Gravitational methods of extraction of precious metals from ores

Gravitational processes of concentration are processes in which separation of mineral particles with various density, sizes and form is caused by difference in character and speed of their movement. The high density of grains of native precious metals promotes their separation from easier grains of barren rock and concentration in the certain places of earth's crust. The method of gravitational separation is based on this property.

To gravitational processes concern jigging, float-and-sink separation, concentration on tables, concentration in sluices, shutes, concentrators, separators, pneumatic concentration.

Extraction of gold from placer deposits. Gravitational processes are especially widely applied to extraction of precious metals from placer ores.

The first operation at mining of placer deposits – the opening-out of deposit by the mechanized removal of deposits covering a placer. The second stage is the mining of gold-bearing sand (gold dust) with the subsequent concentration.

The degree of wash-out of sand by water defines the concentration circuit. The degree of wash-out of sand depends on clay content.

The equipment for separation of large pebble and silt is selected according to a category of a placer. Granular sand part of a placer is separated on jigging machines, on sluices, on concentration tables. The received concentrate for gold extraction is milled with mercury - amalgamation.

Gravitational methods of concentration of primary gold-containing ores. To extraction of gold from ores of primary deposits the following devices of gravitational concentration are applied: hydraulic traps, jigging machines, sluices with fabric or rubber covering, concentration tables, drum-type concentrators, hydrocyclones.

Control questions:

1. The content of gold in the earth’s crust.

2. Geochemical data of formation of gold-ore deposits.

3. Kinds of the gold-ore deposits.

4. Explain the process of formation of gold placers.

5. Location of gold-ore deposits on territory of Kazakhstan.

6. Gold minerals.

7. The most widespread silver minerals.

8. Ways of extraction of gold and silver from ores.

9. Aim of crushing and grinding of precious metals ores.

10. Aim of sorting of gold-containing ores.

11. Methods of sorting of gold-containing ores (hand-sorting, float-and-sink separation, nuclear methods, radiometric method of sorting of uranium-containing gold ores, automatic sorting on color).

12. The basis of gravitational methods of concentration.

13. Which methods concern to gravitational ways of ore concentration?

14. The scheme of gold-bearing sand concentration.

15. Methods of concentration of primary gold-containing ores.

Vocabulary:

Amalgamation – амальгамация

Association – ассоциация

Assumption – предположение

Catching – улавливание

Classifying – классификация

Complicate – затруднять

Concentration – обогащение

Crush – дробить

Crusher – дробилка

Crushing – дробление

Cupreous gold – медистое золото

Deposit – месторождение

Destroy – разрушать

Differentiation – дифференциация

Dispersion – рассеяние

Distribution – распределение

Dressing – обогащение

Eruption – извержение

Extraction – извлечение

Facilitate – облегчать

Float-and-sink separation – обогащение в тяжелых средах

Flotation – флотация

Grading – сортировка

Gravity sedimentation – отстаивание

Grind – измельчать

Grinding – измельчение

Gold-bearing sand – золотоносный песок

Gold grain – золотинка

Hand-sorting – ручная сортировка

Horn silver – роговое серебро

Inclusion – включение

Inspection – осмотр

Intrusion – интрузия

Jigging – отсадка

Lump ore – крупнокусковая руда

Layer – слой

Leaching – выщелачивание

Mill – перетирать

Mining – добыча

Native gold – самородное золото

Non-uniformly – неравномерно, неоднородно

Nugget – самородок

Palladeous gold – палладистое золото

Pebble – галька

Placer deposit – россыпь, рассыпное месторождение

Platinous gold – платинистое золото

Primary deposit – коренное месторождение

Processing – переработка

Rhodeous gold – родистое золото

Riddle – загадка

Rock – горная порода

basic rock – основная порода

enclosing rock – вмещающая порода

barren rock – пустая порода

dead rock – пустая порода

poor rock – бедная порода

shale rock – сланцевая порода

Screen – грохот

Shale – сланец

Shell – оболочка

Shute – желоб

Silt – ил

Silver glance – серебряный блеск

Sluice – шлюз

Sorting – сортировка

Speciation – нахождение

Superficial – поверхностный

Thickener – сгуститель

Thickness – мощность, толща

Trap – ловушка

Vein – жила

Wash-out – размываемость

Widespread – широко распространенный

Literature:

1. И.Н. Масленицкий, Л.В.Чугаев. Металлургия благородных металлов. – М.: Металлургия, 1972.

2. Ю.А. Котляр, М.А. Меретуков, Л.С. Стрижко Металлургия благородных металлов. В 2-х томах. – М.: Руда – Металлы, 2003.