5 Methods of Improving Gold Heap Leaching Effect

Heap leaching refers to a gold extraction process in which low-grade gold ore after crushing to a certain size are piled on a heap leaching site with a liner that does not leak solution and can automatically drain，and gold in the ore are dissolved out by circulating sodium cyanide solution to form a gold-containing pregnant solution to recover gold.

Heap leaching includes two processes: cyanide leaching and gold recovery from gold-containing pregnant solution. The cyanide leaching effect is directly related to the success or failure of heap leaching. The following content mainly introduces how to improve the effect of gold extraction by heap leaching from five aspects.

During the leaching process of gold ore, the ore with too high content of clay and fine-grained materials is not suitable for direct heap leaching, and granulation pretreatment is required to improve the permeability of the ore heap. Granulation pretreatment can increase the leaching speed of gold, and in most cases can greatly strengthen the leaching rate of gold. Depending on the situation, the ore can be fully granulated or fine-grained and partially granulated.

For example, in 1991, a gold mine in Xinjiang, China carried out the largest (24,000 tons) granulation heap leaching for the first time. The leaching time was 35 days shorter than that of direct heap leaching, and the leaching rate increased from 49.69% to 81.5%.

Heap construction is an important link in the process of gold heap leaching. It should make the entire ore pile have similar permeability to avoid channeling or local blockage. Therefore, it is recommended to use advanced arc-shaped heap construction equipment and adopt the process of " stacking in sections, cross spraying, multi-stage countercurrent leaching"; then inject air into the ore heap. At the same time, the liquid collection pipeline is laid to improve the permeability of the ore heap and leaching effect.

Generally, devices that facilitate the entry of oxygen are installed during the construction of the pile to improve the permeability of the pile and leaching speed.

For example, crabstick, bamboo tubes, etc. are buried in the pile. And these buried objects are pulled out after leaching for a period of time to improve permeability for gold leaching; or after heap leaching for a period of time, local loosening blasting is used on the part of the accumulation of water, which can also loosen the mine pile and improve the permeability.

Research results of the Hazen Institute in the United States show that increasing the oxygen content in the ore pile can not only shorten the leaching cycle by nearly 1/3, but also increase the leaching rate of gold.

Cyanidation requires a higher temperature, therefore in a cold climate, the main obstacle to heap leaching is the leaching temperature. At a leaching temperature lower than 10°C, the dissolution rate of gold will drop sharply. In order to break the temperature limit and extend the heap leaching season, the solution needs to be heated before leaching and then sent to the ore pile.

Some mines in Canada make use of waste heat to heat the solution, thus prolonging the heap leaching operation time. The Richmond Hill gold mine in South Dakota, the United States, adopted thetrickle drip irrigation and the heat absorption device of the pile to achieve continuous production throughout the winter.

Sprinkler irrigation and drip irrigation are two different liquid distribution methods in the heap leaching process, which can produce uniform liquid distribution effects.

However, the spray method is not easy to control the amount of gold leaching solvent, and it is difficult to increase the leaching rate. At the same time, the tiny water droplets containing cyanide sprayed into the air are easy to diffuse, which easily pollutes the environment. In order to reduce energy consumption and increase leaching rate, the drip irrigation can be used.

Merits of Drip Irrigation

• The drip irrigation can increase the air content in the solution, which means that the oxygen content participating in the chemical reaction is increased, thereby improving the activity of gold precipitation.

• The drip irrigation can accurately control the concentration of cyanide solution and reduce the loss of sodium cyanide in the air.

• The drip irrigation is easy to add temperature control equipment to achieve the purpose of increasing the chemical reaction temperature of heap leaching.

• The drip irrigation has a high degree of automation, high production efficiency, and relatively low production costs.

As an additive, the leaching aid can increase the contact between cyanide and gold when added to the cyanide leaching slurry; on the other hand, it can eliminate or weaken the influence of harmful impurity elements on the cyanide leaching of gold, thereby enhancing the dissolution and leaching effect of the agent on gold. And ultimately reduce production costs and improve the economic efficiency of enterprises.

Common leaching aids added in the heap leaching process include oxidizing agent, enhanced leaching agent, wetting agent, etc.

• Adding oxygen-containing oxidizing agent (H2O2. CaO2, Na2O2, etc.) to the cyanide leaching process can increase the "effective active oxygen" in the slurry, thereby improving the leaching effect of gold ore.

• Adding an appropriate amount of wetting agent or enhanced leaching agent to the cyanide solution is conducive to the penetration of the cyanide solution and promotes the reaction between the cyanide solution and the encapsulated gold.

We discussed heap leaching of gold in this article. Heap leaching gold has the characteristics of simple infrastructure, convenient operation and economic space occupation, so it is welcomed by many gold mine owners. However, the gold extraction effect of heap leaching is affected in many ways. It is recommended that all mine owners design reasonable heap leaching solutions through scientific experiments and select appropriate heap leaching equipment. It can be adjusted according to the actual situation of the plant and referring to the following five points.

• Application of granulation technology to ores with high fine particles or clay content and poor permeability

• Improvement of ore heap permeability and solution penetrability

• Maintenance of proper leaching temperature

• Application of drip irrigation

• Application of leaching aid

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