Problem with my Sulphuric stripping cell

[Anonymous]

Firstly I would like to thank everyone who has made so much information avaliable to help me even consider trying to process gold plated components. I have particularly found Steve's video's really helpful they are so straightforward and informative.

I have got a large quantity of very small gold plated pins and connectors, still on the boards and believe the way in which i harvest them will be defined by the way i will start processing them in my cell.

My cell is a large Pyrex dish as this was all i could find. In order for the cathode to be submerged it requires 6 cups of Sulphuric Acid (That I got from an automotive shop, car battery acid). I add the prescribed amount of Glycerin and made a cathode as per Steve's video. Just to note the lead i used is around 20 years old from when i used to make lead soldiers (It is possible that there are contaminents in this, I'm thinking maybe tin?)

I have performed the following tests:

With a 12v battery charger:

I used a stainless steel anode with alligator clips and stainless steel wire. When I submerged the single small pin into the acid the whols pin disappeared very quickly in a fiz, amps at around 9 and a small but identifyable wisp of black.

Checking out Steve's video using a copper anode basket i put a small amount of pins on the basket (being careful not to create a faraday cage). When I turned on the power there were loads of white bubbles coming off the cathode and the Amps went as high as 12. After a few minuted I shut the cell down. Some of the pins had a little blackening the copper mesh was really shinny and the cathode seemed to be covered in copper oxid? It was a very red covering all over and easily wiped off with a tissue. I didn't notice any bubbling coming from the pins.

The Sulphuric solution has now turned a really nice blue colour!

With a 6v battery charger

I set up the stainless steel anode again and then using a stainless steel buldog clip i dropped around 100 of these pins in, clamped by the clip and hung off the anode. There was some white bubbling from the cathode and the pins fizzed with white bubbles. This seemed to be my best test althought the pins still didn't seem to strip completely and i couldn't see the black wisps. (maybe I didn't leave it long enough). The system was running at about 2 amps.

I decided to put a fresh batch of pins on my copper basket, clean the cathode of it's red covering and try it at 6v. The cathode fizzed but not as much but once again got covered very quickly in the red oxide. and there seemed to be no bubbling from the gold pins and upon closer inspection didn't seem to be stripping, I left it running for around 10 mins and it ran at about 2 amps.

My solution is still a nice blue colour!

Now I am sure some of you will say i'm wasting my time with small pins but i am really enjoying the chemistry lesson and am hooked on trying to produce even the smallest button of gold. However I don't fancy stripping the tens of thousands of pins i have one by one!

Does anyone have any suggestions as to why i am seeing these results, particularly with the copper basket and if there is anything else i could try in order to process my scrap in batches.

Also is there a reccomendation for another way of processing these. I went for the cell option as I felt it was the easiest to set up and the safest to operate but i am open to other ideas of processing in batches.

Thanks in Advance for any help or advice you can give and thanks for the free advice that I have had access to due to this forum.

Mark

 

[Anonymous]

did you concentrate the battery acid down? I believe that is a required step, I think that could be why you solution is blue - copper sulfate - and plating out copper on your cathode.

jim

 

[lazersteve]

Mark,

James is right on the money.

You'll need to concentrate the battery acid down by boiling out the water.

Battery acid is between 30 and 40% sulfuric acid, the rest is water. Assuming you have 33% acid you must boil off the water until the volume of the acid is 1/3 of it's original volume. Concentrated sulfuric acid absorbs water very easily from the air in humid environments. Excercise extreme caution when handling sulfuric acid as it is very corrosive. Never add water to concentrated acid.

Steve

 

[Anonymous]

Thank You both for your quick response I am pleased that my attempts have not been completely scuppered at the first attempt.

So .... Boiling Acid !!!

I have had a scout around and cannot find any guidlines on this. I have noted that it should be done in small batches and that Sulphiric boils at a higher temperature than water, Don't let the Acid boil. Can I do this safely without a specialist lab rig? Presumably I wil need a Lab container and a controller heat source are there any recommendations for an amateur rig?

Probably my favoured option is to buy concentrated Sulphuric Acid. I noted that Steve used Drain cleaner (presumably commercial grade) is this already concentrated or do you have to boil it?

Does anyone know where I can find this in the UK?

As always thanks for the advice and help

 

[Anonymous]

I just use a hot plate and a 2000ml beaker. I fill the beaker to 1800ml and heat to a small rolling boil. I then wait until the acid has around 5-600 ml left. Also after you do this a couple of times, you can tell when the water is gone because the boiling stops generating bubbles.

WHAT EVER you do, be extremely careful with the boiling acid. Let it cool before you further process it.

Good Luck....Jack

 

[Anonymous]

Guys - Thanks for the advice and cautionary note. Having read and watched and read a bit more everything is starting to sink in.

I tried my acid boiling this evening and after changing my pants have come to tell you all about it! So I don't have any beakers etc for direct heat or actually anything to provide direct heat like a hot plate. So I decided to use my gas bbq. I used a pyrex dish and brought it up to heat slowly. I was a little surprised at what I saw. When everything was up to full heat the acid started producing white whispy steam(?) There were very few bubbles and it did not boil, althought there was a lot of movement in the liquid. The steam seemed to come in fits and starts but after a couple of hours the steam seemed to stop (slow dramatically) and the acid had reduced by at least half. I can't give exat measures because by the time the acid had cooled (that seemed to take a long time) it was late and so it just went straight back into the container. I am planning to do the same tommorow night to produce enough concentrate for my cell. I just want to make sure I am not putting myself in mortal danger!!

Whilst watching over my bbq acid I decided to make a rig as in Steve's video for the acid peroxide set up. This seemed to easy, both to set up and get the chemicals to be productive -WOW instant results! No boiling acid, no electricity, no dipping in and out.

So am I wasting my time with a stripping cell. Maybe I'm not seeing something but this AP seems to deal with everything.

I have processors, fingers, boards covered in pins, gold plated connectors in hard to access plastic housings. Should I just drop all of this in a bucket of AP and wait?

My plan was to do the pins (whilst on the boards, approx 2" * 6") either pushed into the copper mesh anode or clipped by a stainless steel bulldog clip. Is there an advantage of doing the pins in the cell v AP?

Any advice would be welcome before I start boiling acid again !

Cheers

Mark

ps - It is just the best feeling seeing that gold floating around in my AP solution, I'm hooked!