Editing Gold cyanidation (section)

==Application==
The [[ore]] is [[comminution|comminuted]] using grinding machinery. Depending on the ore, it is sometimes further concentrated by [[froth flotation]] or by [[mineral processing#Gravity concentration|centrifugal (gravity) concentration]]. Water is added to produce a slurry or ''pulp''. The basic ore slurry can be combined with a solution of [[sodium cyanide]] or [[potassium cyanide]]; many operations use [[calcium cyanide]], which is more cost effective.

To prevent the creation of toxic [[hydrogen cyanide]] during processing, slaked lime ([[calcium hydroxide]]) or soda ([[sodium hydroxide]]) is added to the extracting solution to ensure that the acidity during cyanidation is maintained over [[pH]] 10.5 - strongly basic.
[[Lead(II) nitrate|Lead nitrate]] can improve gold [[tank leaching|leaching]] speed and quantity recovered, particularly in processing partially oxidized ores.<!--how?--><!--why?, probably some sort of reduction reaction-->

===Effect of dissolved oxygen===
[[Oxygen]] is one of the [[reagent]]s consumed during cyanidation, accepting the electrons from the gold, and a deficiency in [[oxygen saturation|dissolved oxygen]] slows leaching rate. Air or pure oxygen gas can be purged through the pulp to maximize the dissolved oxygen concentration. Intimate oxygen-pulp contactors<!--huh?--> are used to increase the partial pressure of the oxygen in contact with the solution, thus raising the dissolved oxygen concentration much higher than the saturation level at [[atmospheric pressure]]. Oxygen can also be added by dosing the pulp with [[hydrogen peroxide]] solution.

===Pre-aeration and ore washing===
In some ores, particularly those that are partially sulfidized, [[aeration]] (prior to the introduction of cyanide) of the ore in water at high pH can render elements such as iron and sulfur less reactive to cyanide, therefore making the gold cyanidation process more efficient. Specifically, the oxidation of iron to [[iron (III) oxide]] and subsequent [[precipitation (chemistry)|precipitation]] as [[iron hydroxide]] minimizes loss of cyanide from the formation of ferrous cyanide complexes. The oxidation of [[sulfur]] compounds to sulfate ions avoids the consumption of cyanide to [[thiocyanate]] (SCN<sup>−</sup>) byproduct.