gold thiosulfate

[joseph1990]

I am starting to question the whole process of gold thiosulfate refining.
There is a lengthy thread on gold thiosulfate with iron being the main reducer but it offers more criticisms than solutions.
Whenever you use thiosulfate as a leaching mechanism we have to use excess na2s2o3 since the s2o3 compound is used up at an accelerated rate in relation to ph...higher ph equates to the redevelopment of s2o3 but the near elimination of the electrodes. Once we figure out the leaching ratios we have to contend with reducing with na2s possibly with a higher ph.
My issue is with this formula
Na2S + Na2S2O3 + H20 = S + NaOH

if we were to use excess thiosulfate and perhaps we get some gold thiosulfate we know that the gold thiosulfate will in fact reduce to Au2S but it will also produce elemental sulfur.

We could then roast the colloids thereby getting some polysulfide derivative of gold sulfide but this would really cause smelly problems in the neighborhood. I recently bought 1kg NaBH4 and thought of using this instead of the na2s but I have no idea what the products will be but my hunch is that Na2S will be created. So if I successfully reduce the gold thiosulfate to Gold(0) and a side reaction were to occur with Na2S and water we would produce H2S thereby creating Au2S again on the surface of the Gold(0) sediment.
This is essentially a puzzle where the elimination of H2S and Na2S simply cannot be done chemically, the closest solution I currently have to this would be to add NaOH to the lixivant thereby creating Na2S and then reducing the gold thiosulfate to Au2s then adding NaBH4, since NaBH4 is extremely stable in basic solutions I can then add some acid to drop the gold particles but then this would create h2s and then I will need to accept that some gold sulfide is still in solution. Any input would be great.

 

[Lino1406]

1.Gold thiosulphate should react with NaOH to precipitate gold oxide. Formalin can be added to have some gold. Both can melt directly
2.What converts thiosulphate to sulfur is acid, not alkali
3.I would not mess with NaBH4 (the wheel was invented already)

 

[Iggy-poo]

1.Gold thiosulphate should react with NaOH to precipitate gold oxide. Formalin can be added to have some gold. Both can melt directly
2.What converts thiosulphate to sulfur is acid, not alkali
3.I would not mess with NaBH4 (the wheel was invented already)

Gold Oxide will dissolve in HCl, but a couple of drops of Bleach will make it quick.

I make my Gold test solution with some Gold Oxide I picked-up on Ebay. It's very convenient to have around.

 

[Topher_osAUrus]

In some literature I have, it actually suggests using a low percentage of hypo, as it leaches gold and silver more selectively, and at the same rate as much higher concentration.

 

[joseph1990]

1.Gold thiosulphate should react with NaOH to precipitate gold oxide. Formalin can be added to have some gold. Both can melt directly
2.What converts thiosulphate to sulfur is acid, not alkali
3.I would not mess with NaBH4 (the wheel was invented already)

Gold Oxide will dissolve in HCl, but a couple of drops of Bleach will make it quick.

I make my Gold test solution with some Gold Oxide I picked-up on Ebay. It's very convenient to have around.

Interesting so basically just add naoh then hcl into the thiosulfate solution? Has this worked for you in the past?

 

[joseph1990]

1.Gold thiosulphate should react with NaOH to precipitate gold oxide. Formalin can be added to have some gold. Both can melt directly
2.What converts thiosulphate to sulfur is acid, not alkali
3.I would not mess with NaBH4 (the wheel was invented already)

Thanks,
I literally bought so much and don't know what to do. I currently have a headache, I knew BH3 would be produced but not at these high levels. I ended up getting a gold solution with black crap, I'm pretty sure it's gold sulfide since the H2S is being created with Na2S and water reaction, garage really smells. The solution is literally the color of gold not sure if I should keep it or dump it.

 

[joseph1990]

In some literature I have, it actually suggests using a low percentage of hypo, as it leaches gold and silver more selectively, and at the same rate as much higher concentration.

Ideally this for ph, if thiosulfate solutions are below 9 ph then you'll consume all of you s2o3 and start producing sulfur. I prefer Naoh since we only need to use less than a gram for 2 liters for the ph to be above 11.

 

[joseph1990]

1.Gold thiosulphate should react with NaOH to precipitate gold oxide. Formalin can be added to have some gold. Both can melt directly
2.What converts thiosulphate to sulfur is acid, not alkali
3.I would not mess with NaBH4 (the wheel was invented already)

Aren't you scared of formalin? I can survive with H2S exposure since the body essentially oxidizes to sulfur but that stuff remains dormant and introduces you to hospice care in a few years. Also, I'm assuming that would be an exothermic reaction? Even a small amount of excess NaOh can cause it to produce elemental sodium correct?

Any safety and measurements would be appreciated.

 

[joseph1990]

EUREKA!
EUREKA!

I got it!
The sodium borohydride reduced it to elemental form and I ended up with huge clunks. No one mentioned to me that gold is resistant to h2s and na2s......basically I was working with silver so much I thought it was the same stuff but it resisted!!!!!!I love its inertness, it's sort of mythical when you think of it, I was getting ready to throw away some of this borohydride but it's truly amazing. The only problem is a) it smells so bad that even setting the solution outside to settle you can smell the rotten egg since the wind carries it.
b)BH3 is some nasty stuff, I got some on my pinky toe and ripped a small portion of skin so I followed msds and dipped feet in water for 20 minutes.

I will post pics on my next batch with melt, just had the most horrible headache from inhaling the fumes.
Not sure how the neighbors will react if I buy a face mask, might report to city so not sure if I can keep doing this without some sort of neutralization fume hood, sorry for the long talk just happy I got my first gold refining project.

 

[Lino1406]

You asked for a safety measurement, here is one: Check for H2S permissible concentration

 

[Lou]

I don't know what you're trying to do but I would take two steps back and re-evaluate.

Borohydride does not give BH3 (that's spontaneously flammable). It's a kitchen sink reductant.

Try to use conventional precipitating reagents.

Also, gold does form sulfide.

 

[joseph1990]

I don't know what you're trying to do but I would take two steps back and re-evaluate.

Borohydride does not give BH3 (that's spontaneously flammable). It's a kitchen sink reductant.

Try to use conventional precipitating reagents.

Also, gold does form sulfide.

Au2S + 2NaBH4 = 2Au + Na2S + 2BH3 + H2

flammable above 50 degrees celsius, I made sure this wasn't going to happen. But it was violent. I'm getting ready to melt tonight, we'll see what happens next.

 

[Lino1406]

Trying to be serious: I assume, instead of Au2S - Au2S2O3. Assumed products beside Au: H2S, S

 

[Lou]

Yes, and no (di)borane getting on toes.

Really though, what's wrong with just plating it out onto carbon felt or steel wool?

 

[joseph1990]

Yes, and no (di)borane getting on toes.

Really though, what's wrong with just plating it out onto carbon felt or steel wool?

borohydride is selective, I have a supplier if anyone cares to buy some. It can essentially drop gold in any solution. The stuff costs too much, currently paying for 2kg what I would get for 100grams here in the U.S.

To be honest, the reason why I opted to go with borohydride was that fact that Ii took ascorbic acid in a blender with the sulfides....it produced sulfides again since water will always be prevalent. I just gave up and went with the hard stuff.

 

[joseph1990]

this is not a feasible method, the amount of h2s has caused me to rethink the whole process and nabh4 is a good reducing agent but I simply can't use this stuff for my health and others as well.

 

[Lou]

Good, I'm glad you managed to change your own viewpoint when others could not.

Keep in mind that not just borohydride can produce H2S...aluminum and other active metals can as well!

 

[joseph1990]

Good, I'm glad you managed to change your own viewpoint when others could not.

Keep in mind that not just borohydride can produce H2S...aluminum and other active metals can as well!

thanks. I managed to avoid the h2s and now have to deal with SO2 which is a godsend to me, mainly because it doesn't spread beyond the garage into my living room.
The problem is I have a gunk of sulfur covering the black gold.
I have some pictures and as you can see the sulfur is covering the black part in the middle.
How would I get rid of the sulfur? I'm still a student of this field but hopefully I can learn from you old schoolers.