Gold Mining in Siberia as a Source of Mercury Contamination of the Environment
359
- Accumulation of a large amount of concentration tailings with elevated
mercury contents and its emission into the atmosphere, surface water streams
or groundwaters due to the processes of rock oxidation, tailings drainage by
atmospheric precipitation etc.
- Reprocessing of gold-bearing concentration tailings with elevated mercury
contents, which is accompanied by mercury transition into an active
migratory state.
- Reworking of industrial gold placers mined out previously by the dredge
method with the use of sluiced amalgamation and transition of a great deal of
mercury into an active migratory state, which was buried under the layer of
bottom sediments in the old dredge pits in anaerobic conditions at
temperatures near zero in a "preserved" state.
- Refining of gold alloy with natural or technogenic (amalgamation use)
elevated mercury contents at refining plants, which is accompanied by vapour
mercury emission into the atmosphere along with technological gases.
3
Amalgamation of Gold-Bearing Ores, Gravel and Concentrates
The method of gold amalgamation based on a selective wetting of native gold
particles with mercury and their weighting is the oldest technology in gold
extraction from ores. In Russia, the method of amalgamation of gold-bearing
ores came into use on an industrial scale after 1870 (Roslyakov and Kirillova
1995) and was for a long time an obligatory component in traditional schemes of
gold-bearing raw material concentration.
Amalgamation methods are classified into two groups (Vyazelshchikov and
Paritzky 1963):
- Internal amalgamation, when gold trapping occurs inside crushing devices,
simultaneously with rock crushing and native gold particle release from the
mineral shell (in crushers and crusher-roll mills).
- External amalgamation, when gold trapping takes place outside crushing
devices (on sluices, in amalgamators).
Originally, internal amalgamation was widely used in processing gold-bearing
ores and gravels, mined by underground and open methods, and external sluice
amalgamation was used in dredge technology. These methods were accompanied
by great specific mercury expense, with great irreversible losses, and they were
the most harmful for the health of the workers. Maximum mercury expense
occurred in the process of sluice amalgamation, when mercury (up to 420 kg)
was poured over the riffles of gold trapping sluices. In this case, mercury
expenses accounting for 40-130 mg per 1 m 3 of gravel and 3-10% of metal were
additionally extracted. The mercury losses at sluice amalgamation were great and
could account for 55-70 mg/m3 of the processed gravels (Zamyatin et al. 1973).
The mercury content in dredge tailings could reach 0.2 g/m3 due to mechanical
359
- Accumulation of a large amount of concentration tailings with elevated
mercury contents and its emission into the atmosphere, surface water streams
or groundwaters due to the processes of rock oxidation, tailings drainage by
atmospheric precipitation etc.
- Reprocessing of gold-bearing concentration tailings with elevated mercury
contents, which is accompanied by mercury transition into an active
migratory state.
- Reworking of industrial gold placers mined out previously by the dredge
method with the use of sluiced amalgamation and transition of a great deal of
mercury into an active migratory state, which was buried under the layer of
bottom sediments in the old dredge pits in anaerobic conditions at
temperatures near zero in a "preserved" state.
- Refining of gold alloy with natural or technogenic (amalgamation use)
elevated mercury contents at refining plants, which is accompanied by vapour
mercury emission into the atmosphere along with technological gases.
3
Amalgamation of Gold-Bearing Ores, Gravel and Concentrates
The method of gold amalgamation based on a selective wetting of native gold
particles with mercury and their weighting is the oldest technology in gold
extraction from ores. In Russia, the method of amalgamation of gold-bearing
ores came into use on an industrial scale after 1870 (Roslyakov and Kirillova
1995) and was for a long time an obligatory component in traditional schemes of
gold-bearing raw material concentration.
Amalgamation methods are classified into two groups (Vyazelshchikov and
Paritzky 1963):
- Internal amalgamation, when gold trapping occurs inside crushing devices,
simultaneously with rock crushing and native gold particle release from the
mineral shell (in crushers and crusher-roll mills).
- External amalgamation, when gold trapping takes place outside crushing
devices (on sluices, in amalgamators).
Originally, internal amalgamation was widely used in processing gold-bearing
ores and gravels, mined by underground and open methods, and external sluice
amalgamation was used in dredge technology. These methods were accompanied
by great specific mercury expense, with great irreversible losses, and they were
the most harmful for the health of the workers. Maximum mercury expense
occurred in the process of sluice amalgamation, when mercury (up to 420 kg)
was poured over the riffles of gold trapping sluices. In this case, mercury
expenses accounting for 40-130 mg per 1 m 3 of gravel and 3-10% of metal were
additionally extracted. The mercury losses at sluice amalgamation were great and
could account for 55-70 mg/m3 of the processed gravels (Zamyatin et al. 1973).
The mercury content in dredge tailings could reach 0.2 g/m3 due to mechanical