Electrochemistry Gold stripping cell ideas

[richoc]

The hardest part imo is making good contact and stripping items completely.

There are adjustments to be made for each type of part that you are trying to run.
Changes to the cell size or depth can be done as needed to fit the parts you are stripping.
Larger or smaller mesh for baskets or shelfs, clamps, and wire jigs can all be fashioned to contact the parts for easiest running.

Best not to overload the surface of a basket, you are not just filling it up to all it holds, this way good contact is made, but if needed you can stir them a bit to make better second contact to allow a complete removal of the alloy in one pass through the cell.

I used to pop all the caps from the watch bands "gold filled or plated" clean them and run as a batch in a basket.
This was a bunch of extra work and caused incomplete removal of the gold in the basket, stirring and keeping the caps in the cell for too long caused extra heat buildup.

I have found it is better to lay out the bands whole with the caps down on the mesh in more of a contact shelf than a basket, way less work and they strip better this way. The one downside is the amount of acid that stays in the bands to be recovered in the drip station.

 

[MvK]

There are adjustments to be made for each type of part that you are trying to run.
Changes to the cell size or depth can be done as needed to fit the parts you are stripping.
Larger or smaller mesh for baskets or shelfs, clamps, and wire jigs can all be fashioned to contact the parts for easiest running.

Best not to overload the surface of a basket, you are not just filling it up to all it holds, this way good contact is made, but if needed you can stir them a bit to make better second contact to allow a complete removal of the alloy in one pass through the cell.

I used to pop all the caps from the watch bands "gold filled or plated" clean them and run as a batch in a basket.
This was a bunch of extra work and caused incomplete removal of the gold in the basket, stirring and keeping the caps in the cell for too long caused extra heat buildup.

I have found it is better to lay out the bands whole with the caps down on the mesh in more of a contact shelf than a basket, way less work and they strip better this way. The one downside is the amount of acid that stays in the bands to be recovered in the drip station.

So, i will take two pyrex dishes, and make two baskets. One of the dishes will be sunk in a sealed cooling container, the other one next to it for drippy purposes. Nothing too fancy, no mechanical agitation.

I can run one batch, make it drip in the drippy dish. Load up the next basket and and run next batch so the first loaded basket can have drippy time. After drip time move it in the rinsing station.

I did pour a PB bar, but i think i made it too big. Does size matter, in anode/cathode?

 

[stella polaris]

Hi guys,

I got my hands on some material that i would like to de-plate using the sulfuric acid cell method.

I already got my bowl, power supply, copper mesh etc. I did some research, watched some videos but alot if them are messy and with alot exposed sulfuric acid.

I want to make a semi closed cell with a cooling system and a vibrating basket.

Im hoping to use only one cell, without having multiple open bowls or cooldown time. I would like to cool down by running glass pipes trough the cell.

I could suspend the basket in the fume hood, with a vibrator motor somewhere attached with an interval to shake the basket, not having to stir it.

What do you guys think, any tips or ideas i can steal from excisting machines?

Thx,
Mia van Kesselen

1. Remove the risks with the process.
Glasspipes (with water i suppose) can break and create a very unpleasant situation. Cool water, in hot sulfuric acid, is dangerous. Take your time and let it cool down between the batches. Old heatspreaders outside the vessel can help cooling down the acid without major hazards.

 

[Yggdrasil]

I don't remember who, but there was a member who fabricated a system out of mild steel with cooling pipes.
Of course the size and capacity of that, do not fit the average hobby refiner.
It should be somewhat scalable though.

 

[Martijn]

I have never tried one yet but an ultra-sonic jewelry cleaner with a lite solution should do the job.

I does a great job. All that nasty human grease gone.
Just make sure to rinse all soap off before drying amd processing.
You can also use it to get gold powder from in between watchbands. Leaves a great clean scrap metal to sell.

 

[Shark]

Phildreamer is the one that built that advanced cell. A very nice, long term setup.

 

[Yggdrasil]

Phildreamer is the one that built that advanced cell. A very nice, long term setup.

Thanks Shark, I remember now

 

[richoc]

So, i will take two pyrex dishes, and make two baskets. One of the dishes will be sunk in a sealed cooling container, the other one next to it for drippy purposes. Nothing too fancy, no mechanical agitation.

I can run one batch, make it drip in the drippy dish. Load up the next basket and and run next batch so the first loaded basket can have drippy time. After drip time move it in the rinsing station.

I did pour a PB bar, but i think i made it too big. Does size matter, in anode/cathode?

The parts will set the need for entire basket removal or just the parts removed from the cell.

I did the rings you see in my avatar photo a basket full at a time, cell turned off removal of the finished rings with a set of plastic tongs to drip off, place new rings into the basket with the tongs, turn on the cell to strip, repeat until the box was finished.

I really like to use a lead sheet and form it to the cell, to start with, I would make it the full size of the cell side furthest from the basket.

Start simple and run like that, improvements will show themselves as you become more familiar with running a cell.

 

[MvK]

So, i did do some experimenting on a small 1 litre cell. With drippy drip system

I casted a lead bar with copper hooks to suspend it and to attach the lab power supply. Made a basket from copper mesh with a bent copper rod for extra support.

I was running between 5 and 15 volts max 4 amps to see what was happening. Actually i got it fairly under control, i can run plated jewelry for long enough before overheating.
I will just run it in the evenings on the side, max 2 hours and it will be good.

One thing ive noticed, when i started the cell with fresh acid it was working like a charm. After 1 or maybe 2 kilos of scrap it struggled really hard to get in contact with anything in the basket. Sometimes it drew amps like a madman for certain items when it finally found contact. In the end i was just poking the materials with a copper rod connected to the power supply to see something happen. I got most of the sludge out and tried again with the same acid, still struggled to get it going.

Now it could be that the cell is loaaaded with gold, but seeing other peoples yields i dont think this is the case. Especially since ive already took out the sediment once. But maybe my anode cathode dimensions are off.

OR maybe this is just the downside of a small cell and it already is contaminated. Honestly the jewelry was dirty before chucking it in the cell, as my estimated yield was close to nothing i didnt want to clean it properly. Im working on improvements and getting comfortable with this cell.

Im still going to make a cooled, bigger version of this to get rid of my stack of heavy plated iron parts. But u guys were right, this experience was needed and actually fun.

Pics from the current setup. 2x 1.8 litre pyrex dishes in a larger pyrex dish to catch the spills. Left side is drip station, rinse container is far away from the fumehood.

 

[eaglekeeper]

One thing ive noticed, when i started the cell with fresh acid it was working like a charm. After 1 or maybe 2 kilos of scrap it struggled really hard to get in contact with anything in the basket.

I have that same problem with pins. I usually spray the black powder off the basket into a separate beaker, then heat the basket until it's dry and load it back up with pins. I'm sure there's a better way, but that seems to work for me until it loads up again.

At some point I plan on making a rotating drum instead of using a basket....but It's on the list of many projects I haven't finished yet.

 

[Shark]

....but It's on the list of many projects I haven't finished yet.

Sounds like my list, it just keeps growing faster than I can get to them.

 

[MvK]

So, i have run most of my crap jewelry. Got a couple of grams from it but the sulfuric started to act up, i think it was polluted with other metals then gold from the cheap stuff.

I started a new batch of heavy gold plated iron parts. I know they have good plating, in the past i would of tossed them in the acid to be able to peel off the foils. I ditched the basket and made a contraption with crocodile clamps to hold the parts. Worked like a charm in fresh acid.

The used acid will be decanted after sitting for a few days in a closed vessel to keep the 'mud' out of the acid, because theres a conductivity issue when the acid is contaminated. I did not use a closed vessel at first, it atracked water and now i have purple acid full of water, wich is foaming like crazy when its re used. Might try to heat it and get rid of the water to use the acid again.

I am switching between cells to keep it from overheating, the only problem right now is that it is taking ages to get the gold off! Im running 5 plated things at a time, and it takes like 20 minutes to finish the job. 12v 4 amps on a china style lab power supply. From my previous calculations it should take around 1 gram of gold per hour.

Is there any way to speed it up? Or Does anyone have 'safe' maximum settings for the power supply? I tried to crank up the volts but i will get smoke from the cell and im scared. I dont like hot sulfuric all over the place and myself.

The picture below is a bit messy, i took some acid out to start the other cell but you get the point.

 

[Martijn]

The H2SO4 cell can be quite difficult to run. optimal settings are dependent on your situation. in my setup I experience extra foaming from 9 volts and more bad things from 12 volts up. like small smoke plumes. I like to limit it at 7 Volts and a current setting of 2,5 Amps for a 1 liter cell with a approx. 8*8cm lead cathode.
You can cool it to put more power through it, but it will start to foam and bubble like crazy if current is too high or if any moist or as you said pollutants are in there, once the water or base metal content is high enough to dissolve stainless and iron and copper, it goes bad fast. foaming and slow stripping.
one gram of gold can take days in stead of hours when base metals are also attacked.

Might try to heat it and get rid of the water to use the acid again

H2SO4 does not like to release it's moist, you'll need to get it up or over 300 C to get concentrated enough, which is crazy hot and ridiculously dangerous!!!!

Is there any way to speed it up? Or Does anyone have 'safe' maximum settings for the power supply? I tried to crank up the volts but i will get smoke from the cell and im scared. I dont like hot sulfuric all over the place and myself.

Bigger cell. More cathode surface to divide those electrons over, I think when you are seeing smoke coming from sulfuric, you are entering a danger zone.
Better safe than horribly scarred and disabled for life by warm or hot H2SO4.

This cell is messy. The black stuff goes everywhere. you need good lab hygiene and try to limit wash water.

side note: This cell is also a good test to see if you're ready for very dangerous things like PGM salts. If you cant keep the black goo inside the beakers it's meant to stay in, don't even think about going PGM.

Have Fun! stay safe.

 

[MvK]

The H2SO4 cell can be quite difficult to run. optimal settings are dependent on your situation. in my setup I experience extra foaming from 9 volts and more bad things from 12 volts up. like small smoke plumes. I like to limit it at 7 Volts and a current setting of 2,5 Amps for a 1 liter cell with a approx. 8*8cm lead cathode.
You can cool it to put more power through it, but it will start to foam and bubble like crazy if current is too high or if any moist or as you said pollutants are in there, once the water or base metal content is high enough to dissolve stainless and iron and copper, it goes bad fast. foaming and slow stripping.
one gram of gold can take days in stead of hours when base metals are also attacked.

H2SO4 does not like to release it's moist, you'll need to get it up or over 300 C to get concentrated enough, which is crazy hot and ridiculously dangerous!!!!

Bigger cell. More cathode surface to divide those electrons over, I think when you are seeing smoke coming from sulfuric, you are entering a danger zone.
Better safe than horribly scarred and disabled for life by warm or hot H2SO4.

This cell is messy. The black stuff goes everywhere. you need good lab hygiene and try to limit wash water.

side note: This cell is also a good test to see if you're ready for very dangerous things like PGM salts. If you cant keep the black goo inside the beakers it's meant to stay in, don't even think about going PGM.

Have Fun! stay safe.

Thanks! I must say i am keeping everything nice and clean during operation. Every spilled drop gets wiped up and i keep it in a storage container. The pyrex dish gets a frequent wash.
I have the drip basket in a bowl in the fumehood next to the cell, when i go to rinse the stuff i move the drip bowl out of the fumehood to keep water far away. Rinse station is on the workbench.

I will try to get more surface area on the cathode with this cell, im going to cast another one and see if it will help. Mine is about going along the side of the bowl, but i will make it go around like @richoc suggested. I was also thinking to just work on 2 cells at the same time, i have a very large fumehood so there is space to do so.

 

[Martijn]

Thanks! I must say i am keeping everything nice and clean during operation. Every spilled drop gets wiped up and i keep it in a storage container. The pyrex dish gets a frequent wash.
I have the drip basket in a bowl in the fumehood next to the cell, when i go to rinse the stuff i move the drip bowl out of the fumehood to keep water far away. Rinse station is on the workbench.

I will try to get more surface area on the cathode with this cell, im going to cast another one and see if it will help. Mine is about going along the side of the bowl, but i will make it go around like @richoc suggested. I was also thinking to just work on 2 cells at the same time, i have a very large fumehood so there is space to do so.

No need to cast it and breath lead fumes.
I just cut a big plat piece out of roofing lead. bend a smaller lip over the edge and solder the wire to it or screw or clamp it.
The advantage of this is that you can bend the cathode when cleaning to get the brown and black hardened goo off.
They last forever, as lead should in sulfuric.
Casted thick lead is not needed, as i have experienced.
I have about 100 grams of gained gold and experience with this cell over a couple years as a hobbyist.

 

[Martijn]

The acid in the drip bowl wil collect water from the air faster than in the cell, since there is a lot of surface exposed to the air on all the items, on the strainer itself and in the bowl.
In time this will dilute the acid faster and you should keep the exposed surface to air a short as possible or keep a lid on the drip station.
Try to keep it closed to the air or maybe keep the drips separate to use in a separate cell to test the difference.

i was thinking evolution of hydrogen by electrolysis could expell water from the cell, but at concentrated levels it behaves different.

My intended way to (try) to concentrate used acid is adding anhydrous CuSO4 to the acid and electrowin the copper back out to dehydrate the acid. ( no idea if this will work, still waiting for the inert platinum anode)
Boiling H2SO4 is a no-go for me. very scary stuff. Not good for hobbying.

 

[Yggdrasil]

The acid in the drip bowl wil collect water from the air faster than in the cell, since there is a lot of surface exposed to the air on all the items, on the strainer itself and in the bowl.
In time this will dilute the acid faster and you should keep the exposed surface to air a short as possible or keep a lid on the drip station.
Try to keep it closed to the air or maybe keep the drips separate to use in a separate cell to test the difference.

i was thinking evolution of hydrogen by electrolysis could expell water from the cell, but at concentrated levels it behaves different.

My intended way to (try) to concentrate used acid is adding anhydrous CuSO4 to the acid and electrowin the copper back out to dehydrate the acid. ( no idea if this will work, still waiting for the inert platinum anode)
Boiling H2SO4 is a no-go for me. very scary stuff. Not good for hobbying.

I'm not sure but a container/strainer with a molecular sieve of the correct species/pore size,
inside the box where the cell is residing might soak up the extra moisture, maybe...

 

[richoc]

So, i have run most of my crap jewelry. Got a couple of grams from it but the sulfuric started to act up, i think it was polluted with other metals then gold from the cheap stuff.

I started a new batch of heavy gold plated iron parts. I know they have good plating, in the past i would of tossed them in the acid to be able to peel off the foils. I ditched the basket and made a contraption with crocodile clamps to hold the parts. Worked like a charm in fresh acid.

The used acid will be decanted after sitting for a few days in a closed vessel to keep the 'mud' out of the acid, because theres a conductivity issue when the acid is contaminated. I did not use a closed vessel at first, it atracked water and now i have purple acid full of water, wich is foaming like crazy when its re used. Might try to heat it and get rid of the water to use the acid again.

I am switching between cells to keep it from overheating, the only problem right now is that it is taking ages to get the gold off! Im running 5 plated things at a time, and it takes like 20 minutes to finish the job. 12v 4 amps on a china style lab power supply. From my previous calculations it should take around 1 gram of gold per hour.

Is there any way to speed it up? Or Does anyone have 'safe' maximum settings for the power supply? I tried to crank up the volts but i will get smoke from the cell and im scared. I dont like hot sulfuric all over the place and myself.

The picture below is a bit messy, i took some acid out to start the other cell but you get the point.

You are shorting out cell.

You have your lead mounded way to low in the cell and your basket area is way too large for the cell area.
The "black sludge" is making a direct circuit in the cell, exactly what you do not want.

From your pictures, you are not running the cell full of sulfuric acid, it needs to be deeper no parts should contact the bottom of the cell, this shorts out the cell. You need more distance between the anode and the cathode for the sludge to fall to the bottom of the cell. The distance from the edge of the basket to the Lead must be greater than it is in your photos.

To reuse what you have, make it so the lead just comes over the top of the cell touching the surface of the sulfuric acid. and not down in more than half the depth of the cell.

Your basket is way too wide, for this cell. Half the width it is now and as far away from the lead as can be.

Your basket can not contact the bottom of the cell. Shorts it out, with no place for the black sludge to fall to where do you expect the sludge to go. I use spacers to keep the basket from the bottom of the cell.

You are overloading your basket. Way too many parts in it at one time. Contact of the parts to the basket surface is what is needed for the striping to work well. Part to part contact is not going to work well if at all.

You need the distance for the black alloy sludge to move away and fall from the parts, remember this sludge is very conductive.

Never add anything to the sulfuric acid to show larger bubbles.
The gas in these bubbles is highly flammable just likes the gases coming from charging an acid battery for your car.
You are basically work inside an open battery cell while operating a sulfuric acid stripping cell.

I have lost eyebrows dis connecting a boat battery under it cover in the rain once because it made a spark from the charger wires.
I have had the bubbles full of gas blow up with a sparking at the sulfuric cell when I first started as I used an added glycerin, to show the bubbling, that indicated the cell was working. Thank full for all the PPE I had on as hot acid went everywhere with the small flash explosion.
Never again used the glycerin, I watch the action in the cell and the meters.

 

[MvK]

You have your lead mounded way to low in the cell and your basket area is way too large for the cell area.
The "black sludge" is making a direct circuit in the cell, exactly what you do not want.

The lead strip is about 2cm high, and usually hanging so that it is just covered with acid. The bowl is 1.8 litres and im using 1 litre of acid. At the time of the last picture a little bit less, some was still going trough a fibre plug filter.

The basket was a bit too large, but i ran about 4 kilos of jewelry in it so it worked out somehow. I did poke it down for some parts to make better contact so i guess i just pressed it down in the sludge. Good to know.

In my last picture i did not use a basket but clamps to hold the plates, material was not touching the bottom but it was close to it. Good idea to put some kind of spacer in, thanks! I have some plastic honeycomb, maybe that can act as a sludge catcher. I will check what its made out of.

I dont really want to use a bigger bowl, this one is great to handle and decant, im not comfortable enough to go big yet. But i will fill it up more, change baskets and distances and change the lead cathode.

 

[Martijn]

You are shorting out cell.

You have your lead mounded way to low in the cell and your basket area is way too large for the cell area.
The "black sludge" is making a direct circuit in the cell, exactly what you do not want.

You need the distance for the black alloy sludge to move away and fall from the parts, remember this sludge is very conductive.

With all respect, I doubt this is the case, in my experience the black slugde is extremely fine and takes some time to fall through the thick acid to the bottom.
The convenction of cathode and anode bubbles agitating the acid will only spread out the gold dust over the cell, keeping it suspended in the acid longer. It all passes the cathode imo.

Then as far as conductivity goes, I have a plastic cup with holes drilled into sides and bottom, sitting on the bottom in a layer of black sludge and the lead cathode touching the black layer, since its 1cm (3/8") from the bottom.

If what you say is t true, why does my current stop when gold is nearly all stripped? There is full sludge contact between the copper anode pins I insert in between the plated items and the cathode.

If this sludge is as conductive as you say, I would never see low to zero amps with both anode pins, plated items and cathode plate sticking in the layer of goo. There is most of the time a rest current of about 30mA or less, indicating a substantial resistance of said slugde. Sometimes even zero amps.

Repositioning the anode pins finds new plated items and current drops as they are stripped. The contact is from gold plated surface through the acid to the cathode. Not through the goo.

I will measure the resistance in Ohms next time i have a layer and make a video of it.

Were not done perfecting this process yet. That much is certain.

Martijn.