Electrolysis solution longevity

[RedShirtGuy]

I've just made up a 100+lt solution of water/lectric soda (1lt/10gm) in a large camping esky and currently derusting a spindle molder table.
I don't have much other use for the solution at the moment but it would seem to be a shame to pour it down the drain after one use.
Any ideas on how long the solution might "keep" for before becoming useless?

[BobL]

It depends how clean it is. I use carbon anodes which keeps the electrolyte cleaner than use ferrous anodes so I can keep and re-use mine mine for years but I also value my space so there's no way I'd be keeping 100L of it. If you have the space then no worries.

[RedShirtGuy]

YEARS!!!! Holy heck!!!
I'm using two stainless rods for anodes and scrub them between sessions, outside of the solution, and if I was really tight I'd pour out the top part of the clean solution and top it up if I was doing this regularly.
I've got the space I guess...the esky isn't used and takes up room by itself, so why not fill it up :D
Thanks B. Great answer :)

[BobL]

SS is not the best material to use as an anode as it contains Cr and may make the electrolyte toxic. This then become as problem for disposal. I need to do a small scale experiment to confirm this. Carbon electrodes rarely have to be scrubbed and the resulting electrolyte is non-toxic.

[RedShirtGuy]

:2tsup: to that, but I rarely do these rust removal runs. Very good to know otherwise.
I scrub the anodes between each session just for the hell of it.
Disposal = emptying of each deprived solution...at the point of efficient removal.

[ian]

I think that Bob is hinting that if the stainless anodes contain enough Cr, the solution could become toxic partway through a de-rusting session

[BobL]

I think that Bob is hinting that if the stainless anodes contain enough Cr, the solution could become toxic partway through a de-rusting session

Thanks for clarifying Ian. Yes the Cr in the SS will dissolve into the electrolyte which means the solutions should not be disposed of down drains or dumped onto the ground if there is a chance of it finding it's way into water ways. Even in really dilute form, some Cr solutions are highly toxic to aquatic organisms. It's also not just the solutions. Because gas is produced by electrolysis the breaking bubbles will create lots of tiny aerosols/droplets which means if done inside a shed the air may become toxic as will all the surfaces. Risk is lowered by using ventilation and reduced usage however this does not take into account individual sensitivities to Cr.

Like I said WIGRTI I will do an experiment to determine the amount of Cr liberated from SS into an electrolysis solution and compare that to the OHS standards for Cr workplaces etc.

[ian]

Yes the Cr in the SS will dissolve into the electrolyte which means the solutions should not be disposed of down drains or dumped onto the ground if there is a chance of it finding it's way into water ways. Even in really dilute form, some Cr solutions are highly toxic to aquatic organisms. It's also not just the solutions. Because gas is produced by electrolysis the breaking bubbles will create lots of tiny aerosols/droplets which means if done inside a shed the air may become toxic as will all the surfaces. Risk is lowered by using ventilation and reduced usage however this does not take into account individual sensitivities to Cr.

Like I said WIGRTI I will do an experiment to determine the amount of Cr liberated from SS into an electrolysis solution and compare that to the OHS standards for Cr workplaces etc.
perhaps waiting for you to have the time to do an experiment to determine toxicity is not as straight forward as just outright suggesting that using stainless electrodes is a really, really bad idea.

Sadly, my heavy metal expert passed away 8 years ago.

[ian]

Sadly, my heavy metal expert passed away 8 years ago.
but a quick inquiry of Dr Google found these gems:


Many people using the electrolysis method for rust reduction swear by stainless steel, stating (incorrectly) that it's not consumed, stays clean and seems safe.

Stainless steel is indeed consumed when used in the electrolysis process, although slowly. The main problem with using it is the hazardous waste it produces. Stainless steel contains chromium. The electrodes, and thus the chromium is consumed, and you end up with poisonous chromates in your electrolyte. Dumping these on the ground or down the drain is illegal. The compounds can cause severe skin problems and ultimately, cancer. Hexavalent chromate is poisonous. These compounds are not excused from hazardous waste regulations where household wastes are.

These compounds are bad enough that government regulations mandate "elimination of hexavalent chromate by 2007 for corrosion protection."

Does your electrolyte turn yellow? That's a sign of chromates.

If you have been using stainless steel for the anodes (positive electrodes), wear rubber gloves when working with or near the liquids. If you need to dispose of it, allow it to evaporate into powders and dispose of the powders in sealed containers during your local "hazardous waste clean-up days".

Best bet - don't use stainless steel no matter how tempting it is.



and

Chromium is an element. It is forever. There are all sorts of LAWS concerning how you must handle waste containing it. Reducing Cr(VI) to Cr(III) does reduce the hazard, but does not eliminate it. You can not legally dump caustic solutions down the drain in the USA, which means using NaOH is a really bad idea. It is against the law.

Chromium is fairly easy to trace through a sewer system; that means if you dump it, be prepared to spend some time in jail.

[BobL]

Thanks Ian, I've posted the same info as you posted above in these forums several times in the last decade.
The last time I think may have been when the metal work forums were part of WWF.

I still want to do the experiment even if its just for my curiosity. I will do the experiment on a very small scale and can do it safely as I have a suitable fume hood in my shed and can also dispose of any possible Cr waste though my uni contacts. What I suspect happens is folks use car battery chargers for electrolysis. The resulting 12V is completely unnecessary and results in significant anode erosion and the production of large amounts of gasses (ie aerosols) and Cr contaminated electrolytes. What I want to investigate is if a suitable (ie lower) V is used with SS anodes whether this effect can be minimised or eliminated.

[ian]

The chemistry will be the same whether you use a 12V car battery charger or a computer power supply or another source of electrons.
The speed of the reaction and hence rust conversion / removal should vary with the input current. As might the formation of aerosols.

If you do do the experiment are you set up to
1. measure the Cr content of various stainless steels -- and how would a "typical" user know which stainless steel they had if the source is an old piece of cutlery or a bit of rod from a recyclers?

2. measure the concentration of Cr in the solution?

3. measure the "loose" or free Cr on the surface of the anode when it is extracted from the solution for "cleaning"


I can see where the experiment might satisfy your curiosity, BUT in terms of educating forum members and visitors, I think the responsible approach is to "just say no" to stainless electrodes.


I'm sure that you are aware that if you're a middle aged male, the ingestion of a small amount of lead is not all that harmful, but if you're a child or a fertile female ingesting the same amount of lead (by body weight) can be very harmful.

I don't know, but the same is possibly true for Chromium.

[BobL]

Ian, I agree - the experiment is for my own curiosity only. I have a medical condition called Sarcoidosis and exposure to heavy metals is possibly a cause of this so I interested to know if previous exposures may have contributed to this.

FWIW I have performed a number of Cr investigations going back as far as my Masters when I measured Cr in waste engine oil using Neutron Activation Analysis. Then in the USA I spent 2.5 years as a post doctoral Fellow measuring amongst other things, ultra trace amounts of Cr in meteorite grains by Isotope Dilution Mass Spectrometry so I am very familiar with the chemistry side of Cr.

RE: Kids and pregnancy.
That's what I meant in part by
"Risk is lowered by using ventilation and reduced usage however this does not take into account individual sensitivities to Cr."

[ian]

ventilation might reduce risk for the person doing the electrolysis, but I'd also worry about material tracked inside on the person's clothing or footwear.

[dinosour]

Just a thought, is pure dc i.e. from battery or regulated power supply better than that from an unfiltered battery charger ?

[BobL]

Just a thought, is pure dc i.e. from battery or regulated power supply better than that from an unfiltered battery charger ?

Not really - the problem with using any 12V supply is the resulting current can be unnecessarily high even if dilute electrolyte is used. The higher currents produce large volumes of foam which traps hydrogen and oxygen in the bubbles which besides being dangerous can lead to hydrogen embrittlement of parts . The higher currents builds up sludge on steel anodes meaning they need to be regularly cleaned.

Only a few V is required to perform adequately electrolysis and its better if it goes slowly so the gasses get time to dissipate - suggest you do it outside if you do not have adequate ventilation. If you are budget conscious then something like an old PC power supply can be used and use either the 5 or 3.3V outputs which have a max currents of 20A+ so this is not an issue for most electrolysis. There are a zillion "How tos" on the web showing how to set one up safely.

If you have a variable V supply you can optimise the current by adjusting the V but if you don't have a variable V supply then you can vary the current by altering the concentration of the electrolyte/solution. Before I had a variable V PS I used the 3.3V output of a PC power supply and a dilute electolyte, then I mixed in small amounts of concentrated electrolyte slowly till the current reached 4 -> 5 A.

[ian]

I'd suggest going a step further.
The chemistry is the same regardless of whether the power supply is filtered or unfiltered, 3 volts or 12 volts.
the rate of the reaction varies with the power applied which from memory is Volts x current -- the numbers in Bob's example equate to about 15W

[RedShirtGuy]

Hey, thanks guys. I failed chemistry in a big way at school (spent too much time piping water into the gas lines :B) so I'm really enjoying this read and lessons.
I was always under the assumption that SS was they way to go for the anodes...that how it's always been in my readings over the years...so this new info is great to have and quite interesting, particularly in regards to toxic contamination of the solution. The hydrogen bubbles were always just a bit of fun to know about, but I do try to keep the area ventilated just in case of "kabo0m" :)

[ian]

I was always under the assumption that SS was they way to go for the anodes...that how it's always been in my readings over the years...so this new info is great to have and quite interesting, particularly in regards to toxic contamination of the solution. I wouldn't describe it as contamination -- as far as I know, the presence of Chromium salts has no impact on the effectiveness of the solution.


The hydrogen bubbles were always just a bit of fun to know about, but I do try to keep the area ventilated just in case of "kabo0m" :)
the ventilation suggested by Bob is is less about a possible KABOOM and more about dispersing the aerosols which potentially are a source of ingested chromium (VI)

[BobL]

I wouldn't describe it as contamination -- as far as I know, the presence of Chromium salts has no impact on the effectiveness of the solution.

the ventilation suggested by Bob is is less about a possible KABOOM and more about dispersing the aerosols which potentially are a source of ingested chromium (VI)

Actually I was just as serious about a KABOOM , there are several vids on other forums using typical battery charger setups that have resulted in explosions.

Typically what happens is containers are used that are too tall, sometimes covered, and the higher voltages produced too much current hence too much hydrogen.

Then instead of switching the PS off, wires are just disconnected from the objects being electrolysed and any resulting small spark ignites the gasses.

The worst one was a guy using a 200L plastic drum about half full of electrolyte. The explosion set his eyebrows and hair on fire but fortunately it was put out by the 50 odd litres of filthy brown orange electrolyte ejected out of the drum. He also soiled his pants in another way during the process.

[russ57]

I'd love to know more about how the ss is dissolved. I've always thought of electrolytic cleaning as a sort of 'reverse plating' where the oxide on the anode is removed as though it was the plating metal and moved to the cathode where it doesn't actually plate because it is not compatible (so to speak).

So in my mind the ss should be completely inert.

Apparently I am wrong!


Russ

[BobL]

I'd love to know more about how the ss is dissolved. I've always thought of electrolytic cleaning as a sort of 'reverse plating' where the oxide on the anode is removed as though it was the plating metal and moved to the cathode where it doesn't actually plate because it is not compatible (so to speak).

So in my mind the ss should be completely inert.

Apparently I am wrong!

Russ

Actually you make a good point, but it sounds like you are referring to using anodic cleaning.
Most DIY think of electrolysis as a way to convert rust to metal process whereas practically none of the rust is plated back onto the workpiece surface - instead the rust is actually removed or cleaned.

There are two forms of electrolytic cleaning: from https://www.corrosionpedia.com/definition/442/electrolytic-cleaning


Anodic electrocleaning - The workpiece is made the anode in the system. This is performed in a basic solution to facilitate the oxidation reaction 4(OH)- = 2H2O + O2(g) + 4e-. Oxygen gas bubbles are generated directly at the workpiece, beneath the contaminant, which helps lift and remove the rust, deposits and light oils.
Cathodic electrocleaning - The workpiece is made the cathode and a reduction reaction occurs at the surface. In this case, the pH of the system needs to be acidic to provide sufficient hydrogen ions to sustain the reaction 4H+ + 4e- = 2H2(g). In the same manner, it lifts deposits like rust or oxide from the metal surface.

Most DIYers use cathodic cleaning with basic solutions because then you cannot damage the surface of the object being derusted even if you leave the work piece in there for a long period. The belief is longer must be better which is not always the case. If an acid is used and forgotten about the workpiece will dissolve over time.

If anodic cleaning is used the electrolyte must be kept basic and be done for a very short time period otherwise the continual generation of oxygen at the surface will also dissolve your work piece.

The most efficient electrolytic cleaning uses repeated pulses of cathodic and anodic cleaning.
However, the time periods involved are in the seconds to minutes range.
Apparent this also helps keep the electrodes clean so no wiping is need

I have tried anodic cleaning but wanted a set and forget method so I switched to cathodic cleaning with an carbon anode.
I should go back and give the anodic method a try now that I have some more controllable PS.
In recent times I have been using oxalic acid as a rust removal process. Although it is relatively slow its a dunk and forget about process and does not dissolve any of the steel.

What time periods are you using for your anodic cleaning Russ?

[russ57]

I just use a few teaspoons of caustic soda in a few gallons of water but I was using 36v.
Cleaning time usually a few hours.

A little bubbling but not a lot so I assume a low current. (the ps is regulated to 4a so less than that but I didn't ever measure it.)

A large (say 200x350) as plate as electrode


Russ

[BobL]

I just use a few teaspoons of caustic soda in a few gallons of water but I was using 36v.
Cleaning time usually a few hours.

A little bubbling but not a lot so I assume a low current. (the ps is regulated to 4a so less than that but I didn't ever measure it.)

A large (say 200x350) as plate as electrode


Thanks Russ,

Back of the envelope calculation , 3 tsp in coupla gallons is about 15g in 10L, 1.5g/L which will have a pH between 12 and 13.
I'm surprised you don't see any pitting over about two hours.

I use Sodium carbonate (foot bath salts) about 40g/L which has a pH of about 12.
With < 6V with resulting currents are between 3 and 4A and cleaning generally takes so it takes between 4 and 6 hours
However, I'm using cathode cleaning which is know to be slower - I will give anodic cleaning a go next time.

[russ57]

Possibly more like 40l

I'm surprised that the pH would be that high but I've not really considered it.
I havent observed pitting but if I did I would put it down to the result of the rust not the cleaning.




Russ

[BobL]

Possibly more like 40l
OK so ~8 gallons, that would make it about 0.4 g/L so pH around about 12.


I'm surprised that the pH would be that high but I've not really considered it.
I havent observed pitting but if I did I would put it down to the result of the rust not the cleaning.
Fair enough.

[B & HA]

Some great advice on this thread about removing rust.

I, however, have a different problem...

I need a load of rusty nails.
If I put a load of steel nails in some sort of steel mesh bag, on the positive terminal, and dipped it into the bucket with an old rusty horseshoe, on the negative terminal, would it make my new nails look old?

Sounds a bit complicated I know, but a bit of advice would be appreciated. Thanks

[BobL]

Some great advice on this thread about removing rust.

I, however, have a different problem...

I need a load of rusty nails.
If I put a load of steel nails in some sort of steel mesh bag, on the positive terminal, and dipped it into the bucket with an old rusty horseshoe, on the negative terminal, would it make my new nails look old?

Sounds a bit complicated I know, but a bit of advice would be appreciated. Thanks

That will pull metallic iron off the nails and leave behind an orange sludgy mess which will wash off leaving a black pitted surface (is this what you are after?) which will then develop a patina of thin rust if left exposed to air. If you want them to finish up with reasonably thick flakey layers of rust on then you will then have to leave them exposed to air for some time..

Either way any oil/grease dirt etc should be removed by using suitable solvents etc.

If you want the nails to have a thicker layer of rust you might get a quicker result by dunking them in hydrochloric acid for a few minutes and then laying them out so they are fully exposed to air. To speed things up, if they dry out spray them with dilute HCl every day they should work up layers of rust.

The RHS cog was sprayed with vinegar and shows what happens. The rust is friable (physically not robust) - if you want robust layers of rust you have to let it develop by itself in moist warm air.

458581.