YS/T 521.2-2009Methods for chemical analysis of blister copper. Part 2: Determination of gold and silver contents. Fire assay method (English PDF)

3.1 Sodium carbonate. industrial pure, powdery.

3.2 Lead oxide. industrial pure, powdery (gold mass fraction <= 0.05µg/g;

silver mass fraction <= 5µg/g).

3.3 Borax. powdery.

3.4 Starch. industrial pure, powdery.

3.5 Silicon dioxide. industrial pure, powdery.

3.6 Sodium chloride. industrial pure, powdery.

3.7 Gold (mass fraction >= 99.99%).

3.8 Silver (mass fraction >= 99.99%).

3.9 Copper (mass fraction >= 99.95%).

3.10 Sulfuric acid (rho1.84g/mL).

3.11 Nitric acid (1+1).

3.12 Nitric acid (1+7).

3.13 Mercuric sulfate solution (23g/L).

3.14 Sodium chloride solution (10g/L).

3.15 Acetic acid (1+3).

4.1 Balance.

4.1.1 Ultra-micro balance. with a sensitivity of 0.001mg.

4.1.2 Microbalance. with a sensitivity of 0.01mg.

4.1.3 Analytical balance. with a sensitivity of 1mg.

4.1.4 Counter balance. with a sensitivity of 1g.

4.2 Assay furnace.

4.3 Cupel machine.

4.4 Porcelain crucible. low profile, 30mL.

4.5 Clay crucible. with a height of 120mm, an upper outer diameter of 90mm,

and a lower outer diameter of 50mm.

4.6 Cupel. Ash cement cupel or magnesia cupel.

General specifications. with a height of 30mm, an upper inner diameter of

35mm, a lower outer diameter of 40mm, and a depth of 17mm or so.

5.1 Specimen

5.3.1.3 TRANSFER all sediments to the filter paper. USE warm water to

wash the sediments until there is no blue color. PLACE the glass rod and filter

paper on the cup wall, together with the filter paper loaded with the sediments,

in a clay crucible, and then PLACE it in an assay furnace. RISE from room

temperature to about 500°C for ashing until ashing is completed.

5.3.2 Ingredients

COOL the clay crucible containing the ash compound to room temperature.

ADD 20g of sodium carbonate (3.1), 60g of lead oxide (3.2), 7g of borax (3.3),

7g of silicon dioxide (3.5), and 3g of starch (3.4). STIR well, and COVER

10mm thick sodium chloride (3.6).

5.3.3 Melting

PLACE the prepared clay crucible in an assay furnace at 800°C. RISE

temperature to 1,100°C within 30min to 40min, and INSULATE for 15min

(total melting time is 45min to 55min) before discharging. POUR the melt into

a preheated and oiled cast iron mold. After cooling, BEAT the lead buckle into

a square shape. COLLECT the slag into the original clay crucible for later use

(corrected by the method B).

5.3.4 Cupellation

5.3.4.1 PLACE the lead buckle in a cupel preheated in an assay furnace at

900°C for 20min, and CLOSE the furnace door. After the floating film on the

surface of the lead liquid disappears (uncoating), slightly OPEN the furnace

door to lower the furnace temperature to 840°C to 860°C for cupellation. The

cupellation ends when the particles appear to flash. MOVE the cupel to the

furnace door, and PLACE it in a cupel tray after slight cooling.

5.3.4.2 USE a small tweezers to remove the gold and silver particles from

the cupel. PLACE them in a porcelain crucible, and ADD 15mL of acetic acid

(3.15). REMOVE when boiled to about 5mL on an electric hot plate. WASH

with warm water three times, and DISCARD the cleansing solution. PLACE

the gold and silver particles retained in the porcelain crucible on a

high-temperature electric furnace to bake dry, REMOVE and WEIGH

(accurate to 0.01mg) after cooling to room temperature. KEEP the cupel for

later use (corrected by the method B).

5.3.5 Parting

PLACE the weighed gold and silver particles on a small steel anvil to beat into

a sheet. PLACE it in a porcelain crucible. ADD about 5mL of hot nitric acid

(3.12). PLACE it on a low-temperature heating plate for parting. When

steaming to about 2mL, ADD about 5mL of hot nitric acid (3.11). STEAM to

about 2mL, REMOVE, COOL, and WASH three times with hot water. PLACE

m12 - Gold content measured in the second correction, in milligrams (mg);

m13 - Blank content of gold in the total content of lead oxide used in the

ingredients in the absence and presence of correction, in milligrams (mg);

m4 - Content of gold and silver particles measured in the absence of

correction, in milligrams (mg);

m15 - Content of gold and silver particles measured in the first correction, in

milligrams (mg);

m16 - Content of gold and silver particles measured in the second correction,

in milligrams (mg);

m14 - Blank content of silver in the total content of lead oxide used in the

ingredients in the absence and presence of correction, in milligrams (mg);

m0 - Mass of specimen, in grams (g).

The resulting gold content is expressed to one decimal place; and the silver

content is expressed to the integer position.

7.1 Repeatability

The measured values of the two independent test results obtained under the

repeatability conditions are within the range of average values given below.

The absolute difference between the two test results does not exceed the

repeatability limit (r). The case of exceeding the repeatability limit (r) does not

exceed 5%. The repeatability limit (r) is obtained by linear interpolation

according to the data in Table 2.

Table 2 -- Repeatability

Gold mass fraction/(g/t) 9.2 29.9 59.9 100.2 141.4 190.5

Repeatability limit (r)/(g/t) 0.8 1.5 2.2 3.0 3.5 4.0

Silver mass fraction/(g/t) 18 113 505 1017 1962 3098 4154

Repeatability limit (r)/(g/t) 6 15 35 50 70 95 115

NOTE. When the gold mass fraction is 0.5g/t, and the repeatability limit (r) is 0.2g/t.

7.2 Reproducibility

The measured values of the two independent test results obtained under the

reproducibility conditions are within the range of average values given below.

The absolute difference between the two test results does not exceed the

reproducibility limit (R). The case of exceeding the reproducibility limit (R)

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