AGGLOMERATION HEAP LEACHING

Heap leaching is a low-capital-cost alternative to conventional processing techniques for gold recovery from ores containing small gold particles in a porous host rock. For successful heap leaching, the ores must maintain good permeability after stacking so that leach solutions can percolate evenly. Clays, slimes, or excessive fines can severely restrict solution flow, causing channelling and dormant or unleached zones, which lead to long leach periods, poor extractions, or even complete sealing of the heap. The Northern Queensland Company uses the Agglomeration Heap Leach (AHL) technique to overcome these problems by cementing fines with readily available binders into a rigid, porous network that enhances uniform cyanide solution flow. Laboratory testwork includes bottle roll tests to assess gold availability and reagent demand, followed by binder tests to determine optimum cement or lime additions, and column tests to simulate heap conditions and evaluate metallurgical and physical performance. The company’s flowsheet covers crushing, agglomeration, heap construction, solution distribution, solution treatment, and refining, with discussion of alternative equipment and process options, including vat (flooded) leaching. The effects of varying key process variables such as crush size, cement and cyanide additions, and solution application rates are also examined.