Cyanidation is use sodium cyanide solution to soak finely ground ore particles, so that the precious metals are dissolved into solution then use activated carbon recovery the gold. Cyanidation is an important method to process precious metals like gold and silver extracted from the ore..

The process of adding gold from cyanide pulp or solution by activated carbon adsorption
(CIP method), carbon immersion method (CIL method) several types, their processes basically include the following steps: (1) from the cyanide pulp or solution with activated carbon adsorption leaching of gold, production (3) the use of a variety of methods from the gold-containing liquid to recover the gold; (3) the use of gold from the solution of gold; 4) to have been desorbed after the charcoal for regeneration, to restore its activity, the return of adsorption operations reuse.
1 characteristics of activated carbon
Activated carbon from the appearance is divided into two types of powder charcoal and granular carbon. Granular charcoal can be produced from a variety of carbonaceous materials such as various cellulose, wood, coconut shells, fruit shells, nuts and various coal.
The work shows that the structure of activated carbon is similar to that of graphite, and is composed of tiny wafers. The thickness of the wafer is only a few carbon atoms in thickness and 2 to 10 microns in diameter, and the arrangement is very irregular and has a large number of molecules with a large size Open the side wall of the hole. Therefore, activated carbon is a well-developed pore structure and a huge adsorption surface of the active material, it is Au (CN) - a good adsorbent. The pore structure of activated carbon is very complicated, which consists of micropores with diameter between 10 and 100 and large pores with diameter greater than 1000 and transition holes between 100 and 1000. The pore structure is the main factor affecting the adsorption characteristics of activated carbon.
The surface area of ​​the activated carbon is an important index for determining its adsorption capacity. It is usually expressed by the specific surface area (m 2 / g). The surface area of ​​the activated carbon is composed of two parts of the outer surface of the particles and the inner surface composed of fine pores. The internal surface area of ​​the structure has a large area ratio (greater than 90%), so the adsorption characteristics of activated carbon more decisive role in the study and determination of activated carbon specific surface area is large, generally 500 ~ 1400 m 2 / g, some Even up to 2500 m 2 / g.
In the production of gold, the required use of activated carbon must have a high hardness and wear resistance, and adsorption activity and wear resistance is often contradictory. Production practice is often based on the experience and experience to determine the use of what kind of activated carbon.
2 adsorption process of activated carbon
From Au (CN) - to the external surface of the carbon particles, to the internal diffusion and adsorption of carbon particles to complete the three steps to complete.
3, the factors that affect the adsorption of activated carbon
3.1, the type of activated carbon
The adsorption characteristics of coconut shell charcoal and apricot charcoal are much better than that of coal and carbon.
3.2, adsorption equipment structure
Common suction tank has axial flow and runoff type, in contrast, axial flow groove resistance is small, the dead zone is also small, low carbon wear rate, especially when using double impeller is more obvious.
3.3, the nature of pulp
Refers to the particle size characteristics, concentration and viscosity, organic matter content, pulp PH value.
The particle size of the pulp is characterized by the fact that the pulp often contains some wood chips or coarse-grained ores larger than the size of the interstage sieve, which will cause the clogging of the interstage sieve and the grade of gold-bearing charcoal. In addition, The desorption rate is not high.
The concentration of pulp mainly affects the specific gravity and fluidity of the pulp, which will directly affect the floating and uneven distribution of activated carbon, which is not conducive to adsorption. It is proved that the control is generally 40 ~ 45%.
Paste viscosity is mainly determined by the amount of mud, mud, viscosity, poor mobility, easy to cause interstage sieve plug, while leaching, adsorption effect is not good.
The organic matter in the pulp mainly refers to wood chips, oil substances, humic acid, flotation agents and so on. They can be activated carbon adsorption, the impact of gold adsorption rate, and the activated carbon poisoning, to the activation of carbon regeneration difficult.
3.4, the number of adsorption and bottom carbon concentration
The number of adsorbents and the concentration of bottom charcoal are generally determined by experimentation and experience. The number of adsorption faults is generally 4 to 6, and the bottom carbon concentration is controlled between 5 and 25 g / l, and the countercurrent carbon (intermittent and continuous ).
3.5, pulp inflatable
Mineral fuel consumption over the General Assembly to reduce the rate of gold leaching and activated carbon adsorption on the gold, inflatable way generally there are two types of central inflation and pipe inflation, time to prove that the shaft center inflatable method is better.
4 charcoal equipment and process operation
4.1, charcoal equipment
At present, there are three kinds of turbo pump, jet pump and air mixing room.
4.2, process operation
The charcoal is usually started by the first tank, and then by string of string of charcoal, and finally in the end of the tank to add carbon, the number of charcoal based on the test and theoretical calculations as the basis, each class to maintain unity.
5 with gold charcoal desorption
5.1, the principle of gold-loaded carbon desorption
The experimental study shows that the process of adsorption of activated carbon is actually a reversible process. When the carbon is adsorbed, the temperature, pressure, pH and cyanide (CN-) are too high to significantly reduce the amount of gold adsorbed, so it can take effective The gold on the gold is swept into the solution.
5.2, containing gold charcoal desorption methods and process conditions
5.2.1, atmospheric pressure heating desorption method (also known as Zadela desorption method)
This is the earliest simple way to appear. It is carried out by using a mixed aqueous solution of 0.1% NaCN and 1.0% NaOH at a temperature of 85 to 95 ° C to pass the gold-bearing carbon bed, which takes about 28 to 70 hours to complete the desorption requirement.
5.2..2, pressurized desorption method
In the temperature of 150 ~ 1700C, the pressure of 0.3432Mpa, mixed aqueous solution of 0.1% NaCN and 0.4 ~ 1.0% NaOH prepared by desorption 4 to 6 hours can be reduced to less than 50 to 70 grams / ton of decarburization. This method is not long, but the equipment costs are high, desorption of liquid must be cooled before the power supply.
5.2.3, alcohol desorption method
With 10% NaCN and 1.0% NaOH mixture and then add 20% of the volume of alcohol, under the 800C atmospheric pressure desorption, desorption time of 5 to 6 hours, but the alcohol is flammable and volatile substances, difficult to control.
5.2.4, the United States and Britain desorption method
The method for the South American Institute of British and American creation, with 0.5 gold loaded gold volume of 5% and 1.0% mixture pre-treatment of gold for 0.5 to 1 hour, and then with five gold-loaded volume of heated deionized water, The desorption time (including acidity) is about 9 hours at a flow rate of 3 cylinders per hour. The operating temperature is 1100 ° C, the operating pressure is 0.5 to 1.0 kg / cm 2, and the desorption time (including acidity) is about 9 hours.
5.3, desorption equipment and operational precautions
Containing gold charcoal desorption equipment is usually associated with electrolytic deposition equipment, constitute the production cycle of the unit.
Will be prepared by the gold loaded into the desorption tower (column), and then prepared a good desorption pump into the desorption system, the specific mode of operation, depending on the use of equipment, technology may be.
5.4, ​​containing gold carbon desorption should pay attention to matters
5.4.1, when the desorption tower of the aspect ratio is greater than 6, the desorption effect is better, can be easy to operate, shorten the desorption time, it is generally used with a diameter ratio greater than 6 desorption tower.
5.4.2, the flow of desorption fluid in the tower as far as possible the flow rate in the tower within the distribution of uniform, and full contact with the gold loaded.
5.4.3, through the test to select the appropriate desorption time, under normal circumstances, the longer the desorption time, the higher the desorption rate, but too long will reduce the utilization of equipment, production costs.
5.4.4, according to the requirements of the strict control of desorption temperature in the tower evenly distributed points
5.4.5, to ensure that the composition of desorbent meet the requirements
5.4.6, pay attention to the flow of desorption fluid, generally in 1 hour 1 to 5 charcoal bed volume.
5.4.7, pay attention to the load of carbon containing impurities and pore characteristics. Prior removal of carbon impurities (wood chips, plastics, coarse grain ore, etc.) will be conducive to the improvement of desorption rate.
6, the release of gold charcoal
Activated charcoal activity after adsorption, desorption, regeneration has a clear table, the gold from the acid after regeneration, its activity has not improved significantly, can only restore half of the activity, only the use of thermal regeneration is possible to restore the activity to 80 %the above.
The main reasons for the decrease of the adsorption activity of activated carbon are as follows:
First, the pores of carbon are blocked by inorganic matter. For example, quartz sand particles such as Ca (OH) 2 and Mg (OH) 2 in slurry can be easily adsorbed by activated carbon and enter into the pores of charcoal. Clogging, and other excess in the pulp and copper and other base metal complex ions will be carbon particles adsorption caused by microporous poisoning, reduce activity.
Second, organic matter such as lubricants, detergents, flotation agents, humic acid and so on are activated carbon adsorption, greatly affect the activity of carbon.
Thirdly, the degradation of the active sites in the activated carbon and the change of the pore formation of the carbon are also the reasons for the decrease in activity.
Practice has proved that the deductive carbonic acid, its activity can be restored to 50 to 60%, and heat regeneration after its activity can be restored to more than 85%, and some even better than the activity of new carbon. Acid can be used dilute hydrochloric acid or dilute nitric acid (concentration of 1 ~ 5%) at room temperature in a special pickling tank, after 2 to 4 hours washing, can remove carbon on the calcium and other compounds, and 90 ~ 93 ℃ hot acid Solution can remove calcium, zinc, nickel compounds and most of the silicon. If the pores of the carbon are seriously clogged with silicate, only the use of hydrofluoric acid (HF) aqueous solution can only be effective.
The thermal regeneration of the gold is usually done in an external heat rotary furnace, which involves several stages of drying, carbonization and gasification, which can play the following roles:
First, the organic adsorbate in the heating stage desorption volatilization;
Second, the organic pollutants are carbonized at 600 to 700 ° C;
Third, the formation of new carbon pores, increase the specific surface area;
Fourth, a new activation point is formed in the pores of the carbon to increase the activity.

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