Electrochemistry Gold stripping cell ideas

[MvK]

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 am giving up on the first batch of acid i have used, i was saving it to boil down but if even u dont dare to.. Im not gonna mess with that.

Im going to be more careful to avoid moisture, wich is hard in my humid environment.

I did collect the acid from the drip station and added it to the batch of older acid. The old acid that contains more water foamed faster, making bigger bubbles compared to fresher acid. It still worked though, but im running iron parts now. I dont know how it reacts with copper parts.

I might make a drip area in the cell itself to prevent the drip cell from collecting moisture. And cover the parts of the cell that i dont use during operation.

Im just trying to make this run as clean as possible with minimal waste of acid, the main reason im into the cell is lower waste output.

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.

I have a cell standby with about estimated 2/3 grams of gold in it. I think the easy way to test this is to lower the same plated items in the sludge and see how far the amps will drop?

The items i ran in the basket dropped amps until about 0.1 or less, i cant get the items in the clamps below 0.6 amps. I will see if they go lower if i raise the clamps.

Anyways i think the idea of a spacer is nice, if i use the honeycomb it will trap the sludge better because theres less agitation inside..

Will report back this weekend

 

[Martijn]

I am giving up on the first batch of acid i have used, i was saving it to boil down but if even u dont dare to.. Im not gonna mess with that.

It can be done but you need good equipment and safety precautions.
I just started an experiment to clean the used acid with a platinized titanium anode and a copper cathode.
If that works, i will add dehydrated copper sulfate to add (Cu)SO4 salt without water and by electrowinning the copper out, raising the sulfuric concentration.
I make the copper sulfate with the cell's rinsing water and oxidized copper powder. And evaporating that down to collect and purify the blue copper sulfate pentahydrate, then heat it to drive off the water.
If this works, I'll make an instruction video of it. The key is keeping moist out while electrowinning.

I have a cell standby with about estimated 2/3 grams of gold in it. I think the easy way to test this is to lower the same plated items in the sludge and see how far the amps will drop?

Yes, but:

The items i ran in the basket dropped amps until about 0.1 or less, i cant get the items in the clamps below 0.6 amps. I will see if they go lower if i raise the clamps.

Keep the clamps out unless they are clean pure copper. Turn the items to get the part that was not stripped. Plastic tweezers are very useful for this. Then the current drops to milliamps, if it still is concentrated enough.

Edited to make sense.

 

[MvK]

I just started an experiment to clean the used acid with a platinized titanium anode and a copper cathode.
If that works, i will add dehydrated copper sulfate to add (Cu)SO4 salt without water and by electrowinning the copper out, raising the sulfuric concentration.

That is awsome, i think i understand what you mean except the platinized titanium anode part haha. I know you are lightyears ahead of me and i really appreciate your help. But this is way too advanced for me.

If there was an easy way to boil down the acid to get rid of the moisture i would, but im not taking the risk for a 7 euro/litre acid.

However im not sure yet how to treat this waste, im keeping it seperatly from the refining waste for now. Will look into that first.

The gold plated plates in the clamps deplate completely without turning but you are right, they are ferrous so there might be the issue.

This weekend im going to have some fun working on the modifications, i will find some full copper clamps and try to put in more to see what happens

 

[Martijn]

That is awsome, i think i understand what you mean except the platinized titanium anode part haha. I know you are lightyears ahead of me and i really appreciate your help. But this is way too advanced for me.

If there was an easy way to boil down the acid to get rid of the moisture i would, but im not taking the risk for a 7 euro/litre acid.

However im not sure yet how to treat this waste, im keeping it seperatly from the refining waste for now. Will look into that first.

The gold plated plates in the clamps deplate completely without turning but you are right, they are ferrous so there might be the issue.

This weekend im going to have some fun working on the modifications, i will find some full copper clamps and try to put in more to see what happens

Well if you can buy it, don't bother at all.
I can't, but my customer can luckily.
I just like to experiment to save what i can.

We'll get you up to speed.
Watch this video from nerdrage.

It explains the copper winning part from copper sulfate solution.
You need an inert anode that does not dissolve to electrowin(electrolytically reduce) the dissolved metal salts in solution on the cathode.
If i can't clean the concentrated acid this way, i will try to convert only purified copper sulfate to metal and acid, we'll see.
I use a small glass candle cup with a plastic lid to experiment and save on acid.

 

[BGDOCK]

Could the moisture be pulled out by using a vacuum pump . Earlmyer / vacuum flask with rubber gasket glass stopper attached to vaccum pump . Would that boil the water off ?

 

[Martijn]

Could the moisture be pulled out by using a vacuum pump . Earlmyer / vacuum flask with rubber gasket glass stopper attached to vaccum pump . Would that boil the water off ?

I Like your thoughts here. yes. Lowering the pressure of a liquid also lowers the boiling temperature. By lowering the ambient pressure close to the liquids vapor pressure. How far you will have to pull it down to get it "boiling" or evaporating enough to concentrate at an acceptable temperature, is 1.3mBar above absolute zero vacuum, if my calculations is true.
You will have to get a vessel that can withstand both the vacuum and the acid.

From Wiki: Sulfuric acid is a colorless oily liquid, and has a vapor pressure of <0.001 mmHg at 25 °C and 1 mmHg at 145.8 °C, and 98% sulfuric acid has a vapor pressure of <1 mmHg at 40 °C.

So to get from mmHg to Bar: divide the number by 750.062, so 1mmHg is 1/750.062= 1.3 mBar Absolute pressure, so almost vacuum.

 

[MvK]

So ive been at it a little bit. Didnt run the cell yet but i made a liner of lead sheet like @Martijn suggested.
I did make it go all around and the idea is to suspend the clamps/basket in the middle.

Ive also put a plastic grid in the cell acting like a spacer but maybe also a sludge trap.
IF it was shorting out or creating more restistance from the sludge it wont be anymore of a problem. Maybe i will make a double layer to raise it a little bit more.

If this is working i might scale up or make another one to deal with the cooling issues.

Im also rethinking the drip station, this creates more surface area for the sulfuric to gather moisture. I can keep it but i wont add the acid back to the cell.

So what u guys think?

 

[BGDOCK]

Love the egg crate spacer and the lead liner ( good idea M)

 

[Martijn]

Love the egg crate spacer and the lead liner ( good idea M)

Worth a try. Test the plastic on some sulfuric before running with it in the cell. You don't want deteriorating plastic goo with gold dust trapped in it.

 

[MvK]

Worth a try. Test the plastic on some sulfuric before running with it in the cell. You don't want deteriorating plastic goo with gold dust trapped in it.

I think the material is polystyrene so it should hold up in acid. I put a piece in a test tube, we will see tomorrow.

 

[MvK]

Well i did not think about the density of sulfuric acid. The plastics sink in water but float in the acid!

 

[richoc]

This is when I first started and was running pounds of junk plated scrap, figure it at gold alloy 0.006 percent by weight when I was figuring a value for it. Was getting it near free, in 50lb lots. The shipping was more than the price of the scrap. Was the left overs from punching flat shapes from rolls of gold flash plated metal base metals were mixed.

I had used the same one small cell I had built, and I ran it over and over, the alloy sludge became a direct short across the bottom of the cell. The sludge was settled near 1 inch thick and over days of sitting between uses.

Put back in to use I had sparks down in the acid, stripping was not going well, and it was heating up fast.
Having sparks in the basket, with sections of the basket becoming heating elements red hot until the mesh melted off and fell into the sludge alloy.

Stopped running and cleaned the sludge from the stripping cell and reset it up with the lead cut back so it only was down half the side of the cell and made a new basket set up that was held up by spacers well off the bottom of the cell. this gave more room for the sludge to settle, and this never happened to the system again.

 

[BGDOCK]

What were the spacers made of ?

 

[MvK]

I ran the cell yesterday for 3.5 hours until it really started to act up. There was new acid mixed with slightly used decanted acid without sludge. Temps went up to 35c. Amps stopped dropping at around 1 amp when it was hot.
It usually stops at 0.6 amps but i didnt change the clamps to full copper yet, they are on the way from China .

The lead liner seems to work fine, cant really tell too much difference but the foaming from the cathode is less intense, more spread out because of the extra surface. Perhaps this delays the heating.

Im going to see if i can find a stainless spacer grid of some kind to replace my floating plastic artwork.

 

[Martijn]

What were the spacers made of ?

:

I think the material is polystyrene so it should hold up in acid. I put a piece in a test tube, we will see tomorrow.

I ran the cell yesterday for 3.5 hours until it really started to act up. There was new acid mixed with slightly used decanted acid without sludge. Temps went up to 35c. Amps stopped dropping at around 1 amp when it was hot.
It usually stops at 0.6 amps but i didnt change the clamps to full copper yet, they are on the way from China .

The lead liner seems to work fine, cant really tell too much difference but the foaming from the cathode is less intense, more spread out because of the extra surface. Perhaps this delays the heating.

Im going to see if i can find a stainless spacer grid of some kind to replace my floating plastic artwork.

You are tweaking the cell and the variables to your personal need and figuring out what works. this is a crucial step in learning.
i do not say i have all the wisdom in this field but I do have some experience. Good to hear the lead sheet works.

About stainless steel in the cell: I've noticed that when it gets hotter and/or more polluted with copper or other base metals, it will start eating away stainless steel like watchbands and the current does not drop that much anymore, leaving you thinking there is a lot of gold being stripped. This is when the acid turns green and a lot of foam is generated at startup.
This foam decreases in time while running, so i suspect the moist is somewhat expelled by forming of hydrogen at the cathode by the electrolysis itself, not sure. I do get the feeling a cup of acid not in use attracts water a lot faster that one in operation.
I do know that (maybe only some types of or most of them?) Stainless steel will be eaten by this process and will pollute and end your useful electrolyte.
There are lots of different alloys in stainless steel. Which one it is, is actually only clear is industrial applications where spec's are given or required. You won't find it on a salad bowl e.g.

 

[Yggdrasil]

I think the material is polystyrene so it should hold up in acid. I put a piece in a test tube, we will see tomorrow.

I do not think Polystyrene will hold up well against acids, are you sure you do not mean Polypropylene?

 

[MvK]

I do not think Polystyrene will hold up well against acids, are you sure you do not mean Polypropylene?

Well actually it does hold up, it is relativily chemicaly inert as some sources say. So it is not dissolving right away but im not sure how it will do in the long run ofcourse. It is not the foamed type like styrofoam or like coffeecup but a solid 1mm thick type.

It is however very weak to solvents etc.

 

[MvK]

So, my copper clamps came in this week! They were a bit smaller then the old ones that ive used, so i could not get 2 wires in to bridge the clamps.

I had some stuff laying around, some connectors, copper wire and a brass earth bonding strip. Soldered it all together so i can connect as many clamps as i want to the brass strip.

I didnt know how to suspend the new clamp system so i just took a big block of wood, and attached the clamp strip to a wooden arm that i can move up and down. It is hanging from 2 copper wires that ive used as nails, so i can easily take the connector off to replace the material im processing.
This part is going to get some attention. It works for now but it looks like crap. Will look into another suspender/lever thing.

So, i did a few runs. It worked really well but not much different then the previous model. It does not deplate faster but it gives me me more time in beween runs. It did look like it got less hot but i dont have numbers yet to support this.

I left the lead negative in the bowl with the acid for a week by accident. This caused the lead to form a white layer. I saw some of the stuff (PbCl²(?)) fall down, dropping on the layer of accumulated sludge. This indicates that the sludge does not mix while in operation but stays at the bottom. I could see about half an inch of sludge.

Im still looking for a replacement for my plastic spacer, any ideas are welcome.

MvK

 

[Martijn]

Im still looking for a replacement for my plastic spacer, any ideas

What was it's purpose? To hold up a copper basket?
Try hang it on the edge of the glass and leave the spacer out.

I think you still hang your clamps too deep in the acid. The springs are steel and will dissolve in time and pollute the acid.

 

[MvK]

What was it's purpose? To hold up a copper basket?

To prevent larger material poking in the sludge and stirring it up. Longer cell time, cleaner cell maybe.

I will only use a basket when i got really small stuff like pins or earrings, i like the clamps better, i wont have to poke around in a basket.

I raised the clamps a little bit but this is what it takes to fully submerge the items to be deplated. They are just small.