Gold extraction .

· Gravity concentration has been historically the most important way of extracting the native metal using pans or washing tables. This method is based on different densities of Au and sand although extraction of gold does not exceed 25%.

· amalgam method (the yield is higher). The comminuted ore is passed over copper leaf covered Hg. Particles of gold that don’t have oxide film are dissolved quickly in Hg. Mercury can be removed from amalgam by distallitation.

· Chemical method. In the presence of air, gold is attacked by sodium cyanide solution, to give the complex dicyanoaurate(I) ion, in which gold has an oxidation state + 1:

4Au + 8NaCN + 2H₂O + O₂ = 4Na[Au(CN)₂] + 4NaOH.

Free gold can be extracted from solution at the presence of zinc:

2Na[Au(CN)₂] + Zn = 2Au + Na₂[Zn(CN)₄]

· Froth flotation is usually applied when the gold present in an ore is closely associated with sulfide minerals such as pyrite or arsenopyrite, and when such sulfides are present in large quantities in the ore. In this case, concentration of the sulfides results in concentration of gold values. Generally, recovery of the gold from the sulfide concentrates requires further processing, usually by roasting or wet pressure oxidation. These pyrometallurgical or hydrometallurgical treatments are themselves usually followed by cyanidation and carbon adsorption techniques for final recovery of the gold.

Дата добавления: 2015-07-25