Gold heap leach method
The gold heap leach method is a process for extracting gold from ore by using a leaching solution to dissolve the precious metal from the ore material. This method is particularly effective for low-grade gold ore that would not be economical to process through other, more intensive methods. Here’s a detailed look at how the gold heap leach method works:
How Heap Leaching Works:
1 Preparation of the Ore
The ore is crushed into fine particles. It is then heaped into large piles on a pad that is specially designed to collect the leaching solution after it has been sprayed over the ore.
2 Leaching Solution
A leaching solution, also known as a lixiviant, is sprayed over the ore. The type of solution used depends on the characteristics of the target mineral. For example, a dilute solution of sulfuric acid is commonly used for copper and uranium, whereas a cyanide solution is used for gold and silver.
3 Percolation
The solution percolates through the heap, dissolving the target minerals as it travels downwards.
4 Collection of Leachate
The solution, now enriched with the dissolved minerals, collects at the bottom of the heap and is channeled to a collection pond. From there, it is pumped to a recovery plant.
5 Recovery of Gold
In the recovery plant, the gold is extracted from the solution. One common method for gold recovery is the Merrill-Crowe process, which precipitates gold from the solution using zinc dust. Another method is the use of activated carbon to adsorb the gold directly from the solution.
6 Recycling of Solution
The solution, now depleted of gold (referred to as “barren” solution), is often recycled back to the top of the heap for reuse in leaching new ore. This helps to reduce waste and the overall consumption of the leaching agents.
Advantages of Heap Leaching
- Cost-Effective: Heap leaching is generally less expensive than traditional methods, making it an attractive option for lower-grade ores.
- Low Energy Consumption: The process requires less energy compared to other extraction methods.
- Minimal Infrastructure: It does not require elaborate plant facilities.
Disadvantages
- Time-Consuming: The leaching process can take several months to complete.
- Lower Recovery Rates: Recovery rates are often lower than those achieved by conventional methods.
- Environmental Concerns: The use of toxic chemicals (like cyanide for gold leaching) poses environmental risks if not managed properly.
Typical beneficiation plant
Tajikistan Gold Mine: There are few metal minerals in the ore, with gangue minerals accounting for more than 95%. The metal sulfides are mainly pyrite and arsenopyrite, and the metal oxides are mainly limonite and arsenic containing iron oxide. The gold ore is natural gold, and no other gold minerals have been found. The specific process is as follows:
