# Potassium Metabisulfate instead of SMB?



## dbrick81 (Jan 11, 2008)

Can you use "Potassium Metabisulfate" instead of "Sodium Metabisulfate" (SMB)?

Thanks


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## Irons (Jan 11, 2008)

Sodium metaBISULFITE, not sulfate. Only the sulfites will generate SO2, which is what precipitates the Gold.

It shouldn't make much difference if it is the Potassium or Sodium salt, because it's the Sulfite that does the work. The Sodium or Potassium ions are just spectator ions and don't take part in the reaction.
There are several sources of Sodium Sulfite on Ebay that sell it at a very modest cost, even with shipping. 
There are several SULFITE compounds that will do the job.


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## Irons (Jan 11, 2008)

Take note of the comments regarding concentration and temperature. Harold was right in chilling the Gold Chloride.

http://www.freepatentsonline.com/3717481.html


One of the most important aspects of this invention resides in the use of a reducing agent selected from the group consisting of potassium sulfite, sodium sulfite and mixtures thereof. While many other reducing agents are well known and could be used to precipitate a gold powder, it has been found that under specified conditions, this class of reducing agents precipitates the gold powder of this invention having a specified size, shape and density. The amount of reducing agent utilized is not critical; but to obtain maximum precipitation, an excess is generally used.

Another important feature of this invention involves maintaining the temperature of the solution within the range of 0°-30°C. Of course, below 0°C. the solution has a tendency to freeze. Above 30°C., the particles of gold become exceedingly fine and the bulk density becomes too low for purposes of producing good electrical properties. The preferred temperature is within the range of 10°-20°C.

The precipitation (reduction) is performed by adding reducing agent(s) to the aqueous gold chloride solution. The addition of the reducing agent to the gold chloride solution should be carried out as rapidly as possible to provide maximum efficiency of the overall process. It is pointed out that the reducing agent is added to the aqueous gold chloride (not vice versa) to provide gold particles having the proper particle size and shape. For example, the particles become too small when an aqueous gold chloride solution is added to a solution of the reducing agent. Also, although not necessary, it is preferred to agitate the solution while the precipitation reaction takes place. This provides a greater contact between the reducing agent and the gold chloride, and results in a complete precipitation in a shorter period of time.

The process of this invention is not particularly sensitive to the concentration of the reactants. Therefore, concentrated solutions or dilute solutions of the gold chloride and reducing agent may be used. However, somewhat larger particles are obtained when higher concentrations of gold chloride and reducing agent are utilized. Typical and preferred concentrations of gold chloride and reducing agent in their respective solutions are within the ranges of 40-70 gms/liter and 100-200 gms/liter.


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## Harold_V (Jan 11, 2008)

Irons said:


> Take note of the comments regarding concentration and temperature. Harold was right in chilling the Gold Chloride.


That was very interesting, and goes hand in hand with my experiences. Thanks, Irons. 

Harold


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## Irons (Jan 11, 2008)

Harold_V said:


> Irons said:
> 
> 
> > Take note of the comments regarding concentration and temperature. Harold was right in chilling the Gold Chloride.
> ...



My pleasure, Harold. Always give credit where credit is due.

I think GSP deserves credit as well for suggesting the use of Sodium Sulfite.


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## dbrick81 (Jan 12, 2008)

This may seem like a realy stuppid question but....  is there an easy way to tell the difference between Potassium metaBISULFITE, Potassium metaBISULFATE

Thanks


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## lazersteve (Jan 12, 2008)

The bisulfite will produce a very pungent odor when mixed with water.

Steve


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## Irons (Jan 13, 2008)

As mentioned by GSP, Sodium Sulfite has less odor when mixed with water.

Another minor difference is that the metabisulfite is slightly acidic when mixed with water and the Sodium Sulfite raises the Ph (basic). Since the precipitation reaction lowers the Ph of the solution, the Sodium Sulfite will counteract that.


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## dbrick81 (Jan 14, 2008)

So the bisulfate is alkaline and will raise the acidity of a solution, and the bisulfite is acidic and will lower the acidity of a solution?


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## Platdigger (Jan 15, 2008)

The bisulphate, is acidic. It is sold as "ph down"....to lower the ph of your pool or sauna water. Actually makes a weak type of sulfuric acid in water.
Randy


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## Irons (Jan 15, 2008)

dbrick81 said:


> So the bisulfate is alkaline and will raise the acidity of a solution, and the bisulfite is acidic and will lower the acidity of a solution?


The Bisulfate is acidic, not alkaline

http://en.wikipedia.org/wiki/Potassium_bisulfate

A solution of potassium bisulfate behaves like if the two congeners (K2SO4 and H2SO4) were side by side uncombined. 

Think of it as partially neutralized Sulfuric Acid that forms a solid.

http://en.wikipedia.org/wiki/Potassium_metabisulfite



Potassium metabisulfite, K2S2O5, is a white crystalline powder with a pungent sulfur odour. The main use for the chemical is as an antioxidant or chemical sterilant. It is a sulfite and is chemically very similar to sodium metabisulfite, with which it is sometimes used interchangeably. Potassium metabisulfite is generally preferred out of the two as it does not contribute sodium to the diet.

Potassium metabisulfite has a monoclinic crystal structure which decomposes at 190°C, yielding potassium oxide and sulfur dioxide:

K2S2O5(s) → K2O(s) + 2SO2(g)


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## Rexall (Sep 11, 2011)

Question:

I have 250ml of a yellow-green gold chloride solution that I was once going to use to do some gold plating.
Now I would like to precipitate the gold out and sell it to a refiner.

How many grams of Potassium Meta-bisulfite would I need to get the Au out?
I can get Potassium BS at the homebrew shop, so thought i'd use that instead of Na BS.

I'm guessing about 20 grams, since the you-tube video used 8g for 100ml, but could some wizard advise?

Thanks!


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## martyn111 (Sep 11, 2011)

Rexall said:


> Question:
> 
> I have 250ml of a yellow-green gold chloride solution that I was once going to use to do some gold plating.
> Now I would like to precipitate the gold out and sell it to a refiner.
> ...



That would depend on how many grams of gold you have that are dissolved in the 250ml of solution not on the amount of solution.
If the gold content is unknown then I would suggest adding your precipitant of choice in small increments, allow any precipitate to settle, test with stannous and continue adding and testing until a negative result for values is obtained.


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## Palladium (Sep 12, 2011)

You could just use copper then wash good with hcl. Should give you a pretty clean product. Since your selling to a refiner even if a few impurities remain it shouldn't be a problem. You’re not going to get any more for it other than the gold content one way or the other anyway.


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## Harold_V (Sep 12, 2011)

Anyone hear from Irons lately? I noticed he hasn't been on the board since July 27th.

Harold


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## Palladium (Sep 12, 2011)

I sure miss him.


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## Palladium (Sep 12, 2011)

Potassium metabisulfite has a molar mass of 222.32 g/mole 
Sodium metabisulfite is 190.1 g/mole 

So you'll need to use about 17% more (by weight) of the potassium salt to deliver the same effective SO2 as the sodium salt. 

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=48&t=1192&p=12637&hilit=Potassium+Metabisulfite#p12637


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## butcher (Sep 15, 2011)

I too have been concerned about Irons.


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