Assaying the platinum group Elements (PGE’s) is done via the same fire assy analysis technique explained earlier. The standard lead collection scheme used for gold gives good recovery for platinum and palladium as well. They are soluble in aqua regia and can be measured with gold in a multi element instrument such as ICP/OES or ICP/MS. The detection limits are low ppb.
The elements osmium, ruthenium and iridium are lost during the standard lead assay and cupellation process. Instead, they have been determined using the nickel sulphide collection technique. The nickel sulphide technique uses a 10 g of sample, 1 g powdered Ni, .8 g S, 12g soda ash, and 24 g borax.
The mixture is fused at 1010 0C for 1 hr. Then it is cooled and the assayer separates the NiS matte from the slag and pulverizes the NiS matte. The pulverized matte is dissolved in concentrated HCl. A filter is used to collect the PGE sulphides . Once the PGE’s are collect, they are dissolved in aqua regia, dilute, and measure on ICO/OES or ICP/MS. The Ni powder is very toxic and the concentration HCl digestion step can cause serious fume problems and are need to be done with a good exhaust system. The method is expensive, and the PGE’s that are assayed by this method are rare.
Tuesday, August 31, 2010
Assaying and Analysing for Platinum
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