Anyone have experience precipitating Au with Hydroquinone?

[NobleMetalWorks]

Does anyone use Hydroquinone to precipitate Au? Or selectively precipitate Au from a solution that contains PGMs?

Since Hydroquinone is considered a carcinogen, how would you go about reduction and disposing of it responsibly without a waste management company picking it up?

Are there any dangers precipitating out of Ar with Hydroquinone? I have found a patent for precipitating from cons that have been digested with HCl/Cl, but nothing on AR yet. Are there any special considerations, or dangerous chemistry I should be aware of before attempting to precipitate from AR?

Will selectively precipitating Au, with Hydroquinone before precipitating other PGMs make it more difficult to precipitate PGMs later?

Is there any issue using DMG or Ammonium Chloride in a solution that has Hydroquinone in it? Any dangers I should be aware of?

Any help would be appreciated, I have been reading patents for hours, I cannot find answers to these questions.

Scott

 

[Lou]

I have extensive experience with hydroquinone. I use it for gold titrations because it is fast and quite accurate. It is indeed useful for removing gold from PGM solutions without the drag down issues that SO2 has and the time constraints imposed by S/X or oxalic acid. I prefer it for removing gold in the bromate hydrolysis. You should not use hydroquinone to precipitate directly from aqua regia, as the aqua regia will oxidize all of your hydroquinone while leaving the gold untouched and it is not hugely cheap ($10-15 /lb) There are no issues using it in the presence of DMG, or ammonium chloride. Nonetheless, I recommend you eschew its use for other reductants at the present.

Hydroquinone is oxidized by the Au(III) to benzoquinone and other colored (conjugated) products, none of which will complex with PGMs. The big problem with it is that you have to rely only on ORP because benzoquinone is highly colored and obfuscates Au(III). It will also make you think you still have significant PGMs in your solution because of the intense yellow-brown that looks just like Pt(II). If you don't have instrumentation, you're stuck worrying...unless you want to do it on a comparative basis to a flight of stannous chloride-PGM complexes, each serially diluted.

All of the solutions contacting it go into cementation, where they are cemented, filtered, checked for values, then evaporated to a salt cake and sent off for a final disposal.


In processing bulk PGM concentrates, we will add hydrazine sulfate or hydrochloride to an acidic solution of the PM and base metal chlorides at the outset to remove any gold, re-refine that, and put the liquors back in with the PGM solution before platinum/palladium separation.

EDIT: Pt(IV) changed to Pt(II), Pt (II) is brownish yellow. Pt(IV) is orange-yellow all the way up to crystals of chloroplatinic acid.

 

[NobleMetalWorks]

Thanks Lou,

I have used it to precipitate Au out of HCl/Cl, and from an AR solution after the Nitric Acid has been driven off. I really like the way it immediately precipitates and drops Au right out of solutions containing PGMs. I have experienced no problem precipitating Pt after.

I got a really good deal on a large quantity of Hydroquinone, so I shouldn't need to purchase any in the near future. How do you store yours? I understand that if left to interact with Air it oxidizes fairly readily. I am currently keeping it in large glass containers and a poly bag lined chemical barrel. Is there anything else I should do to store it properly, besides filling with some inert gas?

Thank you again Lou,

Scott

 

[NobleMetalWorks]

Lou,

I forgot to say that I ended up buying a nice ORP benchtop meter it's a combo temp/ph/mv etc. I don't know why I didn't think about using one before, I use them in my salt tanks. It works great!

If anyone is thinking about a PH meter, I would spend the little extra and get an ORP meter instead. Being able to test for oxidation reduction potential has a lot of value.

Scott

 

[Osmium]

There's really no need for inert gas any oxidation from the air would be minuscule. I keep my HQ in a sealed glass container on the shelf and it hasn't lost any of its potency over the few years its been there. It's great for gold titration's, but has the downfall in production of all the benzoqinone formed with the Au. I personally don't recommend using it to drop gold from a large batch as the workup can get pretty messy. Benzoqinone not very fun to burn it away, and it doesn't have a great deal of solubility in to many common solvents you can use for washing your product.