Fire assay method for determining gold and silver in lead concentrate
Release time:
2021-07-09
Gold and silver in lead concentrate Fire assay Determination method
1. Except for potassium nitrate, the smelting process for other components is the same as the smelting test. The actual amount of oxidant or reductant required for the sample is calculated through experiments, and the size of the lead button is controlled.
2. Weighing materials: Weigh 20g of sample in a beaker, and mix it with 30g of sodium carbonate, 10g of silicon dioxide, 10g of borax, 100g of lead oxide, and pre-weighed potassium nitrate or starch.
3. Melting: Put the prepared materials into a melting crucible and melt it in a 900℃ gold furnace for 30 minutes. Continue heating to 1100℃ (about 30 minutes) and maintain for about 10 minutes. Immediately remove the crucible and pour the melt into an iron mold. Cool, remove the "lead button" and remove the slag, ensuring that the lead button is between 28g and 35g.
4. Cupellation: Put the "lead button" into a cupel that has been preheated in a 900℃ high-temperature furnace for 20 minutes for cupellation. Close the furnace door and keep it at 900°C. After the "lead button" is completely melted and glowing, control the cupellation at around 860℃. Cupellation is completed in about 1 hour, and the particles show "flashing". Immediately move the cupel to the furnace door, let it stand for a moment, and take out the cupel to cool to room temperature. Use tweezers to remove the particles from the cupel, brush off the debris attached to the bottom of the particles, flatten the particles with a clean stainless steel hammer, and weigh them with a millionth analytical balance. This is the total amount of Au and Ag.
5. Put the gold alloy particles into the original porcelain crucible, add 20ml of boiling HNO3(1%2B7), and heat on a low-temperature hot plate. The crushed particles immediately react with HNO3, changing from silver-white to black, and releasing nitrogen oxide gas. After the reaction stops, pour out the solution, add about 20ml of boiling HNO3(1%2B1), and separate Au twice as above. After decanting the solution, wash with hot water three times. Pour out the water in the crucible, place the crucible on a low-temperature hot plate, and heat the small ball until dry. Then move the crucible to a high-temperature furnace at about 700°C and anneal for a few minutes. At this time, the Au crystals change from a black amorphous shape to reddish-yellow pure gold. After the crucible cools to room temperature, weigh the mass of the gold particles with a millionth analytical balance. The difference between the two masses is the mass of Ag.
6. After secondary smelting, crush the slag and the cupel after cupellation, add 50g of silicon dioxide, 50g of borax, 50g of sodium carbonate, 50g of lead oxide, and 3g of starch, and perform smelting, cupellation, and parting according to the above method, and perform the gold procedure to compensate for the loss of gold and silver respectively.
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