# Potassium sulfate as a precipitant.



## justinhcase (Aug 3, 2015)

I had a member ask if I could do a specialist drop for them.
Apparently the size of particle produced is important for there need's.
They provided instruction's that seemed quite basic.
"The basics
a. preparing an aqueous gold chloride solution;
b. precipitating the gold from solution by rapidly adding an excess amount of a reducing agent selected from the group consisting of potassium sulfite, sodium sulfite and mixtures thereof, while agitating the solution and maintaining the temperature within the range of 0C. 30C.;
c. separating the precipitated gold powder from the solution; and
d. washing the precipitated gold powder until the sulfite and sulfate ions have been removed from the powders.

Potassium sulfate is preferred over sodium sulfite in this class of reducing agents. Precipitates the gold powder of this invention having a specified size, shape and density.; but to obtain maximum precipitation, an excess is generally used.
maintaining the temperature of the solution within the range of 0C. -30C. Of course, below 0C. the solution has a tendency to freeze. Above 30C., the particles of gold become exceedingly fine

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 visa 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.

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.

Produces a gold powder having spherical particles with a particle diameter within the range of 1-10 microns.preferred embodiment of this invention the particle size is within the range of 2-6 microns.

EXAMPLE 1 A gold chloride solution was prepared by dissolving 300 grams of metallic gold in aqua regia.
By successive boil downs of this solution and with several additions of HCl, the oxides of nitrogen were removed;
five liters of water were added to the dissolved gold.
In a separate container, 700 grams of potassium sulfite crystals were dissolved in five liters of cold water.
Then the gold chloride solution was slowly agitated while the potassium sulfite solution was poured into the gold chloride solution as rapidly as possible.
The reaction proceeded very rapidly with no bubbling or frothing. The temperature of the solution was maintained at approximately 20C.
The reaction was complete in less than one minute.
The entire batch was filtered on a sintered glass filter plate and washed with water until the precipitated gold was free of the sulfite and sulfate ions. The gold powder was then washed in methanol to remove the water; the powder was then dried at room temperature.
The gold powder was weighed and found to contain 296 grams of spherical particles; the bulk density was approximately 8.0 gm/cc and the micron size ranged from 2-3 microns.2

The method list's sulphate and sulfite's as reagent's but said Potassium sulphate was proffered so that is what I used.well I was sent something purporting to be Potassium Sulphate but it needed filtering before I had a clear solution.http://mistralni.co.uk/products/potassium-sulphate.
Then absolutely no reaction at all when I mixed the reagent with the Gold chloride solution.
Has any one used this method of dropping?


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## Lou (Aug 3, 2015)

Potassium sulfate does not reduce gold.


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## justinhcase (Aug 3, 2015)

Lou said:


> Potassium sulfate does not reduce gold.


I did think may be they made a spelling mistake on there part.
Thank you for confirming.
J


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## g_axelsson (Aug 5, 2015)

There is no requirement from the patent office that a method should work. A lot of patents adds other chemicals just because they might work and they want to block others from working around the patent.

It's been written countless times on the forum, sulfite, not sulfate to precipitate gold.

Göran


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## justinhcase (Aug 5, 2015)

Do any of you have a supply of Potassium sulfite.
Lisa (Digitaria) and I can not find a U.K. supplier at a good price.
£60 for 100g of reagent seems a bit much.
Thanks
Justin


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## goldsilverpro (Aug 5, 2015)

justinhcase said:


> Do any of you have a supply of Potassium sulfite.
> Lisa (Digitaria) and I can not find a U.K. supplier at a good price.
> £60 for 100g of reagent seems a bit much.
> Thanks
> Justin


I always used photo grade sodium sulfite to drop gold, instead of SMB.

Potassium sulfite is also used as a photo chemical and is often sold as a 45% solution for this purpose. Check places that sell photo chemicals, if any still exist.


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## justinhcase (Aug 5, 2015)

goldsilverpro said:


> justinhcase said:
> 
> 
> > Do any of you have a supply of Potassium sulfite.
> ...


Thank you.
That is a very good tip .
What advantages do you find that make it your choice of precipitant?


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## goldsilverpro (Aug 5, 2015)

No real reason for using sodium sulfite instead of SMB. My mentor used it and so that's what I started with. It's actually a little weaker than SMB (I think) but I've noticed no differences in the results.


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## etack (Aug 5, 2015)

I always got mine from the brewery supply store some time it was cheaper than SMB by a few dollars a pound sometimes it was more. Work just fine. It's food grade I think it was around $2.50#. 

Eric


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