Electrochemistry Interesting idea in an old thread- dissolving gold in a Chlor-alkali cell

[haveagojoe]

While investigating ways to make Hydrochloric acid, I became interested in the Chlor-alkali cell, an electrolytic cell comprising of two compartments containing saline solution and separated by a membrane. On application of a DC current, the electrolyte is reduced to Hydrogen gas at the cathode, and oxidized to Chlorine gas at the anode. Where the electrolyte uses Sodium Chloride (NaCl, aka edible salt), it produces Sodium Hydroxide in the cathode compartment (NaOH aka caustic soda or lye), and the Chlorine produced in the anode compartment is dissolved in, and/or reacted with the water to form Hydrochloric acid. The membrane between the two compartments prevents the two solutions from mixing and neutralizing eachother, while still allowing ion exchange between the electrodes.

At the anode:
2Cl−→Cl₂(g)+2e−

Cl₂+H₂→2HCl

Cl₂+H₂O→HCl+HOCl
- note: HOCl is Hypochlorous acid, which is unstable and wants to lose its Oxygen to become HCl


At the cathode:
2H2O+2e−→H₂(g)+2OH−

This struck me as a simple and very useful proposition for the hobbyist, particularly in areas where HCl is not readily available. There are a few videos on YouTube which show the process using a pair of plastic cups connected with a tube which is stuffed with cotton wool to form the membrane.

Then I came across this little nugget of an idea from an old thread: https://goldrefiningforum.com/threads/do-someone-have-experience-with-this-process.14308/post-143666
@Palladium seems to be proposing to leach gold directly in the anode compartment of the cell, using the Chlorine as it is generated there. I found this a fascinating concept and worthy of revived discussion, I hope it will pique the interest of other members as it did mine.
Sadly @Palladium has not been active for a while so we may not be able to ask him about the idea.

 

[orvi]

This particular setup would be little bit hard to maintain due to that membrane requirement. Chlorine generator is a useful thing to have, if you want to go away from using nitric in bulk. You can very easily produce chlorine gas and use that as oxidant instead. This combo 2 in 1 is even more interesting, but there will be one big problem and that being cross-contamination of compartments. But if you can source membrane materials which are used in industrial membrane process of making Cl2/NaOH - then you probably won

I got an even better idea while reading this... I´ll test it and if it works, ... Okay chances are low, but this would be a big gamechanger

 

[haveagojoe]

if you can source membrane materials

There are a few DIY options used in the Youtube videos, one is vegetarian gelatin, set in the tube; but the most promising seems to be terracotta clay as used to make plant pots. That apparently allows the use of higher currents.

I have been pondering the practical setup:
Firstly how to connect the two compartments easily- I think an "up and over" layout like a salt bridge might be easier to make than a horizontal tube;
Secondly I was wondering if the anode compartment could be sealed, venting through a pipe to a third compartment where it would bubble through water, to recover and dissolve gas which escapes from the electrolyte, thereby producing more HCl.

Youtuber Scrap Science has made some interesting setups- though he is focussing primarily on the Sodium Hydroxide generation side, it's the same process.

 

[Yggdrasil]

There are a few DIY options used in the Youtube videos, one is vegetarian gelatin, set in the tube; but the most promising seems to be terracotta clay as used to make plant pots. That apparently allows the use of higher currents.

I have been pondering the practical setup:
Firstly how to connect the two compartments easily- I think an "up and over" layout like a salt bridge might be easier to make than a horizontal tube;
Secondly I was wondering if the anode compartment could be sealed, venting through a pipe to a third compartment where it would bubble through water, to recover and dissolve gas which escapes from the electrolyte, thereby producing more HCl.

I'm sure if you poke around you will find Muriatic acid around 21% in hardware,
chemical suppliers will carry 31-36% and a plain business license should do for that.
It sure will be cheaper than making it from scratch.
Nitric can also be made but also bought, check with the authorities what kind of licensing they need.
If you have all the papers in order there should not be any stress regarding inspections and such.

 

[haveagojoe]

I'm sure if you poke around you will find Muriatic acid around 21%

Unfortunately 10% is the legal limit now without a licence.

 

[Yggdrasil]

Unfortunately 10% is the legal limit now without a licence.

What are the requirements for a license?

 

[haveagojoe]

What are the requirements for a license?

I think I would need to register as a business. I'd love to do that one day but for now my funds are very limited so I'm just a backyard hobbyist.

 

[Yggdrasil]

I think I would need to register as a business. I'd love to do that one day but for now my funds are very limited so I'm just a backyard hobbyist.

Here, you can register as a one man personal company, no registration fee.
That was sufficient for my current supplier, but for the other chemical companies a larger company form is needed.
Check around, it may not be as hard as you believe.

 

[haveagojoe]

Here, you can register as a one man personal company, no registration fee.
That was sufficient for my current supplier, but for the other chemical companies a larger company form is needed.
Check around, it may not be as hard as you believe.

Yes I will look into it, I have owned a limited company before, but the chemicals licence is issued by the government not the chemical supplier, I think I would need do demonstrate my requirement, show business premises and COSHH compliance and so on, there's a bit of a leap from what I do now to the next level.