Cyanidation with a tank on mining has increased rapidly since the mid-1980s. Extraction of gold by using a tank leaching systems typically use a lot of multiple tanks in series within a building. Different from heap leaching are located at the open air. Gold leaching process carried out by stirring the gold ore is mixed with limestone and added with a solution of cyanide in a tank and aerated with air bubbles. The duration of stirring often for 24 hours to produce the optimum leaching. Tank and leaching efficiency of about 92% to 98% gold content of rocks
Gold is one
of the noble metals and as such it is not soluble in water. A complexant, such
as cyanide, which stabilizes the gold species in solution, and an oxidant such
as oxygen are required to dissolve gold. The amount of cyanide in solution
required for dissolution may be as low as 350 mg/l or 0.035% (as 100% NaCN).
Alternative complexing agents for gold, such as chloride,
bromide, thiourea, and thiosulfate form less stable complexes and thus require
more aggressive conditions and oxidants to dissolve the gold. These reagents
present risks to health and the environment, and are more expensive. This
explains the dominance of cyanide as the primary reagent for the leaching of
gold from ores since its introduction in the later part of the 19th century.
On cyanide leaching of gold in the tank system, activated carbon is very important to use when in the process of recovery of dissolved gold, either by introducing direct to the Carbon In Leach (CIL) in tank or to the Carbon In Pulp (CIP) separately outside the tank after washing. Carbon In Pulp (CIP) leaching occurs in two stages in the process in a different tank, while the Carbon In Leach (CIL) slurry of minerals and activated carbon having a tank leaching simultaneously on the same premises. Carbon is then separated from the slurry by screening and have further treatment to recover adsorbed gold.Gold complexes of carbon absorbed directly as soon as the gold dissolves in cyanide solution. CIL is used if the rock contains a lot of natural carbon, because carbon will naturally absorb the gold complex. Add activated carbon in the CIL is more active than the natural carbon.CIL
investment cost is less expensive when compared with the CIP so that
this method is also used on many people's scale mines are. This method is higher than the absorption of gold compared to the Heap leaching. New
technologies are applied in South Africa using ion exchange resins
Resin In Pulp (RIP) is expected to lower the operational costs. Preparation
of rock (including softening, solution concentration, as well as the
type of solution) and the leaching time is different for each rock. Oxide rocks the size of 65 mesh requires a 0.05% NaCN (50% solids) with a leaching time of 4 to 24 hours. Sulfide rocks the size of 325 mesh needs 0.1% NaCN leaching time up to 72 (Weiss 1995)
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