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Gold heap leaching is a process to pile gold-bearing ore crushed to a certain particle size on a water-tight site, then spray the cyanide solution on the ore pile, making it leaching through the gold ore to extract gold. Gold heap leaching process is widely used in gold processing plants because of its simple process, short process time, and lower investment cost than the conventional cyanidation process. But there are many factors that affect the efficiency of gold heap leaching. If not adjusted properly in production, these factors will affect the economic benefits of the gold processing plant. There are 10 main factors affecting gold heap leaching efficiency.
Gold ore with loose structure and large gaps has good permeability, which is beneficial to the penetration and diffusion of cyanide solution inside the ore. The gold in the ore can fully react with the cyanide solution, so the gold leaching speed is faster. Conversely, if the structure of the ore is dense, it is not conducive to the leaching of gold, and therefore the gold leaching speed is slower.
In gold heap leaching process, the smaller the particle size of the ore, the shorter the leaching time, and the higher the leaching rate. In actual production, gold ore is usually crushed to 5-20 mm for better heap leaching efficiency.
When wetted by the cyanide solution, the clay in the gold ore will expand and increase by 25-30%, which will lead to a decrease in the porosity of the ore pile and the reduction of the solution penetration rate. The higher the clay content, the lower the penetration rate of the cyanide solution and the longer the time required for gold leaching.
When the concentration of cyanide solution is less than 0.05%, the dissolution rate of gold increases rapidly with the increase of the concentration of cyanide solution. When the concentration of the cyanide solution is 0.05% -0.1%, the concentration of the cyanide solution has little effect on the dissolution rate of gold. When the cyanide solution concentration is higher than 0.15%, the dissolution rate of gold will decrease as the cyanide solution concentration increases. The concentration of cyanide solution in China’s gold heap leaching plants is generally controlled between 0.03% and 0.08%.
The proper ore pile height can be determined through experiments. For gold ore with high permeability, the ore pile height can be set higher. For gold ore with poor permeability, the ore pile height should not be too high, otherwise the oxygen supply and permeability of the ore below will be affected, thereby reducing the gold leaching rate. The height of ore pile in China’s gold heap leaching plant is generally 2-4 meters.
Properly increasing the spray intensity of the cyanide solution can shorten the gold leaching time and increase the leaching rate. However, when the spray intensity is too large, the cyanide is lost due to oxidation and the solution concentration will be reduced, thereby reducing the gold leaching rate. Gold heap leaching plants in China generally has a spraying intensity of 8-12 liters per square meter.
During the gold heap leaching process, the leaching rate of gold will increase as the leaching time increases. But when the leaching rate of gold gradually approaches a certain limit value, the leaching speed of gold will decrease. This is because during the leaching process, the gold particles are constantly dissolved, which reduces reaction area between gold particles and cyanide solution, and various impurities are continuously entering the solution, affecting the rate of gold dissolution.
During gold heap leaching, the dissolution rate of gold is directly proportional to the concentration of oxygen in the solution. Therefore it is necessary to increase the concentration of oxygen in the cyanide solution. Air can be blown into the ore pile. The dissolution rate of gold can be increased by 10-20 times, or even 30 times, depending on the characteristics of gold ore.
The dissolution rate of gold in cyanide solution will increase with the rising temperature, reaching the highest level at about 85 ° C. When the temperature is lower than 10 ° C, the dissolution rate of gold will be greatly reduced.
The argillaceous substance will reduce the permeability of the ore pile, thus reduce the leaching speed and the gold recovery rate. Therefore, before gold heap leaching process, the ore can be deslimed to reduce the impact of muddy substances on the gold heap leaching process.
From the above analysis, it can be seen that there are many factors affecting the efficiency of gold heap leaching process. In specific production, specific analysis should be performed according to the actual situation. Only by adjusting the various factors can the gold processing plant achieve good economic benefits. Because the cyanide is highly toxic and has serious pollution to the ecological environment, it is recommended that gold processing plant select the low-toxic alternative to cyanide for gold heap leaching.