Cyanide production: the economics?

This data-file captures the cost of producing cyanide — hydrogen cyanide as a chemical intermediate and sodium cyanide as a crucial input to the gold-silver mining industry. Marginal costs are estimated at $1,500/ton and $1,650/ton respectively, in normal times.

However, the economics are sensitive to gas prices, due to their reagents. HCN is produced via the Andrussow Processes, at 1,126ºC and 14.7 psi, converting methane, ammonia and air into hydrogen cyanide, carbon monoxide and carbon dioxide. Hydrogen cyanide can then be further processed into sodium cyanide in a reaction with sodium hydroxide, derived from the chlor-alkali process, which is also energy intensive.

Thus in periods of gas shortages, the effective cost of producing HCN and NaCN can easily be double normal levels. This matters for the gold and silver mining industries. Gold and silver form soluble coordination complexes with cyanide ions, which in turn makes cyanide dissolution the dominant process for gold and silver extraction from mined ores.

The world’s largest sodium cyanide producer, Draslovka, shut down its European production facilities in 2022, due to high gas and energy prices. In other words, energy shortages in Europe could spill over into causing gold and silver shortages, which would also in turn compound energy shortages in Europe, because silver is an important component in the front contacts of solar cells.

Market sizing. Over 1.1MTpa of hydrogen cyanide is produced each year. Approximately half is used in producing polymers such as perspex (plexiglass), nylon-6,6 and adhesives; and the other half is used to make sodium cyanide, of which 80-90% is used for gold and silver mining. Thus the cost of producing cyanide will impact these value chains.

CO2 intensity of making cyanides is estimated in the data-file, at 3 tons/ton for HCN and 2 tons/ton for NaCN. This is almost all derived from the Scope 1+2 CO2 intensity of reagents. However the Andrussow Process is exothermic and should generate sellable steam.

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