Carbon in pulp
Encyclopedia
Carbon in Pulp is an extraction technique for recovery of gold
which has been liberated into a cyanide
solution
as part of the gold cyanidation
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
or copper
does not prohibit its use.
Activated carbon
acts like a sponge to aurocyanide and other complex ions in solution
.
Hard carbon
particles (much larger than the ore particle sizes) can be mixed with the ore and cyanide
solution mixture.
The gold cyanide complex is adsorbed onto the carbon until it comes to an equilibrium with the gold in solution.
Because the carbon particles are much larger than the ore particles, the coarse carbon can then be separated from the slurry
by screening using a wire mesh.
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Leached pulp and carbon are transferred in a counter current flow arrangement between 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
solution.
At this tank the fresh carbon has a high activity 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
s of gold per tonne
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).
This can be measured by comparing the amount of gold extracted from the carbon to the amount of carbon used.
" or desorption
of gold cyanide at high temperature
and pH
.
Ethanol
can also be used to desorb gold from activated carbon, but safety concerns have slowed its acceptance in the gold extraction
industry.
cells where gold and other metals are precipitated onto the cathode
s.
Smelting
of the cathodes material further refines the gold and produces gold ingot
s suitable for transport to a refinery
.
For further information on gold smelting, see the article on gold extraction.
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
which has been liberated into a cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
as part of the gold cyanidation
Gold cyanidation
Gold cyanidation is a metallurgical technique for extracting gold from low-grade ore by converting the gold to a water soluble coordination complex. It is the most commonly used process for gold extraction...
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
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
or copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
does not prohibit its use.
Activated carbon
Activated carbon
Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...
acts like a sponge to aurocyanide and other complex ions in solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
.
Hard carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
particles (much larger than the ore particle sizes) can be mixed with the ore and cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
solution mixture.
The gold cyanide complex is adsorbed onto the carbon until it comes to an equilibrium with the gold in solution.
Because the carbon particles are much larger than the ore particles, the coarse carbon can then be separated from the slurry
Slurry
A slurry is, in general, a thick suspension of solids in a liquid.-Examples of slurries:Examples of slurries include:* Lahars* A mixture of water and cement to form concrete* A mixture of water, gelling agent, and oxidizers used as an explosive...
by screening using a wire mesh.
Loading gold into carbon
In the final tank, fresh or barren carbon is put in contact with low grade or tailings
Tailings
Tailings, also called mine dumps, slimes, tails, leach residue, or slickens, are the materials left over after the process of separating the valuable fraction from the uneconomic fraction of an ore...
solution.
At this tank the fresh carbon has a high activity and can remove trace amounts of gold (to levels below 0.01 mg/L Au
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
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
Gram
The gram is a metric system unit of mass....
s of gold per tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
of carbon (g/t Au) can be achieved on the final loaded carbon, as it comes in contact with freshly leached
Tank leaching
In metallurgical processes tank leaching is a hydrometallurgical method of extracting valuable material from ore.Tank leaching is usually differentiated from vat leaching on the following factors:...
ore and pregnant leach solution
Pregnant leach solution
Pregnant Leach Solution is acidic metal-laden water generated from stockpile leaching and heap leaching. Pregnant Leach Solution is used in the SX/EW process....
(PLS).
This can be measured by comparing the amount of gold extracted from the carbon to the amount of carbon used.
Removal of gold from carbon
The final loaded carbon then is removed and washed before undergoing "elutionElution
Elution is a term used in analytical and organic chemistry to describe the process of extracting one material from another by washing with a solvent ....
" or desorption
Desorption
Desorption is a phenomenon whereby a substance is released from or through a surface. The process is the opposite of sorption . This occurs in a system being in the state of sorption equilibrium between bulk phase and an adsorbing surface...
of gold cyanide at high temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
and pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
.
Ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
can also be used to desorb gold from activated carbon, but safety concerns have slowed its acceptance in the gold extraction
Gold extraction
Gold extraction or recovery from its ores may require a combination of comminution, mineral processing, hydrometallurgical, and pyrometallurgical processes to be performed on the ore....
industry.
Electrowinning
The rich eluate solution that emerges from the elution process is passed through electrowinningElectrowinning
Electrowinning, also called electroextraction, is the electrodeposition of metals from their ores that have been put in solution or liquefied. Electrorefining uses a similar process to remove impurities from a metal. Both processes use electroplating on a large scale and are important techniques...
cells where gold and other metals are precipitated onto the cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
s.
Smelting
Smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...
of the cathodes material further refines the gold and produces gold ingot
Ingot
An ingot is a material, usually metal, that is cast into a shape suitable for further processing. Non-metallic and semiconductor materials prepared in bulk form may also be referred to as ingots, particularly when cast by mold based methods.-Uses:...
s suitable for transport to a refinery
Refinery
A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value.-Types of refineries:Different types of refineries are as follows:...
.
For further information on gold smelting, see the article on gold extraction.
See also
Other gold cyanidation techniques:- Merrill-Crowe processMerrill-Crowe processThe Merrill-Crowe Process is a separation technique for removing gold from a cyanide solution.The solution is separated from the ore by methods such as filtration and counter current decantation and is then clarified in special filters, usually coated with diatomaceous earth to produce a clarified...
- ElectrowinningElectrowinningElectrowinning, also called electroextraction, is the electrodeposition of metals from their ores that have been put in solution or liquefied. Electrorefining uses a similar process to remove impurities from a metal. Both processes use electroplating on a large scale and are important techniques...
- Resin in Pulp