Day 2: Production Metallurgy (Non Ferrous)

Most malleable and ductile metal, NEVER tarnishes and unaffected by chemicals

Gold

One of the heaviest substances onearth, has a specific gravity of 19.3

Gold

One of the metals with the highest electronegativity

Gold

In the presence of UV radiation from the sun, strong cyanide complexes break down to form free cyanide, which in turn

breaks down under UV radiation to form the less harmful cyanate ion.

Photolitic degradation

Dissolved free cyanide can be oxidised to less harmful cyanate by adding ozone, gaseous chlorine, hypochlorite or hydrogen peroxide. Cyanate in turn slowly decomposes to form nitrate and carbon dioxide or ammonia and bicarbonate

Oxidation to cyanate.

Oxidation of sulphide minerals in tailings or heaps will yield sulphur bearing products. Free cyanide reacts with these sulphur forms to produce less harmful thiocyanate.

Formation of thiocyanate (SCN-)

Conversion of cyanide complexes to stable solids that settle out of water – achieved by adding metals (often iron) to waters.

Precipitation

Conversion of free cyanide to hydrogen cyanide gas (HCN). Reducing pH of waters encourages release of HCN. The gas disperses or converts to ammonium and carbon dioxide.

Volatilisation

Bacteria degrade cyanide into harmless by-products – dissolved formate, nitrate, ammonia, bicarbonate, and sulphate. Bacterial action encouraged by adding bacteria or nutrients to waters.

Biological oxidation.