# Gold refining cell



## elfixx (Sep 26, 2009)

Would it be possible to make a extra small electrolitic gold refing cell to refine 99% gold to 99.99 . By extra small I mean 4-5 ounces at a time. I am not familiar with those type of cell could anyone guide me in making such a device? I was thinking about purchasing cell's equipment from Lasersteve website, would these be suited for that kind of work? Basicly what do I need to get ? Let's say I use a 1L pyrex beaker as the container, then I would have to cast/roll thin sheet of fine gold, attach them to + current, dip em in 30% nitric, set a stainless plate as the collecter with - current on it and regularily collect gold electrolite?


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## 4metals (Sep 26, 2009)

Sure it's possible, it just isn't practical. First off you have to set up a cell, a fizzer cell is one option, to make your gold chloride electrolyte, you will have to commit the gold in solution to stay in solution for the useful life of the cell, until the impurities rise to the level at which you have to refine the electrolyte and start over. 

How are you getting the 99% pure product to start off with? You have to refine it to 99% and I doubt you're using the Miller process. The electrolytic cell only pays when you can get to the 99 fine stage quickly and easily with large quantities of gold, otherwise there are other options.

This method works for small or large lots. 4 to 5 oz lots would be very easy.

Inquart your gold with silver.
Digest in 50% nitric acid
Filter solution.
Cement out the silver and PGM's The 3:1 silver will take all traces of Pt and Pd with the silver
Rinse the gold that is in your filter, it's 99. fine or better already.
Place the gold in Hydrochloric acid
Add sodium chlorate to dissolve the gold
Filter the solution, main impurity is silver so chill the acid add cold water and you will get a solution with very little silver in it.
The solution does not have to be boiled to remove nitric because you never added nitric so the classic three times to remove the traces of nitric is unnecessary.
Bring the solution temperature close to boiling. This makes the oxalic work faster.
Precipitate the gold with oxalic acid solution also close to boiling
When all of the gold drops, filter, wash, and melt
Should be 99.99 fine and its done quickly


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## elfixx (Sep 26, 2009)

That is prety much the standard procedure I actualy use exept I use SMB to drop gold, I tryed oxalic acid once and it didn't work, I guess the precipitation only start after a while when it's boiling hard. I am looking for a method that will yeild .9999 gold at each and every time, the best I can get with SMB is .998. Since I have no way to find BDG in Quebec I have to find another route.


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## 4metals (Sep 26, 2009)

Can you get SO2? Production refineries all over the US get 99.95+ using gas with a single drop. If you inquart to remove the base metals and silver you should be able to do better. You're actually double refining it.

What are your major contaminants? Do you have a good vacuum filter?


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## elfixx (Sep 26, 2009)

I always inquart with silver then refine using AR, drop with SMB then refine it once again with AR drop with SMB. AR is always filtered using a buchner funnel with no1 whatman filterpaper along with a vacuum filtration flask.


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## 4metals (Sep 26, 2009)

Good strong vacuum source? Your gold comes form jewelry scrap? You inquart, digest in nitric then digest solids in AR. Do you use urea to get rid of excess nitric?

Your major impurities are most likely silver and copper. Try an ammonium hydroxide soak with the sponge after you rinse with hot water. That will dissolve both copper and silver. You are actually dropping the gold 3 times, it should be better than you are getting. What grade of SMB are you using? Are you chilling the AR with ice before filtering?


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## Oz (Sep 26, 2009)

When dissolving silver with ammonium hydroxide be sure to acidify the resulting solution afterwards. Dangerous compounds are formed when drying if not acidified.


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## Gold (Sep 27, 2009)

elfixx said:


> I am looking for a method that will yeild .9999 gold at each and every time.



:shock: :shock: :shock: :shock:


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## Noxx (Sep 27, 2009)

Lil' cat has something in his mind...


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## elfixx (Oct 3, 2009)

I am going to try to build a small scale electrolitic cell to try it and understand how it work. Hoke's book has quite some good info on it but I still need some help. As stated in hoke's work, the cell need a electrolyte solution of about 80g to 100g disolved gold per litre, so I am planing on scaling my cell to a pyrex 1L beaker with about 300ml of gold electrolyte ( less than 1 troy oz of gold). 
Here is what I'm wondering now:

Is there a minimum or maximum distance between the anode and cathode to respect?
Will disolving fine gold in AR and then nutralising with urea going to make a proper electrolyte solution?( I know I must add some free HCL)
What Amp/ voltage is optimal for efficient pure gold plating?
Can the cathode be made of stainless steel or does it have to be very fine gold to insure electrolitic grade gold finess( .9995-.9999)?

Maybe if a few people share their knowledge on this topic we could help many( including myself) understand the electrolytic refining process. I am prety shure I am not the only one interested in this process.


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## goldsilverpro (Oct 4, 2009)

Here's a pretty good discussion of the Wohlwill cell. On pages 271-276.
http://books.google.com/books?id=MQANAAAAYAAJ&pg=PA272&dq=wohlwill&lr=&as_brr=1#v=onepage&q=wohlwill&f=false

The urea most likely won't work. The electrolytic fizzer cell mentioned by 4 metals is commonly used to make the solution. It uses a porous cup (essentially, a membrane), that separates the anode chamber from the cathode and prevents the gold from plating out. HCl is the electrolyte. The gold dissolves as HAuCl4.


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## elfixx (Oct 4, 2009)

In fact, AuCl3 is needed to make the electrolyte, which is made of AuCl3 + 10% (1/10 volume)HCL. Disolving gold in AR yeild HAuCl4 which is not suitable for electrolyte making. I have seen AuCl3 marked on Lazersteeve jar many time in his video from his website, is that actualy real AuCl3 that have been produced with the HCL-Clorox use? If this process can efectivly produces AuCl3 and not HAuCl4 that would be the easyest way to make the electrolyte solution.



EDITED BY LOU:

Actually, adding gold (III) chloride, AuCl3 to water will produce HAuCl4. Steve's beaker is actually mislabeled.


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## elfixx (Oct 4, 2009)

I have also found that the cathode can be made of titanium instead of pure gold. And as I am thinking to it, adding HCL to AuCl3 is in fact making HAuCl4 right??? wouldn't that mean that you can make the electrolyte out of disolved gold in AR with the exess nitric boiled off??


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## 4metals (Oct 4, 2009)

If you insist on electrolytic gold refining there are a few things you should keep constant.

First the cathode should be pure gold foil, scraping cathodes just is a messy pain, if it’s gold on gold all you have to do is rinse and melt. Keep the cathode size constant each time you change it because you want to run at a constant current density so keeping your anode and cathode size constant simplifies power requirements.

You can make up the gold chloride using aqua regia and boiling off the nitric, time consuming but do-able.

Keep the distance between the anodes and the cathodes constant, and perfectly parallel to each other. Make a fixture to fit over the beaker to hold the anode and cathode rods so they remain fixed and parallel. The reason for this is the distance between the anodes and cathodes affects the current density. When the cell approaches the end of its useful life, the impurities will plate out at different current densities than the pure gold so you want to keep the cells current density in the range you find to produce the purest gold. 

Current densities can vary from very high when the free HCl is higher to very low. I set up cells running at 17,5 to 20 ASF with a voltage of 2.3 to 2.5 Volts.

Temperature can vary as well, 60 C is the hottest I’ve seen run I like 20 C.

Now for what you don’t want to hear, the reason the cell is ineffective for small production is all of the analytical work needed to run in the “sweet spot”, the range where the impurities in solution are low enough to remain in solution and not plate out on the cathode, thus contaminating your pure gold. Generally the kind of lab you need for control is only available to larger, better financed refiners. 

I pulled Hoke’s book off the shelf to review a few facts and low and behold this is what she had to say, and I quote;

In this writer’s opinion, however, the electrolytic methods cannot be operated economically by the non chemist working alone. It is believed, further, that present electrolytic methods are rarely suited to small scale operation, even under the supervision of a trained electro-chemist. It is true that small systems have been set up – cells holding about a quart of gold chloride, for instance. In such a cell a trained worker can produce cathode gold of as high quality as he might desire, with mental satisfaction, (I like that phrase!) no doubt, but probably at unduly high cost, and the small cell will require almost as much attention as an acid system handling many times the amount of metal per day. And it is a matter of record that electrolytic systems of considerable size have been installed and later abandoned, usually for economic reasons.

I have found from practical hands on experience that refining small lots using classic aqua regia will yield less pure gold than running larger lots with the same methods. A lot of forum members experience this difficulty and have to revert to other options.

Inquarting is one of the pre refining techniques that will allow small lots to be refined to high grade gold. If necessary, add an oxalic acid precipitation to the aqua regia digestion after the inquarting process will give you what classical assayers called proof gold. Probably 99.99 fine or damn close.

I guess if you are looking for mental satisfaction, then go for it! You can also achieve the purity you are looking for with wet chemistry and in my experience, that brings mental satisfaction as well.


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## 4metals (Oct 4, 2009)

Whoops I forgot about the trees. Be careful not to place the anodes too close to the cathodes because the pure gold can grow in irregular crystals which resemble trees. If you are running a cell that will run un-attended or overnight, the trees can short out the cell if they grow to the cathode.


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## elfixx (Oct 4, 2009)

Wow that is some very nice and usefull information, thank you very much 4metal. But I must admit, as you insisted on it, that electrorefining is propably not a usefull and worthy way to chose for small quantity, and I will try different approach in my AR refining technique before trying the electro cell. But still, I am very interested in this process and those info you just gave are just awesome, I will shurly try it in the few next month. But for now I am going to try to get a succesfull oxalic acid precipitation. Hoke suggested to add a tablespoon of ammonia to the water/oxalic acid mix, is it necessary? and what is the purpose of the ammonia? She also suggested to pour the AR into the oxalic acid mixture, is this the proper way to go?


Thank you once again for all those info


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## Oz (Oct 4, 2009)

4Metals,

Seeing as you went this far, how many grams per liter did you use for a starting electrolyte?


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## elfixx (Oct 4, 2009)

From what I have readed you need conc. of 80g to 100g per litre of solution


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## 4metals (Oct 4, 2009)

Gold Chloride solution

Different concentrations work better for different current densities. I prefer 32.15 grams per liter. My reasoning is accountability in the set up of a new cell, makes life easier for the bean counters. 

Oxalic acid

Hoke mentions using ammonia, and solutions almost boiling. I've done it and it works. I poured the gold solution into the oxalic solution like she says. Gold comes down quick! 

Other classic assaying texts don't mention the ammonia and I've done it that way as well but only warm. The gold was always there in the morning. I kept the beaker on a warm hotplate with a watch glass overnight.


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## Oz (Oct 5, 2009)

Thank you for that 4Metals, beyond the use of a starting point that is indeed a nice little gem for accountability of in-process material.


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