Electrochemistry Copper Nitrate Cell

[rusty]

The new cell I'm working on uses copper nitrate for the electrolyte, the anode made from copper alloyed with precious metals such as gold and silver with perhaps a bit of the platinum group.

About the cell, there is a porous membrane divider, the book says they used asbestos rock sheet for the membrane, I'm going to use unglazed tile called quarry tile for the membrane.

The cathode side uses copper sheet, I do not have nor wish to spend money for this, so what I plan on doing is setting up a board with removable pegs that I can weave a copper mesh from wire as my collector. I believe that as the cell deposits copper onto the mesh the small holes will eventually fill giving me pure copper.

From the anode side any silver that is alloyed in the copper anode will go into the copper nitrate solution, every so often the liquor is harvested, the silver is cemented down using copper. The barren liquor is returned to the cell where the copper will be deposited onto the cathode.

Precious metals from the anode settle as slimes in this side to the cell to be further refined. Voltage is the cell is not to exceed 1.5 volts at 20 amps per square ft of anode. However this is in theory, I may be proven wrong as this project moves along.

On a side note, I do not think using a battery charger will give suitable results, the higher voltages will give a mossy deposit at the cathode with possible co-deposit of other metals.

Regards
Rusty

 

[seawolf]

Rusty can you post a few pics of the cell?
Mark

 

[HAuCl4]

Great idea!. I'm interested in the type of membranes that you plan to use. 8)

 

[qst42know]

Isn't copper usually refined to a solid deposit in a copper sulfate electrolyte?

 

[lazersteve]

Gill,

I'll donate a section of copper mesh to your project.

PM me for details.

Steve

 

[rusty]

Gill,

I'll donate a section of copper mesh to your project.

PM me for details.

Steve

That would be great Steve, but I think that we should wait until the jury is in, perhaps Chris could give some advice regarding the pros and cons of using mesh over solid copper sheet for the cathode.

I'm thinking that the weave would not have to be all that tight with maybe holes as large 1/4" in the mesh made from freshly stripped copper wire, the cell based on Quarry Sheet will be 12" by 12" each compartment, the actual box a bit higher to allow for excess electrolyte as the anode is lowered into the cell.

The cathode should be of the same size, I've been toying with the idea of a revolving cathode which would give a nice even deposit all around. Due to the weight that will eventually collect onto the cathode I do not think this plan is going to take root.

My furnace and crucibles are still over at the other house, so melting anodes is still a ways off, and this new shop is just now coming into shape. Missed the lumber yard today but did purchase my T5 lights in 8 footers at $85.00 each from another shop.

Getting stuck with the truck killed a lot of time, then the Quad got stuck high centered on the snow and be damned of I could find reveres. Anyhow it was a fun day supper was on the warmer when I got home and the dog finally ate his supper. Yea the dog won't eat unless I'm home. wife says that I should take him with.

I would but the dumb dog cant see the window glass and he gets dog snot all over the windows and I get tired of cleaning the windows when I have to take the wife with me.

Before I derail this thread entirely, I'm very excited and anxious to try out the copper nitrate electrolyte cell.

Regards
Rusty

 

[Militoy]

I'll be following this new thread with interest. I have NO experience with electrochemistry - but we do design and build power supplies that are used by some of our customers for that purpose, as well as for cathodic protection of pipelines and shipboard cooling systems. I actually have several "DC rectifiers" (power supplies) designed specifically for electroplating in my scrounge junk pile. I'm also lucky enough to have a chemist working (out of his field) with me - whose brain I can occasionaly pick! I'm a newbee at applying chemicals to my own gold - but I might also eventually find it interesting to apply a bit of controlled electrical current to the equation.

 

[nickvc]

Gill I tried the same sort of thing some time back using the ceramic outer from a crucible from an induction casting machine as the membrane. The problem I encountered was that as I was warned by Harold and GSP floating gunk and a poor deposit after a fairly short period of time. I think that you must have a high % of copper and a very low % of precious metals, something over 98% copper is where I'd start if I tried again, if I remember correctly I was around the 93% copper. There's plenty of information about copper refining available so I'd check on the feedstock they use and try to be slightly higher in the % of copper in yours.
I love your imagination when it comes to finding a method and creating the machinery to recover and refine your metals and wish you luck in this latest trial.

 

[Oz]

I would agree with Nick’s statement as to the purity of the anodes. While I have never built a copper electrowinning cell before, I have done a fair bit with silver cells. I have found that anything over 3% insoluble elements such as Pt or Au in my silver anodes gives me grief.

The insoluble elements form a crust that is adherent and all but stops the dissolution of your main metal. The crust is conductive however, so it behaves as an inert anode causing you to deplete your electrolyte. That changes your cell parameters around such as the conductivity of your electrolyte which can in turn change voltage and amps depending on your power supply. The depletion of copper in this case could also allow other elements to plate out that normally would not, the character of your deposit (smooth, rough, nodules, or needles) will change as well.

I would suggest you start with a pure copper anode in the beginning in order to figure out your cell design. After everything works to your satisfaction, then start trying to incorporate copper anodes with low grade values until you find the practical limit. This way you know your cell is fine, but it is the anodes you are running when you have troubles.

 

[rusty]

Good advice Gentleman, you may recall that earlier on in the forum I did a melt from some milled IC's that I cast into rounds, if memory serves me I ended up with a tad under 12 lbs of copper alloyed with various metals which I never did recover successfully due to being a dumb ass by not testing with stannous before you jump on me I made my confession and apologies to Harold_V a very long time ago as he had spent considerable time tutoring me privately and I owed him that much.

All my feedstock is low grade having come from electronic scrap, with proper fluxing during the melt the anode is partially prepared, if the cell proves out I would like to try various anodes were I have added silver contacts, then try some catalytic material, not sure if the copper will pick up rhodium which I'm to understand is now an oxide.

Then my mind rushes forward thinking that some cats are sent to a copper refinery for reclaiming the precious metals within.

At this point in time, it looks like I have an exciting year ahead of me experimenting with the cell, on another front a spin off from refining precious metals I have decided to revisit an old hobby - photography. I have purchased several books on how to use platinum. palladium and gold to make contact prints.

You would be surprised at how close refining and photography are actually related. If you have someone in your neighborhood practicing alternative photography this would be another source of precious metals scraps as most do not have the knowledge to reclaim spent metals from crops and spoiled prints.

Since I will have very little to add to this thread for the moment, will let you gentleman toss some ideas around while I busy myself getting prepared to further my work on this project.

Regards
Rusty

 

[rusty]

I would agree with Nick’s statement as to the purity of the anodes. While I have never built a copper electrowinning cell before, I have done a fair bit with silver cells. I have found that anything over 3% insoluble elements such as Pt or Au in my silver anodes gives me grief.

The insoluble elements form a crust that is adherent and all but stops the dissolution of your main metal. The crust is conductive however, so it behaves as an inert anode causing you to deplete your electrolyte. That changes your cell parameters around such as the conductivity of your electrolyte which can in turn change voltage and amps depending on your power supply. The depletion of copper in this case could also allow other elements to plate out that normally would not, the character of your deposit (smooth, rough, nodules, or needles) will change as well.

I would suggest you start with a pure copper anode in the beginning in order to figure out your cell design. After everything works to your satisfaction, then start trying to incorporate copper anodes with low grade values until you find the practical limit. This way you know your cell is fine, but it is the anodes you are running when you have troubles.

Oz I understand the complexity of the silver cell and how finicky the electrolyte can become with the depletion of silver, the copper nitrate cell is always replenishing copper to the electrolyte as it's being plated out, the silver is harvested from the liquor is reported to be .995 making this material a suitable candidate for the silver cell.

If the cell works as well as I'm hoping, silver contacts would be much better processed from a cell of this design as any palladium and gold will report as slimes, rather than gallons of waste liquids that have to be treated with cementing with aluminum or iron before disposal.

I have many pails with slims on the bottom, which I'm almost positive contain more than copper due to my lack of knowledge for a total recovery. Hoke refers to these wasts as the stock pot, we all have these pails, so I figure why not add the slims to the anode melt.

We have always been advised to incinerate, and we know fluxing can remove a lot of unwanted junk so we have killed two birds with one stone, tin is the only metal I have found that incineration will not effectively remove. After treatment with HCL this should be another good candidate for a chlorate cell to recover the tin which we all value for making up stannous.

All too often gold and silver are found in nature alloyed with copper, from were it is recovered using EMF ( electromotive force ) then moving along to wet chemistry to refine the cell slimes.

Regards
Rusty

 

[rusty]

Casting an anode requires that you have a furnace of some sort along with some accessories. There is tons of information available from the backyard metal casting forum and how to build a foundry furnace with formulas to make DIY refractory for those of you who have that independent streak often referred to as being bone headed and stubborn.

A simple furnace can be constructed using firebrick piled atop one another, you do not even have to cement them together. This was my first furnace used to melt and make my first aluminum casting for a vibratory flat lap used for lapidary work. The furnace was fired using a tiger torch.

I've never attempted to make my own refractory so I am not able to give any pro or cons, the current furnace I have was made using a castible refractory which maybe cost me a couple of hundred bucks to construct with maybe 4 hours of my time. The furnace has served me for over 5 years, now that I plan on heavy fluxing of my melts it's a given that the flux will take a heavy toll on the refractory.

To make the furnace I poured the floor first let this set overnight, then used a plastic garbage pail which I inserted dead center, filled to can with sand and cut in my blower hole in the outer metal shell which I then put in a suitable plastic pipe before pouring the rest of the refractory. During the pour gently tapping on the metal shell to help settle the refractory it;s the same as if you were working with cement doing a foundation.

The lid is made from a metal shell, I drilled holes around the perimeter, then inserted large spikes to hold the refractory in place once dried, welded a couple of grabs onto the top to make lifting easy. Some guys make the furnace so that the top half tilts away or a front load. I use a pneumatic chain hoist to do the lifting, the hoist is on an overhead rail so getting the lid out of the way is a simple task.

The hoist was not purchased specifically for this task, it just one of those gotta have things.

I frown on anyone suggesting the use of crucible made from metal, metals when heated to extreme heats are solvents which will leach into your melt. Use clay or clay graphite combination mix's or silicon carbide crucibles.

Always assure that your metals are free of moisture before adding them into a melt, moist metals have a tendency to cause steam explosions which can splatter hot molten metal on your body. I lay additional metal needed for a melt onto the furnace lid for pre-heating and to get rid of any possible moisture.

My copper melts are poured into an old cast iron frying pan, gives nice rounds that release from the mold with out any difficulties.

Little Johnny not to bright in school the teacher had sent many notes home with the lad for a parent teacher with the father who ignored the requests, the teacher having some spare time on his calender paid the old man a visit.

The old man a Blacksmith asked the teacher to hand him a piece iron fresh from the forge, well you should have seen him hoot and hope when he picked it up, now the old man gives whistle and Johnny comes a running in and says yes paw. The old man asks the kid to hand him the same iron the teacher had dropped, well Little Johnny goes over and spits on the iron, goes over and grabs a set of tongs to hand the old man the hot iron. Old man looks at teacher and says see Johnny ain't so dumb.

If you need further instructions on furnace building or fuels to fire it with go to backyard metal casting.

Regards
Rusty

 

[HAuCl4]

Same process but basically changing the steps a little:

1-Dissolve the alloy in nitric acid. Filter to recover any slimes.
2-Cement any possible palladium, platinum, gold using a super simple specially built iterative filter with silver or sterling silver as filtering medium(see below).
3-Cement the silver using a similar iterative filter with copper as filtering medium.
4-Once every noble metal is out of solution (test with stannous), put the liquid in your copper cell to recover the copper and the nitric, which can perhaps run unattended 24-7.

A couple of iterations of the liquid through the filter at a reasonable speed cements the target metals usually.

 

[Irons]

I have some Copper on Glass Epoxy circuit Board material if you're interested. I have single and double-sided in 4, 8, 16 mil core thickness. It makes great Cathodes.

 

[rusty]

I would like to extend my thanks to both Steve and Irons for their generous offers., however the cathodes will not pose a problem. I have a couple of the old copper wash tubs, I think they are called boilers that I can cut up for sheet copper.

The biggest hurdle I've come to is finding a 12' x '12 unglazed tile, the best I could find this afternoon after calling on several tile shops is these 6" x 6" tiles. I thick that they will do for a test cell, to make them leak proof I'll caulk them with butyl rubber that black sticky stuff they use to install windshields in cars and trucks.

Its cell is slowly coming together, but that truck load of building material is going to take priority one over all else.

Regards
Rusty

 

[Oz]

Its cell is slowly coming together, but that truck load of building material is going to take priority one over all else.

I could not help but notice all the insulation in that load. I would imagine where you live there is no such thing as too much insulation.

 

[Toobigfortx]

I was just thinking, Seeing as how the width of the copper is unimportant but the acual square inch size is why not try a piece of .999 copper foil the roles are cheap on ebay. Oh and I have heard that using a steel plate, after u've removed the copper, will collect the silver, But IDK how true that is. I've always been extremely interested in this. If you get it up and running please let us know.

 

[Toobigfortx]

I just read something about a copper refining plant In Chile that uses ammonia to desolve copper instead of sulfuric acid. I dont know if this helps you at all but supposedly it was WAY more cost effective than the sulfuric acid method

 

[samuel-a]

It will be interesting to hear (and see) your results.
Tough, a few points of concern comes to mind with your cell plans.

The anode compartment will need free nitric at all times to be able absorb silver with the copper... i can't imagine a silver metal (or Pd) giving up it's electron in a saturated copper solution....
given there is a free nitric in the electrolyte, i can't see why Pd won't be dissolved as well.
Then there's the loss of nitric during cementation process (NOx evolution).

What will be the end result of the depleted electrolyte at the cathode side? rejuvenated nitric?

i think you should also count in the voltage/current drop duo to the membrane.

And a Q for the pro's, does a membrane can hold enough negative potential (even though it's neutral) to actually reduce metal on it's surface ??


humm.. that's it, I'm done bugging you :mrgreen:

 

[peter i]

As far as I know, the commercial refiners of copper do not use membranes.

The alternate the plates in large tanks using several hundred amps per square meter, lifting out the cathodes on regular intervals to scrape of the purified copper. (the electrolyte is copper sulphate kept acidic with sulphuric acid)
The slime is collected from the bottom of the tank.

Somewhere I have a very nice description of the process used at Boliden.