Five Methods to Improve the Effect of Gold Ore Heap Leaching

Heap leaching consists of two processes: cyanide leaching and gold recovery from the pregnant gold solution. The quality of cyanide leaching directly impacts the success of heap leaching. The following mainly introduces five aspects on how to enhance the effect of gold extraction by heap leaching.

1. Application of Granulation Technology

During the leaching of gold ore, ores with high clay content or fine - grained materials are not suitable for direct heap leaching and need granulation pretreatment to improve the air permeability of the ore heap. Granulation pretreatment can increase the leaching rate of gold and, in most cases, significantly enhance the gold leaching rate. Depending on the situation, the ore can be fully granulated, or only fine - grained or partial granulation can be carried out.

For example, in 1991. a gold mine in Xinjiang, China, carried out the largest - scale (24.000 tons) granulation heap leaching for the first time. The leaching time was shortened by 35 days compared with direct heap leaching, and the leaching rate increased from 49.69% to 81.5%.

2. Improving the Permeability of the Ore Heap and Solution

Piling is an important part of the gold ore heap leaching process. The entire ore heap should have similar permeability to avoid channeling or local blockages. Therefore, it is recommended to use advanced arc - shaped new ore heap building equipment and adopt the process flow of "segmented stacking, cross - spraying, and multi - stage counter - current leaching". Then, inject air into the ore heap and lay liquid collection pipes to improve the air permeability of the ore heap and the leaching effect.

Usually, devices conducive to oxygen entry should be installed during piling to improve the air permeability and leaching rate of the pile.

For example, in heap leaching, crab sticks, bamboo tubes, etc. are buried. After leaching for a period of time, these buried objects are pulled out to improve permeability for gold leaching. Or, after heap leaching for a period of time, local loose blasting is carried out at the water - accumulated parts, which can also loosen the ore heap and improve permeability.

Research results from the Hazen Research Institute in the United States show that increasing the oxygen content in the ore heap can not only shorten the leaching cycle by nearly one - third but also increase the gold leaching rate.

3. Maintaining an Appropriate Leaching Temperature

The cyanidation method has high requirements for temperature. Therefore, in cold climate conditions, the main obstacle to heap leaching is the leaching temperature. When the leaching temperature is lower than 10°C, the dissolution rate of gold will drop sharply. To break through the temperature limit and extend the heap leaching season, the solution needs to be heated before leaching and then sent to the ore heap.

Some mines in Canada use waste heat to heat the solution, thus extending the heap leaching operation time. The Richmond Hill Gold Mine in South Dakota, USA, uses drip irrigation and heat - absorption devices on the pile body to achieve continuous production throughout the winter.

4. Application of Drip Irrigation

Spray irrigation and drip irrigation are two different liquid distribution methods in the heap leaching process, both of which can produce a uniform liquid distribution effect.

However, the amount of leaching solvent in the spray method is not easy to control, the leaching rate is not easy to increase, and at the same time, the tiny cyanide - containing water droplets sprayed into the air are easy to diffuse and pollute the environment. To reduce energy consumption and increase the leaching rate, the drip irrigation method can be adopted.

Advantages of Drip Irrigation

• Drip irrigation can increase the air content in the solution, that is, the oxygen content participating in the chemical reaction increases, thereby increasing the activity of gold precipitation.

• Drip irrigation can accurately control the concentration of the cyanide solution and reduce the loss of Sodium cyanide in the air.

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

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

5. Use of Filter Aids

As an additive, the leaching aid is added to the cyanide - leached pulp. On the one hand, it can increase the contact between cyanide and gold; 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 leaching aid on gold, ultimately reducing production costs and improving the economic benefits of enterprises.

Commonly added leaching aids during the heap leaching process include oxidants, enhanced leaching agents, wetting agents, etc.

• Adding oxygen - containing oxidants (H₂O₂, CaO₂, Na₂O₂, etc.) during the cyanide leaching process can increase the "effective active oxygen" in the pulp, 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 coated gold.

6. Conclusion

This article mainly discusses the heap leaching process of gold mines. The heap leaching process has the characteristics of simple infrastructure, convenient operation, and economical space occupation, which is welcomed by many gold mine owners. However, the gold extraction effect of the heap leaching process is affected by many aspects. It is recommended that mine owners design a reasonable heap leaching plan through scientific scheme design. Test and select appropriate heap leaching equipment, and adjustments can be made according to the actual situation of the factory with reference to the following five points:

• Application of granulation technology in ores with fine - grained grades or high clay content and poor air permeability.

• Improving the permeability of the ore heap and solution.

• Maintaining an appropriate leaching temperature.

• Application of drip irrigation.

• Application of filter aids.

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