Assaying, Microscopy, Mineralogy & XRF/XRD

Assaying, Microscopy, Mineralogy & XRF/XRD

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Fire assay cupellation process (1 reply and 1 comment)

5 years ago
Imelda 5 years ago

Hello, I am Imelda from Indonesia

In my company, i worked as a melting staff. I used fire assay. They gave me example 27,5% gold sample for analyzing. They want me to check if the concentration is right or not. The flow chart :

take .... mg of sample

Adding Ag

Adding lead

Make into ball shape using lead

Anneal with T = 1095 C for 40 minutes (Pb absorbed into cupel) 

I get the mixture of au and ag and make it into layer shape and cornet

I dissolve the Ag using hno3 to get Au

Anneal it for t = 1 minute T = 1095

I get the final Au

The for determination the concentration i calculated final weight/initial weight

I just want to ask is it the right step? 

How to calculated how much Ag and Pb must be added? (i am a new staff, so i just follow the table of added Ag)

How about the process? I mean the temperature and the time for annealing

Thank you. 

5 years ago
Jorge 5 years ago
1 like by David

The procedures and methodology employed for determining the gold content in bullion and in fixing the purity of proof plate are important. The assay pieces of correct mass are wrapped in lead cases of 4-5 g each, together with 40-45 mg copper and sufficient silver to bring its concentration to 2.5 times that of the gold. Cupellation is performed at 1040 oC for 25-30 minutes in magnesia cupels. The prills are then prepared for parting by hammering, rolling, annealing, followed by rolling into cornets. Parting is carried out by successive treatment with nitric acid solutions of specific gravities 1.2-1.3, respectively, followed by washing, annealing and mass determination.

Samples of mine bullion which do not fall within the normal range of composition, such as those containing excessive amount of base metal or those having appreciable osmiridum content are treated by special methods of assay, mainly by cupellation and parting. For example an impure bullion,  which has a gold content of 11-23%, and the silver content of 78-88%, also needs special assay. The normal 1000 millieme assay piece is given a double inquartation. Before cupellation, 750 millieme of proof gold with sufficient silver to give normal silver/gold ratio of 2.5 to 1 is added. Allowance is made for this gold in calculating the final result.

4 years ago

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