sulfuric stripping cell: My basket got eaten What did I do wrong.

[gregory-d]

Hello all.
Well my first attempt at this was a mess to say the least.
Following a youtube video that seemed to be clear.
I made my basket out of copper mesh I got from aliexpress.
I had a stainless steel anode.
Sulphuric acid 98% but I got it from a friend and it was in a 20 litre drum so it's probably way less than 98%
I built a simple fume hood.
Using variable power supply I set the volts at 3V and left the current unset.
scrap in basket and turned on the power.
Seemed to be going well drawing a bit over 3 amps
so I left it and came back to check it fairly regularly.
Came back at one stage and the current had gone down to 0 so I turned it off
Went to remove the basket and it was gone.
I now have a mess.

I have tried a few things and read a few threads here
Now I have a lead cathode and tried just dipping the larger parts in the sulphuric and that seemed to go ok but I still have some light coloured precipitate at the bottom.
The current this time never went much over 1 amp.

I realise now there is a relationship between the current and what gets stripped. But I still don't quite understand what that is.

I have tried setting the volts to 5V and still not touching amps with:
- an empty copper basket in the solution and I get about 2.8amps
- an empty stainless steel basket gives about 1.8 amps as well.
Could someone explain what I am missing here please.

Thanks I know I haven't done anywhere near enough research on this yet but I will keep reading.
There are some amazingly useful posts on this forum I just haven't found the right one yet.

Thanks.
Gregory

 

[adam mizer]

Are you connecting anode to positive? (your copper).
EDIT ADD: I used a small battery charger and never walked away because stripping happened so fast, there was no time to walk away.
What is your material.
I put 1 pound at a time basically of pins and even mixed stuff and use a poker to make sure all material got stripped.
Even did single parts as I made several leads, attached pieces and worked several hours non-stop stripping.
Do not let the sulfuric acid heat too much. Maybe that was your issue.

 

[gregory-d]

Are you connecting anode to positive? (your copper).
EDIT ADD: I used a small battery charger and never walked away because stripping happened so fast, there was no time to walk away.
What is your material.
I put 1 pound at a time basically of pins and even mixed stuff and use a poker to make sure all material got stripped.
Even did single parts as I made several leads, attached pieces and worked several hours non-stop stripping.
Do not let the sulfuric acid heat too much. Maybe that was your issue.

Yep - to lead and + to copper
I checked it several times but I'll check it again.
I was under the impression at the time that the level of purity stripped by the process was relative to the voltage. It appears from my reading so far in this forum that that is not the case. That was why I was running it at 3v. I will try restricting the current and see what I get from my empty baskets. At the moment I am waiting for the sulphuric to cool as I heated it for a couple of hours to try to increase the concentration.

 

[Yggdrasil]

Yep - to lead and + to copper
I checked it several times but I'll check it again.
I was under the impression at the time that the level of purity stripped by the process was relative to the voltage. It appears from my reading so far in this forum that that is not the case. That was why I was running it at 3v. I will try restricting the current and see what I get from my empty baskets. At the moment I am waiting for the sulphuric to cool as I heated it for a couple of hours to try to increase the concentration.

This kind of cell need to be supervised, and do only run in short intervals.
Another thing is that Sulfuric acid will drag water straight from the air.
So if it is old, it might not be 90% anymore.
Take its specific gravity and see if it still is concentrated enough.

 

[gregory-d]

This kind of cell need to be supervised, and do only run in short intervals.
Another thing is that Sulfuric acid will drag water straight from the air.
So if it is old, it might not be 90% anymore.
Take its specific gravity and see if it still is concentrated enough.

Thanks yes Yggdrasil good call I can't just walk away. That was a silly idea.
Also thank you for confirming my thinking in regards to the concentration.
I haven't seen it yet and I will keep looking but I will ask as well anyway. Is keeping the sulphuric acid on a hot plate set around 200C a reasonable way to drive out the water. I tried this today and did another run with a large gold plated piece and the reaction seemed far less aggressive and didn't go any where near the 1 amp limit I set with a still low voltage limit.

 

[Yggdrasil]

Thanks yes Yggdrasil good call I can't just walk away. That was a silly idea.
Also thank you for confirming my thinking in regards to the concentration.
I haven't seen it yet and I will keep looking but I will ask as well anyway. Is keeping the sulphuric acid on a hot plate set around 200C a reasonable way to drive out the water. I tried this today and did another run with a large gold plated piece and the reaction seemed far less aggressive and didn't go any where near the 1 amp limit I set with a still low voltage limit.

You need very high temperatures to drive off the water.
But first weigh it and see what the concentration is.

Edit to add:
Boiling point of concentrated Sulfuric is 337 C and when it passes 300C it will start to gradually decompose.

 

[gregory-d]

You need very high temperatures to drive off the water.
But first weigh it and see what the concentration is.

Edit to add:
Boiling point of concentrated Sulfuric is 337 C and when it passes 300C it will start to gradually decompose.

Oh ok.
I was thinking that as the boiling point of the water is 100C then if the plate is 200 - 250 C that would raise the water in solution to above it's boiling point and allow it to evaporate out. But hey it's 50 years since my last chemistry lesson.
Is there a way to concentrate the sulphuric acid without actually decomposing it?


And yes I wasn't ignoring your previous suggestion I will weight it as soon as I get a battery for my scales.

 

[Yggdrasil]

Oh ok.
I was thinking that as the boiling point of the water is 100C then if the plate is 200 - 250 C that would raise the water in solution to above it's boiling point and allow it to evaporate out. But hey it's 50 years since my last chemistry lesson.
Is there a way to concentrate the sulphuric acid without actually decomposing it?


And yes I wasn't ignoring your previous suggestion I will weight it as soon as I get a battery for my scales.

Check it first, Sulfuric acid is a nasty acid and boiling Sulfuric is another degree of dangerous.
Proper high quality lab grade glassware will be a must.
If you keep it below 300C
it should not decompose.

There should be tables out there with SG vs concentration

 

[gregory-d]

Check it first, Sulfuric acid is a nasty acid and boiling Sulfuric is another degree of dangerous.
Proper high quality lab grade glassware will be a must.
If you keep it below 300C
it should not decompose.

There should be tables out there with SG vs concentration

Good points indeed. I only using Borosilicate glass beakers and pyrex containers
I will weigh the clean stuff to see where I started.
I would love to know if it makes sense and or if anyone has done the calculations of the watts produce the best results.
I am now working max 12v max 1 amp and most of the gold seems to be gone from the original plate leaving the brass exposed.
It is slower at that rate but the temperature never gets hot.

 

[macfixer01]

Gregory,
Check out this video from Trinity Gold. I haven’t tried this method but I see several advantages to it. Instead of sulfuric acid It uses a solution of ordinary iodized salt in water for the electrolyte. So right there it would seem a lot cheaper and a lot safer? Sulfuric acid is very thick so it’s slow for the black gold powder to settle, and hard to filter it out. It requires a lot of dilution to filter better which creates problems because it needs to be done very carefully and creates a lot of heat. It also creates more volume of waste to handle, or requires boiling to reconcentrate the acid if you plan to reuse it for more stripping. Another thing is he uses a formed copper plate instead of a basket, which is more durable. I noticed apparently some copper goes into solution but I don’t see any big downsides to his process? Anyway, check out this video and see what you think.

 

[Martijn]

Sulphuric acid 98% but I got it from a friend and it was in a 20 litre drum so it's probably way less than 98%

This is what probably went wrong.
You can check by weighing 100 ml and check the density to get an idea of how pure it is. The more accurate you can measure the volume and weight, the better.

As said, H2SO4 boils at 330C. And is extremely dangerous atvthis temp.
Here is a graph of the boiling temp. vs concentration.

 

[Martijn]

Are you connecting anode to positive? (your copper).
EDIT ADD: I used a small battery charger and never walked away because stripping happened so fast, there was no time to walk away.
What is your material.
I put 1 pound at a time basically of pins and even mixed stuff and use a poker to make sure all material got stripped.
Even did single parts as I made several leads, attached pieces and worked several hours non-stop stripping.
Do not let the sulfuric acid heat too much. Maybe that was your issue.

Changing the leads will not corrode the basket as it has become the cathode where metal deposits. This is a way to get copper sulfate back out of solution. The lead is now the anode but is not soluble in sulfuric and will create a coating of lead oxide.

Water will eat the basket.

 

[gregory-d]

Gregory,
Check out this video from Trinity Gold. I haven’t tried this method but I see several advantages to it. Instead of sulfuric acid It uses a solution of ordinary iodized salt in water for the electrolyte. So right there it would seem a lot cheaper and a lot safer? Sulfuric acid is very thick so it’s slow for the black gold powder to settle, and hard to filter it out. It requires a lot of dilution to filter better which creates problems because it needs to be done very carefully and creates a lot of heat. It also creates more volume of waste to handle, or requires boiling to reconcentrate the acid if you plan to reuse it for more stripping. Another thing is he uses a formed copper plate instead of a basket, which is more durable. I noticed apparently some copper goes into solution but I don’t see any big downsides to his process? Anyway, check out this video and see what you think.

Yeah thanks macfixer01
I saw a post somewhere here about it and I got the impression there is much more waste and some pretty nasty by products with the salt method. At the moment I have started with sulphuric and I think I will stick with it until I understand it properly.

 

[gregory-d]

This is what probably went wrong.
You can check by weighing 100 ml and check the density to get an idea of how pure it is. The more accurate you can measure the volume and weight, the better.

As said, H2SO4 boils at 330C. And is extremely dangerous atvthis temp.
Here is a graph of the boiling temp. vs concentration.
View attachment 64043

Thanks Martijn I will weigh it tomorrow carefully so at least I get a paddock figure. I did also see somewhere that concentrated sulphuric acid will react with copper in the presence of heat () so if the concentration isn't the problem perhaps letting the reaction go flat out even though the volts were low may have created that heat at the basket. That or another video when I was looking for an answer said that dilute sulphuric acid was even less likely to react with copper but these are youtube videos and real life is more often than not very much unlike what people say on youtube. I would rather follow the thinking of the experience here.
People seem to reuse sulphuric acid here but do they boil it to bring it back or what do people here actually do?

 

[Yggdrasil]

Thanks Martijn I will weigh it tomorrow carefully so at least I get a paddock figure. I did also see somewhere that concentrated sulphuric acid will react with copper in the presence of heat () so if the concentration isn't the problem perhaps letting the reaction go flat out even though the volts were low may have created that heat at the basket. That or another video when I was looking for an answer said that dilute sulphuric acid was even less likely to react with copper but these are youtube videos and real life is more often than not very much unlike what people say on youtube. I would rather follow the thinking of the experience here.
People seem to reuse sulphuric acid here but do they boil it to bring it back or what do people here actually do?

Yes, the solubility of Copper in Sulfuric goes up with heat.
So the temperature is one of the parameters one need to keep an eye on.
There was a member that built a tank of mild steel with water cooling for this purpose, I'm not sure who it was.

 

[Shark]

Yes, the solubility of Copper in Sulfuric goes up with heat.
So the temperature is one of the parameters one need to keep an eye on.
There was a member that built a tank of mild steel with water cooling for this purpose, I'm not sure who it was.

Phildreamer

 

[Yggdrasil]

Thanks Martijn I will weigh it tomorrow carefully so at least I get a paddock figure. I did also see somewhere that concentrated sulphuric acid will react with copper in the presence of heat () so if the concentration isn't the problem perhaps letting the reaction go flat out even though the volts were low may have created that heat at the basket. That or another video when I was looking for an answer said that dilute sulphuric acid was even less likely to react with copper but these are youtube videos and real life is more often than not very much unlike what people say on youtube. I would rather follow the thinking of the experience here.
People seem to reuse sulphuric acid here but do they boil it to bring it back or what do people here actually do?

Here it is, it is well worth the time to read the whole thread.
https://goldrefiningforum.com/threads/mild-carbon-steel-sulphuric-cell.22603/post-237134

 

[Yggdrasil]

Phildreamer

Found it

 

[adam mizer]

Good points indeed. I only using Borosilicate glass beakers and pyrex containers
I will weigh the clean stuff to see where I started.
I would love to know if it makes sense and or if anyone has done the calculations of the watts produce the best results.
I am now working max 12v max 1 amp and most of the gold seems to be gone from the original plate leaving the brass exposed.
It is slower at that rate but the temperature never gets hot.

Watts amps.
I just looked at it this way.
Work as high as amps on the small charger I could get. Believe it was around 6amp when started.
Stripping was fast..,., like real fast, you could see the removal literally. Amperes moving downward right away.
However at the fairly high amp the acid will heat.
So I started using a thermal gun.
I would go to 110-115f degrees and would stop and cool.
I had 35 pounds of communication coax fittings that I used the multi-lead setup. Heating was minimal because there was no basket.
Ran several pounds of pins and plated jewelry each time in same basket.
Started with thin copper mesh first time no good then got a bit thicker mesh don't know gage though.
However when running batches over consecutive days, storage of copper and lead cleaned and left in water.
The lower ambient temperature I had helped me run for many hours at a time.
Most of my work was done in around winter season up here in north, this helped me run longer outdoors under patio.

 

[macfixer01]

Yeah thanks macfixer01
I saw a post somewhere here about it and I got the impression there is much more waste and some pretty nasty by products with the salt method. At the moment I have started with sulphuric and I think I will stick with it until I understand it properly.

You’re probably confusing it with the salt and vinegar process which is not an electrolysed one and as for dissolving away the copper. In any case, good luck and be safe.