The appropriate amount of a sample is weighed on an analytical balance, mixed with lead collection flux to a homogeneous state (uniform colour) and loaded into a fusion furnace at 1150oC for 50 minutes. The reducing conditions will convert litharge(lead oxide) to metallic lead that will form a lead and three of the PGMs(Pt, Pd, Rh) and Au complex.
The lead button, after being hammered into a form of a cube, is loaded into a cupellation furnace at 1 000oC for an hour. The lead will be absorbed by the cupel and some is oxidized because of the presence of atmospheric oxygen in the furnace. When the cupellation is complete the PGMs & Au and Ag (added as silver nitrate) prill will be left on a hollow surface of the cupel.
Fusion and Cupellation stages are as described above. After the cupellation stage, the silver, PGMs and Au prill, is flattened and transferred into a parting porcelain crucible, 30% HNO3 added to remove silver, dried and analyzed by weighing on the analytical balance and a simple calculation done to determine the PGM concentrations. The detection limit is 0.08 g/t.
Fusion and Cupellation stages are as described above. After the cupellation stage, the silver, PGMs and Au is transferred into a multi-hole cupel and loaded into a higher temperature furnace for 1,5 hours. It is then removed, left to cool and weighed on the analytical balance and a simple calculation done to determine the PGM concentrations. The detection limit is 0.28 g/t.
The prill is transferred into a 50ml beaker and dissolved with aqua-regia on a hotplate. When the dissolution is complete, the solution is transferred into a 25ml volumetric flask containing an appropriate amount of HCI and internal standard,, made up to volume with de-ionized water and assayed on the ICP-OES or ICP-MS, depending on the grade and required detection levels.
The PGMs and Au held by the silver prill is transferred by the forceps into a borosilicate glass tube and aqua regia added. The tube is then sealed and transferred into a metal housing and placed into a dissolution oven. The tube with aqua regia solution and PGMs and Au will be left to dissolve in an oven at 220oC for eight (8) hours. The tube is popped and the solution of PGM and Au transferred into a volumetric flask, internal standard added, made up to volume and assayed on the ICP-OES or ICP-MS, depending on the grade and required detection levels.
The fusion stage is as described above except the type of flux at 1020oC. The NiS button is crushed to fine pieces on the hydraulic press and transferred into a 600ml beaker containing an appropriate amount of reagents, e.g. HCl. The dissolution is carried out on a steam bath for about 16 hours under the fume cupboard to ensure complete dissolution of the PGM’s. The next step is to carefully filter the solution through a Buchner funnel under vacuum, through a 0.45 microns Durapore membrane filter. The PGM’s which remain on the filter paper are dissolved by gently heating the residue in acid on a hot plate. The solution is then transferred into a 25ml volumetric flask with the correct ratio of acid and internal standard, made up to volume and assayed on the ICP-OES or ICP-MS, depending on the grade and desired detection levels.