Fire assay operating procedures, precautions, and requirements
Release time:
2020-12-14
Fire Assay Fire assay is a classic statistical analysis method that applies metallurgical principles and techniques to analytical chemistry. It is one of the long-standing methods in analytical chemistry, with advantages such as good sample representativeness, wide applicability, and enrichment effects. It is an important method for the chemical analysis of gold, silver, and precious metals.
Fire Assay Principle
Fire assay is a quantitative analysis method used to measure the content of precious metals in iron ore and metallurgical products by using solution smelting. Lead assay is predominantly used, and the entire process is divided into three stages:
Melting
It relies on mixing solid reagents with the sample and heating it to melting in a crucible. Gold, silver, and precious metals are collected by lead in the molten state, producing a lead alloy (generally called a lead button). Due to its high specific gravity, the lead alloy sinks to the bottom of the crucible.
In addition, the metal oxides and gangue of base metals in the sample react with fluxes such as silica, borax, and sodium carbonate. They transform into silicates or borates, forming slag that floats on top due to its lower density. This allows for the extraction of gold and silver from the sample. Therefore, the fire assay process simultaneously dissolves the sample and collects the precious metals.
Cupellation
The obtained lead alloy is placed in a cupel and cupelled at a suitable temperature. During cupellation, lead oxidizes into lead oxide and is absorbed into the porous cupel. This removes the lead and a small amount of base metals from the lead button, while gold and silver are not oxidized and remain in the cupel, forming a gold-silver bead.
Parting
The gold-silver bead is dissolved using sodium cyanide, dissolving the silver while the gold remains solid. The obtained gold bead is heat-treated and weighed to determine the gold content. The silver content can be calculated from the difference between the weight of the gold-silver bead and the weight of the gold.
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