Electrochemistry cell membrane

[Geo]

I am thinking about building a copper sulfate cell from some half inch plexi-glass I have handy. I am working on the membrane between the two sides. I am leaning toward making a membrane out of raw plaster of Paris by pouring a half inch, square "sheet" and sealing it in the middle with silicone caulking. will the plaster slab hold up to the copper sulfate? The slab will be roughly 1.5' x 1.5' x .5". Too, will it be porous enough? I would like to place the anodes in without a bag. This may be a production model if I can get it to work. I tried unglazed clay pots but the electrolyte outside the pot would be depleted and the amps would drop to nothing. I'm afraid unglazed tiles would do the same thing. I have a couple of tons of material that needs to be smelted and run through a cell. It's my material so if I can make it work with my stuff and get the bugs out, I may be able to actually make a dollar off of this stuff.

 

[Barren Realms 007]

If I remember right the plaster of paris will break back down if submerged in fluid. Mix up a batch and do a test and find out before you go this route.

 

[nickvc]

Geoff not sure if this will help as I'm not sure if your looking for a membrane that will only allow the copper to pass through or a way of keeping any undissolved material away from the cathodes but when I ran my silver cell I used a form of filter cloth and simply placed the bars on it held in the solution in a large plastic colander, it caught all the values and just needed rinsing to remove them, if you could put this cloth into a frame it might do the job, sorry o can't remember the name but I'm sure it's still available.

 

[upcyclist]

Nick's plan sounds good. I'm sure it was more than cheesecloth, but I'll bet a few layers of cheesecloth might do the trick--just like you can use multiple coffee filters in place of a finer-mesh lab filter.

Another thought might be to use two wire baskets and put the cloth between them. The outer basket is simply a filter frame and doesn't need to be conductive; in fact, it could be wire or plastic. And I'm assuming you use wire baskets in a copper sulfate cell--I've really only retained details on the silver cells, since that'll be the first cell I build.

 

[Lou]

Geo, we are planning a copper cell thread. I'm silly busy lately but we want to do one.

Maybe we can make a dedicated cell thread

 

[Geo]

Geo, we are planning a copper cell thread. I'm silly busy lately but we want to do one.

Maybe we can make a dedicated cell thread

That would be exceptionally helpful. Thank you.

 

[goldsilverpro]

I think the Thum silver cell originally used "duck" canvas underneath the muslin. Either or both the duck and muslin were 100 threads/inch, if I recall. After a run, only the muslin was removed, along with the slimes, and fresh muslin was put on the duck. If the holes in either fabric were too small, the Ag in solution could soon be depleted.

I really don't think that plaster of paris is porous enough.

 

[Shark]

Geo, we are planning a copper cell thread. I'm silly busy lately but we want to do one.

Maybe we can make a dedicated cell thread

That would be exceptionally helpful. Thank you.

Looking forward to that one!

 

[Lou]

I really want to get to it as it would be, to use the hackneyed expression, a "paradigm shift" for forum members.

Everyone seems to have a lot of patience for AP on small quantities of pins. In my opinion, copper cell is the ONLY way to do large quantities of pins.

 

[g_axelsson]

I really want to get to it as it would be, to use the hackneyed expression, a "paradigm shift" for forum members.

Everyone seems to have a lot of patience for AP on small quantities of pins. In my opinion, copper cell is the ONLY way to do large quantities of pins.

That was what I realized back in the eighties when I started to collect gold plated scrap. I have a number of buckets full of pins that waits for the copper cell thread.

Göran

 

[goldsilverpro]

For what it's worth, here's my opinion on the best and worst ways to do large quantities of copper base pins, from a profit standpoint. I've done them all except the slow HCl/H2O2.

(1) By far, without a doubt, the very best way is to strip pins with cyanide/oxidizer in a tumbler (cement mixer works great). Fast, you get it all, and you end up with salable copper.
(2) Second best is to tumble the pins in anodic conc. sulfuric - the ol' sulfuric stripper. Fast and you get it all and you have salable copper. Little more work than cyanide. You MUST have a tumbler, preferably a commercial barrel plater. Those copper mesh baskets are worthless, except for teeny little hobbyist amounts.
(3) Third best would be a copper cell, assuming you can handle the impurities in the copper and get an adherent, solid cathode deposit. More work. Not that fast. Low labor and cost once you get it fired up.
(4) If you have cheap nitric, good fume control, and a good way of handling the waste, I might just dissolve the base metals in 50/50 nitric. Very fast but you lose the copper. Tin is a problem. With certain high grade pins, this might be #1.
(5) The absolute worst method is acid peroxide. Very slow. No copper recovered. Lots of waste. Only for the hobbyists. A pro refiner wouldn't give it the time of day. However, if you could set up a system that was continually re-usable (a must) and if you could recover and find a market for the copper, whatever form it might be in, I might change my mind. I've used slow processes before and the secret is to first fill the pipeline and then have enough material to keep it filled.

Others
(1) KI/I2 stripper has always been interesting. It's expensive but re-usable. I'm talking the real McCoy and not that weak crappy mix you buy in a drug store. KBr/Br2 is similar.
(2) Tumble in anodic 5 oz/gal NaCN + 20 oz/gal NaOH (my invention - the high NaOH prevents attack on the copper - also works for silver plate). Strip and plate out the gold onto stainless sheet, simultaneously. Solution is reusable.
(3) Then there's all these new super-duper strippers, usually from China, that have lately plagued the forum. Jury's still out on these but most have hidden problems, it seems.

 

[Geo]

If it were just pins, I wouldn't be in this dilemma. My material is all electronics from military test fixtures and standards. Almost all of the visible gold has been cherry picked but there's a lot of gold left and quite a bit of PGM's. Most of the pins and legs were chiseled or broken off the boards. The soldered ends are still in the boards. That doesn't include all of the chips and components. Even the boards themselves have gold plated traces under the solder mask. Many have silver solder over gold. Still can't figure that one out. Like I said, test fixtures and standards. And not just military as most it came from auction at Redstone Arsenals Marshal space flight Center. It has to be incinerates and milled. I have a system set up to capture the solids that are light enough to float. After that, smelting is about the only course of action that's going to be open to me. I can get Zep brand copper sulfate crystals for about $11 per kg at Lowe's. I have two 12"x12"x1" graphite plates I bought a couple of years back.

 

[Lou]

Chris,

If there's no nickel diffusion barrier between the gold and the copper, cyanide won't get all of the gold.

Otherwise, yeah, strip them with cyanide, plate out the gold or load onto carbon or resin and burn it.

Iodine works quite well too.


For cost--COPPER CELL.

 

[goldsilverpro]

Chris,

If there's no nickel diffusion barrier between the gold and the copper, cyanide won't get all of the gold.

Otherwise, yeah, strip them with cyanide, plate out the gold or load onto carbon or resin and burn it.

Iodine works quite well too.


For cost--COPPER CELL.

Lou,

While developing my process, I ran quite a few fire assay samples for gold remaining on the copper after cyanide stripping and all showed no gold (occasionally a trace). I was using hot hi-cyanide and hi-H2O2 in a mixer. If done right, the copper comes out a nice uniform pink with no evidence of black (cement gold). Since I was tumbling the pins together, a thin layer of nickel could wear off quickly. This exposed the copper, but still no gold present. In the last 40 years, I would think that all gold plated copper pins used in electronics have had a nickel barrier layer. 50 years ago, when I started, we would occasionally run into 1930-1960 parts with no nickel, bit I haven't seen it since.

Any gold that cements back on the copper is quite visible. A refiner friend used to pay other refiners #1 copper price for cyanide stripped copper that was black and made good money.

Taking everything into consideration, I must disagree with you. I feel that cyanide stripping is much cheaper than a copper cell.

 

[g_axelsson]

There is an interesting cell with electrowinning Cu from a CuCl / CuCl₂ media. It demands a certain finesse as the voltage has to be low enough to reduce 2 Cu⁺ -> Cu²⁺ + Cu while not produce Cl₂. The Cu²⁺ can be reused to etch copper from scrap.
This process is basically moving copper from one place to another via dissolving -> pumping -> electrowinning. Any solids are filtered off along the way.
It is tested and is used by some printed circuit manufacturers, removing a large part of their waste management requirements while keeping down the need for buying an etchant. In theory a self contained system.

To use this in refining would create a couple of problems, fouling of the electrolyte by zinc, lead, tin, iron... and so on. But it is a process that I would like to test some day.

Göran

 

[Topher_osAUrus]

Cyanide could be cheaper, but it would require all of the proper equipment and space for a home refiner that's using acids as well.

The copper cell could be a less expensive "startup" especially if you already have the powersource, and other pieces from other processes.

How much cheaper, and how long before electricty cost surpasses the cost from getting new equipment and safe keepings for the cyanide, etc...

I don't know. I think they could both be great.
I am anxiously awaiting this new thread..

 

[Lou]

Cyanide is dirt cheap and quick but it's $550/55 gallon to dispose of even when it's killed (to cyanate after hitting it with chlorine) as it's a listed waste.

Lot of liquids with stripping versus plating.

 

[nickvc]

If you use zinc to recover the gold from cyanide you have a waste solution that needs treating and disposing of but if you use the carbon tower you recover all the metals and have a reusable solution, it might need a little more cyanide bit it is still a solution that will strip values.

 

[anachronism]

If you use zinc to recover the gold from cyanide you have a waste solution that needs treating and disposing of but if you use the carbon tower you recover all the metals and have a reusable solution, it might need a little more cyanide bit it is still a solution that will strip values.

Prime your tower with a very weak cyanide solution before passing the liquor through and you won't lose any cyanide from the leach.