Recovering gold at neutral pH

[huggybear]

I have a solution containing a few hundred ppm gold which I am trying to recover. The pH of the solution is 4.5

The problem is that the solution contains 3-4 percent sulfur, so when I drop the pH (prior to treatment with SMB or cementation) it forces all of the sulfur to precipitate making a sticky mess!

Just wondering if there are any other ways to drop the gold from solution that don't involve pH modification. Any recommendations appreciated.

Thanks,
huggy

 

[Alondro]

I have a solution containing a few hundred ppm gold which I am trying to recover. The pH of the solution is 4.5

The problem is that the solution contains 3-4 percent sulfur, so when I drop the pH (prior to treatment with SMB or cementation) it forces all of the sulfur to precipitate making a sticky mess!

Just wondering if there are any other ways to drop the gold from solution that don't involve pH modification. Any recommendations appreciated.

Thanks,
huggy

If you are certain that it's elemental sulfur, then adding potassium hydroxide and heating will turn the sulfur into potassium sulfide (which reacts with water to form potassium hydrosulfide) and thiosulfate ion.

There are also certain conditions in which hydrogen peroxide can oxidize the sulfur into sulfite ion, but I don't know how straightforward the reaction is. I do not know if the potassium hydrosulfide of the above reaction will be oxidized to sulfite or sulfate by peroxide.

The other option is to dry the salts out completely in what you already have and roast with high-oxygen flame, which will turn the sulfur into sulfur dioxide gas.

 

[huggybear]

If you are certain that it's elemental sulfur, then adding potassium hydroxide and heating will turn the sulfur into potassium sulfide (which reacts with water to form potassium hydrosulfide) and thiosulfate ion.

There are also certain conditions in which hydrogen peroxide can oxidize the sulfur into sulfite ion, but I don't know how straightforward the reaction is. I do not know if the potassium hydrosulfide of the above reaction will be oxidized to sulfite or sulfate by peroxide.

The other option is to dry the salts out completely in what you already have and roast with high-oxygen flame, which will turn the sulfur into sulfur dioxide gas.

Thanks Alondro,

I should have mentioned that the source of the sulfur is from dissolved sodium thiosulfate which was used as a washing step for the gold.

Normally I would acidify a neutral solution with HCl before dropping gold, but in this case it is causing solid sulfur to precipiptate:

Na₂S₂O₃ + HCl → 2NaCl + SO₂ + S

The solid sulfur turns my solution into a thick slurry making it impossible to treat with SMB or cement out values.

I guess my options are to either treat in a way that doesn't require pH modification, or to first deal with the sulfur then acidify as normal. I have tried filtering off the solid sulfur but it is extremely fine and blocks the filter pores quickly as well as passing through to the filtrate.

Any advice appreciated.

Thanks,
huggy

 

[Lino1406]

This low concentration will require special chemicals or ion exchange resins. So volume needs to be high enough to justify it