# EDTA Gold "Precipitant"



## Gratilla (Feb 13, 2013)

I stumbled upon this oldie (but goodie) from a 2007 post by GoldSilverPro, while searching chelating agents:



goldsilverpro said:


> In 1969, I was head chemist for a large refinery in L.A. Our Wohlwill Cell (gold purification cell) solution was often too contaminated with base metals and required frequent solution changes, in order to maintain high purity gold. I started experimenting with ways to extend the life of the solution. We had a well stocked lab and had quite an assortment of chelating agents. Most were variations of EDTA. Chelate comes from the Greek word Chelos, which means "claw". It grips metals in several places, like a claw, and holds them in solution. I figured that, if I added EDTA to the solution, it would chelate the base metals and prevent them from plating out with the gold.
> 
> When I added the specific type of EDTA to asample of cell solution, all of the gold dropped out. Surprise, surprise. For about a hour, I was very disappointed. I really thought it would work. Then, it dawned on me that I might have a new precipitating agent for gold. I started doing lots of experiments and maximized the process. We melted several batches of gold dropped from heavily contaminated aqua regia, under pristine conditions, and sent off samples to be analyzed for all impurities. To my amazement, none were under 99.99% pure. Some approached 99.999%, believe it or not. Some of these aqua regia solutions were intentionally contaminated with all of the platinum group. Still, the gold was above 99.99% pure, with only one drop. I'm not saying that the company always shipped 99.99% gold, because they could introduce impurities during the melt. I am saying that the powder was most always 99.99%.
> 
> ...



and in a follow up by GSP:



goldsilverpro said:


> Use Dow's Versonal 120 to drop the gold and you'll always get 9999. It's an EDTA derivative that chelates the base metals and prevents their precipitation. It's my invention, by the way. After I saw it worked, it took a couple of months to perfect it. I'm including it as a chapter in my book.



Worth repeating. This post is already long enough so I'll save my comments/questions for later.


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## Lou (Feb 13, 2013)

I have used Versenol quite a bit now. It's nice and works as GSP advertised but it has issues with waste treatment because it is an effective chelant for Cu and Ni. It does not touch silver. It does chelate Pd until higher temperatures, when it is oxidized by Pd(II). It is messy, foamy, and expensive (about $14/gallon by the ton). 

If you look at the structure, you'll see why the gold is being reduced (that hydroxyl group). 

Its real usefulness lies in adding it during the reduction with a conventional reducing agent and precluding additional drag down from solution.
In any case, 4N gold is entirely possible with sulfite alone and good washing/refining practice.


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## Lino1406 (Feb 13, 2013)

Another riddle of nature why DMG and EDTA precipitate Pd
and not Pt
Answer gold riddles No. 1 and 2:
http://www.facebook.com/pages/Gold-electronic-enigma/162208933810735


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