Factors affecting the adsorption of gold by activated carbon
2020-08-21 11:04Introduction：Factors affecting the adsorption of gold by activated carbon in heap leaching Since the end of the 19 th century, activated carbon has been known to adsorb gold and be used in industry. But after the zinc replacement technology appeared, i
Factors affecting the adsorption of gold by activated carbon in heap leaching
1. Effect of gold concentration in solution
The higher the concentration of gold in solution is, the higher the concentration after adsorption equilibrium is. The adsorption capacity of gold by activated carbon increases linearly with the increase of equilibrium concentration. Therefore, the higher the concentration of gold in the solution, the larger the capacity of activated carbon to adsorb gold. When the gold concentration in the solution was 95~164PPm, the loading amount of gold increased from 9960 g / t to 37900 g / t. The capacity of gold adsorbed by activated carbon varies with equilibrium concentration, as shown in Fig. 2-7.
2. Effect of pH value on solution
The high acidity of the solution is favorable to the adsorption of gold by activated carbon, so low pH value will increase the capacity of gold adsorption by activated carbon. However, for cyanide medium, pH is not allowed to be too low, so the pH value of heap leaching-adsorption process should be maintained at 9~11.
3. Influence of impurity concentration in solution
Calcium, magnesium, copper, nickel in solution. Metal ions such as zinc, iron and silicic acid will be adsorbed, while the amount of gold adsorbed by activated carbon will be reduced by decreasing the lattice number of gold adsorbed by activated carbon. The order of the influence of the above metal ions on the adsorption capacity of gold on activated carbon is [Fe(CN)6] 4- > [Ni(CN)4] 2- > [Zn(CN)4] 2- ≈ [Cu(CN)3] 2-. Because copper is easily oxidized into solution, the influence of copper ion is more common. The French Geological and Mineral Survey has tested that 6~10% of copper is adsorbed when the solution contains Au11~12ppm Cu28~33ppm. Because the pH value is adjusted by lime during leaching, calcium and silica in lime increase with the circulation of water, and become the main pollutants of activated carbon, which affect the activity of carbon. When the carbon contains calcium and magnesium, the activity of carbon decreases by 2%. The presence of organic liquids, such as kerosene, lubricants, alcohols, also seriously affects the adsorption of gold by carbon.
4. Influence of Silver in solution
Since the radius and the adsorption potential of the gold cyanide complex ion is larger than that of the silver cyanide complex ion , the gold cyanide complexions are preferentially adsorbed at the same concentration , and the adsorbed silver is also replaced by gold . Therefore , when the concentration is the same , the amount of gold adsorbed is about three times that of the silver cyanide complex ion , but when the content of the silver in the solution is increased , the adsorbed silver will increase the chance of being adsorbed , and compete with the gold , so that the capacity of the activated carbon adsorption gold is relatively reduced .
5. Effect of cyanide concentration
Increasing the concentration of free cyanide in solution will reduce the amount of gold adsorbed by activated carbon. This is because the increase of CN-concentration increases the competitive ability of CN- and Au(CN)2-, and weakens the adsorption of gold by activated carbon, especially at higher temperature, the effect is more obvious, as shown in Fig. 2~8
6. temperature affect
The higher the temperature, the more unfavorable to the adsorption of gold by activated carbon. With the increase of temperature, the adsorption capacity decreases rapidly, especially when the concentration of gold is low. The effect of temperature is shown in figure 2-8. Therefore, the adsorption process is generally carried out at room temperature.
7. Effect of flow rate of solution through activated carbon layer
When other conditions are the same, the velocity of solution passing through the carbon layer is slow, the contact time between the solution and the activated carbon is longer, and the active carbon has sufficient contact with the gold-cyanide complexion, so the capacity of the activated carbon to adsorb gold is higher. However, the adsorption capacity of the adsorption equipment was decreased due to the decrease of the adsorption rate. At the same time, the flow rate of the solution through the carbon layer is fast, and the fluidized carbon bed can be formed, which accelerates the adsorption speed of the activated carbon to the gold-cyanide complex ion, which is beneficial to the improvement of the equipment efficiency. Therefore, reasonable flow rate must be controlled. It is generally controlled at 450 to 600 liters / (m2·min).
8. Effect of activated carbon type and particle size
Different types of activated carbon have different adsorption capacity for gold cyanide complex ion due to the different properties of quality standards. The results showed that activated carbon from coconut shell and fruit shell had higher adsorption capacity of gold than wood, coal and petroleum coke. With the same activated carbon, the particle size has a great influence on the adsorption rate of gold-cyanide complex ion. The fine particle is faster than the coarse-grained activated carbon to adsorb gold-cyanide complex ion, and the adsorption capacity of gold-cyanide complex ion is large in the same time.
