Oxalic Precip Gold Clumped - Need Powder

[kadriver]

Process:

Inquarted karat scrap with silver
Dissolved base metals and silver with dilute nitric
Dissolved gold with aqua regia - minimum nitric
Filtered and dropped with SMB
Rinsed with distilled water and boiled in ammonia
Rinsed and boiled in dilute nitric acid
Dissolved gold again using HCl/bleach (used a little nitric also)
Filtered and precipitated with oxalic acid
Rinsed with boiling distilled water and then boiled in ammonia
Rinsed with distilled water and but the gold in this flask (see photos)

I want some nice fluffly gold powder.

The gold precipitated with oxalic is clumped together.

I tried breaking it up with a bamboo skewer but it just gets tighter.

I am thinking of redissolving the gold again and dropping with SMB to get nice gold powder (instead of the oxalic clumped gold)

I usually just dry and melt the clumped gold so I have no experience with this - Does anyone have some experience that can be shared?

Is my idea to re-dissolve and drop with SMB the way to go, or is there a simpler way to get nice fluffy powered gold from the clumped gold?

kadriver

 

[nickvc]

Kevin I have never used oxalic acid but I think that with double refining and using oxalic as the final precipitant you will have achieved 9999 gold if not 99999 gold powder. I would be tempted to dry some of your powder and melt it in a clean dish. I know Lou has stated that the final product from oxalic precipitation is extremely high grade. I hope this helps.

 

[etack]

To get a powder try dissolving again and diluting the Aucl quite a bit before adding the SMB.

beautiful powder though. nice job.

Eric

 

[qst42know]

What do you need the powder form for?

 

[kadriver]

To sell

 

[kadriver]

Kevin I have never used oxalic acid but I think that with double refining and using oxalic as the final precipitant you will have achieved 9999 gold if not 99999 gold powder. I would be tempted to dry some of your powder and melt it in a clean dish. I know Lou has stated that the final product from oxalic precipitation is extremely high grade. I hope this helps.

nickvc,

I processed this gold this way to get it as pure as possible.

Lou refers to oxalic acid as a "polishing step" and I agree with him.

Using two different precipitants (first SMB, then oxalic acid) progressively eliminates impurities.

I dissolved the gold again using AR with minimum nitric additions, then dropped with chemically pure SMB.

The gold came down and settled almost instantly - it looks very clean.

Will rinse, boil in amomonia, rinse, boil in dilute nitric, rinse, dry and it should be quite nice gold powder.

kadriver

 

[freechemist]

kadriver,

To precipitate gold by reduction with oxalic acid, judging your pictures, you used a magnetic stirring bar for mixing the contents in the beaker. I think, that the rotating and also some collecting/grinding/pressurizing action of the turning stirring bar on the bottom surface of the beaker led to these agglomerates of an originally fine powder. Like Lou's, it is also my experience, that gold, obtained by reduction with oxalic acid is very pure, and as a powder, has a very pronounced tendency, to sinter together, forming bigger, but not yet massive agglomerates. - The last picture of your series reminds me strongly of my own experiments. - Probably you will succeed, if you mix appropriate quantities of diluted gold- and oxalic acid solutions together at room temperature, stop the stirrer, remove it, cover the beaker with a watch glass, and only now begin heating slowly to nearly boiling. If you are lucky, you can observe the formation of small bubbles of CO₂ and the slow formation of individual gold particles, falling slowly down, like golden snow.

 

[kadriver]

kadriver,

To precipitate gold by reduction with oxalic acid, judging your pictures, you used a magnetic stirring bar for mixing the contents in the beaker. I think, that the rotating and also some collecting/grinding/pressurizing action of the turning stirring bar on the bottom surface of the beaker led to these agglomerates of an originally fine powder. Like Lou's, it is also my experience, that gold, obtained by reduction with oxalic acid is very pure, and as a powder, has a very pronounced tendency, to sinter together, forming bigger, but not yet massive agglomerates. - The last picture of your series reminds me strongly of my own experiments. - Probably you will succeed, if you mix appropriate quantities of diluted gold- and oxalic acid solutions together at room temperature, stop the stirrer, remove it, cover the beaker with a watch glass, and only now begin heating slowly to nearly boiling. If you are lucky, you can observe the formation of small bubbles of CO₂ and the slow formation of individual gold particles, falling slowly down, like golden snow.

freechemist,

I'll try this experiment with my next batch - I have seen pictures on this board from others who used oxalic acid and got some beautiful precipitations - looked like golden snow swirling in the beaker - but I can't remember who it was that posted it.

kadriver

 

[butcher]

As I understand it the double refine of using two different reagent like SMB the first refine and Oxalic the second refine, the two different reagent allow different base metals to precipitate with the gold, or to say it another way will not precipitate the same base metals with the gold, so what one solution will precipitate with gold the other reagent would not precipitate this metal on the next refine.

Why couldn’t you do the oxalic acid the first refine, and then do the SMB on the second refine, or do a third dissolution and precipitate with SMB on the third refine to get fine powders.

I find very pure gold when pressed together will form gold metal the brown powder pressed will join the fine powders together to form a sheet of gold metal (I believe you could hammer (or press under high pressure) these powders into a gold bar instead of melting them into a bar), maybe your stirrer is hammering the fine gold powder together in solution, instead of busting it up.

 

[Lou]

Butcher,

You are right--high quality gold powder can be cold pressed to gold pellets.

I'll have to make an example for you gentlemen. I can't upload files anymore but I'll email to someone who can.

 

[kadriver]

Why couldn’t you do the oxalic acid the first refine, and then do the SMB on the second refine, or do a third dissolution and precipitate with SMB on the third refine to get fine powders.

Butcher, This is exactly what I ended up doing - re-dissolving and precipitating a third time with SMB. The gold powder was a joy to work with, very clean and easy to handle and melt.

Here is a photo of the gold powder after drying - nice and fluffy!

kadriver

 

[kadriver]

Here are some photos of the melt - smooth as could be.

kadriver

 

[kadriver]

Butcher,

You are right--high quality gold powder can be cold pressed to gold pellets.

I'll have to make an example for you gentlemen. I can't upload files anymore but I'll email to someone who can.

Lou:

I would be happy to do the uploads for you, just send them to my email [email protected] and I'll post them for you.

Kadriver

 

[butcher]

Simply Beautiful, Thanks for showing us the pictures, Thanks for offering to upload for Lou, I would have offered to do it, but my computer skills are terrible and I do not know if I could do what he was asking.

 

[Auful]

Kadriver,

What is the mass of that button? It's beautiful! What size melting dish are you using? It appears to have thicker walls than others I have seen. Do you mind sharing where you purchased it? Thanks.

 

[kadriver]

Butcher - always glad to help a fellow forum member if I can.

Auful: That dish was a little thicker than I am used to seeing. It came with a group of four dishes I ordered on Ebay back in 2010 when I first started experimenting with refining.

It was sitting there brand new and unused and looked to be the perfect size for this melt.

Sorry to say that I can not remember the seller's name. I would like to have a few more this size - very nice for doing small lots like this.

The button weighed 10.9 grams

kadriver

 

[kadriver]

I went back and found the Ebay seller (jetstools) that sold me the melt dishes:

http://www.ebay.com/itm/MELTING-CRUCIBLE-DISHES-CRUCIBLES-SET-4-Sizes-METAL-MELTING-DISHES-FUSED-SILICA-/221124252337?pt=LH_DefaultDomain_0&hash=item337c0852b1

I have not bought from this seller recently. I buy melt dishes from Miller's Jewelry Supply in Chicago, Il.

I ordered several dozen from Miller's about 1.5 years ago and I am still using them from that lot.

kadriver

 

[maynman1751]

http://www.ebay.com/itm/MELTING-CRUCIBL ... 337c0852b1
I went to this site and if you check his other items for sale he has some very nice stuff for the hobbyist or jeweler. Thanks Pete!

 

[Auful]

Thank you Kadriver and maynman1751!

 

[Noxx]

Why couldn’t you do the oxalic acid the first refine, and then do the SMB on the second refine, or do a third dissolution and precipitate with SMB on the third refine to get fine powders.

I think it's because Oxalic has a tendency to co-precipitate copper. So since it is in higher concentration in the first AR dissolution, you want to use it last.