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Selective precipitation of gold from aqua regia, leaving PGM in solution

February 25, 2010

I am an analytical chemist for a recycler. I am new to this area and have a question regarding a selective precipitation of gold from an analyte solution of 10% by volume aqua regia. The solution also contains PGM. The gold is used to inquart the sample so the PGM materials are soluble. I would like to be able to recover, and reuse the gold without contamination from the other materials. Can anyone offer any insight to how to accomplish this gold selective recovery?

Thanks so much in advance.

Tom Piotrowski
Analyst - Hebron, Ohio
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March 6, 2010

Ferrous Sulfate is commonly used to precipitate gold without precipitating more than traces of the platinum group metals. However, this can only be done by first removing any free nitric acid still present in the aqua regia solution. This is usually done by first doing a triple evaporation process on the aqua regia solution. Details of all this can be obtained on the goldrefiningforum.com website.

Chris Owen
- Nevada, Missouri, USA


March 12, 2010

Thanks Chris.
But I thought that using ferrous sulfate will also precipitate out any Pd along with the Au. I was hoping for a straight up gold selective precipitating agent.

Can you, or anybody else, please clarify? I may be mistaken on the Pd precipitation.

Again many thanks to all for any assistance.

Tom Piotrowski
- Hebron, Ohio, USA


March 13, 2010

You try oxalic acid .if you are trying to know the purity of gold sample, you prefer fire assay system. Pd will precipitate by ferrous not ferrous sulphate. Using ferrous,reduction takes place.ok consider that FeSO4 contaminate your gold. I suggest that you wash the ppt by hot water to remove acid in it.check by pH paper.than you add nitric acid to dissolve your ferrous and Pd in it.
I hope you will understand the process.

Bhupesh Mulik
jewellery - Mumbai, India


March 16, 2010

Ferrous sulfate won't drop either Pt or Pd along with the gold. About the only contaminate in the gold will be a little iron from the ferrous sulfate. If you have Pt or Pd, it is common to first use ferrous sulfate. Then re-dissolve in aqua regia and drop a second time with a sulfite such as sodium metabisulfite, sodium sulfite, or SO2. If you do this right, you should end up with at least 999.5 Fine gold.

If you use urea to eliminate nitric, however, you could drag down some Pt or Pd when using any precipitant. Either use no excess nitric in the aqua regia or correctly evaporate the aqua regia to eliminate any excess nitric for best results.

An excellent reference for the use of ferrous sulfate in the presence of Pt or Pd is C.M.Hoke's, Refining Precious Metal Wastes [link is to info about book at Amazon] It has been re-printed and is available from several places on the internet - IPMI, legend-reno.com, Ganoskin, etc. If they still sell it, I think Ganoskin has the best price. This 360 page book is the bible for refining jewelry scrap.

Chris Owen
- Nevada, Missouri


February 2, 2012

Q. Hi, over the past few years, I have been recovering gold and silver from ores that contain these metals using aqua regia. I am familiar with CW Amen's book as well as CM Hoke. I now have ore concentrates that have gold, silver, and platinum group metals in it and can't find any detailed information on the correct and complete procedure for precipation of all metals when using Aqua Regia. Any help would be appreciated.
Ken
Joshua Tree, CA

Ken Sheppard
- Joshua Tree, California, USA

January 4, 2013

Q. Hi.

I want to know 2 things if you can help me please?

I dissolved gold ore in aqua regia (AR) and then I used urea until the nitric acid was neutralized. The AR was heated at about 75°. First tried to drop silver with salt and nothing happened. I then used oxalic acid to try and drop the gold but nothing happend for 4 hours. I then switched the heat off and went to sleep. The next morning I went to do a bit of cleaning, and I see that the pyrex dish is full of crystals. Can you tell me what the crystals are and why did no silver or gold drop?

The second thing that I want to know is: Can I elecroplate the gold out of AR? Or maybe electroplate the gold out of the gold ore by itself?
Thank you!

Peter William Van Vuuren
hobby - Johannesburg, South Africa
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