I'm using XRS-FP assaying method to determine the concentrations of Au and Pt. Most samples I have on hands consist high concentrations of Zn, making the Zn-Kb peaks covering the Au-La and Pt-La peaks, leading to a result that the existence of Au and Pt cannot be confirmed. I have done several things to remove Zinc but it doesn't seem possible to completely remove all Zinc compounds. The Au and Pt concentrations are expected to be 100ppm to none. Hence, unless Zinc is completely removed, otherwise it is almost impossible to see Au-La and Pt-La peaks from the spectrum. I have tried mixing the sample with diluted HCl solution and it has only removed about 60% of Zinc. The particles have been grinded into certain degree which the elements within are believed to be fully liberated.
Dear Pui,
I think with your method you have to refine your powder after every etching step till reaching the sub nano scale.There is some basic idea, instead to dissolve the majority why not trying to dissolve the minority. This will be more easier to locate the minority.
You can find some suitable selective etching solution of gold for example in the link: https://www.microchemicals.eu/technical_information/gold_etching.pdf
In a similar way you can find some selective wet enchants for platinum.
I am not a chemist but i think logically.
You may spend lot of effort to separate the majorities but sure you will spend much less effort to separate the minorities.
Best wishes
Maybe another question applies: how high is the starting concentration of Zn? And what are the other properties of this matter?
Could it be you should better go for some chemical-analytical method (basically one of the methods traditionally applied to extract Au/Pt and alike from ores)?
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