RU2237734C2 - Assay method of cupellation for gold- and silver-containing lead alloys - Google Patents

Abstract

FIELD: analytical methods.

SUBSTANCE: dripping is charged into working chamber of electric oven and heated to 930-1000^оС, after which lead alloy is added. Alloy is subjected to oxidative fusion to achieve residual weight 1.5 to 4.5 g. Oven temperature is then lowered to 900^оС and cupellation is completed at this temperature. After that, dripping is removed from the electric oven, cooled, freed of gold/silver alloy, and weight of gold and weight of silver in the dripping are determined. For that, one measures diameter of spot formed on dripping under gold/silver alloy. When cupellation process is performed properly, following calculation relationship should be fulfilled: d_meas ≤ D_permit = k·M $\genfrac{}{}{0ex}{}{\text{1/4}}{\text{Ag}}$ , where D_permit is permissible spot diameter, mm; k coefficient of proportionality, mm/mg^1/4, whose value for magnesite fields equals 1,5; and M_Ag is weight of silver in regulus, mg. Novelty resides in that temperature conditions of the cupellation in the two first periods are 930-1000^оС, indirect indication allowing estimation of the quality of performing cupellation procedure is diameter of spot, and use of calculation formula for estimating above quality.

EFFECT: expanded analytical possibilities.

7 ex

Description

The invention relates to the field of analytical chemistry and can be used in assay to separate noble metals from lead.

A known method of cupellation of lead alloys [1, p.99], including oxidative melting of the alloy into droplets in a chamber or muffle furnace. Lead alloys are placed in droplets heated to 850 ° C. As soon as the lead alloy is exposed, the temperature in the muffle is reduced to the formation of cirrus crystals on the front wall of the droplet. At this temperature, almost the entire cupellation process is carried out [1, p. 103]. Before the end of cupellation, the temperature is increased to 900 ° C to ensure the removal of traces of lead [1, p. 100-101].

The quality of the process is assessed visually by the presence of cirrus in drops. The presence of feathery cirrus is not a necessary and sufficient sign of a quality process and a reliable determination of gold and silver, since it characterizes only compliance with the temperature regime. The loss of gold and silver during cupellation can be significant in the presence of cirrus. They increase upon freezing of the alloy [2, p. 150], when the amount of interfering impurities in the alloy is exceeded above the acceptable level, when the wettability of the droplet by the alloy increases due to the droplet's properties (porosity, fracturing), and the droplet with the cake is untimely removed from the furnace.

This method has a long duration, since cupellation is carried out at a low temperature.

Closest to the proposed method is a method for cupellation of lead alloys in assay analysis [2, p. 150], including oxidative melting of the alloy into droplets in three periods and an assessment of the quality of the process based on the use of side effects that differs from the method [1] only in that that the start of cupellation is carried out at a temperature of 850-900 ° C.

This method has the same disadvantages as the method [1].

The technical result of the invention is to reduce the time of cupellation of lead alloys and increase the reliability of determination of gold and silver.

The technical result is achieved by the fact that in the proposed method for cupellation of lead alloys containing gold and silver, in a assay analysis involving oxidative melting of an alloy on a droplet in three periods, and in the third period the process is carried out at temperatures up to 900 ° C, and the quality of the process is evaluated , according to the invention, the alloys are melted in the first two periods until the alloy mass is reduced to 1.5-4.5 g at a temperature of 930-1000 ° C, and the quality of the process is assessed by measuring the diameter of the black spot, image yuschegosya on the surface at the end of the cupel cupellation and comparing the measured values with the allowable values of the ratio

d _meas ≤ d _tolerance = k $\genfrac{}{}{0ex}{}{\text{1/4}}{\text{Ag}}$ ,

where d _ISM - measured spot diameter, mm;

d _perm - allowable spot diameter, mm;

k is the coefficient of proportionality, mm / mg ^1/4 , the magnitude of which for magnesite drops is 1.5;

M _Ag is the mass of silver in the bead, mg.

Cupellation of lead alloys in the first two periods of the process at a temperature of 930-1000 ° C provides a reduction in cupellation time by an average of 11%.

The use of the diameter of the black spot formed on the surface of the droplet at the end of cupellation to control the quality of the process allows to increase the reliability of the definitions of gold and silver, since the increased spot size and its deviation from the round shape indicate freezing of the alloy during the cupellation, the temperature exceeds the end of cupellation, the excess of the allowable amount of interfering impurities in the alloy, the increase in wettability of the droplet by the alloy, due to the droplet’s properties (porous fracture), about the untimely removal of the droplet with the crust from the furnace, or about the simultaneous negative influence of these factors on the course of the cupellation process, and, consequently, on the results of determining gold and silver.

A black spot forms on the surface of the droplet under the king due to oxidation of silver. This implies the relationship between the diameter of the spot and the mass of silver in the king. The greater the mass of silver in the bead, the greater its oxidation surface, which results in a larger diameter of the black spot.

The invention is illustrated by the following examples.

A control sample is analyzed with the contents of C _Au = 27.2 g / t, C _Ag = 208.5 g / t, and the basic cupellation time is 61 minutes.

Example 1. The droplets are loaded into the working chamber of an SNOL-1.6.2.5 1 / P-MIV4.2 type furnace and heated to 960 ° C. Then a lead alloy weighing 37 g is placed in it. The alloy is cupelized at 960 ° C to a residual mass 3 g. Then the temperature is lowered to 900 ° C. At this temperature, cupellation is completed.

The boundaries between periods are established by the following criteria:

- between periods I and II - by exposing the surface of liquid lead [2, p. 150];

- the border between the II and III periods of the cupellation process is to reduce the weight of the lead alloy to a residual value of 1.5-4.5 g. The mass of lead is determined visually. Experimental studies have shown that during cupellation of a lead alloy to a given residual mass, silver losses are not formed in the claimed temperature regime. Further, in order to avoid significant losses of silver, the cupellation temperature should be reduced to 900 ° C, which is the third period of cupellation.

Then, the drops are carefully removed from the electric furnace, cooled, after which the tweezers are separated from the drop with tweezers and flattened with a hammer on a clean anvil. Measure the diameter of the black spot, d _ISM = 2.7 mm. The Korolek is weighed on a VLM scale of 1 g. The mass of the king is the sum of gold and silver in the sample MΣ _{Au + Ag} = 11.87 mg Next, the bead is boiled, calcined and, in a cooled state, the resulting squat of gold is weighed M _Au = 1.37 mg. The mass of silver is determined by the formula M _Ag = MΣ _{Au + Ag-} M _Au , m _ag = 10.50 mg.

The allowable diameter of the black spot is calculated:

d _tolerance = 1.5 · (10.50) ^{l / 4} = 2.7 mm.

The measured diameter is compared with the allowable, it must be less than or equal to the allowable. In this example, d _ISM = 2.7 mm = d _tolerance = 2.7 mm, which indicates a slight loss of gold and silver in the cupellation process.

The established contents: With _Au = 27.5 g / t, C _Ag = 210.0 g / t. Deviations of the established contents from the certified are insignificant.

The cupellation time is 55 minutes, it is reduced compared to the base by 11.3%.

Example 2. Cupellation of a lead alloy weighing 36 g is carried out at 930 ° C to a residual mass of 1.5 g. Then the temperature is lowered to 900 ° C, at this temperature cupellation is completed. Measure the diameter of the black spot, d _ISM = 2.7 mm. The mass of silver is determined according to Example 1-M _Ag = 10.32 mg.

The allowable diameter of the black spot is calculated.

d _tolerance = 1.5 · (10.32) ^{l / 4} = 2.7 mm.

Get d _ISM = 2.7 mm = d _tolerance = 2.7 mm, which indicates a slight loss of gold and silver in the process of cupellation.

The established contents: With _Au = 27.4 g / t, C _Ag = 206.4 g / t, the deviation of the established contents from the certified is insignificant.

Cupellation time is 58 minutes, it is reduced compared to the base by 6.4%.

Example 3. Cupellation of a lead alloy weighing 35 g is carried out at 1000 ° C to a residual mass of the alloy of 4.5 g. Then the temperature is lowered to 900 ° C, at this temperature cupellation is completed.

Measure the diameter of the black spot, d _ISM = 2.3 mm

The mass of silver was determined according to Example 1-M _Ag = 10.31 mg.

The allowable diameter of the black spot is calculated

d _tolerance = 1.5 · (10.31) ^{l / 4} = 2.7 mm.

Get d _ISM = 2.3 mm <d _add = 2.7 mm, which indicates a slight loss of gold and silver in the process of cupellation.

The established contents: With _Au = 26.9 g / t, C _Ag = 206.2 g / t, deviations of the established contents from the certified are insignificant.

Cupellation time is 53 minutes, it is reduced compared to the base by 14.5%.

Example 4. Cupellation of a lead alloy weighing 36 g is carried out according to example 2 at 920 ° C. The diameter of the black spot is measured, d _meas = 2.5 mm. The mass of silver is determined according to Example 1-M _Ag = 10.32 mg.

The allowable diameter of the black spot is calculated

d _tolerance = 1.5 · (10.32) ^{l / 4} = 2.7 mm.

Get d _ISM = 2.5 mm <d _tolerance = 2.7 mm, which indicates a slight loss of gold and silver.

The established contents: With _Au = 27.3 g / t, C _Ag = 206.4 g / t, deviations of the established contents from the certified are insignificant. But the cupellation time was 62 minutes, i.e. reduction of cupellation time compared to the base no.

Example 5. The cupellation of a lead alloy weighing 35 g is carried out according to example 3 at 1010 ° C. The cupellation time was 51 minutes, it was reduced compared to the base by 17.7%. A spot of irregular shape, elongated, confined to the crack, it is impossible to measure its diameter, which indicates alloy losses due to loosening of the droplets and the formation of cracks on their inner surface.

The established contents: With _Au = 26.5 g / t, C _Ag = 200.8 g / t, deviations of the established contents from the certified are significant.

Example 6. Cupellation of a lead alloy weighing 35 g is carried out according to example 3 at a temperature of 1000 ° C to a residual mass of 4.6 g. Then the temperature is lowered to 900 ° C, at this temperature cupellation is completed. The diameter of the black spot is measured, d _ISM = 2.4 mm. The mass of silver is determined according to Example 1-M _Ag = 10.34 mg. The permissible diameter of the black spot d is _calculated d _tole = 1.5 · (10.34) ^1/4 = 2.7 mm. Get d _ISM = 2.4 mm <d _tolerance = 2.7 mm The established contents: With _Au = 27.0 g / t, With _Ag = 200.8 g / t, the deviations of the established contents from the certified are insignificant, but the time of cupellation is 54 minutes, i.e. it increased compared to example 3.

Example 7. Cupellation of a lead alloy weighing 35 g is carried out according to example 3 at a temperature of 1000 ° C to a residual mass of 1.4 g. Then the temperature is lowered to 900 ° C, at this temperature cupellation is completed. The diameter of the black spot is measured, d _meas = 2.8 mm. The mass of silver is determined according to Example 1-M _Ag = 10.04 mg. The allowable diameter of the black spot is calculated d _tole = 1.5 · (10.04) ^1/4 = 2.7 mm. Get d _ISM = 2.8 mm> d _tole = 2.7 mm, which indicates significant losses of gold and silver in the process of cupellation. The established values: With _Au = 26.6 g / t, C _Ag = 200.8 g / t, deviations of the established contents from the certified are significant.

Using the proposed method for cupellation of lead alloys provides the following advantages compared to the base method:

a) reduction of cupellation time by an average of 11%.

b) increasing the reliability of the determination of gold and silver.

It is most advisable to apply the proposed method in exploration.

Sources of information

1. Begby E.E. Assay art. M.: ONTI NKTP USSR, 1937, 291 p.

2. Sampling and analysis of precious metals. / Ed. I.F. Baryshnikov. - M.: Metallurgy, 1978, 432 p. (prototype).

Claims (1)

The method of cupellation of lead alloys containing gold and silver in an assay analysis, including oxidative melting of an alloy into droplets in three periods, moreover, in the third period the process is carried out at temperatures up to 900 ° C, and the quality of the process, characterized in that the alloys are melted in the first two periods until the mass of the alloy is reduced to 1.5-4.5 g is carried out at a temperature of 930-1000 ° C, and the quality of the process is assessed by measuring the diameter of the black spot formed on the surface of the droplet at the end of cupellation and comparing Nia measured value with the allowable value of the ratio

where d _ISM - measured spot diameter, mm; d _perm - allowable spot diameter, mm; k is the coefficient of proportionality, mm / mg ^1/4 , for magnesite drops k = 1.5 mm / mg ^1/4 ; M _Ag is the mass of silver in the bead, mg.