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Gold heap leaching is actually a cyanidation gold extraction process. It is to pile gold crushed to a certain particle size on a specially made liner that can automatically drain the liquid. Under the required pH value, the diafiltration is performed by spraying with sodium cyanide solution to extract gold. To improve the gold heap leaching rate is the key to the heap leaching process, and to improve the gold leaching rate, we need to start from the following 6 ways:ore preparation, gold stacking, PH value control, cyanide concentration, spraying intensity，gold pile management.
Let’s dive in!
Panorama of 100tpd gold leaching plant in Indonesia
Gold heap leaching process is carried out on the surface and voids of the gold ore. The smaller the particle size, the larger the surface area, which is more conducive to the contact between the solution and the natural gold particles, so that the diffusion time of the solution in the ore can be shortened, and the gold leaching speed and diffusion rate can be increased correspondingly.
In the specific production mode, reducing the particle size of gold is mainly involves adjusting the blast hole spacing, increasing the number of explosives, laying out blast hole locations, and mechanical crushing.
It has a great influence on the percolation performance of the gold pile. The reason that affects the permeability of the gold pile is the segregation of coarse and fine materials in the pile, and the compaction of the gold pile by ore trucks and other equipment.
When the ore truck is dumping gold ore into the ore pile, fine-grained ore is formed at each drop point of the ore, and the coarse-grained ore rolls to the bottom or around. The gravity separation phenomenon of ore of different particle sizes during the stacking process is segregation.
The segregation will cause the fluidity of the leachate to pass through the coarse-grained belt to be much greater than that of the fine-grained belt. This unbalanced flow rate will cause the re-transfer and redeposition of fine-grained materials, and finally deposited in a certain part of the gold pile, forming a barrier, thereby affecting the leaching rate of gold heap leaching.
Therefore, the height of the gold pile is also critical. With a small height difference, the gravity separation effect is very weak, so that it does not cause a serious segregation phenomenon.
The cyanide solution must be kept at a certain alkalinity to prevent the decomposition of cyanide. In gold heap leaching production, it is appropriate to control the pH value of the cyanide solution between 9-10.5.
Adding a certain amount of lime or sodium hydroxide during the pile building process is to adjust the pH value before the gold heap leaching. It actually plays the role of pre-leaching and eliminates the adverse effects of acidic minerals (such as pyrite). A layer of insoluble hydroxide is formed on the surface of the mineral, which inhibits the further reaction of the mineral, and at the same time plays a role in increasing the PH value of ore.
Generally, the pile is washed and the alkaline cyanide solution can be sprayed only when the PH value of the precious liquid discharged from the bottom of the pile reaches 9 or more.
In the process of gold heap leaching, under the condition of ensuring the air permeability and PH value, the dissolution rate of gold mainly depends on the CN- concentration in the leaching solution.
In general, the leaching rate of gold increases with the increase of cyanide concentration. However, a large increase in cyanide will also cause unhelpful loss, because the cyanide concentration is too high, other non-precious metals in the ore will be too much dissolved in the high concentration of CN-, which will increase the amount of reagent consumption, and even cause adverse effects.
During the production process, the cyanide concentration in the first 20 days of gold heap leaching is generally controlled at 0.10%. The middle of leaching is 0.05%~0.03%. The late leaching period is maintained at 0.03%. The amount of NaCN used per ton of gold should be maintained at 240~260g, but during the dosing process, it is important to ensure continuous and stable dosing.
The average spraying intensity in gold heap leaching is 20L/mh. When the spraying intensity reaches 25~30L/mh, the water is likely to accumulate at the top of the heap, and the leaching solution from the heap is turbid. Properly increase the spraying intensity, can strengthen the relative movement between the solution and the gold ore, reduce the concentration gradient, play a role in strengthening the dispersion, and shorten the leaching time.
After spraying and washing the ore to saturation, just add the water lost by evaporation, try to avoid the high temperature at noon, spray in the morning and evening, stop spraying when the wind is strong, and minimize the loss of solution and gold.
The leachate reacts with the gold ore and is carried out under oxidizing conditions. In order to replenish the oxygen in the gold pile, an intermittent spray method is adopted, that is, spray for 2 hours and stop for 1 hour. Intermittent spraying is not prone to water accumulation on the top of the pile.
After spraying for a period of time, due to water penetration and gravity, especially when walking on the surface of the gold pile during the operation, the gold pile will be compacted. At this time, strengthen the management of the gold pile and try to avoid walking on the gold pile. It is also necessary to avoid bottom pad leakage, pay attention to observation, and solve problems in time to ensure the safety of the entire gold pile, thereby increasing the gold heap leaching rate.
Increasing the gold heap leaching rate is the key to the heap leaching process, and to improve the leaching rate of gold, it is necessary to pay attention to the ore size, stacking method, spray system, etc. It is recommended that all mine owners consult with manufacturers with the qualification of the dressing plant to design the leaching process, select the appropriate leaching equipment.
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