Introduction of gold extraction process by carbon leaching

1. Application of carbon immersion method

CIL process (the CIL) is developed in the whole mud powder zinc cyanide substitution based on gold extraction process, mainly by dipping the former dense, leaching adsorption, desorption electrospray product loaded carbon, charcoal and thermal regeneration of pickling, the agent Preparation, sewage treatment and gold smelting and other processes. The charcoal leaching method is characterized in that the two operations of leaching and adsorption are carried out at the same time, saving the stirring tank and saving investment. This process has been widely adopted in newly established wet gold extraction plants in recent years.

CIL process suitable for processing sulfur-containing oxide ore more mud, of gold is not suitable for high silver, gold and silver ratio is generally no more than 1: 5. The optimum conditions for domestic carbon leaching method are: PH=10-11, sodium cyanide concentration is not less than 0.015%, activated carbon particle size is 1-3.35mm, charcoal type is coconut shell activated carbon, and leaching pulp concentration is 40-45%.

2. Preparation before cyanidation The carbon extraction process is carried out by carbon leaching. Before cyanide leaching, in addition to ore crushing, grinding, swarf removal, slurry concentration and addition of detergent are also necessary.

2.1 Dedusting operation

Wood chips, grass roots and debris in the pulp are prone to blockage of pipes and screens, and wood chips can also absorb gold, so they must be removed before leaching. Generally, in the grinding process, it is necessary to design two dedusting operations, respectively, in the overflow section of the first and second stages of grinding. The medium-frequency linear vibrating screen is mostly used in the chip removing equipment. In the first chip removing operation, there are also spiral screens and cylindrical screens. The size of the screen of the chip removing screen is required to ensure that the screen surface does not run as much as possible. Small.

2.2 Dense work before immersion

The grinding fineness of the common carbon leaching method is mostly -200 mesh, accounting for 85-95%, and the grinding fineness of the flotation concentrate is -300 mesh, accounting for more than 99%, and the overflow concentration. Mostly 18-22%, not suitable for direct leaching, must be thick pulp.

Dense equipment uses high-efficiency thickeners with small footprint and high work efficiency.

2.3 Adding detergent

In order to reduce the scale on the surface of the activated carbon and on the sieve and other objects, a certain amount of detergent can be added before the slurry is leached.

3, leaching and adsorption

The carbon leaching method is characterized by the simultaneous leaching and adsorption of gold. The number of leaching stages is generally 6-10. Since the first tank has just added sodium cyanide, the amount of gold leaching is small. Most carbon leaching plants use the first tank as a pre-dip tank. The subsequent tank serves as a leaching adsorption tank. A carbon screen is installed on each of the leaching adsorption tanks to separate the carbon and the slurry, the slurry flows in the forward direction, and the activated carbon flows in the reverse direction, that is, the fresh activated carbon is added from the last leaching adsorption tank, and the gold-loaded carbon is leached from the first stage. The adsorption tank is discharged, and after being sieved and washed, it is sent to the desorption electrowinning operation, and the gold grade of the slurry solution adsorbed by the method is generally 0.01-0.03 g/m3.

3.1 Cyanide leaching

During the leaching process, cyanide is used to leach gold and silver from the ore to form a cyanide complex of gold and silver. Lime is used to maintain a high pH to prevent the formation of toxic hydrogen cyanide gas. In a carbon leaching plant with a high level of automation, a hydrogen cyanide gas detector is installed in the leaching and adsorption zone.

Main parameters of leaching

The reaction of gold, silver and cyanide requires the participation of oxygen. In theory, the oxygen consumption per gram of gold is 0.04g, but the oxygen consumption in actual production is much larger. Because the ore often contains various metal sulfides, it also consumes. Oxygen reacts with cyanide. In actual production, 100 kPa of medium-pressure air is used to pass through the hollow shaft of the agitator. Air flow is typically controlled and metered using a rotameter.

In recent years, with the introduction of two key technical and economic indicators such as enhanced leaching and reduction of cyanide consumption, the oxygen-rich leaching gold extraction process (CILO) came into being. The main advantages of using CILO are:

(1) Accelerate the leaching kinetics, reduce the leaching time, and sometimes increase the leaching rate of gold and silver;

(2) reduce cyanide consumption;

(3) The effect of leaching finely ground ore is better than that of air-filling;

(4) Effectively leaching ore containing higher oxygen-consuming minerals;

In a gold mine in Hebei, the compressed air agitation was changed to oxygen-rich leaching. Under the condition that the original equipment was unchanged, only one oxygen-making unit was added instead of the original air compressor. The leaching time was shortened from 36-42h to 20h. Left and right, the leaching rate of gold also increased by 0.89%, and cyanide saved 0.27kg/t of ore. Due to the shortening of the leaching time, the production capacity of the original leaching equipment increased from 300t/d to 643t/d, which created obvious economic benefits.

Hydrogen peroxide or hydrogen peroxide can replace the compressed air to achieve the purpose of oxygen-rich leaching, but the specific effects can be determined by testing and simulation production experiments.

3.2 Activated carbon adsorption

The commonly used activated carbon is coconut shell activated carbon, which has good adsorption performance and anti-wear strength; each adsorption tank should be provided with a carbon screen, and the screen is generally selected from a 24 mesh 304 stainless steel screen.

The carbon screens are mostly cylindrical or V-shaped, and there are also vibrating screens or other forms.

The main factors affecting the adsorption of activated carbon are:

3.2.1 Effects of activated carbon properties

These include the effects of carbon adsorption capacity, the effect of carbon strength; the effect of carbon particle size;

3.2.2 Effect of pulp properties

It mainly includes the effects of coarse sand and wood chips, the influence of slurry concentration and viscosity, the influence of organic matter in the pulp, the influence of the pH value of the pulp, and the influence of carbonaceous ore;

3.2.3 Impact of operating parameters

The operating parameters mainly include the amount of inflation, the method of inflation, the concentration of cyanide, and the amount of carbon stored in the process.

3.3 Detection and control

In the production process, the tester needs to test the slurry concentration, pH value, cyanide, and bottom carbon density. Generally, it needs to be tested once every 2 hours. In the high-automation plant, the slurry concentration and PH can be monitored online and automatically adjusted. Value and cyanide concentration; the operator needs to check the amount of gas, carbon screen, slurry tank surface, etc. at any time.

4. Desorption electromagnetism of gold-bearing carbon

The gold-loaded carbon and slurry are sent to a carbon separation screen (usually a linear vibrating screen) through a carbon pump or an air lifter. The water is washed with water on the screen to separate the charcoal from the slurry, and the gold-bearing charcoal enters the carbon storage tank, the pulp and The flushing water enters the first adsorption tank.

There are several methods for desorption of gold-loaded carbon. The Zhadra method, high temperature and high pressure desorption method and integral pressure desorption system are commonly used in China.

4.1 Zadefa

The Zade process uses 0.1% sodium cyanide and 1% sodium hydroxide solution as the desorption liquid, and operates at 85-95 ° C under normal pressure. The desorption time is 24-72 h. The method is simple, and the investment and production cost are low, but It takes a long time and the working environment is also poor;

4.2 High temperature and high pressure desorption method

The desorption solution in the high temperature and high pressure desorption method is 0.1% sodium cyanide and 1% sodium hydroxide aqueous solution, the temperature is 150-170 ° C, the pressure is 0.35 MPa, and the desorption time is only 4-6 h to reach the process conditions. The method greatly reduces the consumption of the medicament, the desorption rate is fast, and the carbon cycle is short, but before the method desorbs the noble liquid, it must be cooled to prevent boiling and splashing;

4.3 Overall Pressure Desorption System

The basic process of the overall pressure desorption system is similar to the high temperature and high pressure desorption method, but the electrowinning operation is also in the pressure system, there will be no boiling and splashing, and there is no need to cool before entering the electrowinning, and the desorption liquid is only 5% sodium hydroxide solution. Just fine. The desorption temperature is 150 ° C, the desorption pressure is 0.5 MPa, the desorption time is about 6 h, the electrowinning voltage is 2.5-3.0 V, and the electrowinning current is 250 A. This method is most commonly used.

5, carbon regeneration

After the activated carbon is desorbed by adsorption, it needs to be regenerated to restore its good adsorption performance. It is generally divided into pickling regeneration and thermal regeneration, and pickling regeneration is immersed in 5% dilute nitric acid solution. The production of domestic and international practice show only removing a portion of inorganic acid adsorbed on carbon, the iodine value and can only be restored value CTC activated carbon, the carbon reduced inorganic ash content, the adsorption capacity and adsorption rate of carbon improvement incomplete. After several picklings, thermal regeneration is required. The thermal regeneration process includes four steps of drying, carbonization, carbon removal, and cooling. After thermal regeneration, the adsorption capacity and adsorption rate of carbon are fully recovered, and the adsorption activity can be close to or reach the new carbon level.

6. Main equipment of carbon leaching plant

6.1 Preparation equipment before leaching

Including crusher , belt conveyor, vibrating screen, ball mill , classifier, chip removal, thickener, slurry pump, etc.;

6.2 Leaching and adsorption equipment

Including leaching tank, adsorption tank, carbon lifting equipment, carbon screen, safety screen, etc.;

6.3 Desorption and electrowinning equipment

The conventional Zade process desorption electrowinning equipment includes: a desorption column, an electric heater, an electric accumulator, a filter, a heat exchanger, a corrosion resistant pump, etc.; the overall pressure desorption system includes a desorption column, an electric heater, an electric accumulator, Filter, corrosion resistant pump, etc.

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