The objective of the process is oxidizing the base metals from the noble metals such as gold and silver, to provide gold remain apart in order to specify the gold amount in metallic alloy materials and to determine the effect of the parameters such as processing temperature, amount of lead and experiment period on the analysis.
Cupellation (fire assay) is a quantitative analysis technique that is used for determining the amount of precious metals such as gold and silver in ore, concentrate or any other alloy. This process is based on the principle that precious metals do not oxidize or react chemically in high temperatures. By the way since the past, there has been some analysis methods for gold and silver. Some of them can be examined as touchstone, density and parting methods. In spite of lots of methods, the most reliable way is the cupellation process. (That has %0.02 accuracy.)
The Stages of Cupellation Process
The sample should be prepared in an amount between 295 and 300 milligrams.
First of all, since you do not know the carat of the sample, you can use the touchstone method or the XRF Spectrometer. Touchstone gives information about the sample visually. If you can use XRF Spectrometer, you will have information about other metals in the material (Nickel, Palladium etc.)
Touchstone provides people with having an idea the carat of sample.
Determination of Lead Foil Amount
The amount of lead foil to be used varies according to the carat of the product to be used. Lead foil is concerned with removing impurities in the alloy. In the traditional cupellation process for gold and silver, the amount of silver in the gold obtained is very important. A good clean separation is difficult to achieve, as gold protects silver from attack. Therefore, the amount of silver should be sufficient. If it is less, 99.99% pure silver should be added which is called quartation. After this process, the product is made suitable for reaction with acid.
The lead foil is tightly rounded with gold alloy and silvery leaded foil. These lead foils are placed one by one in the small-chamber material.
Sending Samples to The Cupellation Furnace
The prepared lead foil, magnesite or cement is put into the cupels, and it is sent to cupellation furnace. Materials should be kept in the oven for a while. As a result of this process, the lead is removed, and the basic metals are oxidized and absorbed by the cupels. The silver alloy dore metal remains on top of the cup.
The Treatment of Rolling & Annealing
This dore metal hammer is pounded with a small amount and then annealed by a fire blowing machine. The roller surface is then extruded in the crushing machine to expand the surface area as much as possible. In this way, the efficiency of the reaction with acid will increase. The rolled metal alloy is annealed again by blowing fire. After this stage, the material is ready for mixture with chemicals. As a result of chemical treatment, high purity gold and silver are obtained separately.
There are Gas Washing Units that must be observed and compulsory in chemical dissolving process.
These units are the places where poisonous gases coming out of acid-reacting dore metal part are converted into harmless form. Where the reaction takes place, the gases must be discharged to these units. These units are also called Scrubbers.