. It also drastically changes the X-ray
diffraction pattern by increasing the surface overpotential
and inducing three-dimensional nucleation at the higher
overpotential. Specific conductivity is nearly doubled
when the concentration of sulfuric acid is raised from 50
to 100 g L. An additional increase in free-acid concentration
to 200 g L, which is the level widely used in
electrorefining, reduces the resistivity from 4.2–4.3 to
1.6–1.9mV-cm

I think that explains the nodes extending from my anode. If I am understanding this right, it also means that major changes in the amount of acid can play a critical role in how the anode turns out. I will need to re read this some more to get a better grasp of the overall of the article. These nodes could pose a potential problem when running larger numbers of anodes and cathodes that sit fairly close together.

Love the updates Shark, I truly appreciate seeing the progress, changes made, and results. It is giving me inspiration to melt and run my copper that is coming out in the iron stage of my waste treating.

I do have question though (forgive me if I missed the post regarding it), but do you mean the cathodic deposit is nodular? Or are you having some nodules grow on your anode when the cell is operating?
-if the former, the cathode deposit can be altered by acid content, also adding some gelatin or another additive (I cant remember what)

For your darker finish anodes, have you tried doing the melt with some charcoal, or a good flux covering to prevent oxidation?
There are many other things that you can use beside charcoal. A little soda ash may help as well.

 

[Shark]

I do have question though (forgive me if I missed the post regarding it), but do you mean the cathodic deposit is nodular? Or are you having some nodules grow on your anode when the cell is operating?
-if the former, the cathode deposit can be altered by acid content, also adding some gelatin or another additive (I cant remember what)

They grow on the cathode. I am doing another single anode/cathode cell now testing some new things about these growth. I have added some air to agitate the solution, which some books mention will help with these growths. I don't want to change the electrolyte until I could test this stirring idea.

I also got my copy of Modern Electroplating, 5th edition. That will take some time to study.

(I need to edit that quote to correct the "anode" to Cathode.)

 

[Shark]

After 48 hours in my single anode/cathode cell, using the original formula for the electrolyte, this is the growth with only a small amount of air to circulate the solution. The cathode was 2 inch by 2 inch and ran at 1 volt, .75 amps.




I am very happy with this for now. There was no soft, powder type growth that can be a pain to work with. The reduction in the anode weight was 53.2 grams. I can reduce the anode faster but it runs the risk of loosing PM's into the copper that falls off and settles into the bottom of the cell. This provides a potential contact point for a shortage that I prefer to avoid. I am not looking for a super smooth finish, but would like an even growth that the new cathode is exhibiting now. Keep in mind the goal is to remove the copper from, and collect, the PM's. Not to produce high quality copper. I do forget this at times as I study and try to apply what I learn.


This is part of the slime's collected from the bigger, multi electrode cell. A small bit is still attached to the filter bags that I will deal with later. (the glass is 3 3/4 inch in diameter)

 

[nickvc]

The darker coloured anodes may show more values than the others as they appear very similar to cemented values on copper, I could well be wrong but it's worth mentioning.

 

[Shark]

This is what I thought also Nick, but the dark finish was firmly attached. I even tried to brush it off with a tooth brush out of curiosity. It is possible that the dark ones were shorted and this caused some kind of reaction I haven't been able to figure out as well. I am running two of them now in another cell by their selves and they are continually passivating. Is it possible that it is some effect of polarization? I may try and reverse the polarity for a few minutes and see what the effect would be.

Edit to add

From Modern Electroplating 5th Edition

Plate characteristics are improved, solution
conductivity is increased, and anode and cathode polarizations
are greatly reduced when free acid is added to either
solution [26, 66]. The acid also prevents the precipitation of
basic salts.

Might be time to try adding a small amount of sulfuric acid.

 

[nickvc]

It may be that the value content is causing the problem or other metals that do not easily slough off.
I'd suggest re melting with more copper and see if they behave then, using mixed metals it's possible certain bars will have greater contaminants including values that can cause this problem.

 

[upcyclist]

If the discoloration is indeed a skin of metals (precious or otherwise) that are passivating, would it not also be possible to saw or file a notch into the bottom of the anode, thus exposing the purer copper? Then the skin would eventually slough off and end up in the filter bag (or remain as a hollow shell)?

 

[Shark]

If the discoloration is indeed a skin of metals (precious or otherwise) that are passivating, would it not also be possible to saw or file a notch into the bottom of the anode, thus exposing the purer copper? Then the skin would eventually slough off and end up in the filter bag (or remain as a hollow shell)?

I have no idea at this stage. I added one ounce of sulfuric to one liter of the electrolyte with no notable change over a one hour period. I just have used one of the dark anodes and reversed the polarity for 3 minutes. Nothing else was changed except for the addition of sulfuric acid prior. The brown color was lightly covered in clean copper plate. At that point I switched the polarity back and in 5-6 minutes it stopped again. I took the anode out and washed it in my rinse container and the coating came right off. It is now running, although it still passivates every 20 minutes or so. I can shake the anode and it will go back to working for a few minutes. I have no idea why some had a coating hard enough to stick that tight and others didn't. I do know some of the anodes are well above the percentages of PM's that are the normal suggested levels. I will just keep cleaning them until they are done for now.

I am also wonder about sonic stirring. Could it somehow be used to agitate the solution (I know air agitation greatly improved the smaller cells), and shake the PM's from the anodes at the same time? If that would work it would really make these small cells with anodes of higher percentages of PM's less labor intensive.

 

[upcyclist]

I do know some of the anodes are well above the percentages of PM's that are the normal suggested levels.

It sounds like Nick had the right idea, then--add some copper to your anodes to bring the purity up a bit. It'll use fuel & time, but it sounds like it might be faster overall than babysitting the anodes by having to shake them every few minutes.

 

[nickvc]

Shark remember the mantra of any electro refining process, high percentage anodes work for longer and better whether it's gold, silver or copper as it stops fouling of your electrolyte and produces better results for the targeted metal.
When your melting various types of scrap it is hard to get consistent results for your anodes, not your fault it happens but save time and effort and just add more copper, you now have plenty spare, to the resistant anodes and re melt them and put them back in your cell and walk away and let the cell do the hard work.

In fact now you have excess pure copper add some to all your future melts and hopefully the problem will cease altogether.

Edited for an extra thought :shock:

 

[Shark]

I agree guys, adding the copper would be the fastest way to get an anode that runs with least amount of hassle. The anode I ran from a piece of clean copper pipe went very fast, and smooth. Anyone trying to get started in this needs to start with a fairly pure anode to get the feel for it.
BUT.... I got it to work by adjusting my air line in such a way to gently shake the filter bag. Just enough movement to keep a decent sized spot of the slime's cleared off enough to allow it to run all night. In fact just a few minutes ago the wire used for the connection broke(ate to thin by the cell action). The anode is small enough I would normally add it to the pile for remelting, but I am thinking I may try to add a new wire and see if I can run it a little longer. I will post a picture of it later, after attaching a new connecting wire.

Thanks for the input guys, it always help to get new insights into this. This is my first cell as I have never ran one for silver.

 

[Topher_osAUrus]

Shark, how were you homogenizing the melt, before pouring the anodes?
Did you stir with a carbon rod or anything?