# precipitating gold with sodium bisulfite



## arthur kierski (Feb 27, 2008)

When i precipitate gold with sodium bisulfite a white powder precipitates also.
How can i eliminate this white powder from the mixture?
dilute nitric acid?

thank you for answers


Arthur kierski


----------



## lazersteve (Feb 27, 2008)

Arthur,

This can be several things so it's hard to say exactly. The first thing that comes to my mind is CuCl, which can be the result of precipitation from a dirty (copper chloride saturated) solution. SMB will turn Cucl2 to CuCl which is much less soluble in aqueous solutions.

What color is the liquid before you add the SMB?

It could also be many other contaminates depending on your starting material and processing. 

Harold's excellent washing routine should remove the mystery compound.

Steve


----------



## Harold_V (Feb 28, 2008)

arthur kierski said:


> When i precipitate gold with sodium bisulfite a white powder precipitates also.
> How can i eliminate this white powder from the mixture?
> dilute nitric acid?
> 
> ...


Steve has provided you with good information, but I'd like to address one comment you made----the use of nitric to remove contaminants. This is a very heated point of objection with me---one that will cause you more trouble than you may realize, and here's why: 

When you introduce nitric to the precipitated gold, the residual chlorides will dissolve the gold until one of them is exhausted. Assuming that wasn't a problem, regardless of how many times you rinse gold so contaminated (with nitric), you'll find that when you do your wash cycle, some of your gold will get dissolved. Without heating well above the evaporation point of the nitric, force drying the gold after the nitric has been introduced, it borders on the impossible to eliminate. That should help readers understand why it's so important to wash gold after it's been precipitated from dirty solutions. The contaminants, what ever they may be, do not depart gladly. 

Bottom line; Never use nitric once you have a chloride solution. Remember, it takes but one ounce liquid nitric to dissolve an ounce of gold. The traces that remain (and they will) will partially dissolve the values. 

Harold


----------



## arthur kierski (Feb 28, 2008)

thanks to harold and lasersteve,every reply of you is a lesson to me
best regards
Arthur Kierski


----------

