Non-Chemical Using potassium sulfite to precipt -FPonline

[Wyndham]

http://www.freepatentsonline.com/3869280.pdf
There are several interesting things, to me at least, in this patent.
First is the use of potassium sulfite for reduction and the use of Polyvinyl alcohol in the solution to keep the gold percipt from clumping up.
Since I am still filling my thimble with knowledge of gold recovery, I'm wondering if Pot sulfite has any advantages or draw backs to other reducers like SMB or ferrous sulfate.
As to the PVA, could using this help for better % recovery from AuCl
Thanks Wyndham

 

[Irons]

If it's just Gold in the solution, probably no problem. Platinum is another issue. Potassium may form complexes with Platinum and co-precipitate with the gold.

 

[Oz]

Irons,
With you bringing up the possibility of potassium precipitating Platinum I was curious on your opinion if oxalic acid might be the best precipitant in a solution of Au with PGMs?
Thanks for your time.

 

[Wyndham]

later on in the patent it's also mentioned that oxalic acid was used in another test of tere process of keeping the gold precipt from clumping and mentioned a mixture of potassium and sodium sulfite.
I have also found threads here on the preferred use of sodium sulfite. Just wondering how would one make sodium sulfite if it gets impossible to get photo grade. I saw that by scrubbing sulfur this is created but what's the way to do this homebrew? Wyndham

 

[Irons]

later on in the patent it's also mentioned that oxalic acid was used in another test of tere process of keeping the gold precipt from clumping and mentioned a mixture of potassium and sodium sulfite.
I have also found threads here on the preferred use of sodium sulfite. Just wondering how would one make sodium sulfite if it gets impossible to get photo grade. I saw that by scrubbing sulfur this is created but what's the way to do this homebrew? Wyndham

I bought some on Sodium Sulfite and Oxalic Acid Ebay that was of very good quality. If you buy a good quantity, the prices are very reasonable, under $4. per pound.

 

[Irons]

later on in the patent it's also mentioned that oxalic acid was used in another test of tere process of keeping the gold precipt from clumping and mentioned a mixture of potassium and sodium sulfite.
I have also found threads here on the preferred use of sodium sulfite. Just wondering how would one make sodium sulfite if it gets impossible to get photo grade. I saw that by scrubbing sulfur this is created but what's the way to do this homebrew? Wyndham

Sodium Sulfite is made by bubbling Sulfur Dioxide through Sodium Hydroxide. You can make Sulfur Dioxide by burning Sulfur if you live in a cave and don't have mail service. Potassium Hydroxide can be made from wood ashes.

When things get that bad, Gold won't matter.

 

[Wyndham]

Hey how did you know I lived in a cave :lol: And speaking of the mail, even though they know me and my bus name, personal name, and addresses they will return mail addressed to my st # if it does not have a box # also. This is a town of less than 300 people, but has over 100 potters that can't get along. Talk about a heard of squirrels.
Thanks Irons have a great 4th and thanks for the info I'm off to my cave(pottery studio) Wyndham

 

[Irons]

Irons,
With you bringing up the possibility of potassium precipitating Platinum I was curious on your opinion if oxalic acid might be the best precipitant in a solution of Au with PGMs?
Thanks for your time.

Using a mild reducing agent like Oxalic Acid to precipitate Gold Mixed with PGMs has been around for a long time. It might work well with clean solutions but the nightmare I work with, it doesn't work too well. The mining industry seems to be going to solvent extraction.
In SA, the PGM ores only contain about 1% Gold vs PGMs.. It seems all of the new refineries there have moved away from the 'traditional' methods and gone to solvent extraction. It's more profitable and easier on the environment.

 

[Oz]

I have some material that has been precipitated once but is “contaminated” with platinum. I want to get credit for the platinum instead of loosing it. My intention was to take this first precipitation back into solution with HCl-Cl and I should have a rather clean and concentrated solution. My thought was to re-precipitate the Au first then work with what I had left in solution incase it is a mix of PGMs. If anyone has a better suggestion I would love to hear it. If not it would be nice to hear from someone that has used oxalic acid like this that may be able to share a little direction and their observations. Concentration of oxalic acid used and ratio of precipitant to gold dropped would be helpful.

Thanks

 

[eagle2]

Oz, You can use Sodium Nitrite to very well separate Gold from the PGM`s.

Heat a clean solution to about 80 C. The Ph has to be about 3-5. Slowly add the first small potion of NaNO2 and wait a few minutes. This allows the PGM`s to hydrate and they will not precip. Slowly add the rest of the Nitrite 2-3 times in excess to precipitate all the Gold.

The Pgm`s can all be dropped with Sodium Borohydride at Ph 6-12 or handle the solution with your methods.

Al

 

[Oz]

Well that’s resurrecting an old thread. Do you know how hard it is keeping it from oxidizing to sodium nitrate, or a good way to strip an O from NaNO3 to make NaNO2?

 

[eagle2]

I have some in a 10 lb bottle that is at least 30 yrs old and is still very effective. Merck index states it oxidizes very slowly in air. Just keep it sealed well. I happened to leave a solution in a beaker for over a year and it still was usable.
My college chem book states Nitrite is usually made by melting the Nitrate with Lead. NaNO3 + Pb > NaNO2 + PbO. Since I don`t like using lead and I if had to make some, maybe Zinc would work too.
Anyway its a very common chemical and very cheap. you should be able to easily find some.

Using Nitrite in too acid a solution it will produce some brown fumes (NOx) so ventilation is a good idea. I like to use it in solutions that were not very acid to begin with. Also putting it in a boiling solution may cause some momentary foaming.

I use SMB for more acid solutions with contaminents or PGM`s. Then when re-dissolving the Gold for further purfication Nitrite works to make a really nice precip. and separates out the PGM`s.

Al

 

[Lou]

Al, you seem really well informed about chemistry.

Also, in lieu of lead for the reduction, you can alternatively heat sodium or potassium nitrate with fine charcoal at dull red heat, and then digest in water, filter, and recrystallize.

Zinc will not work as a replacement for lead unfortunately.

 

[eagle2]

Thanks Lou, I can tell from your posts that you are.

Actually I did poorly in my college chemistry classes. Only 30 years later when I got interested in Gold, because of some prospecting, did I really study hard. I would go to the local college library 2-3 times a week and read about everything they had on the shelves. Including the Chemical Abstracts :lol:

Looking up Zinc again, I think I see a reason it won`t work, get it hot enough and it will start burning in air.

Al

 

[Oz]

Thanks to the both of you.

It is easier to buy chemicals and in most cases it is cheaper too, but I have always liked to know the low tech methods as well. The fine charcoal with heat is a simple method and nice to know it works with sodium or potassium nitrate. Just checking something I “think” I learned in the past empirically, it seems that sodium displaces potassium in a nitrate solution. Is this correct?

Thanks again!

 

[Lou]

Yes, but not exclusively because their solubilities aren't too different.

 

[eagle2]

In the electromotive series Potassium metal actually is slightly more active than Sodium metal.

But having Sodium and Potassium Nitrate together in solution nothing would happen between them. Both salts ionize almost completely in solution and you just have CL- and K+ and Na+ ions bumping around. (the way I look at it 8) ) There`s nowhere for the Sodium to displace or react to.

Since Potassium is heavier than Sodium you have to use more of it as a reagent to get the same result. It will work just as well as Sodium, since the Nitrite ion is whats reacting.

When it comes to the PGM`s I think Potassium does certain reactions that Sodium can`t or is not used for.

Al

 

[Oz]

As to the potassium with PGMs I have heard of undesirable complexes being formed but lack details as well.

Beyond the reason of liking to know low tech methods, I asked about the K/Na because I used to leach chicken manure until the liquor was high enough in nitrates to float a raw egg then drizzle a solution made from wood ash (KOH primarily) to precipitate potassium nitrate crystals. This was done until no more reaction was visible leading me to believe that if the solution was saturated with sodium (likely considering the source) but still had free nitrates that the potassium had a greater bonding strength with nitrates than sodium, or it was a displacement reaction due to differing saturation rates giving the potassium crystals. The manure should have been higher in sodium than potassium and the wood ash higher in potassium than sodium. Having said that of course neither was exclusively one or the other. The final product that was most desirable was potassium nitrate as it had a lower affinity for absorbing water once dried. I have no idea just how pure of a product I used to get in regards to K/Na exclusivity and have never tested it. Any opinions or input?

 

[eagle2]

I have no idea. It must have been a bit smelly :lol:

But like Lou mentioned the solubility constants are somewhat different and makes for some differences in reactions.
I think thats how fractional crystalization works. Anyway there`s no significant diiference when it comes to Gold

Looking at my Chem handbook, it says Potassium is slightly less soluble than Sodium, but not true in all cases. Potassium with Hexachloroplatinic acid produces K2(PtCl6) a yellow compound which is somewhat soluble in water but only slightly soluble in alcohol, which looks like one of the uses for Potassium with the PGM`s

Al

 

[Lou]

Most potassium salts are indeed less soluble than sodium salts--many pages of salts could be listed.

Salts containing both platinum and potassium are in all cases less soluble, usually by many orders of magnitude. Some of the preparative techniques I use for making pure platinum salts take advantage of differing solubilities in differing solvents/solvent systems.

The easiest way to separate Na/K nitrate would be to use a membrane that segregates one cation from another. Commercially, I'm fairly certain that sodium and potassium nitrate and nitrite are produced by reacting a base (probably something cheap like an alkali carbonate) with nitric acid in a neutralization reaction, then making a sirrup and crystallization.

You would need very good skills and a lot of time to even bother trying to recrystallize salts with these type of solubilities. There isn't enough of a difference, and it would take many, many fractional crystallizations to get a pure product and it would also lead to much loss (which would need further workup to recoup). The take home message is that you should just buy them.

Oz, your KNO3's purity level could have been easily determined by mixing it with sugar and igniting. If there were any sodium present, it's spectral yellow flame would drown out potassium's purple/violet. If you didn't want to do that, you could get a loop of nickel or platinum wire and wet it and put finely pulverised nitrate on it. Put that over a methane flame and look for a color change. Generally speaking, if you see no yellow coloration to a flame, then you would have a very small sodium cation contaminant, probably in the 50ppm or less region.

Lou