Electrochemistry Can i use a plastic dish for a suphuric cell?

[Traveller11]

Metals can react differently to different acids.
Acids of different concentrations will also act differently on a metal.

Lets look at sulfuric acid and iron.

I can take clean soft iron (transformer laminates), and 10% sulfuric acid and dissolve them quite easily, making copperas (ferrous sulfate), (iron sulfate),(FeSO4), if evaporated to crystals I could use these to test for gold in solution (brown), or use the copperas to precipitate dissolved gold from my solutions.
Now lets take the same iron and add 98% COLD H2SO4, now this iron will on its surface be quickly attacked by the sulfuric acid, but the attack will halt, the iron layer of oxidation will protect the iron from the acid, so basically the iron is passivated and the iron is protected from attack by the acid because of this passivated layer, the iron will not dissolve, unless I diluted the acid with water, sulfuric acid has an affinity for water and will absorb water from wherever it can, it will take water from the air so if we do not want the iron to be attacked by this cold sulfuric acid we must try to keep out the water., another thing is if we heated this concentrated sulfuric acid it would attack the iron (I am not sure of at what temperature?), the HOT concentrated sulfuric acid would begin to dissolve our iron making a solution of Iron III sulfate,Fe2(SO4)3, called ferric sulfate.

So the short answer is the iron can passivate in cold concentrated sulfuric acid and will not dissolve.


eddited to add another thought: as the cathode in a cell, the metals in solution wants to deposit its dissolved metal onto this layer of passivated iron, that also could help shield the iron vessel from further attack, of the acids.

This is a real stretch (and I won't be too surprised if it isn't feasible) but, if the material you placed in the cold 98% H2SO4 had iron in it but the iron was already in an oxidised state (ie. fine particles of magnetite (Fe3O4) and haematite (Fe2O3)), would the iron be untouched by the H2SO4?

 

[butcher]

Traveller11,
I am somewhat unclear as to what your saying or asking, the magnetite and hematite are bound to oxygen, (this is a tight bond not easily broken), if you did not crush and roast the ore, I do not think strong cold sulfuric would have much affect, but grinding and roasting, or better yet reduce the ore to iron, either in a melt with coke, and the dilute sulfuric would then attack the iron, or one could smelt it with flux.

 

[pesco]

Also, even using glass you MUST make sure it's tempered, this is the very reason why you see people using the glass Pyrex dishes for their cells. It's tempered and resists acid corrosion.

I disagree with that. Tempered glass is the strongest type, however when damaged it doesn't crack or brake. It shatters into hundreds of tiny pieces. As a result whole content of the cell would flood your workbench and floor. For that reason tempered glass is the worst choice. Besides it is not possible to cut such glass, so if you you plan making tank of it you would have to obtain ready cut sheets or cut float and send it for tempering - impractical and expensive.

The best is laminated glass, the type car windscreens are made of. It is interlayered with sheet (or sheets) of PVB. If damaged the glass will brake or crack, but will be held together by sheet of PVB. In case of disaster your container will not disintegrate and most likely it wont even leak. You can safely empty the cell and dispose it off.
There is however downside of laminated glass - it is possible but difficult to cut if you don't have specialistic tools. I've cut it few times by cutting both sides, pouring little bit of methanol and igniting it to melt the plastic inside. Mixed results

My first choice is ordinary float glass. I had few cells made out of it and none failed, however I also made dozens of aquariums and I did damage few by accident. From this experience I can tell that if small glass vessel is damaged it cracks, sometimes developing small leak on the crack. You have lots of time to empty it safely. Long time ago I made a cell for colouring aluminium after anodizing. The bath was working at around 55-65 C, so to make it safer I wrapped the cell in a layer of duct tape. In case the glass breaks the duct tape should hold it together. Effectiveness of duct tape haven't been tested in practice as the glass never broke or cracked 8) To make it even safer and provide a bit of chemical resistance a layer of aluminium tape used for insulating ductwork could be placed under duct tape.
Alternative I didn't have at the time is plastic window film - it is strong, chemically resistant and translucent - perfect for laminating the cell.


Regarding chemical resistance - tank made out if glass and bond by silicone sealant is 100% safe in any acidic bath excluding HF. No matter how strong HCl, H₂SO₄ or HNO₃ you pour into it the glass vessel will not even flinch
Hydroxides are usually safe at low temperature and low concentration assuming they are not used for prolonged time. Especially NaOH and KOH can dissolve silicone seals and glass.
Glass vessel can still be used for strong (even hot) alkali bath if all internal surfaces are painted with thick layer of epoxy.


Just a few experiences and observations.
Please feel free to correct wherever you find appropriate.

 

[zzz]

I use plastic dish with 88% sulfuric without problem, with a little safety sistem to be more sure...i place the plastic elettroplating dish inside a larger plastic dish with cold water to keep temp lower and recovery the gold powder and acid in case of any eventually breaks...I use transparent plastic dish.
If you want to be more sure, diluite the acid to 50/60%, but this will dissolve more nichel.
Than i think is more sure than glass, because the explosive hydrogen could be transform the glass dish in a granade.

 

[FrugalRefiner]

I use plastic dish with 88% sulfuric without problem, with a little safety sistem to be more sure...i place the plastic elettroplating dish inside a larger plastic dish with cold water to keep temp lower and recovery the gold powder and acid in case of any eventually breaks...I use transparent plastic dish.

zzz,

I know this has been mentioned before, but for the benefit of anyone reading this thread, keeping a container of concentrated sulfuric acid inside a container of water is a recipe for disaster. If, for any reason, your water gets into your acid, you'll likely experience a steam explosion that will send sulfuric acid flying everywhere.

You'd be much safer by eliminating the water bath. If your acid starts getting warm, stop running the cell for a while and let it cool down.

Dave

 

[zzz]

I use plastic dish with 88% sulfuric without problem, with a little safety sistem to be more sure...i place the plastic elettroplating dish inside a larger plastic dish with cold water to keep temp lower and recovery the gold powder and acid in case of any eventually breaks...I use transparent plastic dish.

zzz,

I know this has been mentioned before, but for the benefit of anyone reading this thread, keeping a container of concentrated sulfuric acid inside a container of water is a recipe for disaster. If, for any reason, your water gets into your acid, you'll likely experience a steam explosion that will send sulfuric acid flying everywhere.

You'd be much safer by eliminating the water bath. If your acid starts getting warm, stop running the cell for a while and let it cool down.

Dave

FrugalRefiner,

Temp has never exceeded 35/40°C with cooling system. With an eventually break of primary dish i do not think that all the acid will go in contact with water instantly because the plastic can only open and not break, so you have the time to go away if you notice something...said that, i use an amount of water that is the double of sulfuric, so at limit very very diluited sulfuric acid will fly away.

Have you ever thought about what might happen if exploded your glass dish for hydrogen ignition or if it break instantly for any other reason?

 

[FrugalRefiner]

zzz,

I wasn't debating whether glass or plastic was preferable. I also didn't suggest a problem if your primary container failed.

My concern is having water in close proximity to your sulfuric. If something should happen to fall into your water bath, it could splash water into your acid. So a small quantity of water into a large quantity of sulfuric acid = steam explosion which can spray concentrated sulfuric.

If you're comfortable with what you're doing, I probably won't change your mind. As I said in my first post, my concern is for those who may read this thread and not be aware of the risk.

Stay safe,
Dave

 

[zzz]

zzz,

I wasn't debating whether glass or plastic was preferable. I also didn't suggest a problem if your primary container failed.

My concern is having water in close proximity to your sulfuric. If something should happen to fall into your water bath, it could splash water into your acid. So a small quantity of water into a large quantity of sulfuric acid = steam explosion which can spray concentrated sulfuric.

If you're comfortable with what you're doing, I probably won't change your mind. As I said in my first post, my concern is for those who may read this thread and not be aware of the risk.

Stay safe,
Dave

FrugalRefiner,
I'm sure that any break can happen for quantity, temperature and weight under control...using diluited acid is better cause when go in water or water comes in, will not splash.
I'm a chem expert, people there are not, should not do these things regardless of.
Thanks anyway.

 

[Geo]

zzz, you are probably experiencing more contamination then you would if you were using 96% sulfuric. as a chemistry expert, im sure your aware of concentrated sulfuric acids hygroscopic effects on organics (such as plastics and human flesh). plastics are broken down in sulfuric acid in a process referred to as "wet ashing" which is the process of using sulfuric acid to reduce organics to carbon.using a plastic container for a reverse electroplating cell is an accident waiting to happen. it will fail, no doubt about it.its not a question of if but a question of when. comparing a plastic container to pyrex in this fashion saying the pyrex will shatter and the plastic will only crack is not a fact but an opinion. having water in close proximity to concentrated sulfuric acid is what makes it more dangerous that it already is, not whether the container is plastic or glass. im not a moderator and will not attempt to dictate forum policy to you as thats not my job, but you really should include that it just your opinion so that new members will not take it as acceptable process. it is not recommended by anyone on the forum to use plastic containers for a stripping cell or to use a water bath for one.

WARNING : concentrated sulfuric acid will cause severe life threatening injury (especially when hot) and will cause instant blindness on contact with eyes.

 

[zzz]

zzz, you are probably experiencing more contamination then you would if you were using 96% sulfuric. as a chemistry expert, im sure your aware of concentrated sulfuric acids hygroscopic effects on organics (such as plastics and human flesh). plastics are broken down in sulfuric acid in a process referred to as "wet ashing" which is the process of using sulfuric acid to reduce organics to carbon.using a plastic container for a reverse electroplating cell is an accident waiting to happen. it will fail, no doubt about it.its not a question of if but a question of when. comparing a plastic container to pyrex in this fashion saying the pyrex will shatter and the plastic will only crack is not a fact but an opinion. having water in close proximity to concentrated sulfuric acid is what makes it more dangerous that it already is, not whether the container is plastic or glass. im not a moderator and will not attempt to dictate forum policy to you as thats not my job, but you really should include that it just your opinion so that new members will not take it as acceptable process. it is not recommended by anyone on the forum to use plastic containers for a stripping cell or to use a water bath for one.

WARNING : concentrated sulfuric acid will cause severe life threatening injury (especially when hot) and will cause instant blindness on contact with eyes.

Geo,

yes i know all of this..dehydration start with high concentrated sulfuric at temp close to 80/90°C, for this i use a little bit diluited acid.
I repeat that i have under control weight, temperature and quantity of both water and acid, and i feel very sure. The only thing that I'm worried about, is the hydrogen when is trapped in the formed foam, and nobody talk about this, specially when is in glass dish, that trasform it in a dangerous bomb.
If you use more diluited sulfuric is totally sare, because he don't splash out in case of contact with water.

For inexperts, do not try absolutely anything of that, specially if you don't know what are you doing.

 

[Geo]

of coarse there is danger in most everything we do. the best way to reduce the chance of hydrogen explosion is to never connect or dis-connect the power leads while the power supply is on. also, when working with single pieces, be sure to never let the anode come into contact with the cathode. this will result in sparks which could make bubbles of hydrogen and oxygen explode.

but still, i feel its a question of the lesser of two evils. the possibility of an occurrence or the certainty of an occurrence. im not sure that an explosion will happen but i am quite sure that the plastic container will fail due to the acid attack.

and too, using a diluted acid will cause base metal erosion (especially in the case of anode baskets) and the increased contamination (in the form of nickel which will foul the electrolyte) to the gold you are trying to recover.

 

[zzz]

of coarse there is danger in most everything we do. the best way to reduce the chance of hydrogen explosion is to never connect or dis-connect the power leads while the power supply is on. also, when working with single pieces, be sure to never let the anode come into contact with the cathode. this will result in sparks which could make bubbles of hydrogen and oxygen explode.

but still, i feel its a question of the lesser of two evils. the possibility of an occurrence or the certainty of an occurrence. im not sure that an explosion will happen but i am quite sure that the plastic container will fail due to the acid attack.

and too, using a diluted acid will cause base metal erosion (especially in the case of anode baskets) and the increased contamination (in the form of nickel which will foul the electrolyte) to the gold you are trying to recover.

Nichel go in solution as nichel sulfate (green)...for this the sulfuric become green. Contamination is not a problem because in any case you need to refine powder.

 

[Geo]

zzz, the nickel will foul the electrolyte. some members that have gotten to the point that they want to try the reverse electroplating cell may understand the mechanics of cell operation and still not know how to recycle the electrolyte. as nickel dissolves into the electrolyte, not all will precipitate out with the gold. the nickel stays in solution and will eventually stop the stripping action. a novice just starting out will now have a useless solution because they started with a dilute acid and stripped all the nickel and a large amount of copper. if your thinking "why would anyone try this if they dont understand the chemistry?" you havent been here long enough. people do things that go against the grain when it comes to gold. by understanding the way people are and their capacity to do dangerous and harmful things, we can only try to lead and inform in the safest and most economical ways to process material.

im not saying your way is wrong, its just not the way members try and teach this particular process. consistency in processes lets everyone stand on the same ground so when a problem occurs we dont have to play twenty question's to figure it out.

 

[donnybrook]

Years ago I worked at a plant that manufactured hydroflouric acid. The steel tanks used to store the acid were lined with epoxy resin. Perhaps you could use a plastic tub as a mould and laminate some epoxy resin and cloth to it. Use shellac mixed with methylated spirits as a mould release agent?? Just a thought .
donny

 

[Geo]

Years ago I worked at a plant that manufactured hydroflouric acid. The steel tanks used to store the acid were lined with epoxy resin. Perhaps you could use a plastic tub as a mould and laminate some epoxy resin and cloth to it. Use shellac mixed with methylated spirits as a mould release agent?? Just a thought .
donny

again, concentrated sulfuric will carbonize any organic material given heat or time. resins use organic solvents and contain organic compounds. the plastic jugs the acid is packaged and sent out in is very sturdy HDPE and is much thicker than other containers that package other types of materials. i still feel that it will eventually react to the packaging give enough time or heat.

 

[steyr223]

Ok for. Informational purposes only
Dont try this as this. Is what geo was
Saying about people and reckless actions

When i was running my cell to hot due to
Base metals contaminating my sulfuric acid
I had a lot of hydrogen gases
My anode was a steel box that i clamped
A battary cable to with the current flowing
Above my cell .
The resulting explosion was about as loud
As a fire cracker and a small quick fire
On top of the sulfuric followed.
It only took 7 or 8 times before i learned
To turn off the electricity and not check
For spark :shock:
Point; i never had 1 drop splash out of the cell
Unless you some how contained the gases
You probaly dont need to worry of flying glass
Steyr223 rob

 

[butcher]

Now about the possibility of acid flying around well...
Make sure you have a face shield when you wiggle the wire :lol: