# Gold electrorefining cell



## elfixx (Aug 15, 2010)

I just started making test on the electrorefining of gold and noticed something I simply cannot explain. I use 1 quart of HAuCl4 as the electrolite, made from aqua regia boiled and dilluted with water and about 10-15% HCL. The electrolite have a 35g/L concentration. I run the cell at about 2.5v at 1.5-2 amp. Yesterday I started the device and the anode started bubling prety strongly and it produced strong AR smell as well. I switched it off after a few hour of work then I came back this morining and turned the power on, this time there was no noticable action at the anode. Can anyone explain why it strongly bubbled yesterday and absolutly nothing this morning? Does that mean the anode ain't disolving and I am currently depleating my electrolite?


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## goldsilverpro (Aug 15, 2010)

I would first weigh the dry anode and then run it at a constant amperage for an hour - then, rinse, dry, and re-weigh. At 100% efficiency, assuming you are producing all valence 3 gold, the anode should lose about 2.45 grams per amp-hour (amps X hours). It should be very close to this. Do the same with the cathode to check the gain in weight. If they are not very close to being equal, something is out of balance.

What temperature is the solution? What is the surface area of the anode facing the cathode? Is the 10-15% HCl by weight or by volume? What is the starting purity of the gold anode and what impurities does it contain?


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## elfixx (Aug 15, 2010)

The solution is at around 25C, the anode is a round 1inch diam. 98% gold button containing silver and copper as impurity. The cathode is made of titanium foil, the submerged part is about 4sq inch.


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## elfixx (Aug 16, 2010)

There is defenitly something wrong. I scraped the cathode, melted and weighted both the anode left over and the cathode deposit. 
Here's the result:
Anode initial weight: 39g
Melted anode left over: 6g
Cathode production: 44.5g of not so pure gold
Difference: almost 12g sucked out of the electrolite

Am I using too strong of a current? I ran the cell 2.5-3v at about 2amp.

Thank you


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## Harold_V (Aug 17, 2010)

elfixx said:


> There is defenitly something wrong. I scraped the cathode, melted and weighted both the anode left over and the cathode deposit.
> Here's the result:
> Anode initial weight: 39g
> Melted anode left over: 6g
> ...


Was the anode relatively pure when you started? If not, did it contain much silver?

Regards the deposit, it is commonly accepted that it will be nodular in appearance, and may not look good. That isn't necessarily a sign of impurity.

Talking more about your cell and the feed stock might be helpful. A gold parting cell, like a silver cell, is very best suited to parting relatively pure material. If you process alloys, it isn't likely to yield great results. 

Harold


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## nickvc (Aug 17, 2010)

I have to agree with Harold the only decent size cell I ever saw working was fed slimes from silver cells and gold that had been through inquartation to remove the majority of base metals and silver.


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## elfixx (Aug 17, 2010)

It was in fact prety pure, the anode was made of smb precipitated gold. Probably around 98-99%, impurity being mostly silver and copper.


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## nickvc (Aug 17, 2010)

Another memory just came back I remember that the solution was made up of very high purity gold .999 and the anode was in a bag to catch any pgms etc and the amount of gold in solution was also fairly critical.Don't know if this helps but I had very little to do with the cell as it was installed and run by the director and his senior chemist but details of a gold cell and it's make up are available on the web.


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## goldsilverpro (Aug 17, 2010)

elfixx,

About the only thing I see that could be a problem is the temperature. Most all references I can find call for about 65C (149F).


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## elfixx (Aug 17, 2010)

I just tought about something, I setted the voltage once the cell anode and cathode were hooked to the rectifier instead of setting it before. Which might mean, adding the system resistance the input voltage could have been too high even if the gage on the rectifier was showing 3v. What I mean is that I should set the voltage first and then hook it to the cell. Too much voltage could have lead to impurity plating along with the gold. Plus, the surface of the cathode is about 0,03 square foot, running at 1.5-2amp(49,5-60 amp per square foot) is way above the 17amp per square foot suggested in most documentation, which could explain the surplus metal plating on the cathode vs the disolving rate of the anode. I am going to further experiment on this subject and I'll post result as soon as I can.


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## elfixx (Sep 19, 2010)

Finaly got the result I was looking for, electrolitic grade gold :lol: . Absolutly no sign of oxide or impurity when melted. I guess the secret when using a low concentration electrolite (35g/L) is to use very low voltage. I ran my cell at 1.5v for 70 hour and yeilded 90g. I'll post pics on my next batch.


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