Fire Assay Definition and Solution

-FAQs about fire assay, and some popular science tips

What is Fire Assay?

How to do a gold fire assay?

Why does the fire assay method have advantages?

What is the fire assay clay crucible?

What is a cupel?

What is Fire Assay?

Fire assay is a method to determine the composition and content of precious metals in minerals and metals through high-temperature melting and chemical reactions.

How to do a gold fire assay?

1. Weigh 0.50g or 1.00g sample, accurate to 0.00001g.

Weigh 4 pieces of pure gold standard samples similar to the gold content in the sample, accurate to 0.00001g. Add 1.25g or 2.5g pure silver to each sample and the pure gold standard, and wrap it into a spherical shape with two pieces of lead foil.

2. Number of measurements.

Three measurements were performed independently, and the average value was taken.

3. Cupellation.

The cupellation is preheated at about 950°C for 20 minutes, and the packaged samples or standard samples are placed in the arranged cupel in order. After the molten lead is removed, the furnace door is slightly opened for ventilation, and the cupellation is performed at 920°C±20°C. After the bright spot appears, close the furnace door and cut off the power supply. When the furnace temperature drops below 750°C, take out the cupel to cool.

4. Annealing and milling.

4.1 Use tweezers to take out the gold and silver alloy particles from the cupel. Hit both sides of the particles with a hammer, brush off the attachments,650°C-700°C annealing for 5min. Take it out, cool and grind it into a 0.2mm sheet, and anneal it at 650°C -700°C for 3 minutes.

4.2 Roll the annealed gold and silver sheets into a cylindrical shape and place them in the gold parting basket.

5. Parting.

5.1 The first time of gold parting: Put the gold parting basket into 90°C -95°C nitric acid, heating for 30 minutes, take out the gold parting basket, and wash 3 times with hot water.

5.2 Second gold parting: Put the washed gold parting basket into nitric acid preheated to 110°C degrees Celsius, heating for 40 minutes, take out the parting gold basket, and wash it with hot water 3 times.

5.3 When the sample amount is 1.00g, carry out the third time of gold parting: the operation is the same as the second time of gold parting, the gold is parted for 30 minutes, and washed with hot water 5 times-7 times.

5.4 Burning: After the gold roll is dried, burn it at 650°C -700°C for 3 minutes, cool to room temperature, and weigh.

6. Calculating the analysis results.

Why does the fire assay method have advantages?

Compared to many other analysis methods, fire assay has the following unique advantages.
(1) Good sampling representative. Gold and silver are often unevenly present in samples on the order of < g / t. The fire assay method has a large sample volume, usually 20-40g, and even samples of up to 100g or more can be collected. So the representative of the sample is good. Sampling error is kept to a minimum.

(2) Wide adaptability. It can adapt to almost any sample, from ore, gold concentrate to gold alloy, the fire assay method can accurately determine gold and silver, including those antimonites that cannot be resolved by wet analysis. For the analysis of the composition of pure gold, fire assay analysis can also get satisfactory results, except for very few samples, this method can be adapted to almost all minerals.

(3) High enrichment efficiency more than ten thousand times. A small amount of gold and silver can be quantitatively enriched from tens of grams of samples containing a large number of matrix elements in the assay gold button. Even though micrograms of gold and silver are enriched, the loss is very small, usually only percent. Due to the simple composition of the combined granules (or enriched slag), it is beneficial to use various test methods to determine in the future.

(4) The analysis result is reliable and accurate. In determining the gold content of gold ore, compared to the traditional wet analysis method, the gold analysis results of the fire assay method cannot be affected by the lithology of the mineral sample, ensuring the reliability of the gold content analysis.

What is the fire assay clay crucible?

Fire assay rucible is an important part of chemical instruments. It is a vessel for melting ores and metals. It is a necessary tool to ensure the smooth progress of chemical reactions.

The clay assay crucible has the characteristics of corrosion resistance, no cracking, and extreme cold and extreme heat resistance.

Raw material: clay, mullite.

Operating temperature 1100-1350℃.

Features: high strength, thermal vibration resistance, good thermal conductivity.

Application: Used for the smelting of gold, silver, copper, iron and other metals, fire assays, mining laboratories, laboratory testing, and mineral analysis.

What is a cupel?

Cupels are a cup-shaped container made of magnesia or bone ash, which is used in Pb-fire assaying to separate precious metals from base elements. Qingdao Decent Group cupel is a shallow, porous crucible with about 96% magnesia content. It has a smooth surface, high mechanical strength, and will not crack and pit during high-temperature cupellation.
AMERICAN DICTIONARY DEFINITIONS FOR CUPEL
noun
1. a small, cuplike, porous container, usually made of bone ash, used in assaying, as for separating gold and silver from lead.
2. a receptacle or furnace bottom in which silver is refined.
verb
to heat or refine in a cupel.
BRITISH DICTIONARY DEFINITIONS FOR CUPEL
noun
1. a refractory pot in which gold or silver is refined
2. a small porous bowl made of bone ash in which gold and silver are recovered from a lead button during assaying
verb
to refine (gold or silver) by means of cupellation