Platinum Group Metals Fire Assaying Process
Fire assaying is a method of analysis for platinum group elements and gold. This technique dates back centuries.
The basic process in fire assaying for both gold and platinum are roughly the same and can be accomplished with four steps:
Step 1: Fusion Stage
Flux (which includes lead) and silver are added to the pulverized sample and melted together.(Note: silver acts as a collector for the precious metal).
Step 2: Cupellation Stage
In cupellation, the cooled lead button (containing precious metal) is placed into a small porous crucible, called a cupel, and heated. Heat causes lead to oxidize and it becomes absorbed into the cupel, leaving a small silver/precious metal bead in the cupel.
Step 3: Separation Stage
The silver/precious metal bead is placed in a test tube with nitric acid and the tube is given a hot water bath which causes silver to melt, leaving a small particle of a precious metal floating.
Step 4: Determining the Grade
If the resulting sample of the Fire assaying is large enough, it will be weighed. However, if the sample is too small then gold will be dissolved in hydrochloric acid and gold concentration will be measured using AAS. Platinum group elements readings are done using ICP.