The carbon slurry process (CIP) is one of the gold ore treatment processes and a cyanide gold extraction process. The full name is the all-mud cyanide carbon slurry process for gold extraction. The process of adsorbing gold cyanide complexes is often used for the flotation of gold concentrate or mercury amalgamation, gravity separation of tailings, and muddy oxidized ores.
The carbon slurry method (CIP) gold extraction process refers to crushing, grinding, and muddying the gold-bearing ore to make a slurry and then performing cyanide leaching with the help of chemicals. Then, activated carbon is used to adsorb the dissolved gold from the slurry directly, and the gold-loaded carbon is desorbed and electrocuted. A technological method is obtained to separate gold mud for purification and smelting directly.
- Strong adaptability, suitable for sulfide ores, oxidized ores, and mixed ores;
- Simple operation, less equipment, and short process;
- Few operators;
- Save investment and low cost.
The steps of the carbon slurry process (CIP) mainly include seven operation stages: preparation of leaching slurry, cyanide leaching, activated carbon adsorption, gold-loaded carbon desorption, electric shock to obtain gold mud, recycling of gold-depleted carbon, and processing of leaching slurry.
1. Preparation of leaching slurry
Crush the gold-bearing ore to a particle size suitable for cyanide leaching and remove impurities from the slurry, mainly removing wood chips to prevent them from clogging the carbon screen.
2. Cyanide leaching
The slurry is stirred and leached with the help of chemicals.
3. Activated carbon adsorption
The slurry after cyanide leaching is introduced into the adsorption tank, and the dissolved gold in the slurry is adsorbed by activated carbon to become gold-loaded carbon.
Activated Carbon Characteristics
It divides activated carbon into two categories: powder carbon and granular carbon. We can produce granular carbon from various carbon-containing materials, such as celluloses, wood, coconut shells, nut shells, fruit cores, and coals.
Research shows that the structure of activated carbon is similar to graphite, which is composed of tiny wafers. The thickness of the wafers is only a few carbon atoms, and the diameter is 2 to 10 microns. The arrangement is very irregular, with many significant amounts of molecules the size of molecules—the side wall of the open cavity. Therefore, activated carbon is an active material with a developed pore structure and a vast adsorption surface machine. It is a good adsorbent for Au(CN)-. The pore structure of activated carbon is very complex, consisting of micropores with a diameter between 10 and 100, macropores with a diameter greater than 1000, and transition pores between 100 and 1000. The pore structure is the main factor affecting the adsorption characteristics of activated carbon.
The surface area of activated carbon is an important indicator that determines its adsorption capacity. It can usually be expressed by a specific surface area (m2/g). The surface area of activated carbon consists of the outer surface of the particles and the inner surface composed of pores. In comparison, the surface area of activated carbon is composed of pores. The inner surface area of the structure has a vast area ratio (greater than 90%), so it is more decisive for the adsorption characteristics of activated carbon. Research has determined that the specific surface area of activated carbon is huge, generally 500~1400 m2/g, and some Even up to 2500 m2/g.
In gold extraction production, the activated carbon must have high hardness and wear resistance, but adsorption activity and wear resistance often need to be revised. In actual production, the type of activated carbon used is usually determined based on experiments and experience.
The adsorption process of activated carbon
It is completed by three steps: outward diffusion of Au(CN)- to the surface of the carbon particles, inward diffusion, and adsorption into the interior of the carbon particles.
Factors affecting activated carbon adsorption
- Types of activated carbon
The adsorption characteristics of coconut shell charcoal and apricot kernel charcoal are much better than those of coal- and coke-based charcoal.
- Structure of adsorption equipment
Standard adsorption tanks include axial flow type and radial flow type. In comparison, the axial flow tank has smaller resistance, smaller dead zones, and a lower carbon wear rate, especially when using double impellers.
- Slurry properties
It refers to the particle size characteristics, concentration, and viscosity of the slurry, organic matter content, PH value, etc.
The particle size characteristics of the slurry mean that the slurry often contains some wood chips or coarse-grained ore that are larger than the mesh size of the inter-stage sieve, which will cause the blockage of the sieve holes between the stages and reduce the grade of the gold-loaded carbon. In addition, the gold-loaded carbon-containing wood chips desorption rate is not high either.
The concentration of the slurry mainly affects its specific gravity and fluidity, which will directly affect the flotation and distribution imbalance of activated carbon, which is not conducive to adsorption. The practice has proved that controlling it at 40~45% is generally better.
The content of fine mud mainly determines the viscosity of the slurry. If there is too much mud, the viscosity is high, and the fluidity is poor, it is easy to cause clogging of the interstage screen, leaching, and poor adsorption effects.
The organic matter in the pulp mainly refers to wood chips, oil substances, humic acid, flotation reagents, etc. They can be adsorbed by activated carbon, affecting the adsorption rate of gold, poisoning the activated carbon, and making it difficult to activate and regenerate the carbon.
- Number of adsorption stages and bottom carbon concentration
Experiments and experience determine the number of adsorption stages and bottom carbon concentration. The number of adsorption stages is generally 4 to 6, and the bottom carbon concentration is controlled between 5 and 25 g/L. Counter-current carbon stringing (intermittent and continuous) is used. ).
- Slurry aeration
Excessive aeration of the slurry will reduce the leaching speed of gold and the adsorption of gold by activated carbon. There are generally two aeration methods: center aeration and pipe aeration. Time has proven that the in-axis center aeration method is better.
4. Gold-loaded carbon desorption
Separate gold-loaded carbon from the slurry with the help of a carbon extraction screen and replace the gold complex in the desorption system.
5. Gold mud is obtained by electric shock
The noble liquid obtained by desorption of gold-loaded carbon is recovered by electric shock to obtain gold mud.
6. Recycling of degold carbon
After desorption, the activated carbon is treated to remove other aggregates and enters the recycling adsorption tank.
7. Treatment of leaching pulp
Cyanide-containing leaching pulp cannot be discharged directly. It can be treated with the help of a sodium hypochlorite generator or chlorine gas and acidified volatile alkali absorption method.
In actual production, the carbon slurry method (CIP) has achieved good results with its advantages, such as high adsorption and recovery rates. The carbon slurry method is good for gold-bearing ores with higher mud quality.