Heap Leaching Process for Gold and Silver Ore

Heap leaching is the predominant hydrometallurgical process for the resource utilisation of low-grade gold and silver ores. In this process, the ore is piled in an impermeable heap and continuously sprayed with leaching reagents, causing the gold and silver minerals to dissolve into the liquid phase; the precious metals are then recovered through solution treatment. Owing to its low-cost advantage, this process is widely applied in precious metal mines.

Basic Principles of Heap Leaching

Heap leaching relies on chemical leaching reactions to separate valuable metals. The leaching solution permeates the ore heap, where it undergoes complexation reactions with the gold and silver in the ore, converting them into soluble complexes that enter the leaching solution. The cyanide system is the most widely used leaching system; in the presence of oxygen, gold and silver combine with cyanide ions to form stable complexes, thereby facilitating subsequent recovery.

Complete Heap Leaching Process Flow

The ore first undergoes crushing and screening operations to control particle size and increase the surface area of the gold and silver minerals. The crushed ore is then layered to form a leaching heap, with an impermeable liner laid at the base of the heap to prevent leachate leakage. Once the heap is constructed, a spray system continuously and uniformly applies leaching reagents; the solution permeates the heap to leach out the gold and silver.

The leachate, rich in precious metals, is collected via a collection system and fed into an activated carbon adsorption unit, where the precious metals are concentrated by the activated carbon to form gold-bearing carbon. Subsequently, high-purity gold and silver products are obtained through desorption, electrolysis and refining processes. The tailings remaining after leaching are subjected to harmless disposal, whilst residual leaching agents are recovered simultaneously.

Scope of Application

The heap leaching process is suitable for treating low-grade gold and silver ores, gold-bearing tailings, smelting slag and mine waste rock. Heap leaching offers significant value for materials with low grades that are difficult to mine economically using conventional mineral processing methods, and can handle large volumes of ore on a large scale.

Analysis of Process Advantages and Disadvantages

The advantages of heap leaching are particularly notable: overall capital and operational costs are low, and no complex, large-scale equipment is required; the process flow is straightforward, site layout is flexible, it can be established on the site of disused mining areas, and the time to production is short; when equipped with an impermeable lining system, it facilitates the control of pollutants, and resource utilisation is highly cost-effective.

At the same time, the process has clear limitations: the leaching cycle is lengthy, often taking several months; process operations are significantly affected by the climate, with severe cold and heavy rainfall disrupting production; and the process requires a large footprint. It is difficult to achieve ideal leaching parameters using heap leaching for sticky ores and complex sulphide ores that are difficult to leach.