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1. Temperature and Dynamics The temperature of the desorbent is an important kinetic factor for the desorption of gold from gold-loaded charcoal. As the temperature increases, the equilibrium capacity constant of gold adsorbed by activated carbon decreases extremely rapidly. Therefore, the higher the temperature, the more complete the desorption of gold. The various desorption methods currently used must achieve higher desorption rates at higher temperatures. However, at present, the desorbent is generally an aqueous solution, and the temperature does not exceed 100 ° C under normal pressure, so that the temperature can only be controlled at 90 to 95 ° C in production. The desorption temperature can be further increased by using a pressurizing device. When the pressure is increased to 3 kg/cm 2 , the temperature can reach 140 ° C. Under this condition, the desorption rate of gold is about 10 times higher than that under normal pressure.
2. Cyanide concentration Cyanide concentration has a significant effect on the equilibrium capacity of gold-loaded carbon. Especially at high temperatures, increasing the concentration of cyanide can greatly increase the desorption rate of gold, and also prevent the precipitation of desorbed gold, which is advantageous for desorption. Therefore, in production, the concentration of sodium cyanide in the desorbent can be controlled to about 5%.
3. Concentration of alkali The higher the concentration of alkali, the higher the concentration of OH- in the solution, which will displace the adsorbed gold to a greater extent, which is advantageous for desorbing gold from activated carbon. However, if the concentration of the alkali is too high, corrosion and handling difficulties will occur, and thus the concentration of alkali (usually NaOH) in the desorbent is controlled to be 1-2%.
4. Adding methanol or ethanol Methanol or ethanol is more easily adsorbed by activated carbon than gold. Therefore, the addition of methanol or ethanol can replace the lattice ion of gold, which is beneficial to desorb gold and silver . However, the addition of alcohol increases the cost and complexity of safe production.
Activated carbon desorbed with alcohol has a significantly reduced activity. At the same time, the desorption rate of silver is low, which causes the silver content of the regenerated activated carbon to increase, which affects the utilization rate of the recycled activated carbon.
Factors affecting the desorption of gold from gold- loaded carbon are: