Factors affecting desorption of gold from gold-loaded carbon
2020-08-21 11:08Introduction：Factors affecting desorption of gold from gold-loaded carbon in heap leaching of gold deposits In recent ten years, alkaline cyanide (NaOH-NaCN) was used as desorption agent in industry. By heating and pressurizing, the solution is dissolv
Factors affecting desorption of gold from gold-loaded carbon in heap leaching of gold deposits
In recent ten years, alkaline cyanide (NaOH-NaCN) was used as desorption agent in industry. By heating and pressurizing, the solution is dissolved in the form of Au(CN)2 -. Some are desorbed by organic solvents at normal temperature. The factors affecting the desorption of gold from gold-loaded carbon are as follows:
1. Effect of temperature and pressure
The temperature of desorption solution is an important kinetic factor for desorption of gold from gold loaded carbon. Because the equilibrium capacity constant of gold adsorbed by activated carbon decreases rapidly with the increase of temperature, the desorption of gold becomes more complete with the increase of temperature. All kinds of desorption methods used at present must obtain high desorption rate at higher temperature. However, desorption agents are generally aqueous solution. The maximum temperature must not exceed 100 ℃ under atmospheric pressure, so it is generally controlled at 90 ~ 95 ℃ under atmospheric pressure. The desorption temperature can be further raised by using pressurized equipment. When the pressure is increased to 3 × 10 5 Pa, the temperature reaches 140 ℃, and the desorption rate of gold under this condition is about 10 times higher than that at normal pressure. Of course, high- pressure equipment and operation are more complex than normal pressure.
2. Effect of cyanide concentration
The concentration of cyanide has a significant effect on the equilibrium capacity of gold loaded carbon. Especially at high temperature, the desorption rate of gold can be greatly increased by increasing the concentration of cyanide. The addition of CN- can also prevent the reduction and precipitation of desorbed gold and is beneficial to desorption. Therefore, the concentration of sodium cyanide in desorption solution is up to 5%.
3. Effect of alkali concentration
The higher the concentration of alkali (sodium hydroxide) is, the higher the concentration of OH- is, and the higher the concentration of OH- is, the greater the amount of adsorbed gold is, which is beneficial to the desorption of gold. However, excessive concentration of alkali will lead to serious corrosion and operation difficulties. So the concentration of sodium hydroxide is generally controlled at 1%~ 2%.
4. Effect of adding Organic solvent
As mentioned earlier, the desorption rate and desorption rate of gold can be increased by adding organic solvent. With the increase of the concentration of organic solvent, the activity ratio of CN- and Au(CN)2- in solution increases, and the desorption rate and desorption rate of gold increase. In the presence of CN-, alcohols, ketones, and nitriles all promote the desorption of gold. Their desorption ability depends on the length of functional groups and carbon chains and increases in the following order: simple alcohols < dipolarity versus protons, Inert solvent < higher alcohols < ketones < nitriles.
