Carbon in pulp (CIP) is an extraction technique for recovery of
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...
which has been liberated into a
cyanide
Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms.
In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
solution as part of the
gold cyanidation
Gold cyanidation (also known as the cyanide process or the MacArthur-Forrest process) is a hydrometallurgical technique for extracting gold from low-grade ore by converting the gold to a water-soluble coordination complex. It is the most commonl ...
process.
Introduced in the early 1980s, Carbon in Pulp is regarded as a simple and cheap process. As such it is used in most industrial applications where the presence of competing
silver
Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
or
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish ...
does not prohibit its use. In the case of high (i.e., 1%) copper content, froth flotation is more typical.
Activated carbon
Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area avail ...
acts like a sponge to
dicyanoaurate, the main soluble gold species in gold extraction technologies.
Hard carbon particles (much larger than the ore particle sizes) can be mixed with the solution. The gold cyanide complex
adsorb
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...
onto the carbon and is proposed to be reduced back to the metal. Because the carbon particles are much larger than the ore particles, the coarse carbon can then be separated from the
slurry
A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal p ...
by screening using a wire mesh.
Loading gold into carbon
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Leached pulp and carbon are transferred in a
countercurrent flow arrangement involving a series of tanks, usually numbering 4 to 6. In the final tank, fresh or ''barren'' carbon is put in contact with low grade or
tailings
In mining, tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction ( gangue) of an ore. Tailings are different to overburden, which is the waste rock or other material that overl ...
solution. At this tank the fresh carbon has a high affinity for gold and can remove trace amounts of gold (to levels below 0.01 mg/L
Au in solution).
As it moves up the train, the carbon loads to higher and higher concentrations of gold, as it comes in contact with higher grade solutions. Typically concentrations as high as 4000 to 8000
gram
The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram.
Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to ...
s of gold per
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
of carbon (g/t Au) can be achieved on the final loaded carbon, as it comes in contact with freshly
leached ore and
pregnant leach solution (PLS).
Removal of gold from carbon
The final loaded carbon is removed from the machinery and extracted with a hot alkaline solution of cyanide.The elute solution passes through an electrowinning cell where the gold metal is deposited.
[ The solution then passes back through the loaded carbon, extracting more gold and other metals. This process continues until the carbon has been stripped of its metals.
The cathodes (wire wool, now plated with gold and other metals) are removed and placed in acid. The acid burns off the wire wool and other metals such as copper, and leaves a sediment of gold and a solution of acid and dissolved silver. The acid and silver are drained off, after which the gold sediment is washed with water numerous times.
]
See also
Other gold cyanidation techniques:
* Merrill-Crowe process
*Electrowinning
Electrowinning, also called electroextraction, is the electrodeposition of metals from their ores that have been put in solution via a process commonly referred to as leaching. Electrorefining uses a similar process to remove impurities from a ...
References
{{DEFAULTSORT:Carbon In Pulp
Cyanidation
Metallurgical processes
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