Gold heap leaching is a common method for gold extraction. However, despite the simplicity of the process, the heap leaching of gold ore also requires professional guidance, otherwise it’s difficult to guarantee the heap leaching effect and obtain high-grade gold concentrate. If your gold ore heap leaching effect is poor, we suggest you to pay attention to the following six factors.
For ore with good permeability, the ore heap height can be set higher; for ore with poor permeability, the ore heap height should not be too high. A too high heap pile will affect the oxygen supply and permeability of the gold ore below, thereby reducing the leaching rate. Under normal circumstances, it is recommended to set the height of the ore pile to about 2-4 meters.
Under normal circumstances, the smaller the ore particle size is, the shorter the leaching time is, and the higher the leaching rate. However, it should be noted that the ore particle size is not as small as possible. If the amount of fine ore after crushing is large (that is, the content of 200 mesh exceeds 35%), the heap leaching will cause the surface of the ore heap to form a channel, which will affect the penetration of the solution and lead to the leaching rate somewhat reduced. Therefore, it is recommended to crush the gold ore to a particle size of 30-50 mm before heap leaching.
During the cyanidation leaching process, due to chemical action, sulfuric acid, carbonic acid, etc. will be produced in the solution, which will react with cyanide to decompose the cyanide. Therefore, it is necessary to control the pH value of the solution. If the pH value is too high, the formation of calcium peroxide film on the metal surface will significantly reduce the dissolution rate of gold. It is recommended to add a certain amount of lime to maintain the pH value between 9.5-11 to prevent the decomposition of cyanide.
When the cyanide solution is low, the solubility of gold is high, but the solubility of other non-metals is low, and the consumption of cyanide will be greatly reduced. When the concentration of the cyanide solution reaches 0.05%, the dissolution rate of gold increases rapidly with the increase of the concentration of the cyanide solution. The effect is not significant; when the concentration of the cyanide solution is greater than 0.15%, the dissolution rate of gold not only does not increase, but also tends to decrease. Therefore, it is recommended to control the concentration of cyanide solution in the range of 0.05-0.1% to obtain a more ideal heap leaching effect.
Increasing the spraying intensity of the solution can shorten the leaching time of gold ore, and at the same time can strengthen the relative movement between the gold ore and the solution, which can strengthen the diffusion. However, when the spraying intensity is too large, the amount of impurities leaching in the ore will increase, thereby relatively reducing the ratio of the gold concentration in the leaching solution to the sum of the impurity concentrations, increasing the difficulty of the next step. In actual operation, it is recommended to control the spray intensity at 8-12 liters/square meter.
The dissolution rate of gold is affected by both dissolved oxygen concentration and temperature.
Dissolved oxygen concentration: In a cyanidation solution, the higher the concentration of oxygen in the solution is, the faster the gold will dissolve. In order to increase the oxygen content, air can be blown into the ore heap, thereby increasing the dissolution rate of gold and shortening the leaching time of gold.
Temperature: In general, the higher the temperature is, the higher the dissolution rate of gold in the cyanide solution will be. When the temperature is lower than 10 °C, the dissolution rate of gold is greatly slowed down; when the temperature exceeds 85 °C, as the temperature increases, the oxygen content in the cyanide solution decreases, and the chemical relationship between non-precious metal and cyanide decreases. The increased reaction rate affects leaching; the solubility of gold reaches a maximum when the temperature is at 85 °C. During heap leaching at room temperature, it is recommended to control the temperature between 10°C-85°C. While for cold regions, it’s necessary to maintain the temperature at about 15-20°C.
The above are the factors that affect the heap leaching efficiency of gold mines and corresponding solutions. It is recommended to choose a formal and experienced manufacturer before heap leaching, and do a heap leaching test in advance. During the heap leaching process, you can make appropriate adjustments according to the above suggestions when the heap leaching efficiency is found to be low.
