A-Closer-Look-at-Gold-Bullion-Fire-Assay-AR25.pdf

1、A Closer Look at Gold Bullion Fire AssayMichael W.HindsMHinds Analytical Consulting Inc.Jon Sewell and Charles DaoustRoyal Canadian MintLiteraturePaulo Battaini,Edoardo Bemporad,Daniele De Felicis,The fire assay reloaded,Gold Bull.,2014,47,9-20.I.Ciabatti(2019)Gold parting with nitric acid in gold-s

2、ilver alloys.Substantia 3(1)Suppl.:53-60.doi:10.13128/Substantia-606 Fire Assay required for Au settlement Parallel determinations Ag,Pd,Pt determined by XRF Saves time,labour,material Frees furnace time Can use XRF for provisional settlementsXRF&Fire Assay 50 mg Cu added 2.5 x Ag to Au added(Inquar

3、tation)Wrap in lead foil Place in cupel in furnace 1060oC Pb and sample melt PbO&base metal oxides form and absorbed into cupel Ag-Au bead remainsAssay Fire Cupellation For Determining Au500 mg samplePhoto courtesy of Rand Refinery,SAElement Determination in Used Cupel by XRFCross Sectioned and Top

4、Viewfrom Battaini,et al,2014Assay Button(Ag Au alloy)-Rough bottom surface-Easy to pick up cupel material-Cleaning important(from Battaini,et al,2014)Transmission Electron Microscopy(TEM)images of:a)Hammered or rolled(work hardened)bead.b)The same piece in a)after flame annealing.Re-crystallization

5、reduces dislocationsEasier to roll out (from Battaini,et al,2014)Annealing Rolled Assay ButtonsAfter Cupellation Assay Fire ButtonSEM backscattered electron image of a cross sectioned button after cupellation.-Fine grain structure due to micro-segregation of the silver.-The concentration of silver a

6、long the grain boundaries is 75%.The black spots are Cu and Ag oxides.(from Battaini,et al,2014)Copper in Silver Button After Cupellation(Assay Fire)All procedures add Cu with Inquartation Ag No Copper Silver Button Cracks during rolling X Addition of Copper required for good rolling Is Cu retained