# Sodium Metabisulphite or Potassium Metabisulphite?



## Traveller11 (Jun 27, 2013)

In our remote location, the only place to purchase sodium metabisulphite is our local U-brew store, where it is used in wine making. However, they tell me they quit purchasing sodium metabisulphite a few years ago and now only sell potassium metabisulphite.

Will potassium metabisulphite work equally well for precipitating gold from solution?

Also, our pharmacy had ferrous sulphate tablets, but the pharmacist felt there might be too many impurities and fillers in the tablets, sold as iron supplements. Anyone ever use these as a precipitant for gold?


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## jimdoc (Jun 27, 2013)

Traveller11 said:


> In our remote location, the only place to purchase sodium metabisulphite is our local U-brew store, where it is used in wine making. However, they tell me they quit purchasing sodium metabisulphite a few years ago and now only sell potassium metabisulphite.
> 
> Will potassium metabisulphite work equally well for precipitating gold from solution?
> 
> Also, our pharmacy had ferrous sulphate tablets, but the pharmacist felt there might be too many impurities and fillers in the tablets, sold as iron supplements. Anyone ever use these as a precipitant for gold?



I seem to remember that you can use potassium metabisulphite, but need to use a bit more than you would if it was sodium metabisulphite. A forum search should bring up more information.

Jim


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## FrugalRefiner (Jun 27, 2013)

I agree with Jim. I know I've read the potassium metabisulfite will work. You should be able to find the ratio with a search.

I agree with your pharmacist, the tablets probably contain a lot of fillers and binders you don't want in your process. If you can buy battery acid, you can make your own ferrous sulphate (copperas). You can dissolve iron in dilute sulphuric acid (battery acid). Search for copperas with author butcher for better instructions.

Dave


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## Lino1406 (Jun 27, 2013)

What does the job is the bisulphite portion of the molecule.
Also FeSO4 tablets additives are well dissolved is not it?


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## freechemist (Jun 29, 2013)

Principally potassium-metabisulfite, K2S2O5, will do a perfect job, as long as there are not significant amounts of Pt (and/or eventually Pd) present in solution. Both, in their +IV-oxidation states, form only sparingly soluble potassium-hexachlorometallates, K2PtCl6 (and K2PdCl6), which also can precipitate, together with metallic gold, after addition of potassium-metabisulfite to e.g. a solution of dental gold, quite frequently containing significant amounts of Pt and/or Pd.


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## Traveller11 (Jun 29, 2013)

Thanks for the info, everyone.


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## Lino1406 (Jul 3, 2013)

Not clear how Pd and Pt in highest oxidation state are precipitated
by a reducer


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## solar_plasma (Jul 3, 2013)

I use only potassium metabisulfite, because I got it quickest at the local pharmacy. If you are particular about it, you have convert the gramm values, because 1 mol of potassium is almost double the weight of 1 mol sodium. So, it should be a little more than smb.


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## Traveller11 (Jul 3, 2013)

solar_plasma said:


> I use only potassium metabisulfite, because I got it quickest at the local pharmacy. If you are particular about it, you have convert the gramm values, because 1 mol of potassium is almost double the weight of 1 mol sodium. So, it should be a little more than smb.



Once again, thanks for the info! 8)


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## freechemist (Jul 4, 2013)

It's not the bisulfite (reducer), which precipitates the hexachlorometallates. The precipitant is the potassium-ion, contained in K2S2O5. If you add much more potassium-metabisulfite to a solution of dental gold-alloy-scrap, than is necessary to precipitate all gold (through reduction to metal), Pd(IV), if present, will be reduced to Pd(II), and Pt(IV), to some extent, to Pt(II). Thus, on oxidation of the filtrate with NaClO3 and addition of ammonium chloride a mixture of ammonium and potassium-hexachlorometallates will be obtained.


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