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Method of fire assay ingredients

2021/12/24

The compounding method of the assay must be determined according to the nature of the sample, and the amount of various reagents added should be calculated according to the required silicic acidity range.The operating procedure is to fill in the form, and then weigh the reagents and samples in turn, put them in the crucible and stir the reagents and samples with a stirring spoon, and gently shake the crucible to make small particles attached to the inner wall of the crucible.

If it contains sulfur, insert the required iron nails and add a layer of covering agent. When the temperature of the electric furnace rises to 800°C, the crucible with the materials is put into the furnace, and the furnace temperature is increased to 1150°C within 1 to 1.5 hours, and the furnace temperature is kept for 10 minutes.

Due to the different types of ore, the method of assaying gold ingredients is also different. According to the type of ore and the ingredients, there are three methods of ingredients in the crucible melting method: flour method, sodium nitrate-coke method or iron nail method, saltpeter method.


1. The flour method is the most commonly used ingredient method. When the sample itself has no or very low reducing power, flour needs to be added as a reducing agent. This method has many advantages. It can control the size of the lead button. It has a wide range of applicable minerals and materials, and is suitable for silicate ore, carbonate ore and oxide ore. Roasted ore after sulfide ore is roasted to remove sulfur can also be used in this method.

The requirements for the batching of silicate ore-based samples are:

(1) The silicic acidity of the slag is 1.5-20;

(2) Weigh 30-50g of sample;

(3) Add sodium carbonate as the sample amount;

(4) The amount of borax added is 0.2 to 0.3 times the amount of the sample;

(5) The amount of lead oxide should not be less than 30g of the weight of the lead button.

(6) The amount of flour should be equal to 30-(sample size × sample reducing power) /12.

Oxide ore and carbonate are alkaline minerals, and their compounding method is basically similar to that of silicate samples. The difference is that the products after smelting are mostly alkaline substances such as CaO, MgO, FeO, so a large amount of SiO2 must be added However, the melting temperature of Fe SiO2, MgSiO2, and CaSiO2 is relatively high. The amount of PbO should be increased in the ingredients to increase the composition of PbSiO2 in the slag and reduce the melting temperature.


2. The iron nail method (sodium nitrate-coke method) The iron nail method is not suitable for sulfide ore containing more copper, nickel, arsenic and antimony, but can only be used for medium galena (PbS) and sphalerite The basic principle of the samples of (ZnS) and pyrite (FeS2) is to use metallic iron as a desulfurizing agent to decompose the sulfide in the sample, and form FeS with the sulfide, and use FeS or Fe(Ⅱ)-Na- The form of S enters the slag, and the iron nail also acts as a reducing agent, reducing lead oxide to metallic lead, and trapping precious metals. If the sample contains copper, nickel, arsenic, antimony, bismuth and other metals in the reduction order before iron, the iron will be reduced to metal, enter the lead button, and form an alloy with lead. So this method is not suitable for such samples.

The ingredients principle of the nail method:

(1) The silicic acidity of the molten slag is 0.5;

(2) The amount of sodium carbonate is 2 to 3 times the sample amount;

(3) The amount of lead oxide is 30 to 35 g;

(4) ) The amount of borax added is 1/2 to 1/3 of the sample amount;

(5) The sample amount is 20 to 30g.


3.Saltpetre method is a batching method for processing samples with strong reducing power. The oxidation of potassium nitrate is used to weaken the reducing power in the sample, so as to obtain a lead button with an appropriate weight, so that the effect of capturing precious metals is good

The ingredients principle of the saltpeter method:

(1) The reducing power of the sample must be measured before the ingredients to determine the amount of potassium nitrate added. Saltpeter should not exceed 25g.

(2) The total volume of the materials after batching does not exceed 2/3 of the crucible volume, and it is easy to overflow when it is overfilled and smelted.

(3) The silicic acidity of molten slag is required to be 10, and if the acidity is too large, it is easy to generate matte and cause gold and silver loss.

(4) The amount of lead oxide added is 12 to 14 times the total reducing power of the sample. The reducing power above 30 is 12 times, and the reducing power below 30 is 14 times.

(5) The dosage of borax is not less than 5g.

(6) In order to completely decompose the sulfur in the sample, add sodium carbonate at least equal to the sample amount, and add 1/4 of the amount of potassium nitrate.

It is necessary to use the calculation method to make ingredients in the assay work, but in actual work, it is often difficult to know the content of the composition of the sample sent, which requires us to identify it by eye observation and experience. First look at the color and quality of the sample, determine which ore type it belongs to, and decide which assay method to adopt.


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