Impurities appear when precipitating gold from aqua regia with nitric acid & sulfuric acid

Are you talking about a lightweight, red precipitate that obviously isn't gold? I commonly see this. I generally assume that it weighs little relative to the gold, and ignore it. When we analyze such samples via "fire assay" techniques, we see answers that are very slightly lower.

You should be heating the aqua regia/sulfuric acid sample prep. to the point where all of the HCl and HNO3 are fumed off, and white fumes of SO3 are observed.

Thanks, David, for the information.

However, there is large amount of impurity in my sample. The impurity must influence my result when I am using the gravimetric analysis. The impurity is not red color and it is grey in color.

In addition, I had tried to do this experiment by evaporated the aqua regia almost to dry, let it cool and addition of water and sulfuric acid to relux it. Nevertheless, eventually, impurity still appear after addition the hydrogen peroxide solution in the final step.

I do want to know how to eliminate the impurities that can be precipitated out in this method.

Thanks all!

I guess there was some complication in the GA process. I would prefer you using HCl + Nitric to form AQ, nevertheless it still can be done; your impurities may be due to too high a mixture you couple with such a problem it should be advise to inquart it with silver to purify it. if you know the way of doing
Jimi

I am gold refining officer.you take precautions mainly by filtering the sample,purity about your chemicals,and also with water.

If you are using sulfuric acid when refining and if you have lead in the materials being refined it (sulfuric acid) will precipitate out the lead. This could be what is being reduced or dropped out.
Donnybrook Australia