# Sulphuric cell.



## jason_recliner (Mar 14, 2015)

Hello all.

I have a slowly growing pile of bluetooth antennas I would like to deplate. I posted something almost a year ago about my first attempts to put them through AP / copper(ii) chloride but soon discovered what a fool's pursuit it is, to try to dissolve so much base metal for such a thin coating of gold.

I've been researching sulfuric cells for a little while now. The forum is just loaded with a wealth of information on the topic and I've spend many hours of reading. Not only here, but other sites including wiki, Nurdrage and even Tom's Hardware. There are however a few things that are still a little unclear to me. So I would like to ask for some help before I make a complete balls-up of it, er, "start".

Please pardon me if I ramble a little; I'm trying to put my thoughts out there with my two questions.

I have not yet happened across copper mesh. But the antenna bodies, once the steel wire is removed, have a central hole. So I'm intending to simply suspend them on bare copper wire. Cheap. Easy. Disposable. Ok, onto the two questions.


1: Required sulphuric acid strength.

Forum posts generally indicate 98% is used. Easy if you can buy it at 98%. One post says 95%+. I'm having just a little trouble finding such concentration locally. Of course battery acid is always plentiful. My bike's top up bottle doesn't indicate its concentration but I will assume it to be in the order of 30%. So I can just concentrate it and I believe this is most easily done "by volume". But I don't necessarily trust my own evaporation accuracy to 98%, especicially if I don't know whether I'm starting with 28% or 35% in the first place.

From my studies I know diluted sulfuric will chew through copper like a hot knife through a leper but there must be a point where passivation gradually begins. You'd think this would be easy to find. But no. WHERE? Is 90% ok? 92%? 95%? 80%? My understanding behind the theory of passivation is "marginal" to say the least but I will presume that it will have a gradual curve rather than a sharp cutoff point. With that in mind, it would be good to start with a rough percentage. One thing in my favour is that I'm planning to use just a cheap wire for suspending the target (assuming it works) and that means all is not lost if it happens to dissolve, unlike some hard to find copper mesh.


2: Deplated metals

I'm finding it hard to determine what metals will deplate under electrolysis, while the current is turned on.
Gold, obviously. As I undertand the process, it's dissolved only under current so that when ions move away from the current source (or when current stopped) they are no longer held in solution and drop as black powder.
(2.1: why black? If it's gold, why not brown as when precipitated from auric chloride?)

Other than the steel wire which I yank out with pliers, I am not really sure what my antennae are even made of. Steel, brass, nickel, who knows?

What will NOT dissolve in sulfuric and under current?


3 (because I can't count to 2): Electrode Material: +Cu -Pb

So gold dissolves in the presence of current near the anode, for some kind of electrony reason I don't need to understand in order to accept. Copper and Stainless both work.
But if the ions move too far from the anode, or if the current stops, then gold precipitates as black pwder. But gold ions don't go even near the cathode. So why must the cathode specifically be lead?


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## solar_plasma (Mar 14, 2015)

Lead as the cathode is somewhat inert in conc. sulfuric.

Copper will dissolve to some degree if sulfuric is under 95% and/or too hot. Further conc. sulfuric gets far more dangerous beyond let's say 60-80°C, at its boiling point it will even generate SO3 smoke (never tried, don't want to!). Btw. remember NEVER to put water into conc. sulfuric.

At the anode formed persulfuric will dissolve the gold, but this compound is instable and gold will reduce to metallic state as finest black dust as soon as it leaves the anode. It is black because it is impure.

Yes, dilluted sulfuric can be heated until all water is vaporized. (never tried, never dared to)

Sulfuric cell works with base metals like copper, iron, nickel, cobalt and their alloys. I would not try other metals without further research or testing.


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## MarcoP (Mar 14, 2015)

Jason I feel your pain as I've some of your questions too however I think I'm able to answer some of your doubts.

From an unknown concentration I reckon controlling the temperature could be the key. [stt]Temperature wont go over 100°C till all water is gone, so if it raise over that point should means the water is gone.[/stt] Also 1ml of 98% sulfuric acid weights 1.83gr, having a good scale it could be another tool to help you out. [stt]If I correctly remember, while evaporating, if you see white smoke coming out you are already at ~98%.[/stt]

At the anode, when current passes trough, sulfuric acid gains one atom of oxygen forming persulfuric acid and this is able to hold oxidized gold. Moving from the anode to the cathode the persulfuric acid chase to exist releasing the black gold powder.

Why black? No idea. But I guess it's just the way it reflect/absorb the light. Might be the just shape of the powder.

Why lead? Would be great to know! I always promised my self to learn more about anodes, cathodes and electrolytes, how, when and why.

Please accept my answers as not correct ones, sometimes when I feel to be able to answer I take the opportunity to also test my learning.

P.S.: just noted solar_plasma's reply but I'll post anyway, cheers.


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## Shark (Mar 14, 2015)

I can't find the thread now, but I think it was GSP that suggested 85% concentration would work but keep the temperature down. The combination of excess moisture with heat will speed up copper dissolving more that just the heat or the moisture alone. I will keep looking and see if I can find the thread again.

If you can't find the mesh, and aren't doing tiny pins, you might find some window screen made of copper. I found a large roll at the local scrap yard and traded 5 pounds of aluminum scrap for it.


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## Long Shot (Mar 14, 2015)

Jason,

I too have been studying a bit on this subject and have a partially constructed cell - waiting for good weather so I can work outside.

On the copper mesh front, yes, it is hard to come by, and expensive. Some of the suggestions were to check a hobby store -I did and they used to carry it but no longer. I live in a small city with only one store so if you are in a bigger center you may find it there. I wound up finding it on eBay out of California and got a little less than 2 sq ft to my door for about $25 CND. 

In regards to why the powder is black - I read that because the particles are so fine that they diffuses light in all directions, hence, appears black or having no color.

A source of 96% H2SO4 can be found in certain drain cleaners. I called up the MSDS for the stuff I have here and that confirms it. If you want the brand I can go dig it out of storage and advise. I believe it was GSP that said he doesn't like to use it because of the additives and agents in it but don't quote me that it was him. The stated problem is with foaming. That said, I am going to try it as I have 4 quarts of it and because I am in no hurry or am not a production outfit so I can slow things down to control that (hopefully). If it doesn't work out then I will go the concentrating battery acid route - there is good information here about doing that with a jeweller's scale (think LazerSteve has posts on it but again don't quote me).

And finally, I do not want to insult your intelligence, but I will reinforce - NEVER add water to conc H2SO4! Always H2SO4 to water. The way I remember that is that Acid comes before Water alphabetically, thus, A to W.

Regards, Jeff B


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## goldsilverpro (Mar 14, 2015)

I just re-read the original patent, 2185858, and it uses sulfuric acid of specific gravity of 1.65. That computes to a solution of 68% sulfuric/32% water, by volume, assuming you're starting with 96%, by weight, sulfuric acid. I've never used it that weak (and probably never will) but, since it's a Western Electric patent, I assume it will work. The purpose of the patent is to strip faulty gold plating without damaging the substrate so the parts can be re-plated. The patent says to keep the solution temp under 100F. Doesn't mention current density

Would be interesting if someone tried this weaker solution. Might work faster. I know that sulfuric absorbs moisture from the air and becomes more dilute. Therefore, in production, I would probably start with a minimum of 85%, by volume. It seems that about any strength will work if it's strong enough to form a passive layer on the copper to prevent dissolution. I know that even battery acid (32%, +/-, by weight) will strip the gold but it also will eat copper.


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## GotTheBug (Mar 14, 2015)

Is there any reason not to use stainless for an anode?


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## g_axelsson (Mar 14, 2015)

MarcoP said:


> From an unknown concentration I reckon controlling the temperature could be the key. Temperature wont go over 100°C till all water is gone, so if it raise over that point should means the water is gone. Also 1ml of 98% sulfuric acid weights 1.83gr, having a good scale it could be another tool to help you out. If I correctly remember, while evaporating, if you see white smoke coming out you are already at ~98%.


*That is so wrong!* The sulfuric acid is grabbing hold of the water and raises the boiling point of the acid. All the way up above 300 C / 570 F. Imagine what damage that hot acid would do to you in case of an accident.

The behaviour of sulfuric acid and water at different concentrations is shown here
http://www.jacobs.com/uploadedFiles/wwwjacobscom/20_Learn_About_Us/25_Products/252_Chemetics/Sulfuric%20Acid%20Concentration.pdf
And as shown, there is sulfuric acid going off as vapor even at lower concentration but becomes severe above 90%.

Concentrating sulfuric acid by evaporation is dangerous and should only be done with proper equipment and security procedures. Always plan for an accident.

Göran


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## goldsilverpro (Mar 14, 2015)

GotTheBug said:


> Is there any reason not to use stainless for an anode?


The only metal I've had problems with was nickel when I was stripping gold from inconel, which has a very high nickel content. The stripper tended to dissolve the nickel and, after only a couple of cycles, the solution became saturated with nickel and stopped stripping the gold. I would guess that cobalt (like in a Stellite alloy) would cause similar problems.

300 series stainless (non-magnetic) contains nickel and might cause problems. However, I have stripped gold from 410 stainless (magnetic - no nickel) hundreds of times with no problems.

A big disadvantage with any stainless steel is that it's not very electrically conductive. It's like a big resistor. Copper is 44 times more conductive than 316SS and 79 times more conductive than a 400 series hi-chromium alloy.

If you can keep the temperature low, I would think that copper would be the best choice. I once used plating racks to hold all-gold IC's for stripping, using spring contacts made from magnetic 400 series SS piano wire. The racks, themselves, were made from uncoated 1/4" square yellow brass stock (probably 65Cu/35Zn). Each rack spent at least 2 hours a day in the sulfuric (about 90%, by volume), as the anode. After 2 years, there was no visible attack on the brass or the spring contacts. I would guess the temp of the soln. didn't exceed 105F during that time.

A lead cathode was probably chosen because of its inertness in the sulfuric. I never have used lead. I always used mild carbon steel as the cathode(s), with nary a problem. In fact, the 50 gallon mild steel tank I used for the solution was made the cathode.


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## goldsilverpro (Mar 14, 2015)

H2SO4 concentration vs boiling point in Fahrenheit.


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## MarcoP (Mar 14, 2015)

g_axelsson said:


> MarcoP said:
> 
> 
> > From an unknown concentration I reckon controlling the temperature could be the key. Temperature wont go over 100°C till all water is gone, so if it raise over that point should means the water is gone. Also 1ml of 98% sulfuric acid weights 1.83gr, having a good scale it could be another tool to help you out. If I correctly remember, while evaporating, if you see white smoke coming out you are already at ~98%.
> ...


Thank you for correcting me! I should study more  
While learning about it I never noticed any reference to vacuum distillation and thought about it as a relatively easy method ... I'll edit my post just in case.


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## jason_recliner (Mar 14, 2015)

Thank you all for your wonderfully helpful replies. I still have a few more rabbit holes to wander down, but I think I'm nearly ready to give this a go on a very small scale. 

Göran, I couldn't access your link as the server is playing up. I'll try again later. You have me a little worried now about concentrating my own. I was aware it evaporated out to 300°C and I am used to working with large pots and waves of molten solder. I will be extremely careful and start testing with just 100ml.

I tried two major hardware chains last week plus some little local stores looking for sulphuric drain cleaner. All I can find is sodium hydroxide, and even that's now 98%. (Last time, I was able to get 100% so I will assume it's got a decaking agent.) It might be an "Australia" thing.

Based on GSP's advice, I think I shall try it at 85%, which means I have will to evaporate battery acid to about 230°C. Not wanting to put the cart before the horse, but if that works well I will try progressively lower concentrations, running as cool as possible and report back my findings. It sounds like some people might be interested.

I should have been more specific in Q3. I understand _that_ it turns into persulfuric near the electrode. (How exactly that electrony stuff happens is a bit beyond my basic chemistry, but I don't need to know everything.) I can't find it now but remember reading perhaps a few months ago; Harold made a point about target items not even needing to touch the anode but just be within the zone, about half an inch or so (current dependent). So then, if at the cathode it's just plain sulphuric acid, and if the copper anode can survive sulfuric/persulfuric, perhaps a copper cathode would too. I have access to heaps of copper shim but no lead handy. On the other hand, my objective should not so much be preventing loss of cheap electrode but preventing loss of quality of acid.

Finally, Jeff, I am not the slightest insulted by you telling me something I should already know: "Do as you oughta, add acid to water". Safety before hurt feelings.

My grateful thanks to all.


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## goldsilverpro (Mar 15, 2015)

Actually, I think the evaporation of weak sulfuric acid to make strong sulfuric should be on the list of very dangerous processes discussed recently on another thread.


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## solar_plasma (Mar 15, 2015)

goldsilverpro said:


> Actually, I think the evaporation of weak sulfuric acid to make strong sulfuric should be on the list of very dangerous processes discussed recently on another thread.



Especially when looking on who would most likely want to try it: hobbyists with poor experience. Almost everyone else would rather be able to buy sulfuric in all concentrations.


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## bswartzwelder (Mar 15, 2015)

For those of you looking for copper mesh, go to lasersteve's store at goldrecovery.us and he sells it for a very reasonable price.

Edit: A simple search using "copper mesh" as the search criteria would have found it very easily as well.


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## jason_recliner (Mar 16, 2015)

goldsilverpro said:


> Actually, I think the evaporation of weak sulfuric acid to make strong sulfuric should be on the list of very dangerous processes discussed recently on another thread.


I would go along with that. Everything to do with it had me rather on edge. I will share what I did and if you think it inappropriate to share then please delete my post and I will not be offended.

As I intended, I started with a 100ml beaker. I only ultimately used 75ml because

that's the highest graduated marking on my 100ml beaker, and,
the first time you work with something that can scar you for life, you DON'T want to fill it to the top
As it evaporates through the 50ml mark, I am smart enough to NOT top up hot acid with another 25ml of cold 32% acid.
The initial 75ml weighed 93g, which is an SG of 1.24 or 32%. I figured there was therefore 24ml of acid in it.

I left it on the portable outdoor gas stove until it was down to 30ml, letting it continue to evaporate as it cooled. Final volume "about 27ml", or "about 88%", assuming the 24ml of acid was still in there. However, that ~27ml weighed 44.6g or SG 1.65, or around 78%. So some acid has fumed out too but I figured that was close enough to test concept. (I'm probably making weight/volume errors.)

I bend some copper wire into a small basket that would hang in a 50ml beaker, into which I could put just 3 or 4 antennas as a time. I also used copper wire bent several times for the cathode. It seemed to work quite well and I put a few cycles through with no degradation noticed. The temperature stayed below 27°C.

But then my power supply gave out. Instead of 6V limited to 0.5A, it slammed up to 40V unlimited current. My single strand wire basket broke in the centre even before I could kill the power. I don't have a photo of the little wire basket handy.

Nevertheless, I have proof of concept with 78+ % and I had made this: There's a nice layer of brown forming on the bottom. It's still not completely settled, but it is settling enough now to see there's a tinge of green in the remaining solution: probably indication of a little copper being chewed up.
Overall I'm pleased with the result. It would be better if it were stronger acid but I also prefer the idea of working with 85% than 96%: I expect it to be a little more forgiving around water, should I make any accidental slipup.

I'll have to repair my power supply before I can try anything else, or on a larger scale.


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## solar_plasma (Mar 16, 2015)

I have read a little about concentrating sulfuric on a german chemistry forum: One should be knowing, that concentrating sulfuric to about 85% implicates temperatures about 200°C and sulfuric acid vapors. A water containing liquid at this temperature is high stress for the glass ware and obviously it happened to more than one, that their (low quality) glass ware exploded on the thermal stress.

Thinking of drops of water condensing at the colder glass areas might run back into the acid would cause me nightmares. Not to think of, if someone would make this experiment in a closed rigg and forgets to prevent water to get sucked back into the acid when he is reducing the heat.

Again one should also be aware of, that 1l hot H2SO4 is exponentially harder to control than 10ml, - in case of something unexpected is going to happen!

While this might be safe for most of the seniors and chemists, this is an accident waiting to happen for everyone else, included myself - even though I have a large school lab to do a lot of not harmless experiments safely.


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## jason_recliner (Mar 16, 2015)

You know Björn, you are starting to talk me out of repeating a perfectly good first test run. :lol: 
I am not certain either way about cool 80% being as susceptible to small water droplets as hot 96%, which is part of my reason for wanting lower % in the first place. But I can also see the wisdom in what you are saying.

Since the probability of horrible accident = individual chance of accident * times repeated, I think I will likely keep reusing what I already have as long as possible and not evaporate down any more, but instead wait until I can find a local source of supply.


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## Barren Realms 007 (Mar 16, 2015)

solar_plasma said:


> Thinking of drops of water condensing at the colder glass areas might run back into the acid would cause me nightmares.



This should not be a problem because the water droplets that condense should be close to the temp of the solution you are heating up.


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## Barren Realms 007 (Mar 16, 2015)

jason_recliner said:


> goldsilverpro said:
> 
> 
> > Actually, I think the evaporation of weak sulfuric acid to make strong sulfuric should be on the list of very dangerous processes discussed recently on another thread.
> ...




The material in your beaker looks to be more copper than gold.


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## goldsilverpro (Mar 16, 2015)

> The material in your beaker looks to be more copper than gold.


That's what I thought when I first looked at it. If so, the solution was probably allowed to get too hot. Too much amperage.


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## solar_plasma (Mar 16, 2015)

@Jason and Barren Realms

I don't want to spread panic. But being prepared for the worst case scenario is not the most stupid thing.

Barren Realms I am not sure you are right. In my logic the temperature would make it even worse. The only fact that might prevent small steam explosions would be, if the condensed "water" is actually more or less dilluted sulfuric acid.

Fact is, some people have blown their probe glasses (obviously a bad choice) and I can only see two possible reasons: thermal stress and/or condensed water drops. I might be wrong.

Whatever you guys do, be prepared and stay safe!


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## goldsilverpro (Mar 16, 2015)

In the plating industry, the old standard method of analyzing gold in a cyanide solution was to use about a 5ml sample and "wet ash" it in 100-150ml of very hot concentrated sulfuric (FUME HOOD!!!). It takes awhile but the end result is that all the gold ends up quite pure on the bottom of the 250ml erlenmeyer flask (in this case, an erlenmeyer is safer than a beaker - splattering becomes less of a problem due to the pinched top of the flask). The gold is then separated (fairly dangerous in itself), rinsed, dried, and weighed. *NOTE:* I haven't given all the information on how to exactly do this, so don't try it!

The main purpose of this post is the SO3. 

Most of the published instructions for the above method say to heat until "copious" white fumes of SO3 appear (they are obvious - you can't miss them). Copious means abundant or present in large quantities. When evaporating weak sulfuric to the point where most of the water is gone, a certain concentration/temperature level will start producing these dense white SO3 fumes, in VAST quantities. If you breathe them or your skin is exposed to them, they react with the water in or on your body to produce sulfuric acid (H2O + SO3 = H2SO4). What I'm saying is that you must take every possible precaution against contact with the white SO3 fumes. An excellent fume hood is an absolute MUST when evaporating sulfuric. I would never do this outside because you can't predict wind changes. Also, the SO3 will react with the water in the air and produce a heavy H2SO4 atmosphere. If you're going to evaporate sulfuric, first get a good well-designed fume hood. Please!


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## Barren Realms 007 (Mar 16, 2015)

solar_plasma said:


> @Jason and Barren Realms
> 
> I don't want to spread panic. But being prepared for the worst case scenario is not the most stupid thing.
> 
> ...



You are correct in being prepared for the worse case scenario.

First off if you are evaporating the water off you should not have a top on your beaker or container. The top needs to be left off so the water vapors can escape other wise it lengthens the evaporation process.

Second fact any water that will condense will be on the insides of your beaker or container and will roll back down the inside of your container into your solution and they will be at or close to the same temperature as what the solution you are evaporating off is so there will be little temperature difference.

This is not a guess or something I read. This is from practical experience of doing the process.

Breaking beakers is always a posability. But if you use quality glass ware the posability of failures is less likely. Or if your glassware is badly scratched it should not be used in this process.


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## solar_plasma (Mar 16, 2015)

Barren Realms 007 said:


> so there will be little temperature difference.
> 
> This is not a guess or something I read. This is from practical experience of doing the process.



Since you have seen it in real, then it is no condensed water, but dilluted H2SO4. Another possibility that I haven't tried (and don't want to): 85% sulfuric won't act the same like oleum, not even like 98%. Maybe both explanations will fit. So, it must have been the thermal stress, that blew those guys' probe glasses. 

When you dillute concentrated sulfuric, an exotherm process is taking place (I need to read it again, but if I remember correctly, it is a chemical reaction). It is exotherm, if the water is cold or hot. If both are hot, water will vaporize even quicker. 

@gsp
Great post! Thank you! 

A larger quantity of hot smoking H2SO4, that won't stop smoking until it has cooled down by itself must be the absolute horror for everyone, who is not prepared for this. That is, what I always try to say: reactive chemicals get exponentially harder to control in relation to the quantity! 10ml can easily get covered with sand. 1l not.


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## Barren Realms 007 (Mar 16, 2015)

solar_plasma said:


> Barren Realms 007 said:
> 
> 
> > so there will be little temperature difference.
> ...



That is not necessarily true, you will have some water that condenses on the sides and falls back into the solution till you have evaporated the water out of the acid. 

That is correct that it was probably thermal stress that caused the failure of the container. Either from a scratched beaker, cheap glass ware or improper glass ware used to do the process.

Yes pouring water into the sulphuric acid will cause an exothermic reaction and possible eruption of the solution if a lot of water is poured into a small amount of acid. If it is just a drop or 2 in a large quantity of acid there is less of a posability of this happening but it is still the posability of this happening.

Pouring your acid into the water also causes an exothermic reaction and less of a chance of an eruption of your solution unless you pour a lot of acid into a small amount of water. You can counter react this exothermic reaction to a degree by adding ice to your water and cooling the temperature of the water then add your sulphuric acid to the water. You will still have an exothermic reaction just not as sever of a rise in temperature.


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## solar_plasma (Mar 16, 2015)

> That is not necessarily true, you will have some water that condenses on the sides and falls back into the solution till you have evaporated the water out of the acid.


There is also condensing H2SO4. Yes, sulfuric doesn't vaporize on low temperatures, but at 200°C it will.


> Yes pouring water into the sulphuric acid will cause an exothermic reaction and possible eruption of the solution if a lot of water is poured into a small amount of acid. If it is just a drop or 2 in a large quantity of acid there is less of a posability of this happening but it is still the posability of this happening.



This is not correct, a drop can cause an eruption, though I can't remember at which concentration 18M or 10M, - or even both.



> Pouring your acid into the water also causes an exothermic reaction and less of a chance of an eruption of your solution unless you pour a lot of acid into a small amount of water. You can counter react this exothermic reaction to a degree by adding ice to your water and cooling the temperature of the water then add your sulphuric acid to the water. You will still have an exothermic reaction just not as sever of a rise in temperature.



I do not know the explanation, but water is a much better heat conductor than conc. sulfuric, if I remember right. If so, this alone could prevent the violent reaction.


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## rickbb (Mar 16, 2015)

Maybe I've misread some information in this post, (wouldn't be my first time). But;

For evaporating water off of sulfuric wouldn't it be safer to use a lower temperature and let it take longer? 

I concentrate battery acid by using a 1L beaker in a sand bath in a slow cooker, (crock pot). At 190F and let it run overnight I can bring 1L of 30% battery acid down to 300ml that will not reduce any further, leaving a viscous, oil like concentration. All done in a fume hood of course and I never see any of the white SO3 smoke, just small amount of water vapor which gradually reduces in volume as it concentrates down.

I don't see a need to do this at 200C if just concentration is the goal. Was it recommended to separate the gold from the copper in the solution?


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## solar_plasma (Mar 16, 2015)

:shock: I didn't know, it would work like this. Sounds comparably safe to me. Would be fine, if some seniors could evaluate this. 

30% is by weight, not volume, so do you know the end concentration or density?


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## Barren Realms 007 (Mar 16, 2015)

solar_plasma said:


> This is not correct, a drop can cause an eruption, though I can't remember at which concentration 18M or 10M, - or even both.



Ok. 

No need to get into a heated discussion on this. 

I've only worked with it for 30 years.


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## solar_plasma (Mar 16, 2015)

I agree.

I try this drop thing on a little quantity of cold 18M in an erlenmeyer under safe conditions tomorrow and find out if it is a myth.


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## solar_plasma (Mar 16, 2015)

I googled a little. At least for 98% sulfuric it is a myth, look here: https://www.youtube.com/watch?v=_f0vK8Wffgg

Though we weren't talking about 18M, I will try, if it won't work here either. 

The drop thing is a widely believed myth and you can read it everywhere. Interesting. Thank you Barren Realms! (By the way, since I also use conc. sulfuric over 30 years, 19 years professional, this is obviously a bad argument, since I was wrong :mrgreen: )


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## Barren Realms 007 (Mar 16, 2015)

solar_plasma said:


> I googled a little. At least for 98% sulfuric it is a myth, look here: https://www.youtube.com/watch?v=_f0vK8Wffgg
> 
> Though we weren't talking about 18M, I will try, if it won't work here either.
> 
> The drop thing is a widely believed myth and you can read it everywhere. Interesting. Thank you Barren Realms! (By the way, since I also use conc. sulfuric over 30 years, 19 years professional, this is obviously a bad argument, since I was wrong :mrgreen: )



I would not consider you as being wrong. It's just a matter of learning the limitations of what we do.

Edit: I'm also not suggesting that anyone go and try this just for the fun or experience. That is when mistakes and accident's happen.


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## jason_recliner (Mar 17, 2015)

I am not a chemist, nor do I play one on a weekly radio show. But I believe it's not a myth; it just needs the right conditions.

I found a you-kill-yourself video recently which I can't dig up right now; I'm at work. It had a guy in the desert trying to add water to all sorts of acids including small volumes of water into large volumes of concentrated sulphuric. He was measuring temperature rise, and while he got some, everything stayed below about 170°F I think (about 80 for the rest of us).

What he failed to try was to put water into hot acid. As a firefighter I know only too well what happens when well-intending people throw water onto an oil fire. You can quite literally lose face doing this. It's reasonable to expect if water is dropped into acid over 100°C it quickly becomes boiled and will similarly steam and spurt nasty, hot acid everywhere. It's not the acid spurting. It's the water.

Sulfuric acid will adsorb water through its surface (or absorb it at the surface? Whatever). But I think I can say that presence of a fine fog is not going to acid to spray everywhere, rather gently dilute it while also providing some cooling. But even if I believed it were safe to drop small amounts of water into sulphuric acid, I would still probably not be willing to make any definite statements to the effect.

Now, GSP made an excellent point about the SO3 cloud. I had considered that, but only partly, out of ignorance. For me it was just "don't want any sulphuric vapours". Further reason to not evaporate to 90%. In my case, I may or may not have lost some acid to vapour, outside, over about 2 hours. At no time was there any condensation visible on the sides of the spotlessly clean borosilicate beaker.

Part of my contingency plan was a long stick to turn off the gas if required from upwind (and that method tested), plus a charged hose nearby preset to fine fog/mist. As scarey as it sounds keeping water on hand for acid, my plan was for in case of something worse than a bit of acid splash. Though I did not know it fully at the time, this fog would also apparently be good for reducing SO3 to localised acid rain, which I'd rather on my property than in my skin. Not that I likely got anywhere near massive clouds of SO3 at 78%.

I can't say I would recommend evaporating sulphuric acid if it is at all avoidable.

Also, taking a look at my settled powder, it _does_ look an awful lot like copper...


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## solar_plasma (Mar 17, 2015)

Also being a hazmat firefighter  (doesn't mean much, we have a lot of books we use before doing ANYthing) I agree with you on throwing down hygroscopic vapors always might be considered a plan. I do not agree on spraying water on the surface (even if it would work). It would free extra energy. And it would be very hard to argument for having done this in front of any court, which only will look at the [stt]W[/stt] in the hazmat diamond. If it is a closed metal tank without leakage, cooling the outside from a safe distance might be investigated as an option. In your experiment I would still see sand as the state of the art.

edit: On the other side, right is, who has succeeded. So, it is hard to determine if it is this or that and not one accident is like the other. We have a saying that translated says something like "Live the case!" (=Lebe in der Lage!)


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## solar_plasma (Mar 17, 2015)

I tried drops an splashes of water on what once has been 18M (I doubt it still is, since it is a maybe 20 years old bottle, need to measure) and nothing happened beside it got warm. So, I learned something new.

Nevertheless, don't try this at home. As jason said, it might be something else under some circumstances.


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## Barren Realms 007 (Mar 17, 2015)

solar_plasma said:


> I tried drops an splashes of water on what once has been 18M (I doubt it still is, since it is a maybe 20 years old bottle, need to measure) and nothing happened beside it got warm. So, I learned something new.
> 
> Nevertheless, don't try this at home. As jason said, it might be something else under some circumstances.



:lol: See, it is possible to teach an old dog new tricks.


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## solar_plasma (Mar 17, 2015)

When we stop getting better, we're not good anylonger.


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## rickbb (Mar 17, 2015)

solar_plasma said:


> :shock: I didn't know, it would work like this. Sounds comparably safe to me. Would be fine, if some seniors could evaluate this.
> 
> 30% is by weight, not volume, so do you know the end concentration or density?



No, I don't have the means, (or knowledge) to accurately measure the concentration. But it looks and works like 98% that I have purchased.


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## solar_plasma (Mar 17, 2015)

If you know the weight of a given volume, you can calculate the density. Then you can find the respective density in a chart density vs. concentration.

weight (g) / volume (ml) = density (g/cm³)


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## jason_recliner (Mar 17, 2015)

I used this: http://www.sschemical.com/wp-content/uploads/2013/05/Conversion_Table.pdf
Although on looking at it again I realise I made an error. I accidentally read from the "% 66 Baume" column instead of "% H2SO4". So 78% of 93% acid. Understanding the high concentrations takes a bit of getting your head around for new players!
So my evaporated acid was only ~73%, not ~78%, which is becoming a fair way short of the ideal 85%. No wonder I have a copper powder collection!


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## Barren Realms 007 (Mar 17, 2015)

jason_recliner said:


> I used this: http://www.sschemical.com/wp-content/uploads/2013/05/Conversion_Table.pdf
> Although on looking at it again I realise I made an error. I accidentally read from the "% 66 Baume" column instead of "% H2SO4". So 78% of 93% acid. Understanding the high concentrations takes a bit of getting your head around for new players!
> So my evaporated acid was only ~73%, not ~78%, which is becoming a fair way short of the ideal 85%. No wonder I have a copper powder collection!



What were you deplating and how long did you leave it in the cell to deplate the material? I don't think the concentration of the acid is what caused your copper build up.


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## jason_recliner (Mar 17, 2015)

Yes, but the low concentration won't help. I am sure the advice already given is right, that the current was limited to too high a value.

The material I have accumulated is a pile of gold plated Bluetooth stub antennas. The plastic covers rip right off the nut; the steel antenna wire pulls out with pliers. I was only able to deplate about a dozen before my adjustable 40V 5A power supply spat the dummy. I built it 25 years ago from scratch using a magazine design and it has been brilliant until Sunday. 

Each test set of 3 was in probably < 5 mins. I was expecting < 10 mins. Some still look like they should run a little longer. I left each set in until they looked like the gold plating was gone or until the current dropped off significantly, however the latter may have been caused by the power supply starting to fail. I really don't know. No more cell work for me until I dig up a 30 year old circuit diagram for an ETI163.


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## Emmjae (Mar 19, 2015)

Here is the company I use to buy my copper mesh. They also carry a lot of other hard to find items.

http://www.mcmaster.com/

Just type in "copper mesh" in their search box and you'll find what you need. 

You can purchase a piece as small as 12"x12" or as large as you want.

Regards,

Mike


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## MarcoP (Mar 19, 2015)

Or in U.K. http://www.themeshcompany.com/ that's where I've got mine.


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## bemate (Oct 22, 2016)

This might have been covered already, but I couldn't find any information on it: does the orientation of the cell play a role?

I have no definite plans for any of my scrap yet, but I try to get as much input as possible while I'm still reading and learning.

The reason I ask is simple : I have a sheet of pure copper that would make a great anode (or cathode? Can't remember right now as I have had a few too many at a party...). The thought, drunkenness aside, is to place the plate at the bottom if the cell, connect it to the power supply with copper wire and pile my pins on top in a heap and suspend my lead electrode at the top.

I realize this would make for more work cleaning the pins of black gold dust, but the question is rather if it would affect the efficiency of the cell as opposed to the usual horizontal setup?


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## FrugalRefiner (Oct 22, 2016)

Yes.

Dave


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## Barren Realms 007 (Oct 22, 2016)

bemate said:


> This might have been covered already, but I couldn't find any information on it: does the orientation of the cell play a role?
> 
> I have no definite plans for any of my scrap yet, but I try to get as much input as possible while I'm still reading and learning.
> 
> ...



This would create a problem because the gold that deplates from the material will settle on top of the material and not allow for conductivity to deplate the material. You need to have both the anode (material being deplated) and cathode (lead) suspended in your solution so that the deplated gold can settle to the bottom of the cell. You also need to to make sure they are not separated too far.


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## nickton (Aug 5, 2018)

what does this mean: "In fact, the 50 gallon mild steel tank I used for the solution was made the cathode." ? :mrgreen:


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## g_axelsson (Aug 5, 2018)

He is using the steel tank as cathode instead of having a separate cathode.

Göran


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## LT_golden (Oct 30, 2018)

This _is_ an old thread, and hopefully by now, solar_plasma has found his answer or an equally viable solution.

In case not or if anyone is curious, let's try out catfish's method.


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## anachronism (Oct 30, 2018)

No disrespect but I would rather not. It's horrible stuff to heat to that temperature. You have no margin for error whatsoever.


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